JPS5827027A - Photo detector - Google Patents

Abstract

PURPOSE:To miniaturize a device, to prevent the production of light volume loss, and to facilitate detection of a focus error signal as well as an information signal, by constituting a device such that reflecting light from a disc, producing an approximately parallel luminous flux through the working of an objective, is collected by a photo sensor as it is. CONSTITUTION:A laser luminous flux rectilinearly polarized from a semiconductor laser 1 is collected on a disc 6 through a collimater lens 2, a polarizing prism 3, a lambda/4 plate 4, and an objective 5. The reflecting light, reversing and passing the polarizing prism 3, enters a photo sensor 10 in a manner to produce an approximately parallel luminous light. The photo sensor 10 consists of a small diameter part 10a and a large diameter part 10b which form a concentric circle, and each of outputs Va and Vb changes resulting from the change in a diameter of an incident luminous flux corresponding to a focus. A difference between two signals is obtained by a subtracting circuit 11, the difference signal is compared with a difference signal at a focusing time by a comparing circuit 12 to output a focus error signal SP. A critical prism is not used, and this miniaturizes a device, prevents the occurrence of a light volume loss, and facilitates an operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photodetection device used in an optical video disc player, etc., and in particular to a photodetection device that can easily detect a focus error signal for correcting a focus shift caused by displacement of a disc. Regarding equipment.

A photodetector used in an optical disc player, etc., irradiates a spot light such as a laser beam onto a bit engraved on a disc through an objective lens, and then sends the reflected light back through the objective lens to a photo sensor. It receives the light and obtains a bit signal, that is, an information signal (generally a video signal, also called an RF signal), but at the same time a focus error signal and a focus error signal to correct the focus shift due to the vertical movement of the disc are obtained. It is also necessary to obtain a tracking error signal 1- for correcting tracking deviation due to eccentricity or the like.

The conventional photodetecting device was configured as shown in FIG. 1, for example, in order to obtain a focus error signal.

To explain this simply, a linearly polarized laser beam from a semiconductor laser 1 is made into a parallel beam by a collimator lens 2, deflected upward by 90 degrees by a polarizing prism 3, and converted into circularly polarized beam by a λ/4 plate 4. , a minute spot light having a diameter of 1 to 2 μm is focused by an objective lens 5 and irradiated onto a disk 6 in which pits (not shown) are carved.

The reflected light from the disk 6 of this spot light becomes circularly polarized light in the opposite direction to the incident light, passes through the objective lens 5 again, becomes a parallel light beam, and is changed by the 2λ/4 plate 4 so that the direction is 9
Since it is converted into a linear polarization that differs by 0°, it passes through the polarizing prism 3 and enters the critical prism 7.

The reflective surface 7a of the critical prism 7 is configured to form a critical angle with respect to the optical axis indicated by the dashed line in the figure, and the reflected light beam is transmitted to the light receiving surface PD1. Light is received by a two-split photosensor 8 having a PD2, and the difference in output from each light receiving surface is detected by a subtraction circuit 9 to generate a focus error signal SF.
I was getting .

That is, at the time of focusing, the incident light beam on the critical prism 7 is a parallel light beam parallel to the optical axis, so the outputs that are all reflected and incident on the two-split photosensor 8 are also equal, so the focus is the output of the subtraction circuit 9. The error signal becomes zero.

On the other hand, if the disc 6 approaches the in-focus position or is too far away, the light beam incident on the critical prism 7 becomes a diverging light beam or a convergent light beam. The angle at which the light beam on the right side enters the critical prism 7 is smaller than or equal to the critical angle, and the magnitude relationship is reversed depending on whether it is too close or too far away.

Therefore, there is a difference in the amount of light that is reflected by the reflective surface 7a of the critical prism 7 and reaches the light receiving surfaces PD1 and PD2 of the photosensor 8, and the output of the subtraction circuit 9 has different polarity depending on whether it is too close or too far away. The difference signal appears as a focus error signal.

However, such conventional photodetecting devices use a critical prism, which is not only inconvenient for miniaturization, but also requires precision in setting the critical angle of the reflecting surface, making position adjustment difficult.

Furthermore, since the amount of light that is not reflected by the critical prism is lost due to focus deviation, the level of the information signal obtained by the sum of the outputs from each light-receiving surface of the two-part photo sensor also decreases due to focus deviation. be.

This invention solves all the above problems and is suitable for miniaturization.
It is an object of the present invention to provide a photodetection device that is easy to adjust and can detect a focus error signal together with an information signal without loss of light amount.

Therefore, the photodetector according to the present invention does not use a critical prism, but instead uses a photosensor to directly receive the reflected light from the disk, which is made into a substantially parallel beam by an objective lens, and the light-receiving surface of the photosensor is
It is formed by a small diameter part and a large diameter part that form concentric circles or parts of concentric circles with different radii from the center, and a focus error signal is obtained from the difference between the output of the small diameter part and the output of the large diameter part. .

Hereinafter, the contents of the present invention will be explained in detail with reference to the drawings.

