JPH0498887A - Optical device - Google Patents

Abstract

PURPOSE:To enable an optical device to operate normally even if one of laser diodes is deteriorated by a method wherein a power is supplied to one of other laser diodes through a power switching means when an operating laser diode is deteriorated. CONSTITUTION:A switching circuit 62 supplies a power to a transistor 56 when an optical pickup is made to start operating, so that a laser diode 40A out of a laser diode array is made to emit laser rays, and record or regeneration is carried out by the use of the laser rays concerned. Thereafter, when the laser diode 40A is deteriorated after it is used for a long term as a source of an optical pickup, it decreases in brightness when an operating current is kept the same in intensity, so that a current fed to the diode 40A is made to increase in intensity through the action of an APC circuit 61. When the fed current reaches to a prescribed upper limit in intensity, the switching circuit 62 is operated to turn only another transistor 57 ON, and another laser diode 40B is made to emit laser rays.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical device suitable for application to, for example, an optical pickup for an optical disk device.

[Summary of the Invention] The present invention relates to an optical device suitable for application to, for example, an optical pickup for an optical disk device, and relates to a laser diode array in which a plurality of laser diodes are integrated, and a monitor for receiving output light from the laser diodes. a light receiving element, a power switching means for supplying power to one of the laser diodes so that the output signal of the monitoring light receiving element reaches a predetermined level, and the laser diode to which the power is supplied. and deterioration detection means for detecting deterioration of the laser diode, and when the laser diode to which power is supplied deteriorates, one of the laser diodes is supplied with power to the other one of the laser diodes. The optical device is designed to operate normally even if the laser diode deteriorates.

[Prior Art] In optical disc devices such as optical video disc playback devices, so-called compact disk playback devices, and magneto-optical recording and playback devices, optical pick amplifiers are used to record or play back information signals. In addition, a relatively inexpensive and small laser diode is used as the light source for the optical beam.

Laser diodes generally have a longer lifespan than gas lasers, etc., but there is still a probability that laser diodes will deteriorate due to electrostatic damage caused by surge currents or the growth of lattice defects (dark lines) in the crystal itself that makes up the diode. occurs in When a laser diode deteriorates, the dark value of the current generally increases, so more power must be supplied to obtain the same light output, and eventually the light output will decrease even if the maximum power is supplied. It no longer reaches the specified value.

In addition, the laser diode is fixed inside the optical pickup, and adjusting the optical axis for normal recording or playback is relatively complicated. If the diode deteriorates and the specified light output cannot be obtained, the entire optical pickup must be replaced.

[Problems to be Solved by the Invention] However, when one laser diode deteriorates, sending the optical disk device to a service center or the like to replace the optical pickup does not require the use of the optical disk device during the replacement. There are disadvantages in that the optical pickup cannot be used and the cost required to replace the optical pickup is large.

In view of this, the present invention improves product reliability in optical devices such as optical pickups that use laser diodes by allowing the optical devices to operate normally even if one laser diode deteriorates. The purpose is to

[Means for Solving the Problems] The optical device according to the present invention includes a laser diode array (40) in which a plurality of laser diodes (40A, 40B) are integrated, as shown in FIGS. 1 to 3, for example. A monitoring light receiving element (42) that receives the output light of these laser diodes, and power that supplies power to one of the laser diodes so that the output signal of the monitoring light receiving element reaches a predetermined level. Switching means (61, 6
2) and a deterioration detection means (58, 62) for detecting deterioration of the laser diode to which power is supplied, and when the laser diode to which power is supplied deteriorates, one of the laser diodes is any other one
It is designed to supply power to each individual.

[Function] According to the present invention, for example, when the laser diode in use deteriorates, the power switching means (61
, 62) to continue using the optical device.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this example, the present invention is applied to an optical pick amplifier of an optical disk device.

FIG. 4 shows the optical pickup of this example, in which (1) is the base, (2) and (3) are the side walls of the base (1), and these side walls (2) and ( 3)
Buttons (4A) and (4B) are installed in the coaxial through-holes of
and insert the guide shaft (5) extending in the radial direction of the optical disc into these bushes (4A) and (4B),
The guide shaft (5) is connected between the side wall (2) and the side wall (3).
) onto the tilt sensor (
Attach the tilt sensor) (7). Also, the base (1) is located on the opposite side of those side walls (2) and (3).
A U-shaped guide portion (8) is provided in the. There is a rotating shaft of the optical disc approximately on the extension of the guide shaft (5), and the optical pickup is slid in the radial direction (R direction) of the optical disc along the guide shaft (5) by a drive mechanism (not shown). .

(9) is first mounted on a plate, and a pair of U-shaped yokes (10) and (13) are mounted on the base (1) so as to face each other through the plate (9). the law of nature(
Magnetized bodies (11) and (10) and (13) are respectively placed on the inner surfaces of
14), and small inverted U-shaped yokes (12) to close the magnetic paths of these yokes (lO) and (13).
) and (15). The base (1) and mounting are on the board (
A through hole for laser beam passage is provided in the portion between the yoke (10) and the yoke (13) of 9).

(16) is a U-shaped second mounting plate, and its first
For installation, one yoke (13) is placed on top of the plate (9), and for the second installation, the plate (16) is fixed with the screws 17).
This installation involves bending one end of the plate (16) and attaching the plate spring (19), which is made up of four parallel plates, to the relay member (18).
) at one end. A bobbin (20) was attached to the free end of this leaf spring (19) via a stopper (21), and a focusing coil (22) and a tracking coil (23) were attached to this bobbin (20). Later, these coils (22) and (23) are both positioned in front of the magnetized body (11) and the magnetized body (14).

A through hole is formed in the focusing direction of the bobbin (20), and an objective lens (24) is attached to one end of the through hole to prevent the objective lens (24) from directly colliding with the optical disc. Put on the protective cover (25). The bobbin (20) and the objective lens (24) are connected to the leaf spring (1).
9) allows the optical disc to swing freely in the radial direction (R direction) and axial direction (Z direction, see Figure 5), and the action of coils (22) and (23) allows it to swing freely in the R direction.
Positioning can be performed in any direction and at desired coordinates in two directions. That is, this constitutes a two-axis actuator.

(26) is a storage member for optical components, (27) is a light receiving board attached to one end of this storage member (26), and this storage member (26) is attached to the lower surface of the base (1).

FIG. 5 shows the arrangement of the optical components of this example. In this FIG. Half mirror (30), collimator lens (31)
), the reflected light from this optical disc (33) is guided to an optical disc (33) via a prism (32) and an objective lens (24) for converting the optical path to a right angle. -(30) is reached.

The semiconductor laser light source (
A light-receiving substrate (27) is arranged approximately symmetrically with 28), and this half mirror (3o) receives the reflected light from the optical disk (33).
The light transmitted through the concave lens (34) and the cylindrical lens (3
5) to the light receiving substrate (27). Six light-receiving elements are arranged on the light-receiving substrate (27), focusing is performed by, for example, an astigmatism method, and tracking is performed by, for example, a three-spot method.

FIG. 1 shows the structure of the semiconductor laser light source (28) of this example. In this FIG. 1, (36) is a stem, (37) is a cap, (38) is a light-transmitting window, and (39) is a a conductive heatsink, (40) is a laser diode array;
The N-side electrode of the laser diode array (40) is attached to the stem (36) via a heat sink (37). (4
1) is the bottom plate facing the window (38), (42) is the photodiode for automatic gain control (APC), (43) to (4)
6) shows the electrodes of the lead wires, and the photodiode (42) is fixed on the bottom plate (41) with a slight inclination, and the N side electrode of the photodiode (42) and the laser diode array (40) are connected to each other. Electrode the N side electrode (43)
Connect to. In addition, as will be described later, the laser diode array (40) has two P-side electrodes, and these two P-side electrodes are connected to the electrodes (44) and (4) via lead wires, respectively.
5) and P'/@N of photodiode (42).
The pole is connected to the electrode (46) via a lead wire.

Fig. 2 shows the laser diode array (4o) of this example, and in this Fig. 2, (47) is an N-side electrode of planar width w x length, and on this N-side electrode (47) sequentially N-
GaAs layer (4B), N-GaxAll-IAS layer (
49), P-Ga.

A1. , As layer (50) (y>x), PG
axAlr-xAs layer (51) and P-GaAs layer (5
2) to a thickness H, and on top of this P-GaAs layer (52) are striped first pHJts each having a width d and an interval t.
A pole (53) and a second P-side electrode (54) are formed. Width W of this laser diode array (4o).

The length L and thickness H are 4200 to 300 mm. ! /II,
It is set to about 200 to 400μ and 100 to 300μ. In addition, striped electrodes (53) and (54)
) are selected from 1 to several μ-, and the width d of these electrodes (53
) and (54) is set, for example, to about several μIl to 30 μ−.

In this example, a rond-shaped electrode (44) and an electrode (45) are connected to the first electrode (53) and the second electrode (54), respectively, and a voltage is applied to the first electrode (53). Then, the projection of the electrode (53) onto the N-side electrode (47) and the P-
One end on the window (38) side of the region where the GayAl+-y-As layer (50) intersects becomes the first light emitting part (55^),
When a voltage is applied to the second electrode (54), the projection of the electrode (54) onto the N-side electrode (47) and the P-GayAI
One end on the window (38) side of the region where the +-yAs layer (50) intersects becomes a second light emitting section (55B).

That is, in the laser diode array (40) of this example, it can be considered that single laser diodes (40A) and (40B) are formed corresponding to the electrodes (53) and (54), respectively. In this case, the output light of both laser diodes (40A) and (40B) is monitored by one APC photodiode (42).

Furthermore, when positioning a conventional semiconductor laser light source having a single laser diode in the arrangement shown in FIG. 5, the positional accuracy of its light emitting part is about ±50 μm. On the other hand, the distance t between the electrodes (53) and (54) in the example in Fig. 2 is 30μ.
Since it is set smaller than about m, the first light emitting part (
55A) and the second light emitting part (55B) is also 30 μm.
less than the degree. Therefore, when using the laser diode array (40) of this example, if the first light emitting part (55A) is positioned so that it can emit light and normal recording or playback can be performed, then the light emitting part (55B) of the cylinder 2 can be ), there is the advantage that recording or playback can be performed normally even if the light emitting unit is switched to ().

FIG. 3 shows the drive circuit of the semiconductor laser light source of this example, and in this FIG. 3, the laser diode (40A) and (
40B) common N-side electrode and photodiode (42
) is grounded, and the P-side electrodes of the laser diodes (40A) and (40B) are connected to NPN for switching, respectively.
) is connected to the emitters of transistors (56) and (57), and the collectors of transistors (56) and (57) are connected to each other through a resistor (58).
), and the collector of the transistor (58) is connected to a DC power supply (60).

(61) shows an automatic gain control 1 (APC) circuit, and the P-side electrode of the photodiode (42) and the base of the transistor (59) are connected to the current detection terminal and current output terminal of this APC circuit (61), respectively. . This APC circuit (6
I) is a transistor (59) so that the current flowing through the photodiode (42) becomes a predetermined value.
control the base current. As a result, the laser diode (40^) or (40B) always emits light with constant brightness.

(62) shows a power switching circuit, both ends of a resistor (58) are connected to a pair of voltage detection terminals of this switching circuit (62), and two current output terminals are connected to a transistor (58).
6) and (57). This switching circuit (62) initially makes only one transistor (56) conductive and sets the other transistor (57) to a non-conductive state. Then, when the voltage across the resistor (58) reaches a predetermined level and the current flowing through the resistor (58) becomes too large, the switching circuit (62) switches one of the transistors (56) to The other transistor (57) is made conductive.

To explain the overall operation of the optical pickup in this example,
When the optical pickup starts to be used, the switching circuit (62) shown in FIG. 5 makes one of the transistors (56) conductive, so that one of the laser diodes (40A) in the laser diode array (40) emits light. Recording or reproduction is performed using this light. After that, if one of the laser diodes (40A) deteriorates as a result of using this optical pickup for a long period of time, the brightness will decrease with the same current, so the APC circuit (61) will reduce the supply current to that laser diode (40A). increases.

When the supplied current reaches a predetermined upper limit, the switching circuit (62) operates and only the other transistor (57) becomes conductive, and the other laser diode (40B
) will now emit light. This laser diode (40
The light emitting part (55B) of B) is the light emitting part (55B) that was emitting light initially.
55A), this laser diode (
Recording or reproduction can be performed normally with the light of 40B). Therefore, the optical pickup of this example has the advantage that even if one laser diode (40A) deteriorates, recording or reproduction can be continued normally by switching to the other laser diode (40B).

In general, the probability that one laser diode deteriorates and its emission output falls below a predetermined value during a predetermined service life is expressed as x (x<<
l), the failure rate due to conventional laser diodes is X. On the other hand, in this example, two laser diodes can be switched and used, so the failure rate due to the laser diode is X2, but since X times 1, According to the method, the defect occurrence rate can be significantly reduced to almost zero compared to the conventional example.

Further, although two laser diodes are provided in this example, it is obvious that the failure rate can be further reduced if three or more laser diodes are provided.

Furthermore, although the laser diode array (40) of the above embodiment has two laser diodes (40A) and (40B) formed in a common substrate, the laser diode array is composed of a plurality of independent laser diodes. You may use those arranged as close as possible.

Furthermore, although the above-mentioned embodiment is an application of the present invention to optical pickup, the present invention includes, for example, a pen-shaped barcode league with a built-in laser diode for reading, and a built-in laser diode to output a thin laser beam. It can also be applied to pointers, etc.

As described above, it goes without saying that the present invention is not limited to the above-described embodiments, and can take various configurations without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, since a plurality of laser diodes are switched and used, even if one laser diode deteriorates, the optical device operates normally and reliability is improved. There is profit.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a semiconductor laser light source according to an embodiment of the present invention, FIG. 2 is an enlarged perspective view showing the structure of a laser diode array according to the embodiment, and FIG. 3 is a perspective view of the semiconductor laser light source according to the embodiment. FIG. 4 is a block diagram showing a drive circuit for a semiconductor laser light source, FIG. 4 is a perspective view showing an optical pickup of the embodiment, and FIG. 5 is a perspective view showing the arrangement of optical components in the example shown in FIG. (40) is a laser diode array, (40A) and (40B) are laser diodes, (42) HaA
Photodiode for PC, (58) is resistor, (6
1) is an APC circuit, and (62) is a power switching circuit.

Claims (1)

[Scope of Claims] A laser diode array in which a plurality of laser diodes are integrated, a light receiving element for monitoring that receives the output light of the laser diode, and a light receiving element for monitoring in any one of the laser diodes. The laser diode, which is supplied with power, has a power switching means that supplies power so that the output signal of the element becomes a predetermined level, and a deterioration detection means that detects deterioration of the laser diode that is supplied with power. An optical device characterized in that when a diode deteriorates, power is supplied to one of the laser diodes.