JPH05135398A - Optical pickup - Google Patents

Abstract

PURPOSE:To miniaturize the constitution and to improve productivity by reciprocating a light beam outgoing from a semiconductor laser in the inside of an optical system by a first and a second reflection mirror parts, a reflection hologram part and a transmission type grating lens and constituting adjustably a distance from the lens. CONSTITUTION:The light beam 7 outgoing from the semiconductor laser 15 becomes the light beam 21 propagating, to a second surface 20 as a reflected and a zero-order diffracted light beams in a reflection mirror part 19a forming reflection hologram on the first surface 19 of a lens member 18. By the mirror coating on the surface 20, the light beam 21 is reflected again and becomes the light beam 22 propagating to the surface 19 and becomes a converged laser beam 23 by the transmission type grating lens 19b, and is converged on an optical disk 16. The reflected flected light beam from the disk 16 becomes 1st-order diffracted light beams 25 and the image is formed on a multi-sected phtosenser 26. Further, a distance P between the laser 15 and the surface 20 is adjusted in accordance with the dispersion of a laser wavelength. Thus, a required optical path length is held and a pickup is miniaturized, and the productive yield and the productivity of the pickup is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup of an optical information recording device for recording or reproducing information by light.

[0002]

2. Description of the Related Art There has been a demand for miniaturization of an optical disk device which records and reproduces information using laser light, and attempts have been made to miniaturize and reduce the weight of an optical pickup. The reduction in size and weight of the optical pickup is advantageous not only for downsizing the entire device but also for improving performance such as shortening access time.
In recent years, the size and weight of optical pickups have been reduced by using hologram optical elements, and some of them have been put to practical use.

An optical pickup using a conventional hologram optical element will be described below. FIG. 6 is a block diagram of a conventional optical pickup. In FIG. 6, the semiconductor laser 1 has one end fixed on a heat dissipation plate 2 which also serves as heat dissipation and reinforcement, and a thin flexible wiring member 3 provided on the heat dissipation plate 2.
Electrically connected to. Similarly, the electrical signal of the multi-division photo sensor 4 is also electrically joined to the flexible wiring member 3. The other end of the semiconductor laser 1 is adhesively fixed by a sealing resin 7 in a state of being in contact with the second surface 6 of the lens member 5.

An optical path from the semiconductor laser 1 to the optical disc board 8 will be described. Light emitted from the semiconductor laser 9
Spreads and reaches the first surface 10. In the vicinity of the optical axis of the first surface 10, there is a reflection mirror portion 10a having a reflection hologram formed on the entire surface or a part thereof, and the emitted light 9 is reflected by the reflection mirror portion 10a and the next time of the reflection hologram. It becomes a light ray 11 which goes to the second surface 6 as folding light.
Since the second surface 6 is mirror-coated on the second surface 6 except for the entrance and exit windows of the semiconductor laser light as will be described later, it becomes a light ray 12 which is reflected again toward the first surface 10. The light beam 12 becomes a focused laser beam 13 by the transmission type grating lens 10b provided around the reflection mirror section 10a, and is converged at a point 14 on the optical disc board 8 to the diffraction limit of the laser beam.

Next, the reflected light path of the laser light from the optical disk board 8 will be described. The reflected laser light modulated by the recording information from the optical disk board 8 passes through the transmission type grating lens 10b in the opposite direction to the forward path, and becomes a light beam 11 from a light image 12.
It reaches the reflection mirror portion 10a in which a reflection hologram is formed on a part or all of it. Here is one of reflection hologram
Unlike the outward path, the next diffracted light 13 is reflected, then passes through the multi-segment photo sensor emission window provided in the mirror coating portion of the second surface 6, and is imaged on the multi-segment photo sensor 4. The reflection hologram is composed of at least two regions having different interference cycles and has a focus error detection function and a tracking error detection function.

[0006]

However, in the above-described grating lens, when the wavelength variation occurs with respect to the wavelength of the laser light used in determining the grating pitch, the wavefront aberration at point 14 becomes large. It has the drawback. In particular, this effect becomes large when the numerical aperture NA of the grating lens is large.

FIG. 7 shows NA = 0.45 and lens member length 5 m.
6 is a graph showing wavefront aberration (RMS) at an image forming point with respect to a laser wavelength when m is 2 m and the working distance is 2 mm.

On the other hand, the oscillation wavelength of the semiconductor laser 1 has an individual difference of about ± 15 nm due to variations in mass production. For this reason, conventionally, it has been complicated to select and use the semiconductor laser 1 or to prepare a grating pattern corresponding to each wavelength.

