CA1255139A - Optical frequency converter device and a rate gyro containing such a device - Google Patents
Optical frequency converter device and a rate gyro containing such a deviceInfo
- Publication number
- CA1255139A CA1255139A CA000443990A CA443990A CA1255139A CA 1255139 A CA1255139 A CA 1255139A CA 000443990 A CA000443990 A CA 000443990A CA 443990 A CA443990 A CA 443990A CA 1255139 A CA1255139 A CA 1255139A
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- 230000003287 optical effect Effects 0.000 title claims abstract description 59
- 239000000758 substrate Substances 0.000 claims description 56
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 19
- 239000000463 material Substances 0.000 claims description 18
- 230000005855 radiation Effects 0.000 claims description 16
- 150000002500 ions Chemical class 0.000 claims description 13
- 230000001902 propagating effect Effects 0.000 claims description 13
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 11
- 239000010936 titanium Substances 0.000 claims description 11
- 229910052719 titanium Inorganic materials 0.000 claims description 11
- 239000013307 optical fiber Substances 0.000 claims description 10
- 230000010363 phase shift Effects 0.000 claims description 8
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 238000001514 detection method Methods 0.000 claims description 4
- 238000001465 metallisation Methods 0.000 claims description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims 4
- 229910001416 lithium ion Inorganic materials 0.000 claims 4
- 230000008878 coupling Effects 0.000 abstract description 20
- 238000010168 coupling process Methods 0.000 abstract description 20
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- 230000000694 effects Effects 0.000 description 9
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- 230000003993 interaction Effects 0.000 description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 238000009792 diffusion process Methods 0.000 description 5
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- 230000000737 periodic effect Effects 0.000 description 4
- 235000012239 silicon dioxide Nutrition 0.000 description 4
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- 239000000835 fiber Substances 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 101100366710 Arabidopsis thaliana SSL12 gene Proteins 0.000 description 1
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- 206010013710 Drug interaction Diseases 0.000 description 1
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- 101100366563 Panax ginseng SS13 gene Proteins 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 210000001520 comb Anatomy 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- VKYKSIONXSXAKP-UHFFFAOYSA-N hexamethylenetetramine Chemical compound C1N(C2)CN3CN1CN2C3 VKYKSIONXSXAKP-UHFFFAOYSA-N 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- KRTSDMXIXPKRQR-AATRIKPKSA-N monocrotophos Chemical class CNC(=O)\C=C(/C)OP(=O)(OC)OC KRTSDMXIXPKRQR-AATRIKPKSA-N 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
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- 239000010453 quartz Substances 0.000 description 1
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- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/33—Acousto-optical deflection devices
- G02F1/335—Acousto-optical deflection devices having an optical waveguide structure
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/72—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
- G01C19/721—Details
- G01C19/722—Details of the mechanical construction
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/31—Digital deflection, i.e. optical switching
- G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
- G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Electromagnetism (AREA)
- Power Engineering (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Optical Integrated Circuits (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
AN OPTICAL FREQUENCY CONVERTER DEVICE AND A RATE GYRO
CONTAINING SUCH A DEVICE
The invention concerns a frequency converter device made in integra-ted optics in which the coupling between the wave-guides is made through an acoustic network formed by an acoustic wave which propagates colinear-ly with the optical wave carried in one of the wave-guides.
AN OPTICAL FREQUENCY CONVERTER DEVICE AND A RATE GYRO
CONTAINING SUCH A DEVICE
The invention concerns a frequency converter device made in integra-ted optics in which the coupling between the wave-guides is made through an acoustic network formed by an acoustic wave which propagates colinear-ly with the optical wave carried in one of the wave-guides.
Description
3L2~ 3~
N OPTICAI FREQUENCY CONVERT~R DEVICE AND A RATE GYRO
CO~YTAINING SUCH A DEVICE
BACKGROUND OF THE INVENTION
The invention covers an integrated optical frequency converter device.
Classical op~ical frequency conver~ers are well known. The frequency converter most usually used is certainly the one based on acousto-optical interactlon. In this method, an acoustic network which propagates in a 5 medium produces periodic refractive index variations in the form of a travelling wave. This moving network diffracts the light. If the in~eraction lenght is sufficient, a single order may predominate. In the diffracted order (~" D~ the optical wave frequency ~ has been modified by a quantity eyual to the acoustic wave frequency Q .
Hense, ~D = ~+ Q
Fundamental frequency rejection may be excellent because the con-verted wave and the direct wave ~undiffracted) are then separated in space.
It is then possible to study what this gives in integrated optics. Under this name are designed thin layer monilithic s~ructures intended for lumi-nous signal processin~ which are obtained by the techniques of deposit, diffusion and engraYing by masking analogous to those used in the production of electronic integrated circuits. With these techniques, in particular, i~ is known how to produce linear structures characterized by a refractive index higher than that of the surrounding medium and forming wave-guides along 20 which the li~ht propagates by a series of total reflections or progressive refractions. 1~ is known how to combine two such wave-guides by arranging them in para~lel one with respect to the other along part of the path to produce directional couplers. Thanks to the vanishing wave phenomenon, the energy carried in the first wave-guide is passed progressively in to the 25 second wave-guide and it is found that the maxirnum energy is transferred at the end of a certain lenght, called ~he coupling lenght, which depends on the geometrical and optical parame~ers of the structure and9 in particular, on the value of the refractive indices of the materials formin~ the two waves-guides and the me~ium which separates ~hem. Then $he energy passes . ~
progr2s~sively from the second guide into the first and so on. When an electro-optical material is used for one of the materials forming the wave-guides or the medium which separates them, it is also known how ~o cause the index to vary under the effect of an electric field, which makes it 5 possible, by acting on the coupling lenght, to control electrically the part of the energy transfered from one wave-guide to the other. It can be seen that it is also possible to make a ligh~ modulator by arranging, in parallel with the wave-guide wh;ch carries the luminous wave, a section of wave-guide in which a more or less large part of this energy will be transferred.
Also, there are frequency converters intended to produce, from a guided electromagnetic radiation of frequency ~, a guided electromagnetic radiation wh~se frequency is a multiple of the frequency ~ . These conver-ters are used, in particular, in the integrated optical field, thus named by analogy with electronic in~egrated circuits, which are monolithic structures 15 using thin layers.
Converters of the type already described have been produced in integrated optics but they require the use of a flat wave-guide and this is not applicable to microguides. Techniques usable with microguides have already been suggested in which electro-optical modulation can be used.
20 lhis may then be a serrodyne or balanced rnodulator system. Such an optical frequency conver~er contains a wave-guide used as phase mo~ulator, which is controlled by a signal in the form of a saw-tooth. Such a si~nal has the same effect as a voltage gradient which allows a variation of the index as a function of time. It may also be an acoustic modulation in which a TE type 25 wave is converted into a TM type with a change in frequency. In this case, the application of a transverse electric field enables the pass-band of a TE-TM rnode acousto-optical converter to be modified by the colinear interac-tion of acoustic surface waves and a guided optical wave.
These two techniques have several disadvantages .
- the two waves propagate in the same wave-guide (the frequency translated wave and the fundamental wave) ans this can cause problems in separating them;
- in certain cases, the effectiveness of the conversion is very closely related to the wave shape (case of the serrodyne translator);
- 3 - 1~55~
- i.n the case of a TE-TM conversion, one of the problems that may be met with is the extreme sensi-tivity of the device to wave-length (variation of ~/KTE - ~/KT~) which may, however, allow this type of device to be used as a filter.
The device of the invention enables these dis-advantages to be attenuated. In this devi.ce, the converted and unconverted waves are separated in space because the diaphony is related to simple geometrical parameters and can be reduced arbitrarily. Also, the two waves keep the same polarizing. The device can be extended and used in the case in which it is required to produce frequency filters.
In accordance with the present invention, there is provided a rate gyroscope including an interferometer for measuring a non-reciprocal phase-shift undergone by first and second radiations circulating in opposite direc-tions in a ring wave-guide, comprisingO
said ring wave-guide with ends;
a monochromatic luminous source;
means Eor photo-detecting an interference of said first and second radiations;
an optical separator and mixer connec-ting the ends of said ring wave-guide to said luminous source and said photo-detecting means;
an electrically controlled optical phase shifter;
and - at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
a flat substrate;
~SS13~
at least two wave-guides with different characteristics integxated into said substra-te, one of which is intended to receive an incident wave, said two wave-guides being parallel with one another over a predeter-mined length and separated from one another by a distance such that the incident wave radiation is transferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
In aeeordanee with the invention, there is also provided a rate gyroseope ineluding an interferometer for measuring a non-reeiproeal phase-shift undergone by first and seeond radiations cireulating in opposite directions in an optical fiber ring wave-guide, comprising:
said optical fiber ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and seeond radiations;
an optieal separator and mixer conneeting the ends of said ring wave-guide to said luminous souree and said photo-deteeting means, said luminous source, photo-detecting means and separator and mixer being inte-grated on a single substrate;
first and second wave-guides integrated onto said substrate, said first wave-guide having a first end cou-pled to said monoehromatie luminous source, and said second wave-guide having a .first end coupled to said photo-detecting means, said first and seeond wave-guides having respective seeond ends coupled to different ends of said optical fiber ring;
::
: ~ :
- 3b -an electro-optical phase modulator comprising a pair of electrodes positioned one each on opposite sides of one of said first and second wave-guides; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, the two wave-guides being parallel with one another over a pre-determined length and separated from one another by a distance such that the incident wave radiation is trans-ferable from one wave-guide to another; and means for generating an acoustic wave colli-near with an incident wave propagating direction in one of the said two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
According to the invention, there is further pro-vided an integrated ring interferometer, comprising:
a substrate;
a source branch port;
a de-tection branch port;
a first Y-shaped wave-guide integrated into said substrate, said first wave-guide having first and second branches and a trunk portion, said first branch being coupled to said source branch port and said second branch being coupled to said detection branch port;
a monomode filter formed by a metallization over said trunk portion;
a second Y-shaped wave-guide integrated into said substrate, said second wave-guide having first and second branches and a -trunk portion, said trunk portion - 3c - ~ ~5S~3~
of the second wave-guide being coupled to said trunk portion of said first Y-shaped wave-guide;
a first phase modulator coupled to said first branch of said second Y-shaped wave-guide, said first phase modulator being constituted by a pair of electrodes on opposite sides of said first branch of the second wave-guide;
a second phase modulator coupled to said second branch of said second Y-shaped wave-guide, said second phase modulator being constituted by a pair of electrodes on opposite sides of said second branch of the second wave-guide;
a first optical frequency converter integrated into said substrate and optically coupled to said ~irst branch of said second Y-shaped wave-guide, said first optical frequency converter including:
third and fourth wave-guides integrated into said substrate and having different optical charac-teristics from one another, said third wave-guide being optically coupled to said first branch of said second Y-shaped wave-guide, and said fourth wave-guide having a portion that is substantially parallel with a portion of said third wave-guide over a predetermined length thereof;
first means for generating an acoustic wave collinear with an incident wave propagating direc-tion of said third wave-guide, said generating means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said third and fourth wave-guides;
a second optical frequency converter integrated into said substrat:e and optically coupled to said second branch of said second Y-shaped wave-guide, sai d second optical ~requency converter including:
..~
- 3d -fifth and si~th wave-guides inteyrated into said substrate and having different optical characteristics from one another, said fifth wave-guide being optically coupled to said second branch of said second Y-shaped wave-guide, and said sixth wave-~uide having a portion that is substantially parallel with a portion of said fifth wave-guide over a predetermined length thereof;
second means for generating an acoustic wave collinear with an incident wave propagating direction of said fifth wave-guide, said generatiny means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said fifth and sixth wave-guides; and an optical fiber ring having a first end optically coupled to said fourth wave-guide and a second end opti-cally coupled to said sixth wave-guide.
