JPH01296437A - variable focus device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a variable focus device for an automatic focus adjustment device of an optical disk head, and more particularly to a small, lightweight, and high-speed variable focus device using a thin film wave path. Regarding.

[Conventional technology]

In the conventional device, an objective lens is attached to the voice coil as a variable focus device for automatic focus adjustment, as described in, for example, "Introduction to rCD Player" (Fujio Mari, Kenji Hayashi, Corona Publishing), p. 49.

[Problem to be solved by the invention]

The above-mentioned conventional technology has problems in that the response speed is not high because it is a mechanical actuator, and the device is large, making it difficult to make it into a one-size-fits-all type.

An object of the present invention is to perform variable focus operation electrically. As a result, the response speed can be expected to be on the order of μS. Furthermore, by providing this mechanism in the condensing grating in the optical core wave path, it is possible to achieve a reduction in size and weight.

/9) [Means for solving the problem] As shown in FIG. This is achieved by applying an appropriate voltage, expanding and contracting the grating 3 by the inverse piezoelectric effect according to the voltage, changing the grating pitch, and changing the focal point of the incident light 2 as shown in 7.8.9.

The voltage applied to the electrodes is a voltage modulated by a focal position shift signal obtained by a separately provided focal position detection mechanism.

[Effect]

This will be explained using FIG. Two electrodes 4 arranged in a direction perpendicular to the main axis direction of the crystal material forming the photosensitive wave path 1
, 5 according to the defocus signal, the crystal expands and contracts due to the inverse piezoelectric effect, and at the same time the interval between the gratings 3 also expands and contracts. Then, the position of the point where the light is diffracted and focused by the grating changes accordingly, like 7, 8.9.

Next, the operating range of the focal length that specifically operates is shown.

First, the strain X J k due to the inverse piezoelectric effect is a symmetric second-order tensor, and X Jh = d t ah E + (1+J+
, can be written as: The deformation distortion X2□ in the length in the Z direction when arrow 10) is added is X zz = d 2zz E z
−(2) can be written. Here, the definition of X2□ is fl-Q"X2□=□ (3) α.

Here, if we take B a T j, Os as an example,
In the main axis direction d=392X10-12 [C/N
), and the central focal length of the focusing grating 4. β-cho,
When the electrode spacing is 3 mm and the interelectrode voltage is 1 kV, XdE
=1.3X10' (4). For the sake of simplicity, if we make an analogy with the zone plate of 0N-AXIS and assume that the focal length f is 4.5 square meters, the change in focal length will be as follows. Furthermore, in this case, since the capacitance between the electrodes is small, even if the voltage is increased, power consumption is small.

〔Example〕

FIG. 3 shows an example of application of the present invention to an optical disk head system. The light propagating through the waveguide from the semiconductor laser 2 bonded to the end face of the optical waveguide 1 made of piezoelectric material is
First, it is collimated by the geodesic lens 13,
After being deflected by the surface acoustic wave 17 generated from the transducer 14 to which a voltage modulated by the TR error signal is applied, it enters the condensing grating 3 . Electrodes 4 and 5 are provided on both sides of the condensing grating 3, to which a voltage modulated by an AF error signal 24 is applied by a power source 16. Note that this voltage is modulated so that the light is focused on the optical disk 18. The light reflected by the optical disk enters the grating 3 again and travels along the same path to be focused onto photodetectors 21 and 22 by grating lenses 19 and 20. For each signal from this detector, the difference and sum are calculated as shown in the figure to obtain a focal position shift signal 24, a tracking error signal 23, and a readout signal 25. According to this embodiment, the actuator for autofocus can also be operated using a pure electric mechanism, allowing high-speed operation, and since an objective lens is not required, the camera can be made smaller and lighter.

〔Effect of the invention〕

According to the present invention, since the variable focus mechanism can be integrated into the thin film waveguide, the device can be made smaller and lighter.

Furthermore, since there is no mechanical actuator, the speed can be increased by more than 100 times.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the principle of the present invention, Fig. 2 is an explanatory diagram showing the direction of an electric field and distortion caused by it, and Fig. 3 is a signal processing device showing an embodiment of the present invention in an optical disk head. FIG. 2 is a perspective view of a circuit block and main parts of an optical system. DESCRIPTION OF SYMBOLS 1... Optical waveguide, 3... Condensing grating coupler, 4.5... Electrode, 12... Semiconductor laser, 13 Geodesic lens, 14... Transducer, 17...
・Surface acoustic waves, 19.20... Concentrating grating.

Claims (1)

[Claims] 1. A thin film optical waveguide, a semiconductor laser that generates an optical surface wave therein, a waveguide lens that collimates the laser light, and a condensing grating coupler that focuses the laser light outside the waveguide. an electrode for applying a voltage to a grating coupler in an optical pickup having a means for converting light reflected by a disk back into an optical surface wave, and a means for detecting the intensity of the reflected optical surface wave; A variable focus device characterized in that a power source is provided for applying a voltage modulated by a focus position signal to the variable focus device. 2. Variable according to claim 1, which has a function of providing a transducer that generates surface acoustic waves on the substrate surface and adjusting the angle of Bragg diffraction so that the light spot always scans the track on the disk. Focusing device.