JPH10111524A - Light deflector and optical scanner using the light deflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an outgoing light whose light intensity is constant in a deflection range even without adding a new control to control systems of a light source and a high frequency signal generator. SOLUTION: A waveguide type light deflector is roughly constituted of a substrate, a piezoelectric thin film optical waveguide formed on the substrate, a chirp type comb-shaped electrode 5, a grating coupler for light incidence and a grating coupler for light emission. In the chirp type comb-shaped electrode 5, respective electrode fingers are weighted by an apodizing method so that the intensity of the outgoing light of the light deflector becomes constant in the deflection range. That is, plural electrode fingers 23 (231 , 232 ...) exist alternately toward the pads of other sides from two opposed pads 21, 22 and widths of respective electrode fingers 23 and intervals among the fingers and crossing widths among the fingers are made to be successively changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflector,
An acousto-optic light deflector using an optical waveguide, comprising an optical computer optical switch and optical modulator, an optical communication optical switch and an optical demultiplexer and an optical modulator, a laser beam printer, a copier,
The present invention relates to an optical deflector used for an optical deflector such as a scanner or an optical modulator, and a scanning optical device using the optical deflector.

[0002]

2. Description of the Related Art Various types of optical deflectors have been proposed which use a known technique in which a light beam traveling in an optical waveguide is deflected by acousto-optic interaction (Bragg diffraction) with a surface acoustic wave propagating in the optical waveguide. ing. Generally, an optical deflector generally includes an optical waveguide made of a piezoelectric material, a comb-shaped electrode provided on the optical waveguide for generating a surface acoustic wave, and light for entering a light beam into the optical waveguide. It is provided with an incident means and a light emitting means for emitting a light beam traveling through the optical waveguide to the outside. Then, the frequency of the high-frequency signal applied to the comb-shaped electrode is changed to change the wavelength of the surface acoustic wave propagating in the optical waveguide, and the deflection angle of the light beam traveling in the optical waveguide is controlled at high speed and with high accuracy.

By the way, conventionally, in order to enlarge the deflection range of the light emitted from the optical deflector, a broadband surface acoustic wave is excited using a comb-shaped electrode called a chirp type. In this chirp type electrode, the width and interval of the electrode fingers constituting the electrode are sequentially changed, and a wider surface acoustic wave is excited compared to a normal type electrode or the like in which the width and interval of the electrode fingers are constant. can do.

[0004]

However, the conventional chirped comb-shaped electrode can excite a wide range of surface acoustic waves. However, the energy of the excited surface acoustic waves differs depending on the wavelength, and is uniform. It was not something. Further, the propagation loss of the surface acoustic wave propagating through the optical waveguide differs depending on the wavelength of the surface acoustic wave, and is not uniform. Furthermore, the efficiency of the acousto-optic interaction between the surface acoustic wave and the light beam (Bragg diffraction) differs depending on the wavelength of the surface acoustic wave and is not uniform.
Due to these causes, there is a problem that the intensity of the light emitted from the optical deflector is not constant over the entire deflection range.

Conventionally, as a countermeasure, the intensity of the light beam emitted from the light source is controlled for each wavelength of the surface acoustic wave to make the intensity of the light emitted from the optical deflector constant or applied to the comb-shaped electrode. There has been proposed a method of controlling the power of a high-frequency signal for each wavelength of a surface acoustic wave to make the intensity of light emitted from an optical deflector constant. However, these methods require new control in the control system of the light source and high-frequency signal generator,
In addition, there is a problem that the durability of the light source is reduced, resulting in an increase in cost.

It is an object of the present invention to provide an inexpensive light deflection device that can obtain emission light having a constant light intensity within a deflection range without adding new control to a control system of a light source or a high-frequency signal generator. And a scanning optical device using the optical deflector.

