JPS61113038A - Waveguide type opto-acoustic collimator - Google Patents

Abstract

PURPOSE:To obtain a waveguide type AO collimator which utilizes Bragg diffraction by providing a plane optical waveguide terminal that transmits light which is not deflected with a surface acoustic wave, but reflected only deflected light. CONSTITUTION:Light 16 which is emitted by a light source 11 provided at the end part of a thin-film waveguide 22 and has a spread angle is converted by a plane lens 12 into collimated light 17, which is deflected with a surface acoustic wave generated by a surface acoustic wave generating electrode 20; deflected light 18 and undeflected light 19 are propagated at an angle twice as the Bragg angle to reach an end surface 21. The end surface 21 is so formed as to has the angle (thetad) of nearly total reflection to the optical axis of the deflected light 18 and an angle (thetad) close the the angle of transmission to the optical axis of the undeflected light 19. The undeflected light 19 is therefore removed and the deflected light 18 is reflected totally and detected by a detector 23.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a waveguide optical-acoustic (AO) correlator.

(Prior art and its problems) A waveguide type AO correlator that uses light diffraction by surface acoustic waves can instantly obtain a correlation of double order, and can speed up correlation processing and determination processing. .

A waveguide type An correlator converts light having a divergence angle incident from the end face of a thin film optical waveguide formed on a dielectric surface into collimated light using a plane lens, and converts this collimated light into a wavelength of light using a surface acoustic wave. The excitation frequency and propagation speed of the surface acoustic wave are deflected at an angle twice the plug angle determined by the refractive index of the thin film optical waveguide, and this deflected light is detected as a correlation signal using an accumulation type photodetector. . At this time, collimated light that is not deflected by the surface acoustic wave (hereinafter referred to as unpolarized light) is also propagating through the thin film optical waveguide. Therefore, in order to detect only the correlation signal, it is necessary to separate polarized light and non-polarized light.

Society of Optical Instrument Engineers (sprE) 1s as a method for separating polarized light and non-polarized light in a waveguide AO correlator using plug diffraction.

vol., 1979, pages 160-162, proposes a method using three plane lenses and a spatial filter in a thin film optical waveguide. FIG. 4 is a plan view showing the principle. Thin film optical waveguide 5 provided on the dielectric surface
1, the light having a divergence angle emitted from the light source 52 is guided from the end face, and the light 5 propagates while having a divergence angle.
9 is converted into collimated light (hereinafter referred to as incident light) 60 by a plane lens 53. The incident light 60 is the input signal S+(t
), and on the other hand, the surface acoustic wave 62 generated from the surface acoustic wave generation electrode 57 becomes the input signal 5t(1).
After being amplitude-modulated by S, the polarized light 61 diffracted by the surface acoustic wave 62 becomes a signal of the product of 51(t) and S,(t). At this time, since the intensity of the polarized light 61 is determined by the deflection efficiency of the incident light 60 by the surface acoustic wave 62, unpolarized light 63 remains. This unpolarized light 63 is an unnecessary signal for the waveguide type AO correlator and must be removed because it causes malfunctions and the like.

A plane lens 54 is used to separate the polarized light 61 and non-polarized light 63. That is, the polarized light 61 and the unpolarized light 63, which are collimated lights, are made incident on the plane lens 54, and are respectively condensed and separated spatially on the thin film optical waveguide. A waveguide space frame 4 is formed at the condensing position of the unpolarized light.
・The filter 56 blocks only the non-polarized light 63, and the polarized light 6
1 is again incident on the plane lens 55, converted into the original collimated light, and made incident on the light receiving element 58, thereby making it possible to easily detect only the correlation signal. Therefore, by using three planar lenses 53, 54, 55 and a waveguide spatial filter 56, a waveguide AO correlator utilizing plug diffraction is realized.

The light source 52 is made of a semiconductor laser, the thin film optical waveguide 51 is made of, for example, an optical waveguide provided by thermally diffusing titanium (Ti) over the entire surface of a lithium niobate (T, 1Nb03) substrate, and flat lenses 53, 54 are used. 55 consists of a Fresnel lens, a geodesic lens, etc. However, regarding waveguide spatial filters, specific elements and
No method for realizing this has been proposed, and therefore it is difficult to realize the integration of waveguide type optical/acoustic correlators.

(Object of the Invention) An object of the present invention is to provide a waveguide-type AO correlator using plug diffraction that can be integrated without using a waveguide-type spatial filter.

(Structure of the Invention) The optical/acoustic correlator of the present invention includes a planar optical waveguide formed on a dielectric surface, and light having a divergence angle that is incident on one end face of the planar optical waveguide and propagates through the planar optical waveguide. one plane lens that collimates the beam, a surface acoustic wave generation electrode that generates a surface acoustic wave that deflects the light beam collimated by the plane lens, and a surface acoustic wave generation electrode that transmits unpolarized light that is not deflected by the surface acoustic wave; It includes one or more planar optical waveguide ends that reflect only the polarized light, and a photodetector installed at the planar optical waveguide end from which the light beam polarized by the surface acoustic wave and reflected by the planar optical waveguide ends is emitted. The structure is as follows.

