JPH02211430A - Optical scanner - Google Patents

Abstract

PURPOSE:To maintain the specified deflection angle of guided light and to eliminate the deviation in optical scanning by executing the frequency control of a surface acoustic wave when the propagation speed of the surface acoustic wave is change by a cause, such as temp. change. CONSTITUTION:The wavelength of the surface acoustic wave 4 is changed by the fluctuation in the propagation speed of the surface acoustic wave 4 which arises from the disturbance, such as temp. change, of a light guide 2. The frequency of a voltage control oscillator 10 and the frequency of the surface acoustic wave 4 detected by the 2nd electrode 8 are compared by a comparator 11 at this time and the frequency obtd. as the result of subtraction is sent to an adder 15 to change the frequency of the voltage control oscillator 10. The wavelength of the surface acoustic wave 4 excited by the 1st electrode 3 is thereby maintained at the wavelength of the surface acoustic wave before the fluctuation, by which the deviation in a deflection angle theta is corrected and the deviation in the optical scanning is eliminated.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention is an optical scanning device that deflects guided light using the acousto-optic effect of surface acoustic waves and scans the light by changing the deflection angle. This is about B.

(b) Conventional technology Conventionally, mechanical types such as galvanometer mirrors and polygon mirrors have been used as optical scanning devices such as printer heads, but these have the drawbacks of complicated optical systems and large devices. . To overcome these drawbacks, optical scanning devices have recently been proposed that perform optical scanning by deflecting guided light traveling in an optical waveguide through interaction with surface acoustic waves and changing the deflection angle. ing.

FIG. 4 is a configuration diagram showing an example of an optical scanning device.

In Figure 4,! is a piezoelectric material such as LiNb0a, 2
3 is an optical waveguide formed by T+ diffusion on the surface of piezoelectric material 1;
\r1 pole, 5 is a voltage controlled oscillator, whose output terminal is connected via an amplifier 19 to a comb type? 'lX pole 3, and its input end is connected to the triangular wave oscillator 13, thereby generating a high frequency signal. Further, 6 is guided light (incident light) propagating in the optical waveguide 2, and 7 is a polarized light that is deflected by the incident light 6 or the surface acoustic wave 4.

Here, the polarization βJO of the polarized light is calculated by shifting the wavelength and effective refractive index of the guided light 6 to λ and N, respectively, and the wavelength, frequency, and velocity of the surface acoustic wave 4 to E and v, respectively, and then θ=25 in-
'(λ/2N△) λr/Nv (1).

Next, the operation will be explained.

Figure 3 shows the output of the 3 μm wave generator 13, and the frequency corresponding to the output (the vertical axis in Figure 3 is the voltage controlled oscillator 5).
The voltage-controlled oscillator 5 oscillates at a frequency f corresponding to the output frequency of the surface acoustic wave 4, thereby changing the frequency of the voltage applied to the comb-shaped electrode 3 via the amplifier 19.
By changing , the deflection angle θ changes according to equation (1), and optical scanning can be performed.

That is, since the deflection angle θ is proportional to the frequency f of the surface acoustic wave 4, which is equivalent to the output frequency of the voltage controlled oscillator 5, the deflection rr+0 changes θ according to the waveform of the triangular wave, as shown by the solid line in FIG. Varies within the range of ~01.

(c) Problems to be Solved by the Invention However, in the optical scanning device of this construction, when the propagation velocity V of the surface acoustic wave changes due to an external factor such as a temperature change in the optical waveguide, as can be seen from equation (1), The deflection angle θ changes, making it impossible to obtain a desired deflection angle, and when the device is used for optical scanning of an optical printer head, problems arise such as deviations in the deflection angle resulting in printing deviations.

That is, in FIG. 2, the deflection angle 0 is originally Oo~θ
, changes within the range of θ° due to temperature change, as shown by the broken line. ~ θ°, there are 4 degrees of variation, resulting in a deviation of ΔO.

