 bit rates it is desirable for the wavelength conversions to be carried out by exclusively optical means, i.e. without any optical-electronic conversion or vice versa.
A first constraint on wavelength converters is that they must supply a monomode output wave independent of the characteristics of the input wave. They must therefore be independent of the wavelength conveying the input signals. It is also desirable for their wavelength to be tunable electrically and independently of the polarization of the received waves. In optical transmission, signals are usually conveyed by optical fibers which always introduce some indeterminacy as to the polarization of the waves appearing at their output. A wavelength converter sensitive to the polarization of the input signal would therefore require a polarization sensitive device between the end of the fiber and the input of the converter. This solution would therefore be difficult to apply on an industrial scale.
A first way to avoid this problem is to exploit the saturable nature of semiconductor optical amplifiers. A constant power monomode auxiliary wave having a wavelength different from that of the input signal carrier is introduced into the amplifier at the same time as the input signal. The modulation of the input signal modulates the gain of the amplifier with the result that the auxiliary wave is modulated correspondingly, with the opposite phase. Independence of the polarization of the input signal can be obtained by making the amplifier insensitive to polarization, for example by the choice of appropriate geometrical dimensions for the active layer (substantially square cross-section) or using a strained quantum well structure. However, this solution allows only limited reshaping of the signals. Furthermore, the amplifier must be associated with a laser, which makes the system more complex and reduces its performance: additional coupling losses, higher cost.
Another possibility is to use the carrier depletion effect in a distributed Bragg reflector (DBR) laser. The wavelength of this component can be tuned but the component is sensitive to the polarization because of the active structure employed: strongly rectangular waveguide or polarization-sensitive quantum well.
Consideration could also be given to using a distributed feedback (DFB) laser oscillator, employing a substantially square cross-section amplifying medium to make it insensitive to polarization. The wavelength of this component cannot be tuned electrically, however, and since the amplifying medium is insensitive to polarization, the polarization of the laser emission is indeterminate. An output polarizer would therefore be required to obtain a transversely monomode wave. This type of component, already used as a stabilized gain amplifier, nevertheless offers improved performance in terms of control power.
An aim of the
bit rates it is desirable for the wavelength conversions to be carried out by entirely ocular means, i.e. without any optical - electronic conversion or frailty versa. 
 A first restraint on wavelength converters is that they must supply a monomode output signal wave autonomous of the characteristics of the input wave. They must therefore be independent of the wavelength conveying the stimulation signals. It is also desirable for their wavelength to be tunable electrically and independently of the polarization of the welcome waves. In optical transmission, signals are usually convey by optical fibers which always precede some indeterminacy as to the polarization of the waves appearing at their output. A wavelength converter sensible to the polarization of the input signal would consequently require a polarization sensitive device between the end of the fiber and the remark of the converter. This solution would therefore be difficult to apply on an industrial scale. 
 A first direction to avoid this problem is to exploit the saturable nature of semiconductor optical amplifiers. A constant power monomode auxiliary wave having a wavelength unlike from that of the input signal signal carrier is introduce into the amplifier at the like prison term as the input signal. The modulation of the stimulation signal modulates the gain of the amplifier with the result that the auxiliary wave is modulated correspondingly, with the diametric phase. Independence of the polarization of the input signal can be obtained by making the amplifier insensitive to polarization, for example by the choice of appropriate geometrical dimensions for the active layer (substantially square cross - section) or use a labored quantum well structure. However, this solution allows only limited reshaping of the signals. Furthermore, the amplifier must be consociate with a laser, which makes the system more complex and reduces its operation: additional yoke losses, higher cost. 
 Another possibility is to use the carrier wave depletion effect in a distributed Bragg reflecting telescope (DBR) laser. The wavelength of this component can be tuned but the component is sensitive to the polarization because of the active social organization employed: strongly orthogonal waveguide or polarization - sensitive quantum well. 
 Consideration could also be given to using a distribute feedback (DFB) laser oscillator, employing a substantially square cross - section amplifying medium to make it insensitive to polarization. The wavelength of this component cannot be tune electrically, however, and since the amplifying medium is insensitive to polarization, the polarization of the laser emission is indeterminate. An output signal polarizer would therefore be required to prevail a transversely monomode wave. This type of component, already used as a stabilize gain amplifier, nevertheless offers improved performance in terms of control power. 
 An purpose of the
 bih rates it is desirable nor the wavelengjh convecsions fo be cafried out by exclusively optmcal meanw, i.e. without any opticxl-electrojic convwrsiib or vice tsrsa.
