CA1261048A - Acousto-optic modulator - Google Patents
Acousto-optic modulatorInfo
- Publication number
- CA1261048A CA1261048A CA000515779A CA515779A CA1261048A CA 1261048 A CA1261048 A CA 1261048A CA 000515779 A CA000515779 A CA 000515779A CA 515779 A CA515779 A CA 515779A CA 1261048 A CA1261048 A CA 1261048A
- Authority
- CA
- Canada
- Prior art keywords
- block
- acoustic
- face
- acousto
- degrees
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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
- G02F1/01—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 intensity, phase, polarisation or colour
- G02F1/11—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 intensity, phase, polarisation or colour based on acousto-optical elements, e.g. using variable diffraction by sound or like mechanical waves
Abstract
ABSTRACT:
An acousto-optic modulator for generating a modulated diffracted beam 14 from a laser beam 10 by refractive Bragg dif-fraction from a longitudinal compressional acoustic wave directed into a germanium block 21 by a transducer 2. By tilting the end face 26, 30, so that the angle of incidence is 44 degrees, all the acoustic wave energy is reflected as a shear wave S, at 27 degrees and then dissipated in layers 24 of indium or lead on the upper and lower surfaces 19, 22, of the block. The end face 26 is also disposed obliquely in plan angle to further reduce retroreflection.
An acousto-optic modulator for generating a modulated diffracted beam 14 from a laser beam 10 by refractive Bragg dif-fraction from a longitudinal compressional acoustic wave directed into a germanium block 21 by a transducer 2. By tilting the end face 26, 30, so that the angle of incidence is 44 degrees, all the acoustic wave energy is reflected as a shear wave S, at 27 degrees and then dissipated in layers 24 of indium or lead on the upper and lower surfaces 19, 22, of the block. The end face 26 is also disposed obliquely in plan angle to further reduce retroreflection.
Description
The invention relates to an acousto-optic modulator for modu-lating a beam of optical radiation by interaction with acoustic waves in an acoustic medium in accordance with the Bragg relation-ship, said modulator comprising a block of material transparent to the optical radia-tion to be modulated and having respective oppo-site side faces of optical quality to provide input and output sur-faces for a beam of said optical radiation, an end -Face provided with electroacoustic transducer means for directing a beam of acoustic waves into said block to set up an interaction region for said beam of optical radiation between said input and output sur-faces~
The principle of operation of such a modulator, as well as embodiments according to the invention will be described with re-Ference to the figures of the accompanying drawing, in which Figure 1 is a diagram illustrating the principle of operation of said modulator, Figure 2 diagrammatically illustrates an acousto-optic laser modulator arrangement in accordance with the invention, Figure 3 is a diagram illustrating acoustic wave paths at a boundary;
Figure 4 is a diagrammatic longitudinal sectional detail illustrating acoustic wave paths in a simple embodiment of the invention;
Figure 5 is an isometric perspective view of the modulator block shown in Figure 2, and Figure 6 is a side view o^F the modulator block of Figure 3.
The operation of a modulator of the kind specified is dis-cussed, for example, by E. I. Gordon in Proc. IEEE Vol. 54, October 1966, pages 1391-1401. Fiyure 1 of the accompanying drawings is a diagram illustrating the principle of operation of such a modulator. A planar electroacoustic transducer 2, in the form of a piezoelectric wafer 3, formed for example from a mono-crystal of lithium niobate, with upper and lower metallised elec-trodes 4 and 5, is mounted on one end face 6 of a block 1 of optically transparent material formed for example from a mono-crystal of germanium. The transducer 2 is energ;sed at a suit-3L~ 3~.2~
The principle of operation of such a modulator, as well as embodiments according to the invention will be described with re-Ference to the figures of the accompanying drawing, in which Figure 1 is a diagram illustrating the principle of operation of said modulator, Figure 2 diagrammatically illustrates an acousto-optic laser modulator arrangement in accordance with the invention, Figure 3 is a diagram illustrating acoustic wave paths at a boundary;
Figure 4 is a diagrammatic longitudinal sectional detail illustrating acoustic wave paths in a simple embodiment of the invention;
Figure 5 is an isometric perspective view of the modulator block shown in Figure 2, and Figure 6 is a side view o^F the modulator block of Figure 3.
The operation of a modulator of the kind specified is dis-cussed, for example, by E. I. Gordon in Proc. IEEE Vol. 54, October 1966, pages 1391-1401. Fiyure 1 of the accompanying drawings is a diagram illustrating the principle of operation of such a modulator. A planar electroacoustic transducer 2, in the form of a piezoelectric wafer 3, formed for example from a mono-crystal of lithium niobate, with upper and lower metallised elec-trodes 4 and 5, is mounted on one end face 6 of a block 1 of optically transparent material formed for example from a mono-crystal of germanium. The transducer 2 is energ;sed at a suit-3L~ 3~.2~
2 PHB33190 able high frequency, for example several MHz, causing a corres-ponding regular succession of parallel acoustic wavefronts, indi-cated by parallel lines 7, to propagate in the block as, for example, a longitudinal wave disturbance with the velocity ~JrL
of a longitudinal acoustic wave in the direction indicated by the arrows 8. The associated local stress variations in the medium of the block will result in corresponding local variations in refractive index thus forming a corresponding diffraction structure which will propagate along the acoustic wave propagation path 9 in the direction 8.
A beam 10 of optical radiation to be modulated, in the pres-ent case coherent radiation generated by a laser (not shown), is directed via a lens 11 and an optical side face 12 of the block 1, across the path of the propagating acoustic wave 7 in an inter-action region 13 at the Bragg angle ~B with respect to the propa-gating wave structure 7, causing a diffracted beam 1~ to be gen-erated which is inçlined at twice the Bragg angle ~B to the direction of the input beam 10 in the interaction region 13. The amplitude of the diffracted beam l4 will depend on the amplitude of the acoustic wave 7, and therefore is used to form the modu~
lated beam after passing out of the block 1 via the opposite optical side face 15. It should be noted herein that such a modu-lator can function equally well when non-coherent optical radiation is employed provided that the Bragg diffraction conditions are satisfied.