BRIEF DESCRIPTION OF THE URAWINGS
Other characteristics and advantages of the present invention will appear in the following non-restrictive description made with reference to the accornpanying drawings in which:
Figures 1 to 3 which are labelled as " PRIOR ART"
show a device known in the art;
Figure 4 shows the device in accordance with the invention;
Figure 5 which is labelled as " PRIOR A~T"
shows a device known in the art;
Figures 6 and 7 show a system containing the device in the invention; and - Figure 8 which is disposed on the same sheet of formal drawings as Figure 5 shows a variant of the system.
~ 3e ~
DETAILED DESCRIPTION OF THE PREFERRED EM _DIMENTS
Figures 1 and 2 show a sectional view and a view from above respectively of a switch produced in ': . : ' ' "' '' ~uides 1 and 2 are inserted in the sub~trate 3. The materlal through~ which csuplin~ is made is the one forming susbstrate 3. To insert wave-guides 1 and 2, it Is possible9 for example, to cause titanium to diffuse in a substrate formed of a monocrystalline shee~ of lithium niobate (LiNbO3~ e tita-5 niurn, in the diffusion zone, replaces the niobium in part to ~ive a mixedcompound with the formula LiTiXNbl ~03 with a refractive index higher than that of the pure nioba~e. These diffused ~ones, with an index higher than that of the substrate, form wave-guides I and 2. If the diffusion temperature is higher than the Curie point for the ma~erial, the cooling I0 phase which follows is used to subject the plate to a uniform electric field in order to polarize the plate uniformly and produce a "sin~le domaine"
structure.
When a voltage is applied between the electrodes 10 and 20, a distribution of field lines is produced which is shown as reference 4 on figure 15 1. The field component in the directlorl C perpendicular the substrate surface 23 has the sarne absolute value but opposite direction in one guide and the other, which gives refractive index var;ations of the same absolute value and opposite sign. Nonetheless, the existence, in a direction perpendi-cular to the direction of the substrate axis C, the susbtrate having its 20 extraordinary index, of a non-zero field component, and the fact that the electric field applied also causes the index value to vary in the part of the substrate 22 contained between the two wave-guides cause a certain dissymetry of the phenomenon. The coupling obtained varies in accordance with the polarity of the voltage applied between the electrodes 20 and 21.
2s The polarity of the voltage supplying the maximum coupling can be deduced from the crystallographic orientation of the material forming the substrate~
If this orientation is unknown, it is very easy to determine experimentally the optimum polarity by the measurement of the luminous intensity trans-mitted by ore of two wave-guides fortwo polari~ies of opposite signs.
If the metallic electrodes are arranged directly on the wave-guide surfaces, the existence of a vanishin~ wave moving in the relatively abs~rbent metallic medium can cause energy losses in the coupler. To avoid them it ls possible to fit in between as shown ln figure 1, a transparent dielectric layer 11 and 21 between wave-guides 1 and 2 and electrodes 10 and 20. This isolating layer is made of a material wi~h good tr~nsmission for the iuminous wave-len~ht carried by the wave-guide and a refractive Index lower than that of the wave-guide. Silicon dioxide (SiO2) is a ma~erial perfec~ly adap~ed to the case previously described in which the substrate is 5 formed by lithium niobate.
The two wave-guides9 as shown in figure 2, are parallel one with ~he other on a rectilinear section of lenght L, which is a flmction of the parameter, called the coupling lenght, which will be defined later. 1 he distance between the rectilinear parallel parts is of a value d which must 10 not exceed a few wave-lengths (calculated in the medium separating the two wave ~uides) of the light carried by the wave-~uides. The two waves-guides are formed by the ~ame electro-optical ma~erial which, when subjected to an electric field, has a refractive index that varies as a function of the applied field value. The refractive index of this material is so chosen that, 15 even in the presence of the applied electric field, it remains higher than the index of the material forming substrate 3.
Because of the electro-optical character of the material forming wave-guides 1 and 2, the distribu~ion of the ~ield lines in the wave-guides produces within them refractive index varia~ions roughly equal in absolute 20 value but of opposite signs.
When a wave is carried by wave-guide, part of the energy propagates outside the wave-guide, in the medium which surrounds it in the form of a vanishing wave. The amplitude of this wave decreases exponentially on leaving the wave-guides walis. If a second wave-guide is arranged parallel to 25 the first one, it picks up progressively, throu~h this vanishing wave, the energy carried in the first wave-guide and, the closer are the wave-guides, the more quickly it does it. AEter a given distance, called the coupling lenght, which depends on the geometrical and optical parameters of the two wave-guides and of the medium separating them (and of the refractive 30 indices in particular), the maximum of energy has been transferred from the first wave-guide to the second. Beyond this lenght, the reverse phenomenon occurs. The energy transfers pro~ressively from the second wave-guide to the ~irst to leave ~he minimum value in the second wave-guide. Any :' :
modification of the index of one of the media present acts in one direction or the other along the coupling lenght.
In the device shown in figures 1 and 2, the lenght L can be cho~en equal to th~ couplin~ len~h~ in the absence of this applied electric field.
5 Because of the perfect symetry of the two waves-guides in the coupling zone, the energy transfer is complete from the first wave-~uide to the second (or from the second to the first). The application of a voltage between electrodes 20 and 21 reduces the coupling lenght and part of the energy is retransferred from the second wave-guide to the first (or from the 10 first to the second). The final result is then that, as the voltage is increased, the energy transferred from the first wave-guide to the second (or from the second to the first), measured at the end of the coupling zone, is reduced to reach a zero value. The coupling between the two wave-guides thus decreases from 100 % to 0 % when the voltage applied to the electrodes 15 increases. The result would be ~he same if the lenght L was made equal to and odd multiple of the coupling lenght with a zero field.
It is also possible to give the lenght L a value equal to an even multiple of the coupling lenght with a zero field. The energy transferred at the output, from one wave-guide to the other, increases from zero when the 20 voltage applied between the electrodes increases from zero.
A device has then made which, when controlled by an electric signal, enables part or all of the energy carried by one wave-guide to be switehed to the other associated with it in the coupling zone.
It goes without say;ng that, if one of the two wave-guides is limited to 25 a section whose minimum lenght is the lengh~ L of ~he coupling zone, this device enables the energy carried in the other wave-guide to be modulated no%.
In the case in which the two wave-guides are different, a periodic structure made behveen them can make it possible to increase the exchan-30 ges between them. When the wave carried in one wave-guide has the same propagation speed as one of the orders diffracted in the other wave-guide, there is then an energy exchange.
To produce this exchange several means can be used, in particular the production of an electric field between two electrodes, for example, of -' - ., .
periodic structures 18 and 29 fitted on one side and on the other of ~he two wave-guides 5 and 6 as shown in figure 3. A luminous wave 24 propagating in the first wave-guide produces, by coupling due to the presence o~ a polarization Vo9 a coupled wave 25 which propagates in the second wave-5 guide 6. It can also be the production of a network engraved in the substratebetween the two wave-guides. In the device of the in~ention, acoustic waves 12 are produced by the électrodes 13 and 14 in the form of interdigi~al combs, at whose terminals a genera~or V is connected, which propagate between the two waves-guides as shown in figure 4. However, the electrodes 10 can be deposited on a thin layer 26 of a piezoelectric material, a ~inx oxide(ZnO) for example, the thin layer being deposited on substrate 3 consisting o~
another material, silicon dioxide for example. Thin layer 26 can be made of the same material as the substrate, crystalline quartz, gallium arsenide or lithium niobate for example.
The device in accordance with ~he invention has be advantage of allowing an adjustement of the coupling between wave-guides 5 and 6 which is a function of the acoustic wave frequency. This acousto-optical deflector allows a frequency translation. The luminous waves carried by one of the wave-guides 5 and diffracted by these acousto-optical waves are then 20 converted in frequency and transmitted in the second wave-guide 6. These two wave-guides are not necessarily of the same width.
If a medium 30 is considered in which a beam of elastic waves 31 of frequency f is propagating, as shown in figure 5, if an incident luminous beam 32 is passed in this medium, a ~roup of diffracted beams 33 is obtained 25 with frequencles F + + kf, in which k is a positive or negative whole number.The sinusoidal variation oE the index, produced by the elastic wave, has an effect on the luminous wave analogous to that of a phase network.
