CA2225865A1 - Wavelength converter - Google Patents
Wavelength converter Download PDFInfo
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- CA2225865A1 CA2225865A1 CA002225865A CA2225865A CA2225865A1 CA 2225865 A1 CA2225865 A1 CA 2225865A1 CA 002225865 A CA002225865 A CA 002225865A CA 2225865 A CA2225865 A CA 2225865A CA 2225865 A1 CA2225865 A1 CA 2225865A1
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- wavelength
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
- H01S5/0608—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by light, e.g. optical switch
Abstract
The invention concerns a wavelength converter for converting a first light signal used for data-transmission and having a first wavelength (.lambda.In) into a second light signal having a second wavelength (.lambda.Out). The wavelength converter signal comprises a signal input for picking up the first light signal, a signal output for emitting the second light signal, a modulatable optical semiconductor amplifier (4) with an input, an output and modulation input and a first laser light source (L1), which forms a first stage (1) with the semiconductor amplifier (4). The input of the semiconductor amplifier (4) is connected to the first laser light source (L1) and the modulation input of the semiconductor amplifier (4) is connected to the signal input for cross-amplification modulation. The first laser light source (L1) emits light with a third wavelength (.lambda.int). Arranged downstream of the first stage (1) by means of an optical coupler (3) is a second stage (2) which contains a modulatable second laser light source which emits light at the second wavelength (.lambda.Out) and has a modulation input and an output. The modulation input of the second laser light source is connected to the output of the semiconductor amplifier and the output of the second laser light source is connected to the signal output.
Description
Dec Z9 97 02:Z2p Karl H~CA 02225865 1997-12-29 617-~91-8877 p-zg , At~rney D~cket 970239 Wavelength Converter 5 S~ecification The invention relates to a waveiength converter for convertin~ a first light signal of a first wavelength for transmitting data into a second light signal 10 of a second wave-length, having signal input ~r receiving the first light signal, a signal output for emittlng the second light signal, a modulatable optical serniconductor amplifier with an input, an output and modulation input, a first laser light source which wit!~ the semiconductor amplifier forms a first stage, with the input of the semiconductor amplifier belng connected to the first laser1~ 7ight source and the moci~lation input of the semiGon~uctor ampiifier being connected to the signal input for cross amp~ification modulation and the first laser light source ernittin~ !ight of a third wavelength, and wherein a second stage is connected to the output first stage by a coupilng element, the second sta~e being provided with a second laser light source emitting light of the ~0 second wavelength and with a modulatable cornponent.
WaYelength converters are required, interal~a, in optical data transmission systems in which data is transmitted by time or wavelength n~ultiplexing .
2j In digital data transmission, data may be tr~nsrnitted by light signals of two different levels, each corresponding to a binary signal. Sir~ce in data transmission, the error rate is influeneed by the spacing between the two logic levels, it is desira~le that the inter-level spacing of the input si~jnal be not30 reduced by any wavelenyth conversion. in wavelength conversion the level spacing is determined by the so-called extinction factor, the extinction factor Dec 29 97 02:22p Karl HorCA 02225865 1997-12-29 617-~91-B877 p.30 achievable with a single semiconductor ampliher being as a rul~ too low to maintain the level spacing of the input signal in the output slgnal. Cascading two semiconductor ampJifi~rs for wavelength conversion will resutt in an increasing deterioration ot the extinction, i.e., in a reduction of the extinction 5 factor.
In SIMON, J.C., et al.. Two-stages wav~length cor-lverter with irnproved extin~tion ratio, OFC 199~, San C)iego, U.S.A., there is described a dual stage optical wavelength ~onverter, by which a light signal rnay be converted 10 frorn a first wave!ength to a second wavelength.
The wavelengll, converter described in this prior publication is provicled with two optical series-connected semiconductor amplifiers each of which amplifies a light sign~l applied tc its input. A light signai from a laser light15 source having a wa~le-length of Aint ~nd operatin~ in a continuolls wave is applied to the input of the first amplifier and does not, thercfore, tr~nsmit ~ny data. Furthermore the two semiconductor amplifiers are each equipped with a modulation input ~onnected to the signal input of the wavelength conYerter.
~ 20 Hence, the light signal of wavelength ~'4n applied to the signal input ~f the wavelength converter modulates the amplification of the two semlconductor arnplifiers, the amplification factors of which, because of saturation effecP, will decrease as the level of the modulation signal increases.
The modulation signal of wavel~ngth Am and the light signal of wav~
length Ant are coupl~d into the semiGonductor amplifi~rs in opposite directions so that only the signal of wavele.~gth Aln~ will leave the semiconductor arnpli-fiers in the direction of the si~nal outp;-t.
3~) If the level of the modulation signal of wavelen3th A,n is relatively high, Dec Z9 97 02:22p Karl HolcA 02225865 1997-12-29 617 4 p.31 the semiconductor amplifiers are driven to saturation so that the amplification factor and. hence, the levels of any output signals wil! be reJatively low. If.by contrast, the level of the modulation signai of wavelen~th Aj~, in relatively low, then the amplification factor of the semiconductor amplifiers and the level nf S any output signals will ~e relatively high. That is to say that the polarity of the output signals of the two semiconductor amplifiers is inyerted relative to the input signal of the wavelength converter.
Betweon the two semiconductor amplifiers there is arranged, on the 10 one hand, a unidirectionally effective optical isolator and, on the other hand~
an optical dampenin~ rnem~er. The isolator block~ the light emitted by the second stage semiconductor arnp~ifier in the direction of the first stage and this prevents disturbance of the first stage. The darnpening member, on the other hand, sets the level of the output signal of the first semiconductor I ~ amplifier.
The described wavelength converter advantageously allows conver-sion of a first wavelength in a striotly optical manner into a second wavelengthwithout intermediate electro~ptic transducers.
Advantageously, the conversion is substantia~ly immune from changes of the polarity and of the wavelength of the input signal, since arnplification by the semiconductor amplifiers is substantially independent of polari~ation and wavelengths.
WaYelength converters are required, interal~a, in optical data transmission systems in which data is transmitted by time or wavelength n~ultiplexing .
2j In digital data transmission, data may be tr~nsrnitted by light signals of two different levels, each corresponding to a binary signal. Sir~ce in data transmission, the error rate is influeneed by the spacing between the two logic levels, it is desira~le that the inter-level spacing of the input si~jnal be not30 reduced by any wavelenyth conversion. in wavelength conversion the level spacing is determined by the so-called extinction factor, the extinction factor Dec 29 97 02:22p Karl HorCA 02225865 1997-12-29 617-~91-B877 p.30 achievable with a single semiconductor ampliher being as a rul~ too low to maintain the level spacing of the input signal in the output slgnal. Cascading two semiconductor ampJifi~rs for wavelength conversion will resutt in an increasing deterioration ot the extinction, i.e., in a reduction of the extinction 5 factor.
In SIMON, J.C., et al.. Two-stages wav~length cor-lverter with irnproved extin~tion ratio, OFC 199~, San C)iego, U.S.A., there is described a dual stage optical wavelength ~onverter, by which a light signal rnay be converted 10 frorn a first wave!ength to a second wavelength.
The wavelengll, converter described in this prior publication is provicled with two optical series-connected semiconductor amplifiers each of which amplifies a light sign~l applied tc its input. A light signai from a laser light15 source having a wa~le-length of Aint ~nd operatin~ in a continuolls wave is applied to the input of the first amplifier and does not, thercfore, tr~nsmit ~ny data. Furthermore the two semiconductor amplifiers are each equipped with a modulation input ~onnected to the signal input of the wavelength conYerter.