A difficulty with this form of modulator is that when the acoustic wave 7 reaches the far end face 16 of the block it will tend to be reFlected, and some of the acoustic energy may then follow a retroreflective path back towards the transducer 2, as indicated by the arrows 17. As this reflected wave passes in the reverse direction through the ;nteraction region 13 crossed by the beam of optical radiation 10, it may generate a weak diffracted beam but the direction of motion of the corresponding acoustic diffraction structure will be reversed relative to the optical beam and the original Bragg angle relationship will not be pro--
of a longitudinal acoustic wave in the direction indicated by the arrows 8. The associated local stress variations in the medium of the block will result in corresponding local variations in refractive index thus forming a corresponding diffraction structure which will propagate along the acoustic wave propagation path 9 in the direction 8.
A beam 10 of optical radiation to be modulated, in the pres-ent case coherent radiation generated by a laser (not shown), is directed via a lens 11 and an optical side face 12 of the block 1, across the path of the propagating acoustic wave 7 in an inter-action region 13 at the Bragg angle ~B with respect to the propa-gating wave structure 7, causing a diffracted beam 1~ to be gen-erated which is inçlined at twice the Bragg angle ~B to the direction of the input beam 10 in the interaction region 13. The amplitude of the diffracted beam l4 will depend on the amplitude of the acoustic wave 7, and therefore is used to form the modu~
lated beam after passing out of the block 1 via the opposite optical side face 15. It should be noted herein that such a modu-lator can function equally well when non-coherent optical radiation is employed provided that the Bragg diffraction conditions are satisfied.
A difficulty with this form of modulator is that when the acoustic wave 7 reaches the far end face 16 of the block it will tend to be reFlected, and some of the acoustic energy may then follow a retroreflective path back towards the transducer 2, as indicated by the arrows 17. As this reflected wave passes in the reverse direction through the ;nteraction region 13 crossed by the beam of optical radiation 10, it may generate a weak diffracted beam but the direction of motion of the corresponding acoustic diffraction structure will be reversed relative to the optical beam and the original Bragg angle relationship will not be pro--
3 PHB33190 perly met. ~lowever, the reflected wave will continue to propagate until it reaches the transducer face 6 where some o-F the acoustic energy will be reflected as indicated by the arrows 18 so as to travel back in the initial propagation direction for which the Bragg relationship will be correct, and as it passes again through the interaction region 13, a corresponding delayed modulation sig-nal will be imposed on the modulated beam 14, whose amplitude will depend on the amplitude of the reflected acoustic wave. The pres-ence of this delayed signal whose delay will be that of the round trip of the acoustic wave via the various points of reflection, is undesirable and will adversely affect the performance of the modu-lator especially for data transmission and ranging.
In the paper referred to above, a modulator is illustrated in which the transverse far end wall of the block has a layer of acoustic absorber to reduce reflection, and this is also indicated in Figure 1 by the reference 19. Examples of a suitable acoustic absorbing material in the case of a germanium block, are indium and lead although neither have the same acoustic impedance as germanium and the resulting impedance mismatch will generate a significant reflected signal which will be greater in the case of indium.
In order to reduce the direct mirror reflection from the far end face it has been proposed to incline the end face with respect to the acoustic wavefront so that the acoustic wave is reflected towards a non-optical side face of the block to which an acoustic absorbing layer, e.g. indium, has also been applied. In designing this wedge form of termination it was usual to avoid an inclina-tion or wedge angle of 45 degrees for which it was thought that the reflected incident acoustic wave would be directed perpendicularly at the side face thus providing an ideal retroreflective condition for generating an undesired return reflection. In practice, there-fore, a wedge angle of about 30 degrees was employed so that acoustic energy which was not absorbed by the absorption layer on the inclined face, would undergo multiple absorptive reflections at the side faces of the block and thus be dissipated.
~Jhile some improvement has been achieved by this arrangement 3~
In the paper referred to above, a modulator is illustrated in which the transverse far end wall of the block has a layer of acoustic absorber to reduce reflection, and this is also indicated in Figure 1 by the reference 19. Examples of a suitable acoustic absorbing material in the case of a germanium block, are indium and lead although neither have the same acoustic impedance as germanium and the resulting impedance mismatch will generate a significant reflected signal which will be greater in the case of indium.
In order to reduce the direct mirror reflection from the far end face it has been proposed to incline the end face with respect to the acoustic wavefront so that the acoustic wave is reflected towards a non-optical side face of the block to which an acoustic absorbing layer, e.g. indium, has also been applied. In designing this wedge form of termination it was usual to avoid an inclina-tion or wedge angle of 45 degrees for which it was thought that the reflected incident acoustic wave would be directed perpendicularly at the side face thus providing an ideal retroreflective condition for generating an undesired return reflection. In practice, there-fore, a wedge angle of about 30 degrees was employed so that acoustic energy which was not absorbed by the absorption layer on the inclined face, would undergo multiple absorptive reflections at the side faces of the block and thus be dissipated.
~Jhile some improvement has been achieved by this arrangement 3~
4 P~IB33190 it has been found that the residual unwanted delayed modulationsignal cannot be reduced to the extent required For some applica-tions.
It is an object of the invention to provide an improved acousto-optic modulator in which return acoustic echos and re-sultant unwanted delay modulation signals can be reduced to very low amplitudes relative to the primary modulation signal.
According to the invention there is provided an acousto-optic modulator of the kind specified characterised in that the other end face of the block is free so as to form an optimally reflecting surface for incident acoustic waves, and is inclined to the initially propagating acoustic beam incident thereon directly From the transducer, at an angle such that substantially all the acoustic energy in the incident propagation mode is con-verted into reflected acoustic beam energy in a different propag-ation mode and is directed towards at-least one side face of the block in a manner which is substantially not retroreflective with respect to the initially propagating acoustic beam incident on the inclined end face of the block.
In the course of realising the invention it was identified that the problem of unwanted reflected acoustical signal energy is caused in part by the presence of scatter centres in the acoustic absorbing layer, e.g. oF indium, applied to the inclined end plane, which cause a direct reflection of acoustic energy to occur back towards the interaction region and the transducer, and in further part because when an acoustic wave having a given mode of propa-gation in a solid body, for example a longitudinal wave, is reflected at an inclined boundary surface, some acoustic energy is in general transferred to another mode, e.g. to form a shear wave. Because the different modes propagate with correspondingly different velocities, the angles of reflection of the two waves will differ thus increasing the likelihood that a significant amount of acoustic energy will be reflected retroactively back towards the transducer and the interaction region instead of being 3~ dissipated by multiple reflection at the si~e -Faces of the block.
3~
For example, in the case of a 30 degree wedge angle, although the longitudinal wave may be reflected so as to enable scattering to take place, the shear wave component will be reflected at an angle of about 30 degrees and will be directed more or less perpendic-ularly towards the side face of the block thus following an idealretroreflective path.
