JPH01213839A - Optical pick-up and information recording and reproducing device with optical pick-up - Google Patents

Abstract

PURPOSE:To obtain a necessary optical spot even when the oscillating wavelength of a semiconductor laser is dislocated from a designing wavelength by changing the wavelength of a light from the semiconductor laser so as to coincide with a reference wavelength. CONSTITUTION:A wavelength divider 112 is designed so that the wave guiding light of the same wavelength as the designing wavelength of a condensing grating coupler 107 can be converged to one point 113 in an optical wave guiding layer 103 when the wave guiding light is incoming. When the design is executed so that the condensing point 113 can go to the dividing center of two-dividing photo-diodes 114a and 114b, in case that a semiconductor layer 104 is oscillated with the same wavelength as the designing wavelength, a differential output 117 of the two-dividing photo-diode goes to be zero. On the other hand, when the semiconductor layer is not oscillated as the design, the differential output 117 does not go to be zero. When the oscillating output of the laser 104 is changed and matched to the designing wavelength by an oscillating wavelength control means 118 so that this differential output 117 can go to be zero, aberration is not generated in an optical spot 108 which is made by the coupler 107.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup used for recording or reproducing information using light, and an information recording/reproducing apparatus equipped with the optical pickup.

[Prior Art] As a conventional optical pickup that is small and lightweight, there is a technique described in the Transactions of the Institute of Electronics and Communication Engineers' 8615 Vol. J69-CNo.
5, pp. 609-615. This structure will be briefly explained using FIG. 6. A glass thin film is formed by sputtering on a thermally oxidized Si film 602 formed on a Si substrate 601, and this is the leading wave layer 6.
It becomes 03. The light emitted from the semiconductor laser 604 enters the end face of the optical waveguide layer 603 and becomes a diverging waveguide light 605.
becomes. A grating beam splitter 606 consisting of a grating structure and a condensing grating coupler 607 are formed on the surface of the leading wave layer 603, and the guided light 605 that reaches the condensing grating coupler 607 is extracted into space and forms a light spot 608. make. If the information 610 of the recording medium 609 is located at this spot,
The reflected light containing information is returned to the optical waveguide layer 603 by a condensing grating coupler 607. The light returned to the optical waveguide layer 603 is split into two guided waves 611 by a grating beam splitter 606 and enters a photodiode 612 formed on the Si substrate 601. From the signal detected by the photodiode 612, an optical disk signal and a focus/tracking error signal indicating that the optical spot 608 is deviated from the position of the information 608 are obtained.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the light focusing performance of the focusing grating lens, which functions as an objective lens, is very sensitive to wavelength, so the oscillation wavelength of the semiconductor laser, which is the light source, is When the light spot fluctuates due to changes in temperature, etc., aberrations occur in the light spot, making it impossible to write or read information on the optical disc.

Also, the wavelength of a semiconductor laser is 10
If the wavelength differs from the design wavelength of the condensing grating coupler because it differs in the nm range, the required 1
μ! The problem is that it is not possible to obtain a light spot diameter of about n.

Therefore, the present invention is intended to solve these problems, and its purpose is to provide an optical pickup that can obtain the required optical spot even if the oscillation wavelength of the semiconductor laser deviates from the design wavelength. It is in.

Another object of the present invention is to provide an information recording and reproducing apparatus that can stably record and reproduce information even in an information recording and reproducing apparatus using an optical pickup having a wavelength-sensitive condensing grating coupler as an element, as described above. It is located where the equipment is provided.

[Means for Solving the Problems] The optical pickup of the present invention includes means for condensing light emitted from a semiconductor laser onto a recording medium, means for detecting reflected light from the recording medium, and means for detecting reflected light from the semiconductor laser. The present invention is characterized by comprising means for detecting the wavelength of the emitted light, and means for changing the oscillation wavelength of the semiconductor laser so that the wavelength matches the reference wavelength.

Further, the information recording and reproducing apparatus of the present invention is characterized in that information is recorded on a recording medium or read out from the recording medium using the optical pickup described above.

[Operation] The oscillation wavelength of the semiconductor laser is guided to the photodiode array through a wavelength demultiplexer designed to have the same design wavelength as the objective lens, and changes in the oscillation wavelength are interpreted as changes in the incident position of light on the photodiode array.

On the other hand, an element is connected to the semiconductor laser that changes the oscillation wavelength of the semiconductor laser depending on the temperature or an external resonator, and the oscillation wavelength of the semiconductor laser is adjusted to the designed wavelength of the objective lens by a signal from the photodiode array. The signal from the photodiode array is made to represent a deviation from the signal obtained when the semiconductor laser is oscillating at the design wavelength.

In other words, by detecting the oscillation wavelength of the semiconductor laser and feeding it back to the oscillation wavelength control section of the semiconductor laser, the semiconductor laser is oscillated at the wavelength that matches the design wavelength of the objective lens. A compact and lightweight information recording/reproducing device capable of high-speed access can be constructed thereby.

Hereinafter, the details of the present invention will be shown by examples.

Embodiments Embodiment 1 FIG. 1 is a perspective view of the main parts of a first embodiment of an optical pickup according to the present invention.

