JPS60133432A - Thin film type optical deflecting device - Google Patents

Abstract

PURPOSE:To realize a wide angle of deflection by providing a reflecting surface for diffracted waveguide light corresponding to part of a circle which runs on a diffraction position of a waveguide. CONSTITUTION:The Bragg angle to a surface acoustic wave 44 is denoted as thetaB and incident waveguide light 43 is incident at the Bragg angle to the surface acoustic wave 44. One point on a straight line in the wave front direction of the surface acoustic wave 44 from the point A of mutual operation between the incident waveguide light 43 and surface acoustic wave 44 is denoted as O. The angle psi of deflection of reflected light 46 to the incident light 43 is pi-4thetaB. When the surface acoustic wave is varied in pitch by varying the high frequency, waveguide light 47 diffracted with the surface acoustic wave 44 is deflected by -2thetaB-DELTAtheta to the incident light 43 and the angle psi' of deflection of reflected light 48 to the incident light 43 becomes pi-4thetaB-3DELTAtheta. The angle DELTApsi of deflection of a device when the high frequency is varied is 3DELTAtheta, and an angle of deflection which is three times that of a conventional optical deflecting device is realized. Consequently, the frequency band of the applied high frequency of a transducer for obtaining a specific angle of deflection by a deflecting device may by reduced greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Technique 8j] The present invention relates to a thin film type optical deflection device that utilizes diffraction of guided light.

[Prior art]

Ultrasonic beam printers (hereinafter referred to as A10 deflectors) can achieve higher speed and fixed distribution compared to mechanical deflectors such as polygon mirrors and galvanometer mirrors, so they are very popular in business. , it is expected to be applied to TV display temples. However, the conventional A10IJiil deflector has a drawback in that its deflection angle (scannable angular range) is small.

Here, the conventional A10-circuit and its problems will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of a conventional Ijt type A10 deflector. In FIG. 1, reference numeral 1 denotes a transducer made of a piezoelectric material such as PLZT, and this ultrasonic transducer 1 is closely attached to an ultrasonic waveguide 2 made of TeO2 or the like. This transducer 1 is
When a high-frequency α pressure in the 1000 MHz-Wi range is applied, the ultrasonic wave propagates through the waveguide 2 in a rough shape, and a diffraction grating structure is formed in the waveguide 2 due to a change in the refractive index. Ru.

When a laser beam 3 is made incident on this waveguide 2, the beam undergoes Sibrag diffraction by the above-mentioned diffraction beam 4, and is emitted as a diffracted light beam 4. At this time, the angle formed by the fourth-order diffracted light beam 5 and the diffracted light beam 4, that is, the diffraction angle θ, changes depending on the frequency of the high frequency wave applied to the transducer 1, and θ is given by the following equation.

Here, V is the speed of the ultrasonic wave, f is the frequency of the applied high frequency,
λ is the wavelength in live air at the end of the YS (incidence), and n is the refractive index of the waveguide 20 mm.

From the above equation, it is understood that by changing the additional frequency f, it is possible to change θ and cause the emitted light beam 4 to travel in the feed direction. The maximum deflection angle is determined by the angular selection range of Bragg diffraction, and when the frequency exceeds a certain level, the incident light beam deviates from the Cassilling striations of the diffraction grating structure due to the threat of ultrasonic waves, and the diffraction efficiency decreases. Therefore, the maximum t@direction angle is limited, and in the conventional example, it was about 3 degrees at most.