The invention is based on the realisation that by a suitable inclination of the far end face of the block it is possible to cause substantially the whole of the incident acoustic energy in a wave of one propagation mode, e.g. a longitudinal wave, to be con-verted into a wave of a different propagation mode, e.g. a shear wave, and furthermore that by removing the acoustic absorbing material and hence the associated scatter centres from the inclined end surface, a further significant reduction in the return acoustic signal energy can be effected. In fact, in the case of a longi-tudinal acoustic wave in a block of germanium it has been found that a wedge angle of about 45 degrees gives the smallest return wave, a surprising result since this angle could be expested to provide an ideal retroreflective path condition for such a wave.
In one form of acousto-optic modulator in accordance with the invention in which the block is formed from a crystal of germanium the acoustic beam is launched by the transducer means in the long-itudinal compression mode along the ~lO0] crystal direction and the angle of inclination of the inclined end face to the propa-gation direction of the incident acoustic wave lies in the range 38 degrees to 50 degrees, and is preferably about ~4 degrees.
In a further form of acousto-optic modulator in accordance with the invention in which the block is formed from a crystal of germanium, the acoustic beam is launched by the transducer means in the longitudinal compression mode along the [lll] crystal direction, the lncident coherent optical radiation to be modulated is polarised so that the electric vector lies in the plane con-taining the acoustic and optical beams, and the angle of inclin-ation of the inclined end face to the propagation direction of the incident acoustic wave lies in the range 38 degreès to 50 degrees1 and is preferably about 44 degrees.
In accordance with a feature of the invention, the edges re-spec-tively formed by the intersections of the inclined end face with the corresponding non-optical side faces of the block which are preferably loaded with an acoustic absorbing layer, can be inclined to the wavefront of the initially propagating acoustic wave beam, and this inclination preferably lies in the range 25 degrees to 35 degrees. The acoustic absorbing layer on the side faces of the block can comprise a layer of indium or a layer oF
lead.
An acousto-optic modulator manufactured in accordance with the invention can be employed in an optical ranging system for surveying or for radar, or as a modulator For optical communi-cations.
Referring to Figure 2 which illustrates an acousto-optic laser modulator arrangement in accordance with the invention, elements corresponding to those described with reference to Figure 1 are given the same reference numerals. A C02 laser 20 provides a beam 10 of coherent optical radiation having a wave-length ~ = 10.6 ~m, and a diameter of about 2mm. A germanium lens 11 is used to focus the beam so that in the interaction region 13, the beam has a waist with a minimum diameter of about 200 ~m in order to provide the modulator with a short rise time.
Because the optical beam is focussed in the present example, the divergence of the optical beam is preferably matched by a corres-ponding divergence of the acoustic beam in order to provide an optimally high modulation efficiency. If it is not important to provide a short rise time, the optical radiation need not take the form of a focussed beam but can, for example, comprise a normally collimated laser beam.
The modulator block 21 is formed from a monocrystal of ger-manium and in one example was of width 20mm, thickness 5mm and overall length about 22mm. The -transducer 2 comprised a wafer 3, 35 degree Y-cut from a monocrystal of lithium niobate and operating in the fundamental thickness mode, which is pressure bonded to the 3L~ 3~ ~
end face 6 of the block 21. One of the electrodes, namely 5, comprises a conductive film made up of layers of chrornium~ gold and indium applied prior to pressure bonding. The other electrode 4, whose dimensions determine the active region of the transducer 2 and hence the initial cross section of the acoustic beam 7, is applied after lapping the bonded wafer 3 to the correct thickness for resonance at the required acoustic frequency. In the present example the transverse dimensions of the waFer 3 were 12mm in the plane of Figure 2 and 3mm in the direction perpendicular thereto, the corresponding dimensions of the electrode 4 were 6mm and 0.3mm respectively.
The orientation of the block 21 relative to the germanium crystal axes will depend on the application of the modulator as follows. If the highest modulation efficiency is required and the use of plane polarised light is permissible, the block 21 is cut so that the acoustic wave propagation path direction 9 lies along the [111] crystal axis and the incident light must be polarised with the plane of the electric vector parallel to the acoustic wave propagation direction 9. If this use of plane polarised light is not acceptable, the block 21 is cut so that the acoustic wave pro-pagation direction 9 lies along the ~100] germanium crystal axis.
In this case the polarisation plane direction is not critical and the device can operate with circularly polarised light~ however the modulation sensitivity for two directions at right angles will, in general, be different and in the latter case the output will tend to become elliptically polarised.
In the case of the present modulator, the Bragg angle OB is given by:-o = sin ~l ( ~ ) where ~ is the optical wavelength in the acoustic medium and JA~ isthe acoustic wavelength in the medium. Thus in the case of german-ium, for which the re~ractive index n = 4, the light from the C02 laser 20, whose free space wavelength Ao = 10.6 ~m, will have a wavelength ~ in the medium of 2.65 ~m. The acoustic wavelength ; ~ , will depend of course on the frequency and on the acou~tic velocity which latter will depend on directlon. Thu~, for example, an acoustic wave having a frequency of 60MHz directed along the [100]
axi~ for which the velocity of a longitudinal ~ave VL Y 4.72 x 103m/sec, will have a wavelength A ~ 78.7ym glvlng a value for the Bragg angle ~B ~ 0.96 degree. In a ~econd example, an acoustic wave having a Erequency of 100 MHz directed along the ~111] direction for which VL ~ 5.5 x 103m/~ec, will have ~ ~ 55~m giving a value for the Bragg angle of ~ 3 1.38 degree~.
In order to reduce optical reflectlon fro~ the optical faces 12 and 15 of the block 21, the faces are each provided with an anti-reflection layer. In the pre~ant example both faces, although parallel to one another, are inclined by 2 degrees from the acoustic wave propagation direction 9 which i5 perpendlcular to the end face 6. Thi~ arrangement wa~ employed in order to ~ake the ~odulator block 21 readily interchangeable in a ~oun~ with other dulator~ for other frequencies or orientation~. In general, however, it ~ pr~ferable for the avoidance of reflections, ~hat the faces 12 and 15 should not be parallel to one another. Because of the smallne~ of the inclination angles and of other ray angle~, and for the sake of clarlty of illustration, the~e angles are depicted ln Figure 2 with their magnitudes enlarged, e~pecially within ~he block 21. Figure 2 i~ intended to repre~ent the case for which the Bragg angle 19 0.96 degree3.
