JP2560684B2 - Laser light source for multiple beams - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention focuses a light beam on a disc-shaped recording medium,
The present invention relates to a laser beam source for multiple beams used in an optical head of an optical information recording device for recording or reproducing information.

[Prior art and its problems]

In recent years, techniques for optically reproducing information such as images and sounds recorded as a series of minute pits on a disc-shaped recording medium have been advanced, and have been put to practical use as video discs, digital audio discs, and the like. In addition, development is underway in which not only reproduction but also recording is performed and used as a memory. This optical memory device has features such as small size and light weight, high recording density, and high reliability as compared with conventional magnetic disk devices and the like, and is expected to be applied to file devices and file memories in terminals.

The optical head that actually records / reproduces information in this optical disk device usually uses one semiconductor laser (LD) as a light source. However, a monitor of the recording state immediately after recording is unavoidable in order to detect a recording error. It takes two rotations. Further, since a high output pulse is generated during recording, the servo circuit becomes complicated and unstable. Therefore, it is desirable to use a structure with multiple beams, in which recording and reproduction are performed by different LD beams. But multiple
The beam combining type configuration, in which the emitted light from the LD is collimated by different collimating lenses and then combined by the beam splitter or polarization beam splitter and incident on the converging lens, is not easy to adjust the beam spot position, and the number of parts is large. There is a drawback that there are many. On the other hand, when the array LD in which a plurality of LDs are integrated on the same semiconductor substrate at intervals of several tens of μm is used as a light source and a converging optical system is configured by a common collimator and a converging lens, the above-mentioned drawbacks can be solved.

Also, by using the array LD in a laser printer or a laser facsimile apparatus, the recording time can be shortened and the transfer speed can be increased. An array LD in the case of an optical head is usually used for reproduction and servo signals at low output of one LD and for recording at high output of the other LD, and it is necessary to drive each LD independently. is there. However, when the distance is several tens of μm, mutual thermal interference of LDs cannot be avoided.

Fig. 4 shows the other L when one LD (LD ₂ ) is driven.
It is a drive current 1 light output characteristic figure of D (LD ₁ ). The light output characteristic A of LD ₁ when LD ₂ is not driven changes like characteristics B and C as the drive current of LD ₂ increases. This is because when LD ₂ is driven, the threshold current increases due to the temperature rise due to thermal interference. Therefore, like an optical head, if one reproducing LD is driven at low output near the threshold and the other recording is driven at high output, when the recording LD is driven, it will be reproduced due to its thermal interference. The output level for use will be drastically reduced and the servo system will become unstable. For example, when the reproduction output is about 2 mWCW drive and the recording output is about 20 mW duty 50% pulse drive, the optical output of the reproduction LD is reduced to about 1/2 during recording.

Also, in a laser printer or a laser facsimile, it is necessary to drive each LD independently, and fluctuations in the optical output level of the LD cause a recording error. Particularly in the case of a laser facsimile, a change in the light level determines the density of the surface of the recording photosensitive paper, so that a change in the light level due to an external factor such as thermal interference causes a deterioration in image quality.

As described above, when the array LD is used for an optical head, a laser printer, a laser facsimile, etc., it is desired that each LD can be driven independently, but it is difficult to realize it due to thermal interference between the LDs.

The thermal interference between the LDs can be reduced to some extent by providing a groove between the LDs, but in this case it is necessary to form a groove with a width of about 10 μm and a depth of several tens of μm, which is difficult with the current dry or wet etching technology. Is. Also the array
Since the size of the LD chip is about 10.0 μm in width and about 100 μm in thickness, there is a problem in strength.

[Object of the Invention] An object of the present invention is to eliminate these drawbacks of the prior art and to provide a laser beam source for multiple beams, which is an array LD capable of independently driving each LD.

[Structure of Invention]

According to the configuration of the present invention, a plurality of semiconductor lasers adjacent to each other are integrated and arranged on the same semiconductor substrate, and a laser beam source for a plurality of beams that outputs output beams from these semiconductor lasers is provided. At least one semiconductor laser driving circuit is provided. However, when the other semiconductor laser is driven, the driving current is increased to keep the optical output of the one semiconductor laser at a preset constant value.