FIG. 2 is a perspective view of a conventional thin film waveguide type A10 deflector. In FIG. 2, an optical waveguide 7 is formed by diffusing T1 on the surface of a piezoelectric crystal substrate 6 such as LiNbO5. This optical waveguide 7 has a thickness of about 2 μm, and its refractive index is about 0.0 higher than the refractive index of LiNbO3 of the substrate 6, which is 2.2. High refractive index 8 in optical waveguide 7
are placed close to each other, and a laser beam 9 is introduced from the outside into the prism 8.
is made incident, and the light beam is guided into the waveguide 7. A comb-shaped electrode 10 for excitation of ultrasonic waves is placed on the surface of the waveguide 70. By applying a frequency wave to this polarization 10, ultrasonic excitation is generated on the surface of the crystal 60. The light beam 11 that has entered the waveguide 7 is diffracted by this super-high-frequency wave 1Hj wave and becomes a light beam 12 directed toward one tube. ? As in the case of the volume type A/0 circular deflector described in iJ, the light beam 12 is directed in four directions by changing the frequency of the high frequency applied to the electrode 0. The -direction light beam 12 is directed to the grism 13 for injection In the case of this waveguide type A/O deflector, the maximum direction angle is also
+tJ: Subjected.

Several attempts have been made to increase the deflection angle in waveguide type A10 deflectors. Examples of this kind are, for example:
LiteratureIEEFJ* Transactions onc
Ircutand Systems, vol. CA
S-26No, 12 + p 1072 [Gulded
-Wave Acouato -0pt lc Br
agg Modulations for Wide −
Band Integrated 0ptic Cor
rrnunications and Signal P
Processing J by C,S, TSAI. An example of this is as shown in FIG.
It is devised so that the incident light beam is cascaded in the area of 1↑ by placing the 2 and 2 beams slightly apart from each other by 1 point. In an example using four transducers, a band of 680 Mf (z) is obtained.

The deflection angle at this time is about 4°. Also, another example is the fourth
As shown in the figure, the pitch p of polarization 15 in the current state of the comb
By sequentially changing ψ and 1, the direction of propagation of the ultrasonic waves changes as the range goes from low to high, so that the incident light flux is cascaded over a wide 4jf range.

Even with these improved flattened devices, there are limitations such as driver technology and /4' turn processing technology for both electrodes of the comb. Although an oscillator for voltage application with a frequency band is required, it is difficult to obtain an oscillator with a wide frequency band.

As a method of widening the deflection angle without widening the frequency band, transducers of the same frequency band are arranged in a random arrangement as shown in Fig. 5, and their angles are changed and the direction of the incident light beam is also changed. It is also conceivable to obtain a wide deflection angle by changing the angle of inclination of each transducer and sequentially selecting combinations of each incident light beam and each transducer. In this case, there is an advantage that the ultrasonic transducer frequency does not become extremely high. However, the difference in this case is due to the influence of the fourth-order diffracted light existing in this type of deflector. That is, in FIG. 5, when the first light beam 18 is made incident on the ultrasonic wave 17 excited by the first transducer 16, a part of it becomes a deflected light beam, but a part of the light beam is diffracted. Instead, it becomes zero-order light 19. This first transducer IC+fF IQ IJ-+1Fil marriage 4
b Q l'1 product, r-edge IF test up to child 9A; the angular range of the capital 21 is scanned.

Following this first deflection range 21, a diagonal line between a maximum diffraction angle 24 and a minimum diffraction angle 26 is formed by a combination of a second transducer 22 and an incident light beam 23 which are switched in time series. One bucket direction range of group 25 is scanned. Within this deflection range 25, there are q zero-order diffracted lights 19 caused by the first light beam 18. Therefore, when this deflector is used for laser beam recording or laser display, this zero-order light beam 19 becomes a stationary light beam with respect to the deflected light beam, so even if its original value is somewhat low, the deflection range 21
．． During the 25th, it becomes a noise and becomes very useful for recording or recording.

[Object of the present invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional technology with a diameter of .mu.m, it is an object of the present invention to provide a 4J wide deflection device capable of realizing a wide deflection angle.

The above objects are achieved by providing a diffractive waveguide light reflecting surface corresponding to a portion of a circle passing through the diffraction position of the waveguide.