The luminous beam 32 penetrating the crystal 30 in parallel with the elastic wave planes is separated into several beanns symmetriAcally inclined with 30 respect ~o ~he incident beam by angles ~ N: Sin ~N = k ~ in whlch ~ is the wave plane step and ~ the incident beam wave-lenght. However, the elas~ic beam thiclsness e must be less than a critical value ec. The side waves are produced all long ~he carrier wave path inside the ultrasonic beam and not only at the output, on the frontier. If, in throught, the elastic beam is divided into thin slices parallel to the propagation direction, for each of these slices parallel to the propagation direction, for each of these slices9 ~he preceding spectral analysis is valid. The frequencies Q ~ k~ and ~he direction of propagation ~ N oE ~he side wavcs are the same for the absclssa slices x and x ~ Q . iE9 for a given order, the contribu~ions of these two sl~esQ apart are added, there is phase opposition for a dis~ance Q N = A
N The interference of the waves emitted by the slices QN apart may then be destructive. If the width o~ the beam is greater than Q N~ the effect of a slice is cancelled by ~he silice Q N away. Under the best conditions, the elastic beam 2thickness e must not exceed a first order critical value:
ec= Rl= A .
For a Bragg angle incident of the luminous beam 32 with respect to ~he elastic wave planes, the interaction is the biggest because it enables the interferences to be made constructive for the first order of angular frequency Q + ~. Hence, it only supplies a single deviated beam.
The device as in the invention uses a directional coupler whose two wave-guides are not identical. In this case, if B /K 1 and B/K~ are the propagation constants of the modes in these two wave-guides of the coupler~
the relative energy in one of the wave-guides when the other is energized will be written: E = 12 2 Sin2V 1 + ~B 7i~cL in which L is l ~ a~ l~c the interaction lenght, c is the coupling constant and ~B = 2N (~ IK1 -C2) in which ~ is the wave-lenght in a vacuum. The relative energy present in this wave-guide at the coupler output depends on three parameters, L, c and ~ . If ~B is large with respect to c, it can be sen that, in any case, no 25 matter what the value of L, the maximum energy exchanged can be smallO
~or example, if c _ 1.510 4 /um9 2 ~ = 0-0001, EMAX = 0.0017 and if c - 1.5 10-4 /um, 2Tr ~= O-Ol~ EMAx = 0.000017 These values are very small and can be reduced further arbitrarily by changing the lenght L.
1~ is known ~hat, if the propagation constants in the two ~ave-guides are made to vary periodically and the corresponding period is carefully chosen, the exchange between the two wave-guides can be increased by comprising the ~ ~ with the network vector K.
.
~25~
The interaction is then vrit~en, because of the conservation of the nts ~ 29 l e- ~ K - ~ 2/K) = ~ in which A is the network period.
Hence, if the network is formed, as produced in the device of the 5 invention shown in figure 4, by an acoustic wave propagating colinearly ~o the optical wave, there will be a frequency translation of the coupled wave.
The effectiveness of the interaction depends on the value of the index variation induced by ~he acoustic wave and hence nf the power injected. A
directional coupler produced in lithium niobate (LiNbO3) by titanium diffu-10 sion can be taken as an example. The variation in index corresponding totitanium is usually of the order of: ~ n ~ 510 3.
1~ can be seen then that it is possible to produce the two wave-guides with ~ B/K = 210 3. This can be obtained by changlng the width and/or the thickness of the titanium for these two wave-guides in the coupler. For an 15 interaction lenght of lO mm9 the maximum energy exchanged will be: for )~ = 0.83/um, EMAX = 4 10 4. The acoustic wave-length required for com-pensation will be: 415tum, i.e. in the case of lithium niobate (LlNbO3) a frequency transla~ion of 7.2 MHz. The wave picked up at the output of the second wave-guide (which was not initially energized) will then be obtained 20 with a frequency translation of 72 MHz and the maximum quantity of fundamental in this wave-guide will be - 33 d~ with respect to the total optical energy.
The device as in the invention can also be produced by making one of the wave-guides by proton exchange and the other by titanium dif Eusion ~or 25 the two by proton exchange but different characteristics3. In this case, ~ ~/K ~ 0.1 can be obtained with an interaction lenght of lO mm, the maximum energy exchanged: - 6~ dB OI the total energy is ob~ained with an acous~ic wave-lenght of 8.3 /um, i.e. an acoustic frequency of the order of 361 MHz.
Hence, in the device of the invention shown in figure 4, a wave 23 passed in the firs~ wave-~uide causes by coupling the existence of a wave 25 in ~he second wave-guide, this wave then heing translated in fre~uency.
Sever~l wave-guide configurations are possible, wlth a substrate 3 of lithium niobate, for exampleO lhe two wave-guides are obtained by diffusion of titanium in the substrate. The waves L~uided in ~he two wave-guides are either twc TE waves or two TM waves. ~ of the order of a few l0 3 i5 then obtained.
Ig is also po~sible to have a crossed interaction, i.e. a TE wave in the 5 first wave_guide and a TM wave in the second or YiC2 versa. K of the order c>f 0.l is then obtained One Qf the two wave-guides can be obtained by titaniuM diffusion and the second one by proton exchange. If an axis C perpendicular to the substrate surface is considered, there is a TM wave in each of the two wave-10 guides. There could also be twn TE waves. ~ of the order of 0.l is then obtained. The two waves-guides can be obtained by proton exchange but their characteristics must then be different. ~ ~ û.l is then obtained.
By changing the acoustic frequency, which can vary from l0 to 3D0 MHz, a tunable filter can be obtained. The birefringence of the material varies as function of the frequency.
The pass-band of the device in the invention is a function of the optical wave to acoustic wave interaction lenght. The greater the number of wave planes in the acoustic wave seen during this coupling9 the narrower the pass-band.
The device described here can be used then as a filter by using, for example, ~he variation of the birefringence of a rna~erial with the wave-lenght. It can be considered then that it is a TE (TM) wave in the first wave-guide and TM (TE) wave in the second which are coupled by means oE the acoustic wave. In this case, for lithium niobate, ~ ~ B /KTM - ~B KTE) ^ 0.l and again an acoustic wave frequency of about 361 MHz. This filter i5 adjustable because it is sufficient to change the acoustic wave frequency.
In the device of the invention, electrodes can be deposited, on one side and on the other of the two wave-guides, for example, or on these wave-guides. An insulating buffer layer can also be deposited between the electrodes and the substrate. The electric field produced between these two electrodes enables the device of the invention ~o be adjusted in its initial or its final state.
The device of the invention has an application in the field of the optical fibre ra~e gyro.
~55~3~
Figure 6 shows schematically a ring interferometer of known design. A
laser source S transmits a beam of parallel rays 41 to a separa~or deYice formed by a semi-transparent sheet M.
A certain number of mirrors, 15~ M2, M3, define an optical path 5 forming the interferometer ring. This ring can be made, for example~ with a monomode op~ical fibreO The sensitiYi~y of the measurement is increased by the use of a long optical path. This ring is looped back on the separator device M which also acts as a mixer device and determines an outpu~ branch 43. Two waves, then, propagating in opposite directions, pass trough the 10 ring, one clockwise (direction 2) and the other anticlockwise (direction 1).
These two waves recombine on the separatin~ sheet M. The result of this recombinaison can be seen in the output branch 43 with detector D. Part of the beams is picked up a~ain in the input arm by the separating sheet M' and passes through filter device F again. At the output the two waves recombine 15 on separating sheet M~. The result of this recombina~ion can be seen in the output branch 44. The fact that the filter device F has been fitted in the interferometer input arm makes the arm strictly reciprocal. Hence, a wave contained in a single optical mode passes through it. This filter device consists of a mode filter followed by ~ polarizer. The incident beam 41 20 passes throu~h this filter and the fraction which comes out is in a single mode. It is possible then to consider either the emerging beam 43 correspon-ding to the Interference of the two beams which have not passed through the mode filter device or the part of the beams which is picked up again in the input arm by semi-transparent sheet M. This part of the beams passes 25 through filter device F again. At its output, the two beams passed through arm 44 by means of semi-transparent sheet M' are contained in the same mode and this makes the interferometer insensitive to 'reciprocal' disturban ces.
If ~ ~ is the difference in phase between the two waves which 30 propagate in opposite directions in the ring and PS is the optical power which can be measured in output branch 44, then, when there is 'non reciprocal' disturbances; ~ 4 is zero.
If a rate gyro using this ring interferometer is considered, a 'non reciprocal' disturbance will be produced when the rate gyro is spun. The ~s~
phase difference ~ ~ is not zero and ~ Q in which n Is the speed of rotation and a = k ~C in which k is a constant dependin~ ~n the rate gyro geometry7 L the lenght of the optical path9 A the length o~ ~he ligh~ wave ~mitted by the laser source S and C the speed of the li~ht in rin~ 42. When the speed of rota~ion n increases, ~he pha.se di~ference ~ ~ increases in ~he same proportion because coefficient a remains constant. The optical power PS changes according ~o a cosine law.
~, .
Ps = PlS + P25 + 2 Y PlsP2~ Cos ~ ~ ~ ) in which PlS corresponds to direction 1 and P2S to direction 2. The measurement sensitivity for a ~iven dPS
value ~ ~ is given by the derivative of Ps~ d(~ ) 2V~Sin ~ ~ ~ 3 The interferometer sensitivity is very low if the phase difference 15 is little different from zero. This is the case in a rate gyro if it is required to measure small rotational speeds Q . The variation in optical power in the output branch is shown in the dia~ram in figure 7.
It may be considered that the terms PlS and P2S are equalO It follows that, for a phase difference ~ = 7r, the power detected is a minimum. It 20 passes through a maximum PSmax when Q ~ = 0; 21r and so on.
To increase the interferometer sensitivity, a constant 'non reciprocal' bias can be introduced in the phase of the two waves circulatin~ in opposite directions in order to move the interferometer operating point.
In the case of a func~ion varying In accordance with a cosine law9 the 25 greatest sensitivity point is obtained for angles ~2k + 1) ~r/2 in which k is a whole number. A bias can then be chosen which introduces a phase variation for each wave with an absolute value of rr /4 but with opposite signs. In the absence of 'non reciprocal' disturbance, ~he phase diff erence then be-comes: ~ ~' = Q~ + ~ ~ o in which ~ ~ o = 7r/2. This is point A in figure 7.
