JPS62266742A - light pick up - Google Patents

Abstract

PURPOSE:To improve light utilization efficiency and to obtain an excellent S/N by allowing a detector to detect partial light which is projected in another direction without returning to a laser beam source in light which passes through a converging diffraction grating. CONSTITUTION:Light guided from a semiconductor laser device 60 to an optical waveguide layer 30 travels as shown by an arrow 1 and is diffracted by the converging diffraction grating 50 in two directions shown by arrows 2 and 3, and the light shown by the arrow 2 forms its optical image on a disk 80. The reflected light from the disk 80 is incident on the grating 50 as shown by an arrow 4 and diffracted in two directions shown by arrows 5 and 6. The diffracted light shown by the arrow 6 is made incident on a photodetector 15 and a light signal which contains information from the disk 80 and control information necessary for a signal read is converted into an electric signal. Consequently, the light utilization efficiency is improved and the excellent signal- to-noise ratio is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to optical pink-up for recording or reproducing information on an optical disc, and in particular, it improves light utilization efficiency and is suitable for miniaturization and weight reduction. The present invention relates to such a light pink-up composition.

[Conventional technology]

Conventionally, this type of optical pick-up knob was published in Technical Research Report 0QE85-72 (September 19F15).
Month) As described on pages 39 to 46, a beam splitter is provided to separate the light projected from the optical pink amplifier onto the disk and the light reflected from the disk and returned to the optical pickup. However, no consideration was given to the light utilization efficiency, i.e., how much of the light emitted from the laser light source is reflected by the disk and returned to the photodetector in the optical pickup.

FIG. 6 is a perspective view showing the conventional optical pickup described in the above-mentioned document. In the figure, S is a substrate, B is a buffer layer, W is a waveguide layer, FGC is a focusing grating coupler (diffraction grating for focusing light), BS is a twin grating focusing beam splitter,
H is a photodiode, L is a laser diode, and P is an optical disk.

The operation is as follows. That is, the laser diode L
The laser light emitted from the laser beam propagates through the waveguide layer W, passes through the beam splinter BS, and passes through the focusing grating.
The laser beam is diffracted by the coupler FGC and focused on the external disk P, and then reflected by the disk P, and enters the focusing grating coupler FGC.
The light reaches the beam splitter BS, changes its optical path, and reaches the photodiode H.

In other words, the laser light emitted from the laser diode L passes through the beam splinter B both on its way to the disk P and back.
beam splitter BS.
has the function of separating outgoing light and returning light, but due to this function, an optical pickup using a beam splinter has the disadvantage that the light utilization efficiency is extremely poor.

[Problem that the invention seeks to solve]

The problem to be solved by the present invention is to improve the light utilization efficiency and obtain a good signal-to-noise ratio in an optical pickup. Therefore, an object of the present invention is to provide an optical pickup that makes the above possible.

[Means for solving problems]

In order to achieve the above object, in the present invention, a beam splitter is not provided, and instead of the returned light that comes out after having its optical path separated by the beam splitter, the returned light that has passed through the focusing diffraction grating is used. Taking advantage of the fact that some of the light does not return to the laser light source and has been emitted in other directions, the detector detects the light emitted in this different direction. , eliminating the need for a beam splitter.

[Effect]

The above-mentioned condensing diffraction grating that constitutes the optical big amplifier is a grating whose groove spacing and curvature gradually change, and the light beam that has traveled through the guiding wavepath is directed onto the external disk surface by the grating. It has the function of forming an image.

However, at the same time, apart from the emitted light beam that heads toward the disk surface, there is also a light beam that is diffracted toward the side opposite to the disk surface direction. The two-beam coupling conditions for generating light beams in two directions are the effective refractive index determined by the configuration of the guiding waveguide, the average groove spacing of the focusing diffraction grating, and
This can be obtained by appropriately setting the normalized spatial frequency determined by the wavelength of the laser beam. In addition, this focusing diffraction grating has a similar function for the light beam that is reflected by the optical disk and returns to the optical disk. It can be divided into

In the present invention, since the light beam penetrating the leading waveguide and emerging from the bottom is detected by a photodetector,
There is no need for a beam splitter, and therefore, since no beam splitter is used, there is no reduction in light utilization efficiency.

Furthermore, in the case of conventional technology in which light traveling through an optical waveguide is detected by a photodetector, it is difficult to increase the optical coupling efficiency between the leading wave/path and the photodetector due to its structure. ,
In the present invention, since the light can be made incident at a large angle with respect to the light detection surface of the photodetector, even if a coupling means is especially provided between the leading waveguide and the photodetector, the light utilization efficiency is improved. is expensive.

Furthermore, in order to improve the light utilization efficiency, a lens layer can be easily provided between the guide waveguide and the photodetector.

〔Example〕 An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a front view showing an optical pickup as an embodiment of the present invention.

In the figure, a photodetector 15 is provided on a substrate 10, and a craft layer 20 and an optical waveguide layer 30 are laminated thereon. Further, a condensing diffraction grating (focusing grating coupler FGC) 5Q is provided in a part of the upper part of the optical waveguide layer 30. The laser device 60 includes a laser light source (not shown),
A coupling means (not shown) is provided for guiding the laser light to the optical waveguide layer 30.

The laser device 60 is generally a gas laser (H, -N
,,A,) and a semiconductor laser are guided to the optical waveguide layer 30 by various coupling means (end face packing, prism coupling, grating coupling, etc.), but if the latest process technology is used, It is also possible to fabricate a semiconductor laser monolithically on the substrate 10.

An S-, G-, or A-based substrate is suitable for the substrate IO, and a PIN photodiode is suitable for the photodetector 15. The cladding layer 20 is made of a material having a refractive index smaller than that of the optical waveguide layer 30. There is a wide range of materials to choose from for forming the optical waveguide layer 30, and one example is (air: refractive index 1) optical waveguide layer:
Corning 97059 glass refractive index approx. 1.53 Cladding layer: S direct refractive index approx. 1.47 groups
Plate: S, refractive index approximately 3.4.

The condensing diffraction grating 50 has the function of disturbing the above-described structural requirements of the optical waveguide layer and extracting the light propagating through the optical waveguide layer 30 to the outside. Therefore, a material having a higher refractive index than the optical waveguide layer 30, such as S or N (refractive index: about 2), is used as the light focusing diffraction grating.

The grating pattern of the condensing diffraction grating 50 that forms an optical image on the optical disk 80 has a shape in which the groove interval ΔV and the curvature of the groove gradually change, as schematically shown in FIG. belongs to. The average value of this groove interval Δ■ varies depending on various conditions, but is, for example, about 0.4 μm. Various methods for such microfabrication have been studied, including a method using an electron beam direct exposure device, for example.

The light guided from the semiconductor laser device 60 to the optical waveguide layer 30 travels in the direction of arrow 1 in FIG.
It is diffracted at 0. If the focusing diffraction grating 50 is designed to satisfy the two-beam coupling condition, the guided light will be diffracted in two directions shown by arrows 2 and 3, and will proceed in the direction of arrow 2:
The light forms an optical image on optical disk 80 .

Light Aiyu, 807 The reflected corpse is arrow 4. ) direction, the condensing diffraction grating is again tilted at 50° C., and similarly diffracted in two directions indicated by arrows 5 and 6. Diffracted light in the direction of arrow 6 enters the semi-detector 15, and the light is De, isk 80
The photodetector 15 converts the optical signal 4 containing the information and control information necessary for reading the signal into an electrical signal.

If the light detection part patterns and their connections in the photodetector 15 are configured as shown in FIG.
Adders A1 to A5 and subtractor S add electrical signals from d.
By performing arithmetic processing using the UI and SU2, control signals such as a focus error signal and a tracking error signal can be obtained, and information recorded on the optical disc can also be read as a reproduction signal.

The light utilization efficiency in the embodiment shown in FIG. 1 is approximately 3 to 30%, although it varies depending on the efficiency of the semiconductor laser device 60.
becomes.

In the conventional method, assuming that the efficiency of the diffraction grating for the beam splitter is 50%, the coupling efficiency of the guiding waveguide and the photodetector is 60%, and the efficiency of other parts is equivalent to that of this embodiment, the overall light utilization efficiency is is 0.45 to 4.5%. Therefore, it can be said that the light utilization efficiency of this embodiment is more than 6 times better than that of the conventional system.

FIG. 4 is a front view showing another embodiment of the present invention. In this figure, the same parts as in FIG. 1 are given the same reference numerals. In addition, 40 indicates a lens layer, and 45 indicates a lens straw.

In the embodiment shown in FIG. 4, a lens layer 40° is provided between the Crabstone layer 20 and the photodetector 15 to increase the degree of freedom in design. It is possible to provide a lens function as the lens section 45, or to incorporate a prism or wedge function for separating and generating servo control signals.

In this embodiment, the craft layer 20 and the lens layer 40 can be integrated into a simpler structure depending on the material selection of each part.

FIG. 5 is a front view showing still another embodiment of the present invention. In this figure, the same parts as in FIGS. 1 and 4 are given the same reference numerals. In addition, 70 is a lens,
51 is a diffraction grating.

In the embodiment shown in FIG. 5, by performing the light condensing function with a well-known spherical or aspherical lens 70, the grating pattern of the diffraction grating 51 can be made linear, and the manufacturing process is simple. It becomes easier. Furthermore, this lens 70
There is an advantage that focus control or tracking control can be performed by moving only the lens.

〔Effect of the invention〕

As described above in detail, according to the present invention, the light utilization efficiency of the optical pickup can be increased, so that a good signal-to-noise ratio can be obtained.

Furthermore, since the light utilization efficiency is high, the amount of light from the laser light source is also small, and the amount of heat generated is reduced accordingly, so the heat sink used for heat dissipation can also be made smaller, and further miniaturization can be achieved.

[Brief explanation of drawings]

FIG. 1 is a front view showing one embodiment of the present invention, and FIG. 2 is a front view showing one embodiment of the present invention.
A schematic diagram showing an example of a pattern of a condensing diffraction grating in the figure,
3 is a circuit diagram showing an example of the photodetecting part pattern of the photodetector in FIG. 1 and its related connections, FIG. 4 is a front view showing another embodiment of the present invention, and FIG. 5 is a further embodiment of the present invention. FIG. 6 is a front view showing another embodiment, and FIG. 6 is a perspective view showing a conventional optical pickup. Explanation of symbols 10... Substrate, 15... Photodetector, 20... Clad layer, 30... Optical waveguide layer, 40... Lens layer, 4
5... Lens portion, 50... Diffraction grating for focusing, 51.
...Diffraction grating, 60...Semiconductor laser device, 80...
・Optical Disc Agent Patent Attorney Akio Namiki 125J

Claims (1)

[Claims] 1. Laser light input to the optical waveguide layer is partially outputted in the first direction via a diffraction grating formed on the surface of the optical waveguide layer so as to be transmitted to the outside as required. In the optical pickup, the laser beam is directed toward the target object, and the remaining part is left to travel in a second direction different from the first direction, in which the laser beam reflected from the target object is directed toward the diffraction grating. When input to the optical waveguide layer through the optical waveguide layer, a part of the laser light is allowed to propagate along the optical waveguide layer toward the original direction (third direction), and the remaining part is When outputting toward a fourth direction different from the third direction, a photodetector is arranged in the fourth direction, and the photodetector detects the light headed in the fourth direction. An optical pickup characterized by: 2. The optical pickup according to claim 1, wherein the photodetector receives the laser beam directed in the fourth direction through a lens layer.