[Example of the present invention]

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 6 is a plan view showing the first implementation of the present invention's model optical deflection device. In FIG. 6, 31 is a Ti diffused Y plate L i N b O5 optical waveguide, 32, 33 is a grating optical coupler, 34 is a shoulder surface of the optical waveguide which is IνtM in an arc shape, and 35 is an Al thin film etc. deposited on it. The reflective film 36 is a B1 electrode. External TE mode He-Ne laser incident source (wavelength 63
28X) 37 is guided into the optical waveguide 31 through the grating optical coupler 32 and becomes guided light 38. This guided light 38 is diffracted by a surface acoustic wave 39 generated by the comb-shaped core 36, and becomes a diffracted guided light 40. The diffracted light 40 is at the end of the waveguide provided with the reflective film 35.
It is reflected by l134 and becomes reflected guided wave light 41. reflected light 4
1 is emitted to the outside through the output grating optical coupler 33.

FIG. 7 is a detailed explanatory diagram of the present invention. In Fig. 7, 43 is the waveguide light, 44 is the connected table top 1 wave, and 45.47 is the z
J≠The diffracted guided light generated by the wave source 43 being diffracted by the surface acoustic wave 44, 46.48 is the reflected guided light generated by the diffracted guided light 45.47 reflected at the waveguide end [lX149. The Bragg angle with respect to the surface acoustic wave 44 is set to θ8, and the incident guided light 43 is arranged so as to be incident with the surface acoustic wave 44 at the Bragg angle. As shown in FIG. 7, the position of the interaction between the incident guided wave 43 and the surface acoustic wave 44 is defined as A, and the wavefront direction of the surface acoustic wave 440 starts from point A (here, the wavefront direction refers to the surface acoustic wave The direction perpendicular to the direction of movement of
Let one point on the straight line be 0. It is assumed that the shape of the waveguide end face 49 is a circular arc whose center is at point 0 and whose radius is Ao.

When the wavelength of the surface acoustic wave 44 satisfies the Bragg condition, the diffracted light 45 is deflected by -2θB with respect to the incident guided light 43. However, the sign of the angle is assumed to be positive when counterclockwise. The diffracted light 45 is reflected at point B of the waveguide end face 49, but if the shape of the waveguide 1l18 end 1111 is a circle with point O as the center +l'>, the diffracted light 45 incident on the end face The incident angle of is θB. Therefore, write 1
Due to reflection at three points, the diffracted light 45 undergoes π-2θB1M times. Finally, 1 h of reflected light 46 with respect to incident light 43
Ti direction angle ψ is ＼ ψ=-208+π-20. =π−40. ...(1)
becomes.

Next, when the frequency of the high frequency wave applied to the comb-shaped pond was changed and the pitch of the surface acoustic wave was changed, the surface acoustic wave 44 was diffracted. ! The four-wave light 47 is -2 with respect to the incident light 43.
08- Δθ deflection. The diffracted light 47 is transmitted to the waveguide end face 49
Since the triangle AOB' is also an isosceles triangle, the incident angle of the diffracted light 47 entering the end face is θ8+Δθ. Therefore, due to the reflection at the point B', the diffracted light 47 is deflected by π-20Il-2Δθ, and finally the deflection angle ψ' of the reflected light 48 with respect to the incident light 43 is ψ1--208-Δθ+π-2θB- 2Δθ=
π-4θB-3Δθ (2).

In this way, the deflection angle Δψ when changing the frequency of the high frequency wave applied to the comb-like pattern is calculated using equations (1) and (2).
From the formula, Δψ=ψ′−ψ=3Δθ (3), and a deflection angle that is three times as large as one bulge angle Δθ of the diffracted light at point A can be obtained. Although the luminous flux is approximated as a light ray in FIG. 7, a luminous flux with a finite width does not strictly satisfy the relationship of equation (3) above. However, if the radius OA is made sufficiently large with respect to the beam width, the relationship in equation (3) holds true with good approximation.

