JPS61215534A - Waveguide type optoacoustic correlator - Google Patents

Abstract

PURPOSE:To integrate a waveguide type AO correlator by allowing undeflected light which is not deflected with a surface acoustic wave as a noise signal to the waveguide type AO correlator to enter a waveguide type spatial filter consisting of an ion exchange area with polarization dependency and then cutting off the undeflected light. CONSTITUTION:Light 19 with an angle of divergence which is guided from a light source 12 to a plane light guide 11 formed on the surface of a dielectric substrate 24 is converted by a plane lens 13 into collimated light (incidence light) 20; the incident light 20 is deflected with the surface acoustic wave 22 generated by a surface acoustic wave generating electrode 17 to have a deflected component 21 and undeflected light 23 also remains. At this time, the deflected light 21 and undeflected light 23 are propa gated containing an angle twice as large as a Brangg's angle to enter a plane lens 14. The deflected light 21 as collimated light and undeflected light 23 which enter the plane lens 14 are converged on different points, so they are separated on a plane light guide 11. The waveguide type spatial filter 16 consisting of an ion exchange area with polarization dependency is formed at the convergence point of the undeflected light 23 and then the undeflected light 23 is cut off there, so that only the deflected light 21 is detected by a photodetector 18.

Description

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

[Prior art and its problems]

A waveguide type AO correlator that utilizes light diffraction by surface acoustic waves can instantaneously obtain a double correlation, and can speed up correlation processing and determination processing.

A waveguide type AO correlator exchanges light with a divergence angle incident from the end face of a planar optical waveguide formed on the surface of a dielectric substrate into collimated light using a plane lens, and converts this collimated light into a wavelength of light using a surface acoustic wave. 1 deflects the light at an angle twice the plug angle determined by the excitation frequency and propagation speed of the surface acoustic wave and the refractive index of the planar optical waveguide, and detects this deflected light as a correlation signal using a storage type photodetector. be. 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 planar optical waveguide.

Therefore, in order to detect only the correlation signal, it is necessary to separate polarized light and non-polarized light.

As a method for separating polarized light and non-polarized light in a waveguide AO correlator using plug diffraction, Society for Optical Instrument Engineering (SPIE) Volume 180.

According to a document published in 1979, pages 160 to 162, a method using three planar lenses and a spatial filter in a planar optical waveguide is proposed.

FIG. 2 is a plan view showing the principle of the dielectric substrate 4.
4. Light having a divergence angle emitted from a light source 32 is guided from its end face to a plane optical waveguide 31 provided on the surface of the optical waveguide 31, and the light 39 propagating while having a divergence angle is collimated by a plane lens 33 (hereinafter referred to as 40 (referred to as incident light). The incident light 40 is the input signal S.

The intensity is modulated by (1), and the surface acoustic wave generation electrode 37
When the surface acoustic wave 42 generated by is amplitude-modulated by the input signal 32(t), the polarized light 41 diffracted by the surface acoustic wave 42 is generated by the input signals 5t(t) and 82(1).
The signal is the product of At this time, since the intensity of the polarized light 41 is determined by the deflection efficiency of the incident light 40 by the surface acoustic wave 42,
Unpolarized light 43 remains. This unpolarized light 43 is an unnecessary signal for the waveguide type AO correlator and must be removed because it causes malfunctions and the like.

A plane lens 34 is used to separate polarized light 41 and non-polarized light 43. In other words, polarized light 4 which is collimated light
1 and the unpolarized light 43 are made incident on the plane lens 34, and are respectively condensed and separated spatially on the plane optical waveguide. A waveguide spatial filter 3 is located at the position where the light is focused.
6, only the unpolarized light 43 is blocked, and only the polarized light 41 is made incident on the plane lens 35 again, exchanged with the original collimated light, and made incident on the light receiving element 38, thereby making it possible to easily detect only the correlation signal. Therefore, three plane lenses 3
By using 3.34.35 and the waveguide spatial filter 36, a waveguide AO correlator using plug diffraction is realized.