(Example) Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a plan view showing a first embodiment of a waveguide type optical/acoustic (A-0) correlator according to the present invention.

Light 16 having a divergence angle emitted from the light source 11 provided at the end of the thin film optical waveguide 22 is converted into collimated light (hereinafter referred to as incident light) 17 by the plane lens 12, and the incident light 17 is used to generate surface acoustic waves. It is deflected by the surface acoustic wave generated by the electrode 20, producing polarized light 18, and also leaves unpolarized light 19. At this time, the polarized light 18 and the unpolarized light 19 are connected to a plug angle (θB −λopf/2nv
An end face (hereinafter referred to as an end face) 2 formed in a thin film optical waveguide to propagate at an angle twice that of s) and remove unpolarized light.
Reach 1.・The end surface 21 is - with respect to the optical axis of the polarized light 18
C is formed so as to form an angle (θ lid) that substantially transmits the total reflection angle (θd) to the optical axis of the non-polarized light 19, and at this time, the end surface 21 is polished to a mirror surface. Make it.

Therefore, the unpolarized light 19 is removed to the outside and the polarized light 1
8 is totally reflected, and only the polarized light 18 propagates through the thin film optical waveguide 22 and is detected by the detector 23.

Further, in order to prevent the totally reflected polarized light 18 from interacting with the surface acoustic waves again, a surface acoustic wave absorbing region 13 is provided by applying silicone rubber or the like. When the light source 11 is a semiconductor laser with a wavelength of 089 μm and the thin film optical waveguide is formed by dielectric LiNbo and thermally diffused Ti on the substrate, the refractive index of the four thin film optical waveguides 22 is about 2.17. At this time, the critical angle at the end face 21 is 2744 degrees, and the breaster angle is 24.74 degrees.

FIG. 2 shows the energy reflectance at the end surface 21 of a light beam having P polarization with respect to the end surface 21 under the above conditions.
FIG. 2 is a characteristic diagram of the principle used by the waveguide type AO correlator according to the present invention.

In FIG. 2, the incident angle (
If θi) is 26.5° or less, more than 90 degrees of unpolarized light 19 can be removed into the air. Further, if the incident angle (θd) of the polarized light 18 is equal to or greater than the critical angle of 27.44°, the polarized light 18
8 can be totally reflected. The angle formed by the polarized light 18 and the unpolarized light 19 (the angle twice the plug angle (20B)) is given by 2θB = λop f /nvs, as described above, so if f = 150 Mllz, 2θB = 1
．． 01". Therefore, in FIG. 1, for example, if the end face 21 is formed at an angle of 26.5 degrees with respect to the optical axis of the non-polarized light 19, and the excitation frequency of the surface acoustic wave is 15011 Jz, the polarized light The angle of incidence (θd) on the end surface 21 of 18 is 2
7.6°, and the polarized light 18 is totally reflected at the end face 21,
It is detected by the detector 23. Further, at this time, the excitation frequency of the surface acoustic wave may be any frequency as long as it is 150 K (Hz or more), and the polarized light 18 and the non-polarized light 19 can be easily separated.

Furthermore, the angle of incidence (θi) of the unpolarized light 19 on the end surface 21 is
The angle of incidence (θd) of the polarized light 18 on the end face 21 determined by the sum of θi and twice the plug angle (20B) may be approximately 2744° or more. The wavelength of the light source used and the excitation frequency of the surface acoustic wave may be other combinations.

Furthermore, the dielectric material forming the thin film optical waveguide is not limited to the LiNbO3 substrate, for example, Ti i Ta
Any substrate may be used as long as it can form an end face that removes unpolarized light into the air and totally reflects polarized light, such as the 03 substrate.

As mentioned above, the waveguide type A using plug diffraction according to the present invention
By using the configuration of the O-correlator, it is possible to easily integrate the wave-guiding type & O-correlator using plug diffraction without using a wave-guiding spatial filter, which has not been realized yet. In addition, a high-precision correlator can be realized if necessary.

FIG. 3 shows a second embodiment of a waveguide optical-acoustic (AO) correlator according to the present invention.

Light 36 having a divergence angle emitted from a light source 31 is collimated by a plane lens 32 (hereinafter referred to as incident light).
The incident light 37 is converted into a surface acoustic wave generating electrode 40.
The generated surface acoustic waves generate polarized light 38, and at the same time, unpolarized light 39a remains.

At this time, the polarized light 38 and the unpolarized light 39a form an angle (20B) twice the plug angle, propagate through the thin film optical waveguide 33, and reach the unpolarized light removing thin film optical waveguide end face (hereinafter referred to as end face) 4].

As described above, the end face 41 is formed so as to remove 90% or more of the non-polarized light 39a into the air and totally reflect the polarized light 38.

