JPS61215533A - Waveguide type optoacoustic spectrum analyzer - Google Patents

Abstract

PURPOSE:To obtain a waveguide type AO spectrum analyzer which removes undeflected light and has a high dynamic range by forming two plane lenses and a surface acoustic wave generating electrode on a plane light guide and forming a plane light guide end surface where undeflected light which is not deflected with a surface acoustic wave is transmitted and deflected light is reflected. CONSTITUTION:Light which is emitted by a light source 12 and has an angle of divergence is guided in the plane light guide 11 from its end surface, and the light 14 having the angle of divergence is converted by a plane lens 13 into collimated light 15. The collimated light 15 is deflected with a surface acoustic wave 19 generated by an electrode 18 for surface acoustic wave generation; deflected light 16a is generated and undeflected light 17 remains. The removal end surface 23 is formed at an angle theta1 to the optical axis of the undeflected light 17 that light is nearly transmitted. Therefore, the undeflected light 17 is removed, deflected light 16a is reflected totally, and deflected light 16b is converged by a plane lens 13 and detected by an array detector 22.

Description

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

[Prior art and its problems]

A waveguide type A0 spectrum analyzer that uses light diffraction by surface acoustic waves instantly analyzes the frequency of a signal.

A waveguide type AO spectrum analyzer converts light having a divergence angle incident from the end face of a thin film optical waveguide formed on the surface of a dielectric substrate or a Si substrate into collimated light using a plane lens, and converts this collimated light into a surface acoustic wave. Therefore, the wavelength of light (λ) is twice the plug angle θB (θ, = fλo/2nVs) determined by the excitation frequency (f) and propagation velocity (Vs) of the surface acoustic wave, and the refractive index (n) of the planar optical waveguide. The beam is deflected at an angle (2θ, ), and this deflected light is focused by a plane lens and detected by an array of photodetectors.

That is, as described above, since the deflection angle (20B) is proportional to the excitation frequency (f) of the surface acoustic wave, the focusing position of the deflected 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 important performances of this waveguide type AO spectrum analyzer is the dynamic range, and it is currently desired to improve it.

Currently, the waveguide type A○ spectrum analyzer is in the form of the Society of Optical Instrument Engineers (SPIE), Volume 321, 1982.
References, pages 134-140, and Force International Conference.

On Integrated Optics and Optical Fiber Communication Technical Digest, 1983, pp. 258-259, and according to this, two planar lenses are mainly used in a planar optical waveguide.

FIG. 4 is a plan view showing the principle.

Emitted from the light source 52 from the end face of the planar optical waveguide 51 provided on the surface of the dielectric substrate or the surface of the 81 substrate,
Light having a divergence angle is guided, and the light 56 that propagates while having a divergence angle is collimated by a plane lens 53.
Convert to 0.

The collimated light 60 has the above-mentioned deflection angle (2θB) due to the surface acoustic wave 64 generated from the surface acoustic wave generation electrode 62.
The light is deflected by the plane lens 54 and detected by the array photodetector 63. At this time, the intensity of the polarized light 58 is determined by the deflection efficiency of the collimated light 60 by the surface acoustic wave 64. Therefore, there remains unpolarized light 59 that is not deflected by the surface acoustic wave 64, and the unpolarized light 59 is also the same as the polarized light 58. The light is condensed by the plane lens 54 and reaches the output end face.

This unpolarized light 59 is not necessary for the waveguide type AO spectrum analyzer.

The light source 52 is made of, for example, a semiconductor laser, and the planar optical waveguide 51 is formed by thermally diffusing, for example, titanium (TI) on the substrate surface when the substrate is lithium niobate (LiNbO3), and when the substrate is Si, For example, arsenic sulfide (A S2
33) is formed by depositing it.

Further, the plane lenses 53 and 54 are made of Fresnel lenses, geodesic lenses, or the like.

According to the above-mentioned literature, the dynamic range of the waveguide type AO spectrum analyzer shown in Fig. 4 is 30 d.
The upper limit is B level. What limits this dynamic range is loss due to scattering and the like caused by light propagating through the planar optical waveguide 51. This loss mainly includes propagation loss and scattering loss at the plane lens 53 and 54 parts, and since it is difficult to eliminate these losses, the detection signal of the array photodetector 63 also detects a noise signal due to the loss. This limits the dynamic range. Furthermore, if the deflection efficiency is, for example, 10%, most of the loss due to scattering etc. occurring in the plane lens 54 is due to the non-polarized light 59 which is not necessary for the waveguide type AO spectrum analyzer.
This means that it is occurring more frequently. Therefore, in the waveguide type A○ spectrum analyzer with the structure shown in Fig. 4, the light source 5
2 to the planar optical waveguide 51 reaches the installation position of the array detector 63 without causing the scattering loss. Therefore, the detection signal of the array detector 63 includes the polarized light. Irrespective of the scattering losses generated from the light beam 58 and the unpolarized light 59, noise signals due to all the losses are also detected, making it difficult to improve the dynamic range.

