JPH011123A - optical head - 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 Field of the Invention The present invention relates to an optical head used in a device for optically recording and reproducing information.

BACKGROUND OF THE INVENTION The principle of this type of device will be explained with reference to FIG. Regarding the recording medium 1 on which optical information is recorded.

A laser beam L is emitted from the light emitting unit 2. In the process, the laser beam L is made into parallel light beams by the collimator lens 3, transmitted through the polarizing beam splitter 4 and the 174-wave plate 5, and condensed by the objective lens 6 to form a spot on the recording medium 1. . Further, this objective lens 6 is equipped with an actuator 7, and this actuator 7 performs focusing servo and tracking servo. On the other hand, the laser beam L reflected from the recording medium 1 has its polarization direction changed by passing through the 174-wavelength plate 5, and is reflected off the polarizing beam splitter 4 at right angles. The principle is that the reflected laser beam L is focused on the light receiving section 10 by the convex lens 8 and the cylindrical lens 9 provided in the direction of reflection, and the optical information on the recording medium 1 is converted into an electrical signal. Note that FIG. 7 is a diagram only for explaining the principle, and the shapes of various structures are schematically shown.

Therefore, in order to accurately convert the laser beam L emitted from the light emitting unit 2 into parallel light beams by the collimator lens 3, it is necessary to maintain a constant distance between the light emitting unit 2 and the collimator lens 3. .

However, due to temperature changes during use due to heat generation of the light emitting part 2, etc., the holder holding the light emitting part 2, etc. may expand or contract, and the distance between the two may vary. and 1
If the distance between the light emitting unit 2 and the collimator lens 3 repeatedly fluctuates, there is a possibility that the distance between them will not return to its initial state. Therefore, Japanese Patent Application Laid-Open No. 61-206927 discloses a structure in which even if the distance between the light emitting part 2 and the collimator lens 3 changes once, it returns to its initial state once the influence of temperature changes disappears. It is proposed that

That is, as shown in FIG. 8, a semiconductor laser 11 is used as one light emitting section, and this semiconductor laser 11 is attached to a cylindrical lens barrel 12 so as to close the upper part thereof. Further, the outer peripheral lower surface of this lens barrel 12 is a threaded portion 12a, and a cylindrical member 13 having an opening on the lower surface is screwed into this threaded portion 12a. A collimator lens 14 is housed within the lens barrel 12, and the collimator lens 14 is pressed against the cylindrical member 13 by a coil spring 15 similarly provided within the lens barrel 12.

Therefore, for example, the lens barrel 12 expands due to the heat generated by the semiconductor laser 11, and the semiconductor laser 11 and the collimator lens 1
Even if the distance between 4 and 4 changes, this distance will similarly return to its initial state if the temperature returns to its initial state. The collimator lens 14 is always connected to the cylindrical member 13 by the coil spring 15.
This is because they are being forced to. The distance between the semiconductor laser 11 and the collimator lens 14 during assembly of the device is adjusted by rotating the cylindrical member 13 and moving the collimator lens 1.4 in the direction of its transmission optical axis.

Problems to be Solved by the Invention However, when the lens barrel 12 is expanded or contracted, changes in the distance between the semiconductor laser 11 and the collimator lens 14 cannot be avoided. It is impossible to always maintain the luminous flux of the laser beam L that has passed through the collimator lens 14 in parallel throughout the entire operating time. Therefore, there is a drawback that the spot shape of the laser beam L on the recording medium may exceed a predetermined error range, and an error may occur when reading or writing to the recording medium.

Means for Solving the Problems The present invention provides a temperature detection section that detects the temperature of a lens barrel that holds a light emitting section, and a piezoelectric actuator that changes the relative distance between the light emitting section and the collimator lens. A correction circuit was provided that applies a voltage to the piezoelectric actuator corresponding to the amount of displacement that makes the distance between the light emitting part and the collimator lens constant according to the detection result by the detection part.

action The lens barrel expands or contracts due to temperature changes.

