JP2000149307A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax severe design conditions for a polarizing film used for the separation between light from a light source and light returning from an optical recording medium. SOLUTION: This optical head is provided with a semiconductor laser 101 emitting a diverging light beam, an object lens 104 for focusing the diverging light beam on an optical recording medium 105, a polarizing film 304 for separating the light beam returning from the optical recording medium 105 from the light beam from the semiconductor laser 101, a polarized light separation prism 301 for polarizing and separating the light beam returning from the optical recording medium 105, and a signal detector 306 for detecting information contained in the light beam returning from the optical recording medium. The polarizing film 304 is positioned in the light path between the semiconductor laser 101 and the object lens 104, and is placed for the main beam of light of the diverging light beam from the semiconductor laser 101 to be made incident thereon with an incidence angle of 50 deg. or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording and reproducing information on an optical recording medium such as an optical disk and a magneto-optical disk. In particular, the present invention relates to an optical head that separates light from a light source and return light from an optical recording medium using a polarizing film exposed to the atmosphere or a gas in which the optical head is sealed.

[0002]

2. Description of the Related Art In an optical head, a polarizing film is often used to separate light from a light source and return light from an optical recording medium. The polarizing film is generally a dielectric multilayer film and does not become an independent component by itself, but is usually provided on an optically transparent member for supporting the polarizing film.

As optical components provided with such a polarizing film, there are a type in which a polarizing film is sandwiched between two right-angle prisms, and a type in which a polarizing film is provided on one surface of a transparent member. The former has an advantage that a polarizing film satisfying desired characteristics can be relatively easily produced because the polarizing film is sandwiched between transparent members.

In the latter, one side of the polarizing film is exposed to the atmosphere or a gas (such as nitrogen gas) (hereinafter referred to as a gas) in which the optical head is sealed, so that a polarizing film satisfying desired characteristics can be obtained. Although there is a disadvantage in manufacturing that the number of laminations is larger than that of the former, it is advantageous in terms of cost because the number of parts is small, and it is preferable to use this in order to reduce the cost of the optical head. In addition, the point that occupies less space is
This is suitable for downsizing the optical head.

Japanese Patent Application Laid-Open No. Hei 5-31005 discloses an example of an optical head that separates light from a light source and return light from an optical recording medium by using such a polarizing film exposed in a gas. . FIG. 3 schematically shows the configuration of the optical head.

In FIG. 3, a linearly polarized divergent light beam from a semiconductor laser 101 is incident on a polarizing film 304 provided on a multi-image parallel plane plate 301. The light beam transmitted through the polarizing film 304 and the multi-image parallel plane plate 301 is received by a light amount monitoring photodetector 305, and the output light amount of the semiconductor laser 101 is controlled based on the output. The light beam reflected by the polarizing film 304 on the multi-image parallel plane plate 301 is
The beam is converted into a parallel light beam by the collimator lens 310 and is irradiated as a minute spot on the information track of the magneto-optical recording medium 105 by the objective lens 104.

The return light reflected by the magneto-optical recording medium 105 is transmitted to the objective lens 104 and the collimator lens 3.
Then, the light enters the polarizing film 304 after passing through the polarizing film 304, and the returning light passing through the polarizing film 304 is spatially separated from the outward path and is incident on the multi-image parallel flat plate 301. The return light that has entered the multi-image parallel plane plate 301 undergoes refraction and transmission through the multi-image parallel plane plate 301, undergoes astigmatism and is polarized and separated, and the polarized and separated light beam is used as a signal detection photodetector. The light is received at 306, and the MO signal and the FE are
The S signal and the TES signal are detected.

[0008] The semiconductor laser 101 is arranged so that linearly polarized light of the emitted light is incident on the polarizing film 304 as S-polarized light. The multi-image parallel plane plate 301 is formed by bonding a first triangular prism 302 and a second triangular prism 303 each made of a birefringent crystal, and a divergent light beam from the semiconductor laser 101 and a magneto-optical recording medium. First triangular prism 30 on which return light from 105 enters
The polarizing film 304 is formed on the second surface.

The optical axis of the first triangular prism 302 is M
In order to detect the O signal by the differential method, the first triangular prism 3 is set to be perpendicular to the optical axis of the incident light linearly polarized in the y direction and inclined by 45 ° in the direction perpendicular to the paper.
Reference numeral 02 divides the return light into two parts, an ordinary light and an extraordinary light, whose vibration components are orthogonal to each other. The optical axis of the second triangular prism 303 is set to be inclined at a predetermined angle with respect to the optical axis of the first triangular prism 302 in a plane perpendicular to the optical axis, that is, around the optical axis.

The signal detecting photodetector 306 for receiving return light emitted from the multi-image parallel flat plate 301 has a light receiving surface whose best image plane position of astigmatism by the multi-image parallel flat plate 301, ie, a multi-image position. The focal plane in the x direction and the focal plane in the y direction by the plane-parallel plate 301 are disposed so as to be located substantially in the middle.

[0011]

In the above-described optical head, the light beam emitted from the semiconductor laser 101 is a divergent light beam, and the principal ray of the light beam enters the polarizing film 304 at an incident angle of 45 °. Therefore, the semiconductor laser 101
Approximately half of the light beams included in the light beam from the light incident on the polarizing film 304 at an incident angle smaller than 45 °.

The return light beam from the magneto-optical recording medium 105 is a convergent light beam. Similarly, the principal ray of the light beam enters the polarizing film 304 at an incident angle of 45 °. Therefore, about half of the light beam included in the return light beam enters the polarizing film 304 at an incident angle smaller than 45 °.

Usually, the optical separation characteristic of the polarizing film 304 is 4
It is significantly reduced for light rays incident at an angle of incidence smaller than 5 °. In other words, to obtain the desired separation characteristics even for light rays incident at an incident angle smaller than 45 °,
Strict design conditions are imposed on the polarizing film 304.

For example, with respect to the entire divergent light beam having a full width at half maximum of 10 ° with linearly polarized light having a wavelength of 680 nm, the reflectance is 80% for S-polarized light, the reflectance is 20% for P-polarized light, and the transmission phase difference is 60 °. In order to satisfy the condition (1), the dielectric multilayer film as the polarizing film 304 needs about 30 stacked layers. Variations in the thickness of each layer of the dielectric multilayer film are superimposed on each other. Therefore, as the number of stacked layers increases, the overall variation increases. Therefore, such requirements make film fabrication very difficult. The present invention has been made to overcome such difficulties, and an object of the present invention is to provide an optical head that does not require strict design conditions for a polarizing film.

[0015]

According to the present invention, there is provided an optical head comprising: a semiconductor laser for emitting a divergent light beam; an objective lens for condensing a light beam from the semiconductor laser on an optical recording medium; It is located on the optical path between the objective lenses, reflects the light beam from the semiconductor laser, transmits the return light beam from the optical recording medium, and returns the light beam from the semiconductor laser and the return light from the optical recording medium. A polarizing film exposed in a gas that separates a beam, and a detection system that receives the return light beam transmitted through the polarizing film and detects information included in the return light beam, In the incident light beam, all the rays included in the full width at half maximum enter the polarizing film at an incident angle of 45 ° or more.

In a preferred example of the above-mentioned optical head, the polarizing film is located on an optical path between the semiconductor laser and the objective lens. Therefore, a divergent light beam is incident on the polarizing film, and The chief ray of the divergent light beam incident on the polarizing film is incident on the polarizing film at an incident angle of 50 ° or more.

In another preferred embodiment, the optical head further comprises a collimating lens for converting a divergent light beam from the semiconductor laser into a parallel light beam.
The polarizing film is located on an optical path between the collimating lens and the objective lens, so that a parallel light beam is incident on the polarizing film, and the parallel light beam incident on the polarizing film has an angle of 45 ° or more. The light enters the polarizing film at an incident angle.

[0018]

FIG. 1 shows an optical system of an optical head according to a first embodiment. As shown in FIG. 1, the optical head includes a semiconductor laser 101 for emitting a divergent light beam.
A collimating lens 310 for converting a divergent light beam from the semiconductor laser 101 into a parallel light beam, an objective lens 104 for condensing the parallel light beam from the collimating lens 310 on an optical recording medium 105, and a light beam from the semiconductor laser 101 A polarizing film 304 for separating the light beam from the optical recording medium 105 and a light beam from the semiconductor laser 101 transmitted through the polarizing film 304 and monitoring the light amount of the light beam from the semiconductor laser 101. A photodetector 305 for monitoring the amount of light, a polarization separation prism 301 for separating the return light beam transmitted from the optical recording medium 105 through the polarization film 304, and a polarization separation prism 30
And a signal detection detector 306 that receives the return light beam from the optical recording medium 105 that has passed through the first light-receiving device 1 and detects information included in the return light beam.

The semiconductor laser 101 emits a linearly polarized light beam. The polarizing film 304 is a dielectric multilayer film and has, for example, a reflectance of 80% for S-polarized light and a reflectance of 20% for P-polarized light. The positions of the semiconductor laser 101 and the polarizing film 304 are adjusted so that the linearly polarized light beam from the semiconductor laser 101 enters the polarizing film 304 as S-polarized light.

The polarizing film 304 includes a polarization splitting prism 301
And is exposed to the gas. The polarizing film 304 is located on the optical path between the semiconductor laser 101 and the collimating lens 310, so that a divergent light beam enters the polarizing film 304. Polarizing film 304
Are arranged such that the principal ray of the divergent light beam enters the semiconductor laser 101 at an incident angle of 50 ° or more, for example, an incident angle of 60 °.

The light amount monitoring photodetector 305 is provided on one surface of the polarization splitting prism 301,
And receives a light beam from the semiconductor laser 101 that has passed through and outputs a signal corresponding to the light amount.

The polarizing film 304 is provided on the optical recording medium 105.
Satisfactorily transmits the return light beam from. The polarization splitting prism 301 is made of a birefringent substance, for example, lithium niobate, and separates and refracts light incident thereon into two polarized lights whose polarization planes are orthogonal to each other. Gives astigmatism.

The signal detection detector 306 uses the astigmatism method to calculate the MO signal and the FE based on the incident light beam.
Generate an S signal and a TES signal. Next, the operation of the optical head will be described.

A part of the divergent light beam emitted from the semiconductor laser 101 passes through the polarizing film 304 and the rest is reflected toward the collimator lens 310. Polarizing film 304
Is incident on the polarization splitting prism 301, and the light amount monitoring photodetector 3 provided on one end face thereof is provided.
05. The light amount monitoring photodetector 305 outputs a signal corresponding to the received light amount, and based on this output signal, the semiconductor laser 101 is controlled so that the emitted light amount is kept constant.

The divergent light beam reflected by the polarizing film 304 is converted into a parallel light beam by a collimating lens 310, and the parallel light beam is condensed by an objective lens 104, and is minutely spotted on an information track of an optical recording medium 105. To form

Optical recording medium 1 reflected on information track
The divergent return light beam from 05 is converted into a parallel light beam by the objective lens 104, and this parallel light beam is converted into a convergent return light beam by the collimating lens 310 and is incident on the polarizing film 304.

The return light beam from the optical recording medium 105 passes through the polarizing film 304 well. The light beam that has passed through the polarizing film 304 is separated and refracted by the polarization splitting prism 301 into two polarized lights having polarization planes orthogonal to each other, so that the signal detection photodetector 30 has astigmatism.
6 is incident. The signal detection detector 306 uses the astigmatism method to calculate the MO signal and the FE based on the incident light beam.
Generate an S signal and a TES signal.

In the optical head of this embodiment, the polarizing film 30
The divergent light beam incident on the polarizing film 304 has a chief ray having an incident angle of 50 ° or more, for example, an incident angle of 60 °.
Incident on. In general, the full width at half maximum of the diverging light beam from the semiconductor laser 101 is about 10 ° in relation to the intensity with respect to the divergence angle, so that all rays included in the full width at half maximum enter the polarizing film 304 at an incident angle of 45 ° or more. Incident.

As a result, in order to obtain desired characteristics, the polarizing film 3
The design conditions required for 04 are relatively loose. Therefore, it is relatively easy to manufacture the polarizing film 304 under the design conditions. That is, the optical head of the present embodiment
Strict design conditions are not imposed on the polarizing film for separating the light from the light source and the return light from the optical recording medium.

In this embodiment, the configuration using two groups of the collimator lens 310 and the objective lens 104 is shown. However, the same operation and effect can be obtained by using only the finitely designed objective lens.

Next, FIG. 2 shows an optical system of an optical head according to a second embodiment. As shown in FIG. 2, the optical head includes a semiconductor laser 101 that emits a divergent light beam,
A collimator lens 310 for converting a divergent light beam from the semiconductor laser 101 into a parallel light beam, an objective lens 104 for condensing the parallel light beam from the collimator lens 310 on an optical recording medium 105, and a light beam and light from the semiconductor laser 101 A polarizing film 304 for separating a returning light beam from the recording medium 105; and a light amount monitor for receiving the light beam from the semiconductor laser 101 transmitted through the polarizing film 304 and monitoring the light amount of the light beam from the semiconductor laser 101. Optical detector 305, a polarization separation prism 301 for separating the return light beam from the optical recording medium 105 transmitted through the polarizing film 304, and a return light beam from the optical recording medium 105 passing through the polarization separation prism 301. A condensing lens 311 that emits light and a return light beam condensed by the condensing lens 311 And a signal detecting detector 306 for detecting information contained in the received light by the return light beam.

The semiconductor laser 101 emits a linearly polarized light beam. The polarizing film 304 is a dielectric multilayer film and has, for example, a reflectance of 80% for S-polarized light and a reflectance of 20% for P-polarized light. The positions of the semiconductor laser 101 and the polarizing film 304 are adjusted so that the linearly polarized light beam from the semiconductor laser 101 enters the polarizing film 304 as S-polarized light.

The polarizing film 304 is composed of a polarization splitting prism 301
And is exposed to the gas. This polarizing film 304 is located on the optical path between the collimating lens 310 and the objective lens 104,
04 receives a parallel light beam. The polarizing film 304 is arranged so that the principal ray of the parallel light beam enters the semiconductor laser 101 and the collimating lens 310 at an incident angle of 45 ° or more.