[Purpose of the invention]

An object of the present invention is to provide a waveguide AO spectrum analyzer that removes unpolarized light that is not required by the waveguide AO spectrum analyzer and has a high dynamic range.

[Structure of the invention]

The present invention provides a waveguide type optical/acoustic spectrum analyzer in which a light beam propagating through a planar optical waveguide formed on the surface of a substrate is deflected by a surface acoustic wave, and the polarized light is detected by a photodetector. two planar lenses and a surface acoustic wave generating electrode are formed on the surface acoustic wave, and a planar optical waveguide end face that transmits unpolarized light that is not deflected by the surface acoustic wave and reflects polarized light is provided at the end of the planar optical waveguide.
It is characterized by having more than one formation.

〔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 a first embodiment of a waveguide optical/acoustic (AO) spectrum analyzer according to the present invention.

Light with a divergence angle emitted from a light source 12 is guided through the end face of a planar optical waveguide 11 provided on a dielectric surface or a Si substrate surface, and the light 14 with a divergence angle is collimated by a plane lens 13 into collimated light 15. is converted to When the substrate is LiNbO3, the planar optical waveguide 11 is formed by thermally diffusing Ti onto the surface of the substrate, and when the substrate is Si, it is formed by depositing, for example, A S2S. Further, the plane lenses 13 and 14 are made of Fresnel lenses, geodesic lenses, 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 16 a and the unpolarized light 17 have a plug angle determined by the wavelength (λo) of the light, the excitation frequency (f) and propagation velocity (Vs) of the surface acoustic wave, and the refractive index (n) of the planar optical waveguide. (θ, = λof/2nVs) and propagates at an angle (la) twice that of
The unpolarized light reaches an end face (hereinafter referred to as a removed end face) 23 of the planar optical waveguide from which the unpolarized light is removed, which was formed in 1.

The removal end surface 23 is formed so as to form an almost total reflection angle (θ, ) with respect to the optical axis of the polarized light 16a, and an angle (θl) that almost transmits the non-polarized light 17 with respect to the optical axis thereof. to 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 here, and the polarized light 16
a is totally reflected, and after entering the removed end face 23, it becomes the planar optical waveguide 1.
1, mainly the polarized light 16b propagates, and the polarized light 16b is focused by the plane lens 14 and detected by the array detector 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 array detector 22 does not face the optical axis of the collimated light 15, it is hardly detected by the array detector. Furthermore, since the scattering loss generated by the plane lens 14 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 will be reduced to one-tenth. Therefore, the noise signal detected by the array detector 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 T1 on 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 degrees, and the IJ and -star angles are about 24.4 degrees.

FIG. 2 shows the dependence of the energy reflectance at the removed end surface 23 of a light beam having P polarization with respect to the removed end surface 23 on the incident angle of the light beam on the removed end surface 23 under the above conditions. It is a characteristic diagram of the principle used by a wave type AO spectrum analyzer.

In FIG. 2, if the angle of incidence (θi) of the non-polarized light 17 on the removal end surface 23 is 26° or less, more than 90% of the non-polarized light 17 can be removed into the air. Furthermore, if the incident angle (θ, ) of the polarized light 16a is equal to or greater than the critical angle of about 27°, the polarized light 1
6a can be totally reflected.

As mentioned above, the angle formed by the polarized light 16a and the non-polarized light 17 (the angle (2θ, ) twice the plug angle) is 2θ8=λo f
/nVs, so if f=160MHz, 2θ, ′=, 1.06°. Therefore, in FIG. 1, for example, the removed end face 23 is formed to be inclined at 26 degrees with respect to the optical axis of the unpolarized light 17, and the excitation frequency of the surface acoustic wave is set to 1.
If the frequency is 60 MHz, the removed end face 23 of the polarized light 16a
The incident angle (θ, ) is 27.06°, and the polarized light is 16
The light a is totally reflected by the removed end face 23, focused by the plane lens 23, and detected by the array detector 22. Also at this time,
Similar effects can be obtained at any excitation frequency of surface acoustic waves of 160 MHz or higher, and the dynamic range is greatly improved. For example, if the deflection efficiency is 10%,
Assuming that the reflectance of the unpolarized light 17 at the removed end face 23 is 10%, the loss in the plane lens 14 is reduced to about one-fifth compared to the conventional structure, and the dynamic range is improved by about 7 dB. Furthermore, the angle of incidence of the unpolarized light 17 on the removed end surface 23 (
θ1) may be approximately 26° or less, and the end face 2 of the polarized light 16a to be removed is determined by the sum of θ1 and twice the plug angle (20B).
If the angle of incidence (θ, ) on
The excitation frequencies of the wavelength 9 surface acoustic waves of the light source used in the O spectrum analyzer may be other combinations.

Furthermore, the substrate forming the planar optical waveguide is not limited to the LiNbO3 substrate, but may be other dielectric substrates, such as L
It may be an iTaO3 substrate, a Si substrate, or any substrate that can form an end face that removes unpolarized light into the air and totally reflects polarized light.

As described above, by using the configuration of the waveguide type AO spectrum analyzer according to the present invention, it is possible to realize a waveguide type AO spectrum analyzer with improved dynamic range compared to the conventional structure.

