JPH0743402B2 - Waveguide optical / acoustic spectrum analyzer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a guided wave type optical / acoustic spectrum analyzer in which two surface acoustic wave electrodes and two planar lenses are provided on a planar waveguide.

[Conventional technology]

Interaction between surface acoustic wave and light on optical waveguide (Bragg diffraction)
Since the optical / acoustic signal processing device using is capable of high-speed processing, small size and light weight, it has been realized as a waveguide type optical spectrum analyzer and optical correlator, and its practical use has been actively carried out.

This guided-wave optical spectrum analyzer (hereinafter referred to as "optical spectrum analyzer") is a frequency analyzer that analyzes the frequency of an unknown signal in real time. It has already been published by Professor Tsai of the University of California, USA. Lee Transaction on Circuit Systems (IEEE Transacti
on on Circuit Systems), December 1979, page 1072, “Guided Wave Acoustic Optic Plug Modulators for Wideband Integrated Opticom Communications and Signal Processing (Guided-Wave
Acoustoptic Bragg Modulation for Wide-Band Integ
rated Optics Communications and Signal Processin
g) ”.

FIG. 2 is a perspective view showing the main plane of the optical spectrum analyzer shown in this paper. In the figure, reference numeral 1 denotes a substrate, which is made of a ferroelectric substance such as lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or a semiconductor such as silcon (Si) or gallium arsenide (GaAs). The substrate 1 optical waveguide layer 2 corresponding to the top, for example, LiNbO ₃ substrate if T _i diffused light waveguide layer is formed, as further illustrated in FIG, planar lens 4,7, surface acoustic wave electrode 5 is provided . As the plane lenses 4 and 7,
Usually, a geodesic lens with depressions on the substrate is used, but there is a chirped grating lens using a non-periodic grating.

With the configuration of these optical elements, the light emitted from the light source 3 composed of a semiconductor laser or the like is converted into parallel light by the flat lens 4, further deflected by the surface acoustic wave 9 emitted from the electrode 5, and then the flat lens 7 again. The light is collected by and is projected onto the photodetector array 10. In this case, since the angle of the deflected light of the parallel light changes depending on the frequency value of the electric signal applied to the electrodes, the focused light by the plane lens 7 changes the position of the focusing point with respect to the frequency value. . Therefore, by providing the photodetector array 10 on the end face, the frequency component of the electric signal can be read in real time corresponding to the position of each photodetection array.

[Problems to be solved by the invention]

As described above, the optical spectrum analyzer described with reference to FIG. 2 corrects the difference in the diffraction angle depending on the frequency by using the condenser lens to change the position,
It is intended to directly read the frequency with the detector array 10. Therefore, the state of focusing of the light beam on the detector array is extremely important for detecting the frequency. That is, the diameter of the condensed light beam should be as small as possible, but this is limited because it is determined by the width of the parallel light and the focal length of the condenser lens. Further, it is desirable that distortion of the condensed beam is small, but this is influenced by the quality of the flat lenses 4 and 7. Usually, the aberration due to this plane lens becomes spherical aberration, which spreads the focused light beam.

When the velocity of the surface acoustic wave is V and the beam width of the parallel light is W, when a signal of a time shorter than the time t = W / V is input, a surface acoustic wave is generated when the signal of the parallel light beam is input. ,
The surface acoustic wave propagates in a part of the parallel light beam, but in the case of such a short pulse, the left and right distortions on the detector array are different astigmatisms or coma. This means that the beam shape of the focused light is different at the time when the surface acoustic wave collides with the parallel light beam and at the time when it becomes the parallel light beam, which makes it difficult to measure the frequency of the signal more accurately.

Therefore, even if the spherical aberration of the flat lens exists,
It is extremely effective if it is possible to realize a device that does not cause astigmatism and coma even when a short pulse is applied.

An object of the present invention is to provide a waveguide type optical spectrum analyzer which does not generate astigmatism and coma by a plane lens even when a short pulse of a time shorter than a time determined by a parallel light beam width and a surface acoustic wave velocity is applied. It is provided.

[Means for solving problems]

The guided wave type optical / acoustic spectrum analyzer of the present invention comprises a substrate body provided with an optical waveguide on one surface of a plate made of a ferroelectric material or a semiconductor; and converting a light beam incident from an end portion of the optical waveguide into parallel light. A first plane lens and a first side surface of the parallel light so as to diffract the parallel light.
Of the first surface acoustic wave electrode for radiating the surface acoustic wave of the first surface acoustic wave, and the first surface acoustic wave electrode on the opposite side of the parallel surface between the first surface acoustic wave electrode and the propagation direction of the first surface acoustic wave. A second surface acoustic wave that is parallel to the first surface acoustic wave electrode and is arranged at positions where the propagation times of the surface acoustic waves up to the central axis of the parallel light are equal to each other and a signal having the same frequency as that of the first surface acoustic wave electrode is applied. A second surface acoustic wave electrode, and a second plane lens for condensing parallel light Bragg-diffracted by one of the surface acoustic waves emitted from the first or second surface acoustic wave electrode. Optical circuits respectively provided on the optical waveguides; and a photodetector array for detecting the position of the light condensed by the second planar lens at the other end of the optical waveguides. And