The ~Ddulated diffracted output beam 14, after refraction at the exit face 15 of ~he block, i8 directed along the modulator output axi~ and i8 collimated by a second germanium lens ?3. An apertured diaphragm 25 is used to remove the undiffracted co~ponent of the emergent beam.
In order to reduce as far as pos~ible any acoustic energy uhich can be re~lected back along the acoustic propagation path 9, the far end face 26 of the block i~, in accordance with the l~vention, inclined to the initial acou~tic beam of wavefront~ 7 launched by the transducer 2 and propagating along the a~i~ 9 in ~ 3 ehe directlon 8, at an angle such that substantlally all the acoustlc energy in the incident propagation mode, in the pre~ent example a longl~udinal compression wave, ls converted on reflection at the face 26 which ls free of any surface loading, into reflected a~oust$c beam energy in a dlfferent propagation mode, tn the present example a shear wave, and i3 directed towards the side faces of the block 21 in a manner which ls substantially not retroreflective with respect to the initially propag~tlng acoustic beam incident on the incllned end face 26 of the block 21.
In order to e~plain the invention reference i~ msde to the ray dlagram shown in Figure 3. A longltudinal compression acoustlc wave of a~plltude L is direceed in a ~olid acou3tic ~edlum 31 at 8 free boundary surface 30 at an angle of incident PL. A
corresponding reflected longitudinal wave component Ll ~ould be reflected at an angle of reflection of ehe same magnitude 0L-Because the m~dium 31 is a ri8id m~dium and the incident wave is inclined to the boundary surface, a shear wave component Sl ~ill also be formed and will be reflected at an anBle of reflection 4S A germanium crystal is an anisotropic acoustic mediu~, however, for ea e of calculation an equivalent lsotroplc medium is as~um~d ~here the average value~ of the longitudinal and ~hear ~ave velocities are taken as ~rL ' 5.56km/sec and ~S 5 3.55km/sec, respectively. Thus by the u~ual considerations of reflectlon, the reflection angles are related by the following:
sin 0L _ ~in ~5 (1) It can further be shown that for an acoustic wave of amplltude L lncident at a solid/aiL interface whereat stresses perpendicular to the surface mus~ be zero and the coresponding displace~nt can assu~e any value, the amplitude of th~ reflected longieudinal and ~hear waves Ll and Sl are given by:
2(L-Ll)sin ~s.cos ~L ~ Sl.co~ 2~s ~ (2) and (L~Ll)9in 0L-C8 20S - Sl.sin 0S.sin 20s ~ 0~ (3) Equations (2) and (3) can be solved for the relatlve .3f~
smplitudes Ll/L and Sl/L to yield L~ A ¦
where:
s A ~ tan ~L
2 ~ln2 0S tan 20S
and Sl _ 2 co~ 0L- sin 0$ ~ Ll ¦ (5) L cos 20S I L
It will be apparent from equation (4) that the amplitude of the reflected longitudinal wave Ll will become zero when A ~ 1 and hence tan 0L ~ 2 ~in2 0S.tan ~0S~ (6) Using the relation3hlp (1) between 0L and 0S and the values given above for ~rL and ~rs~ it can be seen that ¦L1/L¦
wlll become zero when 0L ~ 46 degrees. Thu3 for ~hi~ angle of lncidence there will be a subs~antially complete conver~ion of the incident longitudinal wave into a shear wave Sl reflected at an angle ~8 ~ 27 degree~.
Figure 4 ls a detail illu~trating a simple embodi~ent of the invention which corresponds to the arrnngement so far de~cribed with reference to Flgure 7 except that the far end face 30 of the germanium block 31 is square-cut with a wedge angle of 45 degrees.
Figure 4 i~ a longltudlnal sectional view of the far end of the block 31 and illustrate~ the path taken on reflection by a longitudinal acouselc wave L propagating slong the axls 9 and incident on the free boundary face 30 lnclined at 45 degrees, which is approximately the angle as di~cu~sed above for which ~he amplitude of the reflected longitudinal wave component Ll repres nted by a dashed line in Figure 4, become~ zero and therefore unable to give rise to a retroreflective echo by reflection at nor~al incldence with the upper ~ide face 19 of the block. Thus the acou3tlc energy i8 all reflected as the shear wave Sl at an angle of reflection of 27 degree3. ThiR wave will be reflected at the upper face 19 to for~, in genersl, both ~hear ~ave "
., ~ . . .
:
" '' ~"
.
f*'~
11 P~IB33190 and longitudlnal wave components S2, L2, whlch are directed into the body of the block 31 for further reElection~ from the upper and lower faces 19 and 22. Since the~e face~ are preferably loaded wlth an acoustic absorbing layer 24 of indium or lead, acou~tic energy will be dis~ip2ted a~ each reflectlon.
Returning to the embodiment illu~trated in Figure 2, the chance~ of acou~tic energy being returned retroactively are reduced still further by cutting the inclined end face 26 for the block 21 obliquely ~o that the inter~ectlon~ of the face 26 with the corresponding upper and lower, i.e. non-optical, ~de faces 19, 22, of the block are incllned to the wavefront~ 7 of the acoustlc wave dlrected along the axi~ 9. The plan angle between the inter~ection line and the wavefront i~ preferably 30 degrees but can lie in the range ~5 degrees to 35 degree~. It ~hould be understood that in lS the case of tha obliquely inclined end face 26, the critical angle of incidence for which the refleeted longitudinal wave amplitude becomes zero will be that measured in an oblique plane containing ~he incident axis 9 and the perpendicular from ~he face 26 at the point of incidence, and will therefore not corre~pond to the complement of the wedge angle ~easured at the optical side face 12 or 15 of the block 21.
Figure 5 1llu~trates the form of the block 21 in isometric perspective and Figure 6 i8 a side view of the block 21 ln the direction of the optical side face 12. It will be understood that the inclin2d end face 26 may equally well be cut obliquely ln the other direction and can 810pe the other way while being equally effective in reducing the reflective return of acou~tic ~Lgnal energy.
In a compari~on of the performance of the prior modulator employing an indium loaded incllned end face at a wedge angle of 30 degrees w~th that of a dulator in accordance with the invention, the Eormer provided an attenuation of about -55 dB for ~he unwaneed delayed modulatlon ~lgnal, whlle a ~dulator as de~crlbed with reference to Figures 2, 5 and 6 provided an attenuation of at lea~t -75dB. Even in a case ln which no acoustic absorbing layer 24 wa~
applied to the block, an attenustlon of -62dB was ~easured.