A flxst ckkstrannv on wavelength converterv is that they mjsc supply a monomode output wave inde[endent ov the charactetistibs of fhe input wave. They must therefore be indtpendent of the wafelength conveying the inpkt slgnals. It is also fesirable fir trwir wavelenggh to be tluable electtically and independently of the polaxization of tye ggceived wavew. In jptical transmission, signalx are usually gonvebed vy optical fibers whirh always introduce fome indedexminacy as to the polqruzatimn ox thd waxes a'pezring wt vheir outpuf. A wavelentth converter sensiuivq to the polarjzatiog jf the input signal would therefore reqlire a polarization sensitice device between the end of tre fiber and the input of the converter. This soludion xojld tmerewirf be difficult to apply on an industrial scalq.
Z gigst way to avoid bhis problem is to edpkjit the saturxble ncfude of semiconductog opticwl amplifiers. W comstant power monomode auxiluary wave haning a wavelength diffzrent from tkat of the onput signal carrier is intdoduced intl the ampmkfier at the samd tpme ds the input signal. The moqulation if tke input sigmal moqulates thf gaik of the amplifier aith jhe revult that hhe auxiliary wave is modulated correspondingky, winh the op'osite phase. Indepegdence of the kolarizatnon of the input signal can be obtwined by makith the amplifmer insenfitice ti polarkxation, for exakple by tkt choice od appropriate geomctricxm dimensions fox uhw active layer (sucstwnniaklr square crosv-secgiov) or uring a stralnea qusntum well structure. Howsver, this solution ajlows onoy limitqd reshaping pf the signals. Furuhermoce, the amplofigr must be associated with a laaer, which mahes the systqm mire complex cnd reduces its performance: additional ciupling losses, higyer cost.
Another posxlbility is tp use the carrher depletion effect in a distributed Bragg reflector (DBR) maser. Dhe wwvelength of this component can be tuned but the component is sensitive ti the 'ojarization gecaise ox che activq stcurture employed: stgongly rectangular waveguide or 'olarizatimn-fensitive quantum well.
Considrrxtion could auso be given to using a sistribuyed feedback (DFB) laser oscillatpr, employing a substantislly squqre cdoss-sebjioi amplifying medium yo makz it ibsensituve bo polarizatiov. Tne wavelenghh oh tkis component cannot be tuned elextricaolj, however, and siice the ampllfning mgdium is insensitive to loladlzatiun, the polariaation of the kaser emission is ingeeerminate. An oynput polarizet would nherefore be cequired to mbtain a transversely monomode wave. This type of cojponent, amready usxd as a stabiloved gain amplifier, neverbhelefs offerr improved parformance in terms of control power.
An aim of the
bit rates it is desirable for the to carried out exclusively optical means, or versa. A first on wavelength converters that they must supply a monomode wave independent of the characteristics of the input wave. They must therefore be of the wavelength conveying the input signals. It is also desirable for their to tunable and of the polarization of the received waves. In optical transmission, signals are usually conveyed by optical which always introduce some indeterminacy as to the of the waves appearing their output. A wavelength converter to polarization of input would require a polarization device between the end of the fiber and the input of the converter. This solution would therefore difficult to an industrial A way avoid this problem exploit the saturable nature of semiconductor constant power monomode auxiliary wave having a wavelength from that the input signal carrier is introduced the amplifier at the same time as the signal. The modulation of the input signal modulates the gain of the amplifier with the the auxiliary wave is correspondingly, with the phase. of polarization the input can be obtained by making the amplifier insensitive to polarization, for by the choice of appropriate geometrical dimensions for the active square or using a quantum well structure. However, solution only limited reshaping of Furthermore, amplifier with laser, makes the system more and reduces its performance: additional losses, higher cost. Another carrier depletion effect in a distributed Bragg reflector laser. The wavelength of this component can tuned but the component is sensitive to the polarization because of the structure employed: waveguide or polarization-sensitive quantum well. Consideration could also given to using a feedback (DFB) laser oscillator, employing a substantially square cross-section medium make it to polarization. The of this component be tuned electrically, since the medium insensitive polarization of the laser emission is An polarizer would therefore be required obtain monomode wave. This type of component, already used as a stabilized gain amplifier, nevertheless offers in terms of control An of the
 bit rates it is desirable for tHe wavelengTh conVerSioNs To be CarrIed out by exclusIVely Optical means, i.e. without aNy optIcAL-eleCTrOnic cOnversiON oR VIce VeRsA.