[0007]

In order to achieve the above object, in the optical deflector according to the present invention, the comb-shaped electrode has a chirp type, and the light emitted from the waveguide type optical deflector is provided. The electrode fingers of the comb-shaped electrode are weighted so that the intensity is substantially constant within the deflection range. Here, the weighting is performed by measuring a frequency deflection characteristic of a waveguide type optical deflector provided with an unweighted chirp type comb-shaped electrode and obtaining an inverse function of the frequency deflection characteristic. It is preferable that the method further includes a step of calculating an impulse response waveform by performing Fourier transform, and a step of obtaining a position and an intersection width of the electrode finger of the chirped comb-shaped electrode based on the impulse response waveform. The cross width means the length of the portion where the adjacent electrode fingers face each other, in other words, the opening length effective for exciting surface acoustic waves.

With the above arrangement, the intensity of the light emitted from the optical deflector can be easily made uniform within the deflection range only by setting the positions of the electrode fingers and the cross width of the comb-shaped electrodes to predetermined dimensions. Therefore, it is not necessary to add new control to the control system of the light source and the high-frequency signal generator. Further, the scanning optical device according to the present invention is arranged such that the comb-shaped electrodes are chirped, and that the emission light of the waveguide type optical deflector has a substantially constant intensity within a deflection range. Are provided with a weighted optical deflector. According to the above configuration, the intensity of the light emitted from the deflector becomes substantially constant within the deflection range, so that an image with excellent quality can be stably obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical deflector according to the present invention and a scanning optical apparatus using the optical deflector will be described below with reference to the accompanying drawings. [Schematic Configuration of Optical Deflector] As shown in FIG. 1, a waveguide type optical deflector 1 generally includes a substrate 2, a piezoelectric thin film optical waveguide 4 formed on the substrate 2, a chirped comb tooth. Electrode 5
And an input grating coupler 15 and an output grating coupler 16.

As the substrate 2, a glass substrate, a Si substrate, a sapphire substrate or the like is used. The optical waveguide 4 is formed on the substrate 2 by a method such as a laser ablation method, a sputtering method, a vacuum evaporation method, a CVD method, and a sol-gel method. As a material of the optical waveguide 4, a material having piezoelectricity such as ZnO is used. A chirped comb-shaped electrode 5 of a transducer is formed on the optical waveguide 4 near the center of the optical waveguide 4 by A1 or the like by a method such as a photolithography method, a lift-off method, or an etching method. The comb-shaped electrode 5 is for converting a high-frequency electric signal generated by the high-frequency signal generator 8 into a surface acoustic wave, and excites the surface acoustic wave 9 in the optical waveguide 4.

As shown in FIG. 2, the electrode fingers 23 of the chirped comb-shaped electrode 5 are weighted by an apodizing method described later so that the light emitted from the optical deflector 1 has a constant intensity within the deflection range. ing. That is, the plurality of electrode fingers 23 (23 ₁ , 2
3 ₂ ,...) Alternately extend toward the pad of the other party,
The width, interval, and cross width D (D ₁ , D ₂ ,...) Of each electrode finger 23 are sequentially changed. In the present embodiment, the width and the interval are d _a to
It has been changed to d _b. Here, the cross width D is the length of the portion where the adjacent electrode fingers 23 face each other, in other words,
The aperture length is effective for exciting the surface acoustic waves 9.

Further, an input grating coupler 15 and an output grating coupler 16 are disposed on both right and left sides of the optical waveguide 4. The incident grating coupler 15 is provided with a light beam L emitted from a light source (not shown).
Is made to enter the optical waveguide 4. The emission grating coupler 16 is for emitting the light beam L traveling in the optical waveguide 4 to the outside. These grating couplers 15 and 16 are provided at a constant pitch, respectively, and for example, the same material as that of the optical waveguide 4 is used. Grating coupler 15,
Reference numeral 16 is formed by a method such as an electron beam drawing method, a photolithography method, and a two-beam interference method.

