JP2607064B2 - Waveguide type optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] In an optical head for an optical disk, a small and light
In order to simplify the structure and reduce costs, the optical head is composed of an optical waveguide, and the misalignment detection waveguides provided in parallel on both sides of the optical pickup waveguide are displaced in the track direction. Is detected, and the focal position deviation is detected by the inclined waveguide for detecting the focal position deviation.

[Industrial applications]

In the field of optical disks, when information is optically read from a disk medium, reading is performed by moving an optical system for an optical pickup at high speed. Therefore, as for the optical pickup, reduction in size and weight has been studied in order to shorten the access time, and simplification of the structure has been studied in order to reduce the cost. In order to meet such demands, research has been made on using an optical waveguide instead of a conventional glass lens or the like. The present invention relates to an optical head using such an optical waveguide.

[Conventional technology]

FIG. 4 is a side view of an optical pickup using a conventional optical lens. The light emitted from the semiconductor laser LD is converted into parallel light by the collimating lens 1, passes through the optical path of the perfect circle correction prism 2 → deflection beam splitter 3 → 1/4 wavelength plate 4, and is stopped by the objective lens 5. The optical disk 6 is irradiated. Then, the reflected light from which the information has been read is transmitted to the objective lens 5 →
1/4 wavelength plate 4 → polarization beam splitter 3 → condenser lens 7
→ The light passes through the optical path of the light detector 8 and is converted into an electric signal by the light detector 8. The focal position of the lens 5 is adjusted
This is performed by the drive coil 9.

As described above, the conventional optical head is a combination of a large number of group lenses, prisms, and the like. The large size and heavy weight of the optical pickup hinder high-speed driving. Also, since a large number of optical lenses must be spatially adjusted and arranged, it is difficult to assemble them.

[Problems to be solved by the invention]

To solve this problem, as shown in FIG.
A waveguide 12 from a laser light source LD to an emission end 11 and a waveguide 14 from an emission end to a photodetector 13 are provided on a single substrate 10, a laser beam is emitted from the emission end 11, and an optical disk is An optical head that converges to 6 has been proposed. The reflected light from the optical disk 6 enters the waveguides 12 and 14 from the emission ends via the objective lens 15, is received by the photodetector 13, and is converted into an electric signal.

Such a waveguide type optical head is extremely effective because it can be formed on a substrate made of thin silicon or the like, is small and lightweight, and has a simple configuration. However, focus alignment,
It is difficult to confirm whether the positioning in the track direction or the like is correctly performed. It is a technical object of the present invention to solve such a problem in the conventional optical head, and to enable simultaneous detection of a positional deviation in a track direction and a focal position in a light guide type optical head.

[Means for solving the problem]

FIG. 1 is a front view for explaining the basic principle of the waveguide type optical head according to the present invention. Reference numeral 16 denotes an optical head substrate according to the present invention, on which an optical pickup waveguide 17 for connecting a laser light source and a light receiving element to an emission end is formed. Parallel waveguides A1 and A2 are provided parallel to both sides of the optical pickup waveguide 17. On the emission end 11 side, oblique waveguides B1, B2 intersecting the ends of the parallel waveguides A1, A2 in a V-shape are provided. This parallel waveguide
Independent photodetectors are connected to the other ends of A1, A2 and the oblique waveguides B1, B2.

The distal ends of the waveguides 17, A1, A2, B1, B2 face the single objective lens 15, and are disposed at the emission end 11.

[Action]

An objective lens 15 is arranged between the emission end 11 and the optical disc 6. Light emitted from the central optical pickup waveguide 17 is applied to the optical disk 6 via the objective lens 15, and the reflected light is incident on the optical pickup waveguide 17 via the objective lens 15. Reading is performed by detecting this light with a light detector and converting it into an electric signal.

If the light reflected from the optical disk 6 is accurately focused on the exit end position of the waveguide 17, the incident light power to the other parallel waveguides A1 and A2 and the oblique waveguides B1 and B2 is small. It is possible to detect that the optical pickup waveguide 17 is in focus by the detection signals from the optical detectors in the waveguides A1, A2 and the oblique waveguides B1, B2.

As shown in FIG. 2 (a), when the emitting end 11 is located before the focal position f, the parallel waveguide on both sides of the waveguide 17 is used.
Since the incident light power to A1 and A2 is strong and the incident light power to oblique waveguides B1 and B2 is weak, the amount of light detected by parallel waveguides A1 and A2 is larger than the amount of light detected by oblique waveguides B1 and B2. Can be detected. As described above, when it is detected that the emission end 11 is located at a position closer to the focus position, control is performed so as to come to the focus position shown in FIG.

As shown in FIG. 2 (b), when the emission end 11 is located before the focal position, the light is diffused at the position of the emission end 11, so that the amount of light incident on the parallel waveguides A1 and A2 is smaller than that. The amount of light incident on the oblique waveguides B1 and B2 is large. Therefore, it can be detected by comparing the outputs of the respective photodetectors. As described above, when it is detected that the emission end 11 is located at a position ahead of the focal position, it is controlled to come to the focal position shown in FIG.