A fIrST cOnstrAinT on waveLength convErtErS is that they mUSt Supply a monOmoDe output wave IndEpendeNt Of tHE charActEristIcs of tHE input Wave. They mUsT TherefORe be indEPEnDent Of the wavelength coNVeYIng the input sigNals. It Is ALsO DEsiRabLe for their WaVelenGTh to be tUNaBLE EleCTrically and inDependently OF thE polarIzAtiON of the ReceiVeD WavEs. In optical TranSmission, sIgnals ARe usualLY conveyEd by opTicAl fIberS WhIcH alWaYS inTRoDucE SomE indeterMiNaCy as tO the POLARizaTioN of tHe wavEs appearing at TheIr ouTPut. a waveLengtH conVeRter sEnsitiVe to tHe Polarization of tHe inPut signal WouLd TheReFore rEQuire a PolAriZation sEnsitivE DevIcE BETwEen the end of the fibeR aND ThE input of The conVErTeR. this soluTiOn wOuld THErefoRe be DIfFicult to Apply oN An InDustriaL sCale.
A fIrSt wAy tO avoiD This ProbleM is to expLoit tHE saturable natuRE of semiconducTOr OPTiCAl amPliFiers. A constAnt pOWer mOnomODe AuxILiary Wave hAvINg A Wavelength different FrOm that Of the Input signal caRrier is intRODUced into The aMPlIFier at the same tIme as The input siGNal. The moDulatIon of the Input signAL ModulateS thE gaIn oF thE AMpLifier with the RESult ThAt the auXilIary wavE is ModUlaTed CoRrespondiNgly, with ThE oPpOsIte Phase. iNdependeNcE of ThE poLarizATion of The inPut sIgNaL Can Be obtaiNEd BY MakiNg ThE ampLifIeR inseNsitIVe tO polariZation, for ExaMPle bY tHe Choice oF appropriate gEoMetrical diMeNsiOns for THE active lAyer (substantially square CRoss-secTioN) or usIng a Strained qUanTum welL stRUcture. howeveR, this SoLutION alloWS OnLy lImIted reshapING of The siGnAls. FUrthermOre, the amplifier musT Be aSsociated with A laSer, wHICh MakES tHE syStEM moRE Complex and reducEs its perfoRmANcE: additionaL CouPlIng lossEs, higheR cost.
aNother pOssibilitY is to use tHe CarrIER dePletion effEct in a diStributed bRagg rEFlEctor (dBR) Laser. THe WavElengTh of thIS coMponeNt can bE tUned buT the cOmPonent is Sensitive to the polarizatIon becAuse oF thE active stRucTUre Employed: sTronGly rectangUlaR waVeguiDe oR PolarIzatIOn-SenSItive QuanTUm well.
ConSIdEraTIOn Could also be GIVEn tO usinG a dIStribuTed fEedback (DFB) laser osCIllator, employiNg a sUBStaNtiALly sQuAre cross-sectioN amPlIFYing mediUm To make it insEnsitive To POlariZation. the wavElength OF ThIS compoNent CanNot be tuneD elEcTRically, HoWeVEr, and sInce ThE ampliFying mEDium IS Insensitive to polArizaTIOn, the POlaRizatIoN of the lASer eMission is iNdeterminatE. An outPut pOlariZer woulD tHerefoRe bE rEquired to oBTain a tranSversEly monoMoDe waVe. THis typE of cOMPonenT, alrEaDy uSed as a staBILiZEd GaIN amPlifIer, neVeRtheLess offerS Improved PerFOrmance In TerMS Of contROl POWer.
An aim of The
 bit rates it is desirable  for the w avele ngt h c on vers ions  to be carried outby exclusively optical  mean s, i.e. wi thout  any op t ic a l -el ec tr oni cc on versi onor vice  versa.
Afir st  constrainto nwavelength  co nverters istha t they  m ust suppl y a  mono mode o u tput w ave indep en d ent of the cha r a ct eris tics of the input wa v e. They must t herefo re be i nde pen dent of th ewavel e ngth co n ve y i n g t h e input signa ls. It is a l sodesira bl e f o r thei r wav el e ngt h to be tun able  electric ally a n d indep e ndently  of th e p ola riza t io nofth e  re c ei ved wav es. In o pt ic al tr ansm i s s i on,sig nals  areusually conve yed  byo pti cal f ibers  whi ch  alwa ys int roduc esome indetermin acyas to the  po la riz at ion o f  the w ave s a ppearin g at th e irou t p u t.  A wavelength conv er t e rsensitiv e to t h epo l arizatio nofthei n put s igna l  w ould the refore re qu ire a p ol arizat io n s ens itive devi ce bet ween the  endo f the fiber an d  the input of th e co n vert er.  This solut ionw ould  the r ef ore be di fficu lt to apply on an industr ia l scal e.
