JPS6361431A - Optical pickup - Google Patents

Abstract

PURPOSE:To miniaturize an optical pickup, and to make it light weight, by detecting a reflected beam from an optical recording medium passing through a grating lens, by a photodetector which reads a bit of recording information, detects a tracking error, and detects a focus error. CONSTITUTION:On the optical pickup, a block 12 formed in such a way that it can be moved freely along rods 11, 11 extending in a direction almost vertical to a paper plane, is provided. In the block 12, a semiconductor laser 16 which emits a light beam 15 to the reflecting plane of an optical disk 13, is provided. The grating lens 22 is arranged setting the surface of the lens so as to receive a reflected beam 15' reflected on the disk 13. The lens 22 is formed by providing condensing diffraction gratings 31 and 32 adjacent to each other on a transparent member 23. Furthermore, on the block 12, the photodetectors 24 and 25 which detect a diffracted and condensed reflected beam 15'. In this way, it is possible to miniaturize the optical pickup, and to make it light weight, and to make the pickup read the bit of recording information, detect the tracking error, and perform the detection of the focus error.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical pickup for reading signals recorded on an optical recording medium such as an optical disk, and particularly relates to an optical pickup using a guiding waveguide. It is.

(Prior Art) In recent years, optical recording media such as optical disks have been widely used as recording media for image signals, audio signals, and the like. Signals recorded on this optical recording medium in the form of pits, differences in reflectance, etc. (the following explanation will be given using pits as an example) are read by an optical pickup, a so-called optical pickup. This optical pickup irradiates the surface of an optical recording medium with light, such as a laser beam, and detects the level of the light reflected on the recording medium to detect the presence or absence of the pits.

In such an optical pickup, recorded information is read as described above, and the optical beam for tracking error detection (in other words, beep) is irradiated with a deviation to the left or right from the center of a predetermined bit string (track). and a focus error detection function, that is, a function for detecting whether the focus of the light beam is closer or farther than the reflective surface of the optical recording medium. Desired. In other words, the tracking error and focus error detection signals are controlled by tracking control so that the signals are canceled.
It is used to apply focus control to correctly irradiate a predetermined track with a light beam, and to properly focus the light beam on a reflective surface of an optical recording medium. Conventionally, the push-pull method, heterogain method, and VR inter-instrument difference detection method are known as tracking error detection methods, while the astigmatism method, W angle detection method, and Foucault method are known as focus error detection methods. The law is known.

In order to provide the above-mentioned 11-penetration capability, conventional optical pickups require a beam splitter to separate the beam reflected by the optical recording medium from the light beam directed toward the medium, or a photo-optical device to convert this reflected beam. It consisted of a lens for focusing near a photodetector such as a diode, and micro optical elements such as a prism and a cylindrical lens for carrying out the tracking error detection method and focus error detection method described above.

(Problem to be solved by the invention) However, the above-mentioned microscopic optical elements require precise processing;
Further, since mutual position adjustment is troublesome when assembling the pickup, an optical pickup using such an optical element has inevitably become expensive. Furthermore, the optical pickup having such a configuration is large and heavy, which is disadvantageous in terms of downsizing the reading device and shortening the access time.

In order to solve the above-mentioned problems, various attempts have been made to simplify the configuration of the pickup by using special optical elements such as aspherical lenses. However, this type of optical element is particularly expensive, so even if the configuration of an optical pickup using such an element is simplified, it is not much different from the optical pickup described above in terms of cost. .

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical pickup that is small, lightweight, and can be formed at extremely low cost.

(Means for Solving the Problems) The optical pickup of the present invention is one in which the functions performed by the beam splitter, lens, prism, etc. described above are performed by one grating lens, and the optical pickup can be used for optical disks, etc. a light source that irradiates a light beam onto the surface of the optical recording medium; an objective lens that focuses the light beam on the reflective surface of the optical recording medium; and an objective lens oriented such that one surface receives the reflected beam reflected by the optical recording medium. A grating lens is arranged to branch and focus the reflected beam from the optical path of the light beam toward the optical recording medium, and the reflected beam that has passed through the grating lens can be used to read recorded information, detect tracking errors, and detect focus errors. The device is characterized in that it is comprised of a photodetector that detects as follows.