A buffer layer 102 made of a thermally oxidized Si film and an optical waveguide layer 103 made of a glass film formed by sputtering are laminated on the surface of a Si substrate 101. Semiconductor laser 1
04 is coupled to the end face of the optical waveguide layer 103, and guided light 105 is excited.

This guided light 105 is transmitted through a beam splitter 106 formed by etching the optical waveguide layer 103 to a width of about 2 μm, and the guided light is transmitted toward a condensing grating coupler 107.
The light is separated into guided light beams that are reflected toward the grating type wavelength demultiplexer 112. The guided light incident on the condensing grating coupler 107 is radiated into space and is also reflected on the recording medium 10.
The light is focused on 9 to form a light spot 108 with a diameter of about 1 μm. Information 110 is recorded on the recording medium 109 with this light spot 108, or information 110 is recorded from the recording medium 109.
Read out 10. Information 11 is reflected by the recording medium 109
The reflected light containing 0 returns to the optical waveguide layer 103 again by the condensing grating coupler 107, and this time the optical path is bent toward the photodiode 111 by the beam splitter 106. The photodiode 111 is formed on the Si substrate 101, and by dividing the photodiode, it is possible to detect the signal from the recording medium 109 and detect the deviation of the optical spot 108 from the required position on the recording medium 109. Then, an error signal is detected for moving the optical system to align the light spot 108 with the correct position. In this embodiment, the photodiode 111 is divided into two parts, and the information on the recording medium 109 is obtained from the sum signal of each.
Further, if the rotation direction of the recording medium 109 is the direction of the arrow 119, a deviation of the light spot in the track direction, that is, a tracking error signal, can be detected from the difference signal of each photodiode. The focus error signal can be obtained by the so-called wobbling method, which detects changes in the signal by slightly vibrating the optical system in the focus direction.

Note that the arrangement of the photodiode for signal detection is not limited to being divided into two as in this embodiment, and an element such as a lens may be arranged in front of the photodiode.

On the other hand, the guided light that is bent toward the wavelength demultiplexer 112 by the beam splitter 106 will be explained. Wavelength demultiplexer 11
2 is designed to converge at a point 113 in the leading wave layer 103 when guided light having the same wavelength as the design wavelength of the condensing grating coupler 107 is incident. 2° split photodiodes 114a and 114b are on the Si substrate 101
The output of each divided photodiode is connected to a differential amplifier 115 to obtain a differential output between the photodiodes 114a and 114b.

The focal point 113 is divided into two photodiodes 114a and 11
4b, the differential output 117 of the two-split photodiode becomes zero when the semiconductor laser 104 oscillates at the designed wavelength. When the oscillation wavelength of the semiconductor laser 104 deviates from the design wavelength of the condensing grating coupler 107, the light that has passed through the wavelength demultiplexer 112 is condensed onto a condensing point 116 through an optical path indicated by a dotted line, for example. . In this case, the amount of light incident on the photodiode 114a increases, the output of the photodiode 114a becomes larger than the output of the photodiode 114b, and the differential output 117 is no longer zero. If the oscillation wavelength of the semiconductor laser 104 is changed by the oscillation wavelength control means 118 to match the design wavelength so that the differential output 117 becomes zero, no aberration will occur in the light spot 108 created by the condensing grating coupler 107. .

The oscillation wavelength control means 118 is shown in FIG. FIG. 2 is a cross-sectional view in which a temperature controller 203 is connected to the semiconductor laser 104. The temperature controller 203 utilizes the Beltier effect, and inputs the differential signal 117 from the wavelength demultiplexer to the input terminal 201, and outputs the differential signal 1
By changing the polarity of the current 202 supplied to the temperature controller 203 depending on the positive or negative value of 17, the surface 204 of the temperature controller 203 on the side of the conductor laser 104 can be heated or cooled to change the temperature of the semiconductor laser 104.
This changes the oscillation wavelength of 04.

The means for changing the oscillation wavelength of the semiconductor laser is not limited to changing the temperature, and means for changing the temperature may also be used. For example, as shown in FIG. 3, an oscillation wavelength control region 30 is provided on the same substrate as an active region 301 of a semiconductor laser.
The oscillation wavelength can be changed by forming the current 2 and flowing the current 3 in the oscillation wavelength control region 302. Such a semiconductor laser is described in Lecture No. 287 in the Proceedings of the National Conference of the Semiconductor and Materials Division of the Institute of Electronics, Information and Communication Engineers in 1988. Control current I
, are controlled by differential signals 117 from the wavelength demultiplexer.

Embodiment 2 FIG. 4 is a main sectional view showing a second embodiment of the optical pickup of the present invention.

A micro Fresnel lens 403 is used as an objective lens. The pattern of the micro Fresnel lens 403 is drawn by an electron beam, but this lens is also greatly affected by changes in wavelength, and a slight change in wavelength will cause aberrations in the light spot 405 focused on the optical disk 404, causing information loss. It becomes impossible to record or play back.

The light emitted from the semiconductor laser 401 passes through a prism-type beam splitter 402 and is focused onto an optical disk 404 by a micro Fresnel lens 403 .