It is an object of the invention to provide an improved acousto-optic modulator in which return acoustic echos and re-sultant unwanted delay modulation signals can be reduced to very low amplitudes relative to the primary modulation signal.
According to the invention there is provided an acousto-optic modulator of the kind specified characterised in that the other end face of the block is free so as to form an optimally reflecting surface for incident acoustic waves, and is inclined to the initially propagating acoustic beam incident thereon directly From the transducer, at an angle such that substantially all the acoustic energy in the incident propagation mode is con-verted into reflected acoustic beam energy in a different propag-ation mode and is directed towards at-least one side face of the block in a manner which is substantially not retroreflective with respect to the initially propagating acoustic beam incident on the inclined end face of the block.
In the course of realising the invention it was identified that the problem of unwanted reflected acoustical signal energy is caused in part by the presence of scatter centres in the acoustic absorbing layer, e.g. oF indium, applied to the inclined end plane, which cause a direct reflection of acoustic energy to occur back towards the interaction region and the transducer, and in further part because when an acoustic wave having a given mode of propa-gation in a solid body, for example a longitudinal wave, is reflected at an inclined boundary surface, some acoustic energy is in general transferred to another mode, e.g. to form a shear wave. Because the different modes propagate with correspondingly different velocities, the angles of reflection of the two waves will differ thus increasing the likelihood that a significant amount of acoustic energy will be reflected retroactively back towards the transducer and the interaction region instead of being 3~ dissipated by multiple reflection at the si~e -Faces of the block.
3~
For example, in the case of a 30 degree wedge angle, although the longitudinal wave may be reflected so as to enable scattering to take place, the shear wave component will be reflected at an angle of about 30 degrees and will be directed more or less perpendic-ularly towards the side face of the block thus following an idealretroreflective path.
The invention is based on the realisation that by a suitable inclination of the far end face of the block it is possible to cause substantially the whole of the incident acoustic energy in a wave of one propagation mode, e.g. a longitudinal wave, to be con-verted into a wave of a different propagation mode, e.g. a shear wave, and furthermore that by removing the acoustic absorbing material and hence the associated scatter centres from the inclined end surface, a further significant reduction in the return acoustic signal energy can be effected. In fact, in the case of a longi-tudinal acoustic wave in a block of germanium it has been found that a wedge angle of about 45 degrees gives the smallest return wave, a surprising result since this angle could be expested to provide an ideal retroreflective path condition for such a wave.
In one form of acousto-optic modulator in accordance with the invention in which the block is formed from a crystal of germanium the acoustic beam is launched by the transducer means in the long-itudinal compression mode along the ~lO0] crystal direction and the angle of inclination of the inclined end face to the propa-gation direction of the incident acoustic wave lies in the range 38 degrees to 50 degrees, and is preferably about ~4 degrees.
In a further form of acousto-optic modulator in accordance with the invention in which the block is formed from a crystal of germanium, the acoustic beam is launched by the transducer means in the longitudinal compression mode along the [lll] crystal direction, the lncident coherent optical radiation to be modulated is polarised so that the electric vector lies in the plane con-taining the acoustic and optical beams, and the angle of inclin-ation of the inclined end face to the propagation direction of the incident acoustic wave lies in the range 38 degreès to 50 degrees1 and is preferably about 44 degrees.
In accordance with a feature of the invention, the edges re-spec-tively formed by the intersections of the inclined end face with the corresponding non-optical side faces of the block which are preferably loaded with an acoustic absorbing layer, can be inclined to the wavefront of the initially propagating acoustic wave beam, and this inclination preferably lies in the range 25 degrees to 35 degrees. The acoustic absorbing layer on the side faces of the block can comprise a layer of indium or a layer oF
lead.
An acousto-optic modulator manufactured in accordance with the invention can be employed in an optical ranging system for surveying or for radar, or as a modulator For optical communi-cations.
Referring to Figure 2 which illustrates an acousto-optic laser modulator arrangement in accordance with the invention, elements corresponding to those described with reference to Figure 1 are given the same reference numerals. A C02 laser 20 provides a beam 10 of coherent optical radiation having a wave-length ~ = 10.6 ~m, and a diameter of about 2mm. A germanium lens 11 is used to focus the beam so that in the interaction region 13, the beam has a waist with a minimum diameter of about 200 ~m in order to provide the modulator with a short rise time.
Because the optical beam is focussed in the present example, the divergence of the optical beam is preferably matched by a corres-ponding divergence of the acoustic beam in order to provide an optimally high modulation efficiency. If it is not important to provide a short rise time, the optical radiation need not take the form of a focussed beam but can, for example, comprise a normally collimated laser beam.
The modulator block 21 is formed from a monocrystal of ger-manium and in one example was of width 20mm, thickness 5mm and overall length about 22mm. The -transducer 2 comprised a wafer 3, 35 degree Y-cut from a monocrystal of lithium niobate and operating in the fundamental thickness mode, which is pressure bonded to the 3L~ 3~ ~
end face 6 of the block 21. One of the electrodes, namely 5, comprises a conductive film made up of layers of chrornium~ gold and indium applied prior to pressure bonding. The other electrode 4, whose dimensions determine the active region of the transducer 2 and hence the initial cross section of the acoustic beam 7, is applied after lapping the bonded wafer 3 to the correct thickness for resonance at the required acoustic frequency. In the present example the transverse dimensions of the waFer 3 were 12mm in the plane of Figure 2 and 3mm in the direction perpendicular thereto, the corresponding dimensions of the electrode 4 were 6mm and 0.3mm respectively.
The orientation of the block 21 relative to the germanium crystal axes will depend on the application of the modulator as follows. If the highest modulation efficiency is required and the use of plane polarised light is permissible, the block 21 is cut so that the acoustic wave propagation path direction 9 lies along the [111] crystal axis and the incident light must be polarised with the plane of the electric vector parallel to the acoustic wave propagation direction 9. If this use of plane polarised light is not acceptable, the block 21 is cut so that the acoustic wave pro-pagation direction 9 lies along the ~100] germanium crystal axis.
In this case the polarisation plane direction is not critical and the device can operate with circularly polarised light~ however the modulation sensitivity for two directions at right angles will, in general, be different and in the latter case the output will tend to become elliptically polarised.
In the case of the present modulator, the Bragg angle OB is given by:-o = sin ~l ( ~ ) where ~ is the optical wavelength in the acoustic medium and JA~ isthe acoustic wavelength in the medium. Thus in the case of german-ium, for which the re~ractive index n = 4, the light from the C02 laser 20, whose free space wavelength Ao = 10.6 ~m, will have a wavelength ~ in the medium of 2.65 ~m. The acoustic wavelength ; ~ , will depend of course on the frequency and on the acou~tic velocity which latter will depend on directlon. Thu~, for example, an acoustic wave having a frequency of 60MHz directed along the [100]
axi~ for which the velocity of a longitudinal ~ave VL Y 4.72 x 103m/sec, will have a wavelength A ~ 78.7ym glvlng a value for the Bragg angle ~B ~ 0.96 degree. In a ~econd example, an acoustic wave having a Erequency of 100 MHz directed along the ~111] direction for which VL ~ 5.5 x 103m/~ec, will have ~ ~ 55~m giving a value for the Bragg angle of ~ 3 1.38 degree~.
In order to reduce optical reflectlon fro~ the optical faces 12 and 15 of the block 21, the faces are each provided with an anti-reflection layer. In the pre~ant example both faces, although parallel to one another, are inclined by 2 degrees from the acoustic wave propagation direction 9 which i5 perpendlcular to the end face 6. Thi~ arrangement wa~ employed in order to ~ake the ~odulator block 21 readily interchangeable in a ~oun~ with other dulator~ for other frequencies or orientation~. In general, however, it ~ pr~ferable for the avoidance of reflections, ~hat the faces 12 and 15 should not be parallel to one another. Because of the smallne~ of the inclination angles and of other ray angle~, and for the sake of clarlty of illustration, the~e angles are depicted ln Figure 2 with their magnitudes enlarged, e~pecially within ~he block 21. Figure 2 i~ intended to repre~ent the case for which the Bragg angle 19 0.96 degree3.
The ~Ddulated diffracted output beam 14, after refraction at the exit face 15 of ~he block, i8 directed along the modulator output axi~ and i8 collimated by a second germanium lens ?3. An apertured diaphragm 25 is used to remove the undiffracted co~ponent of the emergent beam.
In order to reduce as far as pos~ible any acoustic energy uhich can be re~lected back along the acoustic propagation path 9, the far end face 26 of the block i~, in accordance with the l~vention, inclined to the initial acou~tic beam of wavefront~ 7 launched by the transducer 2 and propagating along the a~i~ 9 in ~ 3 ehe directlon 8, at an angle such that substantlally all the acoustlc energy in the incident propagation mode, in the pre~ent example a longl~udinal compression wave, ls converted on reflection at the face 26 which ls free of any surface loading, into reflected a~oust$c beam energy in a dlfferent propagation mode, tn the present example a shear wave, and i3 directed towards the side faces of the block 21 in a manner which ls substantially not retroreflective with respect to the initially propag~tlng acoustic beam incident on the incllned end face 26 of the block 21.
In order to e~plain the invention reference i~ msde to the ray dlagram shown in Figure 3. A longltudinal compression acoustlc wave of a~plltude L is direceed in a ~olid acou3tic ~edlum 31 at 8 free boundary surface 30 at an angle of incident PL. A
corresponding reflected longitudinal wave component Ll ~ould be reflected at an angle of reflection of ehe same magnitude 0L-Because the m~dium 31 is a ri8id m~dium and the incident wave is inclined to the boundary surface, a shear wave component Sl ~ill also be formed and will be reflected at an anBle of reflection 4S A germanium crystal is an anisotropic acoustic mediu~, however, for ea e of calculation an equivalent lsotroplc medium is as~um~d ~here the average value~ of the longitudinal and ~hear ~ave velocities are taken as ~rL ' 5.56km/sec and ~S 5 3.55km/sec, respectively. Thus by the u~ual considerations of reflectlon, the reflection angles are related by the following:
sin 0L _ ~in ~5 (1) It can further be shown that for an acoustic wave of amplltude L lncident at a solid/aiL interface whereat stresses perpendicular to the surface mus~ be zero and the coresponding displace~nt can assu~e any value, the amplitude of th~ reflected longieudinal and ~hear waves Ll and Sl are given by:
2(L-Ll)sin ~s.cos ~L ~ Sl.co~ 2~s ~ (2) and (L~Ll)9in 0L-C8 20S - Sl.sin 0S.sin 20s ~ 0~ (3) Equations (2) and (3) can be solved for the relatlve .3f~
smplitudes Ll/L and Sl/L to yield L~ A ¦
where:
s A ~ tan ~L
2 ~ln2 0S tan 20S
and Sl _ 2 co~ 0L- sin 0$ ~ Ll ¦ (5) L cos 20S I L
It will be apparent from equation (4) that the amplitude of the reflected longitudinal wave Ll will become zero when A ~ 1 and hence tan 0L ~ 2 ~in2 0S.tan ~0S~ (6) Using the relation3hlp (1) between 0L and 0S and the values given above for ~rL and ~rs~ it can be seen that ¦L1/L¦
wlll become zero when 0L ~ 46 degrees. Thu3 for ~hi~ angle of lncidence there will be a subs~antially complete conver~ion of the incident longitudinal wave into a shear wave Sl reflected at an angle ~8 ~ 27 degree~.
Figure 4 ls a detail illu~trating a simple embodi~ent of the invention which corresponds to the arrnngement so far de~cribed with reference to Flgure 7 except that the far end face 30 of the germanium block 31 is square-cut with a wedge angle of 45 degrees.
Figure 4 i~ a longltudlnal sectional view of the far end of the block 31 and illustrate~ the path taken on reflection by a longitudinal acouselc wave L propagating slong the axls 9 and incident on the free boundary face 30 lnclined at 45 degrees, which is approximately the angle as di~cu~sed above for which ~he amplitude of the reflected longitudinal wave component Ll repres nted by a dashed line in Figure 4, become~ zero and therefore unable to give rise to a retroreflective echo by reflection at nor~al incldence with the upper ~ide face 19 of the block. Thus the acou3tlc energy i8 all reflected as the shear wave Sl at an angle of reflection of 27 degree3. ThiR wave will be reflected at the upper face 19 to for~, in genersl, both ~hear ~ave "
., ~ . . .
:
" '' ~"
.
f*'~
11 P~IB33190 and longitudlnal wave components S2, L2, whlch are directed into the body of the block 31 for further reElection~ from the upper and lower faces 19 and 22. Since the~e face~ are preferably loaded wlth an acoustic absorbing layer 24 of indium or lead, acou~tic energy will be dis~ip2ted a~ each reflectlon.