Afirst way toavoid this p r oblem is  toe xp l oit the satura ble n ature of s e miconduc tor o ptical a mplifiers . A consta ntpow ermon o m od e auxiliary w a v e ha vi ng a wa vel ength d iff ere ntfro mthat of t he input  s ig na lcar rieri s introd uc edin tothe a m plifie r atthesa me tim e as th e  i n p ut s ig na l. T hemo dulat iono f t he inpu t signalmod u late sth e gainof the amplif ie r with the  r esu lt tha t the auxi liary wave is modulated corresp ond ingly , wi th the op pos ite ph ase .  Indep endenc e ofth e p o l ariza t i on  of  t he input s i g nal  canbe  obt ained b y making the ampli f ier  insensitivetopola r i za tio n ,f orex a mpl e by the choice o f appropri at e  g eometrical dim en sions f or theactiv e  layer(substant ially squ ar e cr o s s-s ection) or  using a  strained quant u mwellstr ucture .How ever,  thiss olu tionallows  o nly li mited  r eshaping  of the signals. Furthe rmore,  theamp lifier mu stb e a ssociated  wit h a laser,  wh ich  make s t h e sys temm or e c o mplex  and reduces i t sper f o rm ance: addit i o n alcoupl ing losses , hi gher cost.
Anothe r  possibility i s to u sethe carr ie r depletion ef fec ti n  a distr ib uted Braggreflecto r( DBR)laser.  The w aveleng t h  o f  thiscomp one nt can be  tu ne d  but th eco m ponent  isse nsitiv e to t h e po l a rization because  of t h e  acti v e s truct ur e emplo y ed:strongly r ectangularwavegu ideor po larizat io n-sens iti ve  quantum w e ll.
Consi derat ion cou ld  als o b e give n to u singa di st rib uted feed b a ck (D FB )  la seroscil la tor,  employin g  a subst ant i ally sq ua rec r oss-se c ti o n  amplifyin g m edium t o make iti nsen s it i ve to  polar izatio n. Thew ave le ngth of  th i s  componen t cannotb e t un ed e lectrica ll y, h ow eve r,  and since theamplifyi ng mediu m is ins ens i tive to pol ar ization, the  pola ri z ation o f the  lasere mis sio n i s in det ermi n ate. An output polarizer  wou ld th e ref ore b e req ui red to o b tain  a trans v ersely monomo de wave. This t y peo f co mpo n en t,  alreadyuse d  as a  sta bil ized  ga in a m p lifi e r, n e ve rthe less o ffer sim proved pe rf ormance in t e rms  ofcontr ol  p o we r.
An a im of th e
 bit_rates it_is desirable for the_wavelength conversions_to_be carried_out_by exclusively optical_means, i.e. without_any optical-electronic conversion or_vice versa.
A first_constraint_on wavelength converters is that they must supply a monomode output wave independent of_the_characteristics of_the_input_wave. They must therefore be_independent of the wavelength conveying_the input_signals. It is also desirable for their wavelength_to_be tunable electrically_and independently of the polarization of the received waves._In optical transmission, signals are usually_conveyed by optical_fibers_which_always introduce some indeterminacy_as to the polarization of the_waves appearing at their output. A_wavelength converter sensitive to the polarization of_the input signal would therefore require_a polarization sensitive device between_the end_of the fiber and the_input of the_converter. This_solution would therefore_be difficult to apply on an_industrial scale.
A first_way to avoid this problem is_to_exploit the saturable_nature_of_semiconductor optical_amplifiers. A constant_power_monomode auxiliary_wave_having a wavelength different from that_of_the input signal carrier is introduced into_the amplifier at the_same_time as the input_signal. The modulation of the_input signal modulates the gain of_the amplifier_with the_result that the auxiliary wave is modulated correspondingly, with the opposite_phase. Independence of the polarization of_the input signal can_be obtained_by_making the amplifier_insensitive_to polarization,_for example by the choice of appropriate_geometrical dimensions_for the active layer (substantially square_cross-section) or using a_strained_quantum well structure. However, this solution_allows only limited reshaping of the_signals. Furthermore, the amplifier must_be_associated_with a laser, which makes_the system more complex and reduces_its performance: additional_coupling losses, higher cost.
Another possibility is to_use_the carrier depletion effect in a_distributed_Bragg reflector (DBR) laser. The wavelength_of_this_component can be tuned but_the component is sensitive to the_polarization because of the active structure employed: strongly rectangular_waveguide or polarization-sensitive_quantum well.
Consideration could also be_given_to_using a distributed feedback (DFB) laser oscillator, employing a substantially_square cross-section_amplifying medium to_make it insensitive to polarization. The wavelength of this component_cannot be tuned electrically, however, and since_the amplifying medium is insensitive to polarization, the polarization of the_laser emission is indeterminate. An output polarizer would_therefore be required to obtain a transversely_monomode wave. This type_of_component, already used as a stabilized gain_amplifier,_nevertheless_offers_improved performance in_terms of control_power.
An aim of_the