On the other hand, the optical path of the light emitted from the semiconductor laser 401 is bent by a beam splitter 402 and enters a wavelength demultiplexer 406 made of a diffraction grating. This wavelength demultiplexer 406 is designed so that the condensing point 408 is located at the division center of the division photodiodes 407a and 407b for light having the same wavelength as the design wavelength of the micro Fresnel lens 403. The differential output 409 of photodiodes 407a and 407b is set to zero. When the semiconductor laser 401 oscillates at a wavelength different from the design wavelength of the micro Fresnel lens 403, the focal point of the wavelength demultiplexer 406 moves to 410, and the differential output 409 is no longer zero. This output signal causes the oscillation wavelength control means 412 as shown in FIGS. 2 and 3 to control the semiconductor laser 40.
The oscillation wavelength of the micro Fresnel lens 403 is adjusted to match the design wavelength of the micro Fresnel lens 403.

The return light from the optical disk 404 is sent to the beam splitter 40
2 toward the photodiode 414, and the lens 4
13, an information signal of the optical disc, a focus error signal, and a tracking error signal are detected.

Embodiment 3 FIG. 5 is a main configuration diagram of an embodiment of the information recording/reproducing apparatus of the present invention.

The optical pickup 501 described in Example 1 is arranged in the focusing and tracking direction 510.
01, and a voice coil motor 503 that sends the optical pickup 501 in the track direction 509.
6, information is recorded on the rotating optical disk 504 or information is reproduced. These are controlled by a control circuit 507 and connected to an external processing device by an interface circuit 508.

[Effects of the Invention] As described above, according to the present invention, the deviation of the oscillation wavelength of the semiconductor laser, which is the light source of the optical pickup, from the design wavelength of the bull lens is detected, and the signal of the deviation is transmitted to the semiconductor laser. By inputting the oscillation wavelength into a means for changing the oscillation wavelength and making the oscillation wavelength match the design wavelength, it is possible to suppress the occurrence of aberrations in the optical spot even if a grating type objective lens is used.

Furthermore, since the optical pickup of the present invention is smaller and lighter than conventional optical pickups using bulk optical elements, the information recording and reproducing apparatus using the optical pickup of the present invention can be made smaller and lighter, and has the advantage of being able to access at high speed. has.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the optical pickup of the present invention. FIG. 2 is a sectional view of a main part showing means for changing the oscillation wavelength of a semiconductor laser used in the first embodiment of the present invention. FIG. 3 is a sectional view of main parts showing another means for changing the oscillation wavelength of a semiconductor laser used in the first embodiment of the present invention. FIG. 4 is a main sectional view showing a second embodiment of the optical pickup of the present invention. FIG. 5 is a main configuration diagram showing an embodiment of the information recording/reproducing apparatus of the present invention. FIG. 6 is a perspective view of the main parts of a conventional optical integrated pickup. 101... Si substrate 102... Buffer layer 103... Leading wave layer 104... Semiconductor laser 105... Waveguide light 106... Beam splitter 107... Concentrating grating coupler 108...
Light spot 109...Recording medium 110...Information 111...Photodiode 112...Wavelength demultiplexer 113...Focusing points 114a, 114b...Photodiode 115
... Differential amplifier 116 ... Focus point 117 ... Differential output 118 ... Oscillation wavelength control means 119 ... Recording medium rotation direction 201 ... Control terminal 202 ... Current supply means 203 ... Temperature controller 204 ... Surface 301 ... Semiconductor laser active region 302 ... Oscillation wavelength control region 303 ... Control terminal 304 ... Heat sink 401 ... Semiconductor laser 402 ... Beam splitter 403 ... Micro Fresnel lens 404 ...
Optical disc 405... Optical spot 406... Wavelength demultiplexer 407a, 407b... Photodiode 408...
...Focusing point 409...Differential output 410...Focusing point 411...Differential amplifier 412...Oscillation wavelength control means 413...Lens 414...Photodiode 501...Light Pickup 502...Actuator 503...Voice coil motor 504...Optical disk 505...Light beam 506...Spindle motor 507...Control circuit 508...Interface circuit 509...Voice coil motor movement Direction 510...
- Actuator movement direction 601 ... Substrate 602 ... Buffer layer 603 ... Optical waveguide layer 604 ... Semiconductor laser 605 ... Waveguide light 606 ... Grating beam splitter 607
... Concentrating grating coupler 608 ... Light spot 609 ... Recording medium 610 ... Information 611 ... Waveguide light 612 ... Photodiode and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Tsutomu Mogami ( 1 other person) - Figure 1 Figure 5 Figure 6

Claims (2)

[Claims] (1) means for condensing light emitted from a semiconductor laser onto a recording medium, means for detecting reflected light from the recording medium, means for detecting the wavelength of the light emitted from the semiconductor laser; An optical pickup comprising means for changing the oscillation wavelength of the semiconductor laser so that the wavelength matches a reference wavelength. (2) An information recording and reproducing apparatus characterized in that the optical pickup according to item 1 records information on a recording medium or reads information from the recording medium.