Returning to the embodiment illu~trated in Figure 2, the chance~ of acou~tic energy being returned retroactively are reduced still further by cutting the inclined end face 26 for the block 21 obliquely ~o that the inter~ectlon~ of the face 26 with the corresponding upper and lower, i.e. non-optical, ~de faces 19, 22, of the block are incllned to the wavefront~ 7 of the acoustlc wave dlrected along the axi~ 9. The plan angle between the inter~ection line and the wavefront i~ preferably 30 degrees but can lie in the range ~5 degrees to 35 degree~. It ~hould be understood that in lS the case of tha obliquely inclined end face 26, the critical angle of incidence for which the refleeted longitudinal wave amplitude becomes zero will be that measured in an oblique plane containing ~he incident axis 9 and the perpendicular from ~he face 26 at the point of incidence, and will therefore not corre~pond to the complement of the wedge angle ~easured at the optical side face 12 or 15 of the block 21.
Figure 5 1llu~trates the form of the block 21 in isometric perspective and Figure 6 i8 a side view of the block 21 ln the direction of the optical side face 12. It will be understood that the inclin2d end face 26 may equally well be cut obliquely ln the other direction and can 810pe the other way while being equally effective in reducing the reflective return of acou~tic ~Lgnal energy.
In a compari~on of the performance of the prior modulator employing an indium loaded incllned end face at a wedge angle of 30 degrees w~th that of a dulator in accordance with the invention, the Eormer provided an attenuation of about -55 dB for ~he unwaneed delayed modulatlon ~lgnal, whlle a ~dulator as de~crlbed with reference to Figures 2, 5 and 6 provided an attenuation of at lea~t -75dB. Even in a case ln which no acoustic absorbing layer 24 wa~
applied to the block, an attenustlon of -62dB was ~easured.
Claims (10)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An acousto-optic modulator for modulating a beam of optical radiation by interaction with acoustic waves in an optical medium in accordance with the Bragg relationship, said modulator comprising a block of material transparent to the optical radiation to be modu-lated and having respective opposite side faces of optical quality to provide input and output surfaces for a beam of said optical radi-ation, an end face provided with electroacoustic transducer means for directing a beam of acoustic waves along a propagation axis in said block to set up an interaction region for said beam of optical radi-ation between said input and output surfaces, characterised in that the other end face of the block is free so as to form an optimally reflecting surface for incident acoustic waves and is inclined to the initially propagating acoustic beam incident thereon directly from the transducer, at an angle such that substantially all the acoustic energy in the incident propagation mode is converted into reflected acoustic beam energy in a different propagation mode and is directed towards at least one side face of the block in a manner which is sub-stantially not retroreflective with respect to the initially propagat-ing acoustic beam incident on the inclined end face of the block.
2. An acousto-optic modulator as claimed in Claim 1, charac-terised in that the inclined end surface is oriented obliquely rela-tive both to the two side faces forming respectively the optical in-put and output surfaces, and to the other side faces.
3. An acousto-optic modulator as claimed in Claim 2, charac-terised in that the side faces of the block which do not form the respective input and output faces for the beam of optical radiation are each loaded with a layer of acoustic absorbant.
4. An acousto-optic modulator as claimed in Claim 3, charac-terised in that the acoustic absorbant is a layer which is chosen from the group consisting of indium and lead.
5. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the block is of rectangular cross section and is formed from a monocrystal of germanium and the transducer is arranged to launch a beam of longitudinal compression waves, characterised in that the crystal axes are oriented relative to the block so that the acoustic wave propagation axis is directed along the [100] crystal direction and the angle of incidence of the acoustic wave on the inclined end face lies in the range 40 degrees to 52 degrees.
6. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the block is of rectangular cross section and is formed from a monocrystal of germanium and the transducer is arranged to launch a beam of longitudinal compression waves, characterised in that the crystal axes are oriented relative to the block so that the acoustic wave propagation axis is directed along the [100] crystal direction and the angle of incidence of the acoustic wave on the inclined end face is 46 degrees.
7. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the block is of rectangular cross section and is formed from a monocrystal of germanium, and the transducer is arranged to launch a beam of longitudinal compression waves, characterised in that the crystal axes are oriented relative to the block so that the acoustic wave propagation axis is directed along the [111] crystal direction, the incident coherent optical radiation to be modulated is polarised so that the electric vector lies in the plane containing the acoustic and optical beam axes, and the angle of incidence of the acoustic wave on the inclined end face lies in the range 40 degrees to 52 degrees.
8. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the block is of rectangular cross section and is formed from a monocrystal of germanium, and the transducer is arranged to launch a beam of longitudinal compression waves, characterised in that the crystal axes are oriented relative to the block so that the acoustic wave propagation axis is directed along the [111] crystal direction, the incident coherent optical radiation to be modulated is polarised so that the electric vector lies in the plane containing the acoustic and optical beam axes, and the angle of incidence of the acoustic wave on the inclined end Face is 46 degrees.
9. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the cross section of the block is rectangular, characterised in that the intersection edges of the inclined end face and the respective side faces which do not form the input and output surfaces for the optical radiation beam, are inclined to a line parallel to the transducer end face at an angle in the range 25 degrees to 35 degrees.