The grating lens has a curved and chirped or curved diffraction grating formed on the surface of a transparent member, and diffracts incident light and focuses the diffracted light.

(Function) The reflected beam from the optical recording medium is separated from the optical path of the light beam heading toward the optical recording medium by the diffraction effect of the grating lens. This is the same effect as the beam splitter described above. The grating lens also focuses the reflected beam, which is the same function performed by the lenses described above.

Furthermore, by arranging two such grating lenses, the reflected beam from the optical recording medium can be branched into two systems in the tracking direction for tracking error detection and focus error detection. Furthermore, by using an astigmatism lens as the grating lens, astigmatism can be created in the reflected beam for tracking error detection and focus error detection. This is the same effect as the prism and cylindrical lens described above.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an optical pickup according to a first embodiment of the present invention, and FIG. 2 shows the planar shape and electric circuit of a grating lens of this optical pickup.

As shown in FIG. 1, this optical pickup has a block 12 that is movable along a rod 11.11 extending in a direction substantially perpendicular to the plane of the paper. This block 1
In order to follow the bit string (track), the optical disc 2 is moved by, for example, a precision feed screw and an optical system feed motor.
It is arranged to be moved in a direction perpendicular to the direction in which the two sets of bits No. 3 are lined up (in the direction of arrow U at the beam irradiation position), or in a direction close to it.

The block 12 includes a semiconductor laser 16 that emits a light beam (laser beam) 15 toward the reflective surface 14 of the optical disk 13, and a collimator lens 17 that converts the diverging beam emitted from the semiconductor laser 16 into a parallel beam. An objective lens 18 that focuses the parallel light beam 15 on the reflecting surface 14 is attached. It is supported so as to be movable in the direction perpendicular to the direction of arrow U (direction perpendicular to the direction of arrow U) and the direction of arrow V (direction of focus), and is moved in the above-mentioned directions by tracking coil 19 and focus coil 20, respectively.

A grating lens 22 is provided between the collimator lens 17 and the objective lens 18, with the grating lens 22 oriented such that its surface receives the reflected beam 15' reflected by the optical disk 13.
is placed with ^. This grating lens 22 is placed on a transparent member 23 such that the first. The second condensing diffraction grating (hereinafter referred to as FG) is provided with >31.32 adjacent to each other.
Alternatively, it may be a curved diffraction grating, each formed to diffract the reflected beam by 15 degrees and focus it at a point outside the grating lens 22. These FGs 31 and 32 are arranged in parallel across an axis on the lens surface (the y-axis in Fig. 2) that is perpendicular to the tracking direction and passes approximately through the center of the reflected beam 15', and each , are formed so as to focus the reflected beams 15' at positions separated from each other across a plane that passes through the y-axis and is perpendicular to the lens surface. F that performs this kind of action
The m-th lattice pattern shape formula of G31 and G32 is defined by defining the spatial coordinates by the above y-axis, the X-axis (tracking direction axis) shown in FIG. 2, and the two axes shown in FIG.
, 32, respectively (−Fx
.

The above FGs 31 and 32 are placed on the transparent member 23 with 5i
It can be formed by a method such as depositing -N by PCVD, forming a resist pattern by electron beam direct writing, and then transferring it to a 5i-N film by RIE.

On the other hand, in the block 12, a first
The set of photodetectors 24J3 and the second set of photodetectors 25 are fixed. The first phase photodetector 24 is, for example, a photodiode PD1. PD2, and the second set of photodetectors 25 also include similar photodiodes PD3. Consists of PD4. These photodiodes PDI~4 are fixed on a support 28.

