JPH10320822A - Composite optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite optical element capable of obtaining a characteristic for the reduction of stray beam also in the structure to detect the front surface emission beam of laser diode for automatic laser beam output control. SOLUTION: The beam emitted from a laser diode 12 strikes against the prism surface 16a with an angle of 45 deg. of a prism 16, is reflected perpendicularly, and then is separated into a beam proceeding to a disk and into a beam passing through the interior of prism. This beam further passes through a reflection protective film 17 formed on the rear surface of prism 16, is detected by an optical detector 15, and then is applied to automatic output control to keep the emitted power of laser diode 12 at a constant level. Among the beams transmitted to the interior of prism 16, the stray beam generated through reflection, scattering and the like are absorbed by a absorption film 18 formed on the rear surface of prism 16. Thereby, it is attainable to detect the beam signal for automatic control and to reduce the stray beam at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite optical element, and more particularly to a composite optical element suitable for being incorporated in an optical pickup for an MD (mini disc) employing automatic output control based on light emitted from a front end face of a laser diode.

[0002]

2. Description of the Related Art A composite optical element incorporated in an optical pickup for a CD (compact disc), in which a laser diode, a prism, and the like are mounted, and from laser emission to reception and signal processing are performed in one package, has already been realized. I have.
In this composite optical element, the emitted laser light reflects on the surface of the prism toward the recording surface of the CD, but a part of the laser light enters the prism and becomes harmful stray light for the composite optical element. Since the compound optical element also has elements that receive optical signals for focus adjustment and tracking adjustment of the objective lens, stray light may reduce the measurement accuracy when those light-receiving elements measure optical signals. Has become.

Therefore, in a composite optical element for a CD, an absorption film is formed on the back surface of the prism as a measure for reducing stray light. When the stray light inside the prism reaches this absorption film,
Take out without reflecting inside, absorb in the film,
The stray light is reduced by preventing light from leaking out of the film.

As in the case of the composite optical element for CD, when considering the development to a composite optical element for MD in which a laser diode, a prism and the like are mounted, how to reduce stray light is important.

[0005] In the composite optical element for CD, of the laser light emitted from the front and rear end faces of the laser diode, the laser light emitted from the front end face uses a prism to read a signal on a disk surface, and performs focus servo and tracking. The laser light emitted from the rear end face of the laser diode used for the servo is monitored as an automatic output control signal and used for controlling the light output of the laser diode.

However, in the composite optical element for MD, since a high-output laser beam is essential for recording and erasing information, it is necessary to increase the reflectivity of the rear end face of the laser to increase the light output from the front end face. is there. For this reason, since the light emitted from the rear end face employed in the composite optical element for CD cannot be used for the automatic output control of the laser light, the light emitted from the front end face is used. FIG. 2 shows an example of a composite optical element for MD that performs automatic output control using the light emitted from the front end face.

FIG. 2 is a diagram showing a configuration of a conventional composite optical element. 2, the composite optical element for MD has a block 11 having a predetermined height formed on a substrate 10, and a laser diode 12 formed on the block 11. Further, on the substrate 10, the photodetectors 13, 14a,
14b and 15 are formed. Photodetectors 13 and 14
a and 14b detect a focus error signal for focus servo, a photodetector 13 detects a tracking error signal for tracking servo, and a photodetector 15b.
Is used to detect the signal for automatic output control. Further, on the substrate 10, the photodetectors 13, 14a, 14b
Is formed so as to cover. The prism 16 is placed 45 in front of the laser diode 12.
The laser diode 12 has a 45-degree surface 16a inclined at an angle of 45 °, and guides the laser light emitted from the front end surface of the laser diode 12 to the disk. An antireflection film 17 is attached to the entire back surface of the prism 16. This is because it is necessary to guide a part of the laser light emitted from the laser diode 12 to the photodetector 15 for automatic output control via the prism 16.
This is to increase the transmission of light on the back surface of No. 6.

In the above configuration, the laser diode 12
When the laser light is emitted from the prism 16, a part of the laser light is reflected by the prism 45-degree surface 16a of the prism 16 toward the disk, and a part of the laser light enters the prism 16, and the anti-reflection film 17 through the photodetector 15
Incident on. The photodetector 15 generates a current corresponding to the amount of incident light and supplies the current to a laser diode driving circuit (not shown) formed on the substrate 10. In the laser diode drive circuit, the drive current of the laser diode 12 is controlled to keep the amount of emitted light constant.

[0009]

As described above, in the composite optical element for MD, the light emitted from the rear end face employed in the composite optical element for CD cannot be used for the automatic output control of the laser beam. , Light incident on the prism 16 from the light emitted from the front end face and leaking from the rear face of the prism is detected by the photodetector 1.
5 to perform automatic output control.

However, in order to detect the light emitted from the front end face that has passed through the prism 16,
Since a composite optical element for CD cannot use an absorbing film that is effective in reducing stray light, there has been a problem that a good optical characteristic for reducing stray light cannot be obtained with a composite optical element for MD.

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and it is possible to obtain a stray light reduction characteristic even in a configuration in which front end face emission light is detected as a signal used for automatic output control of laser light. It is an object of the present invention to provide a composite optical element capable of performing the following.

[0012]

According to the present invention, a laser diode and a prism are mounted and automatic output control of the laser diode is performed by detecting light emitted from the front end face of the laser diode transmitted through the prism. In the composite optical element, there is provided a composite optical element in which a partial anti-reflection film and a partial absorption film are formed on an end face of the prism on a side where the light emitted from the front end face exits from the prism.

According to the above construction, a partial anti-reflection film is formed on the end face of the prism on the side from which the light emitted from the front end face of the laser diode is emitted, and an optical signal for automatic output control is detected outside the prism. By forming the partial absorption film so as not to block the optical path of the optical signal for automatic output control, stray light is reduced. As a result, in the composite optical element of the type in which the automatic output control of the laser diode is performed by detecting the light emitted from the front end face of the laser diode transmitted through the prism, the detection of the optical signal for the automatic output control and the reduction of the stray light can be achieved. It is possible to achieve both at the same time.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the composite optical element of the present invention. In FIG. 1, components having the same or equivalent functions as the components shown in FIG. 2 are denoted by the same reference numerals.

The basic structure of the composite optical element for MD is the same as the conventional one shown in FIG. That is, a laser diode 12 is formed on a substrate 10 via a block 11 having a predetermined height. On the substrate 10, photodetectors 13, 14a, 14b, and 15 are formed. Further, on the substrate 10, the photodetectors 13, 14a, 14
A prism 16 is formed so as to cover b.

The prism 16 has a prism 45-degree surface 16a having a reflectance of, for example, 60% inclined at 45.degree. In front of the prism 16, and an anti-reflection film 17 is deposited on the lower surface of the prism 16 over approximately the lower half thereof. , About the upper half, the absorbing film 18 is deposited. In this way, the back surface of the prism 16 is divided into two in the vertical direction, and the anti-reflection
The reason for vapor-depositing 8 is that, in consideration of the divergence angle of the laser, the ray tracing was performed on the light passing through the prism 45-degree surface 16a. In the figure, it behaves as if it advances in the shaded area, and does not reach the upper half of the back surface of the prism 16.

In the structure of the composite optical element described above, first, when the laser light is emitted from the laser diode 12, the laser light is
6a, 60% of which is reflected at a right angle and travels toward the disk surface. In addition, a part of the laser beam passes through the prism 45-degree surface 16a and enters the prism. Light that has entered the prism further passes through the antireflection film 17 having a function of reducing reflection and increasing transmission from the rear surface of the prism 16 to irradiate the photodetector 15. Photodetector 1
5 is converted into a current corresponding to the amount of incident light, and this current signal is used for automatic output control for controlling the amount of light to be emitted, that is, the drive current of the laser diode 12 so as to keep the laser emission power constant. .

On the other hand, the light reflected from the disk and returned is transmitted through the prism 45-degree surface 16a of the prism 16 and enters the prism. The entered light is first incident on the photodetector 13, where it is detected as a tracking error signal for tracking servo. Photodetector 1
A part of the light traveling toward 3 is reflected at the lower boundary surface of the prism 16, further reflected at the upper boundary surface of the prism 16, and then enters the photodetectors 14a and 14b. In the photodetectors 13, 14a and 14b, the incident optical signal is
It is detected as a focus error signal for focus servo.

Further, the stray light that enters the prism 16 and is reflected and scattered inside the prism 16 is absorbed by the absorbing film 18 and does not return to the prism. Thereby, stray light can be reduced.

[0020]

As described above, according to the present invention, an anti-reflection film is formed on the lower half portion of the back surface of the prism, which corresponds to the optical path of the optical signal for automatic output control, and is formed on the upper half portion which does not block the optical path. Was configured to form an absorbing film. This makes it possible to detect stray light signals for automatic output control and at the same time significantly improve stray light reduction characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a composite optical element of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional composite optical element.

[Explanation of symbols]

10 ... substrate, 11 ... block, 12 ... laser diode, 13, 14a, 14b, 15 ... photodetector, 1
6 ... Prism, 16a ... Prism 45-degree surface, 17 ...
... Anti-reflection film, 18 ... Absorption film.

Claims (3)

[Claims] 1. A composite optical element having a laser diode and a prism mounted thereon and performing automatic output control of the laser diode by detecting light emitted from the front end face of the laser diode transmitted through the prism. Wherein a partial anti-reflection film and a partial absorption film are formed on an end face of the prism on a side where light exits from the prism. 2. The composite optical element according to claim 1, wherein the partial anti-reflection film is formed on an end face of the prism in a region of an optical path where the light emitted from the front end face exits from the prism. 3. The composite optical element according to claim 1, wherein the antireflection film is formed on a lower half of an end face of the prism, and the absorption film is formed on an upper half.