At this time, temperature changes in the lens barrel are detected by the temperature detection section,
The voltage value applied to the piezoelectric actuator is corrected by the correction circuit according to the detection result, and the distance between the light emitting part and the collimator lens is kept constant by the operation of the piezoelectric actuator. Therefore, the laser beam passing through the collimator lens is always made into a parallel beam, thereby preventing errors during reading or writing.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. The optical system is the same as the optical system shown for explaining the principle in FIG.

Identical parts are indicated by the same reference numerals and explanations will be omitted. A semiconductor laser 20 as a light emitting section is provided, and this semiconductor laser 20 is attached to a plate 21. On the other hand, a lens barrel 23 having a flange 22 at the top is provided, and a temperature sensor 24 as a temperature detection section is attached to the flange 22. An optical path hole 25 is formed in the lens barrel 23, and the mounting plate 21 is fixed to the flange 22 with screws 26 so as to close the optical path hole 25 from above. Naturally, the semiconductor laser 20 is directed toward the optical path hole 25 side. Further, a collimator lens 27 is slidably housed in the optical path hole 25. A step portion 25a is formed in the optical path hole 25, and this step portion 25a and the collimator lens 27
A coil spring 28 is provided in a compressed state between. A cylindrical member 29 with a bottom opening is crimped to the lower part of the lens barrel 23, and a piezoelectric actuator 30 is disposed between the cylindrical member 29 and the collimator lens 27.
is provided. This piezoelectric actuator 30 is of a laminated type having an annular shape, and has a structure that is displaced in the lamination direction according to an applied voltage.

Next, a correction circuit 31 for operating the piezoelectric actuator 30 is shown in FIG. 3, an amplifier 33 is connected to the output side of the comparator 32, and this amplifier 33 is connected to the piezoelectric actuator 30. Further, a bias power supply 34 is connected to a midpoint between the piezoelectric actuator 30 and the amplifier 33. Then, the comparator 32
The temperature sensor 24 is connected to the input side of the sensor so that the detected temperature is input. The assumed normal temperature setting is input to one input terminal.

In such a configuration, when the detected value by the temperature sensor 24 is the same value as the preset temperature, the output of the comparator 32 is 0, there is no amplification by the amplifier 33, and therefore, the piezoelectric voltage is not output from the bias power supply 34. When no voltage is applied to the actuator 30, that is, at room temperature, the lens barrel 23 and the cylindrical member 29 do not expand or contract, and the distance between the semiconductor laser 20 and the collimator lens 27 remains constant. Therefore, it is not necessary to operate the piezoelectric actuator 30.

On the other hand, if the detected value by the temperature sensor 24 deviates from the preset temperature value, the comparator 32 outputs the comparison value. Therefore, an amplified signal is outputted from the amplifier 33 with an amplification factor commensurate with this comparison value, and a voltage corresponding to this amplified signal is applied to the piezoelectric actuator 30 from the bias l[34. This causes the piezoelectric actuator 30 to operate, displacing the collimator lens 27 in the direction of its transmission optical axis. Here, the amplification factor by the amplifier 33 is determined by an amount of displacement sufficient to keep the distance between the semiconductor laser 20 and the collimator lens 27 constant, which is expected to vary due to expansion or contraction of the lens barrel 23 and the cylindrical member 29. It is set to be applied to the piezoelectric actuator 30.

That is, the correlation between the distance between the semiconductor laser 20 and the collimator lens 27 and the temperature detected by the temperature sensor 24 is measured in advance, and the amplifier 33 is adjusted according to this measurement value.
This determines the amplification factor.

In this way, by displacing the collimator lens 27 according to temperature changes, the collimator lens 27 and the semiconductor laser 2
The distance between 0 and 0 is always kept constant. Therefore, the luminous flux of the laser beam L that has passed through the collimator lens 27 is always parallel, and errors in reading or writing to the recording medium 1 are reliably prevented.

Furthermore, the piezoelectric actuator 30 is not only operated in response to temperature changes by the correction circuit 31.

It may also be activated for adjustment during assembly of the device. Thereby, the distance between the semiconductor laser 20 and the collimator lens 27 can be easily adjusted, and such adjustment can be performed in a short time and with high precision. In this case, when operating the correction circuit 31, the displacement amount of the piezoelectric actuator 30 after adjustment is set to 0, and the piezoelectric actuator 3
Activate 0.