~ 20 Hence, the light signal of wavelength ~'4n applied to the signal input ~f the wavelength converter modulates the amplification of the two semlconductor arnplifiers, the amplification factors of which, because of saturation effecP, will decrease as the level of the modulation signal increases.
The modulation signal of wavel~ngth Am and the light signal of wav~
length Ant are coupl~d into the semiGonductor amplifi~rs in opposite directions so that only the signal of wavele.~gth Aln~ will leave the semiconductor arnpli-fiers in the direction of the si~nal outp;-t.
3~) If the level of the modulation signal of wavelen3th A,n is relatively high, Dec Z9 97 02:22p Karl HolcA 02225865 1997-12-29 617 4 p.31 the semiconductor amplifiers are driven to saturation so that the amplification factor and. hence, the levels of any output signals wil! be reJatively low. If.by contrast, the level of the modulation signai of wavelen~th Aj~, in relatively low, then the amplification factor of the semiconductor amplifiers and the level nf S any output signals will ~e relatively high. That is to say that the polarity of the output signals of the two semiconductor amplifiers is inyerted relative to the input signal of the wavelength converter.
Betweon the two semiconductor amplifiers there is arranged, on the 10 one hand, a unidirectionally effective optical isolator and, on the other hand~
an optical dampenin~ rnem~er. The isolator block~ the light emitted by the second stage semiconductor arnp~ifier in the direction of the first stage and this prevents disturbance of the first stage. The darnpening member, on the other hand, sets the level of the output signal of the first semiconductor I ~ amplifier.
The described wavelength converter advantageously allows conver-sion of a first wavelength in a striotly optical manner into a second wavelengthwithout intermediate electro~ptic transducers.
Advantageously, the conversion is substantia~ly immune from changes of the polarity and of the wavelength of the input signal, since arnplification by the semiconductor amplifiers is substantially independent of polari~ation and wavelengths.
2~
Nevertheless, the mentiened wavelength converter suffers from a variety of disadvantages~
Firstly, ~his wavelength converter inverts the signal polarity of the input ~0 signal. Thus, if several wavelength converters are arranged in a cascading manner. the number of cascaded wavelength conve~ers must l~e considered -Dec 29 97 02:23p Karl Hor~A 02225865 1997-12-29617-491-e877 p.32 in evaluating the signal. In an optical data transmission system this would be entail signihcant complexity, and it would limit flexibility.
Secondly. con~ersïon by optical semiconductor amplifiers is dependent S upon the position of the wa\~elengths of input and output signal. Thus, conversion by optical semiconductors works best when converting lar~er Into smaller wavelen~ths.
Moreo~,er, a distorted input signal is reproduced as a distorted signal o at the output. This is a particular drawback where several wavelength conYerters are arranged in a cascade, as in such an arrangement noise is accumulated thus limiting the number of c~scaded waYelength converters.
Moreover, the wavelength converter provides an output signal of a I 5 relatively unclean frequency spectrum ("chirp"~. Because of the dispersion inherent In light wave~uides, this, in transn,illii1g the output signal through a ~ight waveguide, will result in a distortion of the transmitted signal and, therefore, to a restriction of the distance over which transmission is possible without intermediate amplifiers or repeaters.
In U.S. Patent 5,2~4,96~, there is described a wavelength converter which is constructed of two stages, each stage being based upon the cross gain modul~tion (XGM - cross gain modulation~ and provided with a modulatable optical semiconductor arnplifier having an input, an output and a 2~ rnodulation input and a laser light source, the two stages being connected toeach other by an optical coupling element. However, when cascading two XGM converters a chirped signal will resulkt which is imprecise in terrns of itswavelength. In the transmission of date over standard single-mode fibers this spectral uncleaness is, however, disadvantageous because it makes 30 trànsmission of 10 Gbit/s impossibie even over a small distance of 20 km and because signal distrotions are recognizable at low bit r~tes already ~ ~ide J.S.
Dec 29 97 02: lSp Karl H~rrCA 02225865 1997 12 29617-491 -8B77 P- ~
Perino J.M. Wiesenfeld LProceedings of 1994 Conference on Lasers and Electro-Optics and the International Electrani~s Conference C:LEO/IQEC, Anaheim, CA, USA, 8-13 May, pp. 298-299).
S It is, thereforel a particular task of the invention to provide a wavelength converter of the kind mentioned supra which makes possible a conversion of wavelengths at high precision substantially without distortions and with a high extinction factor.
The task is accomplished by a wavelength c~nverter of the kind referred to supr~ the modulatable component of the second stage of which in accordance with the invention is ,orovided with a Fabry-Perot laser provided with an input for the second laser light source feeding light of the second wavelength into the Fabry-Perot laser, with an output and a modulation input, l ~ whereby ~he output of the Fabry-Perot laser is connected to the signal output and the modulation input of the Fabry-Perot laser is connected to the output of the semiconductor amplifier and the coupling element is provided with at least one circulator.
In the two-stage wavelength con~erter in accordance with the inventlon the first stage consists essentially of an optical semiconductor arnplifier provided with an input, ~n output and a modulation input. The light signal of a fi~s~ laser light source operating in a continuous wave mode at wa~Jelength ~, is applied to the input of the semiconductor ampliher. The modulation inpùt of 25 the serniconductor laser is connected to the signal input of the wavelength converter.
Therefore, the light signal applied to the signa1 input of the wavelength converter modulates the light signal from the first laser with wavelength Aint In 30 this process, the rno~ulation is carried out by a cross arnplification rnodulation.
Dec 29 97 02: 16p Karl HcCA 0222586~ 1997-12-29 61 ,'-491-81377 p.9 ~ he crGss amplification modulation is based upon the dependency of the amplification factor from the input level. Thus, as the level of the modL~lation signal becomes larger, the amplification factor becomes smaller with increasing saturation of the amplifien If the level of the modulation si~nal is relatively high, the amplification factor and, accordingly, the level of the output signal of wavelength Ajnt will be relatiYely low. ConverseJy, ~t a relatively low level modulation signal the amplification factor and, hence, the level of the output signal of wavelen3th A;" will be rel~tively high Therefore, the signal polarit~l~ of the output signal of the semicon~uctor amplifier will be of ld inverted polarity relative to the modulation signal.
The optical semioonductor arnplifier delivers an output signal of a defined wavelength Ajnt substantially independently o~the wavelength and polarization of the in~ut signal. For that reason, the wavelength convelter ~s 15 substantially insensitive to deviations of the polarity or changes in the wavelen~th of the input signa~ and accord~n~ly it is very flexi~le at its input side.
In a preferred embodiment fhe modulation input and the oufput of the 20 sen~iconductor amplifier are located at one side of semiconductor amplifier, and the input is located at the opposite side. The modulation signal and the continuous wave sight si~nal of the first laser are, therefore, coupled into thesemiconductor amplifier from different directions. Thus, it is chiefly light of wavelength Alrt which leaves the semiconductor amplifier, whereas hardly any 25 of the light of wavelength An emitted by the signal input of the wavelength conve~er and entering the ~en,icc,nductor amplifier at its modulalion input is conducted in the direction of the second stage. This is irnportant so that the inp~Jt signal of wavelength Ajn~ of t~le fir~t stage is not deleteriously superposed on the o~tput signal of wavelength hjr,t thereof. In this embodiment, and with a30 sufficiently high antireflection, the wavelength Aj,. of the input signal rnay be equal to the wa~elength A,,~, of the laser since the light signal applied to the Dec 29 97 OZ: l~p Karl HocA 0222~86~ 1997-12-29 617 49 p. lO
input of the wavelength converter cannot leave the semiconductor amplifier becal~se of the disposition of modulation input and output.