10. An acousto-optic modulator as claimed in Claim 1, 2 or 3, in which the cross section of the block is rectangular, characterised in that the intersection edges of the inclined end face and the respective side faces which do not form the input and output surfaces for the optical radiation beam, are inclined to a line parallel to the transducer end face at an angle of 30 degrees.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08520706A GB2183358A (en) | 1985-08-19 | 1985-08-19 | Acousto-optic modulator |
GB8520706 | 1985-08-19 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1261048A true CA1261048A (en) | 1989-09-26 |
Family
ID=10583977
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000515779A Expired CA1261048A (en) | 1985-08-19 | 1986-08-12 | Acousto-optic modulator |
Country Status (5)
Country | Link |
---|---|
US (1) | US4759613A (en) |
EP (1) | EP0212736A3 (en) |
JP (1) | JPS6250729A (en) |
CA (1) | CA1261048A (en) |
GB (1) | GB2183358A (en) |
Families Citing this family (17)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4902087A (en) * | 1988-09-19 | 1990-02-20 | Unisys Corporation | Fiber optic bypass switch |
US4979176A (en) * | 1988-11-28 | 1990-12-18 | Spectra-Physics | Acousto-optical device with lithium tantalate transducer |
US5254112A (en) * | 1990-10-29 | 1993-10-19 | C. R. Bard, Inc. | Device for use in laser angioplasty |
EP1037044B1 (en) | 1997-12-02 | 2011-07-20 | Hitachi Chemical Company, Ltd. | Method for measuring iodine using an hermetically sealed reaction instrument for specimen pretreatment |
DE19829986C1 (en) * | 1998-07-04 | 2000-03-30 | Lis Laser Imaging Systems Gmbh | Process for direct exposure of circuit board substrates |
EP1794324A4 (en) * | 2004-09-20 | 2010-04-14 | Wisconsin Alumni Res Found | Nonlinear spectroscopic methods for identifying and characterizing molecular interactions |
US7295153B2 (en) * | 2004-09-29 | 2007-11-13 | Lockheed Martin Corporation | Acousto-radio frequency modulator and applications therefore |
US7760342B2 (en) * | 2007-12-21 | 2010-07-20 | Wisconsin Alumni Research Foundation | Multidimensional spectrometer |
JP5740265B2 (en) | 2011-09-21 | 2015-06-24 | 株式会社東芝 | Acoustooptic device |
US9305237B2 (en) | 2011-11-04 | 2016-04-05 | Polestar Technologies, Inc. | Methods and systems for detection and identification of concealed materials |
RU2476916C1 (en) * | 2011-11-30 | 2013-02-27 | Научно-технологический центр Уникального приборостроения РАН (НТЦ УП РАН) | Acousto-optical modulator |
WO2015129775A1 (en) * | 2014-02-25 | 2015-09-03 | 株式会社フジクラ | Multicore fiber |
JP5851573B2 (en) * | 2014-09-01 | 2016-02-03 | 株式会社東芝 | Acoustooptic device |
CN104597632B (en) * | 2015-01-29 | 2017-09-01 | 中国电子科技集团公司第二十六研究所 | Large aperture acousto-optical device |
US11327348B2 (en) | 2018-09-18 | 2022-05-10 | Eagle Technology, Llc | Multi-channel laser system including optical assembly with etched optical signal channels and related methods |
US11042052B2 (en) | 2018-09-18 | 2021-06-22 | Eagle Technology, Llc | Multi-channel laser system including an acousto-optic modulator (AOM) with beam polarization switching and related methods |
RU192668U1 (en) * | 2019-02-08 | 2019-09-25 | Федеральное государственное бюджетное учреждение науки Научно-технологический центр уникального приборостроения Российской академии наук (НТЦ УП РАН) | CELL FOR REVERSE COLLINEAR DIFFRACTION OF THERAHZ RADIATION ON THE ULTRASONIC LIQUID |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3421003A (en) * | 1965-03-17 | 1969-01-07 | Corning Glass Works | Apparatus and method for optical signal processing |
US3419322A (en) * | 1965-08-03 | 1968-12-31 | Zenith Radio Corp | Ultrasonic transducer matching for bragg reflection scanning |
FR2095944A5 (en) * | 1970-06-05 | 1972-02-11 | Quantronix Corp | |
US3767286A (en) * | 1971-07-23 | 1973-10-23 | J Kusters | Acousto-optic filter having means for damping acoustic resonances |
DE2140548B2 (en) * | 1971-08-12 | 1973-08-30 | ACOUSTO-OPTICAL LIGHT DEFLECTOR | |
GB1401084A (en) * | 1972-04-10 | 1975-07-16 | Hewlett Packard Co | Acousto-optic filters |
JPS5431816B2 (en) * | 1973-12-14 | 1979-10-09 | ||
GB2119947B (en) * | 1982-04-01 | 1985-07-31 | Marconi Co Ltd | A cousto-optic device |
JPS6010229A (en) * | 1983-06-30 | 1985-01-19 | Hoya Corp | Acoustooptic deflector |
GB8510700D0 (en) * | 1985-04-26 | 1985-06-05 | Philips Electronic Associated | Pressure bonding two bodies together |
-
1985
- 1985-08-19 GB GB08520706A patent/GB2183358A/en not_active Withdrawn
-
1986
- 1986-08-04 EP EP86201365A patent/EP0212736A3/en not_active Withdrawn
- 1986-08-12 CA CA000515779A patent/CA1261048A/en not_active Expired
- 1986-08-12 US US06/895,655 patent/US4759613A/en not_active Expired - Fee Related
- 1986-08-16 JP JP61191206A patent/JPS6250729A/en active Pending
Also Published As
Publication number | Publication date |
---|---|
EP0212736A3 (en) | 1988-08-10 |
US4759613A (en) | 1988-07-26 |
GB2183358A (en) | 1987-06-03 |
EP0212736A2 (en) | 1987-03-04 |
JPS6250729A (en) | 1987-03-05 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
CA1261048A (en) | Acousto-optic modulator | |
EP0015685B1 (en) | Acousto-optical modulator | |
US4346965A (en) | Light modulator/deflector using acoustic surface waves | |
US4468084A (en) | Integrated optical time integrating correlator | |
US7894125B2 (en) | Acousto-optic devices | |
US4945539A (en) | Acousto-optic tunable filter | |
US4735485A (en) | Acousto-optic frequency shifter using optical fiber and method of manufacturing same | |
EP0867744B1 (en) | Multi-channel acousto-optic modulator | |
US4105953A (en) | Chirped acousto-optic Q switch | |
JPS6029725A (en) | Acoustooptic modulator | |
US4117424A (en) | Acoustic wave devices | |
GB2183359A (en) | Acousto-optic modulator | |
US4558926A (en) | Acousto-optic beam deflector | |
US3891308A (en) | Acoustooptic modulator | |
US3529886A (en) | Iodic acid acousto-optic devices | |
US3654575A (en) | Wave transmission time device | |
US3805196A (en) | Acousto-optical systems | |
EP4354216A1 (en) | Optical beam intensity modulator | |
JPH0554285B2 (en) | ||
SU797378A1 (en) | Acousto-optical device for controlling optical radiation | |
CN117930533A (en) | Optical fiber coupling type acousto-optic device and optical fiber laser | |
JPH0230493B2 (en) | ||
JPS62195620A (en) | Reflector for optical fiber | |
KR100278634B1 (en) | AOM generating the same optical axes between the in-cident beam and the first order diffraction beam | |
Hulme et al. | Improved Acousto-Optic Modulators For CO [sub] 2 [/sub] Heterodyne Laser Systems |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
MKEX | Expiry |