JPH0325764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an apparatus for performing bright spot scanning. The present invention utilizes a thin film waveguide to provide a novel and compact bright spot scanning device.

[Prior art]

Conventional bright spot scanning devices have used laser beams, and these include polygon rotating mirrors for deflecting laser beams and f-θ mirrors for condensing the deflected beam and converting it into linear bright spot motion. It consists of lenses, etc. However, in these conventional devices, each operating part requires a certain distance between each optical path, making assembly and precise adjustment very complicated, and the assembled device becomes large. It had the following drawbacks.

On the other hand, a bright spot scanning element has been proposed in Japanese Patent Application Laid-open No. 68307/1983, which solves the above drawbacks by integrating an ultrasonic optical deflector and a thin film lens in a part of a thin film waveguide.

However, in such an element, when a bright spot is imaged by emitting a deflected light beam from the end face of the waveguide, a problem arises in that a good imaging state cannot be obtained due to the influence of aberrations. That is, among the deflected light beams emitted from the thin film lens, the refraction effect received by the waveguide end face is different for the axial and off-axis light beams, and coma aberration may occur off-axis, and astigmatism may occur depending on the angle of view. The amount of aberration changed.

[Summary of the invention]

An object of the present invention is to provide a bright spot scanning element which is compact and does not require assembly and adjustment, and which is also less affected by aberrations associated with scanning when imaging a bright spot outside a waveguide. There is a particular thing.

The above-mentioned object of the present invention is to provide a part of the thin film waveguide with an optical deflection section for deflecting the light beam guided into the waveguide, and to direct the deflected light beam out from the end face of the waveguide to the outside of the waveguide. This is achieved by a bright spot scanning element which is provided with a thin film lens for condensing light, and the end face of the waveguide has a cylindrical surface shape concentric with the center of the thin film lens.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the basic configuration of a bright spot scanning element to which the present invention is applied. In this bright spot scanning element, a waveguide 2 formed on a substrate 1 is provided with a prism coupler 3, a comb tooth-shaped electrode 6, and a thin film lens 9. Now, the laser parallel beam 4 is guided through the prism coupler 3 into the waveguide 2 as a beam 5. The light beam 5 propagating through the waveguide is deflected by the ultrasonic surface acoustic wave 7 excited by the comb-like electrode 6 provided in a portion of the waveguide 2. Furthermore, this deflected light beam 8 is condensed by a thin film lens 9 and exits from an end surface 10. In such a configuration, the bright spot scanning element of this embodiment changes the frequency of the high-frequency voltage applied to the comb tooth-shaped electrode 6 to change the wavelength of the ultrasonic surface acoustic wave on the waveguide, thereby deflecting the ultrasonic surface acoustic wave. Control the angle and perform bright spot scanning. As described above, the bright spot scanning element of this embodiment is extremely compact because the optical deflector and condensing lens are provided on the same substrate, and a bright spot is formed near the exit end face of the waveguide for scanning. It also has the advantage of not requiring precise adjustment.

Next, each component of the bright spot scanning element of the above embodiment will be explained in more detail.

The substrate 1 is suitably made of a material that has a piezoelectric effect and allows high-frequency ultrasonic waves to propagate efficiently, such as LiNbO ₃ ,
LiTaO ₃ , ZnO, etc. are preferable. Moreover, the waveguide 2 is
In the case of LiNbO ₃ substrate, Ti is heated at high temperature (approximately 1000℃).
It is formed in-diffuse on the substrate to a thickness of several micrometers. In addition, in the case of LiTaO ₃ substrate, Nb or Ti is injected.
- Obtained by diffusing. Yet another example is T.Tamir
As described in "Integrated Optics" by Spinger Verlag (1975), the waveguide of this example has a high refractive index and has a large refractive index difference with the substrate, so that even if the waveguide is made thin, light will not propagate. It is desirable that it be made of a material that

