JPS61267035A - Waveguide type opto-acoustic spectrum analyzer - Google Patents

Abstract

PURPOSE:To obtain a high dynamic range and to reduce the size of a device by combining a plane waveguide end removing undeflected light which is not deflected with a surface acoustic wave while reflecting deflected light totally with a plane light guide end which reflects both deflected light and undeflected light totally. CONSTITUTION:Divergent light 16 emitted by a light source 11 provided at an end part of a plane light guide 22 is converted by a plane lens 12 into collimated light 17, which is defected with the surface acoustic wave generated by an electrode 20 for generating the surface acoustic wave to generate deflected light 18 while undeflected light 19 also remains. The majority of the undeflected light 19 is removed and the deflected light 18 is reflected totally, so that the deflected light 18 and remaining undeflected light 19 are propagated in the plane light guide 22. Then, the deflected light 18 and undeflected light 19 are incident on a plane lens 26 and propagated while converged to reach the light beam total reflecting plane light guide end 25 which reflects the light beams totally. Then, the deflected light 18 and undeflected light 19 are reflected totally by the total reflecting end 25 and detected by a photodetector 23 at their convergence point.

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 spectrum analyzer that utilizes the deflection of light by surface acoustic waves instantly performs frequency analysis of a signal input to a surface acoustic wave generating electrode.

A waveguide type AO spectrum analyzer is a system that converts light that enters from the end face of a planar optical waveguide formed on the surface of a substrate and has a divergence angle into collimated light using a plane lens, and then deflects this collimated light using a surface acoustic wave. Since the deflection angle is approximately proportional to the excitation frequency of the surface acoustic wave, the frequency of the signal input to the surface acoustic wave generation electrode is analyzed by focusing the deflected light with a plane lens and detecting the focal point with a photodetector. It is something.

The structure of the waveguide type AO spectrum analyzer is described in the literature of the Society of Optical Instrument Engineers (spIa), Vol. 321, 1982, pages 134-140, and the Force International Conference on Infrared Optical and Optical fiber
4th Conference
100C) Technical Daiji Crystal Strike 1983 25
According to the literature on pages 8 to 259, there are two
A method using two plane lenses, an electrode for generating surface acoustic waves, and a photodetector has been proposed. FIG. 4 is a plan view showing the principle. Planar optical waveguide 5 provided on the substrate 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 55 by a plane lens 53. The collimated light 55 is deflected by a surface acoustic wave 60 generated by the surface acoustic wave generating electrode 57. The deflection angle is approximately proportional to the excitation frequency of the surface acoustic wave 60, and the power of the deflected light 61 is approximately proportional to the excitation power of the surface acoustic wave 60.

The polarized light 56 is focused by the plane lens 54, and the frequency spectrum of the input signal to the surface acoustic wave generation electrode 57 is determined by detecting the position of the focused point and the power of the deflected light 56 by the photodetector 58. can be detected.

The light source 52 is composed of a semiconductor laser or a light emitting diode, and the planar optical waveguide 51/fi is, for example, an optical planar waveguide formed by thermally diffusing titanium (Tt) onto a lithium niobate (t, 1Nbos) substrate. It consists of an fL7j optical waveguide formed by depositing, for example, 8i3N4 or As283 on an 8i substrate, and also consists of plane lenses 53 and 54H, such as a Fresnel lens or a geodesic lens.

However, in the waveguide type AO spectrum analyzer having the structure shown in FIG. 58 and propagates to the fixed plane waveguide end 62. The main causes of deterioration of the dynamic range of the waveguide type AO spectrum analyzer are noise generated by propagation loss due to scattering of light propagating through the planar optical waveguide 51 and loss due to scattering in the planar lenses 53 and 54.

