JPS62218876A - Waveguide type light-sound spectrum analyzer - Google Patents

Abstract

PURPOSE:To attempt a miniature construction of a higher efficiency dynamic range, by separating unpolarized light of a noise source and polarized light of a signal element in a plane waveguiding path and reflecting the polarized light by removing the unpolarized light from the end of the waveguiding path. CONSTITUTION:To a plane light waveguiding path 11 installed on a substrate surface, (a) light beam 24 provided wit a diverging angle and irradiated from a light source 12 from its end surface is guided and converted into a collimated light beam 17 by a flat-surface lens 13. This light beam 17 is polarized by an elastic surface wave 19 generated from an elastic surface wave generating electrode 18 and generates a polarized light beam 20 and further, an unpolarized light beam 21 remains. These beams 20 and 21 propagate by exciting frequency (f) of the wave 19 and propagation speed VS and double angle of the flag angle thetabeta determined by the equation I defined by the index of refraction (n) of the waveguiding path 11 and consequently, they are separated in the air. And, the beam 21 passes through a waveguiding path 31 and dispersed into the air and the beam 20 is reflected by a reflecting mirror 32 formed only by a portion irradiated by a polarized beam on the path 31 and later collected by a flat-surface lens 14 and it reaches a waveguiding path end 33 and subjected to detection for an array condition 22.

Description

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

Prior Art and its Problems] A waveguide type AO spectrum analyzer that utilizes the original deflection caused 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 an 8i substrate to a wavelength λ1 of the light and an excitation frequency f of the surface acoustic wave.

Using the propagation speed Vs and the plane waveguide refractive index n, the polarized light is deflected at an angle (20B) twice the plug angle θB determined by the following formula, and this deflected light is focused by a plane lens and then detected by an array photodetector. It is something to detect.

θn=s+n [f λ/2nV) That is, since this deflection angle 2θB is proportional to the excitation frequency f of the surface acoustic wave, the focusing position of the deflection source 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 the same dynamic range is desired.

The form of the waveguide type AO spectrum analyzer is described in the magazine "Society on Optical Instrument Engineer-x".
y of Photo-optical Instrument
mentEngineers; 8PIE) J, 32
Volume 1 (1982), pages 134-140, as well as the proceedings of ``Force International Conference on Integrated Ontics and Optical Fiber Communication'' 4
th International Conference
ce onIntegrated 0ptics an
d 0ptical FiberCommunica
tton) J Technical Digest (198
3rd year) published in the literature on pages 258 to 259, and according to these, the main method was to use two plane lenses in a plane optical waveguide.

Figure 4 is a plan view showing the principle of this human spectrum analyzer. A source 1 is attached to the planar optical waveguide 11 provided on the surface of the dielectric substrate or the surface of the Si substrate.
The light beam 24 emitted from the light source 2 and having nine angles is guided, and the light 24 that propagates while having nine angles is converted into collimated light 17 by the plane lens 13.

This collimated light 17 is deflected at the aforementioned deflection angle (20
B), the light is focused by the next plane lens 14, and detected by the array photodetector 22. At this time, the polarized light 20
The intensity of is determined by the deflection efficiency of the collimated light 17 by the surface acoustic wave 18. Therefore, the unpolarized light 21 that is not deflected by the surface acoustic wave 19 remains, and the unpolarized light 21 also becomes the polarized light 20.
Similarly, the light is condensed by the plane lens 14 and reaches the output end face. This unpolarized light 21 is not necessary for the waveguide type AO spectrum analyzer.

Note that the light source 12 is formed by, for example, a semiconductor laser, and the planar optical waveguide 11 is formed by thermally diffusing titanium (T) on the surface of the substrate when the substrate is made of lithium niobate LiNbO3, and when the substrate is made of Si. For example, the sulfide element Ag2
Formed by depositing 8 layers. Also, plane lenses 13.14
can be constructed using a Fresnel lens, a chirp grating lens, a geodesic lens, etc.

Another conventional example is the magazine “IEE-QE Journal on Quantum Electronics (IEE-QE
) J, QE-18 (1982), 1057~
According to a document on page 1059, there was a structure in which two reflection type chirped grating lenses were end face-coupled to the ends of a planar optical waveguide.

FIG. 5 is a plan view showing the principle of this AO spectrum analyzer. Planar optical waveguide 11 diverging from light beam 12
The light 24 having a divergence angle, which is input waveguide light to
After being deflected by the surface acoustic wave 19 generated by the
The light is focused by At this time, the unpolarized light 21 that is not deflected by the surface acoustic wave 19 is also focused by the chirped grating lens 41 in the same way as the polarized light 20 and reaches the output end face where the array photodetector 22 is installed. This unpolarized light 21 is of a waveguide type A, similar to the conventional example shown in FIG.
This is not necessary for the O spectrum analyzer.