The light detector 305 for monitoring the amount of light is provided on one surface of the polarization splitting prism 301.
And receives a light beam from the semiconductor laser 101 that has passed through and outputs a signal corresponding to the light amount.

The polarizing film 304 is provided on the optical recording medium 105.
Satisfactorily transmits the return light beam from. The polarization splitting prism 301 is made of a birefringent substance, for example, lithium niobate, and separates and refracts light incident thereon into two polarized lights whose polarization planes are orthogonal to each other. Gives astigmatism.

The detector 306 for signal detection uses the astigmatism method and the MO signal and FE based on the incident light beam.
Generate an S signal and a TES signal. Next, the operation of the optical head will be described.

The divergent light beam emitted from the semiconductor laser 101 is converted into a parallel light beam by a collimating lens 310, and a part of the light beam is transmitted through a polarizing film 304.
The rest is reflected towards the object 104. The light beam transmitted through the polarizing film 304 enters the polarization splitting prism 301,
A light amount monitoring light detector 305 provided on one end surface thereof
Incident on. The light amount monitoring photodetector 305 outputs a signal corresponding to the received light amount, and based on this output signal,
The semiconductor laser 101 is controlled so that the emitted light amount is kept constant.

The parallel light beam reflected by the polarizing film 304 is condensed by the objective lens 104,
A minute spot is formed on the information track 05. The divergent return light beam from the optical recording medium 105 reflected on the information track is converted into a parallel light beam by the objective lens 104 and enters the polarizing film 304.

The return light beam from the optical recording medium 105 passes through the polarizing film 304 well. The light beam that has passed through the polarizing film 304 is separated and refracted by the polarization splitting prism 301 into two polarized lights having polarization planes orthogonal to each other, so that the signal detection photodetector 30 has astigmatism.
6 is incident. The signal detection detector 306 uses the astigmatism method to calculate the MO signal and the FE based on the incident light beam.
Generate an S signal and a TES signal.

In the optical head of this embodiment, the polarizing film 30
4 is incident on the polarizing film 304 at an incident angle of 45 ° or more. Therefore, almost all rays included in the parallel light beam enter the polarizing film 304 at an incident angle of 45 ° or more.

As a result, to obtain desired characteristics, the polarizing film 3
The design conditions required for 04 are relatively loose. Therefore, it is relatively easy to manufacture the polarizing film 304 under the design conditions. That is, the optical head of the present embodiment
Strict design conditions are not imposed on the polarizing film for separating the light from the light source and the return light from the optical recording medium. The present invention is not limited to the above-described embodiment, but includes all implementations that do not depart from the gist of the invention.

[0042]

According to the optical head of the present invention, most of the light included in the light beam incident on the polarizing film used for separating the light from the light source and the return light from the optical recording medium has an incident angle of 45 ° or more. Since the light enters the polarizing film at an angle, strict design conditions are not required for the polarizing film, which is preferable for reducing the cost of the entire optical head.

[Brief description of the drawings]

FIG. 1 shows an optical system of an optical head according to a first embodiment of the present invention.

FIG. 2 shows an optical system of an optical head according to a second embodiment of the present invention.

FIG. 3 schematically shows a configuration of an optical head according to a conventional example.

[Explanation of symbols]

 Reference Signs List 101 semiconductor laser 104 objective lens 105 optical recording medium 304 polarizing film 306 signal detection detector 310 collimating lens

Claims (3)

[Claims] A semiconductor laser for emitting a divergent light beam; an objective lens for condensing a light beam from the semiconductor laser on an optical recording medium; and an optical path between the semiconductor laser and the objective lens; Polarized light that is reflected in a gas that reflects the light beam from the semiconductor laser and transmits the return light beam from the optical recording medium, and separates the light beam from the semiconductor laser and the return light beam from the optical recording medium. And a detection system for receiving the return light beam transmitted through the polarizing film and detecting information included in the return light beam, wherein the light beam incident on the polarizing film is included in its full width at half maximum. An optical head, wherein all light rays incident on the polarizing film have an incident angle of 45 ° or more. 2. The polarizing film is located on an optical path between the semiconductor laser and the objective lens. Therefore, a divergent light beam is incident on the polarizing film, and a divergent light beam incident on the polarizing film is , Its chief ray is 5
The optical head according to claim 1, wherein the light is incident on the polarizing film at an incident angle of 0 ° or more. 3. A collimating lens for converting a divergent light beam from the semiconductor laser into a parallel light beam, wherein the polarizing film is located on an optical path between the collimating lens and the objective lens. The optical head according to claim 1, wherein a parallel light beam is incident on the polarizing film, and the parallel light beam incident on the polarizing film is incident on the polarizing film at an incident angle of 45 ° or more.