Therefore, in the waveguide type AO spectrum analyzer shown in FIG. 8PIE) Volume 32) 1982 1
According to the literature on pages 34 to 140, the dynamic range Fi is about 30 dB, which is not good. In addition, in the waveguide type AO spectrum analyzer shown in FIG. 4, the photodetector 58 is normally a play-shaped one, but in order to obtain the desired frequency step that can be read and abraded, it is necessary to use an array-shaped photodetector. The focal length f of the plane lens 54 is determined in accordance with the pitch of the array. That is, the shift in the detection position caused by the difference in the excitation frequency of the surface acoustic waves on the photodetector 58 is proportional to the focal length of the plane lens 54.

Therefore, in order to reduce the frequency step that can be read, it is necessary to increase the focal length of the plane lens 54. However, in the waveguide type AO spectrum analyzer shown in FIG. /' has the disadvantage of increasing the size of the device.

(Objective of the Invention) An object of the present invention is to provide a waveguide type optical/acoustic spectrum analyzer which eliminates the above-mentioned drawbacks, has a high dynamic range, is compact, allows reading and viewing, and has a small frequency difference. be.

(Structure of the Invention) The waveguide type optical-acoustic spectrum analyzer of the present invention includes a planar optical waveguide formed on the surface of a substrate, and an expanded signal that is incident on one end face of the planar optical waveguide and propagates through the planar optical waveguide. One plane lens that converts a light beam having nine angles into collimated light, one surface acoustic wave generation electrode that generates a surface acoustic wave that is collimated by the plane lens and deflects the fluorescent beam, and a non-deflector that is not deflected by the surface acoustic wave. One or more planar waveguide ends that transmit light and reflect polarized light, one or more planar waveguide ends that allow total reflection of both polarized and unpolarized light, and one or more planar waveguide ends that transmit light and reflect polarized light. Many configurations include one plane lens for focusing and a photodetector installed at the end of a plane optical waveguide from which polarized light and non-polarized light are emitted.

(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 optical/acoustic (AO) spectrum analyzer according to the present invention.

The light 16 having a divergence angle emitted from the light source 11 provided at the end of the planar optical waveguide 22 is converted into scollimated light 17Vc by the plane lens 12, and the collimated light 17 is generated from the surface acoustic wave generation electrode 20. Polarized light 18 is generated by the surface acoustic wave, and unpolarized light 19 that is not polarized also remains.

At this time, the plug angle ( A planar optical waveguide end (hereinafter referred to as a removal end) 21 for unpolarized light that propagates at an angle twice as large as θB=sin″″1 (λop−f/2nvs) and removes the unpolarized light 19.
reach. The removal end 21 is formed so as to form an angle (θI) with respect to the optical axis of the polarized light 18 so as to have an approximately total reflection angle (θd)e and an angle (θI) with respect to the optical axis of the non-polarized light 19. ,
At this time, the removed end 21 is made into a mirror surface by polishing or the like.

Therefore, most of the unpolarized light 19 is removed here, the polarized light 18 is totally reflected, and the polarized light 18 and the remaining unpolarized light 19 propagate in the plane optical waveguide 22 . Thereafter, the polarized light 18 and the unpolarized light 19 enter a plane lens 26, propagate while converging, and reach a total reflection plane optical waveguide end (hereinafter referred to as a total reflection end) 25 for total reflection of the light beam. reach Therefore, the polarized light 18 and the non-polarized light 19 are totally reflected at the total reflection end 25 and detected by the photodetector 23 at the condensing point. In order to prevent the polarized light 18 and unpolarized light 19 from interacting with the surface acoustic waves again, silicone rubber or the like is applied to the surface acoustic wave absorption region 13.
will be established. With the structure shown in FIG. 1, the noise generated by the unpolarized light 19 is reduced, the dynamic range is improved, and the focal length of the plane lens 26 that condenses the polarized light 18 and the unpolarized light 19 is as shown in FIG. When the distance between the plane lens 26 and the photodetector 23 is the same as that of the conventional waveguide type AO spectrum analyzer shown in FIG.

When the light source 11 is a semiconductor laser with a wavelength of 0.89μ and a planar optical waveguide f7I is formed by thermally diffusing Ti on a LiNbO3 substrate, the refractive index of the planar optical waveguide 22 is approximately 2.1.
It is 7. At this time, the critical angle at the removal end is 27.4
40. The Priest angle is 24.74°.