The deflector is preferably one that utilizes ultrasonic surface acoustic waves, and in this embodiment, as shown in FIG. do. Pitch a of comb tooth electrode
is set to 1/2 of the center wavelength of the ultrasonic wave to be excited.
For example, if the electrode pitch a is set to 16.5 μm on a LiNbO ₃ substrate, ultrasonic waves with a wavelength of 33 μm can be excited when a high frequency voltage of 200 MHz is applied. (The speed of ultrasonic waves is approximately 6.6 x 10 ⁶ mm/sec.) The band of the deflector obtained with this one electrode is determined by the angular selection width of the Bragg-type diffraction grating created by the excited ultrasonic waves and the piezoelectric It is controlled by the band of the transducer itself, which consists of material and electrodes. The band limited by the former Bragg diffraction is Proc IEEE 64 , 779
(1976) EGLean et al “Thin Film Acoustooptic
Devices” is given by the following formula.

Δν ₁ = 2nv/λ ₀ Λ/L (1) where n: refractive index of the waveguide λ ₀ : wavelength of the incident light flux v: velocity of the ultrasonic surface acoustic wave Λ: wavelength of the same elastic wave L: also the elastic wave It is the width of

Further, the deflection angle Δφ when the applied frequency is biased by Δν is given by the following equation.

Δφλ ₀ /nvΔν (2) The number N of scanning points that can be separated from each other within this deflection angle is given by the following equation. However, W is the width of the incident light beam.

N=Δν・W/v (3) For example, Δν=50MHz, W=10mm, v=6.6×10 ⁶
When mm/sec, N=75 points.

When further expanding the number of scanning points, it is possible to use a broadband deflector etc. shown by CSTasi et al. (SPIE vo1 139, P139, 1978) This is the third
As shown in the figure, a plurality of electrodes with different pitches are arranged at an angle that satisfies the Bragg diffraction condition with respect to the incident light according to each wavelength band, and each transducer 12 is assigned a part of the wide band. Then, a so-called chirp signal, whose frequency changes continuously, is input to the electrodes to change a wide band of 500MHz. This makes it possible to obtain 1250 scanning points.

Next, as the thin film lens 9, IEEE Qun Elect
vol QE−13, P129, 1977 (by DWVakey &
A mode index lens, a Luneburg lens, a geodesic lens, etc., as shown in Van E. Wood, are suitable. These latter two types of lenses provide performance close to the theoretical resolution limit.

The size (diameter) δ of the bright spot in the x direction focused by the thin film lens is given by the following equation.

δ=2.44λ ₀ f/nW (4) =2.44(λ ₀ /n)F (5) Here, F is the F number given by f/W.

In this manner, in the bright spot scanning element of the present invention, since the deflector and the condenser lens are formed on the same substrate, the element is compact and stable without any displacement.

Furthermore, in the present invention, the exit end surface 15 of the luminous flux
As shown in FIG. 4, the lens 9 has a cylindrical surface shape with the center of the lens 9 being concentric. With such a configuration, no matter which direction the light beam is deflected, the refraction effect on the light beam by the end surface 15 is uniform;
It is possible to prevent the occurrence of aberrations associated with scanning. When the light beam is focused on the outside of the exit end face 15 as in the present invention, the light is focused in the x direction, but is in a defocus state in the y direction, which is the direction perpendicular to the film.
Therefore, in order to focus light in both the x and y directions, it is better to provide an external cylindrical lens that focuses light only in the y direction, and to match the focus point in the y direction with the focus point in the x direction. .

Further, in the case shown in FIG. 1, the light beam is guided to the waveguide via the coupling prism 3, but a semiconductor laser may be installed close to the end face of the waveguide and the light beam may be directly incident on the waveguide. However, in this case, since the light beam becomes diverging light within the waveguide 2, a thin film lens is required to convert the light beam into a parallel light beam.

Next, some embodiments to which the bright spot scanning element of the present invention is applied will be described.

FIG. 5 shows an embodiment in which the bright spot scanning element of the present invention is applied to film recording of TV images. A bright spot 17 emitted from the bright spot scanning element 16 of the present invention is guided onto the film surface by an enlarged projection lens 18. The bright spot scanning element 16 is composed of each optical IC section shown in FIG. The substrate 1 in this case is a LiNbO ₃ substrate, and the waveguide is obtained by in-diffusing Ti. Now, N=500, λ ₀ =0.82μ, f=15mm, n=2.2,
When F=f/W=2 and v _A =3.5×10 ⁶ mm/sec, the bandwidth Δν, swing angle Δφ, bright spot diameter δ, scanning width l, and response τ are as follows. .