〔Example〕

 The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the guided wave type optical / acoustic spectrum analyzer of the present invention. In this embodiment, an optical waveguide 2 corresponding to each substrate 1, for example, a Ti diffusion optical waveguide is formed if the substrate is lithium niobate (LiNbO ₃ ) on a substrate 1 made of a ferroelectric material, a semiconductor, glass or the like. . Two planar lenses 4 and 7 and surface acoustic wave electrodes 5 and 6 are provided on this optical waveguide. As described above, the planar lenses 4 and 7 are formed by forming depressions on the substrate 1 and forming a geodetic lens having an optical waveguide on the depressions, or a grating made of metal strips. There is a chirb grating lens arranged on the substrate so that

These optical elements are arranged as follows. That is, the light beam emitted from the light source 3 such as a semiconductor laser is incident on the waveguide 2 and propagates, and is further converted into parallel light by the plane lens 4. This parallel light travels straight without being deflected by the surface acoustic wave 8 emitted from the surface acoustic wave electrode 5 and deflected by the surface acoustic wave 9 emitted from the surface acoustic wave electrode 6. It is divided into one that is not deflected by the radiated surface acoustic wave 8 but goes straight and is deflected by the surface acoustic wave 9 radiated from the surface acoustic wave electrode 6, and these deflected parallel lights are respectively collected by the plane lens 7. The illuminated photodetector array 10 is reached. In this case, the surface acoustic wave electrodes 5 and 6 are arranged so as to be point-symmetric with respect to one point of the central axis of the parallel light beam, and the same input electric signal is applied.

In this case, when the same electric signal is input to the two surface acoustic wave electrodes, the parallel light is subjected to the same Bragg diffraction by the surface acoustic waves 8 and 9. Therefore, the second surface wave 8 is not subjected to the Bragg diffraction by the first surface acoustic wave 8.
The parallel light that is Bragg-diffracted by the surface acoustic wave 9 and the parallel light that is Bragg-diffracted by the first surface acoustic wave 8 and is not subjected to the Pragg diffraction by the second surface acoustic wave 9 are collected by the second plane lens. When it is illuminated, it will be focused at the same point. Therefore, on the photodetector array 10, these 2
Parallel light of various types is focused on the same point, and surface acoustic wave electrodes 5 and 6 are
It indicates the frequency of the electric signal input to.

〔The invention's effect〕

As described above, according to the present invention, the two surface acoustic wave electrodes are point-symmetric with respect to one point of the central axis of the parallel light beam converted by the plane lens. The surface acoustic wave signal propagating inside has the same propagation direction and the same signal in the light beam. Therefore, the electric signal of a time shorter than the time T = W / V whose frequency change is determined by the parallel light beam width W and the surface acoustic velocity V is the surface acoustic wave electrodes 5, 6
Is input, the surface acoustic wave shorter than the beam width of the parallel light is located at a symmetrical position with respect to the central axis of the parallel light and propagates in the opposite direction. Therefore, such 2
For parallel light that is Bragg-diffracted by surface acoustic waves of various types, astigmatism that occurs in the light beam other than Bragg diffraction,
It is possible to reduce the influence of asymmetrical aberration that occurs when the diffractive portion such as coma aberration is shorter than parallel light. That is, since the surface acoustic waves are always present in symmetrical positions, the optical aberration of the parallel light diffracted by Bragg has symmetry. Therefore, more accurate frequency measurement of the input applied signal becomes possible.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a perspective view showing an example of a conventional guided wave type optical / acoustic spectrum analyzer. 1 ... Substrate, 2 ... Optical waveguide, 3 ... Light source, 4,7 ... Planar lens, 5,6 ... Surface acoustic wave electrode, 8,9 ... Surface acoustic wave, 10 ... Photodetector array .

Claims (1)

[Claims] 1. A substrate body provided with an optical waveguide on one surface of a plate made of a ferroelectric material or a semiconductor; a first flat lens for converting a light beam incident from an end portion of the optical waveguide into parallel light; A first surface acoustic wave electrode that emits a first surface acoustic wave from the side surface of the parallel light so as to perform Bragg diffraction of the parallel light, and the first surface acoustic wave electrode on the opposite side of the parallel light with the parallel light interposed therebetween. At a position where a second surface acoustic wave parallel to the direction of propagation of the first surface acoustic wave is emitted in parallel and the propagation times of the surface acoustic waves up to the central axis of the parallel light are equal to each other. A second surface acoustic wave electrode which is arranged and to which a signal having the same frequency as that of the first surface acoustic wave electrode is applied, and one of the surface acoustic waves radiated from the first or second surface acoustic wave electrode. The second to collect parallel light that is Bragg diffracted by An optical circuit in which a plane lens is provided on each of the optical waveguides; and a photodetector array for detecting the position of the light condensed by the second plane lens at the other end of the optical waveguide. A guided-wave optical / acoustic spectrum analyzer characterized in that