(d) Means and Effects for Solving the Problems This invention provides an optical scanning device in which guided light propagating through an optical waveguide formed on the surface of a piezoelectric substrate is deflected by a surface acoustic wave, and the guided light is optically scanned. a signal generator that generates a first signal that periodically increases and decreases in order to periodically change the deflection angle of the guided light; and a second signal generator that receives the first signal and has a frequency that corresponds to the magnitude of the first signal. an oscillator that outputs a signal; a first electrode provided on the surface of the piezoelectric substrate and excited by the second signal to cause the optical waveguide to generate a surface acoustic wave having a frequency corresponding to the frequency of the second signal; A second electrode is provided on the surface of the optical waveguide and detects the frequency of the surface acoustic wave generated in the optical waveguide and outputs it as a third signal. It is equipped with a comparator that subtracts a signal and outputs a fourth signal as a result of the subtraction, and an adder that adds the fourth signal to the first signal and sends the added signal to the oscillator. Even if the wavelength of the surface acoustic wave changes due to fluctuations in the propagation speed of the surface acoustic wave due to disturbances such as changes, the frequency of the second signal is changed by the fourth signal generated by comparing the second signal and the third signal. This optical scanning device corrects deviations in the deflection angle by making it possible to maintain the wavelength of the surface acoustic wave excited by the first electrode at the wavelength of the surface acoustic wave before the change.

That is, the present invention forms an optical waveguide on the surface of a piezoelectric substrate, and also provides a first electrode for surface acoustic wave excitation,
In an optical scanning device that deflects guided light using an acousto-optic effect and scans the light by changing the polarization f, a signal from a signal generator is received and a 17th [ ! A surface acoustic wave is generated by outputting a periodic signal to the pole to periodically change the deflection angle of the guided light.
A second electrode is provided on the surface of the piezoelectric substrate to detect the wavelength of the surface acoustic wave generated in the optical waveguide by excitation by the 11th RI pole, and a comparator is used to detect a change signal corresponding to the amount of change in wavelength. , this is configured to be added to a periodic signal (this is added and a signal corresponding to this added signal is output to the tm-th pole, so that even if the signal input to the comparator fluctuates, the amplitude of the output change signal is always maintained) In addition to being able to maintain a constant value, after outputting the addition signal, a signal corresponding to the addition signal is manually applied to the first electrode, so that the frequency corresponding to the periodic signal whose frequency has been corrected is output at the 21'I! pole. surface acoustic waves can be detected.

(e) Examples Examples of the present invention will be described below based on the drawings. Note that this invention is not limited by this.

In FIG. 1, the optical scanning device includes LiNb0. The guided light 6 propagating through the optical waveguide 2 formed on the surface of the piezoelectric substrate l of the hat is deflected by the surface acoustic wave 4, and the guided light 7 is optically scanned. A triangular wave generator 13 generates a triangular wave signal (first signal) S that periodically increases and decreases in order to periodically change the deflection angle 0 from 00 to θ [see Figure 2]; A voltage-controlled generator Into receives the signal and outputs a second signal (high frequency signal) having a frequency corresponding to the magnitude of the first signal (see FIG. 3); a comb-shaped flt for surface acoustic wave excitation that is excited by the waveguide and generates a surface acoustic wave of a frequency corresponding to the frequency of the second signal in the optical waveguide 1;
4￥1 (11th! Pole) 3 and a surface acoustic wave detection device provided on the surface of the piezoelectric substrate l to detect the frequency of the surface acoustic wave 4 generated in the optical waveguide 2 and output it as a third signal B. Comb-shaped electrode (second electrode) 8, second signal A and third signal B
Compare and subtract the third signal B from the second signal A (A-B)
L, a comparator that outputs a fourth signal C as a result of subtraction, and an adder 15 that adds the fourth signal C to the first signal S and sends the added signal to the oscillator 10.

Furthermore, the comparator compares the phase of the third signal B received by the comb-shaped electrode 8 with the phase of the second signal Δ generated by the voltage controlled oscillator 10, and generates a voltage based on the phase difference.
A low-pass filter 12 is inserted between the comparator and the adder 15. This is a phase comparator
The voltage controlled oscillator 10, phase comparator 11, and low-pass filter 12 form a PLL circuit (Phase L).
(locked Loop) 14.

Further, the comb-shaped electrode 8 is placed at a distance from the comb-shaped electrode 3, and the comb-shaped electrode 9 amplifies the second signal generated from the voltage-controlled oscillation mIO. This is an amplifier for exciting the mold electrode 3.

When LiNb0* is used for the piezoelectric substrate 1, the optical waveguide 2 is formed by diffusing Ti on the surface of the substrate.

Next, the operation of the optical scanning device of the present invention will be explained based on FIG.

In FIG. 1, a high frequency signal A generated by a voltage controlled oscillator IO is amplified by an amplifier 9, and then excites a comb-shaped electrode 3 to generate a surface elastic plate 4.

