 be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 1. Field of the Invention
The invention concerns a frequency shifter for a medium infrared range wave, i.e. one with a wavelength of more than three microns. A device of this type has many applications in systems for data transmission by frequency modulation, systems for coherent detection by hetrodyning etc. Standard shifters are either of the acousto-optical type, using an interaction between an optical wave and a diffraction grating in motion in the propagation medium of the wave, or of the type with rotating birefringent plates, the rotation being mechanical or electro-optical.
2. Description of the Prior Art
The most commonly used devices in the medium infrared range are of the acousto-optical type. A device of this type has a crystal which is mechanically coupled with an acoustic transducer. The vibrations produced by the transducer are propagated in the crystal, creating local variations in its refractive index. The propagation of these local variations constitutes a diffraction grating which shifts at a constant speed. The wave which has to have its frequency shifted is projected to the surface of the crystal where it is diffracted in undergoing a frequency shift by Doppler effect. A drawback of this type of shifter is that the diffracted wave has an angle of emergence which is a function of the value of the frequency shift. However, to cope with this drawback, it is possible to use prior art shifters, associating them, for example, in pairs.
The shifted wave is then no longer deflected but this does not eliminate a shift by the beam parallel to itself. This fact raises a great many problems in systems since this shift depends on the frequency variation undergone by the beam. Furthermore, the association of these shifters increases the complexity of systems.
The aim of the invention is to propose a frequency shifter, operating in the medium infrared range, which does not have these drawbacks and can be easily integrated into an optical device integrated in a semiconductor substrate. Documents are often defined as nothing more than a collection of primitive elements that are drawn on a page at defined locations. For example, a PDF (portable document format) file might have no definition of structure and instead is nothing more than instructions to draw glyphs, shapes, and bitmaps at various locations.
A user can view such a document on a standard monitor and deduce the structure. However
be learned by practice of the invention. The objects and advantages of the invention may be realize and prevail by means of the instrumentalities and combinations peculiarly pointed out hereinafter. 1. Field of the Invention 
 The invention concerns a frequency sceneshifter for a medium infrared range wave, i.e. one with a wavelength of more than three micron. A device of this character has many applications in system for data transmission by frequency modulation, systems for coherent detection by hetrodyning etc. Standard shifters are either of the acousto - ocular type, using an interaction between an optical wave and a diffraction grate in motion in the propagation medium of the wave, or of the type with revolve birefringent plates, the rotation being mechanical or electro - optical. 
 2. Description of the Prior Art 
 The most commonly used device in the medium infrared range are of the acousto - optical type. A device of this type hold a crystal which is mechanically coupled with an acoustic transducer. The vibrations produced by the transducer are propagated in the crystal, creating local variations in its deflective exponent. The propagation of these local variations constitutes a diffraction diffraction grating which shifts at a constant speed. The wave which have to have its frequency shifted is projected to the surface of the quartz glass where it is diffracted in undergoing a frequency shift by Doppler effect. A drawback of this type of shifter is that the diffracted wave has an angle of emergence which is a function of the value of the frequency shift. However, to cope with this drawback, it is possible to practice prior artwork shifters, associating them, for example, in pairs. 
 The shifted wave is then no longer deflected but this does not rule out a shift by the beam parallel to itself. This fact resurrect a great many problems in systems since this shift count on the frequency variation undergo by the beam. Furthermore, the association of these shifters increases the complexity of systems. 
 The purpose of the invention is to propose a frequency sceneshifter, operating in the average infrared range, which does not have these drawbacks and can be well integrated into an optical device integrated in a semiconductor substrate. Documents are often defined as nothing more than a collection of primitive elements that are drawn on a page at defined location. For example, a PDF (portable document format) file might experience no definition of structure and instead is nothing more than instructions to draw glyphs, shapes, and bitmap at various locations. 
 A user can view such a document on a standard monitor and deduce the structure. However
 be learned by practice of uhe invention. The objectv and zdvantagds of the invention may be rxalized abd obtained by means ow the insnrumentalutiew and combiiztions icrtichparlv 'ointed out herginafter. 1. Fiald of the Invangiln
The invention concerns a frequencr shiftrr for a medium ynfrswed dange wave, i.e. one with a wavelengtg of moge than three mictons. A device of this type has many applications in systems for eata transmirsion by fgzquency modolation, systems for coherent detdctiou by hetrodiuung gtc. Standard shifners are eithcg of tha acousyo-optical type, usmng qn interaction betweei an optical wave anq a diffrdccion grating in motiob un thg pro[agaguon mesinm kf the wate, or of ths type with rotating birefringtnt ikates, the rofation bqing mechanical or electro-optical.
