JPS62100731A - Bragg cell - Google Patents

Abstract

PURPOSE:To obtain a high diffraction efficiency over a wide band by changing the variation of a light refractive index due to diffusion in respectively positions on the surface of a piezoelectric base. CONSTITUTION:An optical surface waveguide 2 increases the variation of the light refractive index in an area that an elastic surface wave in a high frequency band is transmitted, and reduces the variation in an area that an elastic surface wave in a low frequency band is transmitted. The diffraction efficiency of the optical surface wave depends upon a value obtained by integrating the product of space distribution of the optical surface wave along the depth direction from the surface of the piezo-electric base 1 and the similar space distribution of the elastic surface wave in the depth direction and the diffraction efficiency is increased in accordance with the increase of the value. Consequently, the diffraction efficiency can be increased over a wide frequency band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of industrial application] This invention relates to a black cell that performs frequency analysis using black diffraction of optical surface waves by surface waves.

[Conventional technology]

Figure @2 is, for example, from the document Proceedings of
TheIEEE, vol, 64. No, 3. Ma
rch 1976, pp318-328, Appl.
ied 0ptics, vol, 19. No.1
8,15 September1980, pp, 3
033-3034, etc., is a diagram illustrating a conventional black cell of this type. v; FIG. 2(a) is a plan view, and FIG. 2(b) is a sectional view. %2 figure) is the second
This is a diagram showing the optical layer refractive index distribution in the AA/cross section of (al). In the second fill (al, (bl), (1+ is a piezoelectric substrate such as LiNbO3, This is an optical surface wave waveguide formed by external diffusion or internal diffusion of metal. (31 is a ridge-shaped electrode for surface acoustic wave excitation, (41 is a laser diode,
(51 is a lens, (6) is a light receiving element array.
FIG. 2(c) shows the optical layer refractive index distribution accompanying external diffusion or internal diffusion, and is constant in any cross section in FIG. 2(a).

That is, the amount of change in the optical refractive index Δn on the surface of the piezoelectric substrate fli is constant over the entire piezoelectric substrate or surface, and the functional form of the distribution along the depth direction of the piezoelectric substrate +l+ is also the same as the surface of the piezoelectric substrate +11. It is constant throughout.

Next, the operation buttons will be explained. The optical surface wave that enters the optical surface wave waveguide (2) from the laser diode (4) is converted into parallel light by the lens (6), and is transmitted to the end face where the photodetector array (6) is attached by the other lens (61). When the surface acoustic wave beam excited by the interdigital electrode 13) and the optical surface wave beam are crossed at a certain angle, the optical surface wave beam is diffracted and the surface acoustic wave is focused. The light is focused on a different light-receiving element than when there is no light. The above-mentioned diffraction angle changes depending on the frequency of the surface acoustic wave. Therefore, by monitoring which light receiving element in the light receiving element array (6) has a large output, it is possible to know the frequency of the surface acoustic wave. In other words, radio waves received from radar etc. are converted into RF
By converting the signal into a band and using this signal to excite surface acoustic waves via the interdigital electrode (3), it is possible to perform frequency analysis of the received radio wave.

By the way, the diffraction efficiency in this type of black cell, that is, the intensity ratio of diffracted light and incident light, is described in, for example, the document Pr.
oceading of the IBBE, vo
l, 54°No, 3. March 19'76, p
318-328, the piezoelectric substrate of the incident light [11] Spatial distribution along the depth direction, 2. Similar spatial distribution of the diffraction source, and 3. It depends on the value obtained by multiplying and further dividing by t along the depth direction.

The larger this value is, the greater the diffraction efficiency is. The above spatial distribution of the incident light and the diffracted light is determined by the amount of change in the optical refractive index Δn due to diffusion.
The larger Δn is, the larger the incident light and the diffracted light,
It is distributed more concentrated near the piezoelectric substrate tl+ surface.

On the other hand, the above spatial distribution regarding surface acoustic waves is as the frequency increases (fX).

It is more concentratedly distributed near the surface of the piezoelectric substrate (11).

[Problem that the invention seeks to solve]

Now, conventionally, this type of black cell is @sU.

As shown in FIG. 4, the amount of change in the optical refractive index Δn due to diffusion was constant over the entire surface of the piezoelectric substrate (li. Therefore, the spatial distribution of the optical surface waves was also is constant throughout, so
The frequency range of surface acoustic waves in which good diffraction efficiency can be obtained is limited, and the diffraction efficiency and signal frequency analysis cannot be performed over a wide band.

This invention was made to eliminate the above-mentioned drawbacks, and aims to obtain a black cell that can perform frequency analysis with high diffraction efficiency over a wide band.

[Means for solving problems]

In the black cell according to the present invention, broadband characteristics are obtained by varying the amount of change in the optical refractive index due to diffusion at different locations on the surface of the piezoelectric substrate (11).

[Function] In other words, in the black cell of the present invention, the amount of change in the optical refractive index is increased in the region where surface acoustic waves in the high frequency band occur, and the amount of change in the optical refractive index is increased in the region where the surface acoustic waves in the low frequency band occur. By reducing the amount of change in the optical refractive index, high diffraction efficiency can be obtained over a wide band.