As shown in figure 6, it is possible to add in the wave path in ring 42 a phase modulator 45 which uses a rexiprocal effect to obtain better sensitivi-ty with the device. This modula~or is so energized as to produce a phase variation in $he wave passin~ through it. This variation is periodic, the period being 2 T in which T iS the time for a wave to pass in the ring.
5~3~
The difference ~hen becomes ~ + ~ (t-T ) in which each o~ the waves circulatin~ in the opposite direction undergoes this phase shift when it passes through the modulator with ~ ~t~ = ~ (t + 2T )-The operating point then describes the curve P5 = ~( a~ ) in figure 7 5 symmetrically between a pair of end points.
The device (reciprocal phase modulator) which enables the disturbance~ (t~ to be introduced can~ with advantage, be divided into two devices, 4S
and 46, one at each end of the path as shown in figure 6, one giving the phase shift ~ l(t) and the other the phase shift ~ 2(t). These phase modula~or 10 devices, symmetrically placed at the two ends of the optical path may be in opposition. This arrangement adds additional symetry to the phenomena and reduces the second order errors due to possible non-linearity in the modulators.
The ideal is to work at points A and B on the curve shown in figure 7 15 to start with. To work at A, ~ l(t) = 4 and ~ 2(t~ = - 74 and then to work at point B, ~ 1(t) = - 4 and ~2(t~
This result can be obtained by using two square-shaped signals with two levels,- 4 and 1l .
If the phase modulation signals are frequency F, if the gyroscope is not 20 rotating, a rectified signal at frequency 2F is obtained after detection.
However, if the gyroscope is rotating, frequencies F and 2F are obtained.
This device has the disadvantage of not lncluding a zero technique. Also9 the measurement is not linear.
If a zero method is required, a non reciprocal effec~ compensating the 25 rotational effect must be considered. A component at frequency F in the signa3 detected which is zero must then be obtained. The modified parame-ter enabling the rotational speed to be found is then measured.
The Iield applied to the modulator electrode terminals can be altered if it is electro-optical. The difference of frequency in the modes which are 30 propagating can be altered and this résults in a phase shift at the detector output.
The device in the invention finds its application in this optical fibre rate gyro field ln which two frequency converters o~ the invention can be arranged in the two arms working at frequencies such that the non ~5~3~
reciprocity, introduced by the fact that the two waves in the interferometer are not at the same frequency9 compensates for that due to the Sagnac eff ect.
Two converters, 62 and 63, arranged beside the modulators, 45 and 46, 5 as shown in figure 6 can be considered.
l he deYice in the invention then makes possible digital adjustement. If two frequertcy converters are placed beside ~he two modulators9 i~ is possible to compensate for the component of frequency F which is due to the Sagnac effect, when there is rotation. There are then two frequencies, 10 Fl and F2, in the two converters.
In the standby condition, ~l = F2 should be obtained. When ~he gyroscope rotates at constant speed, frequencies Fl and F2 beat and the number of beats can be counted.
The progress made in the production of low loss op~ical fibres makes it 15 possible to uce optical fibres to produce these ring interferometers as it has already been said. An example of the production of a ring interferometer complying with the invention is shown in figure 8. The fibre 52 wound round itself forms ring 42 of the interferometer. The various branches of the interferometer are made of in~egrated optics. The wave-guides are made by 20 integration in a substrate. The substrate can be chosen~ for example, from among the following materials: lithium niobate or tantalum niobate in which, to make the wave-guides, titanium or nlobium respec~ively have been diffused.
The frequency conver~er is broken down into two converters, 54 and 25 S5, placed at the ends of the fibre. These conver~ers, are the devices already described in the invention which make it possible to compensate for the Sagnac effect, when the two frequencies of the two acoustic waves ~58, 59), generated by the elec~rodes ~S6, 57) are altered. The phase modulators, 60 and 61J shown by the electrodes placed on one side and the other of ~ach 30 o~ ~he wave-guides are in the loop to make it possible to find out the instants at which the gyroscope rotates. In this case, a component of the signal at frequency F is detected as it has already been explained.
The optical radia~ion separators consist of monomode wave-guides connected between themselves to form Ys, these Ys being connec~ed ::L25~
between themselves by one of their branches acting the role previously played by the semi-transperent sheets in figure 6. The l,vave-guide ~8 actrs ~he role of the monomode filter in figure 1, a polarizer being made, for example, by metallizing 49 on the substrate surface over wave-guide 48.
The devlce in the invention also finds applications in optical 2elecom-munica~ions to multiplex/demultiplex optical waves in wave-length.
, .
. ' ~ ' ., ' ~ '' -
N OPTICAI FREQUENCY CONVERT~R DEVICE AND A RATE GYRO
CO~YTAINING SUCH A DEVICE
BACKGROUND OF THE INVENTION
The invention covers an integrated optical frequency converter device.
Classical op~ical frequency conver~ers are well known. The frequency converter most usually used is certainly the one based on acousto-optical interactlon. In this method, an acoustic network which propagates in a 5 medium produces periodic refractive index variations in the form of a travelling wave. This moving network diffracts the light. If the in~eraction lenght is sufficient, a single order may predominate. In the diffracted order (~" D~ the optical wave frequency ~ has been modified by a quantity eyual to the acoustic wave frequency Q .
Hense, ~D = ~+ Q
Fundamental frequency rejection may be excellent because the con-verted wave and the direct wave ~undiffracted) are then separated in space.
It is then possible to study what this gives in integrated optics. Under this name are designed thin layer monilithic s~ructures intended for lumi-nous signal processin~ which are obtained by the techniques of deposit, diffusion and engraYing by masking analogous to those used in the production of electronic integrated circuits. With these techniques, in particular, i~ is known how to produce linear structures characterized by a refractive index higher than that of the surrounding medium and forming wave-guides along 20 which the li~ht propagates by a series of total reflections or progressive refractions. 1~ is known how to combine two such wave-guides by arranging them in para~lel one with respect to the other along part of the path to produce directional couplers. Thanks to the vanishing wave phenomenon, the energy carried in the first wave-guide is passed progressively in to the 25 second wave-guide and it is found that the maxirnum energy is transferred at the end of a certain lenght, called ~he coupling lenght, which depends on the geometrical and optical parame~ers of the structure and9 in particular, on the value of the refractive indices of the materials formin~ the two waves-guides and the me~ium which separates ~hem. Then $he energy passes . ~
progr2s~sively from the second guide into the first and so on. When an electro-optical material is used for one of the materials forming the wave-guides or the medium which separates them, it is also known how ~o cause the index to vary under the effect of an electric field, which makes it 5 possible, by acting on the coupling lenght, to control electrically the part of the energy transfered from one wave-guide to the other. It can be seen that it is also possible to make a ligh~ modulator by arranging, in parallel with the wave-guide wh;ch carries the luminous wave, a section of wave-guide in which a more or less large part of this energy will be transferred.
Also, there are frequency converters intended to produce, from a guided electromagnetic radiation of frequency ~, a guided electromagnetic radiation wh~se frequency is a multiple of the frequency ~ . These conver-ters are used, in particular, in the integrated optical field, thus named by analogy with electronic in~egrated circuits, which are monolithic structures 15 using thin layers.
Converters of the type already described have been produced in integrated optics but they require the use of a flat wave-guide and this is not applicable to microguides. Techniques usable with microguides have already been suggested in which electro-optical modulation can be used.
20 lhis may then be a serrodyne or balanced rnodulator system. Such an optical frequency conver~er contains a wave-guide used as phase mo~ulator, which is controlled by a signal in the form of a saw-tooth. Such a si~nal has the same effect as a voltage gradient which allows a variation of the index as a function of time. It may also be an acoustic modulation in which a TE type 25 wave is converted into a TM type with a change in frequency. In this case, the application of a transverse electric field enables the pass-band of a TE-TM rnode acousto-optical converter to be modified by the colinear interac-tion of acoustic surface waves and a guided optical wave.
These two techniques have several disadvantages .
- the two waves propagate in the same wave-guide (the frequency translated wave and the fundamental wave) ans this can cause problems in separating them;
- in certain cases, the effectiveness of the conversion is very closely related to the wave shape (case of the serrodyne translator);
- 3 - 1~55~
- i.n the case of a TE-TM conversion, one of the problems that may be met with is the extreme sensi-tivity of the device to wave-length (variation of ~/KTE - ~/KT~) which may, however, allow this type of device to be used as a filter.
The device of the invention enables these dis-advantages to be attenuated. In this devi.ce, the converted and unconverted waves are separated in space because the diaphony is related to simple geometrical parameters and can be reduced arbitrarily. Also, the two waves keep the same polarizing. The device can be extended and used in the case in which it is required to produce frequency filters.
