Optical head device

Details Optical head device Optical head device

2000-12-04

2003-01-21

Edun, Muhammad (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112140, C369S044370, C369S044230

Reexamination Certificate

active

06510119

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head device for optically recording/reproducing information to and from an information recording medium (a so-called optical disk), and particularly to a technique for reducing unstableness of operation caused by a difference in wavelength between lights used in recording and reproduction.
2. Description of the Background Art
The characteristics such as reflectance of an information recording medium (a so-called optical disk) used to optically record/reproduce information have wavelength dependence. Accordingly it is necessary to record/reproduce information by using light at a given wavelength corresponding to the information recording medium. Optical head devices having light sources of different wavelengths are suggested, where the light emitted from each light source is applied to the information recording medium.
FIG. 10
is a schematic diagram showing the structure of a first conventional optical pickup device
201
P. The optical pickup device
201
P is disclosed in Japanese Patent Application Laid-Open No. 11-296893 (1999).
The optical pickup device
201
P has a beam shaping prism (hereinafter referred to also as shaping prism)
31
P, a light source
32
P emitting light at a wavelength &lgr;
1
, a light source
33
P emitting light at a wavelength &lgr;
2
(>&lgr;
1
), a prism
34
P, a collimator lens
35
P, a beam splitter
36
P, a deflection prism
37
P, an objective lens
38
P, an optical disk
39
P, a condenser lens
40
P, a cylindrical lens
41
P and a photodetector
42
P.
In the optical pickup device
201
P, the light at the wavelength &lgr;
1
emitted from the light source
32
P and the light at the wavelength &lgr;
2
emitted from the light source
33
P are combined by the prism
34
P and then sequentially enter the collimator lens
35
P and the shaping prism
31
P. The collimator lens
35
P converts the lights into approximately parallel rays and the shaping prism
31
P shapes their beam form.
The lights exit from the shaping prism
31
P at about the same angles and their optical paths are deflected by 45 degrees by the deflection prism
37
P. The lights are then focused by the objective lens
38
P to form very small spots on the optical disk
39
P. Information is recorded/reproduced to and from the optical disk
39
P through the small spots.
The lights reflected at the optical disk
39
P are converted again into approximately parallel rays by the objective lens
38
P, reflected at the beam splitter
36
P, and condensed by the condenser lens
40
P. The cylindrical lens
41
P introduces astigmatism to the lights and the lights are received at the photodetector
42
P. The photodetector
42
P outputs an information signal and a servo signal.
Next,
FIG. 11
is a diagram schematically showing the structure of a second conventional optical pickup device
202
P. The optical pickup device
202
P is disclosed in the above-mentioned reference. The optical pickup device
202
P has a light source unit
43
P in place of the light sources
32
P and
33
P in the above-described optical pickup device
201
P. The light source unit
43
P has two light sources, or two semiconductor laser chips (hereinafter also referred to as LD chips) sealed in a single can. The two LD chips are spaced at an appropriate interval on the same plane which is vertical to the optical axis of the collimator lens
35
P. The LD chips respectively emit light at a wavelength &lgr;
1
and light at a wavelength &lgr;
2
. The lights emitted from the two LD chips are converted into approximately parallel rays by the collimator lens
35
P and shaped by the shaping prism
31
P. After passing through the shaping prism
31
P, the lights travel the same optical path as that in the optical pickup device
201
P.
The conventional optical pickup devices
201
P and
202
P have the following problems. First, the optical pickup device
201
P has the two light sources
32
P and
33
P prepared as separate parts and disposed separately. Therefore the device has a larger number of parts and a complex structure, and must be large in size.
On the other hand, in the optical pickup device
202
P, the two LD chips (light sources) are disposed in the single can and the lights at the two wavelengths are received at a single photodetector. Therefore it can solve the above-mentioned problem. However, the two LD chips are just arranged at an appropriate interval on the same plane which is vertical to the optical axis of the collimator lens
35
P. Accordingly, the wavelength dependence of the refractive index in the optical axis direction of each optical part causes offset in a servo signal corresponding to at least one of the two lights of different wavelengths, which leads to another problem that the operation becomes unstable.
Furthermore, when two LD chips are separately prepared and simply arranged in a hybrid manner using an assembling machine, the relative position of the two LD chips depends on the mechanical accuracy of the assembling machine etc. That is to say, the positions of the two optical sources are likely to shift relative to each other. Such positional shift will cause offset in the servo signal and then the lights at the two wavelengths cannot be received accurately enough.
SUMMARY OF THE INVENTION
(1) According to a first aspect of the present invention, an optical head device comprises: a light source comprising a first light emitting point for emitting a first light at a first wavelength and a second light emitting point for emitting a second light at a second wavelength in approximately the same direction as the first light, the first wavelength and the second wavelength differing from each other; a collimator lens disposed to face to the first light emitting point and the second light emitting point, for converting the first light and the second light into approximately parallel lights; and a beam shaping prism having a plane of incidence, the first light and the second light as the approximately parallel lights obliquely entering the plane of incidence, the beam shaping prism changing sectional intensity distributions of the first light and the second light to approximately circular shape; wherein the collimator lens and the beam shaping prism have refractive indexes dependent on a wavelength of incident light, and the first light emitting point and the second light emitting point are placed in different positions from each other in a direction parallel to and a direction vertical to an optical axis of the collimator lens.
(2) Preferably, according to a second aspect, in the optical head device, the first wavelength is shorter than the second wavelength and the refractive index of the collimator lens to the first wavelength is larger than the refractive index to the second wavelength, and wherein the first light emitting point is placed closer, than the second light emitting point, to the collimator lens.
(3) Preferably, according to a third aspect, in the optical head device, the first wavelength is shorter than the second wavelength and the refractive index of the beam shaping prism to the first wavelength is larger than the refractive index to the second wavelength, and wherein the first light enters the plane of incidence of the beam shaping prism at an angle of incidence which is larger than an angle of incidence at which the second light enters the plane of incidence.
(4) Preferably, according to a fourth aspect, in the optical head device, the first light emitting point and the second light emitting point are formed monolithically.
(5) Preferably, according to a fifth aspect, the optical head device further comprises a first optical system comprising the beam shaping prism, for directing the first light and the second light from the light source to a recording medium, a photodetector having a light receiving portion receiving the first light and the second light reflected at the recording medium, a sensor lens having a refractive index dependent on a wavelength of incident light, for converging the firs

Affiliated with

Also associated with

Rating

Optical head device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical head device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical head device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3060351