JPS63229377A - Waveguide type light/sound spectrum analyzer - Google Patents

Abstract

PURPOSE:To achieve a higher dynamic range, by providing a wavelength filter on a light waveguide before non-deflected light is removed therefrom. CONSTITUTION:An unnecessary wavelength component of a light beam which is incident into a light waveguide 11 and a removal end face 23 from a light source 12 is removed with a wavelength filter 25 using a diffraction grating. As the filter 25 transmits a specified wavelength component, a wavelength component of light propagating after passing through the filter 25 is limited to that used for a waveguide type AO spectrum analyzer. Therefore, the wavelength of light incident into the end face 23 gives a single wavelength, which allows the removal of non-deflected light 17 into the air from a light waveguide 11 eliminating non-deflected light which may be reflected on the end face 23. Deflected light 16a also gives a single wavelength thereby eliminating the need for detecting errors of intensity spectrum and an error signal in a detection signal of an array photodetector 22. This can realize a higher dynamic range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a waveguide type optical/acoustic (hereinafter referred to as waveguide type AO) spectrum analyzer.

[Conventional technology]

A waveguide type AO spectrum analyzer that utilizes the deflection of light by surface acoustic waves instantly analyzes the frequency of a signal.

This waveguide type AO spectrum analyzer uses a surface acoustic wave to convert collimated light propagating through a planar optical waveguide formed on the surface of a dielectric substrate or a semiconductor substrate such as Si to Speed V3. The plug angle θ8 is determined by the following formula using the refractive index n of the planar optical waveguide.
The polarized light is deflected at an angle twice as large as (20B), and this deflected light is focused by a plane lens and detected by an array of photodetectors.

θ, = sin-' (fλ/2nVs) That is, this deflection angle 203 is proportional to the excitation frequency f of the surface acoustic wave, so the focusing position of the polarized light also differs depending on the difference in the excitation frequency f of the surface acoustic wave. .

Therefore, by detecting the difference in the focusing position of this polarized light using an array of photodetectors, it is possible to analyze the frequency components of the signal applied to the surface acoustic wave.

One of the performances of this waveguide type AO spectrum analyzer is the dynamic range, and in order to improve this dynamic range, according to the specification of Japanese Patent Application No. 60-54645, unpolarized light is collimated with a Fourier lens. A structure has been invented in which the light is removed from the optical waveguide between the conversion lenses.

FIG. 2 is a plan view showing the structure of the waveguide type AO spectrum analyzer described above.

Light having a divergence angle emitted from a light source 12 is guided through the end face of the planar optical waveguide 11 provided on the surface of a dielectric material or the surface of a semiconductor substrate such as Si, and the light having a divergence angle 1
4 is converted into collimated light 15 by a plane lens (collimating lens) 13. The planar optical waveguide 11 has a substrate made of LiNb0. In this case, Ti is formed by thermally diffusing onto the substrate surface, and when the substrate is Si, for example, As25. , is formed by depositing.

Further, the plane lenses 13 and 26 are made of a Fresnel lens, a geodesic lens, or the like.

The collimated light 15 is deflected by the surface acoustic wave 19 generated by the surface acoustic wave generation electrode 18, producing polarized light 16a and also leaving unpolarized light 17. This unpolarized light 17 is not necessary for the waveguide type AO spectrum analyzer.

At this time, the polarized light 16a and the unpolarized light 17 have a wavelength (
λ), surface acoustic wave excitation frequency (f) and propagation velocity (V
, ) and the refractive index (n) of the planar optical waveguide.
The unpolarized light is propagated at an angle (20B) twice that of reach

The removal end surface 23 forms an almost total reflection angle (θd) with respect to the optical axis of the polarized light 16a, and an angle (θ, ) that almost transmits the unpolarized light 17 with respect to the optical axis thereof. Form. In this case, the removed end surface 23 is made into a mirror surface by polishing or the like. Therefore, the unpolarized light 17 is removed to the outside, and the polarized light 16a
is totally reflected, and after entering the removed end face 23, the plane optical waveguide 11
Mainly, the polarized light 16b propagates, and the polarized light 16b is collected by a plane lens (Fourier transform lens) 26 and detected by an array photodetector 22.

