JPH0778901B2 - Optical head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical head for recording or reproducing information on an optical disc.

2. Description of the Related Art The configuration of a conventional optical head will be described below with reference to the drawings. FIG. 4 is a plan view of a conventional optical head, and FIG. 5 is a front view. Reference numeral 1 is a semiconductor laser, 2 is a collimator lens that collects light from the semiconductor laser into parallel light, and 3 is a triangular triangular prism that expands or reduces one beam width of the laser light collected by the collimator lens 2. Reference numeral 4 is a rising prism that converts the traveling direction of light into a right angle, and 5 is an objective lens that focuses the beam on the disk 6.

In the optical head constructed as described above, the surface deflection of the disk 6, defocus due to decentering, and correction of off-track are performed by driving the objective lens 5 in the ZZ direction and the XX direction.

Problems to be Solved by the Invention However, in the above-mentioned configuration, the objective lens 5 is Z-
It is necessary to drive in both the Z direction and the XX direction to perform focus control and tracking control. Since the objective lens 5 is driven in two directions orthogonal to each other in this way, the driving mechanism becomes large and the seek load becomes large. Further, since it is necessary to movably support the objective lens 5 in the tracking control direction, the seek lens propels the objective lens 5 to vibrate and the relative displacement between the focused beam and the track increases.
The tracking pull-in cannot be performed smoothly after the seek ends. Due to such problems, it has been difficult to realize high-speed access to the optical disk device.

In view of such a point, the present invention performs tracking control by changing the emission wavelength of the semiconductor laser 1 and drives the objective lens 5 only for focus control, thereby reducing the size of the objective lens drive mechanism. By supporting the objective lens movably only in the focus control direction, it is possible to reduce the seek load and provide an optical head that prevents vibration of the objective lens due to seek propulsion force and enables high-speed access to the optical disc. To aim.

Means for Solving the Problems The present invention relates to a semiconductor laser, a condensing unit that condenses light from the semiconductor laser into parallel light, and expands one beam width of the condensed laser light. An optical head comprising: a beam-shaping prism that is reduced in number; and emission wavelength varying means for the semiconductor laser.

Operation The present invention changes the wavelength of the incident light to the triangular prism by changing the emission wavelength of the semiconductor laser with the above-described configuration, and changes the emission angle of the outgoing light of the triangular prism by the wavelength dispersion of the glass material of the triangular prism. As a result, the incident angle of the incident light of the objective lens changes and tracking control can be performed by moving the focusing position of the objective lens, so the objective lens only needs to move in the focus control direction. Vibration of the objective lens can be prevented, and high-speed access of the optical disk device can be achieved.

Embodiment 1 FIG. 1 is a plan view of a first embodiment of the present invention. Reference numeral 1 is a semiconductor laser, 2 is a collimator lens that collects light from the semiconductor laser and makes it parallel light, 3 is a triangular prism that expands or reduces one beam width of the laser light that is collected by the collimator lens 2, 4 Is a rising prism that converts the traveling direction of light into a right angle, and 5 is an objective lens that focuses the beam on the disk. Reference numeral 7 is a photodetector for detecting the emission power of the semiconductor laser 1 from the back surface of the semiconductor laser 1. Reference numeral 8 denotes an APC circuit (Automatic P) for controlling the output of the photodetector 7, that is, the emission power of the semiconductor laser 1 to a constant value by the reference voltage supplied by the variable reference voltage generating means 9.
ower Control circuit). The emission wavelength varying means 10 is composed of a power control means including the photodetector 7, the APC circuit 8 and the variable reference voltage generating means 9.

The operation of the first embodiment of the present invention configured as described above will be described below with reference to FIGS. 1 and 2. FIG. 2 is an operation explanatory diagram of this embodiment.

When the reference voltage of the APC circuit 8 is changed by the variable reference voltage generating means 9, the output of the APC circuit 8, that is, the injection current into the semiconductor laser 1 changes until the output voltage of the photodetector 1 becomes equal to this reference voltage. However, the emission power of the semiconductor laser 1 changes. Since the emission wavelength of the semiconductor laser 1 has power dependence, the emission wavelength changes due to the change of the emission power. As a result, as shown by the broken line in FIG. 2, the emission direction of the emitted light from the triangular prism 3 changes, and the focus position on the disk 6 changes by ΔX.

