JPS63194236A - Light deflecting device - Google Patents

Abstract

PURPOSE:To quicken the rise time of turning-on/off of an optical signal by successively deflecting the straight going light incident on light deflecting elements by respective light deflectors to attain a large angle of diffraction in the whole of diffracting operations. CONSTITUTION:The transducer attaching face of a light deflecting element 11A of a first light deflector is defined as the reference face, and the transducer attaching face of a light deflecting element 11B of a second light deflector is set at a prescribed angle of inclination, for example, 2theta (theta is the angle of incidence of the straight going light) to the reference face. The incident straight going light is deflected at the angle theta by a first light deflecting element 11A, and the deflected light is made incident on a second light deflecting elements 11B and is deflected at the angle theta furthermore, and therefore, a large angle of diffraction is obtained as the whole even if the wavelength of a driving ultrasonic wave is extended to reduce the angle theta. Three or more light deflectors may be used to deflect the light similarly. Thus, the size of a device is not changed but only the shape and the arrangement are changed to quicken the rise time of turning-on/off of the optical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvement of a light deflection device using an acousto-optic effect.

(Prior Art) This type of optical deflection device applies a high frequency voltage from a drive circuit that oscillates a high frequency to an electrode of a transducer attached to an optical deflection element, thereby converting straight light at a predetermined incident angle into Due to the diffraction effect caused by the sound waves inside the optical deflection element, the angle of incidence of the straight light is
It extracts diffracted light that is deflected at twice the angle.

The diffraction efficiency η and rise time Tr of this type of optical deflection device are as follows: Tr = (0,55A + 0.8)Wo /
It can be expressed as V-(2). However, A
〉1, and A-(2/π)・(λL/WOA)...(3
). In the above formula, λ is the wavelength of light, Ps
is the output power of the drive circuit, and L is the electrode length of the transducer 2 extending in the optical direction (Fig. 5(b)).

In (c), L-1, +12), H is the electrode width of transducer 2, Wo is the radius of the light beam 1M2゜, and A
are the performance index of optical deflection element 1, respectively.

The sound speed and wavelength of the ultrasonic wave inside the optical deflection element are determined by the material, and are shown in the table below as an example.

Therefore, when deciding the material to be used for the optical deflection element 1, (
Since the figure of merit M2 is determined in formula 1), 10
Driving ultrasonic power P required to obtain a diffraction efficiency η of 0%
The size of s is determined by the electrode length and electrode width H. That is,
The driving ultrasonic power Ps can be reduced as the electrode length increases and the electrode width H decreases.

Conventionally, such an optical deflection device includes one transducer 2 and one electrode 3 mounted on the same plane of an optical deflection element 1 (FIG. 5a), as shown in FIG. One transducer 2 is placed on the same plane as the other, and this transducer 2 is divided and two electrodes 3 are attached (see figure b), or an optical deflector 1 is arranged on the same plane.
The transducer 2 is divided and arranged on the same plane,
There is also a transducer 2 in which an electrode 3 is individually attached to the transducer 2 (see C in the same figure). The reason for using a plurality of transducers 2 or a plurality of electrodes 3 in this way is to facilitate matching with the drive circuit and to facilitate the production of a thin film (for example, several tens of micrometers) transducer 2. Examples include making it easier.

(Problem to be Solved by the Invention) Therefore, when the material of the optical deflection element 1 is determined, since the figure of merit M2 is determined in equation (1), the drive required to obtain 100% diffraction efficiency η is The magnitude of the ultrasonic power Ps is determined by the electrode length and electrode width H. In other words, the driving ultrasonic power Ps can be reduced as the electrode length increases and the electrode width H decreases.

(2) However, if the electrode length is increased, the driving ultrasonic power Ps can be decreased, but as is clear from the above equation (2), the rise time Tr becomes slower.

This means that when obtaining an optical deflector with a fast rise time Tr, the electrode length cannot be increased.

Conversely, if the electrode length is shortened, the rise time T' becomes faster, but Bragg diffraction becomes closer to Ramannus diffraction, and the diffraction efficiency substantially decreases.