In the above case, the output values of the parallel waveguides A1 and A2 and the output values of the oblique waveguides B1 and B2 are almost equal to each other. become. In the figure, the horizontal direction is the tracking control direction. If the reading light in each track enters the central waveguide 17, no tracking shift occurs, and the amount of incident light on the parallel waveguides A1 and A2 becomes uniform. However, when the optical head is displaced to the left from the target track, the read light is also incident on the right parallel waveguide A2, so the light detection amounts of the two parallel waveguides A2 and A1 are compared, and It can be detected when A2> A1. When the optical head is displaced to the right from the target track, the reading light is also incident on the left parallel waveguide A1, so the light detection amounts of the two parallel waveguides A1 and A2 are compared, and the light amount is determined. When A1> A2, detection is possible. When the amount of light incident on the parallel waveguides A1 and A2 is unbalanced as described above, the tracking error is corrected by moving the optical head in the left-right direction until the amount of light is balanced.

〔Example〕

Next, how the waveguide type optical head according to the present invention is actually embodied will be described with reference to examples. FIG. 3 is a side view showing an embodiment of the waveguide type optical head according to the present invention. The central optical pickup waveguide 17 has a laser light source
The LD and the photodetector 13 are connected, and the other ends of the parallel waveguides A1, A2 and the oblique waveguides B1, B2 are photodetectors 18, 19, and 2, respectively.
0 and 21 are connected. The light detectors 18 and 19 are connected to the arithmetic circuit 22 and compare the output values of the two light detectors 18 and 19 to detect the amount of displacement of the optical head in the track direction. 24 is a track direction positioning coil,
The polarity and the current value are determined by the output signal from the arithmetic circuit 22. That is, when the output value on the left photodetector 18 side is large, the optical head is driven to the left side in the figure by the drive coil 24, and when the output value on the right photodetector 19 side is large, it is moved to the right side in the figure. Driven. At this time, the light detector 18 and
Driven until the 19 output values are balanced.

The light detectors 18, 19 and 20, 21 are connected to another arithmetic circuit 23. Therefore, light detectors 18, 19
Is compared with the output values of the photodetectors 20 and 21, the shift of the focal position can be detected. That is, light detector 1
When the output values of the light detectors 8 and 19 are larger than the output values of the light detectors 20 and 21, the light emitting end 11 is located closer to the focus position than the focal position as shown in FIG. Conversely, light detector 18,
When the output value of 19 is smaller than the output values of the photodetectors 20 and 21, as shown in FIG.
11 will be located.

25 is a focus direction positioning coil of the objective lens 15,
The polarity and the energizing current value are determined by the output signal from the arithmetic circuit 23. That is, when the output values of the parallel waveguides A1 and A2 are large, the objective lens 15 is driven toward the optical disk 6, and when the output values of the oblique waveguides B1 and B2 are large, the objective lens 15 is driven toward the emission end 11. . At this time, the light detectors 18, 19, 20,
It is driven until the output value of 21 becomes minimum.

The positioning in the focal direction is performed by each of the waveguides 17, 18,.
Can be performed by driving the optical element side having

〔The invention's effect〕

As described above, according to the present invention, in place of an optical lens or a prism, an optical head including a waveguide can accurately detect a tracking shift and a shift in a focus direction of the optical head, and can perform alignment. The practical use of a waveguide type optical head becomes possible.

Further, according to the present invention, as described above, since the detection waveguide is provided so as to face a single lens, only one laser beam is required to detect the tracking shift and the focus shift. In addition, means for distributing laser light is not required, and the optical head can be easily reduced in size, weight, and thickness.

Furthermore, as described above, since the focus shift is detected by the light distribution after passing through a single lens in such a configuration, the direction of the focus shift can also be detected.

[Brief description of the drawings]

FIG. 1 is a side view for explaining the basic principle of the waveguide type optical head according to the present invention, FIG. 2 is a side view showing the operation of the waveguide type optical head according to the present invention, and FIG. FIG. 4 is a side view showing a conventional optical head, and FIG. 5 is a side view showing a conventional waveguide type optical head. In the figure, LD is a laser light source, 6 is an optical disk, 11 is an emission end, 15 is an objective lens, 17 is an optical pickup waveguide,
A1, A2 are parallel waveguides, B1, B2 are oblique waveguides, 13, 18-21
Denotes photodetectors, respectively.

Claims (2)

(57) [Claims] A reading device receives a reading light condensed by an objective lens, and focuses the reading light on a tip of an optical pickup waveguide provided on a substrate to perform reading. In the waveguide type optical head, at least a pair of waveguides (A1) on the same substrate and on both sides of the waveguide (17) are parallel to the waveguide (17).
(A2) and at least one pair of the parallel waveguides (A1);
At least a pair of waveguides (B1) and (B2) adjacent to the outside of (A2) and having an inclined region are provided, and the waveguide (17), the parallel waveguides (A1), (A2) and Both ends of the waveguides (B1) and (B2) having inclined regions face the single objective lens (15) and the emission end (11).
Tracking deviation is mainly detected by the parallel waveguides (A1) and (A2), and the parallel waveguides (A1) and (A2)
And a waveguide (B1) and a waveguide (B2) having a tilted area, wherein a focus shift is detected. 2. A waveguide (A1) and (B1) located on the same side with respect to the optical pickup waveguide (17) out of the two types of detection waveguides, or a waveguide (A1). Claims (1) wherein (A2) and (B2) are such that their tips are integrated at the emission end (11).
13. The waveguide type optical head according to item 9.