JPH07326064A - Laser output monitor device - Google Patents

Abstract

PURPOSE:To prevent influence of rotation of plane of polarization of a laser beam. CONSTITUTION:The laser beam outputted from a laser diode 2 is made incident on a PBS 6. If the plane of polarization is rotated, 93% of an S polarized light component (Y component) is emitted as a main beam. 5% of the S polarized light component is emitted as a monitoring beam. Further, (95%+95%) of the P polarized light component (X component) of the laser beam is emitted from the PBS 6. The P polarized light component is removed to zero when this component is made incident on a PBS 13. Then, the exact detection of the monitor beam is made possible at an FPD 15.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a WO (Write Once)
TECHNICAL FIELD The present invention relates to a laser output monitor device suitable for application to an optical disc device and the like.

[0002]

2. Description of the Related Art Conventionally, in an optical disk device, a laser beam emitted from a laser light source is monitored, and the monitor output is controlled by a laser light source through an APC (automatic power control) circuit so as to respond to recording or reproduction. The optical disk can be irradiated with laser light.

As a method of obtaining this monitor output, a rear APC (RAPC) for monitoring with a photodetector placed at a position opposite to the laser light emission side inside the package of the laser diode, or a parallel light flux in the optical path of the emission side optical system is used. There is a front APC (FAPC) for monitoring.

[0004]

However, the above-mentioned AP
In C, mode hopping or scooping easily occurs in the laser diode due to the effect of the return light to the laser diode due to reflection from optical components or optical discs in the optical path, but the output power is accurate at that time. There was a problem that it was practically impossible to know.

Further, when a multi-beam laser light source consisting of a multi-channel monolithic type laser diode for emitting a plurality of laser beams is used as a light source, it is structurally impossible to monitor without interference with each other. There is a problem that the influence of the heat of the laser cannot be ignored.

On the other hand, in the above-mentioned front APC, since monitoring is performed in a parallel light beam, when a multi-beam light source is used as a light source, inter-channel interference is large, and a plurality of laser beams emitted from the multi-beam laser light source are accurately measured. There was a problem that it was impossible to monitor.

Also in the front APC, the laser diode becomes unstable due to the influence of the returning light and the ambient temperature, and the following influence is caused by the rotation of the polarization plane. That is, when the plane of polarization is rotated, in addition to the polarization component (S) of the laser light that is originally intended to be used as a monitor beam, a part of the polarization component (P) in a direction perpendicular to this is also irradiated in the same direction as the monitor beam, Since this is detected, it becomes difficult to accurately monitor the laser light.

In particular, recently, in order to achieve high density and high transfer rate recording, the disk rotation speed is increased and the output of the main beam tends to be increased, which reduces the ratio that can be used as a monitor beam. However, if a part of the P-polarized component enters at the same time, it may not be possible to accurately detect a monitor beam having a small output.

Therefore, the present invention solves the above-mentioned problems, and proposes an output monitor device for laser light which has a simple structure and can prevent the influence of rotation of the polarization plane. is there.

[0010]

In order to solve the above-mentioned problems, in the invention described in claim 1, collimator lens means for converting a plurality of laser beams emitted from a multi-beam laser light source into parallel rays and parallel rays are provided. Beam splitting means for splitting the light into a main beam and a monitor beam at a predetermined splitting ratio, and a condenser lens means for separately focusing the monitor beam,
A plurality of light receiving means, which are arranged so as to be displaced from the focus position of the condensing lens means in the optical axis direction by a predetermined distance, receive the separated and condensed monitor beams, and are arranged between the beam dividing means and the light receiving means. And a polarized beam splitting means for removing the P-polarized light component in the direction of the light receiving means generated by the rotation of the polarization planes of the plurality of laser lights, and the outputs of the plurality of laser lights emitted from the multi-beam laser light source are respectively divided into a plurality of outputs. It is characterized in that monitoring is performed by the light receiving output of the light receiving means.

According to a second aspect of the present invention, collimator lens means for collimating a plurality of laser beams emitted from the multi-beam laser light source into parallel light, and the parallel light into a main beam and a monitor beam at a predetermined division ratio. The beam splitting means for splitting, the condenser lens means for separating and condensing the monitor beam, the condenser lens means are arranged so as to be displaced from the focal position of the condenser lens means by a predetermined distance in the optical axis direction, and at a predetermined angle with respect to the optical axis. The multi-beam laser light source is provided with a plurality of light receiving means that are arranged to be tilted only for receiving the separated and collected monitoring beams and crosstalk canceling means that subtracts the adjacent light receiving output from each light receiving output of the plurality of light receiving means. It is characterized in that the outputs of the plurality of laser beams emitted from each are monitored by the light reception outputs of the plurality of light receiving means.

[0012]

In FIG. 1, the laser light output from the laser diode 2 enters the PBS 6. Then, when the polarization plane of the laser light is not rotated, as shown in FIG. 5A, only the Y component (S polarization component) of the laser light is absorbed by the PBS.
6 enters, 93% of which passes as the main beam as shown in FIG. 6B, and 5% as shown in FIG.
% Is emitted as a monitor beam.

However, when the plane of polarization of the laser light is rotated for some reason, both the Y component and the X component (P polarized component) of the laser light are incident on the PBS as shown in FIG. 6 (A). If there is no PBS 13, 93% of the Y component is emitted from the PBS 6 as the main beam and 5% of the Y component is emitted as a part of the monitor beam, as shown in FIG. Further, in this case, as shown in FIG. 7C, the X component of the laser light is reflected by the B surface and C surface of the PBS 6 by 95% and emitted as a part of the monitor beam. Therefore, the monitor beam is detected by the FPD 15 as a value larger than the actual value.

On the other hand, when the PBS 13 is arranged between the PBS 6 and the FPD 15, the output (0.95 × 0.95) · X2 of the monitor beam due to the X component of the laser light is removed by the PBS 13, As shown in FIG. 7C, only the output 0.05X2 due to the Y component of the laser light is detected as the monitor beam.

Further, when the FPD 15 is tilted by an appropriate angle α with respect to the optical axis as shown in FIG. 9, the return light of the FPD 15 does not adversely affect the laser diode 2, so that the polarization plane of the laser light is rotated. It can be prevented. This makes it possible to accurately detect the output of the monitor beam without disposing the PBS 13. However, in this case, since the crosstalk becomes large as shown in FIG. 10B, the crosstalk cancel circuit 2 as shown in FIG.
By providing 0, the monitor beam can be accurately detected.

[0016]

EXAMPLE Next, an example in which the laser output monitor device according to the present invention is applied to an optical disk device of a WO (Write Once) system will be described in detail with reference to the drawings.

FIG. 1 shows the structure of an optical disk device 1 of a WO system to which a laser output monitor device according to the present invention is applied. In this optical disc device 1, a monolithic type two-channel laser diode 2 is used as a laser light source.
Is used. The laser light emitted from the laser diode 2 is collimated by the collimator lens 3. The collimated light is beam-corrected by the anamorphic prism 4, and then is incident on a polarization beam splitter (PBS) 6 via a grating 5, where the main beam is condensed on a WO disk 9 and a front photodetector (F).
It is split into a monitor beam that is separately focused on the PD) 15 and the photodetector (PD) 11. This split light amount ratio is selected to be about 10: 1 to 20: 1.

Of these, the main beam is focused on the disk surface of the WO disk 9 via the λ / 4 plate 7 and the objective lens 8. As a result, the WO disc 9 is recorded and reproduced. The monitor beam is the aperture 12 and P.
Front A via BS (polarizing beam splitter) 13
The light enters the condenser lens 14 for PC, is separated and condensed here, and is irradiated onto the front photodetector (FPD) 15. The monitor beam is transmitted through the condenser lens 10 to the PD.
11 is also irradiated. The distance between the separated beams is determined by the focal lengths of the collimator lens 3, the condenser lens 14, and the inter-channel distance of the laser diode 2.

Since the WO system needs to be recordable, the front monitor signal obtained from the FPD 15 is also required to maintain linearity from reproduction to recording (0 to 60 [mw]). Uses FPD1
This is solved by providing an appropriate aperture 12 in front of the condenser lens 14 in accordance with the capacity and sensitivity of 5.

FIG. 2 shows the details of each part in the optical path of the monitor beam. The PBS 6 is of a laminated mirror type, and its film characteristics are shown in FIG. The PBS 13 in FIG. 2 is arranged between the PBS 6 and the FPD 15 in order to cancel the P-polarized component irradiated on the FPD 15 side, as will be described later. In this example, the PBS 13 is interposed between the aperture 12 and the condenser lens 14. It is installed, but as shown in FIG.
6 and the aperture 12, or may be arranged between the condenser lens 14 and the FPD 15 as shown in FIG. The PBS 13 is arranged so as to match the polarization direction of the monitor beam.

Now, the influence of the monitor beam when the plane of polarization of the laser light emitted from the laser diode 2 rotates for some reason will be described. here,
In order to simplify the explanation, the component parallel to the paper surface of the laser light is defined as the X component (P polarized light component), and the component perpendicular to the paper surface is defined as the Y component (S polarized light component).

As shown in FIG. 5A, when two-channel laser light in a state where the plane of polarization is not rotated passes through the PBS 6, as shown in FIG.
Only the component output Y1 is dissipated by 93% or more as the main beam, and 5% as the monitor beam as shown in FIG.
The above is separated. At this time, the laser diode 2 is arranged so that the polarization direction of the laser light is only the Y component with respect to the PBS 6.

On the other hand, the laser diode 2 may be in an unstable state due to the influence of the returning light and the ambient temperature as described above, and its polarization plane may rotate. For example, as shown in FIG. 6 (A), when the polarization plane of the laser light is rotated by θ ° and the output of the Y component is Y2 and the output of the X component is X2, when passing through the PBS 6, As shown in (3), 93% of the output Y2 passes through the C surface of the PBS 6 and becomes the main beam. Further, 5% or more of the output Y2 of the Y component of the laser light is reflected and emitted. When the PBS 13 is not arranged as in the conventional case, the spectrum 0.005Y2 enters the FPD 15 through the condenser lens 14 and is detected as a part of the monitor beam as shown in FIG. It Further, in this case, since the plane of polarization of the laser light is rotated by θ °, the output X2 of the X component of the laser light is incident on the PBS 6, which reflects 95% or more on the B surface and further 95 on the C surface.
% Or more of the reflected light enters the FPD 15 and is detected as a part of the monitor beam as shown in FIG. Therefore, as the monitor beam, a spectrum 0.93Y2 by the Y component of the laser light and a spectrum (0.95 × 0.9) by the X component are obtained.
5) It becomes the sum of X2. Rotation angle θ of the plane of polarization of laser light
If the angle is large, the output of the spectrum as a monitor beam (0.95 × 0.95) X2 generated by the X component of the laser light
Becomes large, and the accurate output of the main beam cannot be detected.

In order to prevent the influence of the rotation of the polarization plane of the laser beam from appearing on the monitor beam, the optical disc apparatus 1 of this embodiment is provided with the PBS 13.
That is, here, the X-component spectrum associated with the rotation of the polarization plane of the laser light is removed from the monitor beam so that the ratio of the main beam to the monitor beam becomes an accurate value as in the case where the polarization plane does not rotate. Is.

Now, as shown in FIG. 7A, the plane of polarization of the laser light emitted from the laser diode 2 is shown in FIG.
When rotating by θ ° as in (A), the Y component of the laser light is Y2, and the main beam emitted from the PBS 6 is 0.93Y2 as shown in FIG. 7 (B). The output of the spectrum emitted from the PBS 6 to the FPD 15 side is 0.05Y2. The spectrum 0.05Y2 is incident on the PBS 13 via the aperture 12. In the PBS 13, this spectroscopic 0.05Y2 passes as it is, and the condenser lens 1
As shown in (C) of FIG.

On the other hand, the output X2 of the X component of the laser light is PB
It reflects 95% or more on the B surface of S6, and reflects 95% or more on the C surface and enters the PBS 13. The PBS 13 is arranged so that the spectrum (0.95 × 0.95) X2 of this X component is removed. Therefore, the spectrum of the X component output from the PBS 13 and incident on the FPD 15 is shown in FIG.
As shown in FIG. 4, the monitor beam detected by the FPD 15 is only the spectral output 0.05Y2 of the Y component of the laser light. This is the same as the case where the polarization plane of the laser light shown in FIG. 5 is not rotated, and the ratio of the main beam and the monitor beam can be accurately detected.

FIG. 8 shows P when the plane of polarization of laser light is rotated.
The difference of the monitor beam depending on the presence or absence of BS13 is shown. Here, a case where only the CH1 laser light is emitted will be described. When there is no PBS 13, the monitoring voltage of CH1 is disturbed as shown in FIG.
In the case of No. 13, the disturbance of the monitoring voltage is almost eliminated as shown in FIG. Actually PBS1
3 is arranged and the laser beam is subjected to high frequency superposition, which further stabilizes the monitoring voltage as shown in FIG.

In the above-mentioned embodiment, the case where the accurate ratio of the main beam to the monitor beam is detected by canceling the X component (P polarized component) generated by the rotation of the polarization plane of the laser beam by the PBS 13 has been described. It is possible to prevent the return light from here from entering the laser diode 2 by inclining the FPD 15 that has the largest influence on the laser diode 2 among the return light from each part with respect to the optical axis. . As shown in FIG. 9, the optical path length is, for example, 7 without the PBS 13.
At 7.0 mm, as shown by the chain double-dashed line in the figure, the FPD
When 15 is arranged at right angles to the optical axis, as shown in FIG. 10A, the polarization plane of the laser light rotates due to the influence of the returning light, and the disturbance of the monitoring voltage becomes large. On the other hand, as shown by the solid line in FIG. 9, the FPD 15 is α (α = 2 to 2) with respect to the optical axis.
10 °), in this example, when tilted by α = 2 °, FPD15
Return light does not enter the laser diode 2 and the polarization plane does not rotate. Therefore, at this time, FIG.
As shown in (B), the disturbance of the monitoring voltage is eliminated, which makes it possible to accurately detect the ratio of the main beam and the monitor beam.

When the FPD 15 is tilted with respect to the optical axis as described above, the crosstalk becomes large as shown in the figure when the tilt angle α is large. In this case,
By providing the crosstalk cancel circuit 20 as shown in FIG. 3, it becomes possible to perform electrical calculation to cancel crosstalk and to accurately detect the monitoring voltage. That is, this crosstalk cancel circuit 20
, The received light output PD for 2 channels of FPD15
1 and PD2 are input to low-pass filters 21A and 21B for noise removal having an operational amplifier configuration, and the outputs thereof are subtraction circuits 22A and 22 having an operational amplifier configuration, respectively.
Input to B.

The light receiving outputs PD1 and PD2 of the other channel are resistance-divided and input to the subtracting circuits 22A and 22B, respectively, and the light receiving outputs of CH1 and CH2 are changed to CH.
By subtracting the components corresponding to the light reception outputs of 2 and CH1, the crosstalk can be canceled and the monitor output can be obtained correctly.

By arranging the PBS 13 shown in FIG. 1 so as to be inclined with respect to the optical axis, it is possible to prevent the return light from entering the laser diode 2 and rotating the polarization plane of the laser light. . In addition, the PBS 13 is arranged in the optical path of the monitor beam as in FIG.
The crosstalk canceling circuit 20 can be provided by arranging 15 with an appropriate angle α with respect to the optical axis. PBS 13 and cancel circuit 20 are provided, and FPD 1
The inclination angle α of 5 may be 0.

[0032]

As described above, according to the first aspect of the present invention, the collimator lens means for converting a plurality of laser beams emitted from the multi-beam laser light source into parallel light and the parallel light with a predetermined division ratio. A beam splitting means for splitting the main beam and the monitor beam, a condenser lens means for separately collecting and converging the monitor beam, and a focusing lens means which are arranged so as to be offset from the focal position of the condenser lens means in the optical axis direction by a predetermined distance, and are separated and A plurality of light receiving means for receiving each of the emitted monitoring beams, and P in the direction of the light receiving means which is disposed between the beam splitting means and the light receiving means and is generated by rotation of the polarization planes of the plurality of laser beams.
A polarization beam splitting means for removing a polarization component is provided, and outputs of a plurality of laser beams emitted from the multi-beam laser light source are monitored by light reception outputs of a plurality of light receiving means.

Therefore, according to the present invention, even when the polarization plane of the laser light is rotated, the influence of the P-polarized component on the monitor beam can be prevented, so that the monitor beam can be accurately detected and the laser output can be accurately measured. There is an effect that it can be controlled.

The invention described in claim 2 is a collimator lens means for converting a plurality of laser beams emitted from a multi-beam laser light source into parallel light, and a main beam and a monitor beam with a predetermined splitting ratio of the parallel light. A beam splitting means for splitting the monitoring beam, a condensing lens means for separating and condensing the monitor beam, and a predetermined distance from the focal position of the condensing lens means in the optical axis direction. The multi-beam laser is provided with a plurality of light receiving means that are arranged to be tilted by an angle and that receives the separated and collected monitoring beams, and crosstalk canceling means that subtracts the adjacent light receiving output from each light receiving output of the plurality of light receiving means. The outputs of a plurality of laser beams emitted from a light source are monitored by the light receiving outputs of a plurality of light receiving means.

Therefore, according to the present invention, it is possible to prevent the polarization plane of the laser light from rotating, so that the monitor beam can be accurately detected, and thereby the laser output can be accurately controlled. There is an effect such as.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical disk device 1 to which a laser output monitor device according to the present invention is applied.

FIG. 2 is a detailed view of the optical path of the monitor beam of FIG.

FIG. 3 is a diagram showing the film characteristics of PBS6.

FIG. 4 is a diagram showing another arrangement example of the PBS 13.

FIG. 5 is a diagram showing the output of each beam when the plane of polarization of laser light is not rotated.

FIG. 6 is a diagram showing the output of each beam when the PBS 13 is not installed when the polarization plane is rotated.

FIG. 7 is a diagram showing the output of each beam when the PBS 13 is installed when the polarization plane is rotated.

FIG. 8 is a waveform diagram of the monitor beam of FIG.

FIG. 9 is a diagram showing another embodiment.

10 is a waveform diagram of the monitor beam of FIG.

FIG. 11 is a configuration diagram of a crosstalk cancel circuit 20.

[Explanation of symbols]

 1 Optical Disk Device 2 Laser Diode 3 Collimator Lens 6,13 Polarization Beam Splitter (PBS) 12 Aperture 14 Condensing Lens 15 FPD 20 Crosstalk Cancel Circuit

Claims (4)

[Claims] 1. A collimator lens unit for collimating a plurality of laser beams emitted from a multi-beam laser light source into parallel beams, and a beam splitting unit for splitting the parallel beams into a main beam and a monitor beam at a predetermined split ratio. Condensing lens means for separating and condensing the monitor beam, and a plurality of condenser lenses arranged to be displaced from the focal position of the condensing lens means by a predetermined distance in the optical axis direction and receiving the separated and condensed monitor beams. Is disposed between the beam splitting means and the light receiving means,
Polarization beam splitting means for removing a P-polarized component in the direction of the light receiving means generated by rotation of the polarization planes of the plurality of laser lights, and outputs of the plurality of laser lights emitted from the multi-beam laser light source. A laser output monitor device characterized in that each is monitored by the received light output of the plurality of light receiving means. 2. A collimator lens means for collimating a plurality of laser beams emitted from a multi-beam laser light source into parallel rays, and a beam splitting means for splitting the parallel rays into a main beam and a monitor beam at a predetermined splitting ratio. Condensing lens means for separating and condensing the monitor beam, and a displacement from the focal point of the condensing lens means by a predetermined distance in the optical axis direction, and a tilt angle with respect to the optical axis. The multi-beam laser light source is provided with a plurality of light receiving means for receiving the separated and collected monitoring beams, and a crosstalk canceling means for subtracting an adjacent light receiving output from each light receiving output of the plurality of light receiving means. Outputs of the plurality of laser beams thus generated are respectively monitored by light reception outputs of the plurality of light receiving means. Nita apparatus. 3. A laser output monitor device according to claim 1, further comprising crosstalk canceling means for subtracting adjacent light receiving outputs from respective light receiving outputs of said plurality of light receiving means. 4. The monitor beam separated and condensed as described above is arranged so as to be displaced from the focal position of the condenser lens means by a predetermined distance in the direction of the optical axis and inclined by a predetermined angle with respect to the optical axis. 4. The laser output monitor device according to claim 3, further comprising a plurality of light receiving means for receiving light.