As a result, incident light 6 generated from a light source such as a semiconductor laser and entering the surface acoustic wave generation region 4a via the lens system is Bragg diffracted by the surface acoustic wave 4 and becomes polarized light 7.

At this time, the interaction between light and elastic waves is called the so-called acousto-optic effect, and under Bragg conditions the deflection angle θ is (
As shown in equation 1), θ=λf /Nv.

Here, λ and N are the wavelength and effective refractive index of the guided light 6, respectively, and f and v are the frequency and velocity of the surface acoustic wave 4, respectively.

On the other hand, the surface acoustic wave 4 appears on the opposite side of the comb-shaped electrode 3 (, - also appears and is converted into a voltage at the comb-shaped electrode 8. In the case of the same shape, it is determined only by the phase difference due to the propagation distance a of the surface acoustic wave 4, a = 2 nQf /v
−・”(2).

This phase difference is converted into a voltage by the phase comparator 2, and changed to a control voltage by the low-pass filter 12, and the voltage controlled oscillation '741
Controls the 0 oscillation frequency. In other words, the frequency is controlled by the PLL circuit 14 so that the phase difference a is constant.

If we rewrite the deflection rrjo using the phase difference a from equations (1) and (2), we get θ=λa/2πN! 2 ......(3) can be written.

In other words, the propagation velocity V of the surface acoustic wave 4 due to temperature changes etc.
If the frequency f of the surface acoustic wave is changed so that the phase difference & remains constant even when the deflection ffJl changes, the deflection ffJl can be kept constant.

Further, the triangular wave generated by the triangular wave generator 13 is added to the control voltage of the voltage controlled oscillator 10, and the frequency changes continuously according to the signal. If the response speed of the PLL circuit 14 is made sufficiently slower than the triangular wave signal, the PLL circuit 14 will not follow the triangular wave signal, but will only follow slow changes such as temperature changes, centering on the frequency determined by the l'LL circuit 14, It will be deflected according to the triangular wave signal.

As described above, in this embodiment, the deflection angle O is originally θ, as shown by the solid line in FIG. Those that change up to O1 are
In the conventional case, where there is no circuit to correct deviations in the deflection angle θ, surface acoustic waves By detecting the change in the frequency of 4, the deviation in the deflection angle can be corrected.

(F) Effects of the Invention As described above, according to the present invention, even if the propagation speed of the surface acoustic wave changes due to factors such as temperature changes, the deflection angle of the guided light can be kept constant by frequency control of the surface acoustic wave. This has the effect of eliminating deviations in optical scanning.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram showing changes in the deflection angle of guided light, Fig. 3 is a waveform diagram showing the output voltage of the triangular wave signal, and Fig. 4 is an explanatory diagram showing the change in the deflection angle of the guided light. FIG. 2 is a configuration explanatory diagram showing a conventional example. 1st rgj...Piezoelectric substrate, 2...Optical waveguide,...17th! ! Extreme, 4...
Surface acoustic wave 1.7... Guided light, 8...
...Second electrode, 0...Voltage controlled oscillator, 1...Phase comparator, 13...Triangular wave oscillator.

Claims (1)

[Claims] 1. In an optical scanning device that optically scans the guided light by deflecting the guided light propagating through the optical waveguide formed on the surface of the piezoelectric substrate using a surface acoustic wave, the deflection angle of the guided light is periodically set. a signal generator that generates a first signal that increases and decreases periodically to change the magnitude of the signal; an oscillator that receives the first signal and outputs a second signal having a frequency that corresponds to the magnitude of the first signal; a first electrode provided on the surface of the piezoelectric substrate and excited by the second signal to generate a surface acoustic wave having a frequency corresponding to the frequency of the second signal in the optical waveguide; A second electrode that detects the frequency of the surface acoustic wave generated in the second signal and outputs it as a third signal compares the second signal and the third signal, subtracts the third signal from the second signal, and outputs the third signal as the result of the subtraction. It is equipped with a comparator that outputs four signals, and an adder that adds the fourth signal to the first signal and sends the added signal to the oscillator. Even if the wavelength of the surface acoustic wave changes due to fluctuations in
The frequency of the second signal is changed by a fourth signal generated by comparing the signal with the third signal, thereby maintaining the wavelength of the surface acoustic wave excited by the first electrode at the wavelength of the surface acoustic wave before the change. An optical scanning device that corrects deviations in deflection angle by making it possible to