As shown in FIG. 2, the outputs of the photodiodes PD1 and PD2 are added together by an adding amplifier 33, and the outputs of the photodiodes PD3. The outputs of PD4 are similarly summed by the summing amplifier 36, and the outputs of the photodiodes PD1 . The output of PD4 is added by the addition amplifier 34, and the inner photodiode P
D2. The outputs of the PD3 are added by the adding amplifier 35. Further, the outputs of the summing amplifiers 33 and 36 are input to the summing amplifier 37 and the differential amplifier 39, and the summing amplifier 34
．． The output of 35 is input to a differential amplifier 38. The output S1 of the summing amplifier 37, the output $2 of the differential amplifier 38, and the output S3 of the differential amplifier 39 are respectively output to the reading circuit 4.
0 is input to the focus coil drive control circuit 41 and the tracking coil drive control circuit 42.

Next, the operation of the optical pickup having the above configuration will be explained. A parallel light beam (laser beam) 15 emitted from the semiconductor laser 16 passes through the grading lens 22 and is focused by the objective lens 18 so as to be focused on the reflective surface 14 of the optical disc 13 . The optical disk 13 is rotated by a rotation driving means (not shown) so that the rows (tracks) of two sets of bits move in the direction of arrow U at the irradiation position of the light beam 15. As is well known, the bit 21 carries image signals, audio signals, etc., and the reflected beam 15° from the optical disk 13 has a high level in the part where these two sets of bits are not present, and the bit 21 carries an image signal, an audio signal, etc.
The level is low in the part where the set exists. This reflected beam 15' passes through the objective lens 18 and is diffracted by the grating lens 22FG31.32 as described above. The reflected beam 15', which has been diffracted and separated from the optical path of the light beam 15, comes to be focused at two points sandwiching a plane that passes through the y-axis and is perpendicular to the lens surface, due to the beam focusing action of each of the FGs 31 and 32. The light intensity of the reflected beam 15' focused by FG31 is determined by the photodiodes PDI and PD2.
The reflected beam 15 detected at -10,000 FG32
'The amount of light is determined by the photodiode PD3. Since it is detected by the PD 4, the output S1 of the summing amplifier 37 that adds the respective outputs of the summing amplifiers 33 and 36 indicates the overall light amount of the reflected beam 15' reflected on the optical disk 13, that is, the presence or absence of two sets of bits. This will indicate the following. This output S1 is subjected to reading processing in the reading circuit 40, and is then read out from the optical disc 13.
The information recorded in is read.

As mentioned earlier, the block 12 is driven by the optical system feed motor in a direction perpendicular to the direction of the arrow U, or in a direction close to it, so that the irradiation position of the light beam 15 on the optical disk 13 (disc radial direction position ) is changed and bit 21 is read successively. Here, the light beam 15 must be correctly irradiated onto the center of a predetermined bit string (track). Hereinafter, control for maintaining the correct irradiation position of the light beam 15 in this manner, ie, tracking control, will be described. When the center of the reflected beam 15' is located exactly between [G31 and PO32, the first set of photodetectors 24 (photodiodes PD1 and P
O2) and the amount of light detected by the second set of photodetectors 2
5 (photodiodes PD2 and PO4) coincide with each other. Therefore, in this case, the output S3 of the differential amplifier 39 becomes O (zero). On the other hand, light beam 1
5 becomes incorrect and the center of the reflected beam 15' shifts upward in FIG.
The amount of light detected exceeds the amount of light detected by the second set of photodetectors 25. Therefore, the output S3 of the differential amplifier 39 is + (plus)
becomes.

On the other hand, when the center of the reflected beam 15° is displaced downward in FIG. 2, the output S3 of the differential amplifier 39 becomes - (minus). In other words, the output S3 of the differential amplifier 39 indicates the direction of the tracking error (the direction of the arrow X in FIG. 2). This output S3 is sent to the tracking coil drive control circuit 42 as a tracking error signal. Note that the method of detecting tracking errors by processing the outputs of the photodiodes PD1 to PD4 in this manner has been conventionally established as a push-pull method. The tracking coil drive control circuit 42 receives the tracking error signal S3, supplies a current It to the tracking coil 19 according to the direction of the tracking error indicated by the signal S3, and moves the objective lens 18 in the direction in which the tracking error is eliminated. Avoid moving. As a result, the light beam 15 is always correctly irradiated onto the center of the bit string.

Next, focus control, that is, control for correctly focusing the light beam 15 on the reflective surface 14 of the optical disk 13 will be explained. The light beam 15 hits the reflective surface 14 of the optical disc 13
When the above is focused, the reflected beam 15' focused by G31 is focused at an intermediate position between the photodiodes PD1 and PO2.At this time, the reflected beam 15' also focused by PO32 is focused by the photodiode It is focused at an intermediate position between PO3 and PO4.Therefore, the output of the pruritic amplifier 34 and the output of the summing amplifier 35 become equal, and the output S2 of the differential amplifier 38 becomes O (ZO).On the other hand, the light beam 15 When focused at a position closer than the reflecting surface 14, the reflected beam 15' incident on the POs 31 and 32 becomes a convergent beam, and the reflected beam 15' on each of the photodetectors 24 and 25 (the blade position is is displaced inward (to the photodiode PD2 side and the photodiode PDa side). Therefore, in this case, the output of the addition amplifier 34 is lower than the output of the addition amplifier 35, and the differential amplifier 38
] S2 becomes - (minus). On the other hand, when the light beam 15 is focused at a position farther than the reflecting surface 14, the reflected beam 15' incident on the POs 31 and 32 becomes a diverging beam, and the reflected beam 15° at each of the photodetectors 24 and 25 becomes a divergent beam. The irradiation positions are respectively displaced to the outside (photodiode PDI side a3 and photodiode PDJ side). Therefore, in this case, the output of the summing amplifier 34 exceeds the output of the summing amplifier 35, and the output of the differential amplifier 38 $
2 becomes + (plus). In this way, the output $2 of the differential amplifier 38 indicates the direction of the focus error. This output S2 is sent as a focus error signal to a focus coil driving control circuit 41. Note that the method of detecting focus errors by processing the outputs of the photodiodes PD1 to PD4 in this way has been conventionally implemented in the Foucault method using a Foucault prism. The focus coil drive control circuit 41 receives the focus error signal S2, supplies the focus coil 20 with a current If according to the direction of the focus error indicated by the signal S2, and moves the objective lens 18 in the direction in which the focus error is eliminated. move it. Thereby light beam 1
5 is always correctly focused on the reflective surface 14 of the optical disc 13.

In this actual flow example, the two POs 31 and 32 are formed so that their respective lattices are continuous and close to each other, but these two POs 31 and 32 are separated by a short distance.
3 may be formed independently from each other.

This also applies to the embodiments described below.

In addition, the reflected beams 15' focused by FG31 and 32 are made to intersect with each other. In other words, referring to FIG. 2, the beam focusing position by FG31 is below the y axis,
The FGs 31 and 32 may be formed so that the beam focusing position by the G 32 is located on the −V side of the y-axis.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same elements as those in FIG. 1 are labeled with the same scent, and the description thereof will be omitted unless it is particularly necessary (the same applies hereinafter). This second
In the optical pickup of this embodiment, the collimator lens 17 provided in the apparatus shown in FIG. 1 is omitted, and the reflected beam 15' from the optical disk 13 passes through the grading lens 22 in the form of a focused beam.

Even if you do this, the grating lens 22
The two systems of reflected beams 15' focused by the action of the first beam 15' as shown in FIG. Tracking errors and focus errors can be detected by detecting with the second photodetectors 24 and 25.

In this case, the m-th grating pattern shape equation of FG31, 32 defines the spatial coordinates and the coordinates of the beam focusing position by l':(331, 32 in the same way as in the first embodiment), and also defines the coordinates of the light source. When expressed as (0, O, Lz), it is given by =mλ+const, (x<O, decoding same order).

Next, a third embodiment of the present invention will be described with reference to FIG. In the optical pickup of the third embodiment, the transparent member 23 is made of a material with a sufficiently high refractive index, and the light beam 15 is reflected on the surface of the transparent member 23 and travels toward the optical disk 13. There is. In this case as well, the reflected beam 15' from the optical disk 13 is divided into two "Q3
It is diffracted and focused by 1.32.

FIG. 5 shows an optical pickup according to a fourth embodiment of the present invention. In this embodiment, in J3, the light beam 15 emitted from the conductor laser 1G is deflected 111)1 on the surface of the transparent member 23 while remaining in a diverging beam state, and is made to travel toward the optical disk 13.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, in d5, the grating lens 22 and the pair of lenses 18 are fixed and integrated into one head 60, and this head 60 is supported movably in the tracking direction and the focusing direction with respect to the block 12. has been done. This head 60 is moved by a tracking coil 19 and a focusing coil 20. In other words, in this example, the grating lens 22 is used as the objective lens 18 for tracking control and focus control.
will be moved along with the In this way, objective lens 1
The objective lens 18 is no longer offset with respect to the grating lens 22 due to tracking control, unlike the case where only the grating lens 8 is moved, and the l-tracing control can be performed with higher accuracy.

In the embodiment shown in FIG. 6, the optical disc 13 is irradiated with the light beam 15 reflected on the surface of the grating lens 22, but as described above, the grating lens 22 and the objective lens 18 are integrated. Even when moving the grating lens 2
It is also possible to irradiate the optical disk 13 with the light beam 15 that has passed through the grating lens 22, or the light beam 15 may be transmitted through the grating lens 22 or reflected by the grating lens 22 in the form of a diverging beam. Of course. Further, the semiconductor laser 16 and the collimator lens 17 are also fixed to the head 60, and the leading waveguide 22 is
It is also possible to move it integrally with the objective lens 18.

In the five embodiments described above, FG31°32
The reflected beam 15' is branched into two systems, and the push-pull method is used to detect the tracking error, and the Foucault method is used to detect the focus error, but it is also possible to detect both of the above errors using other methods. be. fZJ For example, in the sixth embodiment shown in FIG. 7, a grating lens 70 consisting of one FG 71 is used, and by setting the FQ 7 set, this grating lens 70 is an astigmatic lens.

Therefore, the ζ reflected beam 15° that passes through the grating lens 70 has astigmatism. Therefore, by detecting this reflected beam 15' with a photodetector 72 consisting of a 4-split photodiode, it is possible to Tracking errors and focus errors can be detected using the heterodyne method and astigmatism method, respectively.

Note that even when detecting tracking errors and focus errors as described above, the light beam 15 may pass through the grading lens 70 in a diverging beam state, or the light beam 15 may pass through the grading lens 70 in a diverging beam state, or the light beam 15 may may be reflected and advanced toward the optical disk 13, or tracking control and focus control may be performed by moving only the objective lens 18, or by moving the objective lens 18 and grating lens 70 integrally. You may do so.

Also, the grating lens 22.7 () was mentioned earlier! It can be formed not only by the Brenna technique but also by the known photolithography method, holographic transfer method, etc., and can be easily reproduced.

(Effects of the Invention) As explained above in detail, in the optical pickup of the present invention, the functions that were performed by optical elements such as beam splitters, lenses, and prisms in the J5 of conventional optical pickups can be obtained only by the grating lens. It has become. Therefore, the optical pickup of the present invention has an extremely small number of parts and is made small and lightweight.
Compared to conventional neck mounting, it is possible to significantly reduce costs and also shorten access time.

Further, since the main parts of the optical pickup of the present invention can be easily mass-produced using brainer technology, a significant cost reduction can also be achieved from this point of view.

Furthermore, in the optical pickup of the present invention, since the above-mentioned position adjustment of the optical element is of course unnecessary, cost reduction can also be achieved in this respect.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the first embodiment of the device according to the present invention, Fig. 2 is a schematic diagram showing the planar shape and electric circuit of the grating lens of the above-mentioned first embodiment device, and Fig. 3.4, 5d5. 2.3.4 and 6 are side views respectively showing neck straps according to 2.3.4 and 5th embodiments of the present invention, and FIG. 7 is a schematic perspective view showing a device according to a 6th embodiment of the present invention. 13... Optical disc 14... Reflective surface of optical disc 15... Light beam 15'... Reflected beam 16... Semiconductor laser 17... Collimating lens 18... Objective lens 19... Tracking Coil 20... Focus coil 21.
...Bits 22, 70...Grating lens 24
, 25.72... Photodetector 31.32.71...
FG33, 34.35.3 [3, 37... Addition amplifier 38, 39... Differential amplifier 40°゛° reading circuit 4
1... Focus coil drive control 20 circuit 42...
Tracking coil drive control circuit 60...head
PD1-4... Photodiode (self-initiated) Mr. Tewadene City Official Director General of the Patent Office October 2, 1986
Patent Application No. 8, No. 61-206258 2, Title of the invention: Optical pickup 3, Relationship with the amended person's case Special edition: Address: 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name: Fuji Photo Film Co., Ltd. 4; Agent address: 7th floor, Uraiya Building, 5-2-1 Roppongi, Minato-ku, Tokyo, 106 Japan (479) 2367 (7318) Patent attorney Yanagi 1) Seishi (and 2 others) 5. Date of amendment order: None 6. Number of inventions added by amendment None 8 Contents of amendment 1) "Optical waveguide" in line 5 of page 4 of the specification is corrected to "grating lens."2> On the same page, line 17, ``Momo desu.'' Correct j to ``Modo desu.'' 3) On page 15, line 11, r PD 2 J is corrected to rPD3j. 4) Correct "center" in lines 15 and 19 of the same page to read "light intensity distribution." 5) Correct "Convergence J" in line 17 of page 19 to "convergence J." 6) Correct "f' (Z - LZ ) 2 J" in line 9 of page 20 to "rLz"J.

Claims (7)

[Claims] (1) A light source that irradiates a light beam onto the surface of an optical recording medium, an objective lens that focuses the light beam on a reflective surface of the optical recording medium, and a surface that receives the reflected beam reflected by the optical recording medium. a grating lens that is arranged in the same direction as the optical recording medium and branches the reflected beam from the optical path of the optical beam toward the optical recording medium and focuses the reflected beam; An optical pickup consisting of a photodetector that performs detection. (2) The grating lenses are arranged in parallel across an axis that passes approximately through the center of the reflected beam and extends approximately perpendicular to the tracking direction, and each of the first and second grating lenses focuses the reflected beam at positions separated from each other. The photodetector consists of two grating lenses, and the reflections are focused by the first and second grating lenses so that the photodetector can detect tracking errors and focusing errors using the push-pull method and the Foucault method, respectively. 2. The optical pickup according to claim 1, comprising a first set and a second set of two-split photodetectors that respectively detect the beams. (3) The grating lens is an astigmatism lens, and the photodetector is a four-segment photodetector arranged so that tracking error detection and focus error detection can be performed by a heterodyne method and an astigmatism method, respectively. The optical pickup according to claim 1, characterized in that: (4) The optical pickup according to any one of claims 1 to 3, wherein the grating lens is disposed between the light source and the objective lens. (5) The grating lens is arranged so as to reflect the light beam emitted from the light source and make it travel toward the optical recording medium. The optical pickup according to any one of item 3. (6) The grating lens and the objective lens are arranged independently of each other, and only the objective lens is moved for tracking control and focus control. The optical pickup according to any one of Items 1 to 5. (7) Claims 1 to 5, characterized in that the grating lens is integrated with the objective lens and is moved together with the objective lens for tracking control and focus control. The optical pickup according to any one of the items.