Now, if the maximum deflection angle of diffraction due to surface acoustic waves when the frequency of the high frequency wave applied to the comb-shaped electrode 36 is continuously changed is Δθ, then the optical deflection device of the first embodiment The maximum deflection angle Δψmax is Δψmax from the relationship of equation (3).
x = 3Δθmax - (4) Therefore, it is possible to obtain a deflection angle three times larger.

FIG. 8 is a plan view showing a second embodiment of the thin film type optical deflection device of the present invention. In FIG. 8, 31 is Ti diffusion y
& LiNbO3 optical waveguide, 32.33 is a grating optical coupler, and 36 is a comb-shaped electrode.

The light deflection principle is the same as that of the first embodiment, but in this embodiment, a grating reflector 42 is used to reflect the diffracted light 40 caused by the surface acoustic wave 44. Since the shape of the grating of the grating reflector is the same as the arcuate shape of the waveguide end face 34 of the first embodiment, the same relationship as equation (3) is satisfied in this embodiment as well. In the case of this embodiment, since there is no need to process the waveguide end face into an arc shape compared to the first embodiment, it has the advantage of being easier to manufacture.

In the above embodiments, a device using the sound quaternary effect has been described, but the present invention is not limited to this, and can be applied to any thin film type optical deflection device that utilizes diffraction of guided light.

For example, Figure 9 uses the electro-optic effect;
Parts common to those in the figure are given the same reference numerals. Ti diffusion yMi
, the incident light 37 coupled to the L1Nb05 optical waveguide 31 via the grating optical coupler 32 becomes guided light 38. When a voltage is applied to the comb-shaped electrode 43 of the optical waveguide 31, the refractive index changes periodically due to the electro-optic effect.
The guided light 38 is diffracted like a diffracted guided light 40. This diffracted waveguide light 40 is reflected by a grating reflector 42 formed in an arc shape corresponding to a portion of a circle passing through the diffraction position by the comb-shaped electrode 43, and guided out of the waveguide by a grating optical coupler 33. . In this example, (
3, and the derived polarized light has a large deflection angle.

Instead of the comb-shaped electrode 43 in FIG. 9, an electrode made of a heater material with a ladder-shaped structure as shown in FIG. The guided light 38 may be diffracted by causing a rate change. Since such a thin film optical deflection device using diffraction generally has a small deflection angle, increasing the deflection angle according to the present invention is very effective.

[Effects of the present invention]

According to the thin, narrow type light control device of the present invention as described above, a deflection angle three times as large as that of a normal light deflection device can be realized. Further, in a deflection device using surface acoustic waves, there is an effect that the frequency band of the high frequency wave applied to the surface may be very narrow.

[Brief explanation of the drawing]

Figures 1 to 3 are perspective views of conventional optical deflectors.
1 and 5 are partial plan views of a conventional optical deflector. 6, 8, and 9 are plan views of the optical deflection device of the present invention, and FIG. 7 is a detailed explanatory diagram of the present invention. 10th
The figure is a plan view showing an example of an electrode structure. 31... Optical waveguide, 32.33... Grating optical coupler, 34.49... Waveguide end face, 35... Reflective film, 36.43... Comb-shaped electrode, 37... Incident Light, 38.43... Guided light, 39.44... Surface acoustic wave, 40.45.47... Diffraction guided light, 41.46.
48...Reflected waveguide light, 42...Grating reflector.゛・ia1 figure @ 2 figure flute 3 figure 4 figure! ! 5 Figure 6 Figure 1 9 @8 Figure 1

Claims (1)

[Claims] (1) In a film-type optical deflection device n that causes a periodic refractive index change in a Brener-type optical waveguide and causes the guided light to be diffracted, for causing the optical waveguide to reflect the diffracted guided light. 1. A thin film type optical deflection device, characterized in that a reflecting surface is formed, the reflecting surface corresponding to a part of a circle passing through a diffraction position of guided light. (2) The reflecting surface is composed of the t4 waveguide end face, (4 model element direction device of item 1. (3) The reflecting surface is composed of the grating attached to the optical waveguide, Paragraph 1, 41, vague type original deflection device O