In another embodiment, a filter which blocks light of wavelength lin is 5 arranged for the same purpose behind the output of the semiconductor.
The second stage of the wavelength converter consists of a Fabry-Perot-laser, and a laser light source emitting light of wa~lelength AoU The CW
light of wa~relength ~)bu~ from this second laser light source and the light of 10 wavelength Aj"~ emitted from the sen~icondt~ctor amplifier are coupled into the Fabry-Perot laser by means of a coupling element and by i'injection induced"
switching it causes modulation of the radiation of wavelength ~OU~. Upon coupliny in of a data pulsel the Fabry-Perof laser converts from a state locked to wavelength Aoul into a non-locked state (inverted modulation) or vice versa 15 ~non-inverted rnodulation .
Inverted or non-inverted modulation may selectively be set -as has already been mentlon- by way of the operating conditions of the second stage.
By double inve~sion by the semiconductor amplifier on the one hand, ~nd by the Fabry-Perot laser of tl~e ser,ond stage on the other hand, the olllput signal will be of the same polarity as the input signal of the waYelength converter. T~is is of especial irnportance whcre several wavelength converter ~5 are cascaded, as otherwise an in~/ersion of the signal polarity by the wavelength converter would necessitate consideration of the number of casca~ed wav~length converters for pur~oses of signal evaluation.
Becau~e of the use of a laser light source as the converter, the 30 transmission function of the second stage is h~hly non-linear, similar to a threshold element. In digital data transmission with two logic levels Dec Z9 97 ~Z: 16~ Kar-l Hor.C.. A 02225865 1997-12 29617-4YI-8877 p. 11 corresponding to the two binary signals, the output signal of the waveiength con~erter of the waYelength converter for this reason has clearly defined levels larg~ly independent of disturbanc~s in the input signal of the second stage. On the one hand, this results in greater flexibility as regards the S requirements for the first stage and, on the other handT in a regeneration of the input signal by the wavelength ~on~erter. Hence, even an input signa with relati~ely strong noi~e superposed thereon c~n be con\lerted correctly and with clearly defined output levels. Advantagecusl~, the regeneration of the input signal makes it possible to cascade a plurality of wa~telength 1 0 converters.
Thus, the wa~length conYerter in the first stage initially converts a light signal of wavelength Ajn into the internal wavelength Ajnt and thereafter, in the second sta~e, into the output wavelength A
In a particular~y advantageous embodiment o~ the inventir~n the waveleng~h of the laser in the se~;ond stage may be tunable. In this fashion, the wavelength converter may address different output channels each having a different wa~elength.
~0 In a fu~her embodiment of the invention the internal waYelength A,nt ~s shorter, on the one hand, than the wavelength ~ of the input signal and, on the other hand? shorter than the wavelength Aout of the output signal. To this end, adY~ntageous use is made of the fact that the second stage with its 25 laser light source as the wavelength converter functions relatively well for converting a shorter waYelength into a longer one whereas the semicon~uctor amplifier IS better suited for converting a light signal ~rom a longer wavelength int~ a shorter one. T~at is to say that the second stage is compensating the fre~uency response of the first stage. The internal wavelength Aj~ is thus 30 selected such that the semicGnductor amplifier operates in an optimum fashion at the predet~rmined wavelength Aj~ ot the input signal.
Dec 2~ 97 02: 17p Karl HorrCA 02225865 1997-l2-29D17-491-8877 p. lZ
The laser light source of the second stage provides a light signal of a relatively narrow ~anded frequency range. For that reason, the output signal of the w~velength converter is subject to relatively low distortion only during transrnission through a light wave~uide in spite of the distortion occurring in S light waveguides. This is of advantage for transmission over relatively large distances without intermediate amplifiers (repeaters~.
Moreover, even at an input signal from the wavelength oonverter of relatively unclean spectral purity ~chirp) the laser of the second stage will 10 deliver a relatively rtarrow-banded output signal. An input si3nal detrimentally affected hy "chirp" is thus regenerated by th~ wavelongth converter. This advantageously lowers the error rate in data transmission or increases the possible transmission distance, as the case may be, and It allows many wavelength converters to be cascaded.
Furtherrnore and as described sup~a, the semiconductor arnpli~ler is substantially independen~ of the wavelength of the Input signal. For that reason, the wavelength converter in accordance with the invention may embrace several input channels of dif.ferent wavelengths. In this connection, ~0 the wavelength dependency of the extinction factor is lelati~/ely insignlficant which is achieved by the utilizin~ the laser light source as a conYerter in the second stage.
In a special variant of the inYention of its own inventive significance the 25 coup!in~ element for connecting the two stages of the wavelength converter essentially consisl~ of a four gate circulator connected to the signal input of the wave!ength converter, the modulat,on input and the output of the semiconductor amplifier, the modulation OUtpLlt and the output of the laser of the second stage as well as with the signal output of the wa~elength ~0 converter.
Dec: 29 97 02: 171~ Karl Ho~A 02225865 1997-12-29 617-491 8877 p. 13 Tl-e circulator couples light from the signal input of the wavelength converter into the modulation input of the semiconductor arnpliher, frorn the output of the semiconductor amplifier to the modulation input of the laser of the second stage, as well as from the output of the ~econd stage into the 5 signal output of the wavelength converter. Such a circulator on the one hand insures optlcal isolation of the two stages of the wavelen~th converter and, on the other hand, it advantageously has a relatively low coupling loss of lëss than 1 d~.
In another variant of the invention the couplin~ element consists of two series-connected circulators, the first circulator being connected to the si~nalinput of the wavelength converter as well as to the modulation input and to the output of the semiconductor amplifier. The second circulator, on the other hand, is connected to the modulation input and the output of the laser of the 15 second stage as well as to the signal output of the wavelength converter.
The first circulator couples light from the signal Input of the wavelength converter into the modùiation input of the semiconductor amplifier and from the output of the semiconductor amplifier into the second circulator. In the ~0 second stage, the seeond circu~ator thereafter couples the light from the first circulator into the modulation input of the laser and feeds the output signal ofthe second stage to the signal output of the wavelength converter. In this operation, the great flexibility is of advantage, as further components, e.g.
optical amplifiers, may be connected be~Neen the two circu~ators.
~5 In another preferred embodiment the optical coupling elernent is provided with conventicnal couplers structured, for instance, as 3dB
directional couplers.
Hence, the wavelength converter in accordance with the invention combines the ad,ranta~es of an optical semiconductor amplifier as the input Dec 29 97 02: 17p Karl Hor~A 0222ci86ci 1997 12 2g~:~l7-49l-8l377 p. 14 stage (indepcndence of polarization and wavelength, reception of several input channels of different wa~el~ngllls) with the advantages of a laser converter as the output stage ~regeneration of the input signal by a threshold-like transmission function, high extinction ratio of the output signal, purity o~
the output spectrum, equally good conversion into longer as well as shorter wavelengths~, and it makes it possible freely to select the data rate over a wide range.
Advantageously. the wavelength converter in accordance with the 10 invention is a hybrid structure with individual components or an opto-electronic integrated circuit on a chip. Other structures are possible as well.
Other advantageous irr provementci of the invention have been characterized ir~ the subclaims or they will hereafter be described in greater 15 detail together with the preferred embodiment of the invention with reference to the ~rawings, in which:
Figure 1 is a block diagram of a wa~relength converter including a four gate circulator as the preferred embodiment of the Invention-20Figure 2 is a block diagram of a further embodlment of the invention including two three ~ate circulatorsi; and Figure 3 is a schematic functional representation of the wavelength 2~ conversion in accordance with the invention.
Tlle wavelength converter shown in Figure 1 makes it possible to convert the wavelength Ain o~ a light signal into the wavelength A~ut- It is particularly suited for use in optical data transmission systems with light ~0 waveguides in which wa~/elength and time multiplexing are employed for optimi~ing the rat~ of transmission.
... , _ .... _ _ .
Dec 29 97 02: 23~ Karl HtcA 02225865 l997-l2-29 617-491-8~77 P- 33 The wa~elength converter consists of two stages 1, 2 which are connected to each other by an optical four gate circulatcr 3.
On the one hand, the four gate circulator 3 couples the light ~ignal of S wavelength Ain present at the signal input of the wavelencTth oonverter into the first stage 1. On the other hanJ, the four gate circulator 3 connects the hN~
stages 1, 2 with each other and feeds the output signal uf the first star~e 1 tothe second stage 2. Furtherrr,ore, the circulator 3 feeds the output si~nal of the second stage 2 to the signal output of the wavelength converter.
Initially the first stage 1 ~onverts the light signal present at the signal input of the wavelength converter into the internal wavelength A~, whereas the second stage 1 thereafter converts this light signal of wavelength Ajnt intothe output wa~lelength Aol,, In essence, the first stage 1 consists of an optical semiconductor amplifier 4 to one side of which is fed the radiation frorn the laser light source 5 (hereafter abbreviated to "laserl'~ of wavelength Aint. and to the other side of which is fed the light signal of wavelength Aj" present at the signal input of the 20 wavelength converter. As the output of the semiconductor amplifier 4 is present on the side to which the input signal of wavelength Ain is fed, it is primarily a light sicTnal of wavelength Aj,,, which leaves tlle semiconductor amplifier 4, while the in,~ut signal of wavelength Ain seNes only for modulationand leaves the semiconductor amplifier 4 in the direction of the second stage 25 in no more than a negligihle quantity.
Modulation of the semiconductor ampTifier 4 is carriPd out by cross amplification modulation. The cross amplification modulation is ~ased upon the dependency of the ~mplification factor from the input level of the ~0 semicondur,tor amplifier 4. Thus the amplificatiGn factor is reduced 2s the input level increa~e~ as the semiconductor amplifier 4 is driven into Dec Z9 97 02: l~p Karl H~CA 0222~86~ 1997-12-29 617-491-8~77 p. 15 saturation.
If a light signal of wavelength ~4n with a relatively high !evel is present at the inpuf of the wavelength converter it will result in a relatively low 5 amplification because of the saturation of the semiconductor amplifier 4 and, hence, in a relativeiy low level of the output signal of wavelength A~
If, on the other handi the input signal of the wavelength converter is of relatively low level the semiconductor amplifier will have a reJatively high 10 amplification factor which will correspondingly result In a relatively high level at the output of the semiconductor amplifier 4 Thus, at the output of the semiconductor a.~plifier 4 there appears a light signal of wavelength Aln, which will be modulated by the input signal and 1~ which relative thereto will be of inverted polari~y.
The semiconductor amplifier 4 is substantially insensitive to deviations of polarlzatiorl and wavelength of the input signal; but it does deliver an out-put signal of a constant wa~/elength A,nt and constant polarization. For that 2V reason the wavelength converter is very flexlble as regards its input and puts low demands on the consistency and wavelength of the input signal. The wavelength conYerter may therefore receive different channeis with different wavelengths.
The output signal of the semiconductor ~mplifier 4 is fed as a rnodula-tion signal through the four gate ~irculator 3 to the Fabry-Perot laser 6 into which there is also coupled CW !ight of wavelength Ain from a further laser light source 7. Depending upon the level of the modulation signal of wave-length Aj"t, because of the so-called "injection-Jocking" the Fabry-Perot laser 6 3(~ Is locked either to wavelength hjnt or to wavelength Aoul of the laser !ight sour-ce 7.
Dec 29 97 02: 18r~ Karl HccA 02225865 1997-12-29 ~17-491 8877 p. lEi If the output signal of the semiconductor ampliher 4 has a high level the Fahry-Perot laser 6 will be locked to wavelength Aln" at a low level output signal from the semiconductor laser 4 the Fabry-Perot laser 6 wilt be locked to the wavelength AOUt Of the laser light source 7.
The two signals of waveiengths Aln~ and Aout are fed from the four gate circulatcr 3 to a filter 8 which blocks light of wavelength Ajnl.
The output s~gna~ of the wavelength converter thus has a relatively ll) high ~evei if the Fabry Perot laser 6 is locked to wavelength A~u~ of the laser light source 7, i.e., if the output signal of the ~emicondu~tor annplifier 4 is of a relatively low level. Conversely, the outp-lt signal of the wavelength converterwill be of a relatively low level if the level of the output signal of the semicon-ductor amplifier 4 is relativeJy high.
The second staye, therefore, inverts the polarity of the signal for a second time se that the output signal and the input signal of the wavelength converter are of the same polarity. This makes cascading of the wavelength converter possible, since otherwise, If the wavelength oonverter inverted the ~0 polarity of the signal, the number of cascaded waYelength converters would have to be taken into consideration during signal ~/aluation.
The waveiength conversion in the second stage is carried out relatively abruptly at a strongly non-linear transfer function, similar to a threshold stage.
2~ During transmisslon of digital signals with a level for each of the two binary signals the spacing between the two logic levels is, therefore improved, and in this manner the ~it errr~r rate is reduced, or the greatest possible distanceof transmission is enlarged. Thus, the second stage with its Fabry-Perot laser 6 regenerates the input signai. This, in turnl makes it possible to cascade 30 numer~us wavelength converters, as the signal in each wavelen~th converter is "refreshened" and, thus, no noise can accumulate.
Dec Z9 97 OZ: 18p Karl HCcA 0222~865 1997-12-29 617 491 ~e77 ~. 17 Moreover, the seeond stage makes possible conversion of the Input signal into different wavelengths A~,u~. For that purpose, if would only ~e necessary to hJne tho laser light source 7 differently which leads to an excitation ot other modes of the Fa~ry-Perot laser 6. The num~er of possible emission frequencies is limited only by the tuning rang~ of the laser light source 7. For frequency tur1able iaser diodes the range may ~e up to 15 nm.
Since the frequency spacing of the Fabry-Perot laser 6 is .7 nm, the wa~relength conv~rter may thus address t~!venty-orle channels. In this manner, and by v~rying the temperature of the laser by less than 3 to 4~C
0 any desired output wavelength Aout may In principle be set within the tuning range.
Irl Fi~ure 2, two three gate clrculators 9', 9" are connected instead of the four gate circulator, all oth~r components and their functions being the 15 same as in Figure 1. Between the tWQ three gate cirsulators 9', 9" there is arranged an optic~l arnplifier 10 which pro~ides for a flexible applicatlon of the wavelength converter.
The diagram depicted in Figure 3 explains tl~e wavelength ccnversion 20 by the wavelength converter in accordance with the invention.
Because of the use of an optical semiconductor arnplifier the first stage ~f the wavelength conYerter ~s relatively insensitive to the wavelength and polari~ation of the input ~ignal~ For that reason, the wavelength converter ~5 may receive input channels with different wavelengths A, to h~. Initially. the first stage then corlverts the input signal regard?ess of its wavelength into the internal wavelenyth Ai"t Since the sernic~nductor am~lifier is substantially rnore ~apable of conversion to shorter wavelengths than to longer ones, the wavelength Ajrl~ iS selected so as to optimize the conversion performance o ~() the semiconductor amplifier. To this en~, the internal wavelength Ain, i~
determined by the wa~/elength of the laser connected to the semiconductor Dec 29 97 02~19p Karl HcCA 0222~865 1997-12-29 617-491-8877 p.18 amplifier.
The second stage thereafter converts the output signal of wavelenyth A;n~ from the tirst stage into output wavelength Al, Az, A3l A4 or As which is S determined by the wa~elength of the laser light source of the second stage.
By tuning the wavelength of this laser light source different output channels may thus be addressed, including ~rl - A~Ut The invention is not limited in its execution to the preferred 10 embo-lt" ,er,t~ describe~ supra. Rather, a number of variants are conceiva~lewhich utiiizes the described snlution even with embodiments cf totally different structures.
Nevertheless, the mentiened wavelength converter suffers from a variety of disadvantages~
Firstly, ~his wavelength converter inverts the signal polarity of the input ~0 signal. Thus, if several wavelength converters are arranged in a cascading manner. the number of cascaded wavelength conve~ers must l~e considered -Dec 29 97 02:23p Karl Hor~A 02225865 1997-12-29617-491-e877 p.32 in evaluating the signal. In an optical data transmission system this would be entail signihcant complexity, and it would limit flexibility.
Secondly. con~ersïon by optical semiconductor amplifiers is dependent S upon the position of the wa\~elengths of input and output signal. Thus, conversion by optical semiconductors works best when converting lar~er Into smaller wavelen~ths.
Moreo~,er, a distorted input signal is reproduced as a distorted signal o at the output. This is a particular drawback where several wavelength conYerters are arranged in a cascade, as in such an arrangement noise is accumulated thus limiting the number of c~scaded waYelength converters.
Moreover, the wavelength converter provides an output signal of a I 5 relatively unclean frequency spectrum ("chirp"~. Because of the dispersion inherent In light wave~uides, this, in transn,illii1g the output signal through a ~ight waveguide, will result in a distortion of the transmitted signal and, therefore, to a restriction of the distance over which transmission is possible without intermediate amplifiers or repeaters.
In U.S. Patent 5,2~4,96~, there is described a wavelength converter which is constructed of two stages, each stage being based upon the cross gain modul~tion (XGM - cross gain modulation~ and provided with a modulatable optical semiconductor arnplifier having an input, an output and a 2~ rnodulation input and a laser light source, the two stages being connected toeach other by an optical coupling element. However, when cascading two XGM converters a chirped signal will resulkt which is imprecise in terrns of itswavelength. In the transmission of date over standard single-mode fibers this spectral uncleaness is, however, disadvantageous because it makes 30 trànsmission of 10 Gbit/s impossibie even over a small distance of 20 km and because signal distrotions are recognizable at low bit r~tes already ~ ~ide J.S.
Dec 29 97 02: lSp Karl H~rrCA 02225865 1997 12 29617-491 -8B77 P- ~
Perino J.M. Wiesenfeld LProceedings of 1994 Conference on Lasers and Electro-Optics and the International Electrani~s Conference C:LEO/IQEC, Anaheim, CA, USA, 8-13 May, pp. 298-299).
S It is, thereforel a particular task of the invention to provide a wavelength converter of the kind mentioned supra which makes possible a conversion of wavelengths at high precision substantially without distortions and with a high extinction factor.
The task is accomplished by a wavelength c~nverter of the kind referred to supr~ the modulatable component of the second stage of which in accordance with the invention is ,orovided with a Fabry-Perot laser provided with an input for the second laser light source feeding light of the second wavelength into the Fabry-Perot laser, with an output and a modulation input, l ~ whereby ~he output of the Fabry-Perot laser is connected to the signal output and the modulation input of the Fabry-Perot laser is connected to the output of the semiconductor amplifier and the coupling element is provided with at least one circulator.
In the two-stage wavelength con~erter in accordance with the inventlon the first stage consists essentially of an optical semiconductor arnplifier provided with an input, ~n output and a modulation input. The light signal of a fi~s~ laser light source operating in a continuous wave mode at wa~Jelength ~, is applied to the input of the semiconductor ampliher. The modulation inpùt of 25 the serniconductor laser is connected to the signal input of the wavelength converter.
Therefore, the light signal applied to the signa1 input of the wavelength converter modulates the light signal from the first laser with wavelength Aint In 30 this process, the rno~ulation is carried out by a cross arnplification rnodulation.
Dec 29 97 02: 16p Karl HcCA 0222586~ 1997-12-29 61 ,'-491-81377 p.9 ~ he crGss amplification modulation is based upon the dependency of the amplification factor from the input level. Thus, as the level of the modL~lation signal becomes larger, the amplification factor becomes smaller with increasing saturation of the amplifien If the level of the modulation si~nal is relatively high, the amplification factor and, accordingly, the level of the output signal of wavelength Ajnt will be relatiYely low. ConverseJy, ~t a relatively low level modulation signal the amplification factor and, hence, the level of the output signal of wavelen3th A;" will be rel~tively high Therefore, the signal polarit~l~ of the output signal of the semicon~uctor amplifier will be of ld inverted polarity relative to the modulation signal.
The optical semioonductor arnplifier delivers an output signal of a defined wavelength Ajnt substantially independently o~the wavelength and polarization of the in~ut signal. For that reason, the wavelength convelter ~s 15 substantially insensitive to deviations of the polarity or changes in the wavelen~th of the input signa~ and accord~n~ly it is very flexi~le at its input side.
In a preferred embodiment fhe modulation input and the oufput of the 20 sen~iconductor amplifier are located at one side of semiconductor amplifier, and the input is located at the opposite side. The modulation signal and the continuous wave sight si~nal of the first laser are, therefore, coupled into thesemiconductor amplifier from different directions. Thus, it is chiefly light of wavelength Alrt which leaves the semiconductor amplifier, whereas hardly any 25 of the light of wavelength An emitted by the signal input of the wavelength conve~er and entering the ~en,icc,nductor amplifier at its modulalion input is conducted in the direction of the second stage. This is irnportant so that the inp~Jt signal of wavelength Ajn~ of t~le fir~t stage is not deleteriously superposed on the o~tput signal of wavelength hjr,t thereof. In this embodiment, and with a30 sufficiently high antireflection, the wavelength Aj,. of the input signal rnay be equal to the wa~elength A,,~, of the laser since the light signal applied to the Dec 29 97 OZ: l~p Karl HocA 0222~86~ 1997-12-29 617 49 p. lO
input of the wavelength converter cannot leave the semiconductor amplifier becal~se of the disposition of modulation input and output.
In another embodiment, a filter which blocks light of wavelength lin is 5 arranged for the same purpose behind the output of the semiconductor.
The second stage of the wavelength converter consists of a Fabry-Perot-laser, and a laser light source emitting light of wa~lelength AoU The CW
light of wa~relength ~)bu~ from this second laser light source and the light of 10 wavelength Aj"~ emitted from the sen~icondt~ctor amplifier are coupled into the Fabry-Perot laser by means of a coupling element and by i'injection induced"
switching it causes modulation of the radiation of wavelength ~OU~. Upon coupliny in of a data pulsel the Fabry-Perof laser converts from a state locked to wavelength Aoul into a non-locked state (inverted modulation) or vice versa 15 ~non-inverted rnodulation .
Inverted or non-inverted modulation may selectively be set -as has already been mentlon- by way of the operating conditions of the second stage.
By double inve~sion by the semiconductor amplifier on the one hand, ~nd by the Fabry-Perot laser of tl~e ser,ond stage on the other hand, the olllput signal will be of the same polarity as the input signal of the waYelength converter. T~is is of especial irnportance whcre several wavelength converter ~5 are cascaded, as otherwise an in~/ersion of the signal polarity by the wavelength converter would necessitate consideration of the number of casca~ed wav~length converters for pur~oses of signal evaluation.
Becau~e of the use of a laser light source as the converter, the 30 transmission function of the second stage is h~hly non-linear, similar to a threshold element. In digital data transmission with two logic levels Dec Z9 97 ~Z: 16~ Kar-l Hor.C.. A 02225865 1997-12 29617-4YI-8877 p. 11 corresponding to the two binary signals, the output signal of the waveiength con~erter of the waYelength converter for this reason has clearly defined levels larg~ly independent of disturbanc~s in the input signal of the second stage. On the one hand, this results in greater flexibility as regards the S requirements for the first stage and, on the other handT in a regeneration of the input signal by the wavelength ~on~erter. Hence, even an input signa with relati~ely strong noi~e superposed thereon c~n be con\lerted correctly and with clearly defined output levels. Advantagecusl~, the regeneration of the input signal makes it possible to cascade a plurality of wa~telength 1 0 converters.
Thus, the wa~length conYerter in the first stage initially converts a light signal of wavelength Ajn into the internal wavelength Ajnt and thereafter, in the second sta~e, into the output wavelength A
In a particular~y advantageous embodiment o~ the inventir~n the waveleng~h of the laser in the se~;ond stage may be tunable. In this fashion, the wavelength converter may address different output channels each having a different wa~elength.
~0 In a fu~her embodiment of the invention the internal waYelength A,nt ~s shorter, on the one hand, than the wavelength ~ of the input signal and, on the other hand? shorter than the wavelength Aout of the output signal. To this end, adY~ntageous use is made of the fact that the second stage with its 25 laser light source as the wavelength converter functions relatively well for converting a shorter waYelength into a longer one whereas the semicon~uctor amplifier IS better suited for converting a light signal ~rom a longer wavelength int~ a shorter one. T~at is to say that the second stage is compensating the fre~uency response of the first stage. The internal wavelength Aj~ is thus 30 selected such that the semicGnductor amplifier operates in an optimum fashion at the predet~rmined wavelength Aj~ ot the input signal.
Dec 2~ 97 02: 17p Karl HorrCA 02225865 1997-l2-29D17-491-8877 p. lZ
The laser light source of the second stage provides a light signal of a relatively narrow ~anded frequency range. For that reason, the output signal of the w~velength converter is subject to relatively low distortion only during transrnission through a light wave~uide in spite of the distortion occurring in S light waveguides. This is of advantage for transmission over relatively large distances without intermediate amplifiers (repeaters~.
Moreover, even at an input signal from the wavelength oonverter of relatively unclean spectral purity ~chirp) the laser of the second stage will 10 deliver a relatively rtarrow-banded output signal. An input si3nal detrimentally affected hy "chirp" is thus regenerated by th~ wavelongth converter. This advantageously lowers the error rate in data transmission or increases the possible transmission distance, as the case may be, and It allows many wavelength converters to be cascaded.
Furtherrnore and as described sup~a, the semiconductor arnpli~ler is substantially independen~ of the wavelength of the Input signal. For that reason, the wavelength converter in accordance with the invention may embrace several input channels of dif.ferent wavelengths. In this connection, ~0 the wavelength dependency of the extinction factor is lelati~/ely insignlficant which is achieved by the utilizin~ the laser light source as a conYerter in the second stage.
In a special variant of the inYention of its own inventive significance the 25 coup!in~ element for connecting the two stages of the wavelength converter essentially consisl~ of a four gate circulator connected to the signal input of the wave!ength converter, the modulat,on input and the output of the semiconductor amplifier, the modulation OUtpLlt and the output of the laser of the second stage as well as with the signal output of the wa~elength ~0 converter.
Dec: 29 97 02: 171~ Karl Ho~A 02225865 1997-12-29 617-491 8877 p. 13 Tl-e circulator couples light from the signal input of the wavelength converter into the modulation input of the semiconductor arnpliher, frorn the output of the semiconductor amplifier to the modulation input of the laser of the second stage, as well as from the output of the ~econd stage into the 5 signal output of the wavelength converter. Such a circulator on the one hand insures optlcal isolation of the two stages of the wavelen~th converter and, on the other hand, it advantageously has a relatively low coupling loss of lëss than 1 d~.
In another variant of the invention the couplin~ element consists of two series-connected circulators, the first circulator being connected to the si~nalinput of the wavelength converter as well as to the modulation input and to the output of the semiconductor amplifier. The second circulator, on the other hand, is connected to the modulation input and the output of the laser of the 15 second stage as well as to the signal output of the wavelength converter.
The first circulator couples light from the signal Input of the wavelength converter into the modùiation input of the semiconductor amplifier and from the output of the semiconductor amplifier into the second circulator. In the ~0 second stage, the seeond circu~ator thereafter couples the light from the first circulator into the modulation input of the laser and feeds the output signal ofthe second stage to the signal output of the wavelength converter. In this operation, the great flexibility is of advantage, as further components, e.g.
optical amplifiers, may be connected be~Neen the two circu~ators.
~5 In another preferred embodiment the optical coupling elernent is provided with conventicnal couplers structured, for instance, as 3dB
directional couplers.
Hence, the wavelength converter in accordance with the invention combines the ad,ranta~es of an optical semiconductor amplifier as the input Dec 29 97 02: 17p Karl Hor~A 0222ci86ci 1997 12 2g~:~l7-49l-8l377 p. 14 stage (indepcndence of polarization and wavelength, reception of several input channels of different wa~el~ngllls) with the advantages of a laser converter as the output stage ~regeneration of the input signal by a threshold-like transmission function, high extinction ratio of the output signal, purity o~
the output spectrum, equally good conversion into longer as well as shorter wavelengths~, and it makes it possible freely to select the data rate over a wide range.
Advantageously. the wavelength converter in accordance with the 10 invention is a hybrid structure with individual components or an opto-electronic integrated circuit on a chip. Other structures are possible as well.
Other advantageous irr provementci of the invention have been characterized ir~ the subclaims or they will hereafter be described in greater 15 detail together with the preferred embodiment of the invention with reference to the ~rawings, in which:
Figure 1 is a block diagram of a wa~relength converter including a four gate circulator as the preferred embodiment of the Invention-20Figure 2 is a block diagram of a further embodlment of the invention including two three ~ate circulatorsi; and Figure 3 is a schematic functional representation of the wavelength 2~ conversion in accordance with the invention.
Tlle wavelength converter shown in Figure 1 makes it possible to convert the wavelength Ain o~ a light signal into the wavelength A~ut- It is particularly suited for use in optical data transmission systems with light ~0 waveguides in which wa~/elength and time multiplexing are employed for optimi~ing the rat~ of transmission.
... , _ .... _ _ .
Dec 29 97 02: 23~ Karl HtcA 02225865 l997-l2-29 617-491-8~77 P- 33 The wa~elength converter consists of two stages 1, 2 which are connected to each other by an optical four gate circulatcr 3.