In addition, in implementation, the collimator lens 27 and the piezoelectric actuator 30 may be fixed by means such as adhesive. In this case, the coil spring 28 becomes unnecessary.

Next, FIGS. 4(a) and 4(b) show modified examples of the piezoelectric actuator 30, respectively. Namely.

The piezoelectric actuator 30 is divided into a plurality of parts in the circumferential direction, and each of the divided parts is operated independently. Therefore, when assembling the device, the semiconductor laser 20
When adjusting the distance between the collimator lens 27 and the collimator lens 27, the angle of the collimator lens 27 can also be adjusted at the same time by individually operating the piezoelectric actuators 30.

Next, a second embodiment of the present invention will be described based on FIGS. 5 and 6. The same parts as in the first embodiment are denoted by the same reference numerals and explanations will be omitted. This example is.

A piezoelectric actuator 30 was provided on the semiconductor laser 20 side. That is, for mounting, a plate 36 having a recess 35 on the lower surface is provided, a ring-shaped laminated piezoelectric actuator 30 is fixed to the recess 35, and the semiconductor laser 20 is fixed to the lower part of the piezoelectric actuator 30. In such an installation, the temperature sensor 24 is attached to the plate 36, and the plate 36 is attached to the flange 2 of the lens barrel 23.
2 with screws 26. Therefore, the device having such a structure also operates in the same manner as the structure shown in the first embodiment, and contributes to preventing read errors and write errors.

Effects of the Invention The present invention provides a piezoelectric actuator that changes the relative distance between the light emitting part and the collimator lens, detects the temperature of the lens barrel holding the light emitting part by a temperature detection part, and generates a voltage according to the detection result. is given to the piezoelectric actuator by a correction circuit to keep the distance between the light emitting part and the collimator lens constant, so even if the lens barrel expands or contracts due to temperature changes, the distance between the light emitting part and the collimator lens remains constant. is kept constant, the beam of the laser beam passing through the collimator lens can always be made parallel, and therefore,
Errors in reading or writing of the recording medium can be effectively prevented, and the relationship between the light emitting part and the collimator lens can be easily and accurately adjusted in a short time when assembling the device. have

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional side view of a semiconductor laser, a collimator lens, and their peripheral mechanisms showing a first embodiment of the present invention, FIG. 2 is an exploded perspective view thereof, and FIG. 3 is a circuit diagram of a correction circuit. 4(a) is a plan view showing a modified example of the piezoelectric actuator, FIG. 4(b) is a plan view showing another modified example, and FIG. 5 is a plan view showing a semiconductor laser according to a second embodiment of the present invention. FIG. 6 is an exploded perspective view of collimator lenses and their peripheral mechanisms, FIG. 7 is a side view of an optical system shown to explain the principle of the optical head, and FIG. 8 is a conventional example. FIG. 3 is a longitudinal sectional side view of a mechanism for holding the semiconductor laser and collimator lens shown in FIG. DESCRIPTION OF SYMBOLS 1... Recording medium, 10... Light receiving part, 2o... Semiconductor laser (light emitting part), 23... Lens barrel, 24... Temperature sensor (temperature detection part), 27... Collimator lens ,
30... Piezoelectric actuator, 31... Correction circuit,
L...Laser beam

Claims (1)

[Scope of Claims] 1. In an optical head that focuses a laser beam emitted from a light emitting part onto a recording medium, and focuses reflected light from the recording medium on a light receiving part, the light emitting part is held. A temperature detection part is provided to detect the temperature of the lens barrel, and a piezoelectric actuator is provided to vary the relative distance between the light emitting part and a collimator lens that focuses the laser beam emitted from the light emitting part into a parallel beam. , an optical head further comprising a correction circuit that applies a voltage to the piezoelectric actuator according to a displacement amount that keeps the distance between the light emitting section and the collimator lens constant according to a detection result by the temperature detection section. . 2. Claim 1, characterized in that the piezoelectric actuator has an annular shape and is divided into a plurality of parts in the circumferential direction.
Optical head described in section.