FIG. 2 shows the removal end 21 and the total reflection end 25 under the above conditions.
This is the incident angle dependence of the energy reflectance at the removal end 21 and the total reflection end 25 of the light beam having P polarization relative to the removal end 21 and the total reflection end 25, and the waveguide type according to the present invention It is a characteristic diagram of the principle used by the AO spectrum analyzer.

In FIG. 2, if the incident angle (θi) of the unpolarized light 19 to the removal end 21 is 26.5° or less, the unpolarized light 19Fi90%
More can be removed into the air. Also, the incident angle (θd) of the polarized light 18 to the removal end 21 is 27.440 which is the critical angle.
If it is more than that, the polarized light 18 is totally reflected.

be able to. Further, if the angle of incidence of the polarized light 18 and the non-polarized light 19 on the total reflection end 25 is 27.44° or more, the polarized light 1
8 and unpolarized light 19 are totally reflected. Angle between polarized light 18 and non-polarized light (twice the plug angle (20B)) fl
, as mentioned above, 20B-=sin-”(λOpf/n
vs), so if /=150MHz then 2
θB == 1.01'. Therefore, in FIG.
0, and the excitation frequency of the surface acoustic wave is 150.
MHz, the angle of incidence of the polarized light 18 on the removal end 21 (
θd) is 27.5°, and the polarized light 18 is totally reflected at the removal end 21. At this time, the excitation frequency of the surface acoustic wave is 15
Any force frequency above 0 MHz may be used. Mako, θ
Polarized light 18 determined by the sum of i and twice the plug angle (20B)
The incident angle (θd) to the removal end 21 may be 27.44° or more, and the wavelength of the light source used in the waveguide type AO spectrum analyzer and the excitation frequency of the surface acoustic wave may be other combinations. Further, at this time, the distance between the plane lens 26 and the photodetector 23 can be reduced by about 20% compared to the conventional structure of the waveguide type AO spectrum analyzer shown in FIG.

In this embodiment, the light emitted from the light source 11 is incident on the planar optical waveguide 22, and the planar waveguide end and the total reflection end 25 are the same, but they do not need to be the same, and the total reflection end is the planar optical waveguide end. Any positional relationship is acceptable as long as the ends of the planar optical waveguide function to totally reflect the light beam propagating through the waveguide (for example, the structure of the second embodiment shown below).

Friend, the substrate that forms the planar optical waveguide is not limited to the L1NbOS substrate, for example, the Si substrate, the L1NbOS substrate, etc.
i Any material that can form an end surface that removes unpolarized light into the air and totally reflects polarized light, such as a TaO3 substrate, and an end surface that totally reflects a light beam propagating through a planar optical waveguide. good.

As mentioned above, by using the configuration of the waveguide type AO spectrum analyzer according to the present invention, a higher dynamic range can be obtained compared to the conventional waveguide type AO spectrum analyzer, and at the same time, it is possible to obtain the same reading frequency difference with less equipment. The amount can be reduced.

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

Light 36 emitted from the light source 31 and having a divergence angle is converted into collimated light 37 by the plane lens 32, and the collimated light 37 is deflected by the surface acoustic wave generated by the surface acoustic wave generating electrode 40, producing polarized light 38. ,
Unpolarized light 39a that is not deflected also remains. At this time, polarized light 3
8 and unpolarized light 39atj angle twice the plug angle (20B)
The unpolarized light propagates through the planar optical waveguide 33 and reaches a non-polarized light removal planar optical waveguide end (hereinafter referred to as removal end) 41.

As described above, the removal end 41 is formed so that the unpolarized light 39ai90 or more is removed into the air, and the polarized light 38t is totally reflected. The remaining energy of just under 101 of the unpolarized light 39j1 is reflected by the removal end 41, which is a source of unnecessary noise for the waveguide type AO spectrum analyzer. Here, since the polarized light 38 and non-polarized light 39b reflected by the removal end 41 interact with the surface acoustic waves again and cause a force, a surface acoustic wave absorbing region 34 is provided by applying silicone rubber or the like.