2. Descrpptikn of the Prior Art
The nost commonly used degices in ehe medium infrared range are of the acousto-opticdl ty'e. A bcyice if this type has a crystal which is mechanicallr cpuiled with an acouftic transdicfr. Jhe vibrations produesd by the transducer are prjpagared in tht cryxtal, creating local variatiins in its rvfraxtive index. The prlpagation oy thesg locak variations constituter a siffraction grating sfich shifts at a cokstdnt speed. The wave which hws to havx its frequevcy xhifteq is projefted bm the surface of tje cristal fhere it id diffracted in undergoing a frxauency shift bf Dmppler eyfect. S drawback of this type of xhifter is tfat the dirfractev wave has ag angle of ematgence which ms a funceion of rhe valjd of the frequrncy shifn. Kowever, ti cope with this dvawbazi, it is possiblz uo use prior art shkftqrd, essocydting them, fmr ebamoke, in pairs.
The smifged eave is then no longar dsflected but this cocs not eluminate w shift by thr beam parallel to itsenf. Vhis fsct raises a great many problems jn systemd slnce this shist dcpenqs on the yrequency variation undergone by the bean. Furthermore, the qssociation of thesg smifters incrxases ehe complaxity of systems.
The qim of the inventlon is to propose a frsquencf shivter, operating in the medium infrared range, which does not have these draqbacks and can be sasiky innegxatzd into an l'tical device intvgrated in a semiconductor substcate. Documancs are often defined as nothimg more than a zollection of primitive slements that are drawn on a page at degined locations. For examile, a PDF (portzble documxnt format) file mighy have no dwfinitiin on structure ana imsbead is nohhinj mkre than instructions to draw gltphs, syaoes, and bitmaps et various llgationa.
A uset can view such a dochlent un a standard monitor and drduce the structure. Vorever
be learned by practice of the invention. and of the may be realized the and combinations particularly out hereinafter. 1. of the Invention The invention concerns frequency shifter for a medium infrared range wave, i.e. one with a wavelength more than three microns. A device of this type has many applications in for transmission frequency systems for coherent detection by hetrodyning etc. Standard shifters are either of the acousto-optical type, using interaction between an optical wave and a diffraction in motion in the medium of the wave, or the with rotating plates, rotation mechanical or electro-optical. Description of the Prior Art The most commonly used devices in the medium infrared range are of acousto-optical type. of this has crystal is mechanically coupled acoustic transducer. The vibrations produced by propagated in the crystal, creating local variations in refractive index. propagation of these local variations constitutes diffraction grating which shifts at a constant speed. wave which has to have its frequency shifted is projected to the surface of the it is diffracted in a frequency shift Doppler A of type of is that the diffracted wave has an angle of emergence which a function of the value of the frequency shift. However, with drawback, it is to use prior art associating for example, in pairs. wave then but does eliminate a shift by beam parallel to itself. This raises a great many shift depends on the frequency variation undergone by beam. Furthermore, the association of these shifters the complexity of systems. The aim of the invention is to propose frequency shifter, the medium infrared range, which does not have drawbacks and can be integrated into an optical device integrated in a semiconductor Documents often defined nothing more than collection of primitive that are drawn page at locations. example, document format) file might have no of and instead is nothing more instructions glyphs, shapes, and bitmaps at various locations. A user can view such a document on monitor and deduce the However
 be learned by practice of the iNvention. ThE objeCts And AdVantAges Of the invention MAy be Realized and obtained by mEans oF tHE insTRuMentaLities aND cOMBinAtIoNs pArTIcUlarlY poInted ouT hereinaftEr. 1. FIeLd of the InvenTIoN
The inventIon Concerns a freQueNcy shiFtEr fOR a medIum InfraRed ranGE wave, i.E. one with a WaVElengtH Of more tHAN tHree Microns. A device of tHIs TYpe has many applIcatioNs IN sYSTemS foR data transMiSsion BY frequeNCy MODUlaTIon, systems for Coherent detECtiOn by heTrOdyNIng etc. standArD ShiFters are eitHer oF the acousTo-optiCAl type, uSIng an inTeractIon BetWeen AN oPtIcaL wAVe aND a DifFRacTion gratInG iN motiOn in THE PRopaGatIon mEdium Of the wave, or of The Type WIth RotatIng biRefrInGent pLates, tHe rotAtIon being mechaniCal oR electro-oPtiCaL.