The remaining energy of slightly less than 10% of the unpolarized light 39a is absorbed by the end face 41.
However, this is a noise signal for the waveguide type AO correlator. Here, in order to prevent the polarized light 8 and non-polarized light 39b reflected by the end face 41 from interacting with the surface acoustic wave again, a surface acoustic wave absorbing region 34 is provided by applying silicone comb or the like. Unpolarized light 3 which is the noise signal
9b, the unpolarized light 39b and the polarized light 38 are made incident on the end face 42 which has the same effect as the end face 41. As a result, the unpolarized light 39b can be further removed into the air by 90 inches or more, and by providing the end surfaces 4] and 4.2, the unpolarized light 39a can be removed into the air by 99 inches or more. On the other hand, since the polarized light 38 is totally reflected at the end faces 41 and 42, there is almost no energy loss, and the detector 4
Detected at 3. Therefore, by using the waveguide type AO correlator with the structure shown in Fig. 3, a waveguide type AO correlator with a good 8N ratio can be easily realized without using a waveguide type spatial filter, which has not been realized yet. . It is easy to see that the S/N ratio improves as the number of thin film optical waveguide end faces for removing non-polarized light increases (this can be inferred by analogy).

In the above-mentioned embodiment, the incident light beam is
In contrast, it has a P-polarization, but it may also have an S-polarization. However, the S-polarized light beam is theoretically inferior in energy reflectance to the P-polarized light beam at an incident angle less than the critical angle. For example, corresponding to FIG. 2, when the incident angle is 2 Da, the energy reflectance of P polarization is 00]6, and in the S1 bucket direction, it is 0.44.

Therefore, in order to obtain an S/N ratio comparable to that of a P-polarized light beam,
In principle, it is necessary to increase the number of thin film optical waveguide end faces for removing non-polarized light.

(Effects of the Invention) As explained above, the present invention removes unpolarized light that is not deflected by surface acoustic waves, which is a noise signal for waveguide type A and O correlators, and removes polarized light, which is a necessary signal. By using a waveguide type AO core leak with an end face that causes total reflection, we can achieve
J! A waveguide type A, O correlator using plug diffraction can be realized without using a wave-type spatial filter. Furthermore, since only one lens is required, manufacturing costs are low, and there is no problem with the relative positional error between the lenses, which was a major problem in the conventional 4-frame construction that uses three lenses. The deterioration of Suku correlator performance can be essentially eliminated.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 is a characteristic diagram of the principle used by the waveguide type AO correlator according to the present invention, and FIG. 3 is a plan view of another embodiment of the present invention. 41'71
1 is a plan view of a conventional waveguide type A, O correlator. In addition, the figure number is 11.31.52 Light source, 12.32, 53, 54゜55... Flat lens, 22, 33. 51... Thin film optical waveguide, 56 Waveguide type spatial filter, 20, 40.57・
・Elastic surface #generation phase' sleep pole, 16.36 ・Light with a spreading angle, 17,37. fin...Incoming light, 18
, 38° 61 ・Iμ direction light, 19.39a, 39b, 6
3-Unpolarized light, 21, 41.42... Path formed in thin film optical waveguide to remove unpolarized light, "I7.1 plane, 2
3.43 Detector, 58 - Photoreceptor, 59 Light propagating with a divergence angle, 62 Surface acoustic wave, 13.
34.Surface acoustic wave absorption region.゛・-15,. Figure 72 Brewster's angle Critical angle 4142 Non-polarized light removal thin film guided waveguide 3rd Polarized light 39a, 39b Non-polarized light procedure amendment m) Fi7.1.29 Showa year Month Day 2, Name of the invention Waveguided light Acoustic Correlator 3, Relationship to the case of the person making the amendment Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation, Representative: Tadahiro Sekimoto (Contact address: Patent Department, NEC Corporation) 5, Amendment Target 1) Detailed explanation of the invention in the specification column 4, brief explanation of the drawings 6, amendment content 1, page 5, line 12 of the specification [Optical/acoustic correlator]
Correct the description to [waveguide type optical, acoustic correlator J]. 2. In the 17th line of page 6 of the specification, the phrase "film-guided optical waveguide" is corrected to "film-guided optical waveguide." 3. In the 19th line of page 6 of the specification, the phrase "unpolarized light" is corrected to "unpolarized light 19." 4. In the 4th line of page 7 of the specification, [polishing J] is corrected to "polishing".

Claims (1)

[Claims] A planar optical waveguide formed on a dielectric surface, one planar lens that collimates a light beam having a divergence angle that is incident on one end face of the planar optical waveguide and propagates through the planar optical waveguide, and a planar lens. a surface acoustic wave generating electrode that generates a surface acoustic wave that deflects a collimated light beam; and one or more planar optical waveguides that transmit unpolarized light that is not deflected by the surface acoustic wave and reflect only the polarized light. 1. A waveguide type optical/acoustic correlator comprising: an end of the planar optical waveguide, and a photodetector installed at the end of the planar optical waveguide from which a light beam deflected by a surface acoustic wave and reflected by the end of the planar optical waveguide is emitted. .