JPH0341903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser, and particularly to a semiconductor laser light source that is composed of a plurality of semiconductor laser elements and is suitable for use in an information processing device for video information or digital information.

[Conventional technology]

Conventionally, so-called optical video disc devices or optical information recording and reproducing devices have used gas lasers such as He--Ne lasers or Ar lasers, making the entire device large and expensive. In order to solve this problem, a method using a semiconductor laser as a light source was invented, but in this method,
The semiconductor laser was simply a replacement of the gas laser.

Furthermore, an optical information processing device using a plurality of semiconductor laser elements as a light source has also been proposed (see, for example, Japanese Patent Laid-Open No. 134516/1983).

[Problem that the invention seeks to solve]

By the way, when multiple semiconductor lasers are used as a light source, since the divergence angle of the light beam from the light emitting end face of a normal semiconductor laser is as large as 30° to 40°, it is necessary to extract the output light of each semiconductor laser separately. To direct light to the photodetector, either reduce the light-receiving area of the photodetector and place it closer to the semiconductor laser, or place a glass fiber between the light-emitting end surface of the semiconductor laser and the photodetector. Although methods such as effective incorporation have been used, the structure becomes complicated and the cost increases in either case.

Therefore, the present invention provides a simple and low-cost semiconductor laser light source that can separately extract the output light of each semiconductor laser using a single photodetector even when a plurality of semiconductor lasers are used. The purpose is to

[Means to solve the problem]

A semiconductor laser light source of the present invention includes a plurality of semiconductor lasers each having a pair of emission surfaces that emit light in opposite directions, a laser driving means for driving the semiconductor lasers with signals of different frequencies or phases, one photodetector disposed close to the semiconductor laser so as to commonly receive light emitted from one emission surface of the semiconductor laser; The present invention is characterized by comprising means for separating and extracting signals corresponding to the light emitted from the semiconductor laser.

[Effect]

In the present invention, a single photodetector receives all the light emitted from one output surface of a plurality of semiconductor lasers each having a pair of output end surfaces that emit light in opposite directions, thereby simplifying the structure. Make it. At this time, in order to distinguish which semiconductor laser is emitting a signal, the semiconductor laser is driven with signals of different frequencies or phases, and the output from the photodetector is determined by the difference in frequency or phase. The signal corresponding to the emitted light is separated and extracted.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments in which the semiconductor laser light source of the present invention is used as a light source for an optical disk device will be described in detail. In the optical disk device in the following embodiments,
Using the self-coupling effect of a semiconductor laser,
Detects information and autofocus error signals. The self-coupling effect of a semiconductor laser refers to the fact that the light emitted from one end facet of the semiconductor laser is focused onto the disk surface (information recording surface) using a lens system such as an objective lens, and the emitted light from the disk surface is re-coupled. By returning the radiation to the end surface using the lens system, the oscillation state of the semiconductor laser as a light source is changed according to the change in the amount of reflected light, and the amount of radiation sent out from the other end surface of the semiconductor laser is changed. By detecting this, changes in the amount of light reflected from the disk are detected.
(Monthly 17th).

With automatic focusing, the amount of light reflected from the disk surface reaches its maximum at the focal point, and gradually decreases before and after that point.
Take advantage of the fact that it is symmetrical with respect to the focal point. The principle of detecting this autofocus error signal will be explained using FIGS. 1 and 2. In FIG. 1, lights 4a, 4 emitted from end faces 2a, 2b and 3c of three semiconductor lasers 1a, 1b and 1c, respectively.
b, 4c are the disk 30 by the objective lens 5.
The spots are narrowed down to the top as spots 6a, 6b, and 6c. Each semiconductor laser has a different distance from the disk surface (for example, about 10 to 500 μm).
They are arranged in the order of 1a, 1b, and 1c so as to move away from each other. However, the above spot 6
Images a, 6b, and 6c are formed at slightly different positions (for example, about 10 to 500 μm) in the direction perpendicular to the disk surface. In Figure 1, spot 6
Since point a is imaged below the disk surface, it becomes a large spot that is slightly out of focus on the disk surface. Since the spot 6a is imaged exactly on the disk surface, it becomes a minute spot with a diameter of about 1 to 2 μm. Since the spot 6c is imaged at a point above the disk surface, it is also a large out-of-focus spot on the disk surface. The appearance of these three spots differs depending on the position on the disk surface. Here, the appearance of the three spots on the disk surface will be explained in more detail using FIGS. 2A to 2C. In the figure, spots 6a, 6b,
Spot 6c is used for autofocus error signal detection, and spot 6b is used for video and digital signal detection. Incidentally, numbers 2A to 2C show changes in the spot diameter when the disk surface is below the reference position, when it is at the reference position, and when it is above the reference position, respectively. As shown in FIG. 2A, when the disk surface becomes lower than the reference position, spot 6a becomes the smallest, and spots 6b and 6c become larger.
As shown in FIG. 2B, when the disk surface is at the reference position, spots 6a and 6c are spots of approximately the same size, and spot 6b is a minute spot. As shown in FIG. 2C, when the disk surface is above the reference position, spot 6c becomes the smallest, and spots 6b and 6a become larger. The spots on the disk surface as described above are reflected by the disk, pass through the lens 5, and then return to each light emitting laser. At this time, the light emitting end face 2 of the semiconductor laser
Since a, 2b and 2c are usually minute openings of 1 .mu.m.times.3 to 5 .mu.m, the amount of reflected light returning into the semiconductor laser varies depending on the spot diameter on the disk. In other words, if it is a minute spot on the disk surface, it will be reflected and become a minute spot on the semiconductor laser aperture, so that the amount of reflected light returning into the aperture will be the largest. As the amount of light returned to the laser increases, the self-coupling effect also increases, and the other light emitting end face 3 of the semiconductor laser
The amount of output light from a, 3b and 3c increases. In other words, when the disk surface is at the reference potential, the output light 7b from the light emitting end surface 3b becomes the maximum, and the output light 7a and 7 from the light emitting end surfaces 3a and 3c reach a maximum.
c will be the same. Next, when the disk surface does not match the reference position and shifts slightly toward the lens, the output lights 7a and 7b decrease, and the output light 7c increases. Similarly, if the disk surface does not match the reference position,
When slightly shifted in the opposite direction to the lens side, the output lights 7b and 7c decrease, and the output light 7a increases.
Therefore, in order to detect the autofocus error signal, it is sufficient to receive the output lights 7a and 7c with a photodetector and detect the difference in output.

In the present invention, as shown in FIG.
Lights 7a, 7b and 7c from light emitting end surfaces 3a, 3b and 3c opposite to the disk side of a, 1b and 1c
are all received by one photodetector 10, simplifying the structure. At this time, the semiconductor lasers 1a, 1b,
1c, the semiconductor lasers 1a, 1b, and 1c are modulated with signals of different frequencies or phases, and from the output of the photodetector 10, the semiconductor lasers 1a, 1b, and 1c are detected depending on the difference in frequency or phase. , 1b, 1c are separated and extracted. FIG. 3 shows one embodiment of an optical disk device using the semiconductor laser light source of the present invention. Parts that overlap with those in FIG. 1 are given the same numbers. The light from the semiconductor lasers 1a, 1b, and 1c is focused on the disk 30 rotating in the direction of the arrow and reflected as explained in FIG. 1. At this time, the semiconductor lasers 1a, 1b, 1c are oscillators 20a, 20, respectively.
Signals from b and 20c (each oscillation frequency is
fa, fb, fc). For example, fa
is about 500KHz, fb is about 80MHz, and fc is about 700KHz. The output from the photodetector 10 is passed through bandpass filters 36 and 37 to output the semiconductor lasers 1a and 1c.
Separate the amount of light from each. band filter 3
The center frequencies of 6 and 37 are selected as fa and fc, respectively.
The outputs of the bandpass filters 36 and 37 are connected to the differential amplifier 34.
to obtain an autofocus error signal 33. The signal 33 is input to the compensation circuit 35 of the servo system, and the output of the compensation circuit 35 is sent to the voice coil (objective lens 5).
is input to the drive circuit 38 (an electromagnetic element that moves in the optical axis direction), and the voice coil 31 is moved to automatically perform focusing. On the other hand, the output from the photodetector 10 is passed through a bandpass filter 39 (with a center frequency of fb) to read out the information signal recorded on the disk and input to a signal processing circuit 32 (not shown).

FIG. 4 shows another embodiment. Elements having the same functions as in FIG. 3 are given the same numbers. No modulation is applied to the semiconductor laser 1b in the middle, and the information signal is passed through a high-pass filter 40 to the signal processing circuit 32.
Enter. At this time, fa and fc are selected to be smaller than the cutoff frequency of the high-pass filter (for example, several
(about 100KHz).

FIG. 5 shows another embodiment. Oscillator 55
After modulating the semiconductor laser 1c with a signal from the oscillator 55 (oscillation frequency f0, for example, about 600 KHz) and passing the signal from the oscillator 55 through the phase variable device 53, the semiconductor laser 1a is modulated with the output signal of the phase variable device 53. . No modulation is performed on the semiconductor laser 1b in the middle. The output from the photodetector 10 is passed through a bandpass filter 50.
(center frequency f0) and input to the high-pass filter 54. The output of the band filter 50 is multiplied by multipliers 51 and 5.
2, multiplication is performed with the signal modulating the semiconductor laser, and synchronous detection is performed to extract a signal related to the signal component modulating the semiconductor laser.
The outputs of the multipliers 51 and 52 are input to a functional element having the same configuration as the embodiment shown in FIG. 3 to correct the focus shift. At this time, the amount of phase shift of the phase variable element 53 is preferably a multiple of 90°×an integral number. Note that the information signal recorded on the disk 30 is extracted by a high-pass filter 54 having a cutoff frequency higher than f0 and sent to the processing circuit 32. In this embodiment, the semiconductor laser modulation means can be configured more easily than in the embodiment shown in FIG.

Although the present invention has been described above according to the embodiments, the modulation waveform is not limited to a sine wave, but may be a triangular wave or a rectangular wave. In order to explain focus detection, we have taken as an example the case where there are three light sources (semiconductor lasers), but for example, another light source is provided for tracking, and this is modulated at a desired frequency to produce at least one light source. It is also possible to receive the light with a detector and separate the tracking signal. In this case, a configuration in which semiconductor lasers are arranged in an array is suitable as the light source. Moreover, although automatic focusing in the case of reproduction has been described, the present invention can also be applied to automatic focusing in the case of recording.
In this case, recording is performed by modulating the semiconductor laser in the middle according to the desired information signal.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a simple, low-cost light source for an information processing device using a plurality of semiconductor lasers.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an optical system of an information processing device using the semiconductor laser light source of the present invention, and FIG.
2C to 2C are diagrams showing the appearance of spots on a disk surface, and FIGS. 3 to 5 are diagrams each showing an optical disc device using the semiconductor laser light source of the present invention.

Claims (1)

[Scope of Claims] 1. A plurality of semiconductor lasers each having a pair of emission surfaces that emit light in opposite directions, laser driving means for driving the semiconductor lasers with signals of different frequencies or phases, and a semiconductor laser that drives the semiconductor lasers with signals having different frequencies or phases. one photodetector disposed close to the semiconductor laser so as to commonly receive light emitted from one emission surface of the laser; 1. A semiconductor laser light source comprising means for separating and extracting signals corresponding to emitted light from the semiconductor laser. 2. The semiconductor laser light source according to item 1, wherein the plurality of semiconductor lasers are arranged offset from each other in the optical axis direction of the emitted light.