〔Example〕

Hereinafter, one practical example of this invention will be explained using FIG. 1.

! FIG. 1(a) is a plan view, and FIG. 1(b) is a sectional view. 1794 (c), (d) (d each 1st
(3 (This is the optical layer refractive index distribution in the AA', BB/cross section of al. In Figure 1 (a) and (b), fil
is a piezoelectric substrate such as I, 1Nbo3, 13+ is a blind-shaped 'tlE right for surface acoustic wave excitation, (4) is a laser diode, (51 is a lens, and (6) is a light receiving element array. These are conventional However, unlike the conventional optical surface wave waveguide (2) formed by diffusion, the optical refractive index change amount △n due to diffusion is
As shown in (d), it is formed so that it is large in the region where the surface acoustic waves in the high frequency band propagate, and small in the region where the surface acoustic waves in the low frequency band propagates.1. ing.

Note that the amount of change in the optical refractive index Δn does not change stepwise from place to place, but changes smoothly to prevent large reflections of optical surface waves.

In the black cell shown in FIG. 1, the optical surface wave that enters the optical surface wave waveguide (21) from the laser diode (4) is converted into parallel light by the lens (51), and the other lens (6) passes the optical surface wave to the light receiving element array. (6) is focused on the attached end face.Also, if the surface acoustic wave excited by the interdigital electric Ti13+ and the optical surface wave are crossed with the same angular change as in the conventional case, the optical surface wave will become an elastic wave. The light is diffracted in an angular direction that depends on the frequency of the surface wave, and is focused on a different light receiving element than when the surface acoustic wave is not excited.Therefore, which light receiving element in the light receiving element array (6) has a large output? By monitoring this, the frequency of surface acoustic waves can be analyzed in the same way as before.

However, unlike the conventional optical surface wave waveguide (2), the amount of change in the optical refractive index of the optical surface acoustic wave waveguide (2) is thicker in the @ region where the surface acoustic waves in the high frequency band is called (and where the surface acoustic waves in the lower frequency band is called). It is made smaller in areas where it is blurred.

As mentioned above, the diffraction efficiency of optical surface waves is determined by the spatial distribution of optical surface waves along the depth direction from the piezoelectric substrate fi+ surface,
It depends on the magnitude of the value obtained by integrating the product with a similar spatial distribution of surface acoustic waves along the depth direction, and the larger this value, the greater the diffraction efficiency.

'@1 In the black cell shown in Figure 1, in the low frequency band, that is, the frequency band of surface acoustic waves where energy is distributed and propagated from the surface of the piezoelectric substrate (1) to a deeper place, an optical surface wave waveguide is used. Since the amount of change in the optical refractive index (2) is made small, the energy of the optical surface waves is distributed even deep.

As a precaution, the value obtained by integrating the product of the spatial distribution of surface acoustic waves and the spatial distribution of optical surface waves along the depth direction is

It will be larger than before. On the other hand, in a high frequency band, that is, a frequency band of surface acoustic waves in which energy is concentrated near the surface of the piezoelectric substrate +lj, the amount of change in the optical refractive index of the optical surface wave waveguide (21) is increased. Optical surface waves also concentrate energy near the surface of the piezoelectric substrate (11).Therefore, the value is the integral of the spatial distribution of surface acoustic waves and the spatial distribution of optical surface waves along the depth direction. In other words, the black cell according to the present invention shown in FIG. 1 has the advantage that the diffraction effect can be extended over a wider frequency band than in the past.

Although the above description has been made regarding the case of the one-cypress example shown in FIG.
; is the interdigital electrode (avoiding the area where 31 is placed,
As shown in FIG. 1, the amount of change in the optical refractive index may be distributed and shaped only in the region where the optical surface waves occur. [Effects of the Invention] As described above, according to the present invention, Optical surface wave waveguide (2
) is made so that the amount of change in the optical refractive index due to diffusion is small in the region where surface acoustic waves in the low frequency band are promoted, and thick in the region where the surface acoustic waves in the high frequency band are promoted, By forming the piezoelectric substrate on the surface of the piezoelectric substrate (11), there is an advantage that the diffraction efficiency can be increased over a wider frequency band than in the past.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a black cell according to an elliptical example of the present invention, and FIG. 2 is a diagram showing a conventional black cell of this type. (1) is a piezoelectric substrate, (2) is an optical surface wave waveguide, (3;
(4) is a laser diode, (5) is a lens, and (6) is a light receiving element array. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 1 2.4 Shinko J Elephant + Are 1

Claims (1)

[Claims] In a black cell, an optical surface wave waveguide is formed by diffusion on the surface of a piezoelectric substrate, and interdigital electrodes for surface acoustic wave excitation are provided, and frequency analysis is performed using black diffraction of optical surface waves caused by surface acoustic waves. The optical surface wave waveguide is connected to the piezoelectric waveguide so that the amount of change in the optical refractive index due to diffusion is large in a region where surface acoustic waves in a high frequency band propagate and is small in a region where a surface acoustic wave in a low frequency band propagates. A black cell characterized by being formed on the surface of a body substrate.