The value of ΔX is about 0.3 to 0.4 μm when the emission wavelength of the semiconductor laser 1 changes from 780 nm to 785 nm when the glass material of the triangular prism 3 is BK7 and the enlargement ratio is about twice. On the other hand, the off-track amount due to the eccentricity of the disk 6 has a frequency characteristic, and the high frequency component of about 1 KHz or more is reduced to about 0.1 μm or less. Therefore, the off-track of the low-frequency component is corrected by the transfer mechanism that moves the optical head in the radial direction of the disk 6, and the off-track of the high-frequency component is emitted by the emission wavelength changing means 10 of the present embodiment. Can be made variable, and the light-collecting position on the disk 6 can be shifted to correct it. Therefore, since it is not necessary to drive the objective lens 5 in the tracking control direction,
Since the seek load can be reduced and the objective lens 5 can be prevented from vibrating due to the seek propulsion force, high-speed access of the optical disk device can be achieved.

Next, a second embodiment of the present invention will be described with reference to FIG.
The numbers 1 to 5 and 9 and 10 in the figure indicate the same as those in FIG. Reference numeral 11 denotes a Peltier element that cools or heats with an electric current and is fixed to the semiconductor laser 1.
A temperature detector 12 detects the temperature of the semiconductor laser 1. 13A. TC circuit (Automatic Tempretare Control circuit), which controls the Peltier element drive current so that the output of the temperature detector 12, that is, the temperature of the semiconductor laser 1 becomes constant by the voltage supplied from the variable reference voltage generating means 9.
The emission wavelength varying means 10 includes a temperature detector 12, a Peltier element 11,
The temperature control means is composed of an ATC circuit 13 and a variable reference voltage 9.

Next, the operation of the second embodiment will be described.
The emission wavelength of the semiconductor laser 1 changes with temperature.
Therefore, when the reference voltage of the ATC circuit 13 is changed by the variable reference voltage generating means 9 to change the output of the temperature detector 12, that is, the temperature of the semiconductor laser 1, the emission wavelength of the semiconductor laser 1 changes, as shown in FIG. As described above, tracking control is performed with the light condensing position on the disk 6 deviated by ΔX.

According to this embodiment, the objective lens 5 is the same as in the first embodiment.
Since it is not necessary to drive the lens in the tracking control direction, the seek load is reduced and the objective lens 5 by the seek propulsion force is reduced.
Vibration can be prevented, high-speed access to the optical disk device can be achieved, and tracking control can be performed regardless of the emission power of the semiconductor laser 1. Therefore, it is not necessary to increase the output of the semiconductor laser 1 and the size of the laser can be reduced. It is also possible to reduce the cost.

Advantageous Effects of Invention The optical head of the present invention includes a semiconductor laser, a condensing unit that condenses light from the semiconductor laser into parallel light, and expands or reduces one beam width of the condensed laser light. By providing a beam shaping prism and a semiconductor laser emission wavelength varying means, tracking control can be performed by changing the emission wavelength of the semiconductor laser, and therefore the objective lens need only be driven in the focus control direction. Therefore, the objective lens driving device can be downsized and the transfer load at the time of seek can be reduced. Further, since it is not necessary to support the objective lens so as to be movable in the tracking control direction, there is no lateral shake of the objective lens due to the seek propulsion force, and high-speed access of the optical disk device can be achieved.

[Brief description of drawings]

FIG. 1 is a plan view of a first embodiment of the present invention, FIG. 2 is an operation explanatory view of this embodiment, FIG. 3 is a plan view of a second embodiment of the present invention, and FIG. 4 is a conventional example. FIG. 5 is a front view of a conventional example. 1 ... Semiconductor laser, 2 ... Collimator lens, 3 ...
Triangular prism, 5 ... Objective lens, 10 ... Emission wavelength variable means.

Claims (3)

[Claims] 1. A semiconductor laser, a condensing means for condensing light from the semiconductor laser into parallel light, and a beam shaping prism for enlarging or reducing one beam width of the condensed laser light. And an emission wavelength changing means for the semiconductor laser. 2. The optical head according to claim 1, wherein the emission wavelength varying means of the semiconductor laser is constituted by an emission power control means of the semiconductor laser. 3. The optical head according to claim 1, wherein the emission wavelength varying means of the semiconductor laser is constituted by a temperature controlling means of the semiconductor laser.