JPH1116199A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optical head thin by a method without requiring a condenser lens since the miniaturizing method of a reflection mirror so as to arrange the reflection mirror on the converging point of an incident convergent light beam has a demerit of increasing the number of the condenser lenses and contrarily has disadvantage for miniaturizing the optical head device due to the condenser lens. SOLUTION: NA (the numerical aperture) of an objective lens 1 is made small by using a light source 12 emitting a light beam of a shorter wavelength than a wavelength suitable for the signal recording density of a signal recording medium to be the object. In this case, making the objective lens 1 thin is attained by making the diameter, of objective lens 1 small so as to secure a minimum required thickness at the peripheral edge part having lens action of the objective lens 1 and make the thickness of central part of the objective lens 1 thin. The miniaturization of a reflection mirror is attained by making the diameter of the luminous flux of a light beam being incident on the objective lens 1 small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an incident optical path in which a light beam emitted from a light source enters an objective lens.
The present invention relates to an optical head device having a configuration in which a reflection mirror that bends the light beam is disposed in front of an objective lens, and particularly to an optical head device that is reduced in thickness.

[0002]

2. Description of the Related Art In an optical head device for optically reading or writing a signal on or from a signal recording medium such as a disk, an objective lens is provided on an incident optical path where a light beam emitted from a light source is incident on the objective lens. A configuration in which a reflection mirror that bends the light beam is disposed on the front side of
A thinner one is known.

[0003] Such an optical head device is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-244325.
In the optical head device disclosed in this publication, the reflection mirror arranged on the front side of the objective lens is arranged at the converging point of the incident convergent light beam, thereby achieving the miniaturization of the reflection mirror and further reducing the thickness. .

[0004]

However, in the optical head device disclosed in the above publication, since the reflection mirror has a converging point, the diffusion angle of the light beam incident on the objective lens becomes steep, and the incidence angle on the incident side of the objective lens is increased. The numerical aperture, the so-called NA, must be large, and the tolerance of the angle and distance of the mounting position of the objective lens and the reflecting mirror becomes small, or the thickness by increasing the curvature of the entrance side of the objective lens. There are disadvantages such as an increase in weight and an accompanying increase in weight.

[0005] Further, a condensing lens is required on an incident optical path through which a light beam emitted from a light source enters an objective lens,
An extra optical component is required, and the condensing lens is a factor that hinders the reduction in thickness.

The present invention provides an optical head device which is reduced in thickness without adversely affecting the objective lens and increasing the number of optical components.

[0007]

According to the present invention, a light source which emits a light beam having a wavelength shorter than the wavelength appropriate for the signal recording density of a target signal recording medium is used as a light source, and the light is focused by an objective lens. In order to reduce the NA of the objective lens in relation to the wavelength of the light beam emitted from the light source so that the diameter of the light spot to be obtained is appropriate for the signal recording density of the target signal recording medium, This is done by reducing the aperture of the lens. This allows the area of the reflecting surface of the reflecting mirror to be reduced, thereby reducing the size of the reflecting mirror itself, and reducing the size of the objective lens.
The thickness of the reflecting mirror and the objective lens can be reduced.

Further, by making the angle of the reflecting surface of the reflecting mirror with respect to the optical axis of the objective lens larger than 45 degrees, the thickness of the reflecting mirror can be reduced without changing the area of the reflecting surface.

[0009]

FIG. 1 is a structural view showing an embodiment of the optical head device of the present invention. First, the configuration of the objective lens driving mechanism will be described.

The objective lens 1 includes a focusing coil 2
And a lens holder 4 on which a tracking coil 3 is mounted. The lens holder 4 includes a frame 5
Are supported displaceably on the frame 5 by four support wires 7 each having one end fixed to a mounting plate 6 mounted on the frame 5.

The frame 5 has a focusing coil 2
Magnets 8 and 9 and yokes 10 and 11 for forming a magnetic field acting on the tracking coil 3 are fixed. Next, the configuration of the optical system will be described.

The optical system includes an incident optical path for guiding a laser beam generated from a laser diode 12 serving as a light source to the objective lens 1 and a laser beam reflected by the disk 13 and returned to the objective lens 1 to a photodetector 14. It has a return optical path for guiding.

The laser beam generated from the laser diode 12 is bent by the half mirror 15, further bent by the reflection mirror 16, enters the objective lens 1, is collected by the objective lens 1, and reaches the disk 13. You.

The laser beam reflected by the disk 13 returns to the objective lens 1 and is bent by a reflection mirror 16 and then passes through a half mirror 15 to which astigmatism used for focus control is given and a photodetector is provided. Reach 14

As the laser diode 12, a laser diode that emits a laser beam having a wavelength shorter than the wavelength appropriate for the signal recording density of the target disk 13 is used.

For example, in the case of an optical head device dedicated to a CD, a laser diode 12 having a laser beam having a wavelength of 780 nm is usually used as a laser diode 12, and is currently used for reproducing a DVD (digital video disk). 650nm or 635nm laser diode
Used for D-dedicated optical head device.

The laser diode 12 having a wavelength shorter than the wavelength appropriate for the signal recording density of the target disk 13
Is used in order to make the diameter of the light spot condensed by the objective lens 1 appropriate for the signal recording density of the target disk 13 and the wavelength of the laser beam emitted from the laser diode 12. Although it is necessary to reduce the NA of the lens 1, this is done by reducing the aperture of the objective lens 1.
Therefore, if the curvature of the objective lens 1 is the same, it is possible to reduce the thickness of the central portion in the case where the minimum necessary thickness is secured in the peripheral portion having the lens action due to the strength and the like, and 1 is advantageous for thinning.

Since the diameter of the objective lens 1 is reduced, the diameter of the laser beam incident on the objective lens 1 can be reduced, and the area of the reflection surface 16a of the reflection mirror 16 can be reduced. Mirror 16
This is advantageous for miniaturization.

Therefore, the thickness of the optical head device can be reduced. The reflection mirror 16 is configured such that the angle of the reflection surface 16a with respect to the optical axis of the objective lens 1 is larger than 45 degrees. That is, the installation surface on which the reflection mirror 16 is perpendicular to the optical axis of the objective lens 1 and the reflection surface 1
The elevation angle which is the angle with 6a is smaller than 45 degrees. Therefore, when the area of the reflection surface 16a is the same, the height from the installation surface can be reduced.

Further, the position at which the laser diode 12, the photodetector 14, and the half mirror 15 are arranged is brought closer to the disk 13 depending on the angle of the reflection surface 16a of the reflection mirror 16. Therefore, it is advantageous to prevent those optical components from projecting below the objective lens driving mechanism.

[0021]

As described above, according to the present invention, a light source that emits a light beam having a wavelength shorter than the wavelength appropriate for the signal recording density of a target signal recording medium is used, and the NA of the objective lens is reduced. Since the objective lens is made smaller by reducing the aperture of the objective lens, the thickness of the central part of the objective lens is made thinner by securing the minimum necessary thickness at the peripheral part having the lens function of the objective lens. This is advantageous in reducing the thickness of the objective lens, and the smaller aperture of the objective lens can reduce the luminous flux diameter of the light beam incident on the objective lens, which is advantageous in reducing the size of the reflection mirror. As a result, it is possible to provide a thin optical head device.

Further, by making the angle of the reflecting surface of the reflecting mirror with respect to the optical axis of the objective lens larger than 45 degrees, the height of the reflecting mirror from the installation surface can be reduced. The position of the optical component on the opposite side of the objective lens with the reflecting mirror interposed can be closer to the signal recording medium side in accordance with the angle of the reflection surface, so that those optical components are located below the objective lens drive mechanism. This is advantageous in preventing overhang, and as a result, the thickness of the optical head device can be reduced.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 12 Laser diode 16 Reflection mirror 16a Reflection surface

Claims (2)

[Claims] 1. An optical head device having a configuration in which a reflection mirror that bends the light beam is disposed in front of the objective lens in an incident light path where a light beam emitted from a light source is incident on the objective lens. A light source that emits a light beam with a wavelength shorter than the wavelength that is appropriate for the signal recording density of the target signal recording medium is used, and the diameter of the light spot focused by the objective lens is In order to reduce the NA of the objective lens from the relationship with the wavelength of the light beam emitted from the light source so as to have an appropriate size for the signal recording density, the NA of the objective lens is reduced by reducing the aperture of the objective lens. Characteristic optical head device. 2. The optical pickup device according to claim 1, wherein the reflection mirror is configured such that the angle of the reflection surface with respect to the optical axis of the objective lens is larger than 45 degrees.