[Principle of Invention]

According to the present invention, by adopting the above-mentioned configuration, the amount of decrease in the optical output due to the increase in the threshold current when adjacent LDs emit light with respect to each LD, and the same optical output as when driven independently is maintained. Since the amount of increase in drive current for this purpose is uniquely obtained in advance from the LD interval and the LD optical output of the thermal conductivity of the LD constituent elements, it is arranged as a drive circuit for at least one LD forming this array LD. A non-feedback circuit is configured so that when the LD emits light, the drive current is increased so that the light output is always constant at a preset value. Therefore, one
Even if the threshold current fluctuates due to the driving state of the LDs adjacent to each other, the optical output thereof is kept constant by the operation of the driving circuit.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In this embodiment, independent LDs 1 and 2 formed of an array LD are connected to respective drive circuits 3 and 4. This embodiment is used as a two-beam optical head composed of two light sources, and LD1 is used for recording and LD2 is used for reproduction and servo detection. Here LD1 is usually a low power (2-3mW) CW
Drive, LD2 is pulse driven with high output (20mW or more) and high frequency (1MHz or more). Reproducing LD2 When recording LD1 does not emit light in the drive current i _1, when LD2 emits light i ₂ (i _2>
Light is emitted at i ₁ ), and the light output is always kept constant at D ₁ . At this time, the current increase amount Δi = i ₂ −i ₁ is
It can be uniquely determined from the LD interval of the LD, the thermal conductivity of the LD constituent elements, the optical output of the recording LD and the calculated temperature rise of the reproducing LD2.

FIG. 2 is a circuit diagram for explaining the operation of the LD drive circuit of FIG. In the figure, 11 is a gate element, and 12 and 13 are its input terminals. When a signal is input to the terminals 12 and 13 of the gate element 11, the gate element 11 is turned on and a current flows through the load resistor 15, and otherwise the current does not flow through the resistor 15 due to the OFF response. When is threshold current of LD2 is increased adjacent recording LD1 has is emitting light, the gate element 11 is turned ON state increases by the amount of current i ₃ flowing through the driving current is also the load resistor 15 of LD2 .
Here, if the resistance value of the resistor 15 is set so that the current i ₃ matches the previously obtained current increase amount Δi, the optical output of LD2 can be maintained at the same level as when LD1 does not emit light.
In addition, the decrease in the optical output of the LD due to the thermal interference of the adjacent LDs,
According to the measurement by the present inventor, since there is a time delay of about 50 μsec, this drive circuit can sufficiently follow up, so that the optical output of LD2 is always kept constant and the optical output of LD2 is maintained stable.

FIG. 3 is a block diagram of an example of an optical head using the laser light source for multiple beams of this embodiment. The array LD of light sources is composed of two semiconductor lasers 1 and 2 with an interval of several tens of μm.
D1 is used for recording and LD2 is used for reproduction. The LDs 1 and 2 are connected to the drive circuits 3 and 4, respectively, and the optical outputs of the LDs 1 and 2 are kept constant. Since the LD1 is used only for recording, the LD1 does not necessarily require the drive circuit shown in FIG.

The radiated lights 31a and 31b from the LDs 1 and 2 are collimated by the common collimator lens 32, go straight without being deflected by the polarization beam splitter 33, pass through the λ / 4 plate 34, and are attached to the actuator 35. Recording medium 37 through converging lens 36
Focused on top. The light reflected by the recording medium 37 performs almost the same optical path, and the polarization beam splitter 33
Is polarized in the y direction (lower side). When the wavelengths of these two beams are almost the same, they are once condensed by a lens, and a pinhole or knife edge is installed at the converging point to separate the recording beam and the reproducing beam and to reproduce the reproducing beam. It is incident on the detection system 38. Further, when the wavelengths of the two beams are different from each other, it is possible to obtain a reproduction signal by making only the reproduction beam incident on the detection system 38 after being separated by a wavelength filter or the like.

〔The invention's effect〕

As described above, according to the configuration of the present invention, it is possible to realize a multi-beam laser light source in which the optical output of each LD is stable even when a disturbance such as thermal interference occurs between adjacent LDs.

In this embodiment, an array LD in which two LDs are integrated is used as an array LD, and a two-beam optical head is used as an embodiment using the LD. However, an array LD having a larger number than that, a multiple-beam optical head, Alternatively, it can be used for a laser printer or the like that uses a plurality of beams.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser light source for multiple beams composed of an array LD according to the present invention, FIG. 2 is a circuit diagram of an example of the drive circuit shown in FIG. 1, and FIG. 3 is for this embodiment. FIG. 4 is a block diagram of an example of the conventional optical head, and FIG. 4 is a characteristic diagram showing the optical output characteristic of the conventional LD. In the figure 1,2 …… Semiconductor laser, 3,4 …… Drive circuit, 11 …… Gate element, 12,13 …… Gate input terminal, 14,15,16 …… Load resistance, 31a, 31b …… Laser light , 32 …… Collimating lens, 3
3 …… Polarizing beam splitter, 34 …… λ / 4 plate, 35 …… Actuator, 36 …… Converging lens, 37 …… Recording medium, 38
...... Detection system.

Claims (1)

(57) [Claims] 1. In a multi-beam laser light source for integrating and arranging a plurality of semiconductor lasers adjacent to each other on the same semiconductor substrate and outputting an output beam from these semiconductor lasers, at least one semiconductor laser driving circuit is provided. A laser light source for a plurality of beams, comprising a circuit for increasing a drive current even when another semiconductor laser is driven to maintain an optical output of the one semiconductor laser at a preset constant value.