In accordance with the present invention, there is provided a rate gyroscope including an interferometer for measuring a non-reciprocal phase-shift undergone by first and second radiations circulating in opposite direc-tions in a ring wave-guide, comprisingO
said ring wave-guide with ends;
a monochromatic luminous source;
means Eor photo-detecting an interference of said first and second radiations;
an optical separator and mixer connec-ting the ends of said ring wave-guide to said luminous source and said photo-detecting means;
an electrically controlled optical phase shifter;
and - at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
a flat substrate;
~SS13~
at least two wave-guides with different characteristics integxated into said substra-te, one of which is intended to receive an incident wave, said two wave-guides being parallel with one another over a predeter-mined length and separated from one another by a distance such that the incident wave radiation is transferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
In aeeordanee with the invention, there is also provided a rate gyroseope ineluding an interferometer for measuring a non-reeiproeal phase-shift undergone by first and seeond radiations cireulating in opposite directions in an optical fiber ring wave-guide, comprising:
said optical fiber ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and seeond radiations;
an optieal separator and mixer conneeting the ends of said ring wave-guide to said luminous souree and said photo-deteeting means, said luminous source, photo-detecting means and separator and mixer being inte-grated on a single substrate;
first and second wave-guides integrated onto said substrate, said first wave-guide having a first end cou-pled to said monoehromatie luminous source, and said second wave-guide having a .first end coupled to said photo-detecting means, said first and seeond wave-guides having respective seeond ends coupled to different ends of said optical fiber ring;
::
: ~ :
- 3b -an electro-optical phase modulator comprising a pair of electrodes positioned one each on opposite sides of one of said first and second wave-guides; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, the two wave-guides being parallel with one another over a pre-determined length and separated from one another by a distance such that the incident wave radiation is trans-ferable from one wave-guide to another; and means for generating an acoustic wave colli-near with an incident wave propagating direction in one of the said two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
According to the invention, there is further pro-vided an integrated ring interferometer, comprising:
a substrate;
a source branch port;
a de-tection branch port;
a first Y-shaped wave-guide integrated into said substrate, said first wave-guide having first and second branches and a trunk portion, said first branch being coupled to said source branch port and said second branch being coupled to said detection branch port;
a monomode filter formed by a metallization over said trunk portion;
a second Y-shaped wave-guide integrated into said substrate, said second wave-guide having first and second branches and a -trunk portion, said trunk portion - 3c - ~ ~5S~3~
of the second wave-guide being coupled to said trunk portion of said first Y-shaped wave-guide;
a first phase modulator coupled to said first branch of said second Y-shaped wave-guide, said first phase modulator being constituted by a pair of electrodes on opposite sides of said first branch of the second wave-guide;
a second phase modulator coupled to said second branch of said second Y-shaped wave-guide, said second phase modulator being constituted by a pair of electrodes on opposite sides of said second branch of the second wave-guide;
a first optical frequency converter integrated into said substrate and optically coupled to said ~irst branch of said second Y-shaped wave-guide, said first optical frequency converter including:
third and fourth wave-guides integrated into said substrate and having different optical charac-teristics from one another, said third wave-guide being optically coupled to said first branch of said second Y-shaped wave-guide, and said fourth wave-guide having a portion that is substantially parallel with a portion of said third wave-guide over a predetermined length thereof;
first means for generating an acoustic wave collinear with an incident wave propagating direc-tion of said third wave-guide, said generating means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said third and fourth wave-guides;
a second optical frequency converter integrated into said substrat:e and optically coupled to said second branch of said second Y-shaped wave-guide, sai d second optical ~requency converter including:
..~
- 3d -fifth and si~th wave-guides inteyrated into said substrate and having different optical characteristics from one another, said fifth wave-guide being optically coupled to said second branch of said second Y-shaped wave-guide, and said sixth wave-~uide having a portion that is substantially parallel with a portion of said fifth wave-guide over a predetermined length thereof;
second means for generating an acoustic wave collinear with an incident wave propagating direction of said fifth wave-guide, said generatiny means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said fifth and sixth wave-guides; and an optical fiber ring having a first end optically coupled to said fourth wave-guide and a second end opti-cally coupled to said sixth wave-guide.
BRIEF DESCRIPTION OF THE URAWINGS
Other characteristics and advantages of the present invention will appear in the following non-restrictive description made with reference to the accornpanying drawings in which:
Figures 1 to 3 which are labelled as " PRIOR ART"
show a device known in the art;
Figure 4 shows the device in accordance with the invention;
Figure 5 which is labelled as " PRIOR A~T"
shows a device known in the art;
Figures 6 and 7 show a system containing the device in the invention; and - Figure 8 which is disposed on the same sheet of formal drawings as Figure 5 shows a variant of the system.
~ 3e ~
DETAILED DESCRIPTION OF THE PREFERRED EM _DIMENTS
Figures 1 and 2 show a sectional view and a view from above respectively of a switch produced in ': . : ' ' "' '' ~uides 1 and 2 are inserted in the sub~trate 3. The materlal through~ which csuplin~ is made is the one forming susbstrate 3. To insert wave-guides 1 and 2, it Is possible9 for example, to cause titanium to diffuse in a substrate formed of a monocrystalline shee~ of lithium niobate (LiNbO3~ e tita-5 niurn, in the diffusion zone, replaces the niobium in part to ~ive a mixedcompound with the formula LiTiXNbl ~03 with a refractive index higher than that of the pure nioba~e. These diffused ~ones, with an index higher than that of the substrate, form wave-guides I and 2. If the diffusion temperature is higher than the Curie point for the ma~erial, the cooling I0 phase which follows is used to subject the plate to a uniform electric field in order to polarize the plate uniformly and produce a "sin~le domaine"
structure.
When a voltage is applied between the electrodes 10 and 20, a distribution of field lines is produced which is shown as reference 4 on figure 15 1. The field component in the directlorl C perpendicular the substrate surface 23 has the sarne absolute value but opposite direction in one guide and the other, which gives refractive index var;ations of the same absolute value and opposite sign. Nonetheless, the existence, in a direction perpendi-cular to the direction of the substrate axis C, the susbtrate having its 20 extraordinary index, of a non-zero field component, and the fact that the electric field applied also causes the index value to vary in the part of the substrate 22 contained between the two wave-guides cause a certain dissymetry of the phenomenon. The coupling obtained varies in accordance with the polarity of the voltage applied between the electrodes 20 and 21.
2s The polarity of the voltage supplying the maximum coupling can be deduced from the crystallographic orientation of the material forming the substrate~
If this orientation is unknown, it is very easy to determine experimentally the optimum polarity by the measurement of the luminous intensity trans-mitted by ore of two wave-guides fortwo polari~ies of opposite signs.
If the metallic electrodes are arranged directly on the wave-guide surfaces, the existence of a vanishin~ wave moving in the relatively abs~rbent metallic medium can cause energy losses in the coupler. To avoid them it ls possible to fit in between as shown ln figure 1, a transparent dielectric layer 11 and 21 between wave-guides 1 and 2 and electrodes 10 and 20. This isolating layer is made of a material wi~h good tr~nsmission for the iuminous wave-len~ht carried by the wave-guide and a refractive Index lower than that of the wave-guide. Silicon dioxide (SiO2) is a ma~erial perfec~ly adap~ed to the case previously described in which the substrate is 5 formed by lithium niobate.
The two wave-guides9 as shown in figure 2, are parallel one with ~he other on a rectilinear section of lenght L, which is a flmction of the parameter, called the coupling lenght, which will be defined later. 1 he distance between the rectilinear parallel parts is of a value d which must 10 not exceed a few wave-lengths (calculated in the medium separating the two wave ~uides) of the light carried by the wave-~uides. The two waves-guides are formed by the ~ame electro-optical ma~erial which, when subjected to an electric field, has a refractive index that varies as a function of the applied field value. The refractive index of this material is so chosen that, 15 even in the presence of the applied electric field, it remains higher than the index of the material forming substrate 3.
Because of the electro-optical character of the material forming wave-guides 1 and 2, the distribu~ion of the ~ield lines in the wave-guides produces within them refractive index varia~ions roughly equal in absolute 20 value but of opposite signs.
When a wave is carried by wave-guide, part of the energy propagates outside the wave-guide, in the medium which surrounds it in the form of a vanishing wave. The amplitude of this wave decreases exponentially on leaving the wave-guides walis. If a second wave-guide is arranged parallel to 25 the first one, it picks up progressively, throu~h this vanishing wave, the energy carried in the first wave-guide and, the closer are the wave-guides, the more quickly it does it. AEter a given distance, called the coupling lenght, which depends on the geometrical and optical parameters of the two wave-guides and of the medium separating them (and of the refractive 30 indices in particular), the maximum of energy has been transferred from the first wave-guide to the second. Beyond this lenght, the reverse phenomenon occurs. The energy transfers pro~ressively from the second wave-guide to the ~irst to leave ~he minimum value in the second wave-guide. Any :' :
modification of the index of one of the media present acts in one direction or the other along the coupling lenght.
In the device shown in figures 1 and 2, the lenght L can be cho~en equal to th~ couplin~ len~h~ in the absence of this applied electric field.
5 Because of the perfect symetry of the two waves-guides in the coupling zone, the energy transfer is complete from the first wave-~uide to the second (or from the second to the first). The application of a voltage between electrodes 20 and 21 reduces the coupling lenght and part of the energy is retransferred from the second wave-guide to the first (or from the 10 first to the second). The final result is then that, as the voltage is increased, the energy transferred from the first wave-guide to the second (or from the second to the first), measured at the end of the coupling zone, is reduced to reach a zero value. The coupling between the two wave-guides thus decreases from 100 % to 0 % when the voltage applied to the electrodes 15 increases. The result would be ~he same if the lenght L was made equal to and odd multiple of the coupling lenght with a zero field.
It is also possible to give the lenght L a value equal to an even multiple of the coupling lenght with a zero field. The energy transferred at the output, from one wave-guide to the other, increases from zero when the 20 voltage applied between the electrodes increases from zero.
A device has then made which, when controlled by an electric signal, enables part or all of the energy carried by one wave-guide to be switehed to the other associated with it in the coupling zone.
It goes without say;ng that, if one of the two wave-guides is limited to 25 a section whose minimum lenght is the lengh~ L of ~he coupling zone, this device enables the energy carried in the other wave-guide to be modulated no%.
In the case in which the two wave-guides are different, a periodic structure made behveen them can make it possible to increase the exchan-30 ges between them. When the wave carried in one wave-guide has the same propagation speed as one of the orders diffracted in the other wave-guide, there is then an energy exchange.
To produce this exchange several means can be used, in particular the production of an electric field between two electrodes, for example, of -' - ., .
periodic structures 18 and 29 fitted on one side and on the other of ~he two wave-guides 5 and 6 as shown in figure 3. A luminous wave 24 propagating in the first wave-guide produces, by coupling due to the presence o~ a polarization Vo9 a coupled wave 25 which propagates in the second wave-5 guide 6. It can also be the production of a network engraved in the substratebetween the two wave-guides. In the device of the in~ention, acoustic waves 12 are produced by the électrodes 13 and 14 in the form of interdigi~al combs, at whose terminals a genera~or V is connected, which propagate between the two waves-guides as shown in figure 4. However, the electrodes 10 can be deposited on a thin layer 26 of a piezoelectric material, a ~inx oxide(ZnO) for example, the thin layer being deposited on substrate 3 consisting o~
another material, silicon dioxide for example. Thin layer 26 can be made of the same material as the substrate, crystalline quartz, gallium arsenide or lithium niobate for example.