FIG. 3 is a plan view of a second embodiment of the waveguide type AO spectrum analyzer according to the present invention. Planar optical waveguide 32
Then, light having a divergence angle emitted from the light source 31 is guided through its end face, and the light having a divergence angle 43 is converted into collimated light 35 by a plane lens 33 . The collimated light 35 is deflected by the surface acoustic wave 40 generated by the surface acoustic wave generating electrode 39, producing polarized light 36a and also leaving unpolarized light 37a.

At this time, the polarized light 36a and the unpolarized light 37a form an angle (2θB) twice the plug angle and propagate through the planar optical waveguide 32,
After removing unpolarized light from the end face of a planar optical waveguide.

38a (referred to as the removed end face) is reached. As described above, the removal end surface 38a removes 90% or more of the non-polarized light 37a into the air,
It is formed so that the polarized light 36a is totally reflected. unpolarized light 3
The remaining energy of 7a, slightly less than 10%, is reflected by the removal end face 38a, and the unpolarized light 37b, which is the reflected light of this unpolarized light 37H, is also unnecessary for the waveguide type Δ0 spectrum analyzer, and is not necessary for the dynamic It is also a source of noise signals resulting from losses that degrade the range.

Here, the polarized light 36b reflected by the removed end surface 38a
In order to prevent the non-polarized light 37b from interacting with the surface acoustic wave 40 again, the surface acoustic wave absorbing region 41 is coated with silicone rubber or the like.
will be established.

In order to further remove the non-polarized light 37b which is the source of the noise signal, the non-polarized light 37b and the polarized light 36b are made to enter the removal end surface 38b which has the same effect as the removal end surface 38a. As a result, 90% or more of the non-polarized light 37b is removed into the air, and by providing the removal end surfaces 38a and 38b, 99% or more of the non-polarized light 37a can be removed into the air. On the other hand, the polarized lights 36a and 36b are
Since the light is totally reflected at ga, 38b, there is almost no energy loss, and after being reflected at the removal end face 38a, the light is focused by the plane lens 34 and detected by the array detector 42.

Therefore, by using the waveguide type AO spectrum analyzer having the structure shown in FIG. 3, it is possible to realize a waveguide type AO spectrum analyzer having a high dynamic range. It can be easily inferred that the dynamic range improves as the number of unpolarized light removed planar optical waveguide end faces increases.

In the embodiments described above, the light beam incident on the end face has P polarization with respect to the end face, but it may also have S polarization. However, the energy reflectivity of the S-polarized light beam is theoretically greater than that of the P-polarized light beam at an incident angle below the critical angle. For example, corresponding to FIG. 2, when the incident angle is 25°, the energy reflectance of P-polarized light is about 0.01, and that of S-polarized light is about 0.45.

Therefore, in order to obtain a dynamic range comparable to that of a P-polarized light beam, it is necessary in principle to increase the number of planar optical waveguide end faces for removing non-polarized light.

〔Effect of the invention〕

As explained above, the present invention eliminates unpolarized light that is not deflected by surface acoustic waves into the air, which is the main source of noise signals that degrade the dynamic range of a waveguide type AO spectrum analyzer, and generates necessary signals. By using a waveguide type AO spectrum analyzer having an end face that totally reflects polarized light, a waveguide type AO spectrum analyzer having a high dynamic range can be realized.

[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, and FIG. 3 is a plan view of another embodiment of the present invention. FIG. 4 is a plan view of a conventional waveguide type A○ spectrum analyzer. 12, 31.52... Light source 1.3.14.33.34.53.54... Plane lens 11, 32.51... Planar optical waveguide 1
4, 43.56... Light with a divergence angle 15,
33.57...Incoming light 1g, 39.62...Surface acoustic wave generation electrodes 16a, 16b, 36a, 36b, 58-Deflected light 17, 37a, 37b, 59--- ---Unpolarized light 19, 40.64...Surface acoustic waves 22, 42
．． 63... Array photodetector 24, 41...
...Surface acoustic wave absorption regions 23, 38a, 38b...
...Unpolarized light removal planar optical waveguide end surface agent Patent attorney Yoshiyuki Iwasa 232 Non-polarized light removal surface leading liquid channel surface 13.14: Face surface f6a, 16b: Deflected light 17 :Unpolarized light Figure 1 Figure 2 333? 38a, 313b: Non-polarized 4e removed planar optical waveguide striped surface 36a, 36b: Polarized light 37α, 37b: Non-polarized light FIG.

Claims (1)

[Claims] (1) In a waveguide optical/acoustic spectrum analyzer in which a light beam propagating through a planar optical waveguide formed on the surface of a substrate is deflected by a surface acoustic wave and the polarized light is detected by a photodetector, A planar optical waveguide end face, which forms two planar lenses and a surface acoustic wave generating electrode, and which transmits unpolarized light that is not deflected by the surface acoustic wave and reflects polarized light, is provided at the end of the planar optical waveguide. A waveguide type optical/acoustic spectrum analyzer characterized by the above structure.