Therefore, it is conceivable to know the lower limit of the electrode length from the relationship with the diffraction efficiency and set it just at the limit. Incidentally, the lower limit of the electrode length is generally (Lλ/2A2) >>1...
It is known that it can be obtained from (4). Therefore, if we transform this equation (4), if (Lλ/2A2) is a constant C, we get the following and null. Kokote, C'-2/2V2. It can be expressed as B-Lf2. Moreover, when formula (3) is expressed using B in the above formula, it becomes as follows. In the above formula, C-2λ/πWo■.

Therefore, from equation (2), the smaller A is, the more the rise time T
r becomes faster. In other words, the higher the frequency, the faster the rise time Tr. However, the transducer becomes thinner and difficult to manufacture. This thickness is determined from the formula: (frequency constant) - (thickness of transducer) x (ultrasonic frequency). Furthermore, the thinner the adhesive, the more difficult it is to adhere.

(2) On the other hand, if the electrode width H is made smaller, the drive ultrasonic power Ps can be made smaller based on equation (1) above, but the radius W of the light beam transmitted through the optical deflection element. Making it smaller than this is not practical because it lowers the diffraction efficiency η.

Therefore, from the above point of view, when increasing the rise time T, the electrode length is made as small as possible based on equation (4), and the electrode width H is made small, thereby suppressing the driving ultrasonic power while diffracting It is desirable to achieve this without significantly reducing efficiency.

However, it is difficult to realize an optical deflector that satisfies these conditions. In practice, problems such as processing precision of component parts and adjustment errors of the optical axis may arise, so it is generally considered that the electrode width H is twice the light beam diameter.゛Also, when calculating the above formula (2) using the wavelength of the ultrasonic wave as a parameter, as shown in Figure 6, the larger the wavelength of the ultrasonic wave, that is, the lower the frequency of the driving ultrasonic wave, the faster the rise. I can understand that time goes by faster. However, in Figure 6, material: As2Se3゜λ: 1
．． 3 μm, WO: 0. 1mm, L: 1
0tnm.

It is a characteristic diagram in the case of H=1 am.

However, since the diffraction angle θ is obtained from the equation (5), the diffraction angle θ becomes smaller as the wavelength of the ultrasonic wave increases, assuming that the wavelength λ of the light is constant.

This means that a very long distance is required to reliably separate the diffracted light and the straight light. The light beam is not completely parallel light but has some spread due to the coherency of the laser light, the diffraction of the light, etc.

Therefore, when a light beam is emitted for a long time in space, the diameter of the light beam increases, the coupling efficiency with the optical fiber decreases, and the substantial diffraction efficiency decreases.

Therefore, it is difficult to make the light beam travel a long distance through space.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical deflection device that can speed up the rise time of turning on and off an optical signal.

(Means and Effects for Solving the Problems) In the optical deflection device according to the present invention, the transducer mounting of the optical deflection element is performed as a plane with respect to the reference surface portion of the first optical deflection element, and the second optical deflection element or A part of the first optical deflection element is formed into an inclined surface portion having an inclination angle of 2(n-1) times the predetermined angle (n is the number of surfaces on which the transducer is attached, including the reference surface portion, and is an integer of 2 or more). The transducers 18.
19 (including electrodes 16 and 17), and by sequentially deflecting the straight light incident on the optical deflection element with each transducer, a large diffraction angle is obtained by the overall diffraction operation, and This is to speed up the rise time derived from equations (2) and (3) above. Furthermore, in the optical deflection device according to the present invention, the second optical deflector is 2 (n-1) times (2(n-1) times (
n is the number of surfaces on which the transducers are mounted, including the reference surface portion, and is arranged on inclined surface portions having an inclination angle of 2 or more), and each optical deflector sequentially deflects the straight light that enters the optical deflection element. By doing so, a large diffraction angle can be obtained by the overall diffraction operation.

(Example) The first example of the present invention will be described below with reference to FIGS. 1 and 2.
This will be explained with reference to the figures. FIG. 1 is a diagram showing the setting state of two optical deflectors, and FIG. 2 is a diagram showing the installation state of the two optical deflectors. In FIG. 1, reference numerals 11A and 11B indicate optical deflection elements of first and second optical deflectors that deflect incident straight light to a desired diffraction angle and output the deflected light. These optical deflection elements 11A
.

11B, the transducers 18 and 19 are individually attached to each surface, but in particular, when the transducer of the optical deflection element 11A of the first optical deflector is attached with the surface as the reference surface, the transducers 18 and 19 of the second optical deflector are attached individually. The transducer mounting surface of the optical deflection element 11B is set so that it has a predetermined inclination angle, for example, 2θ (θ is the angle of incidence of straight light) with respect to the reference plane.

With this configuration, the incident straight light is deflected by θ at the first optical deflection element 11A, and this polarized light enters the second optical deflection element 11B as the incident straight light, where it is further deflected by θ. Therefore, even if the wavelength of the driving ultrasonic wave is made longer and the angle θ is made smaller, the overall diffraction angle can be made larger. Although two optical deflection elements 11A and IIB are used, three or more may be used and tilted in a similar manner. Figure 2 is 2
The mounting of the two optical deflectors 31 and 32 is shown in the state diagram, and the mounting of the two optical deflectors 31 and 32 is shown in FIG.
is fixed.

Next, regarding the second embodiment of the present invention, FIGS.
This will be explained with reference to the figures. FIG. 3 is a schematic diagram of the optical deflector, and FIG. 2 is a diagram showing how the transducer and its electrodes are attached. In these figures, reference numeral 11 denotes a light deflection element that deflects incident rectilinear light to a desired diffraction angle and outputs it, and this light deflection element 11 is provided with three boats.

On the one port side, an optical signal transmission system, that is, a light source (not shown), an optical fiber 12, a lens 13, etc. are arranged, and the optical signal from this light source passes through the optical fiber 12 and lens 13 in this order, and the optical signal is transmitted through the optical fiber 12 and the lens 13 in this order. The light is incident on the deflection element 11.

Note that the optical signal from the light source may be directly input to the optical deflector 11 through the lens 13 without using the optical fiber 12.

The transducer mounting surface of the light deflection cable 11 has a reference plane 1 which is substantially parallel to the diffraction grating in the light deflection cable 11 on the side near the incident end of the straight light from the lens 13, for example. ,1
2! is formed on the side closer to the output side of the diffracted light. An inclined surface portion 11b is formed which is connected to the reference surface portion 11a and is inclined at a predetermined angle of inclination θ with respect to the reference surface portion 11a.

This inclination angle θ is set to an angle that satisfies the above equation (5). In two cases, it is 2θ. That is, once the wavelength λ of the light to be used and the driving ultrasound wavelength are determined, θ can be determined from equation (5). Each reference surface portion 11a and inclined surface portion 11b formed as described above is provided with a transducer 18.1 having an individual electrode 16°17.
9 installed.

I'm being kicked. These electrodes 16, 17 are connected to the drive circuit 2.
A high frequency signal is given from the transducer 18.
1 is applied.

In the optical deflection cable 11, the transducer 18
．． When no ultrasonic waves are applied by 19, the light beam from the optical signal sending system travels straight inside the optical deflector 11 and is emitted from another port. A lens 21 and an optical fiber 22 are arranged in this order in the straight direction of the light beam emitted from the boat. Therefore, the light beam emitted from the port passes through the lens 21, the optical fiber 22, and is received by a light receiver (not shown).

On the other hand, when applying ultrasonic waves to the optical deflection cable 11, the incident straight light is deflected by the application of the ultrasonic waves and exits from another port. A lens 23 and an optical fiber 2 are connected to this port side.
4 is arranged, and the diffracted light deflected within the optical deflector 11 is transmitted to the lens 23 . The light passes through the optical fiber 24 and is received by a light receiver (not shown). Note that when trying to obtain the characteristics of the return light from the optical fiber to be measured, such as in an optical pulse tester, the lens 21. An optical fiber or the like is used as an optical signal transmission system, and lens 1
3 and an optical fiber 12 as a system to be measured, and the return light due to reflection from the optical fiber to be measured passes through an optical fiber 12 and a lens 13 inside the device to an optical deflection element 11.
It is assumed that the

Therefore, in the optical deflector as described above, the incident straight light from the optical signal transmission system or the return light due to reflection from the optical fiber to be measured passes through the optical fiber 12 and is made into a parallel beam by the lens, and then the optical deflector The light is input to the child 11. At this time, if a high frequency signal is supplied from the drive circuit 20 to the transducers 18.19 via each electrode 16.17, an ultrasonic wave is applied from each transducer 18.19 into the optical deflection element 11. As a result, the parallel beam, that is, the straight light that is incident on the optical deflection element 11, is transmitted to the transducer 1.
Deflected by an angle θ by the ultrasonic wave generated by 8,
Subsequently, the ultrasonic wave generated by the transducer 19 further deflects the light by an angle θ, so that the diffraction angle of the diffracted light emitted from the light deflection element 11 is substantially 20
becomes.

Therefore, even if the wavelength of the driving ultrasonic wave is made longer and the angle θ is made smaller, the overall diffraction angle can be made larger.

Simply speaking, in FIGS. 3 and 4, the reference surface portion 11a
Since the angle of the inclined surface portion 11b is θ, even if the wavelength of the driving ultrasonic wave is doubled, the diffraction angle will be 2θ. Therefore, by changing only the shape without changing the size of the device, the optical signal can be improved. It is possible to realize an optical deflector with fast on/off rise time.

In the above embodiment, one inclined surface section 11b is formed with respect to the reference surface section 11a, but it goes without saying that two or more inclined surface sections may be formed.

Also, one transducer may be provided with a plurality of electrodes, for example. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

(Effects of the Invention) As detailed above, the present invention provides an optical deflection device that can speed up the rise time of turning on and off an optical signal by changing only the shape or arrangement without changing the size of the device. Can be provided.

[Brief explanation of the drawing]

FIGS. 1 and 2 show the first part of the optical deflection device according to the present invention.
Figure 1 is a diagram showing the arrangement relationship of two optical deflectors, Figure 2 is a diagram showing the installation state of the two optical deflectors, and Figures 3 and 4 are shown to explain the embodiment. are shown to explain the second embodiment of the optical deflection device of the present invention, FIG. 3 is a diagram showing the overall configuration of the optical deflection device, and FIG. 4 is a diagram showing the transducer and electrodes connected to the optical deflection element. FIG. 5 is a diagram showing an example of how a transducer and electrode are attached to an optical deflection element in a conventional device. FIG. 6 is a diagram showing the relationship between driving ultrasonic frequency and rise time of a conventional device. . 11, 11A, IIB, , optical deflection element, 11 a
-...Reference surface part, llb...Slanted surface part, 16.17.
...electrode, 18.19...transducer, 20.
...Drive circuit, 31...First optical deflector, 32...
Second optical deflector. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 4

Claims (2)

[Claims] (1) A first optical deflector (31) that includes a transducer (18) on one side of the optical deflection element (11) and deflects the light incident on the optical deflection element to a predetermined diffraction angle and outputs the deflected light. , the transducer is mounted sequentially at an angle of 2^(^n^-^1^) times the predetermined angle (n is the number of optical deflectors and n≧2) with respect to the transducer mounting surface of the first optical deflector. 2nd, 3rd, etc. arranged sequentially with faces
..., an n-th optical deflector (32), and the incident light is sequentially deflected by the first, second, third, . . . n-th optical deflectors. A light deflection device. (2) The optical deflection element of the first optical deflector (31) and the optical deflection elements of the second, third, . . . , n-th optical deflectors are composed of a single element. An optical deflection device according to claim 1, characterized in: