JPS59142758A - Optical head for optical memory - Google Patents

Abstract

PURPOSE:To stabilize a focus signal and a tracking signal and to simplify a circuit by using a distributed index type plane microlens array which employs an ion exchanging method as the objective of an optical head for an optical memory. CONSTITUTION:Light passed through a polarization beam splitter 5 and a quater-wavelength plate 6 is split into two spots A and B by two lens arrays 11. The spot A is for a conventional focusing and a tracking signal, and the spot B is a beam dedicated to the reproduction and writing of a main signal. Reflected light from a disk 8 after being passed through the microlens 11 and quarter- wavelength plate 6 again is reflected by the beam splitter 5, and reflected light beams are focused through lenses 12, and 13 and 14 provided corresponding to the beams A and B. A detector 15 is dedicated to a read of the main signal and a detector 16 reads a focus error signal and a tracking error signal. Thus, the light emitted from one light source is made into plural beams by the plane microlens and the respective beams are given different functions to stabilize respective signals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an objective lens used in an optical head for optical memory. More specifically, a gradient index flat plate microlens array is used as the objective lens.

FIG. 1 shows the most standard configuration of an optical head for optical memory, which is used in compact display players for digital audio, or optical memory devices for still image files. Its main components are a semiconductor laser 1 as a light source, an optical system, and a detector 2 as a light receiving element. and a drive system (actuator) 3 for focusing and pit tracing. In the example shown, the light emitted from the semiconductor laser 1 is converted into a parallel beam by the collimating lens 4. This light passes through a polarizing prism 5 and reaches a ten-wavelength plate 6. When laser light (linearly polarized) passes through a ten-wavelength plate twice, the direction of polarization is rotated by 90 degrees. Therefore, the ten-wavelength plate 6. When the light that passes through the objective lens 7 and is reflected by the disk surface 8 passes through the ten-wavelength plate 6 again and reaches the prism 5, it is polarized by 90°.

The reflected light that has received the 90° polarization is reflected by the prism 5 and does not return to the laser beam VC. This prism is called a beam splitter. The reflected light is collected by a condensing lens 9. cylinder lens l
The light is focused on the detector 2 through O.

The detector 2 is a part that converts an optical signal into an electrical signal using a photodiode. Signals obtained from the detector include a focus signal for applying a servo for focusing the RF sound signal as a main signal, and a tracking signal for tracing a track. The photodiode is usually divided into multiple parts, and a servo signal is obtained from the sum and difference of the outputs of each element.The objective lens 7 is driven by a coil, and the relationship between the lens and the coil is that of the speaker cone and voice coil. It can be made to correspond. The structure is such that the lens is focused in the disk direction (focus) and the radial direction (radial) based on the error signal detected by the detector 2. Methods for obtaining a focus signal include an astigmatism method, a knife method, and a critical angle method. Methods for obtaining tracking signals include the three-beam method, push-pull method, synchronous detection method, and heterodyne method. These details are given to specialized books. Now, in this conventional method, as mentioned above, the main signal, focus signal, and tracking signal are obtained using a single laser beam, so there are issues with the stability of each signal and the complexity of the circuit that separates these signals. There was a problem. The present invention eliminates these drawbacks and also provides an optical head with new functions.

FIG. 2 shows the configuration of a novel optical head according to the present invention. The light source includes a semiconductor laser 1 and a collimating lens 4. Polarizing beam splitter5. The configurations of the ten-wavelength plate 6 and actuator 3 remain unchanged. The feature of the present invention is that the objective lens has a recess,
A gradient index flat plate microlens 11 is used.

The gradient index flat plate microlens has a diameter of 0.5 rtm.
It is possible to simultaneously create an array of lenses of approximately 100 to 100 mm in the same process.

Therefore, when two lens arrays as shown in FIG. 2 are used, the laser beam is focused on two points, and each spot is given a different function.

Polarizing beam splitter5. The light passing through the ten-wavelength plate 6't is divided into two spots A and B by two lens arrays 11.
Divided into. A is a conventional focuser, a lens, and a device for obtaining tracking signals, and a spot is a vinyl that specializes in reproducing and writing the main signal. Diyu, from 8. Reflection, microlens 11 again. Although it passes through the ten-wavelength plate 6, it is reflected by the beam splitter 5,
Lenses 12 and 13 installed corresponding to beams A and B
, 14. The detector 15 specifically reads the main signal, and the detector 16 reads the focus error signal and the tracking/null signal. As described above, in the present invention, the light emitted from one light source can be multiplied into multiple beams using the flat plate microlens, and each beam can be given a different function. As a result, each signal is stabilized and it is possible to avoid complicating the circuit. Next, a gradient index flat plate microlens will be briefly described.