On the one hand, the four gate circulator 3 couples the light ~ignal of S wavelength Ain present at the signal input of the wavelencTth oonverter into the first stage 1. On the other hanJ, the four gate circulator 3 connects the hN~
stages 1, 2 with each other and feeds the output signal uf the first star~e 1 tothe second stage 2. Furtherrr,ore, the circulator 3 feeds the output si~nal of the second stage 2 to the signal output of the wavelength converter.
Initially the first stage 1 ~onverts the light signal present at the signal input of the wavelength converter into the internal wavelength A~, whereas the second stage 1 thereafter converts this light signal of wavelength Ajnt intothe output wa~lelength Aol,, In essence, the first stage 1 consists of an optical semiconductor amplifier 4 to one side of which is fed the radiation frorn the laser light source 5 (hereafter abbreviated to "laserl'~ of wavelength Aint. and to the other side of which is fed the light signal of wavelength Aj" present at the signal input of the 20 wavelength converter. As the output of the semiconductor amplifier 4 is present on the side to which the input signal of wavelength Ain is fed, it is primarily a light sicTnal of wavelength Aj,,, which leaves tlle semiconductor amplifier 4, while the in,~ut signal of wavelength Ain seNes only for modulationand leaves the semiconductor amplifier 4 in the direction of the second stage 25 in no more than a negligihle quantity.
Modulation of the semiconductor ampTifier 4 is carriPd out by cross amplification modulation. The cross amplification modulation is ~ased upon the dependency of the ~mplification factor from the input level of the ~0 semicondur,tor amplifier 4. Thus the amplificatiGn factor is reduced 2s the input level increa~e~ as the semiconductor amplifier 4 is driven into Dec Z9 97 02: l~p Karl H~CA 0222~86~ 1997-12-29 617-491-8~77 p. 15 saturation.
If a light signal of wavelength ~4n with a relatively high !evel is present at the inpuf of the wavelength converter it will result in a relatively low 5 amplification because of the saturation of the semiconductor amplifier 4 and, hence, in a relativeiy low level of the output signal of wavelength A~
If, on the other handi the input signal of the wavelength converter is of relatively low level the semiconductor amplifier will have a reJatively high 10 amplification factor which will correspondingly result In a relatively high level at the output of the semiconductor amplifier 4 Thus, at the output of the semiconductor a.~plifier 4 there appears a light signal of wavelength Aln, which will be modulated by the input signal and 1~ which relative thereto will be of inverted polari~y.
The semiconductor amplifier 4 is substantially insensitive to deviations of polarlzatiorl and wavelength of the input signal; but it does deliver an out-put signal of a constant wa~/elength A,nt and constant polarization. For that 2V reason the wavelength converter is very flexlble as regards its input and puts low demands on the consistency and wavelength of the input signal. The wavelength conYerter may therefore receive different channeis with different wavelengths.
The output signal of the semiconductor ~mplifier 4 is fed as a rnodula-tion signal through the four gate ~irculator 3 to the Fabry-Perot laser 6 into which there is also coupled CW !ight of wavelength Ain from a further laser light source 7. Depending upon the level of the modulation signal of wave-length Aj"t, because of the so-called "injection-Jocking" the Fabry-Perot laser 6 3(~ Is locked either to wavelength hjnt or to wavelength Aoul of the laser !ight sour-ce 7.
Dec 29 97 02: 18r~ Karl HccA 02225865 1997-12-29 ~17-491 8877 p. lEi If the output signal of the semiconductor ampliher 4 has a high level the Fahry-Perot laser 6 will be locked to wavelength Aln" at a low level output signal from the semiconductor laser 4 the Fabry-Perot laser 6 wilt be locked to the wavelength AOUt Of the laser light source 7.
The two signals of waveiengths Aln~ and Aout are fed from the four gate circulatcr 3 to a filter 8 which blocks light of wavelength Ajnl.
The output s~gna~ of the wavelength converter thus has a relatively ll) high ~evei if the Fabry Perot laser 6 is locked to wavelength A~u~ of the laser light source 7, i.e., if the output signal of the ~emicondu~tor annplifier 4 is of a relatively low level. Conversely, the outp-lt signal of the wavelength converterwill be of a relatively low level if the level of the output signal of the semicon-ductor amplifier 4 is relativeJy high.
The second staye, therefore, inverts the polarity of the signal for a second time se that the output signal and the input signal of the wavelength converter are of the same polarity. This makes cascading of the wavelength converter possible, since otherwise, If the wavelength oonverter inverted the ~0 polarity of the signal, the number of cascaded waYelength converters would have to be taken into consideration during signal ~/aluation.
The waveiength conversion in the second stage is carried out relatively abruptly at a strongly non-linear transfer function, similar to a threshold stage.
2~ During transmisslon of digital signals with a level for each of the two binary signals the spacing between the two logic levels is, therefore improved, and in this manner the ~it errr~r rate is reduced, or the greatest possible distanceof transmission is enlarged. Thus, the second stage with its Fabry-Perot laser 6 regenerates the input signai. This, in turnl makes it possible to cascade 30 numer~us wavelength converters, as the signal in each wavelen~th converter is "refreshened" and, thus, no noise can accumulate.
Dec Z9 97 OZ: 18p Karl HCcA 0222~865 1997-12-29 617 491 ~e77 ~. 17 Moreover, the seeond stage makes possible conversion of the Input signal into different wavelengths A~,u~. For that purpose, if would only ~e necessary to hJne tho laser light source 7 differently which leads to an excitation ot other modes of the Fa~ry-Perot laser 6. The num~er of possible emission frequencies is limited only by the tuning rang~ of the laser light source 7. For frequency tur1able iaser diodes the range may ~e up to 15 nm.
Since the frequency spacing of the Fabry-Perot laser 6 is .7 nm, the wa~relength conv~rter may thus address t~!venty-orle channels. In this manner, and by v~rying the temperature of the laser by less than 3 to 4~C
0 any desired output wavelength Aout may In principle be set within the tuning range.
Irl Fi~ure 2, two three gate clrculators 9', 9" are connected instead of the four gate circulator, all oth~r components and their functions being the 15 same as in Figure 1. Between the tWQ three gate cirsulators 9', 9" there is arranged an optic~l arnplifier 10 which pro~ides for a flexible applicatlon of the wavelength converter.
The diagram depicted in Figure 3 explains tl~e wavelength ccnversion 20 by the wavelength converter in accordance with the invention.
Because of the use of an optical semiconductor arnplifier the first stage ~f the wavelength conYerter ~s relatively insensitive to the wavelength and polari~ation of the input ~ignal~ For that reason, the wavelength converter ~5 may receive input channels with different wavelengths A, to h~. Initially. the first stage then corlverts the input signal regard?ess of its wavelength into the internal wavelenyth Ai"t Since the sernic~nductor am~lifier is substantially rnore ~apable of conversion to shorter wavelengths than to longer ones, the wavelength Ajrl~ iS selected so as to optimize the conversion performance o ~() the semiconductor amplifier. To this en~, the internal wavelength Ain, i~
determined by the wa~/elength of the laser connected to the semiconductor Dec 29 97 02~19p Karl HcCA 0222~865 1997-12-29 617-491-8877 p.18 amplifier.
The second stage thereafter converts the output signal of wavelenyth A;n~ from the tirst stage into output wavelength Al, Az, A3l A4 or As which is S determined by the wa~elength of the laser light source of the second stage.