The light source 32 consists of a semiconductor laser or the like, and the planar optical waveguide 31
If the dielectric substrate is, for example, LIN b 03, then it consists of a planar optical waveguide etc. provided by thermally diffusing titanium (T1) on the surface of the substrate, and the planar lenses 33, 34° 35 are made of Fresnel lenses, geodesic lenses, etc. Become. However, for the waveguide spatial filter, no specific elements or implementation methods have been proposed yet, and three planar lenses,
Moreover, it is difficult to integrate a waveguide type AO correlator using a waveguide type spatial filter.

[Purpose of the invention]

An object of the present invention is to provide a waveguide-type AO correlator that can be integrated by forming a waveguide-type spatial filter consisting of an ion exchange region having polarization dependence as a waveguide-type spatial filter.

[Structure of the invention]

The present invention deflects a light beam propagating through a planar optical waveguide formed on the surface of a dielectric substrate using a surface acoustic wave, and detects the deflected light with a photodetector, thereby producing a correlation signal between the light beam signal and the surface acoustic wave. In the waveguide type optical/acoustic correlator, three plane lenses and a surface acoustic wave generating electrode that generates a surface acoustic wave are formed in the planar optical waveguide, and the planar optical waveguide is provided with a The present invention is characterized in that a waveguide type space and a filter are formed, which are made of an ion exchange region having polarization dependence that blocks unpolarized light that is not deflected.

〔Example〕

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

FIG. 1 is a plan view illustrating the structure and operating principle of an embodiment of a waveguide type optical/acoustic (AO) correlator according to the present invention.

Light 19 having a divergence angle guided by the light source 11 into the planar optical waveguide 11 formed on the surface of the dielectric substrate 24 is collimated by the planar lens 13 (hereinafter referred to as incident light) 2
0, the incident light 20 is deflected by the surface acoustic wave 22 generated by the surface acoustic wave generating electrode 17, and the incident light 20 is deflected by the surface acoustic wave 22 generated by the surface acoustic wave generating electrode 17,
occurs, and unpolarized light 23 that is not deflected also remains.

At this time, the polarized light 21 and the unpolarized light 23 have a wavelength (λ
op), the excitation frequency (f) and propagation velocity of the surface acoustic wave (
The light propagates at an angle twice the plug angle (θB=λopf/2nVs) determined by the refractive index (n) of the planar optical waveguide and enters the planar lens 14. The polarized light 21 and the non-polarized light 23, which are collimated lights, which entered the plane lens 14 are as follows.
The light is separated on the planar optical waveguide 11 in order to focus the light at different points.

If a waveguide spatial filter 16 made of an ion exchange region having polarization dependence is formed at a point where the unpolarized light 23 is focused, the unpolarized light 23 will not propagate earlier and will be blocked.

Therefore, only the polarized light 21 is converted back into collimated light by the plane lens 15 and detected by the photodetector 18.

The following table shows L+N when the dielectric substrate is L ] N b C)+ substrate and the ion exchange region is H゛ exchange region.
b()+ It shows the cut direction of the crystal axis of the substrate, the propagation direction of light, and the polarization dependence of the H exchange region, and is a characteristic table of the principle used by the waveguide type AO correlator according to the present invention.

X-cut on LiNbO3 substrate, Z-cut for light beam propagation direction
In the case of axial direction, or LiNb○.

If the board has an X cut and the light beam propagation direction is the Z-axis direction, or if the LIN b 03 board has a 128°X cut and the light beam propagation direction is the Z-38° axis direction, the planar light guide Regardless of the polarization of the light beam propagating along the wave path, the non-polarized light can be blocked by forming a waveguide spatial filter consisting of an H exchange region at the point where the non-polarized light is focused.