The graded index flat plate microlens diffuses heavy metal ions (T, /!, , CB) with high electronic polarization in the molten salt through a mask provided on the glass substrate, and causes them to be exchanged with Nα in the glass. It is formed by three-dimensionally controlling the refractive index. Therefore, a lens array as shown in FIG. 3 can be obtained by batch processing.

Currently, the minimum diameter of the lens can be as small as 0.5 mm, and the lens constant can be controlled by controlling the rate of ion exchange and the degree of diffusion. The process is a glass plate ICTj (
After sputtering 1.5 .mu.m), the original shape of the p lens array is created by photoetching, ion exchange is performed in molten salt, and the mask is peeled off. Therefore, there is no need for the spherical polishing process that was done with conventional lenses, and
The feature is that microlens arrays can be easily obtained.

Another embodiment of the invention, shown in FIG. 2, uses spot A as a write-only beam and spot B as its error detection beam. That is, the subsystem A writes data onto the JJ Te optical memory disk using an intensity-modulated beam while performing focusing with the disk.

Substrate B immediately reads this, determines whether the recorded data is correct, and instructs the control system to rewrite the data.

According to this method, errors caused by defects on the recording medium can be prevented, and the error rate of the disk memory, which is currently 10-'-10-', can be brought closer to xo-12. Furthermore, when using one light source, the original light source is pulse modulated, which makes error detection complicated, so if two light sources are used as shown in FIG. 4, the functions can be completely separated. In this example, the collimating lens 19 corresponding to the two laser diodes 17 and 18 is also a gradient index flat plate microlens.

FIG. 5 shows yet another embodiment of the present invention. This embodiment employs a three-beam method for tracking and an astigmatism method using a cylinder lens 22 for b1 focusing. In the three-beam method, as shown in FIG. 6, sub-beams b and c are applied before and after the main beam α, and a tracking signal is obtained by sandwiching the bit string.

The reflected light from the sub-beam is detected by dedicated detectors 24 and 25, and the difference signal is obtained, Q) Wocking error. Conventionally, in order to obtain these two sub-beams, a diffraction grating was placed between the laser diode 1 and the collimating lens 4, and the ±1st-order diffraction light was used. In the present invention, this is performed using a gradient index microlens, and the microlens array 21 is also used to condense light onto the detector.

In this microlens array, diffusion is performed from two directions to form a composite lens and to increase the distance between the spots.

As described above, the present invention uses a gradient index flat plate microlens array produced by the ion exchange method as an objective lens of an optical head for an optical memory.

As a result, the optical head can be made into a multi-beam system, each beam can be given a different function, the signal can be stabilized, and the circuit can be simplified.

Additionally, the gradient index microlens is completely different from conventional lens manufacturing, and can be manufactured at low cost. Furthermore, in the future, it will be possible to make microlenses into microlenses, so a lightweight lens that can be easily servoed will be realized, which will be suitable for the present invention.

As described above, the present invention provides a new head configuration in the field of optical memory, and can be widely applied to digital audio, video disks, still image disk files for documents, and the like.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of a conventional standard optical head. FIG. 2 shows the configuration of an optical head according to the present invention. FIG. 3 is an enlarged view of a gradient index flat plate microlens array used in the present invention. FIGS. 4 and 5 show other embodiments of the present invention. FIG. 6 is a diagram showing the principle of tracking using the three-beam method. Numbers 1, 17, 18 in the diagram... Laser diodes 2, 15, 1
6,23. ．． 24, 25 - Detector 3 - Actuator 4 - Collimating lens 5 - Polarizing beam splitter 6 - Ten wavelength plate 7 - Objective lens 8 - Optical memory disk 9. 12, 13 - Condensing lens 111, 14 , 22 #6 cylinder lens 11
, 19 , 20 , 21...Flat microlens array or more Figure 1 Figure 2 Day 3 Figure 4 Figure 6

Claims (1)

[Claims] (11) In an optical head for writing or reading data on an optical recording medium, an objective lens driven by an actuator and a gradient index therapy microlens array are used. An optical head for optical memory that is characterized by controlling two or more laser beams simultaneously. (2) Optical recording of two (D) laser beams using a gradient index microlens array consisting of two microlenses. The optical memory according to claim 1, wherein the optical memory condenses light onto a medium, and is characterized in that one side is used for laser beam focusing and/or tracking, and the other side is used for recording/reproducing data. Optical head for optical head. (Two by a gradient index microlens array consisting of 312 microlenses) L/-boo light is focused onto the optical recording medium, and one of the leading laser beams is used to store data. An optical head for an optical memory according to claim 1, characterized in that the optical head is used for recording and that another laser beam in the trailing direction is looped around for error detection and reproduction. (413 microlenses) It is characterized by focusing three (DL/-) beams onto an optical recording medium using a gradient index microlens array consisting of a microlens array, and recording/reproducing data while performing tracking using a three-beam method. An optical head for an optical memory according to claim 1.