Therefore, the scattering loss that occurs in the plane lens 13 and the propagation loss that occurs until the light reaches the removal end surface 23 are as follows:
Since the arrayed photodetector 22 does not face the optical axis of the collimated light 15, the collimated light 15 is hardly detected by the arrayed photodetector. Further, since the scattering loss generated by the plane lens 26 is caused only by the polarized light, it is significantly reduced compared to the conventional structure.

For example, if the deflection efficiency is 10%, the loss is 1/10
decreases to Therefore, the noise signal detected by the arrayed photodetector 22 is significantly reduced compared to the conventional structure, and the dynamic range is improved.

Here, in order to prevent the totally reflected polarized light 16b from interacting with the surface acoustic waves again, a surface acoustic wave absorbing region 24 is provided by applying silicone rubber or the like.

Assuming that the light source 12 is a semiconductor laser with a wavelength of 0.89 μm and the planar optical waveguide 11 is formed by thermally diffusing Ti onto a LiNbO3 substrate, the refractive index of the planar optical waveguide 11 is approximately 2.
．． It is 2. At this time, the critical angle at the removed end face 23 is about 27°, and the Brewster's angle is about 24.4°.

[Problem that the invention seeks to solve]

In the waveguide type AO spectrum analyzer shown in FIG. 2, light propagating through an optical waveguide, that is, light having a divergence angle 14. The wavelength dispersion of the collimated light 15 and the like is an important factor for improving the dynamic range and frequency analysis operation.

In order to improve the dynamic range, when light of various wavelengths propagates through the optical waveguide 11, the effective refractive index differs for each wavelength, and therefore the transmittance of the unpolarized light 17 at the removal end face 23 differs for each wavelength. Unpolarized light obtained at wavelength 17
The transmittance becomes smaller than the transmittance of the unpolarized light 17, and the reflected component of the unpolarized light 17 reflected by the removed end face 23 increases accordingly, and the degree of improvement in the dynamic range deteriorates.

Regarding the operation of frequency analysis, since the reflectance of the removed end face of the polarized light 16a differs for each wavelength for the same reason as described above, the error in the intensity spectrum obtained by the arrayed light beam emitter 22 increases, and The reflection angle also differs because the Booth-Hensen shift at the removed end face 23 differs for each wavelength, and the polarized light 16b of each wavelength component is focused by a plane lens (Fourier transform lens) 26 and converged on the play-shaped photodetector 22. The difference is that malfunctions occur in the frequency analysis operation.

Factors causing light of various wavelengths to propagate in the optical waveguide 11 include wavelength dispersion of spontaneous emission components and multi-wavelength oscillation in stimulated emission components when a semiconductor laser is used as the light source 12.

An object of the present invention is to provide a waveguide type optical/acoustic spectrum analyzer having a structure in which unpolarized light is removed from an optical waveguide between a collimating lens and a Fourier transform lens, in which the light incident on the optical waveguide has wavelength dispersion. Another object of the present invention is to provide a waveguide optical/acoustic spectrum analyzer that can improve the dynamic range and perform accurate frequency analysis without deteriorating the dynamic range improvement or causing malfunctions in frequency analysis.

[Means for solving problems]

The present invention relates to a waveguide type optical/acoustic spectrum analyzer having a structure in which unpolarized light is removed from an optical waveguide between a collimating lens and a Fourier transform lens. It is characterized by being equipped with a wavelength filter.

[Effect]

As mentioned above, when various wavelength components coexist in the light beam that enters the optical waveguide from the light source and enters the removal end face, the improvement of the dynamic range deteriorates and the frequency analysis deteriorates compared to the propagation of a single wavelength component. A malfunction will occur. Therefore, the above-mentioned problem can be solved by removing unnecessary wavelength components before the light beam reaches the removal end face.

Since the wavelength filter has the function of transmitting only specific wavelength components, the wavelength components of the light that propagates after passing through the wavelength filter are limited to those used in the waveguide type AO spectrum analyzer. Therefore, the wavelength of the light incident on the removal end face becomes a single wavelength, and removal of unpolarized light from the optical waveguide into the air is performed as intended. As a result, no unpolarized light is reflected at the removed end face, and the deterioration in dynamic range improvement disappears.

Further, since the polarized light reflected by the removed end face also has a single wavelength, errors in the intensity spectrum and detection of false signals are eliminated in the detection signals of the arrayed photodetector.

〔Example〕

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

FIG. 1 is a plan view of an embodiment of a waveguide type AO spectrum analyzer according to the present invention. In the waveguide type AO spectrum analyzer shown in FIG. A wavelength filter 25 is installed between them, and the other configuration is the same as that of the waveguide type AO spectrum analyzer shown in FIG. Therefore, in FIG. 1, the same elements as in FIG. 2 are designated by the same numbers. Note that the diffraction grating as the wavelength filter 25 is
A grating is formed with a pitch of 1/2, 1/4, 1/8, etc. of the wavelength to be used, and only the wavelength to be used is extracted by utilizing Bragg reflection within the diffraction grating. This diffraction grating can be fabricated using an ion beam method or a reactive ion beam method in the optical waveguide 11.

There are a method of forming a groove by digging a groove using an etching method such as a reactive ion method, and a method of forming a diffraction grating by depositing it on the optical waveguide 11.

According to this embodiment, if there are various wavelength components in the light beam that enters the optical waveguide 11 from the light source 12 and enters the removal end face 23, the improvement in the dynamic range deteriorates compared to the propagation of a single wavelength component. And malfunction of frequency analysis occurs. Therefore, if unnecessary wavelength components are removed by the wavelength filter 25 before the light beam reaches the removal end face 23, the above-mentioned problem can be solved. In this embodiment, a diffraction grating is used as the wavelength filter 25. Since the wavelength filter 25 has the function of transmitting only a specific wavelength component, the wavelength component of the light that propagates after passing through the wavelength filter 25 is transmitted through the waveguide type AO.
Limited to those used with spectrum analyzers.

Therefore, the wavelength of the light incident on the removal end face 23 becomes a single wavelength, and the removal of the unpolarized light 17 from the optical waveguide 11 into the air is performed as intended. Therefore, no unpolarized light is reflected by the removed end face 23, and the deterioration of the dynamic range improvement disappears.

Further, since the polarized light 16a also has a single wavelength, errors in the intensity spectrum and detection of false signals are eliminated in the detection signals of the arrayed photodetector 22.

In the above embodiment, the wavelength filter 25 is installed between the collimating lens 13 and the position where the collimated light 15 is deflected by the surface acoustic wave 19. It is preferable to use a portion other than , and any part on the optical waveguide between the light source 12 and the removed end surface 23 may be used.

Furthermore, the wavelength filter 25 is not limited to a diffraction grating, and may be any type of filter that has wavelength selectivity, such as the formation of an etalon on an optical waveguide, or the use of a material that has wavelength selectivity.

〔Effect of the invention〕

As explained above, the present invention provides a waveguide type optical/acoustic structure that uses surface acoustic waves to remove unpolarized light from an optical waveguide into the air between a collimating lens and a Fourier transform lens in order to improve the dynamic range. In a spectrum analyzer, when various wavelength components coexist in the optical beam propagating through an optical waveguide, a waveguide optical/acoustic spectrum analyzer is required, which can cause deterioration in dynamic range improvement and malfunction in frequency analysis. By installing a wavelength filter in the optical waveguide that removes unnecessary wavelength components and extracts only the necessary wavelengths, it is possible to improve the dynamic range by removing unpolarized light as desired, and
Normal operation of steady frequency analysis can be realized.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the present invention, and FIG. 2 is a plan view of a conventional waveguide type AO spectrum analyzer. 11... Optical waveguide 12... Light source 13.26... Plane lens 14... Light with a divergence angle 15... Collimated light 16a, 16b ・Polarized light 17. ...Unpolarized light 18 ...Surface acoustic wave generation electrode 19 ...Surface acoustic wave 22 ...Array photodetector 23 ...Unpolarized light removal plane Optical waveguide end face 24...
...Surface acoustic wave absorption region 25...Wavelength filter

Claims (1)

[Claims] (1) In a waveguide type optical/acoustic spectrum analyzer that has a structure in which unpolarized light is removed from the optical waveguide between a collimating lens and a Fourier transform lens, the unpolarized light is removed from the optical waveguide before being removed from the optical waveguide. A waveguide type optical/acoustic spectrum analyzer characterized by being equipped with a wavelength filter.