FIG. 2 shows the configuration of an optical system of a photodetecting device according to the present invention, and the same parts as in the conventional example shown in FIG. 1 are given the same reference numerals.

What is different about this optical system from the optical system shown in FIG. 1 is that it does not use a critical prism, and the reflected light of the spot light that irradiated the disk 6 is redirected into a parallel light beam (in the case of focusing) by the objective lens 5.
The point is that the light beam is directly received by the photosensor 10 through the λ/4 plate 4 and the polarizing prism 6.

As shown in FIG. 3(b), the light-receiving surface of the photo sensor 10 is formed by a small diameter portion 10a and a large diameter portion 10b forming concentric circles with radii rl and r2 (r2>r+) from the center. There is.

Next, the principle of detecting a focus error signal in the photodetector according to the present invention will be explained with reference to FIGS. 3(A) to 3(C).

In FIG. 6(A), if it is assumed that the disc 6 is in focus when it is at position b, the reflected light flux of the spot light at this time becomes a parallel light flux parallel to the optical axis t by the objective lens 5, The circular part of the light-receiving surface of the 7-otosensor 10 shown in the same figure (b) inside the solid line is irradiated, and the light intensity distribution is shown in the same figure (b).
c) is shown in actual mb.

and t''L, if the disk 6 is at a position far from the in-focus position, for example, at the position indicated by a in FIG. A small circular part inside the broken line a of the light receiving surface of the photosensor 10 shown in b) is irradiated, and the light amount distribution is t in the same figure.
as shown by a broken line a.

Furthermore, when the disk 6 is located closer to the in-focus position, for example, at the position shown by C in FIG. A large circular portion of the light-receiving surface of the sensor 10 inside the two-dot chain line C is irradiated, and the light amount distribution is as shown by the two-dot chain line C in FIG.

In this way, depending on the state of the 7 orcus, the photo sensor 10
The radius and light intensity distribution of the light beam that illuminates the light-receiving surface of the light-receiving surface changes. Therefore, the small diameter portion 10a (radius r1) of the light receiving surface
The detection output va according to the amount of light received by the large diameter part 10
Detection output v according to the amount of light received by b (radius r2)
b changes depending on the focus state.

Therefore, a subtraction circuit 11 using a differential amplifier is used to detect the forces Va and vb by the small diameter part 10a and the large diameter part 10b.
difference (V(1=Va-Vb)tF), comparison circuit 1
2, the reference voltage v corresponding to the difference output Vd at the time of focusing
In comparison with r, a signal corresponding to Vr-Vd is output as a focus error signal SF.

Note that the reference voltage vr is created by dividing a constant voltage generated by a Zener diode ZD using a variable resistor VR. Further, if a constant voltage source is used, the Zener diode ZD is not necessary.

In this way, when in focus, Vd=V, so the focus error signal SF becomes zero, and the disc 6
If the disk 6 is too far away, the ratio of Vb to Va becomes smaller, so vd>Vr, and negative focus error signals S and r appear.If the disk 6 is too close, the ratio of Vb to Va becomes smaller. Since the ratio increases, v
d<vr, and a positive focus error signal SF appears.

By moving the objective lens 5 in the optical axis direction according to the focus error signal SF, the focus shift can be corrected.

By the way, since the total amount of light irradiating the light receiving surface of the photo sensor 10 does not change depending on the focus state, the small diameter portion 10
By taking the sum of detection outputs va and vb from a and the large diameter portion 10b, it is possible to obtain an information signal (RF signal) with high sensitivity without loss of light quantity.

Next, FIG. 4 shows an embodiment in which the present invention is applied to a photodetection device using a 4-division 7-photo sensor so that a tracking error signal can also be detected at the same time. The configuration of the optical system is the same as that shown in FIG. 2, so illustration and explanation will be omitted.

The photosensor 20 used in this embodiment has a light-receiving surface divided into four parts by two orthogonal lines passing through the center, similar to the conventional four-part photosensor. It is divided into 8 parts into 4 A-circular small diameter parts ad and 4 μ fan-shaped large diameter parts eyh.

The outputs from the four small diameter sections a-xd on the light-receiving surface of the photosensor 20 are input to an adding circuit 21 and summed, and the outputs from the four large diameter sections e-h are sent to an adding circuit 22. The inputs are summed, and the outputs of the two-jaw arithmetic circuits 21 and 22 are summed by the adding block 23, that is, an information signal (RF signal) is obtained by outputting from all the light receiving surfaces.

On the other hand, the outputs of the adder circuits 21 and 22 are input to the subtracter circuit 24 to calculate the difference, and the difference output vd is input to the comparator circuit 25 to calculate the sum, as explained in FIG. 6(b). Compared with the reference voltage Vr corresponding to the difference output in focus, V
The signal corresponding to r-Vd is the focus error signal SF.
Output as .

Note that the difference output from the subtraction circuit 24 may be used as it is as the focus error signal.

Further, adding circuits 26 to 29 calculate the small diameter portion and large diameter portion a, e, b, f, c, and g of each A circular portion on the light receiving surface divided into four parts.

The sum of the outputs of d and h is calculated, and the addition circuits 30 and 31VC calculate the diagonal μ-circular portions a+e, c+g, and b.
The sum of the outputs of 10f and d+h is calculated, and the sum signal S
+, S2 are input to the tracking detection circuit 32 to obtain the tracking error signal ST.

The tracking detection circuit 32 uses a known circuit as shown in FIG. Therefore, the operation of this circuit will be briefly explained with reference to FIG. 6 as well.

The sum signal s+l S2 of the outputs of the diagonal parts of the four-divided light-receiving surface of the photo sensor 20 is subtracted by the subtraction circuit Slh.
The difference is taken with the addition circuit AD, and the sum is taken with the addition circuit AD, as shown in Fig. 6 (a).
A difference signal S3 as shown in (b) and a sum signal S4 as shown in (b) are obtained. This RF band difference signal S3 has positional information as to which side the reading spot is on with respect to the pits of the disk. The RF band sum signal S4 means an information signal such as a video signal.

By passing this sum signal S4 through the rising pulse generation circuit RPC and the falling pulse generation circuit FPG, as shown in FIG.
Sampling pulse ss I 8 shown in c) and d)
Generate 6.

With this sampling pulse S5, 56vc,
The difference signal S3 passing through the gate circuit G1 + G2 is sampled at the rising and falling timings of the sum signal S4,
Hold circuit HD1. The signals S shown in FIG. 6 (E) and (F) are held by HD2 and
, , generate Ss.

These signals Sy and Ss are band-converted from the RF band to the tracking error signal band by sampling and holding, and are bipolar signals with the center of the trunk as the boundary. Therefore, each of these signals represents a tracking error (radial error), but in order to make the signals more reliable, the subtraction circuit SB2 subtracts s and -Sa to obtain the tracking error as shown in FIG. 6 (υ). An error signal ST is obtained.7 FIG. 7 is a diagram showing another embodiment of the present invention, and since the optical system is the same as that in FIG. 2, illustration and description thereof will be omitted.

The photosensor 40 in this embodiment has only one of the four A-circular light-receiving surfaces of the conventional 4-division 7-oto-sensor.
That is.

The small diameter portion d of the light receiving surface of this 7-point sensor 40 and the
The outputs of the large diameter portions C are inputted to a subtraction circuit jjNc to take the difference, and the difference signal Vd is inputted to the comparison circuit 42 and compared with the reference voltage vr to generate a 7-occasion error signal sF corresponding to Vr-Vd. get.

On the other hand, the outputs of the large diameter portions a and b of the light receiving surface of the photosensor 40 are input to a tracking detection circuit 43 to obtain a tracking error signal sT. Further, an information signal (RF signal) is obtained by adding the outputs of large diameter portions a and b using an adder circuit 44.

In order to align this photo sensor 40 with the center of the light beam, the deviation in two directions is detected by the difference in the output of large diameter parts a and b of the light receiving surface, and the deviation in the y direction is detected by the difference in the output of large diameter parts a and c. Adjustment is easy because all you need to do is to detect and make both of them zero.

As described above with respect to the embodiments, this invention has excellent effects in that difficult adjustments are not required and there is no loss of light quantity.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional photodetection device, FIG. 2 is a configuration diagram showing an optical system of a photodetection device according to the present invention, and FIGS. FIG. 2 is a diagram for explaining the focus error signal detection principle of the photodetector, in which (A) is an optical path diagram, (O) is a detection circuit diagram, and (C) is the amount of light on the light receiving surface of the photosensor depending on the focus state. It is a curve diagram showing distribution. FIG. 4 is a block diagram showing an embodiment in which the present invention is applied to a photodetection device using a 4-divided 7-point sensor. FIG. 5 is a block diagram of its tracking detection circuit. FIG. 3 is a signal waveform diagram of each part used to explain the operation of the circuit. FIG. 7 is a block diagram showing another embodiment of the invention. 1... Semiconductor laser 2... Collimator lens 3
...Polarizing prism 4...λ/4 plate 5...Objective lens 6...Disc 7...Critical prism 8.10, 20.40...Photo sensor 11.24.
41...Subtraction circuit 12.25.42...Comparison circuit

Claims (1)

[Claims] In a photodetecting device that obtains an information signal by receiving the reflected light of a spot light irradiated on a disk on which one bit is engraved by a photosensor via an objective lens, the light receiving surface of the photosensor is A circuit is provided which is formed by a small diameter part and a large diameter part forming concentric circles or parts thereof having different radii from the center, and obtains a focus error signal based on the difference between the output of the small diameter part and the output of the large diameter part. A photodetection device characterized by: 2 The small diameter part and the large diameter part that form the light receiving surface of the photo sensor are divided into four parts by two lines passing through the center and intersecting at right angles, and from the sum of the outputs of the diagonal A circular parts, The photodetecting device according to claim 1, wherein a tracking 7/'Z5- signal is obtained.