The device in accordance with ~he invention has be advantage of allowing an adjustement of the coupling between wave-guides 5 and 6 which is a function of the acoustic wave frequency. This acousto-optical deflector allows a frequency translation. The luminous waves carried by one of the wave-guides 5 and diffracted by these acousto-optical waves are then 20 converted in frequency and transmitted in the second wave-guide 6. These two wave-guides are not necessarily of the same width.
If a medium 30 is considered in which a beam of elastic waves 31 of frequency f is propagating, as shown in figure 5, if an incident luminous beam 32 is passed in this medium, a ~roup of diffracted beams 33 is obtained 25 with frequencles F + + kf, in which k is a positive or negative whole number.The sinusoidal variation oE the index, produced by the elastic wave, has an effect on the luminous wave analogous to that of a phase network.
The luminous beam 32 penetrating the crystal 30 in parallel with the elastic wave planes is separated into several beanns symmetriAcally inclined with 30 respect ~o ~he incident beam by angles ~ N: Sin ~N = k ~ in whlch ~ is the wave plane step and ~ the incident beam wave-lenght. However, the elas~ic beam thiclsness e must be less than a critical value ec. The side waves are produced all long ~he carrier wave path inside the ultrasonic beam and not only at the output, on the frontier. If, in throught, the elastic beam is divided into thin slices parallel to the propagation direction, for each of these slices parallel to the propagation direction, for each of these slices9 ~he preceding spectral analysis is valid. The frequencies Q ~ k~ and ~he direction of propagation ~ N oE ~he side wavcs are the same for the absclssa slices x and x ~ Q . iE9 for a given order, the contribu~ions of these two sl~esQ apart are added, there is phase opposition for a dis~ance Q N = A
N The interference of the waves emitted by the slices QN apart may then be destructive. If the width o~ the beam is greater than Q N~ the effect of a slice is cancelled by ~he silice Q N away. Under the best conditions, the elastic beam 2thickness e must not exceed a first order critical value:
ec= Rl= A .
For a Bragg angle incident of the luminous beam 32 with respect to ~he elastic wave planes, the interaction is the biggest because it enables the interferences to be made constructive for the first order of angular frequency Q + ~. Hence, it only supplies a single deviated beam.
The device as in the invention uses a directional coupler whose two wave-guides are not identical. In this case, if B /K 1 and B/K~ are the propagation constants of the modes in these two wave-guides of the coupler~
the relative energy in one of the wave-guides when the other is energized will be written: E = 12 2 Sin2V 1 + ~B 7i~cL in which L is l ~ a~ l~c the interaction lenght, c is the coupling constant and ~B = 2N (~ IK1 -C2) in which ~ is the wave-lenght in a vacuum. The relative energy present in this wave-guide at the coupler output depends on three parameters, L, c and ~ . If ~B is large with respect to c, it can be sen that, in any case, no 25 matter what the value of L, the maximum energy exchanged can be smallO
~or example, if c _ 1.510 4 /um9 2 ~ = 0-0001, EMAX = 0.0017 and if c - 1.5 10-4 /um, 2Tr ~= O-Ol~ EMAx = 0.000017 These values are very small and can be reduced further arbitrarily by changing the lenght L.
1~ is known ~hat, if the propagation constants in the two ~ave-guides are made to vary periodically and the corresponding period is carefully chosen, the exchange between the two wave-guides can be increased by comprising the ~ ~ with the network vector K.
.
~25~
The interaction is then vrit~en, because of the conservation of the nts ~ 29 l e- ~ K - ~ 2/K) = ~ in which A is the network period.
Hence, if the network is formed, as produced in the device of the 5 invention shown in figure 4, by an acoustic wave propagating colinearly ~o the optical wave, there will be a frequency translation of the coupled wave.
The effectiveness of the interaction depends on the value of the index variation induced by ~he acoustic wave and hence nf the power injected. A
directional coupler produced in lithium niobate (LiNbO3) by titanium diffu-10 sion can be taken as an example. The variation in index corresponding totitanium is usually of the order of: ~ n ~ 510 3.
1~ can be seen then that it is possible to produce the two wave-guides with ~ B/K = 210 3. This can be obtained by changlng the width and/or the thickness of the titanium for these two wave-guides in the coupler. For an 15 interaction lenght of lO mm9 the maximum energy exchanged will be: for )~ = 0.83/um, EMAX = 4 10 4. The acoustic wave-length required for com-pensation will be: 415tum, i.e. in the case of lithium niobate (LlNbO3) a frequency transla~ion of 7.2 MHz. The wave picked up at the output of the second wave-guide (which was not initially energized) will then be obtained 20 with a frequency translation of 72 MHz and the maximum quantity of fundamental in this wave-guide will be - 33 d~ with respect to the total optical energy.
The device as in the invention can also be produced by making one of the wave-guides by proton exchange and the other by titanium dif Eusion ~or 25 the two by proton exchange but different characteristics3. In this case, ~ ~/K ~ 0.1 can be obtained with an interaction lenght of lO mm, the maximum energy exchanged: - 6~ dB OI the total energy is ob~ained with an acous~ic wave-lenght of 8.3 /um, i.e. an acoustic frequency of the order of 361 MHz.
Hence, in the device of the invention shown in figure 4, a wave 23 passed in the firs~ wave-~uide causes by coupling the existence of a wave 25 in ~he second wave-guide, this wave then heing translated in fre~uency.
Sever~l wave-guide configurations are possible, wlth a substrate 3 of lithium niobate, for exampleO lhe two wave-guides are obtained by diffusion of titanium in the substrate. The waves L~uided in ~he two wave-guides are either twc TE waves or two TM waves. ~ of the order of a few l0 3 i5 then obtained.
Ig is also po~sible to have a crossed interaction, i.e. a TE wave in the 5 first wave_guide and a TM wave in the second or YiC2 versa. K of the order c>f 0.l is then obtained One Qf the two wave-guides can be obtained by titaniuM diffusion and the second one by proton exchange. If an axis C perpendicular to the substrate surface is considered, there is a TM wave in each of the two wave-10 guides. There could also be twn TE waves. ~ of the order of 0.l is then obtained. The two waves-guides can be obtained by proton exchange but their characteristics must then be different. ~ ~ û.l is then obtained.
By changing the acoustic frequency, which can vary from l0 to 3D0 MHz, a tunable filter can be obtained. The birefringence of the material varies as function of the frequency.
The pass-band of the device in the invention is a function of the optical wave to acoustic wave interaction lenght. The greater the number of wave planes in the acoustic wave seen during this coupling9 the narrower the pass-band.
The device described here can be used then as a filter by using, for example, ~he variation of the birefringence of a rna~erial with the wave-lenght. It can be considered then that it is a TE (TM) wave in the first wave-guide and TM (TE) wave in the second which are coupled by means oE the acoustic wave. In this case, for lithium niobate, ~ ~ B /KTM - ~B KTE) ^ 0.l and again an acoustic wave frequency of about 361 MHz. This filter i5 adjustable because it is sufficient to change the acoustic wave frequency.
In the device of the invention, electrodes can be deposited, on one side and on the other of the two wave-guides, for example, or on these wave-guides. An insulating buffer layer can also be deposited between the electrodes and the substrate. The electric field produced between these two electrodes enables the device of the invention ~o be adjusted in its initial or its final state.
The device of the invention has an application in the field of the optical fibre ra~e gyro.
~55~3~
Figure 6 shows schematically a ring interferometer of known design. A
laser source S transmits a beam of parallel rays 41 to a separa~or deYice formed by a semi-transparent sheet M.
A certain number of mirrors, 15~ M2, M3, define an optical path 5 forming the interferometer ring. This ring can be made, for example~ with a monomode op~ical fibreO The sensitiYi~y of the measurement is increased by the use of a long optical path. This ring is looped back on the separator device M which also acts as a mixer device and determines an outpu~ branch 43. Two waves, then, propagating in opposite directions, pass trough the 10 ring, one clockwise (direction 2) and the other anticlockwise (direction 1).
These two waves recombine on the separatin~ sheet M. The result of this recombinaison can be seen in the output branch 43 with detector D. Part of the beams is picked up a~ain in the input arm by the separating sheet M' and passes through filter device F again. At the output the two waves recombine 15 on separating sheet M~. The result of this recombina~ion can be seen in the output branch 44. The fact that the filter device F has been fitted in the interferometer input arm makes the arm strictly reciprocal. Hence, a wave contained in a single optical mode passes through it. This filter device consists of a mode filter followed by ~ polarizer. The incident beam 41 20 passes throu~h this filter and the fraction which comes out is in a single mode. It is possible then to consider either the emerging beam 43 correspon-ding to the Interference of the two beams which have not passed through the mode filter device or the part of the beams which is picked up again in the input arm by semi-transparent sheet M. This part of the beams passes 25 through filter device F again. At its output, the two beams passed through arm 44 by means of semi-transparent sheet M' are contained in the same mode and this makes the interferometer insensitive to 'reciprocal' disturban ces.
If ~ ~ is the difference in phase between the two waves which 30 propagate in opposite directions in the ring and PS is the optical power which can be measured in output branch 44, then, when there is 'non reciprocal' disturbances; ~ 4 is zero.
If a rate gyro using this ring interferometer is considered, a 'non reciprocal' disturbance will be produced when the rate gyro is spun. The ~s~
phase difference ~ ~ is not zero and ~ Q in which n Is the speed of rotation and a = k ~C in which k is a constant dependin~ ~n the rate gyro geometry7 L the lenght of the optical path9 A the length o~ ~he ligh~ wave ~mitted by the laser source S and C the speed of the li~ht in rin~ 42. When the speed of rota~ion n increases, ~he pha.se di~ference ~ ~ increases in ~he same proportion because coefficient a remains constant. The optical power PS changes according ~o a cosine law.
~, .
Ps = PlS + P25 + 2 Y PlsP2~ Cos ~ ~ ~ ) in which PlS corresponds to direction 1 and P2S to direction 2. The measurement sensitivity for a ~iven dPS
value ~ ~ is given by the derivative of Ps~ d(~ ) 2V~Sin ~ ~ ~ 3 The interferometer sensitivity is very low if the phase difference 15 is little different from zero. This is the case in a rate gyro if it is required to measure small rotational speeds Q . The variation in optical power in the output branch is shown in the dia~ram in figure 7.