By tuning the wavelength of this laser light source different output channels may thus be addressed, including ~rl - A~Ut The invention is not limited in its execution to the preferred 10 embo-lt" ,er,t~ describe~ supra. Rather, a number of variants are conceiva~lewhich utiiizes the described snlution even with embodiments cf totally different structures.
Claims (9)
1. Wavelength converter for converting a first light signal of a first wavelength (.lambda.in) serving to transmit data into a second light signal of a second wavelength (.lambda.out), with a signal input for receiving the first light signal, a signal output for emitting the second light signal, a modulatable optical semiconductor amplifier (4) with an input, an output and a modulation input, a first laser light source (L1) forming a first stage with the semiconductor amplifier (4), whereby the input of the semiconductor amplifier (4) is connected with the first laser light source (L1) and the modulation input of thesemiconductor amplifier (4), for cross amplification modulation, is connected to the signal input and the first laser light source (L1) emits light of a thirdwavelength (.lambda.int), and in which a second stage (2) is connected to the output of the first stage (1) by a coupling element, the second stage being provided with a second laser light source emitting light of the second wavelength (.lambda.out) and with a modulatable component, characterized by the fact that the modulatable component of the second stage (2) is provided with a Fabry-Perot amplifier having an input for the second laser light source (L2) feeding light of the second wavelength (.lambda.out) into the Fabry-Perot laser, an output and a modulation input, whereby the output of the Fabry-Perot laser (FP) is connected to the signal output and the modulation input of the Fabry-Perot laser (FP) is connected to the output of the semiconductor amp[lifier (4) and the coupling element is provided with at least one circulator.
2. Wavelength converter according to claim 1, characterized by the fact that the output signal of the semiconductor amplifier (4) modulates the Fabry-Perot laser (FP) by injection locking.
3. Wavelength converter according to claim 1 or 2, characterized by the fact that the third wavelength (.lambda.int) Of the semiconductor amplifier (4) is shorter than the first wavelength (.lambda.in) and the second wavelength (.lambda.out) so that a reduction of the wavelength is performed by the first stage (1) and an increase of the wavelength is performed by the second stage (2).
4. Wavelength converter according to one of claims 1 to 3, characterized by the fact that a filter (8) blocking light of the third wavelength (.lambda.int) is connected to the output of the second stage (2).
5. Wavelength converter according to claim 1, characterized by the fact that the coupling element (3) is provided with a circulator having for connections.
the first connection being connected to the signal input, the second connection being connected to the output and to the modulation input of the semiconductor amplifier (4), the third connection being connected to the modulation input and the output of the second stage (2) and the forth connection being connected to the signal output, whereby the circulator (3) feeds light from the first to the second connection, from the second to the third connection and from the third to the fourth connection.
the first connection being connected to the signal input, the second connection being connected to the output and to the modulation input of the semiconductor amplifier (4), the third connection being connected to the modulation input and the output of the second stage (2) and the forth connection being connected to the signal output, whereby the circulator (3) feeds light from the first to the second connection, from the second to the third connection and from the third to the fourth connection.
6. Wavelength converter according to claim 1, characterized by the fact that the coupling element is provided with two circulators (9',9") each having three connections, whereby the third connection of the first circulator (9') is connected to the first connection of the second circulator (9"), that at the first circulator (9') the first connection is connected to the signal input and the second connection is connected to the output and to the modulation input of the semiconductor amplifier, that at the second circulator (9") the second connection is connected to the output and to the modulation input of the second stage and the third connection is connected to the signal output, that each of the two circulators (9',9") feed light from the first to the second and from the second to the third connection.
7. Wavelength converter according to claim 1, characterized by the fact that for optimizing the conversion performance of the semiconductor amplifier (4) the first laser light source (5) is tuneable
8. Wavelength converter according to claim 1, characterized by the fact that the second laser light source (7) is tuneable for addressing a plurality ofoutput channels.
9. Wavelength converter according to claim 1, characterized by the fact that for blocking the first light signal the output and the modulation input on the one hand and the input on the other hand of the semiconductor amplifier (4) are arranged on opposite sides of the semiconductor amplifier (4).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19525117.2 | 1995-06-30 | ||
| DE19525117 | 1995-06-30 | ||
| PCT/DE1996/001193 WO1997002634A1 (en) | 1995-06-30 | 1996-06-28 | Wavelength converter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2225865A1 true CA2225865A1 (en) | 1997-01-23 |
Family
ID=7766470
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002225865A Abandoned CA2225865A1 (en) | 1995-06-30 | 1996-06-28 | Wavelength converter |
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| Country | Link |
|---|---|
| US (1) | US5940207A (en) |
| EP (1) | EP0835542B1 (en) |
| JP (1) | JPH11509642A (en) |
| AT (1) | ATE176100T1 (en) |
| CA (1) | CA2225865A1 (en) |
| DE (2) | DE19627333A1 (en) |
| WO (1) | WO1997002634A1 (en) |
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|---|---|---|---|---|
| JP3302310B2 (en) * | 1997-12-11 | 2002-07-15 | ケイディーディーアイ株式会社 | Optical amplification transmission system and optical amplifier |
| KR19990055420A (en) * | 1997-12-27 | 1999-07-15 | 정선종 | Fully Optical Wavelength Converter Using Semiconductor Optical Amplifier and Polarization Interferometer |
| JP3438770B2 (en) * | 1998-03-06 | 2003-08-18 | Ｋｄｄｉ株式会社 | Optical digital playback device |
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| KR100470869B1 (en) * | 2000-05-23 | 2005-02-21 | 주식회사 케이티 | Apparatus for converting wavelength of optical signal |
| JP2002232355A (en) * | 2001-01-31 | 2002-08-16 | Kddi Submarine Cable Systems Inc | Optical fiber transmission line |
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| JP2002280959A (en) * | 2001-03-16 | 2002-09-27 | Kddi Submarine Cable Systems Inc | Dispersion compensation light transmission line and optical transmission system |
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| US20030002046A1 (en) * | 2001-05-29 | 2003-01-02 | Myers Michael H. | Compound asymmetric interferometric wavelength converter |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5264960A (en) * | 1992-05-08 | 1993-11-23 | At&T Bell Laboratories | Optical wavelength shifter |
| US5734493A (en) * | 1996-11-01 | 1998-03-31 | Lucent Technologies Inc. | Optical frequency conversion device |
-
1996
- 1996-06-28 CA CA002225865A patent/CA2225865A1/en not_active Abandoned
- 1996-06-28 US US08/983,426 patent/US5940207A/en not_active Expired - Fee Related
- 1996-06-28 EP EP96921888A patent/EP0835542B1/en not_active Expired - Lifetime
- 1996-06-28 AT AT96921888T patent/ATE176100T1/en not_active IP Right Cessation
- 1996-06-28 DE DE19627333A patent/DE19627333A1/en not_active Withdrawn
- 1996-06-28 JP JP9504712A patent/JPH11509642A/en active Pending
- 1996-06-28 WO PCT/DE1996/001193 patent/WO1997002634A1/en active IP Right Grant
- 1996-06-28 DE DE59601194T patent/DE59601194D1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0835542B1 (en) | 1999-01-20 |
| WO1997002634A1 (en) | 1997-01-23 |
| DE19627333A1 (en) | 1997-01-02 |
| JPH11509642A (en) | 1999-08-24 |
| EP0835542A1 (en) | 1998-04-15 |
| US5940207A (en) | 1999-08-17 |
| DE59601194D1 (en) | 1999-03-04 |
| ATE176100T1 (en) | 1999-02-15 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued |