JPS6131297Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] This invention uses one ultrasonic optical deflection element to split one input beam into multiple output beams and modulate the intensity of each output beam. multi-beam optical modulator and variable adjustable multi-beam optical deflector (hereinafter referred to as multi-beam optical modulator and variable-tunable multi-beam optical deflector)
(deflector). [Prior art] By driving one ultrasonic optical deflection element (hereinafter referred to as A-O element) with multiple high-frequency signals, multiple output beams are extracted from one input beam. Obtaining itself has been known for a long time. FIG. 1 is a diagram for explaining this conventional technique. In Fig. 1, 1 is an A-O element, and when this is driven by a high-frequency drive signal 2, a light beam incident at an appropriate angle of incidence is deflected by a diffraction angle proportional to the frequency of the drive signal, and is also diffracted. The intensity of the generated output beam is controlled by the amplitude of the drive signal. Furthermore, the light that has not been diffracted travels straight and is output as undiffracted light. Taking advantage of this property, the AO element is often used as an optical deflector (constant amplitude, variable frequency) or an optical modulator (variable amplitude, constant frequency). Now, in Fig. 1, as the drive signal 2, a high frequency signal having N components with frequencies ₁ , ₂ , ..., _o and amplitudes _A1 , _A2 , ..., _Ao , respectively, is applied. In this case, diffraction occurs for each component signal within a driving amplitude that does not cause higher-order diffraction. That is, one input beam 3
is divided into n diffracted beams (output beams) 4 whose respective diffraction angles φ _k are proportional to the frequency _k of each component, and undiffracted beams 5 . and output beam intensity I
_k is controlled by the amplitude A _k of each component. In this way, by driving the A-O element with a drive signal that has multiple frequency components, it is possible to simultaneously generate multiple output beams whose deflection angle and intensity can be controlled for one input beam. Therefore, it was thought that it would provide an effective means for increasing the speed of display devices and printers that deflect laser beams, for example. [Problem that the invention aims to solve] However, in reality, the intensity of each output beam cannot be determined only by the amplitude of each component signal, but also varies depending on the presence or absence and magnitude of other signals. have. That is, regarding the diffraction by the A-O element, approximately, I _k =
It has the property that KA _k 〓I _p (K, α are constants depending on the element), and for the light flux entering and exiting the A-O element, where the intensity of the input beam is I, There is a relationship. Therefore, the intensity of each output beam is It will be given by That is, there is a serious problem in that the intensity of each output beam varies not only depending on the amplitude A _k of each component signal, but also on the presence/absence and magnitude of other signals. Due to this problem, despite the above-mentioned superior ability, A-O
It has been difficult to put a multi-beam modulator/deflector using elements into practical use. This idea was made to solve the above problem, and the intensity of the necessary n output beams can be determined only by the magnitude of each input signal, regardless of the presence or absence of other input signals. The purpose of this study is to obtain a multi-beam optical modulator/deflector that can be used as a multi-beam optical modulator/deflector. [Means for solving the problem] The multi-beam optical modulator/deflector according to this invention generates, in addition to the necessary output beams, a compensation beam that compensates for the intensity of the output beams, and Each of the input signals applied to modulate the intensity is added through an expansion circuit with expansion characteristics corresponding to the characteristics of the ultrasonic optical deflection element, and this is added to a correction signal obtained through a compression circuit with characteristics opposite to those of the expansion circuit. The intensity of the compensation beam is controlled by. [Operation] In this invention, a compensation beam is generated to prevent each output beam from varying depending on the presence/absence and magnitude of other signals, and at that time, an adder calculates the sum of multiple input signals. The gain applied to the entire input signal is controlled by this summation, and the expansion and compression circuits installed before and after the adder control the gain since the intensity of each output beam will fluctuate if the summation is simply taken and the gain is controlled. The operation is determined only by the magnitude of each input signal. [Example] The content of this invention will be explained below with reference to an example. FIG. 2 shows an embodiment of the multi-beam optical modulator/deflector according to this invention. In the figure, 1 is an A-O element, and 2 is a high-frequency drive signal for driving the A-O element. 6 is a group of input terminals, and an input signal e _k is applied to the terminal (6-K). In this example, e _k (≧0) is an analog voltage that determines the intensity I _k of the kth output beam. 7 is an oscillator group, each oscillator has a different frequency, and the oscillator (7-k)
Let the frequency of be _k . 8 is a group of modulators, and the modulator (8-k) amplitude-modulates the output of the oscillator (7-k) using the input signal e _k . The modulated signals are added together in an adder 9 and amplified in power by an amplifier 10.
It is applied to the A-O element 1 as a drive signal 2. Let the amplitude of each component of the output of the amplifier 10 be A _k . Further, the gain of the cascade circuit of modulator 8, adder 9, and amplifier 10 is normalized to 1, and A _k =e _k . Reference numeral 12 denotes a correction system, which constitutes the main part of this embodiment. Reference numeral 13 denotes a group of expansion circuits, and the k-th expansion circuit (13-k) is applied with the k-th input signal e _k and is configured to generate an output e _k ^a . The outputs of each expansion circuit are added by a second adder 14 and then applied to a compression circuit 15. The compression circuit 15 is configured to have a characteristic of (e _B -e) ^1/a , where e is the input to the circuit. e _B is the bias voltage. The output 17 of the compression circuit 15 is the correction signal _es . The correction signal 17 is applied to a modulator 19, which amplitude modulates the output of the oscillator 18 with a frequency of _s . The output of the modulator 19 is applied to the adder 9 mentioned above. With this configuration, the A-O element 1 receives this frequency _s in addition to the drive signals of the frequencies _i to _o described above.
It is also driven by the correction signal. This frequency _s
Let the amplitude of the component be A _s and regularize it to A _k = e _k as in the case of A _k .

[Table] Driven with a drive signal having (n+1) components. As a result, the input light beam 3 has its respective diffraction angle φ _k at the frequency
It is split into (n+1) output beams 4 and undiffracted light 5 proportional to _k (k=1, 2, . . . n) and _s . (4-s) is the compensation output beam by _s . Note that since this compensation output beam and undiffracted light are not required as modulator outputs, they are shielded by stoppers 11A and 11B, respectively. Now, the operation of this correction system 12 is as follows. First, regarding the diffraction by the A-O element 1, when the intensity of each diffracted light is I _k and the intensity of undiffracted light is I _p , the coefficient representing the magnitude of each diffraction is ξ _k = I _k /I _p (k = 1, 2,..., n) (2) ξ _k is determined, and this ξ _k is approximated by assuming the amplitude of each drive signal as A _k , ξ _k = KA _k 〓 (K, α are constant depending on the element) (3). Also, from the configuration shown in Figure 2, the correction signal e _s is It is becoming. Therefore, the intensity of each output beam is I _k = KA _k 〓I _p = Ke _k 〓I _p (5A), and the intensity of the compensation output beam is It is. On the other hand, regarding the luminous flux entering and exiting the A-O element 1 Since there is a relationship, using equations (5A) and (5B), A relationship has been established. Therefore, the expansion circuit 13
If the characteristic value a of the compression circuit 15 is taken to be equal to the characteristic value α of the AO element 1, the above equation becomes I _p =1/1+Ke _B (7). That is, the intensity I _p of the undiffracted light is determined only by the bias voltage e _B of the compression circuit 15, regardless of the presence or absence and magnitude of each input signal. Therefore, from equations (5A) and (7), the intensity of each output beam is I _k = Ke _k 〓I/1 + Ke _B (k = 1, 2,..., n) (
8), and is determined only by each input signal e _k regardless of the presence or absence and magnitude of other input signals. That is, as in this embodiment, in addition to n output beams, a compensation output beam is generated and the intensity of this compensation output beam is controlled by a predetermined correction signal determined from the input signal, so that each output The intensity of the beam can be determined only by the respective input signal. Furthermore, in the past, expansion/compression circuits were designed to perform compression → transmission → expansion in order to limit the range of change in signal amplitude in a transmission path in a single signal system, as seen in analog signal transmission systems. In contrast, in this invention, as a means to effectively generate a correction signal from multiple signals, each signal is expanded and then added.
We devised a configuration in which compression is performed after addition. If there is no correction system, I _s = 0, so I _p = I/(1+KΣe _j 〓), and since I _p changes depending on the presence or absence of the input signal and its magnitude, I _k changes. be. This was the problem explained with reference to FIG. Next, as a modification of the embodiment shown in FIG. 2, the one shown in FIG. 3 can be considered. However, in this example, whether the input signal is [1] or

[0]
There is a problem that it can only be applied when only two values are taken. In FIG. 3, each input signal is applied directly to adder 14. In FIG. In addition, the characteristics of the compression circuit 15 (e _B
−K ₁ e) Make it ^1/a . The other configurations are the same as in FIG. 2. In this embodiment, the input signal takes only two values, so when [ ] 1, e _k
If we decide that e _k =0 when = e _p , [ ]0, then the correction signal 17 is becomes. Here, m is the number of input signals such that e _k =e _p . Therefore, the intensity of the compensation beam is I _s =Ke _s 〓=K(e _B −mK ₁ e _p ). However, as in the case of FIG. 2, the constant a of the compression circuit is chosen equal to α. On the other hand, since I _k = Ke _k 〓, the intensity I _p of the undiffracted light is I _p = 1/1 + KΣe _k 〓 + K (e _B - mK ₁ e _p ) = 1/1 + Ke _B + mK (e _p 〓 - K _{1 ep} ). Therefore, we define the constant K ₁ of the compression circuit as K ₁ =
By choosing e _p 〓 ^-1 , I _p = I/
The relationship (1+Ke _B ) is obtained. That is, the undiffracted light intensity I _p can be made constant regardless of the number of input signals such that e _k =e _p . As a result, the intensity of each output beam can be constant regardless of the presence or absence of other input signals, as described in detail in the embodiment of FIG. Next, a prior art whose compensation characteristics are worse than this invention will be explained. This prior art, like the one in Fig. 3, is applied when the input signal e _k takes only two values, 0 or e _p , but since it does not include an expansion circuit and a compression circuit, each output This allows for variations in the beam intensity. In FIG. 4, 15A is a differential amplifier with a gain of _K2 , and the output of the adder 14 is applied to one side and the reference voltage e _B is applied to the other side. The other configurations are the same as in the case of FIG. In this configuration, by appropriately selecting the constants of each circuit, the intensity of the undiffracted light can be kept approximately constant. This is shown below. Since e _s =K ₂ (e _B -Σe _k )=K ₂ (e _B -me _p ) in the configuration shown in FIG. 4, I _p =1/1+mKe _p as explained for the previous two examples. 〓+KK ₂ 〓e _B 〓 ^(1-me
o/eB) 〓 becomes. Here, _{e p /}
Select e _B and make K ₂ = n ⁽ 〓 ^-1)/ 〓 again.
Determining K ₂ , I _p = 1/1 + nKe _p 〓 [m/n + (1-m/n)〓
] becomes. An example of I _p obtained in this manner is shown in FIG. FIG. 5 shows the case where α is set to a standard value for an A-O element, α=4, and nKe _p 〓=1. The figure also shows a case where no compensation is performed for comparison. As can be seen from Fig. 5, even if the number of 1's in the input signal changes, the intensity I _p of the undiffracted light can be kept approximately constant, and as a result, the intensity of each output beam can be kept approximately constant. It can be kept constant. However, the compensation characteristic in this case is not flat as shown in FIG. 5, and is worse than the embodiment of this invention shown in FIG. In the above description of the embodiment shown in FIG. 2, only the basic configuration of this invention has been described. For practical applications, measures may be taken to eliminate correction errors due to various non-essential causes, but these do not go beyond the scope of this invention. For example, the error caused by the difference in the diffracted light intensity of the A-O element 1 depending on the driving frequency is
Providing appropriate frequency characteristics to the drive system of the element,
Alternatively, it can be removed or reduced by applying appropriate weights to each input signal when generating a correction signal. Further, errors caused by a signal delay time difference between the drive system and the correction system can also be removed using an appropriate delay circuit. [Effects of the invention] As detailed above, in the multi-beam optical modulator/deflector according to this invention, in addition to the necessary output beam, a compensation beam is generated to compensate for the output beam, and the intensity of each of the output beams is adjusted. Each of the input signals applied for modulation is added through an expansion circuit with expansion characteristics corresponding to the characteristics of the ultrasonic optical deflection element, and this is added by a correction signal obtained through a compression circuit with characteristics opposite to those of the expansion circuit. Since the intensity of the above-mentioned compensation beam is controlled, the intensity of each output beam depends on the presence or absence of other input signals.
A great practical effect can be obtained in that it can be determined only by the magnitude of each input signal, regardless of its magnitude.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventionally known multi-beam optical modulator/deflector, Fig. 2 is a diagram showing an embodiment of the multi-beam optical modulator/deflector according to this invention, and Fig. 3 is similar to Fig. 2. FIG. 4 is a circuit diagram showing a prior art to this invention, and FIG. 5 is an explanatory diagram showing the characteristics of the prior art shown in FIG. 4. be. In the figure, 1 is an ultrasonic optical deflection element, 2 is its driving signal, 3 is an input beam, 4 is an output beam by diffraction, 5 is a non-diffracted light beam, 6 is a group of input terminals for input signals, 7 is a group of oscillators, 8 is a modulator group, 9 is an adder, 10 is a power amplifier, 11A and 11B are stoppers for blocking unnecessary beams, 12 is a correction system, 1
3 is an expansion circuit group, 14 is an adder, 15 is a compression circuit, 15A is an amplifier, 17 is a correction signal, 18 is an oscillator, and 19 is a modulator. In each figure, the same or corresponding parts are indicated by the same reference numerals.

Claims (1)

[Claims for Utility Model Registration] An ultrasonic optical deflection element is driven by a drive signal having a plurality of frequency components, and a plurality of intensity-modulated output beams are generated with respect to an input beam incident on the ultrasonic optical deflection element. Multi-beam optical modulation and
The deflector includes an expansion circuit that expands each of the incident signals applied to modulate the intensity of each of the output beams with expansion characteristics corresponding to the characteristics of the ultrasonic optical deflection element, and each output signal of the expansion circuit. a compression circuit that compresses the output signal of this adder with characteristics inverse to the expansion characteristics of the expansion circuit; and a correction signal obtained from the compression circuit that is a frequency signal different from each frequency component of the drive signal. A modulator that modulates the amplitude of the output beam is provided, and an output signal of the modulator is added to the drive signal to generate a compensation beam that compensates for the intensity of the output beam in addition to the output beam. Multi-beam optical modulator/deflector.