It may be considered that the terms PlS and P2S are equalO It follows that, for a phase difference ~ = 7r, the power detected is a minimum. It 20 passes through a maximum PSmax when Q ~ = 0; 21r and so on.
To increase the interferometer sensitivity, a constant 'non reciprocal' bias can be introduced in the phase of the two waves circulatin~ in opposite directions in order to move the interferometer operating point.
In the case of a func~ion varying In accordance with a cosine law9 the 25 greatest sensitivity point is obtained for angles ~2k + 1) ~r/2 in which k is a whole number. A bias can then be chosen which introduces a phase variation for each wave with an absolute value of rr /4 but with opposite signs. In the absence of 'non reciprocal' disturbance, ~he phase diff erence then be-comes: ~ ~' = Q~ + ~ ~ o in which ~ ~ o = 7r/2. This is point A in figure 7.
As shown in figure 6, it is possible to add in the wave path in ring 42 a phase modulator 45 which uses a rexiprocal effect to obtain better sensitivi-ty with the device. This modula~or is so energized as to produce a phase variation in $he wave passin~ through it. This variation is periodic, the period being 2 T in which T iS the time for a wave to pass in the ring.
5~3~
The difference ~hen becomes ~ + ~ (t-T ) in which each o~ the waves circulatin~ in the opposite direction undergoes this phase shift when it passes through the modulator with ~ ~t~ = ~ (t + 2T )-The operating point then describes the curve P5 = ~( a~ ) in figure 7 5 symmetrically between a pair of end points.
The device (reciprocal phase modulator) which enables the disturbance~ (t~ to be introduced can~ with advantage, be divided into two devices, 4S
and 46, one at each end of the path as shown in figure 6, one giving the phase shift ~ l(t) and the other the phase shift ~ 2(t). These phase modula~or 10 devices, symmetrically placed at the two ends of the optical path may be in opposition. This arrangement adds additional symetry to the phenomena and reduces the second order errors due to possible non-linearity in the modulators.
The ideal is to work at points A and B on the curve shown in figure 7 15 to start with. To work at A, ~ l(t) = 4 and ~ 2(t~ = - 74 and then to work at point B, ~ 1(t) = - 4 and ~2(t~
This result can be obtained by using two square-shaped signals with two levels,- 4 and 1l .
If the phase modulation signals are frequency F, if the gyroscope is not 20 rotating, a rectified signal at frequency 2F is obtained after detection.
However, if the gyroscope is rotating, frequencies F and 2F are obtained.
This device has the disadvantage of not lncluding a zero technique. Also9 the measurement is not linear.
If a zero method is required, a non reciprocal effec~ compensating the 25 rotational effect must be considered. A component at frequency F in the signa3 detected which is zero must then be obtained. The modified parame-ter enabling the rotational speed to be found is then measured.
The Iield applied to the modulator electrode terminals can be altered if it is electro-optical. The difference of frequency in the modes which are 30 propagating can be altered and this résults in a phase shift at the detector output.
The device in the invention finds its application in this optical fibre rate gyro field ln which two frequency converters o~ the invention can be arranged in the two arms working at frequencies such that the non ~5~3~
reciprocity, introduced by the fact that the two waves in the interferometer are not at the same frequency9 compensates for that due to the Sagnac eff ect.
Two converters, 62 and 63, arranged beside the modulators, 45 and 46, 5 as shown in figure 6 can be considered.
l he deYice in the invention then makes possible digital adjustement. If two frequertcy converters are placed beside ~he two modulators9 i~ is possible to compensate for the component of frequency F which is due to the Sagnac effect, when there is rotation. There are then two frequencies, 10 Fl and F2, in the two converters.
In the standby condition, ~l = F2 should be obtained. When ~he gyroscope rotates at constant speed, frequencies Fl and F2 beat and the number of beats can be counted.
The progress made in the production of low loss op~ical fibres makes it 15 possible to uce optical fibres to produce these ring interferometers as it has already been said. An example of the production of a ring interferometer complying with the invention is shown in figure 8. The fibre 52 wound round itself forms ring 42 of the interferometer. The various branches of the interferometer are made of in~egrated optics. The wave-guides are made by 20 integration in a substrate. The substrate can be chosen~ for example, from among the following materials: lithium niobate or tantalum niobate in which, to make the wave-guides, titanium or nlobium respec~ively have been diffused.
The frequency conver~er is broken down into two converters, 54 and 25 S5, placed at the ends of the fibre. These conver~ers, are the devices already described in the invention which make it possible to compensate for the Sagnac effect, when the two frequencies of the two acoustic waves ~58, 59), generated by the elec~rodes ~S6, 57) are altered. The phase modulators, 60 and 61J shown by the electrodes placed on one side and the other of ~ach 30 o~ ~he wave-guides are in the loop to make it possible to find out the instants at which the gyroscope rotates. In this case, a component of the signal at frequency F is detected as it has already been explained.
The optical radia~ion separators consist of monomode wave-guides connected between themselves to form Ys, these Ys being connec~ed ::L25~
between themselves by one of their branches acting the role previously played by the semi-transperent sheets in figure 6. The l,vave-guide ~8 actrs ~he role of the monomode filter in figure 1, a polarizer being made, for example, by metallizing 49 on the substrate surface over wave-guide 48.
The devlce in the invention also finds applications in optical 2elecom-munica~ions to multiplex/demultiplex optical waves in wave-length.
, .
. ' ~ ' ., ' ~ '' -
Claims (23)
1. A rate gyroscope including an interferometer for measuring a non-reciprocal phase-shift undergone by first and second radiations circulating in opposite direc-tions in a ring wave-guide, comprising:
said ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and second radiations;
an optical separator and mixer connecting the ends of said ring wave-guide to said luminous source and said photo-detecting means;
an electrically controlled optical phase shif-ter; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
a flat substrate;
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, said two wave-guides being parallel with one another over a prede-termined length and separated from one another by a distance such that the incident wave radiation is trans-ferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
said ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and second radiations;
an optical separator and mixer connecting the ends of said ring wave-guide to said luminous source and said photo-detecting means;
an electrically controlled optical phase shif-ter; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
a flat substrate;
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, said two wave-guides being parallel with one another over a prede-termined length and separated from one another by a distance such that the incident wave radiation is trans-ferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
2. A gyroscope according to claim 1, wherein said acoustic wave generating means comprises a layer of a piezoelectric material arranged on a surface of said substrate and a pair of electrodes deposited on said layer of piezoelectric material.
3. A gyroscope according to claim 1, wherein said acoustic wave generating means comprises two inter-digital comb electrodes deposited on a surface of said substrate.
4. A gyroscope according to claim 1, wherein said substrate is made of lithium niobate.
5. A gyroscope according to claim 4, wherein at least one of said two wave-guides comprises a bar embedded in said substrate in which titanium is introduced into said lithium niobate.
6. A gyroscope according to claim 4, wherein at least one of said two wave-guides comprises a bar embedded in said substrate and wherein H+ ions are substituted for lithium ions in said lithium niobate.
7. A gyroscope according to claim 1, further comprising means for applying a modulating field to at least one of said two wave-guides.
8. A gyroscope according to claim 7, wherein said modulating means comprises electrodes arranged on opposite sides of a wave-guide.
9. A gyroscope according to claim 7, wherein said modulating means comprises electrodes arranged on a wave-guide.
10. A rate gyroscope including an interferometer for measuring a non-reciprocal phase-shift undergone by first and second radiations circulating in opposite direc-tions in an optical fiber ring wave-guide, comprising:
said optical fiber ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and second radiations;
an optical separator and mixer connecting the ends of said ring wave-guide to said luminous source and said photo-detecting means, said luminous source, photo-detecting means and separator and mixer being integrated on a single substrate;
first and second wave-guides integrated onto said substrate, said first wave-guide having a first end coupled to said monochromatic luminous source, and said second wave-guide having a first end coupled to said photo-detecting means, said first and second wave-guides having respective second ends coupled to different ends of said optical fiber ring;
an electro-optical phase modulator comprising a pair of electrodes positioned one each on opposite sides of one of said first and second wave-guides; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, the two wave-guides being parallel with one another over a prede-termined length and separated from one another by a distance such that the incident wave radiation is transferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the said two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
said optical fiber ring wave-guide with ends;
a monochromatic luminous source;
means for photo-detecting an interference of said first and second radiations;
an optical separator and mixer connecting the ends of said ring wave-guide to said luminous source and said photo-detecting means, said luminous source, photo-detecting means and separator and mixer being integrated on a single substrate;
first and second wave-guides integrated onto said substrate, said first wave-guide having a first end coupled to said monochromatic luminous source, and said second wave-guide having a first end coupled to said photo-detecting means, said first and second wave-guides having respective second ends coupled to different ends of said optical fiber ring;
an electro-optical phase modulator comprising a pair of electrodes positioned one each on opposite sides of one of said first and second wave-guides; and at least one optical frequency converter device in an optical path of said ring wave-guide, said optical frequency converter device including:
at least two wave-guides with different characteristics integrated into said substrate, one of which is intended to receive an incident wave, the two wave-guides being parallel with one another over a prede-termined length and separated from one another by a distance such that the incident wave radiation is transferable from one wave-guide to another; and means for generating an acoustic wave collinear with an incident wave propagating direction in one of the said two wave-guides, the generating means being arranged between the two wave-guides to produce frequency conversion when radiation is transferred from one wave-guide to the other.
11. A rate gyroscope according to claim 10, wherein said acoustic wave generating means comprises a layer of a piezoelectric material arranged on a surface of said substrate and a pair of electrodes deposited on said layer of piezoelectric material.
12. A rate gyroscope according to claim 10, wherein said acoustic wave generating means comprises two interdigital comb electrodes deposited on a surface of said substrate.
13. A rate gyroscope according to claim 10, wherein said substrate is made of lithium niobate.
14. A rate gyroscope according to claim 13, wherein at least one of said two wave -guides of the optical frequency converter device comprises a bar embedded in said substrate in which titanium is introduced into said lithium niobate.
15. A rate gyroscope according to claim 13, wherein at least one of said two wave-guides of the optical frequency converter device comprises a bar embedded in said substrate and wherein H+ ions are substituted for lithium ions in said lithium niobate.
16. An integrated ring interferometer, comprising:
a substrate;
a source branch port;
a detection branch port;
a first Y-shaped wave-guide integrated into said substrate, said first wave-guide having first and second branches and a trunk portion, said first branch being coupled to said source branch port and said second branch being coupled to said detection branch port;
a monomode filter formed by a metallization over said trunk portion;
a second Y-shaped wave-guide integrated into said substrate, said second wave-guide having first and second branches and a trunk portion, said trunk portion of the second wave-guide being coupled to said trunk por-tion of said first Y-shaped wave-guide;
a first phase modulator coupled to said first branch of said second Y-shaped wave-guide, said first phase modulator being constituted by a pair of electrodes on opposite sides of said first branch of the second wave-guide;
a second phase modulator coupled to said second branch of said second Y-shaped wave-guide, said second phase modulator being constituted by a pair of electrodes on opposite sides of said second branch of the second wave-guide;
a first optical frequency converter integrated into said substrate and optically coupled to said first branch of said second Y-shaped wave-guide, said first optical frequency converter including:
third and fourth wave-guides integrated into said substrate and having different optical characteristics from one another, said third wave-guide being optically coupled to said first branch of said second Y-shaped wave-guide, and said fourth wave-guide having a portion that is substantially parallel with a portion of said third wave-guide over a predetermined length thereof;
first means for generating an acoustic wave collinear with an incident wave propagating direction of said third wave-guide, said generating means being posi-tioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said third and fourth wave-guides;
a second optical frequency converter integrated into said substrate and optically coupled to said second branch of said second Y-shaped wave-guide, said second op-tical frequency converter including:
fifth and sixth wave-guides integrated into said substrate and having different optical charac-teristics from one another, said fifth wave-guide being optically coupled to said second branch of said second Y-shaped wave-guide, and said sixth wave-guide having a portion that is substantially parallel with a portion of said fifth wave-guide over a predetermined length thereof;
second means for generating an acoustic wave collinear with an incident wave propagating direction of said fifth wave-guide, said generating means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said fifth and sixth wave-guides; and an optical fiber ring having a first end opti-cally coupled to said fourth wave-guide and a second end optically coupled to said sixth wave-guide.
a substrate;
a source branch port;
a detection branch port;
a first Y-shaped wave-guide integrated into said substrate, said first wave-guide having first and second branches and a trunk portion, said first branch being coupled to said source branch port and said second branch being coupled to said detection branch port;
a monomode filter formed by a metallization over said trunk portion;
a second Y-shaped wave-guide integrated into said substrate, said second wave-guide having first and second branches and a trunk portion, said trunk portion of the second wave-guide being coupled to said trunk por-tion of said first Y-shaped wave-guide;
a first phase modulator coupled to said first branch of said second Y-shaped wave-guide, said first phase modulator being constituted by a pair of electrodes on opposite sides of said first branch of the second wave-guide;
a second phase modulator coupled to said second branch of said second Y-shaped wave-guide, said second phase modulator being constituted by a pair of electrodes on opposite sides of said second branch of the second wave-guide;
a first optical frequency converter integrated into said substrate and optically coupled to said first branch of said second Y-shaped wave-guide, said first optical frequency converter including:
third and fourth wave-guides integrated into said substrate and having different optical characteristics from one another, said third wave-guide being optically coupled to said first branch of said second Y-shaped wave-guide, and said fourth wave-guide having a portion that is substantially parallel with a portion of said third wave-guide over a predetermined length thereof;
first means for generating an acoustic wave collinear with an incident wave propagating direction of said third wave-guide, said generating means being posi-tioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said third and fourth wave-guides;
a second optical frequency converter integrated into said substrate and optically coupled to said second branch of said second Y-shaped wave-guide, said second op-tical frequency converter including:
fifth and sixth wave-guides integrated into said substrate and having different optical charac-teristics from one another, said fifth wave-guide being optically coupled to said second branch of said second Y-shaped wave-guide, and said sixth wave-guide having a portion that is substantially parallel with a portion of said fifth wave-guide over a predetermined length thereof;
second means for generating an acoustic wave collinear with an incident wave propagating direction of said fifth wave-guide, said generating means being positioned so that an acoustic wave generated thereby produces a frequency shift in an optical wave coupled between said fifth and sixth wave-guides; and an optical fiber ring having a first end opti-cally coupled to said fourth wave-guide and a second end optically coupled to said sixth wave-guide.
17. An integrated interferometer according to claim 16, wherein said acoustic wave generating means com-prises a layer of a piezoelectric material arranged on a surface of said substrate and a pair of electrodes deposited on said piezoelectric layer.
18. An integrated interferometer according to claim 16, wherein said acoustic wave generating means comprise two interdigital comb electrodes deposited on a surface of said substrate.
19. An integrated interferometer according to claim 16, wherein said substrate is made of lithium nio-bate.
20. An integrated interferometer according to claim 19, wherein at least one of said third and fourth wave-guides comprises a bar embedded in said substrate in which titanium is introduced into said lithium niobate.
21. An integrated interferometer according to claim 19, wherein at least one of said third and fourth wave-guides comprises a bar embedded in said substrate and wherein H+ ions are substituted for lithium ions in said lithium niobate.
22. An integrated interferometer according to claim 19, wherein at least one said fifth and sixth wave-guides comprises a bar embedded in said substrate in which titanium is introduced into said lithium niobate.
23. An integrated interferometer according to claim 19, wherein at least one said fifth and sixth wave-guides comprises a bar embedded in said substrate and wherein H+ ions are substituted for lithium ions in said lithium niobate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8221630A FR2555769B1 (en) | 1982-12-23 | 1982-12-23 | OPTICAL FREQUENCY CONVERTER AND GYROMETER DEVICE COMPRISING SUCH A DEVICE |
| FR8221630 | 1982-12-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1255139A true CA1255139A (en) | 1989-06-06 |
Family
ID=9280439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000443990A Expired CA1255139A (en) | 1982-12-23 | 1983-12-22 | Optical frequency converter device and a rate gyro containing such a device |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA1255139A (en) |
| DE (1) | DE3346058C2 (en) |
| FR (1) | FR2555769B1 (en) |
| GB (1) | GB2151806B (en) |
| IT (1) | IT1160140B (en) |
| NL (1) | NL192466C (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4799750A (en) * | 1983-11-04 | 1989-01-24 | Canon Kabushiki Kaisha | Optical function element and a method for manufacturing the same |
| JPS60119522A (en) * | 1983-12-02 | 1985-06-27 | Canon Inc | Optical waveguide |
| NL8800939A (en) * | 1988-04-12 | 1989-11-01 | Philips Nv | RADIANT COUPLING DEVICE. |
| US5054873A (en) * | 1989-12-04 | 1991-10-08 | Northrop Corporation | High density integrated optical multiplexer/demultiplexer |
| DE4230300A1 (en) * | 1992-09-10 | 1994-03-17 | Bosch Gmbh Robert | Integrated acousto-optical component |
| DE19640725A1 (en) * | 1996-10-02 | 1998-04-09 | Reinhold Prof Dr Ing Noe | Network analyzer |
| CN109037873B (en) * | 2018-06-24 | 2023-07-25 | 电子科技大学 | Mode composite transmission line with transition structure |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3850503A (en) * | 1972-10-26 | 1974-11-26 | Texas Instruments Inc | Asymmetric waveguide pair acoustic surface wave switch |
| FR2309890A1 (en) * | 1975-04-30 | 1976-11-26 | Thomson Csf | ELECTRO-OPTICAL SWITCH AND MODULATOR USING THIS SWITCH |
| JPS5241541A (en) * | 1975-09-29 | 1977-03-31 | Nippon Telegr & Teleph Corp <Ntt> | Input-output equipment for optical fibers |
| US3992079A (en) * | 1975-12-11 | 1976-11-16 | The United States Of America As Represented By The Secretary Of The Navy | Frequency tunable acoustooptic mode filter |
| US4138196A (en) * | 1977-07-06 | 1979-02-06 | The United States Of America As Represented By The Secretary Of The Army | Fiber interferometer rotary motion sensor |
| FR2399736A1 (en) * | 1977-08-05 | 1979-03-02 | Thomson Csf | METHOD OF MANUFACTURING AN ELECTRO-OPTICAL STRUCTURE INCLUDING AN INTEGRATED ELECTRODE AND OPTOELECTRONIC COMPONENT USING THE SAID STRUCTURE |
| US4157860A (en) * | 1977-10-11 | 1979-06-12 | Bell Telephone Laboratories, Incorporated | Dual polarization electromagnetic switch and modulator |
| US4326803A (en) * | 1979-09-20 | 1982-04-27 | Northrop Corporation | Thin film laser gyro |
| DE3013335A1 (en) * | 1980-04-05 | 1981-10-08 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Acousto-optic modulator - has piezoelectric transducer to modulate light wave in SSB mode |
| DE3115804A1 (en) * | 1981-04-18 | 1982-11-04 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Ring interferometer |
-
1982
- 1982-12-23 FR FR8221630A patent/FR2555769B1/en not_active Expired
-
1983
- 1983-12-14 IT IT68302/83A patent/IT1160140B/en active
- 1983-12-20 GB GB08333905A patent/GB2151806B/en not_active Expired
- 1983-12-21 DE DE3346058A patent/DE3346058C2/en not_active Expired - Lifetime
- 1983-12-22 CA CA000443990A patent/CA1255139A/en not_active Expired
- 1983-12-23 NL NL8304435A patent/NL192466C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2555769B1 (en) | 1986-03-21 |
| NL8304435A (en) | 1985-05-01 |
| GB2151806B (en) | 1986-12-03 |
| IT8368302A0 (en) | 1983-12-14 |
| IT1160140B (en) | 1987-03-04 |
| FR2555769A1 (en) | 1985-05-31 |
| GB2151806A (en) | 1985-07-24 |
| NL192466B (en) | 1997-04-01 |
| DE3346058A1 (en) | 1986-04-24 |
| DE3346058C2 (en) | 1995-11-02 |
| NL192466C (en) | 1997-08-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |