JP2003045063A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a recording/reproducing characteristic by devising the joint of a detection lens and a beam forming prism which lead a part of light emitted from a laser diode(LD) to an optical detector of a front monitor. SOLUTION: A laser beam 24 is made incident to a joined face 15a approximately perpendicularly but a laser beam reflected on a part in which the detecting lens is not joined does not return as a stray light to the LD1 and a signal detection systems 41 and 42 because the joined face 15a is rough. The joined part of the detection lens 16 and the beam forming prism 15 is joined with an adhesive having a refractive index which is the same as that of these elements and the laser beam passes through the joined face without being scattered and is condensed on the detector 17 of the front monitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in an optical information recording / reproducing device.

[0002]

2. Description of the Related Art Normally, in an optical recording / reproducing apparatus, the output of light emitted from a semiconductor laser (LD) is controlled to be constant. For that purpose, a part of the emitted light is separated through an optical component such as a prism, a part of the emitted light is detected by a front monitor photodetector, and the output of the front monitor photodetector is controlled by an LD applied current. It is fed back to the LD through the element.

In such an optical head, as disclosed in, for example, Japanese Patent Application Laid-Open No. 8-249699, the optical system for guiding the light emitted from the LD to the front monitor photodetector is provided with a detection system lens. If it is configured and the coupling efficiency between the detection system lens and the collimator lens is set to be substantially the same as the coupling efficiency between the objective lens and the collimator lens, the amount of light emitted from the objective lens even if the LD spread angle varies It is possible to make the sensitivity of the front monitor photodetector to be constant.

[0004]

However, when a part of the parallel light flux from the semiconductor laser (LD) is guided to the front monitor photodetector through the detection system lens and the beam shaping prism which are integrally joined, the LD Since the parallel light flux from is generally larger than the detection system lens, a part of the parallel light flux is reflected at the portion of the cemented surface where the detection system lens is not cemented.

When the parallel light flux is incident on the cemented surface almost vertically, the reflected light returns through the opposite path and returns to the LD and the signal detection system. When such stray light exists,
LD noise occurs and servo signal offset occurs, so that the S / N ratio of the information signal decreases.

The present invention has been made in view of the above circumstances, and by devising a connection between the detection system lens for guiding a part of the light emitted from the LD to the front monitor photodetector and the beam shaping prism, It is an object of the present invention to provide an optical head capable of stabilizing recording / reproducing characteristics.

[0007]

The optical head of the present invention comprises:
A semiconductor laser that emits laser light, and a collimator lens that collimates the laser light from the semiconductor laser,
A first beam shaping prism for shaping the parallel light flux from the collimator lens into a substantially circular cross section, and a first beam shaping prism for guiding the parallel light flux reflected by the incident surface of the first beam shaping prism to a front monitor photodetector. An optical head including a second beam shaping prism and a detection system lens integrally joined to the second beam shaping prism and having an effective diameter smaller than a parallel light beam, in the joining surface of the second beam shaping prism. The unbonded portion of the detection system lens is formed in a grain shape.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 relate to an embodiment of the present invention, FIG. 1 is a diagram showing the structure of an optical head, and FIG. 2 is FIG.
FIG. 3 is a view showing the outer appearance of the beam shaping prism and the detection system lens of FIG. 3, and FIG. 3 is a view for explaining the operation of the beam shaping prism and the detection system lens of FIG.

In the optical head of this embodiment, as shown in FIG. 1, the laser beam emitted from the LD 1 is collimated by the collimator lens 7 and is incident on the beam shaping surface 9 a of the first beam shaping prism 9. Then, the transmitted light enters the optical recording medium 37, and the reflected light enters the front monitor photodetector 17.

The transmitted light of the first beam shaping prism 9 is
After passing through the second beam shaping prism 10, it is reflected by the reflection mirror 35 and the objective lens 36 forms a minute spot on the optical recording medium 37.

The laser light reflected by the optical recording medium 37 returns on the opposite path and is reflected by the beam shaping surface 9a.
This reflected light is transmitted through the quarter wave plate 11 and the detection system lens 38.
After being transmitted, and after being polarized and separated by the polarization beam splitter 12, they enter the signal detection systems 41 and 42, respectively.
The output signals from the signal detection systems 41 and 42 are converted into an information signal, a focus error signal, a track error signal, etc. after being subjected to various arithmetic processes.

On the other hand, of the laser light collimated by the collimator lens 7, the first beam shaping prism 9 is used.
The laser light 24 reflected and separated by the beam shaping surface 9a of
After entering the surface 15 b of the beam shaping prism 15 coated with the antireflection film, the light passes through the beam shaping prism 15 and is focused on the front monitor detector 17 by the detection system lens 16.

As shown in FIG. 2, the beam shaping prism 15 and the detection system lens 16 are integrally joined at a joint surface 15a. The detection system lens 16 is an objective lens 36.
The focal length and the numerical aperture are set so as to have substantially the same effective diameter as, and the coupling efficiency between the detection system lens 16 and the collimator lens 7 is almost the same as the coupling efficiency between the objective lens 36 and the collimator lens 7. Is set to.

As a result, even if the divergence angle of the LD 1 varies, the sensitivity of the front monitor photodetector with respect to the amount of light emitted from the objective lens can be kept substantially constant.

As shown in FIG. 3, the laser beam 24 is substantially vertically incident on the joint surface 15a. However, since the joint surface 15a has a grain shape, it is not bonded to the detection system lens. The reflected laser light does not return to the LD1 and the signal detection systems 41 and 42 as stray light. Regarding the joint between the detection system lens 16 and the beam shaping prism 15,
Since they are joined with an adhesive with the same refractive index as these,
The laser light passes through the bonding surface without being scattered and is focused on the front monitor detector 17.

If the surface roughness of Ry specified by JIS B0601 is set to 2 μm to 5 μm as the surface roughness of the sand, the laser light is scattered.

As described above, in the optical head according to the present embodiment, in the optical head having the function of controlling the output of the light emitted from the semiconductor laser (LD) to be constant, a part of the parallel light flux from the LD is monitored in front. Of the cemented surface of the second beam shaping prism for guiding to the photodetector for use and the detection system lens integrated with the second beam shaping prism, the portion where the detection system lens is not cemented has a grain shape, and is reflected by this portion. The laser light generated does not return to the LD and the signal detection system, and the LD noise and the offset of the servo signal due to the back talk are reduced.

Further, it becomes possible to provide the second beam shaping prism and the detection system lens which are integrally joined.

[0020]

As described above, according to the present invention, L
There is an effect that the recording / reproducing characteristics can be stabilized by devising a connection between the detection system lens for guiding a part of the light emitted from D to the front monitor photodetector and the beam shaping prism.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an optical head according to an embodiment of the present invention.

FIG. 2 is a diagram showing the appearance of the beam shaping prism and the detection system lens of FIG.

FIG. 3 is a diagram for explaining the operation of the beam shaping prism and the detection system lens of FIG.

[Explanation of symbols]

1 ... LD 7 ... Collimator lens 9 ... First beam shaping prism 9a ... Beam shaping surface 10 ... Second beam shaping prism 11 ... Quarter wave plate 12 ... Polarizing beam splitter 15 ... Beam shaping prism 15a ... Bonding surface 15b ... surface 16 ... Detection system lens 17 ... Photodetector for front monitor 35 ... Reflective mirror 36 ... Objective lens 37 ... Optical recording medium 38 ... Detection system lens 41, 42 ... Signal detection system

Claims (2)

[Claims] 1. A semiconductor laser that emits laser light, a collimator lens that collimates the laser light from the semiconductor laser, and a first beam shaping prism that shapes the parallel light flux from the collimator lens into a substantially circular cross section. A second beam shaping prism for guiding the parallel light flux reflected by the incident surface of the first beam shaping prism to a front monitor photodetector; and a second beam shaping prism integrally joined to form a parallel light flux. In an optical head including a detection system lens having an effective diameter smaller than that of the second beam shaping prism, a part of the bonding surface of the second beam shaping prism where the detection system lens is not bonded has a grain shape. Optical head to do. 2. The surface roughness Ry is 2 using an adhesive having the same refractive index as the detection system lens and the beam shaping prism.
The optical head according to claim 1, wherein the detection system lens is bonded to the beam shaping prism at a bonding surface of the beam shaping prism having a grain shape of μm to 5 μm.