[0009]

In order to solve the above problems, the present invention is provided with a circular first reflecting mirror portion for reflecting light from a semiconductor laser, and a first reflecting mirror portion formed in the first reflecting mirror portion. A reflection-type hologram portion, a disk-side first surface formed of a chirped-type circular grating lens formed around the first reflection mirror portion and having a pitch that becomes smaller toward the outer periphery, and a first reflection mirror Second reflection mirror section for reflecting the light reflected from the lens section to the circular grating lens, an incident light window section for guiding the light from the semiconductor laser provided in the second reflection mirror section into the lens member, and a reflection type The second surface, which is opposed to the first surface and is composed of the outgoing light window portion that guides the diffracted light from the hologram portion to the light receiving sensor, and the semiconductor laser, which is located near the optical axis with a predetermined distance from the second surface. And location, and placed in contact with the sensor substrate having a light receiving sensor to the second surface, and configure them in sealing resin portion of the transparent bonding seal.

[0010]

According to the present invention, since the light emitted from the semiconductor laser reciprocates inside the optical system due to the above structure, the required optical path length can be obtained even with a small prism, so that the optical pickup can be downsized. , When the wavelength of the semiconductor laser is long because the semiconductor laser is adhered by the transparent sealing resin portion with respect to the design reference wavelength of the semiconductor laser for the circular grating lens, the distance from the second surface to the semiconductor reference is set to the design reference value. By making the distance shorter than the design reference value when the wavelength is short, the individual difference in the oscillation wavelength of the semiconductor laser can be absorbed.

[0011]

EXAMPLES Examples of the present invention will be described below. Figure 1
FIG. 3 is a configuration diagram of an optical pickup according to an embodiment of the present invention. In FIG. 1, an optical path from the semiconductor laser 15 to the optical disc board 16 will be described. Semiconductor laser 15
The light 17 emitted from the
Reach surface 19. In the vicinity of the optical axis of the first surface 19, there is a reflection mirror portion 19a having a reflection hologram formed on the entire surface or a part thereof, and the emitted light 17 is reflected by the reflection mirror portion 19a and the next time the reflection hologram is reflected. As a folding light, it becomes a light ray 21 which is directed to the second surface 20. Since the second surface 20 is mirror-coated except for the semiconductor laser light entrance and exit windows, as will be described later, it is reflected again and the first surface 1
It becomes the light ray 22 which goes to 9. This light ray 22 becomes a focused laser light 23 by the transmission type grating lens 19b provided around the reflection mirror portion 19a, and becomes the optical disc board 1
The laser light is focused on the point 24 on the upper surface 6 by the diffraction limit of the laser light. The transmission type grating lens 19b is of a chirped type in which the pitch becomes smaller toward the outer peripheral portion to provide an imaging effect.
At this time, since the central portion of the transmission type grating lens 19b is shielded by the reflection mirror portion 19a, the condensed light spot can be reduced by the super-resolution phenomenon.

Next, the reflected light path of the laser light from the optical disk board 16 will be described. The reflected laser light modulated by the recorded information from the optical disk board 16 passes through the transmission type grating lens 19b in the opposite direction to the light ray 22 to the light ray 21, and a reflection mirror having a reflection hologram formed on a part or all thereof. To the section 19a. Here, the first-order diffracted light 25 of the reflection type hologram is reflected from the second surface 20 after being reflected unlike the outward path.
An image is formed on the multi-division photo sensor 26 through the multi-division photo sensor emission window provided in the mirror coating part of the. The reflection hologram is composed of at least two regions having different interference cycles and has a focus error detection function and a tracking error detection function.

Next, a method of disposing the semiconductor laser 15 will be described. The second surface 20 and the semiconductor laser 15 are separated from each other by a predetermined distance P, and the space therebetween is adhesively sealed with a transparent resin 27 such as an acrylic resin. Semiconductor laser 15
Is fixed on a heat dissipation plate 28 that also serves as heat dissipation and reinforcement, and a thin flexible wiring member 29 provided on the heat dissipation plate 28.
Electrically connected to. Similarly, the electric signal of the multi-division photo sensor 26 is electrically connected to the flexible wiring member 29 through the sensor substrate 30.

FIG. 2 is a diagram showing a layout of a reflection hologram 19c and a transmission grating lens 19b formed on a part or all of the reflection mirror portion 19a formed on the first surface 19. FIG. 3 is an enlarged sectional view taken along the line AA of FIG. The phase hologram of the reflection hologram 19c is more advantageous in terms of diffraction efficiency, and the transmission grating lens 19b is more effective in converging and diffraction.
A chirped in-line type with a stepped or serrated cross section is suitable. The reflective hologram 19c and the transmissive grating lens 19b may be manufactured by a 2P method or the like in which a master shape is transferred by printing or using an ultraviolet curable resin.

FIG. 4 is a plan view of the mirror coating portion of the second surface 20. The second surface 20 has a reflection mirror coating portion 20 a, and the reflection mirror coating portion 20 a
An entrance window 20b for the semiconductor laser light and an exit window 20c for the multi-division photo sensor 26 are provided in a.