In addition, if the LiNbO3 substrate has an X cut and the propagation direction of the light beam is the Y-axis direction, or if the LiNbO3 substrate has an X cut and the light beam propagation direction is the X-axis direction, the light source can be If the polarization of the guided light beam is set to 1M mode, the non-polarized light will be blocked unless a wave-guiding spatial filter consisting of an H exchange region is formed at the point where the non-polarized light is focused. Similarly, X
When cutting, when the propagation direction of the light beam is the X-axis or Y-axis direction, or when the direction of propagation of the light beam is set to
When the propagation direction of the light beam is stopped in the X-axis direction, if the polarization of the light beam guided from the light source to the planar optical waveguide is set to TE mode, the H
``If a waveguide spatial filter consisting of exchange regions is formed, non-polarized light will be blocked.

The effect of blocking unpolarized light using the H-exchange region is, for example, when the LIN b 03 substrate is X-cut and the propagation direction of the light beam is the Y-axis direction, the propagation of the light beam in the H-exchange region is If the length in the direction is 1 mm, an attenuation of 30 dB or more can be obtained. Furthermore, it can be easily inferred that if the length of the H exchange region in the propagation direction of the light beam is increased, the amount of attenuation increases.

The planar optical waveguide is formed, for example, by thermally diffusing T1, and the H exchange region is formed by ion exchange of protons (Hl) and lithium (Li) using benzoic acid. A similar effect can be obtained by using A g N 03 on the surface of the LiNbO3 substrate if the dielectric substrate is LiNb0:+.
It can be obtained by forming a g+ exchange region or by forming a T1+ exchange region using TANO3. Moreover, if the dielectric substrate is LiTaO3, on the surface of the LiTaO3 substrate,
A similar effect can be obtained by forming an Ag" exchange region using AgNO2. Any combination of the dielectric substrate and the ion exchange region is allowed as long as the ion exchange region has polarization dependence. It will be done.

As mentioned above, if the configuration of the waveguide type AO correlator provided with the waveguide type spatial filter made of the ion exchange region having polarization dependence is used to block unpolarized light according to the present invention, the waveguide type, which was difficult to block, can be used. Integration of AO correlators can be easily realized.

〔Effect of the invention〕

As explained above, the present invention allows unpolarized light that is not deflected by surface acoustic waves, which is a noise signal for a waveguide type AO correlator, to enter a waveguide type spatial filter made of an ion exchange region having polarization dependence and is blocked. This makes it possible to integrate waveguide-type AO correlators, which has been difficult.

[Brief explanation of the drawing]

FIG. 2 is a plan view of an embodiment of the present invention, and FIG. 2 is a plan view of a conventional waveguide type AO correlator. 11, 31... Planar optical waveguide 12, 32... Light source 13, 14.15.33.34.35... Planar lens 36... Wave guide Type space filters 17, 37...Surface acoustic wave generating electrodes 18, 38
. . . Photodetectors 19, 39 . . . Light propagating with divergence angles 20, 40 . . . Collimated light (incident light) 21
, 41...Polarized light 22, 42...Surface acoustic waves 23, 43...Non-polarized light 24, 44...Dielectric substrate 16... ...Waveguide type spatial filter agent consisting of ion exchange region Patent attorney Yoshiyuki Iwasa 73, 14.1g: Flat lens ゛16: Ion exchange 41! Deflected light 23: 4P scratched light 24Si*electronic black 11 set i Fig. 1 33, j4.35: Plane lens 36-45 skin type blank filter 4I: *Internal light +3: $ Deflected light Fig. 2

Claims (1)

[Claims] (1) A light beam propagating through a planar optical waveguide formed on the surface of a dielectric substrate is deflected by a surface acoustic wave, and the deflected light is detected by a photodetector to generate a correlation signal between the light beam signal and the surface acoustic wave. In the waveguide type optical/acoustic correlator, three plane lenses and a surface acoustic wave generating electrode that generates a surface acoustic wave are formed in the planar optical waveguide, and the planar optical waveguide is provided with a A waveguide type optical/acoustic correlator characterized by forming a waveguide type spatial filter consisting of an ion exchange region having polarization dependence that blocks unpolarized light that is not deflected.