JPH0633423Y2 - Black cell - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a Bragg cell used for performing frequency analysis by utilizing the interaction between elastic waves and light.

[Conventional technology]

Figure 4 shows, for example, Literature: 1983, Force International Conference on Integrated Optics and Optical Fiber Communication, Technical Digest 29C5-5.
Pages 40-41 (1983 Fourth International Conference
on Integrated Optics and Optical fiber Com
munication, Technical Digest 29C5-5, pp.40-41)
FIG. 3 shows a conventional Bragg cell of this type shown in FIG.

In the figure, 1 is a piezoelectric substrate, and 2 is a comb-shaped electrode provided on the surface of the piezoelectric substrate 1. 3 is a comb-shaped positive electrode,
Reference numeral 4 is a comb-shaped ground electrode provided so that the comb teeth are parallel to the comb teeth of the positive electrode 3, and 5 is a bent shape provided adjacent to the comb teeth of the positive electrode 3 and the ground electrode 4. It is an intermediate potential electrode (hereinafter, referred to as a dog leg electrode), and the interdigital electrode 2 is composed of these. Reference numeral 6 is an AC signal source connected between the positive electrode 3 and the ground electrode 4, and 7 is an elastic wave. In the conventional Bragg cell of this type, the width w ₁ of the dove-leg electrode 5 of the interdigital electrode 2 and the positive electrode 3 is set side by side.
Was set to be equal to the width w ₁ of the doggleg electrode 5 and the ground electrode 4. 8 is a photoconductive waveguide, 9 is light propagating in the photoconductive waveguide 8, 9A is incident light, 9B is diffracted light thereof, and 9C is
Is the non-diffracted light.

Next, the operation will be described. The characteristics of the interdigital electrodes 2 using the dough-legged electrodes 5 having a bent shape are the same when the electrode arrangement intervals are all the same.
EE transaction. Mt-22, No.8, 19
1974, pages 763-768 (IEEE Trans.MTT-22, No.8,1974, pp7
63-768). That is, the electric signal of the signal source 6 causes a potential difference between the positive electrode 3 and the ground electrode 4. At this time, the dogleg electrode 5 is connected to the positive electrode 3
The input voltage is divided between the side adjacent part and the ground electrode 4 side adjacent part. The division ratio at this time is determined by the width of each side, and the amplitude of the elastic wave 7 excited in each side is
It is proportional to the voltage applied to each part. When the electrode arrangement intervals are all the same, the phases of the elastic waves 7 excited at the respective side portions are the same regardless of the ratio between the side width of the positive electrode 3 side and the side width of the ground electrode 4 side. This is because the arrangement intervals of the electrodes are the same for all the electrodes, and therefore the applied voltage phases are the same in both the side electrode on the static electrode 3 side and the side electrode on the ground electrode 4 side.

Now, when the interdigital transducer 2 is used for a Bragg cell, as shown in FIG.
In order to excite, the electrode array interval is changed and used. As a result, when focusing on one dogleg electrode 5, two gaps between two positive electrodes 3 adjacent to each other are two gaps between two ground electrodes 4 adjacent to the same dogleg electrode 5. The intervals are not partly equal, and the positive electrode 3 side and the ground electrode 4 side are asymmetrical. Therefore, the elastic wave 7 excited between the side portion on the positive electrode 3 side and the side portion on the ground electrode 4 side has an amplitude difference and a phase difference.

By the way, a part of the light 9 propagating in the optical waveguide 8 is diffracted by the acousto-optic interaction with the elastic wave 7 and propagates in a direction different from the direction of the incident light 9A. Since the angle formed by the direction of the diffracted light 9B and the direction of the non-diffracted light 9C depends on the frequency of the elastic wave 7, by knowing the angle formed by the direction of the diffracted light 9B and the direction of the non-diffracted light 9C, The frequency of the signal source 6 can be known.

[Problems to be solved by the invention]

Since the conventional Bragg cell is configured as described above, the elastic wave 7 excited by the interdigital electrode 2 has an amplitude difference and a phase difference depending on the location.

The amplitude of the diffracted light at the time of diffraction (corresponding to the overlapping portion of the elastic wave 7 and the light 9 in FIG. 4) depends on the amplitude of the elastic wave 7. The phase of the diffracted light depends on the phase of the elastic wave 7.

The diffracted light 9B is expressed as the vector sum of the lights diffracted at the overlapping portion. The phase of the elastic wave 7 excited at the intersection width w ₁ and the phase of the elastic wave 7 excited at the intersection width w ₂
If the phase of the light is different, some of the diffracted lights have different phases. For example, some are in opposite phase. Then, the intensity of the diffracted light 9B, which is the vector sum thereof, becomes smaller than that when the elastic wave 7 has a uniform amplitude and phase. As a result, there was a problem that the signal-to-noise ratio during frequency analysis deteriorated.

The present invention has been made to solve the above problems, and reduces the amplitude difference and phase difference of elastic waves excited between the positive electrode side adjoining portion and the ground electrode side adjoining portion of the doggreg electrode, The purpose is to obtain a larger diffracted light intensity and obtain a Bragg cell having a larger signal to noise ratio.

[Means for solving problems]

The Bragg cell according to this invention, the hotel's width w ₁ of the positive electrode side features of Dotsugureggu electrode, by forming the interdigital electrode and to the hotel's width w ₂ of the ground-electrode-site portion is different, larger diffraction The light intensity is obtained so as to have a larger signal-to-noise ratio.

[Action]

In the Bragg cell according to the present invention, the adjoining width w _{1 of the} adjoining portion of the positive electrode side of the Dot Greg electrode and the adjoining width w ₂ of the adjoining portion of the ground electrode side are made different, so that the adjoining portion on the positive electrode side and the adjoining portion on the ground electrode side are different. The fact that it is possible to reduce the amplitude difference and the phase difference of the elastic wave excited by is utilized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, the same reference numerals as those in FIG. 4 are the same as those in the conventional example. 2A is a comb-shaped electrode provided on the surface of the piezoelectric substrate 1, 3A is its positive electrode, and 4A is also a ground electrode. , 5A
Is also a Douglegg electrode and 7A is an elastic wave. The interdigital transducer 2A is composed of the components indicated by reference numerals 3A to 5A, and its shape and arrangement are similar to those of the conventional example. However, the interdigital transducer 2A is replaced with the dogleg electrode 5A.
Ground features width w ₁ of the hotel portion of the electrode 4A, and features a width w ₂ of the hotel of the Dotsugureggu electrode 5A and the positive electrode 2A are configured differently with.

Next, the operation of this embodiment will be described. As in the conventional case, the electric signal of the signal source 6 causes a potential difference between the positive electrode 3A and the ground electrode 4A. At this time, the dogleg electrode
The 5A divides the input voltage between the side portion with the positive electrode 3A and the side portion with the ground electrode 4A. In the interdigital electrode 2A with the electrode arrangement interval changed, the elastic wave excited at the side of the positive electrode 3A
Although an amplitude difference and a phase difference occur between 7A and the elastic wave 7A excited at the side of the ground electrode 4A, the amplitude difference and the phase difference are, as described above, the side widths w ₁ and w _2. It can be adjusted by changing the ratio of. That is, by adjusting the adjoining width w ₁ .w ₂ , it is possible to reduce the amplitude difference and phase difference of the elastic waves 7A excited in each adjoining part.
As a result, the amplitude difference and the phase difference of the light 9B diffracted by the elastic wave 7A excited in each juxtaposed part are similarly reduced, and a larger intensity of the diffracted light 9B is obtained, and a larger signal-to-noise ratio is obtained. Obtainable.

In FIG. 2 (a), 7a and 7b are part of elastic waves 7A respectively generated from one end of the interdigital transducer 2A toward the non-light incident side, corresponding to the combined widths w ₁ and w ₂ , 7c, 7d is the combined width w ₁ , w ₂
Corresponding to each of the other portions of the elastic wave generated from the other end of the interdigital electrode 7A toward the light incident side, 10 is one dogleg leg electrode 5A and one dogleg leg electrode adjoining portion showing its adjoining portion, 11 is Input power supply terminal. In FIG. 2 (b), 12 to 15 are acoustic terminals, A _{1 to} A ₄ , B _{1 to} B ₄ are impedance values, C ₁ and C ₂ are capacitance values, and 1: 1 is a transformer conversion ratio. It is a thing. The 1-dogleg-electrode-attached portion 10 shown in FIG. 2 (a) is replaced by an equivalent circuit as shown in FIG. 2 (b), and the equivalent circuit is cascaded to generate elastic wave 7A excitation of the interdigital transducer 2A. Find characteristics. Each element value of the special price circuit shown in FIG. 2 (b) is determined by the piezoelectric substrate 1 to be used, the electrode arrangement interval, and the width of the side by side, and the relationship between them is described in “Surface Acoustic Wave Engineering” edited by The Institute of Electronics, Communication and Communication, p. .63
In detail. The correspondence between each terminal in FIG. 2 (b) and the elastic wave in FIG. 2 (a) is
12a and 12b are elastic waves 7a, terminals 13a and 13b are elastic waves 7b, terminals 14a and 14
b corresponds to the elastic wave 7c, and terminals 15a and 15b correspond to the elastic wave 7d, respectively. According to the conventional shape, due to the difference between A ₁ , A ₃ , B ₁ , B ₃ and A ₂ , A ₄ , B ₂ , B ₄ , between the elastic waves 7a, 7b,
There was a phase difference and an amplitude difference between the elastic waves 7c and 7d. However, the capacitance value _{C 1} which is proportional to the features width _{w 1, w 2, C 2}
By adjusting the value of, the phase difference and the amplitude difference can be reduced.

According to “Surface acoustic wave engineering”, the electrical equivalent impedance of the lower equivalent circuit in FIG. It is represented by. The electrical equivalent impedance of the upper equivalent circuit is It is represented by. Where Z ₁ and Z ₂ are acoustic impedances,
ω ₀ is the central angular frequency, K ² is the electromechanical coupling coefficient, and h is the piezoelectric constant.

For each capacitance value in the equivalent circuit depends on the features width w _1, w _2, by changing the ratio of the hotel's width w _1, w _2, the equivalent circuit the capacitance value is also changed, as a result, the terminal ( 12a, 12
b), (13a, 13b), (14a, 14b), (15a, 15b) change the amplitude and phase of the elastic wave. Therefore, w ₁ and w
By varying the ratio with ₂ variously, the electrical equivalent impedances R ₁ and R ₂ are calculated, and if the phase difference and the amplitude difference are tested based on the calculation results, w ₁ and w that reduce the phase difference and the amplitude difference are obtained. The ratio with ₂ is obtained.

FIG. 3 shows an example of calculation results regarding the phase. This is the phase difference between the elastic waves 7c and 7d, that is, the terminals (14a, 14b), (15
The phase difference between a and 15b) is shown. In FIG. 3 (a), when the ratio (w ₁ / w ₂ ) of the added widths w ₁ and w ₂ is ₁ as in the conventional example, in FIG. 3 (b), the ratio of the added widths w ₁ and w ₂ is This is an example of calculation results for the case of 2.5. It can be seen that the phase difference can be lowered by shifting the ratio of the adjacent widths w ₁ and w ₂ from 1. Regarding the amplitude difference, the side width w is also calculated from the calculation results.
It was found that it can be reduced by shifting the ratio of ₁ and w ₂ from 1. It was also found that the phase difference and the amplitude difference can be adjusted by changing the ratio of the combined widths w ₁ and w ₂ . That is, in the Bragg cell according to the present invention, the combined widths w ₁ , w ₂
By shifting the ratio of 1 from 1, the elastic wave 7A excited at the side part on the positive electrode 3A side and the side part on the ground electrode 4A side compared to the conventional one
The larger diffracted light 9A can reduce the phase difference and amplitude difference of
Strength can be obtained.

Although the case of the embodiment shown in FIG. 1 has been described above, the invention is not limited to this, and each electrode is
Not all need to be parallel to each other and may be applied when each electrode is slightly tilted. Further, for each dogleg electrode 5A, the ratio of the combined width w ₁ of the combined part with the positive electrode 3A and the combined width w ₂ of the combined part with the ground electrode 4 does not need to be the same for all electrodes. You may change to.

[Effect of device]

As described above, according to the present invention, a comb-shaped electrode formed such that the adjoining width w _{1 at} the adjoining portion of the Dot Greg electrode and the positive electrode and the adjoining width w ₂ of the adjoining portion of the Dot Greg electrode and the ground electrode are different from each other. Since it is configured to be provided, it is possible to adjust the amplitude difference and the phase difference of the elastic waves excited by the side-by-side portion. In particular, if the ratio between w ₁ and w ₂ is set to a specific value other than 1, the amplitude difference and phase difference of elastic waves are reduced, and the amplitude difference and phase difference of light diffracted by these elastic waves are also reduced. Similarly, it can be reduced, and as a result, the intensity of the diffracted light is increased, and the one having a larger signal to noise ratio is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a Bragg cell according to an embodiment of the present invention, FIG. 2 (a) is a diagram showing the structure of the interdigital electrode of FIG. 1, and FIG. 2 (b) is a characteristic of the interdigital electrode. FIG. 3 (a) is a diagram showing an equivalent circuit for calculating the above, and FIG. 3 (a) is a line of the calculation result of the phase difference of the elastic wave when the ratio (w ₁ / w ₂ ) of the combined widths w ₁ and w ₂ is 1. Fig. 3 (b) shows the width w ₁ , w
FIG. 4 is a diagram of the calculation result of the phase difference of the elastic wave when the ratio of ₂ is 2.5, and FIG. 4 is a diagram showing a Bragg cell of a conventional example. In the figure, 1 is a piezoelectric substrate, 2A is a comb-shaped electrode, 3A is a positive electrode, 4A is a ground electrode, 5A is a bent intermediate potential electrode (dogleg electrode), 6 is a signal source, and 7A is an elastic wave. , 8 is an optical waveguide, 9 is light, 10 is a part with 1 dog leg electrode, 11 is an electric input terminal, and 12, 13, 14, and 15 are acoustic input terminals. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] 1. An optical waveguide is formed on the surface of a piezoelectric substrate, and a comb-shaped positive electrode and a ground electrode facing each other, a portion provided in a comb tooth portion of the positive electrode, and a comb tooth portion of the ground electrode are provided. An interdigital electrode having a bent portion and an intermediate potential electrode having a bent shape, the electrode arrangement interval of which is changed to excite elastic waves over a wide band. In the Bragg cell for performing the frequency analysis of the alternating current by utilizing the acousto-optic interaction between the light propagating through the optical waveguide and the elastic wave generated by the application of the alternating voltage to the interdigital electrode, the intermediate potential is provided. A Bragg cell, characterized in that an adjoining width of the electrode and the positive electrode is different from an adjoining width of the intermediate potential electrode and the ground electrode.