In order to further remove the non-polarized light 39b, which is the source of unnecessary noise mentioned above, the non-polarized light 39b and the polarized light 38 are made to enter a removal end 42 which has the same function as the removal end 41. As a result, more than 90'% of the unpolarized light 39b is removed into the air, and by providing the removal ends 41 and 42, more than 9996% of the unpolarized light is removed into the air.

After that, the polarized light 38 and the non-polarized light enter a plane lens 44, propagate while converging, and totally reflect the light beam.The light beam enters a total reflection plane optical waveguide end 45, is totally reflected, and is detected at the condensing point. is detected by the device 43.

Therefore, it is clear that by using the waveguide type AO spectrum analyzer having the structure shown in FIG. 3, a higher dynamic range can be obtained and the size can be reduced compared to the waveguide type AO spectrum analyzer having the conventional structure.

In the embodiments described above, the light beam incident on the end face has a P polarization with respect to the end face, but it may have an S polarization. However, the energy reflectance of the S-polarized light beam is fundamentally inferior to that of the P-polarized light beam at an incident angle greater than the critical angle. For example, corresponding to FIG. 2, when the incident angle is 25', the energy reflectance for P polarization is 0.44 for 0.016.8 polarization. Therefore, in order to obtain a dynamic range comparable to that of a P-polarized light beam, it is necessary to increase the number of non-polarized planar optical waveguide ends in principle. It is clear that a higher dynamic range can be obtained by using the waveguide type AO spectrum analyzer compared to the conventional structure of the waveguide type AO spectrum analyzer. In addition, the number and combination of the non-polarized light removal planar optical waveguide end and the light beam total reflection planar optical waveguide end are limited to those in the 11th and 2nd embodiments, and the number and combination are limited. is allowed.

(Effects of the Invention) As explained above, the present invention removes unpolarized light that is not deflected by surface acoustic waves into the air, which is unnecessary for a waveguide type AO spectrum analyzer, and completely reflects the polarized light. By using a combination of a planar optical waveguide end and a planar optical waveguide end that allows polarized and non-polarized light to radiate, a higher dynamic range can be obtained compared to the conventional structured waveguide type AO spectrum analyzer. , it is possible to downsize the device.

[Brief explanation of drawings]

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 spectrum analyzer according to the present invention. FIG. 3 is a plan view of another embodiment of the present invention. , FIG. 4 is a plan view of a conventional waveguide type AO spectrum analyzer. In addition, in the figure, 11.31,52...light source, 12,26,32°34
．． 53.54 --- Planar lens, 22.51 -- Planar optical waveguide, 20, 40.57 -- Electrode for surface acoustic wave generation, 16, 36, 59 -- Light having a divergence angle, 17
．． 37.55...Collimated light, 18,38°56-
...polarized light, 19.39a, 39b, 61-unpolarized light,
21, 41, 42... Planar optical waveguide end formed to remove unpolarized light, 25.45... Planar optical waveguide end formed to totally reflect the light beam, 23, 43
．． 58... Photodetector, 60... Surface acoustic wave, 13.
34...Surface acoustic wave absorption region, 62...Planar optical waveguide end where photodetector is installed'! P 2 Figure Brewster angle Critical angle O 3 Figure procedure amendment (voluntary)

Claims (1)

[Claims] A planar optical waveguide formed on the surface of the substrate, 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 the planar lens. a surface acoustic wave generating electrode that generates a surface acoustic wave that deflects a collimated light beam; one or more planar optical waveguide ends that transmit unpolarized light that is not deflected by the surface acoustic wave and reflect polarized light; , one or more planar optical waveguide ends that cause total reflection of both polarized and non-polarized light, one planar lens that focuses the polarized light and non-polarized light, and a planar light guide that outputs the polarized light and non-polarized light. A waveguide type optical/acoustic spectrum analyzer characterized by comprising a photodetector installed at the end of a waveguide.