[Problem that the invention seeks to solve]

According to the above-mentioned literature, the dynamic range of such a conventional waveguide type AO spectrum analyzer is 30 d.
B level is the limit. In the structures shown in FIGS. 4 and 5, this dynamic range is limited by losses due to scattering and the like caused by light propagating through the planar optical waveguide vI&ll. This loss mainly includes propagation loss and the plane lens 13.
．． 14, or scattering and diffraction losses in the chirped grating lens 40.41,
Since it is difficult to eliminate these losses, noise signals due to the losses are also detected in the detection signal of the array photodetector 22, and the dynamic range is limited. Furthermore, if the deflection efficiency is, for example, 10%, then the plane lens 14.
Alternatively, most of the loss due to scattering etc. occurring in the chirped grating lens 41 is generated from the unpolarized light 21 which is not necessary for the waveguide type AO spectrum analyzer.

Therefore, in the waveguide type AO spectrum analyzer with the conventional structure, all of the light guided from the light @ 12 to the planar optical waveguide 11 reaches the installation position tilt of the play-shaped detector 22 while generating the scattering loss. Therefore, in the detection signal of the array detector 22, regardless of the scattering loss generated from the polarized light 20 and the non-polarized light 21, noise signals are also detected due to all the losses, making it difficult to improve the dynamic range. be.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems, remove unpolarized light that is not needed in a spectrum analyzer, and provide a waveguide type AO spectrum analyzer that has a high dynamic range.

[Means to solve the problem]

The configuration of the waveguide type optical/acoustic spectrum analyzer of the present invention includes a light source provided at one end of a planar optical waveguide on the surface of a substrate, and a first light source provided on each of the planar optical waveguides. Second
a flat lens and a surface acoustic wave generating electrode, an array photodetector provided at an end of the planar optical waveguide, and a reflecting mirror provided at the other end of the planar optical waveguide or on the planar optical waveguide. , the original beam incident on the planar optical waveguide from the light source is made into parallel light by the first plane lens, and the parallel light is deflected by a surface acoustic wave from the electrode,
After this polarized light and unpolarized light are spatially separated by the optical waveguide, the unpolarized light is transmitted through the planar optical waveguide on the side where the reflecting mirror is provided, and the polarized light is totally reflected by the reflecting mirror. After that, the light is focused by the second plane lens,
The present invention is characterized in that the shift amount of the focused polarized light is detected by the photodetector to obtain the frequency spectrum of the surface acoustic wave.

〔Example〕

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

Figure 1 shows the AO spectrum analyzer according to the present invention.
! FIG. 1 is a plan view of the first embodiment. Light 24 having a divergence angle emitted from the light source 12 is guided through the end face of the planar optical waveguide 11 provided on the surface of the substrate, and the light 24 is guided through the planar optical waveguide 11 provided on the surface of the substrate.
It is converted into collimated light 17 by. When the substrate is LiNbO3, this planar waveguide 11 is formed by thermally diffusing, for example, Ti onto the substrate surface, and when the substrate is Si, for example, StO is used as a buffer layer to form the planar waveguide 11.
It is formed by depositing 3. Moreover, the plane lens 13.
The lens 14 can be constructed from a Fresnel lens, a geodesic lens, a chirp grating lens, or the like.

The collimated light 17 is deflected by the surface acoustic wave 19 generated by the surface acoustic wave generation electrode 18, producing polarized light 20 and also leaving unpolarized light 21 that is not deflected. This unpolarized light 21 is not necessary for the waveguide type AO spectrum analyzer, and as described above, the dynamic range of the waveguide type AO spectrum analyzer is limited by the loss generated from the unpolarized light 21.

At this time, the polarized light 20 and the unpolarized light 21 form an angle (2' o!
1), the polarized light 20 and the unpolarized light 21, which are collimated lights, are spatially separated within the planar optical waveguide 11.

θ, = s1n (λo −//2 n v s ) After that, the unpolarized light 21 is transmitted through the planar optical waveguide end 31 and removed into the air, and the polarized light 20 is transferred to the portion where the polarized light enters the planar optical waveguide end 31. After being reflected by a reflecting mirror 32 formed at the center, the light is focused by a plane lens 14 and sent to the end 3 of the plane optical waveguide.
3 and is detected by the array detector 22.

Therefore, according to this structure, compared to the conventional structure, unpolarized light 2
Since the scattering loss and propagation loss occurring in the plane lens 14 due to the structure of the present invention are reduced, the noise signal detected by the play-shaped detector 22 is significantly reduced compared to the conventional structure, and the dynamic range is improved. For example, if the deflection efficiency is 10% and the scattering loss of the plane lenses 13 and 14 is the same, the loss will be at least half or less.

This reflecting mirror 32 is formed, for example, by coating the planar optical waveguide end 32 with a metal film such as Aj, and since the reflectance theoretically reaches nearly 100%, the reflecting mirror 32
It is clear that the loss due to scattering etc. at 2 is almost negligible, and the dynamic range is the same as that of the conventional structure shown in FIG.