Next, the effect of adjusting the distance P between the semiconductor laser 15 and the second surface 20 will be described. 5 is N
A = 0.45, lens member length 5 mm, working distance 2 mm, laser wavelength of 780 nm, when the laser wavelength is changed,
By changing P, the wavefront aberration (RM
It shows how S) changes. Figure 5
As can be seen, when the wavelength is 770 nm, which is shorter than the design wavelength, P becomes about 1.72 mm and the wavefront aberration becomes 0, and conversely, when 790 nm, which is longer than the design wavelength, P
Is about 0.28 mm, the wavefront aberration becomes zero. As described above, by properly adjusting P with respect to the wavelength variation of the semiconductor laser 15 and fixing it with the transparent resin 27, the wavefront aberration can be adjusted to be small.

[0017]

As described above, according to the present invention, the circular first reflection mirror portion for reflecting the light from the semiconductor laser, the reflection hologram portion formed in the first reflection mirror portion, and the first reflection mirror portion The first surface on the disc side composed of a chirped type circular grating lens which is formed around the first reflection mirror portion and whose pitch becomes smaller toward the outer periphery, and the reflection light from the first reflection mirror portion to the circular grating. A second reflection mirror portion that reflects the light to the lens, an incident light window portion that guides light from the semiconductor laser provided in the second reflection mirror portion into the lens member, and receives diffracted light from the reflection hologram portion. A second surface, which is opposed to the first surface and is composed of an emission light window portion leading to the sensor, and a semiconductor laser are arranged in the vicinity of the optical axis with a predetermined distance from the second surface, and have a light receiving sensor. Since the sensor substrate is arranged in contact with the second surface and is composed of the transparent sealing resin portion that adheres and seals the second substrate, the light emitted from the semiconductor laser reciprocates inside the optical system, and a small prism. However, since the required optical path length can be obtained, the size of the optical pickup can be reduced, and since the semiconductor laser is adhered to the design reference wavelength of the semiconductor laser for the circular grating lens by the transparent sealing resin part, the wavelength of the semiconductor laser When the wavelength is long, the distance from the second surface to the semiconductor laser is set shorter than the design reference value, and when the wavelength is short, the distance is set longer than the design reference value. Can be absorbed, and the wavefront aberration due to wavelength variation can be reduced, and selection of semiconductor lasers and grating patterns and wavelengths can be performed. May not be such as matching, improvement in yield, improvement of productivity can be expected.

[Brief description of drawings]

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

FIG. 2 is a layout diagram of a reflection mirror section, a reflection hologram, and a transmission grating lens of an optical pickup according to an embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view taken along line AA in FIG. 2 of the optical pickup according to the embodiment of the present invention.

FIG. 4 is a plan view of a mirror coating portion of an optical pickup according to an embodiment of the present invention.

FIG. 5 is a graph of wavefront aberration at an imaging point with respect to a laser wavelength of an optical pickup and a distance between a semiconductor laser and a lens member according to an embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical pickup.

FIG. 7 is a graph of wavefront aberration at an imaging point with respect to a laser wavelength of a conventional optical pickup.

[Explanation of symbols]

 15 semiconductor laser 16 optical disk board 18 lens member 19 first surface 19a reflective mirror section 19b transmissive grating lens 19c reflective hologram 20 second surface 20a reflective mirror coating section 20b entrance window 20c exit window 24 point 26 multi-split photosensor 27 Transparent resin 28 Heat sink 29 Flexible wiring member 30 Sensor substrate

Claims (2)

[Claims] 1. A cylindrical or prismatic lens member whose both end surfaces are substantially parallel to each other, wherein a circular first reflecting mirror portion for reflecting light from a semiconductor laser and a first reflecting mirror portion are provided in the first reflecting mirror portion. A first surface on the side of a disk, which is composed of a reflection hologram portion formed, a chirped circular grating lens formed around the first reflection mirror portion and having a pitch that becomes smaller toward the outer circumference; A second reflection mirror portion that reflects the light reflected from the first reflection mirror portion to the circular grating lens, and an incident light that guides the light from the semiconductor laser provided in the second reflection mirror portion into the lens member. A second surface facing the first surface, which is composed of an optical window section and an outgoing light window section for guiding the diffracted light from the reflection hologram section to a light receiving sensor, and the semiconductor laser It is arranged in the vicinity of the optical axis while keeping a predetermined distance from the second surface, the sensor substrate having the light receiving sensor is arranged in contact with the second surface, and is composed of a transparent sealing resin portion for adhesively sealing them. An optical pickup featuring. 2. When the wavelength of the semiconductor laser is longer than the design reference wavelength of the semiconductor laser for the circular grating lens, the distance from the second surface to the semiconductor laser is set shorter than the design reference value, 2. The optical pickup according to claim 1, wherein a distance from the second surface to the semiconductor laser is set longer than a design reference value when the wavelength of the semiconductor laser is short.