[Operation and Effect of Optical Deflector] In the optical deflector 1 having the above-described configuration, the light beam L from the light source (not shown) is incident on the optical waveguide 4 by the incident grating coupler 15 and then passes through the optical waveguide. proceed. On the other hand, a high-frequency electric signal generated by the high-frequency signal generator 8 is applied to the comb-like electrode 5. When the comb-shaped electrode 5 has a portion composed of the electrode fingers 23 at the interval Λ, a surface acoustic wave 9 having a wavelength Λ is excited by a high-frequency signal having a frequency f that satisfies the following expression. Are propagated through the optical waveguide 4 in the direction of arrow a in FIG.

Λ = v / f (v: propagation velocity of surface acoustic wave) As shown in FIG. 3, the light beam L traveling in the optical waveguide 4 has a wave front in each cycle traveling in the direction of arrow a. It intersects with the surface acoustic wave 9 of the displayed wavelength Λ. If the intersection angle is θ and the wavelength of the light beam L is λ, when the condition θ = sin ⁻¹ (λ / 2Λ) is satisfied, the Bragg diffraction phenomenon due to the acousto-optic effect occurs, and the light beam L is diffracted. Be deflected. The deflected light beam L is output from the output grating coupler 1.
6 to the outside.

As described above, the electrode fingers 23 of the comb-shaped electrode 5
Since the width and spacing is changed to sequentially d _a to d _b, this comb-shaped electrodes 5, the high-frequency signal having a frequency band from f _a = v / Λ _a to f _b = v / Λ _b the application of a surface acoustic wave 9 wavelength band from lambda _a lambda _b is excited (however, lambda _a
= 4d _a , Λ _b = 4d _b ). Therefore, the deflection angle θ is also θ _a = si
n ^-1 (λ / 2Λ _a) from ^{_{θ b = sin -1 (λ /}} 2Λ b) until it is possible to change. It is desirable that the change in the deflection angle θ be large.

In the above-described light deflector 1, the electrode fingers 23 of the chirped comb-shaped electrode 5 are weighted so that the light emitted from the light deflector 1 has a constant intensity within the deflection range. and without adding a new control to the control system of the high-frequency signal generator 8, as shown in FIG. 4, the outgoing light deflection range (frequency of the high-frequency signal range of f _a ~f _b) over the whole area Is obtained, the intensity of which is substantially constant.
FIG. 4 is a graph showing the frequency deflection characteristics of the optical deflector 1. The vertical axis indicates the relative intensity of the light emitted from the optical deflector 1, and the horizontal axis indicates the frequency of the high-frequency signal applied to the comb-shaped electrode 5.

[Weighting of Comb-Toothed Electrodes] Next, a method of weighting the electrode fingers 23 of the comb-toothed electrodes 5 (apodizing method) to keep the intensity of light emitted from the optical deflector 1 constant in the deflection range will be described. I do. In general, the apodizing method utilizes the fact that the impulse response of a comb-tooth electrode determined by the position and the crossover width of an electrode finger and the frequency response of the comb-tooth electrode are in a Fourier-exchange relationship, and the crossover of each electrode finger is performed. This is a method of changing the width and performing weighting. That is, a desired frequency response waveform is determined, an impulse response waveform having an inverse Fourier transform relationship is determined by calculation, the time axis of the waveform is replaced with the position of the electrode finger, and the impulse response waveform at each electrode finger position is calculated. In this method, the amplitude is used as the relative cross width of the electrode finger.

The present embodiment is characterized by a frequency response waveform on which the calculation is based. First, an optical deflector 25 having an unweighted comb-shaped electrode 26 shown in FIG.
Is measured. As shown in FIG. 6, the comb-shaped electrode 26 of the optical deflector 25 has each electrode finger 27 (27).
_1, 27 _2, 27 _3, a constant chirped cross width D is ...). Then, it is assumed that the graph shown in FIG. 7 is obtained as the frequency deflection characteristic of the optical deflector 25, for example. The vertical axis indicates the relative intensity of the light emitted from the optical deflector 25, and the horizontal axis indicates the frequency of the high-frequency signal applied to the comb-shaped electrode 26.