Further, the transmittance of the unpolarized light 21 into the air at the planar optical waveguide end 31 is determined by the refractive index of the planar optical waveguide 11 when the unpolarized light 21 is incident perpendicularly, for example, the planar optical waveguide 11 t-LiNb
In the case of a Ti diffused waveguide formed on an O3 substrate, the transmittance is about 85%, and this can be further increased by applying an anti-reflection coating to the portion of the planar optical waveguide end 31 where unpolarized light is incident.

In the embodiment shown in FIG. 1, it is clear that the polarized light does not need to be reflected once but can be reflected several times to obtain the same effect.

Here, if the light source is a semiconductor laser beam with a wavelength of 0.89μ, Ti is thermally diffused into the LiNbO3 substrate of the planar optical waveguide 11, and the excitation frequency of the surface acoustic wave is 500MH2.
2 of the plug angle, which is the angle formed by the polarized light 20 and the unpolarized light 21
The double angle (2 oa) is approximately 2.6°.

FIG. 2 shows that under such conditions, the collimated light 17 is deflected, and the polarized light 20 and the unpolarized light 21 are spatially separated by a distance t (FIG. 1) for the beam @d of the collimated light 17. It is a characteristic diagram showing the relationship. This figure shows the distance d at which the diffracted waves due to Gaussian wave propagation of the collimated light 17 are separated by considering 9, but in a waveguide type AO spectrum analyzer, the width of the surface acoustic wave 19 is about 0.5 y. In addition, the beam width d of the collimated light 17 can be controlled by selecting the focal length/l of the plane lens 13, so a light beam width of about 100 μm is sufficient, which is shorter than the conventional type. A sufficient dynamic range can be obtained without increasing the size of the device.

FIG. 3 is a plan view of an embodiment of the arithmetic 2 according to the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that a reflecting mirror 32 is provided within the planar optical waveguide 11. In this case, the reflecting mirror 32 is formed by, for example, etching a structure in the planar optical waveguide 11 by reactive ion etching or ion etching, and coating the surface on which the polarized light 20 is incident with a metal film such as At. Therefore, in this case, there is a feature that the direction in which the polarized light 200 is reflected can be arbitrarily selected.

Also, these I! The structure of the embodiment shown in FIGS. 1 and 3 is as follows.
It is clear that the device can be made smaller compared to the conventional structure shown in the figure, and also compared to the structure shown in FIG. Miniaturization is possible.

〔Effect of the invention〕

As explained above, the present invention spatially separates unpolarized light that is not deflected by surface acoustic waves, which is the main source of noise signals that degrade the dynamic range, and polarized light, which is a signal component, within a planar optical waveguide. By separating the unpolarized light from the end of the planar optical waveguide and polarizing it (by detecting it after reflecting the Ei1 component), it is possible to miniaturize the device and obtain a high dynamic range. There is. In addition, when a reflective mirror for polarized light is provided in the planar optical waveguide,
Since the optical axis of the polarized light can be selected, the selectivity can be further improved.

[Brief explanation of drawings]

Figure 1 is a plan view of one embodiment of the present invention, Figure 2 is a characteristic diagram of the principle used by the waveguide type AO spectrum analyzer according to the present invention, and Figure 3 is a plan view of another embodiment of the present invention. 4 and 5 are plan views of two examples of conventional waveguide type AO spectrum analyzers. 11...Plane optical waveguide, 12...Light source, 13°14...Plane lens, 17...
・Collimated light, 18...Surface acoustic wave generating electrode, 19...Surface acoustic wave, 20...Polarized light, 21...Unpolarized light, 22 ...Array detector, 40.41...Chirped grating lens, 32...Reflector, 31...
...Planar optical waveguide end that transmits unpolarized light, 33...
...The end of the planar optical waveguide where the arrayed detector is installed.尤Hi“-mu1sd (frIyn) Mine Z

Claims (1)

[Claims] a light source provided at one end of the planar optical waveguide on the surface of the substrate; first and second planar lenses and surface acoustic wave generation electrodes provided respectively on the planar optical waveguide; and a light source provided at the end of the planar optical waveguide. It includes an arrayed photodetector and a reflecting mirror provided at the other end of the planar optical waveguide or on the planar optical waveguide, and the light beam incident on the planar optical waveguide from the light source is reflected by the first planar lens. After the parallel light is deflected by a surface acoustic wave from the electrode, and the polarized light and unpolarized light are spatially separated by the optical waveguide, the non-polarized light is provided with the reflecting mirror. The polarized light is transmitted through the end of the planar optical waveguide on the side where the polarized light is transmitted, and after being totally reflected by the reflecting mirror, the light is focused by the second planar lens, and the shift amount of the focused polarized light is detected by the photodetector. A waveguide type optical/acoustic spectrum analyzer characterized in that the frequency spectrum of the surface acoustic wave is obtained by detecting the surface acoustic wave.