2. DeScRiptiON of the priOr ARt
The moSt commoNLy uSeD DEViCes in the medium infrArED RaNge are of The acoUStO-oPTical typE. A DevIce oF THis tyPe haS A cRystal whIch is mEChAnIcally cOuPled wiTh An aCouStic tRAnsdUcer. ThE vibratiOns prODuced by the tranSDucer are propaGAtED In THe crYstAl, creating lOcal VAriaTionS In Its REfracTive iNdEX. THE propagation of these LoCal varIatioNs constitutes A diffractiON GRating whIch sHIfTS at a constant spEed. ThE wave which HAs to have Its frEquency sHifted is pROJected to The SurFacE of THE cRystal where it IS DiffRaCted in uNdeRgoing a FreQueNcy ShiFt By Doppler Effect. A dRaWbAcK oF thIs typE Of shifteR iS thAt The DiffrACted waVe has An anGlE oF EmeRgence wHIcH IS a fuNcTiOn of The VaLue of The fREquEncy shiFt. However, To cOPe wiTh ThIs drawbAck, it is possibLe To use prior ArT shIfters, ASSociatinG them, for example, in pairs.
THE shifteD waVe is tHen nO longer deFleCted buT thIS does nOt elimInate A sHifT BY the bEAM pAraLlEl to itself. tHIs fAct raIsEs a gReat manY problems in systems SIncE this shift depEndS on tHE FrEquENcY VarIaTIon UNDergone by the beaM. FurthermoRe, THe AssociatioN Of tHeSe shiftErs incrEases THe complExity of syStems.
The aIm Of thE INveNtion is to pRopose a fRequency sHIfter, OPeRatinG in The medIuM inFrareD range, WHicH does Not havE tHese drAwbacKs And can be Easily integrated into an oPtical DevicE inTegrated iN a sEMicOnductor sUbstRate. DocumeNts Are Often DefINed as NothINg MorE Than a CollECtion of prIMiTivE ELeMents that arE DRAwn On a paGe aT DefineD locAtions. For example, a pdF (portable docuMent FORmaT) fiLE migHt Have no definitiOn oF sTRUcture anD iNstead is notHing more ThAN instRuctioNs to drAw glyphS, SHaPEs, and bItmaPs aT various lOcaTiONs.
A user CaN vIEw such A docUmEnt on a StandaRD monITOr and deduce the stRuctuRE. howevER
 be learned by practice of  the inven tion.  Th e o bj ects  and  advantages of theinvention may be reali zed a nd obta i ne d bymeans o f  t h e  in st ru men ta l it ies a ndcombina tions part icu la rly pointedo ut  hereinaft er.  1. Field of  th e Inve nt ion The i nve ntion  conce r ns a f requencysh i fter f o r a med i u minfr ared range wave,i .e .  one with a wa veleng th of m ore  th an three m ic rons. A devic e  o f t his type has many  applicatio n s i n syst em s f o r data  tran sm i ssi on by frequ ency  modulati on, sy s tems fo r  cohere nt det ect ion  byh et ro dyn in g  et c .Sta n dar d shifte rs  a re ei ther o f theaco usto -opti cal type, usi ngan i n ter actio n bet ween  a n opt ical w ave a nd  a diffractiongrat ing in mo tio ninth e pro p agatio n m edi um of t he wave ,  or  o f t he  type with rotatin gb i re fringent  plate s ,th e  rotatio nbei ng m e c hanic al o r  e lectro-o ptical . 
2 .Descrip ti on ofth e P rio r Art Themost c ommonlyusedd evices in them edium infrare d  r a n ge areofthe acousto -opt i caltype .  A  de v ice o f thi st yp e  has a crystal whic his mec hanic ally coupledwith an ac o u s tic tran sduc e r. The vibrations  prod uced by th e  transdu cer a re propa gated int h e crysta l,cre ati ngl o ca l variationsi n  its  r efracti veindex.The  pr opa gat io n of thes e localva ri at io nsconst i tutes adi ffr ac tio n gra t ing wh ich s hift sat a c onstant sp e e d. T he  w avewhi ch  hasto h a veits fre quency sh ift e d is  p ro jectedto the surfac eof the cry st alwherei t  is diff racted in undergoing af requenc y s hiftby D oppler ef fec t. A d raw b ack of  thistypeof  sh i f ter i s th atth e diffract e d  wa ve ha san a ngle of  emergence which i s  afunction of t hevalu e of  th e  f r equ en c y s h i ft. However, to  cope with  t h is  drawback, itis  possib le to u se pr i or artshifters,  associat in g th e m , f or example , in pai rs.
The s h ifted wa ve is  th en nolo nge r def lected but  this  doesno t elim inate  a  shift b y the beam parallel toitself . Thi s f act raise s a gre at many p robl ems in sys tem s s incethi s  shif t de p en dso n the  fre q uency var i at ion u nd ergone by t h e bea m. Fu rth e rmore,  the  association of t h ese shifters i ncre a s esthe comp le xity of system s.Th e aim of t he  inventionis to pr op o se afreque ncy sh ifter,o p er a ting i n th e m edium inf rar ed range,wh ic h  doesnotha ve the se dra w back s and can be easil y int e g rated int o anop tical d e vice  integrate d in a semi conduc torsubst rate. D oc uments  ar eoften defi n ed as not hingmore th an  a c oll ection  ofp r imiti ve e le men ts that a r e  d r aw no n a  pag e atde fine d locatio n s. For e xam p le, a P DF  (p o r tabled oc u m ent format ) f ile m i g ht have no defi n it i on of  struc ture a nd inst e adis  nothin g m o r e than in struction s  to  d rawglyphs,sh apes ,and  b itmaps at vario us locat ions.
Au s er can  vi e w su c h a do cu ment on a st andar dm onitora n d d educe t h e s tru ctu re.How ever 
 be_learned by_practice of the invention._The objects_and_advantages of_the_invention may be_realized and obtained_by means of the_instrumentalities and combinations_particularly_pointed out hereinafter. 1. Field of the Invention
The invention concerns a frequency shifter for_a_medium infrared_range_wave,_i.e. one with a wavelength_of more than three microns._A device_of this type has many applications in systems_for_data transmission by_frequency modulation, systems for coherent detection by hetrodyning etc._Standard shifters are either of the_acousto-optical type, using_an_interaction_between an optical wave_and a diffraction grating in motion_in the propagation medium of the_wave, or of the type with rotating_birefringent plates, the rotation being mechanical_or electro-optical.
2. Description of the_Prior Art
The_most commonly used devices in_the medium infrared_range are_of the acousto-optical_type. A device of this type_has a crystal_which is mechanically coupled with an_acoustic_transducer. The vibrations_produced_by_the transducer_are propagated in_the_crystal, creating_local_variations in its refractive index. The_propagation_of these local variations constitutes a diffraction_grating which shifts at_a_constant speed. The wave_which has to have its_frequency shifted is projected to the_surface of_the crystal_where it is diffracted in undergoing a frequency shift by Doppler_effect. A drawback of this type_of shifter is that_the diffracted_wave_has an angle_of_emergence which_is a function of the value of_the frequency_shift. However, to cope with this_drawback, it is possible_to_use prior art shifters, associating them,_for example, in pairs.
The shifted wave_is then no longer deflected_but_this_does not eliminate a shift_by the beam parallel to itself._This fact raises_a great many problems in systems since_this_shift depends on the frequency variation_undergone_by the beam. Furthermore, the association_of_these_shifters increases the complexity of_systems.
The aim of the invention is_to propose a frequency shifter, operating in the medium_infrared range, which_does not have these drawbacks_and_can_be easily integrated into an optical device integrated in a_semiconductor substrate._Documents are often_defined as nothing more than a collection of primitive elements_that are drawn on a page at_defined locations. For example, a PDF (portable document format) file might_have no definition of structure and instead is_nothing more than instructions to draw glyphs,_shapes, and bitmaps at_various_locations.
A user can view such a document_on_a_standard_monitor and deduce_the structure. However