δ=2.44λ ₀ /nF=1.8μ l=1.8×10 ^-3 ×500=0.9mm W=7.5mm Δφ=2tan ^-1 0.9/2/15=3.8゜ Δν=nv _A /λ ₀ Δφ=625MHz τ =W/v _A =2.1 .mu.sec By projecting this scanning bright spot onto a film moving in a direction perpendicular to the bright spot scanning direction using an enlarged projection lens 18, a TV image can be recorded on film.
However, in this case the scanning line repetition frequency is 15.7K
Hz, and it is necessary to scan each scan line of the TV screen at high speed.

The characteristics of the thin film waveguide type scanning element of the present invention are that it is suitable for such high-speed scanning, and that the output of the driver for driving it can be low power.

A second applied embodiment of the present invention is shown in FIG. In this example, a metal thin film recording material 21 such as Ti or Te is placed with a small gap along the emission end surface 20 of the bright spot scanning element according to the second embodiment of the present invention. It is applied to a recording head that records TV image signals by performing high-speed scanning and moving the recording medium relative to the direction perpendicular to the high-speed scanning direction (sub-scanning). The image signal is given by current modulating the semiconductor laser 13.
The recording body may be an amorphous semiconductor such as TeAsGe or GeAs, or an amorphous magnetic thin film such as MnBi, GdCo, GdFe, or TbFe. However, in the case of the latter magnetic thin film recording medium, it is necessary to apply an external magnetic field in a direction perpendicular to the film. In the latter case, the semiconductor laser may be made continuous without being modulated, and an image signal may be provided to the external magnetic field.

In this second application example, the TV signal is reproduced by using the same head used during recording and by utilizing the self-coupling effect of the semiconductor laser, so that the light beam reflected from the recording medium 21 enters the waveguide 2 again. Reproduction is possible by detecting a change in the current of the semiconductor laser that occurs when the laser beam enters the semiconductor laser 13. However, during reproduction, it is necessary to lower the output of the semiconductor laser so as not to damage the recorded signal.

When the recording medium is the above-mentioned magneto-optical recording medium, the reflected light from the recording medium becomes Da circular polarization due to the Kerr effect of perpendicular magnetization, which is converted into an intensity change in the waveguide due to the mode selectivity of the waveguide, and is converted into a semiconductor. laser 1
3, the signal is detected.

In the embodiment shown in FIG. 6, if the TV signal is recorded by setting the scanning width to 1/2 of the width of the thin film recording material 21, twice as many signals can be recorded in a round trip, and one raster of the TV signal can be recorded. By recording with one scanning line, it is possible to record a signal similar to that of a TV image.

〔Effect of the invention〕

As described above, the present invention provides a bright spot scanning element that is compact, highly reliable, and capable of high-speed scanning, and this bright spot scanning element can be applied in various forms.
It is highly usable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of a bright spot scanning element to which the present invention is applied, FIG. 2 is a diagram showing a deflector used in the present invention, and FIG. 3 is a diagram showing a broadband deflector used in the present invention. FIG. 4 is a partial diagram illustrating the characteristic parts of the present invention, FIG. 5 is a diagram showing an embodiment in which the present invention is applied to image signal recording through a lens, and FIG. It is a figure showing an example applied to recording. DESCRIPTION OF SYMBOLS 1... Base, 2... Waveguide, 3... Prism coupler, 6... Comb tooth-shaped electrode, 9... Thin film lens, 10... Output end surface, 11... Bright spot, 21...
Thin film magnetic recording material.

Claims (1)

[Claims] 1. A part of the thin film waveguide includes an optical deflection section for deflecting the light beam guided into the waveguide, and a thin film lens for condensing the deflected light beam emitted from the end face of the waveguide to the outside of the waveguide. A bright spot scanning element comprising: an end surface of the waveguide having a cylindrical surface shape concentric with the center of the thin film lens.