Next, an inverse function of the frequency deflection characteristic is obtained. FIG. 8 is a graph showing an inverse frequency function. This frequency inverse function is used as a base frequency response waveform. By performing an inverse Fourier transform of the inverse frequency function, an impulse response waveform of the chirped comb-shaped electrode is obtained. FIG. 9A shows the obtained impulse response waveform. Next, the time axis of the impulse response waveform 35 is replaced with the position of the electrode finger. That is, in FIG. 9A, as shown in FIG. 9B, the value obtained by multiplying the time at which the impulse response waveform 35 intersects the horizontal axis of the relative intensity 0 by the propagation velocity v of the surface acoustic wave 9 is shown in FIG. This is the relative position of the electrode finger 23. FIG.
As shown in FIG. 9B, the amplitude W of the impulse response waveform 35 at each time in FIG.
The relative intersection width D between them is as follows.

Thus, the chirped comb-shaped electrode 5 having the weighted electrode fingers 23 is obtained. This weighted chirped interdigital electrodes 5, by applying a high-frequency signal having a frequency band from f _a to f _b, comb-shaped electrode 5 in each wavelength from lambda _a to lambda _b, 8 A surface acoustic wave 9 having an uneven energy intensity as shown in FIG. As shown in FIG. 4, the light emitted from the optical deflector 1 that has undergone acousto-optic interaction with the surface acoustic wave 9 having the energy intensity shown in FIG. 8 has a substantially uniform intensity over the entire deflection range. Become.

[Application to Scanning Optical Device] Next, as shown in FIG. 10, the optical deflector 1 in the case where an optical printer is constructed by using the optical deflector 1 together with the lens system 38 and the photosensitive drum 39. The operation and effect of will be described. When a high-frequency signal generated by the high-frequency signal generator 8 is applied, a surface acoustic wave 9 is excited in the optical waveguide 4. The surface acoustic waves 9 excited at this time are weighted chirped comb-shaped electrodes 5.
Has an energy intensity distribution at each wavelength as shown in FIG. The surface acoustic wave 9 propagates in the optical waveguide 4 in the direction of arrow a in the figure. On the other hand, the light beam L emitted from the light source enters the optical waveguide 4 via the incident grating 15, and travels through the optical waveguide 4 as a light beam.

The surface acoustic wave 9 crosses the light beam L.
The light beam L deflected by the acousto-optic interaction with the surface acoustic wave 9 exits through the exit grating 16. The emitted light beam L has the frequency deflection characteristic shown in FIG. 4, and the intensity is constant over the entire deflection range.

The emitted light beam L is applied to a lens system 38.
Is condensed on the photosensitive drum 39 via the
9 is scanned in the direction of arrow b. The photosensitive drum 39 is driven to rotate at a constant speed in the direction of arrow C, and an image (an electrostatic latent image) is formed on the drum 39 by the main scanning in the direction of arrow b by the optical deflector 1 and the sub-scanning of the drum 39 in the direction of arrow c. ) Is formed. Thus, a high-quality output image can be obtained.

[Other Embodiments] The optical deflector according to the present invention and the scanning optical apparatus using this optical deflector are not limited to the above-described embodiments, but variously deflect within the gist of the invention. be able to. A prism coupler or the like may be used as the light inputting means or the light emitting means, or a light input / output means having an end face of the optical waveguide as a light beam input / output surface may be used. Alternatively, the optical waveguide may be provided with a condenser lens unit, a diverging lens unit, a collimating lens unit, and the like.

Further, the comb-shaped electrodes are shown in FIGS.
The weighted inclined finger chirp type comb-shaped electrodes 42, 43, and 44 shown in FIG. In particular, the comb-teeth electrodes 43 and 44 have a dog-leg structure so that impedance matching with an external high-frequency signal generator can be easily performed. These comb-shaped electrodes 42 to 44
By making the propagation direction of the surface acoustic wave of each wavelength different by changing the angle of the electrode finger, the difference of the Bragg angle at each wavelength is considered. The electrode fingers of the comb-shaped electrode are not limited to a single electrode as in the above embodiment, but may be a double electrode or a unidirectional electrode in consideration of internal reflection or unidirectionality of surface acoustic waves. .

In the above-described embodiment, the apodizing method is applied to one method.
Although the case of applying only once is described, the intensity of the emitted light becomes more constant by repeatedly measuring the deflection characteristics of the optical deflector having the chirped comb-shaped electrode weighted in this way and repeatedly applying the apodizing method. May be obtained. Further, since the cross width of each electrode finger is different, there are portions where each electrode finger exists and portions where it does not exist with respect to the same wave front of the surface acoustic wave. Occurs. In order to solve this problem, dummy electrode fingers 50 (50 ₁ , 50 ₂ , 50 ₃ ...) May be provided as shown in FIG.

[0027]

As is apparent from the above description, according to the present invention, the light emitted from the waveguide type optical deflector is substantially constant in the deflection range with respect to the chirped comb-shaped electrode. Weighting, the position of the electrode finger and the crossover width are simply set to predetermined dimensions, and no additional control is added to the control system of the light source or the high-frequency signal generator. An inexpensive optical deflector with a constant intensity can be obtained. Further, by providing the scanning optical device with the deflector, an image with excellent quality can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an optical deflector according to the present invention.

FIG. 2 is a plan view showing a part of a chirp type comb-shaped electrode used in the optical deflector shown in FIG. 1;

FIG. 3 is an explanatory diagram showing a Bragg diffraction phenomenon.

FIG. 4 is a graph showing frequency deflection characteristics of the optical deflector shown in FIG.

FIG. 5 is a perspective view of an optical deflector used for designing the chirped comb-shaped electrode shown in FIG. 2;

FIG. 6 is a plan view showing a part of the chirped comb-shaped electrode used for designing the chirped comb-shaped electrode shown in FIG. 2;

FIG. 7 is a graph showing frequency deflection characteristics of the optical deflector shown in FIG.

8 is a graph showing an inverse function of the frequency deflection characteristic shown in FIG.

9A is a graph showing an impulse response waveform of the inverse function shown in FIG. 8, and FIG. 9B is a plan view showing a part of a chirped comb-shaped electrode weighted based on the impulse response waveform.

FIG. 10 is a perspective view showing a scanning optical device using the optical deflector shown in FIG. 1;

FIG. 11 is a plan view showing a modification of the chirped comb-shaped electrode.

FIG. 12 is a plan view showing another modified example of the chirped comb-shaped electrode.

FIG. 13 is a plan view showing still another modification of the chirped comb-shaped electrode.

FIG. 14 is a plan view showing still another modification of the chirped comb-shaped electrode.

[Explanation of symbols]

1 ... optical deflector 2 ... substrate 4 ... optical waveguide 5 ... chirped interdigital electrode 9 ... surface acoustic wave 15 ... incident grating coupler 16 ... exit grating coupler 23 (23 _1, 23 _2, 23 _3, ...) ... Electrode finger 38... Lens system 39.

Claims (3)

[Claims] A substrate, an optical waveguide provided on the substrate, a comb-shaped electrode provided on the optical waveguide for converting a high-frequency signal to generate a surface acoustic wave; In a waveguide type optical deflector provided with a light incidence unit for entering light and a light emission unit for emitting light traveling through the optical waveguide to the outside, the comb-shaped electrode is chirped An optical deflector characterized in that the electrode fingers of the comb-shaped electrode are weighted so that the intensity of light emitted from the waveguide type optical deflector becomes substantially constant within the deflection range. 2. The method according to claim 1, wherein the weighting is performed by measuring a frequency deflection characteristic of a waveguide type optical deflector provided with an unweighted chirped comb-shaped electrode, and obtaining an inverse function of the frequency deflection characteristic. Inversely Fourier-transforming the function to calculate an impulse response waveform, and determining the position and intersection width of the electrode fingers of the chirped comb-shaped electrode based on the impulse response waveform. The optical deflector according to claim 1. 3. A scanning optical device which condenses a light beam emitted from a light source to a minute point via an optical deflector and an optical element and scans a surface to be scanned in a line. 2. An optical scanning device according to claim 1, wherein said optical deflector is an optical deflector.