JPH0564769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a focus adjustment device used for inspection of a laser optical system such as an optical head in an optical disk.

[Technical background of the invention]

For example, an optical head in an optical disk oscillates a laser beam from a semiconductor laser or the like, converges the laser beam with an objective lens, and irradiates the disk surface with the laser beam. At this time, the focus of the objective lens is adjusted to be located on the disk surface. and,
This reflected laser light from the disk surface is guided to a photoelectric conversion element or the like and converted into an electrical signal.

By the way, when inspecting a laser optical system such as this optical head, it is necessary to install a reflector or the like on the laser optical system in the same state as in use, that is, at the position where the disk surface is in use. To achieve this state, the focal position of the laser optical system is unclear, so this focal position must be detected.

Conventionally, methods for detecting this focal position include, for example, a first method in which a combination of an optical system comprising a microscope and a detection system comprising an optical conversion element is used for detection, and a second method using a slit. The second method is described in Japanese Patent Application No. 59-184526, in which a slit plate with slits is installed near the focal point of the laser optical system.
The slit plate is vibrated and the focal position is detected based on an electrical signal obtained by photoelectrically converting the laser light that passes through the slit.

[Problems with background technology]

However, with the first method, the entire device becomes large and a moving mechanism is required to move the reflector to the focal position, making it very difficult to accurately position the reflector at the focal position. Therefore, highly accurate inspection cannot be expected. On the other hand, in the second method, since the slit plate is vibrated, a drop in inspection accuracy is inevitable.Furthermore, since the slit width is narrow, the detection range becomes narrow when the laser beam that passes through the slit is detected. There is a problem in that work efficiency such as inspections is reduced.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
The object is to provide a focus adjustment device that can detect the focal position of a laser optical system and adjust to this position automatically and with high efficiency.

[Summary of the invention]

The present invention includes a slit plate in which a plurality of slits having different widths are formed, and a first plate arranged in close proximity to photoelectrically convert laser light passing through these slits.
and a second light-receiving element, and the laser beam is passed sequentially from the wide slit to the first light-receiving element.
Then, the focus detection means detects the peak value and the phase between each electric signal from each electric signal from the second light-receiving element to determine the focus shift, and as the slit width becomes narrower, the slit plate is sequentially shifted out of focus. This is a focus adjustment device that moves and adjusts to the focal position.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a focus adjustment device. Base 1
A laser optical system 2 such as an optical head to be inspected is installed above. This laser optical system 2 is
It has a semiconductor laser 3, further includes a collimator lens 5 that converts the laser beam 4 emitted from the semiconductor 3 into a parallel beam, an objective lens 6 that converges the parallel beam from the collimator lens 5, and the converged laser beam. and a (1/4) wavelength plate 7 and a beam splitter 8 for bending the optical path of the reflected laser beam from the slit plate S by 90°, which is parallel to the optical path of the parallel beam. It is comprised of a condensing lens 9 that converges parallel light beams, and a detector 10 such as a photodiode that receives and photoelectrically converts the laser beam condensed by the condensing lens 9.

Now, this apparatus detects the focal position of the objective lens 6 and makes adjustments to arrange the slit plate S at this focal position. Incidentally, the slit plate S is held by a positioning mechanism 11 and moved in the X-axis direction and the Y-axis direction. This positioning mechanism 11 includes an X-axis positioning table 12 and a Y-axis positioning table 13.
, and are driven by drive motors 14 and 15, respectively. A slit plate S and first and second light receiving elements P1 and P are mounted on the upper part of the Y-axis positioning table 13 by means of a support 16.
2 is supported via a cylindrical holder 17. In addition, the slit plate S and each light receiving element P1, P2
are arranged parallel to each other by the holder 17.

Incidentally, the slit plate A is formed as shown in FIGS. 2a and 2b. That is, this slit plate S is made up of a transparent substrate g1, such as a glass plate, and a Cr vapor deposition film g2 formed on one side of this transparent substrate g1. Note that the thickness of this Cr vapor-deposited film g2 is approximately 2000 Å. Then, four slits e1, e2, e3, e4 with different widths are formed.
The width of each slit e1 to e4 is, for example, 20 μm for e1, 10 μm for e2, and 10 μm for e3.
5 .mu.m, e4 is formed to 1 .mu.m, and the interval between them is about 20 .mu.m.

The first and second light receiving elements P1 and P2 are arranged so that their boundaries are in the same direction as the longitudinal direction of these slits e1 to e4, and receive electrical signals a1 and a2 at a level proportional to the amount of light received, respectively. The signal is output to the focus detection circuit 18.

This focus detection circuit 18 has electrical signals a1 and a.
It has a function of detecting the peak value of 2 and the phase between each electric signal a1 and a2. in particular,
An amplifier 19 for electrical signal a1, an amplifier 20 for electrical signal a2, an adder 21 that adds the signals from these amplifiers 19 and 20, and a peak value detector that detects the peak value Q of the added electrical signal K from this adder 21. 22 and the respective signals from the amplifiers 19 and 20, it is determined which signal rises earlier, and the phase detection signal H, for example, if the electric signal a1 side rises earlier, the phase detection signal of "1" is generated. It is composed of a phase detector 23 which outputs a phase detection signal H of "0" or "0" if the electric signal a2 side rises early.

The main control unit 24 receives the peak value Q from the peak value detector 22 and the phase detection signal H from the phase detector 23, and calculates the focus from preset defocus information from the peak value Q and the phase detection signal H. It has a function to calculate and find the deviation. Note that this defocus information is the summed electrical signals K1, K2, K3, K4 as shown in FIG. The first electric signal a1 and the second electric signal a2 obtained when the objective lens 6 is installed so that the center is located on the central axis n of e1 and the objective lens 6 is moved in the direction of the central axis n in this state. is the summed electrical signal of Therefore, K1 is information for slit e1, K2 is information for slit e2, K3 is information for slit e3, and K4 is information for slit e4. In addition, this control section 24 also includes drivers 25 and 26.
The drive motors 15 and 14 are driven by sending motor control signals to the drive motors 15 and 14, respectively.

Next, the operation of the apparatus constructed as described above will be explained with reference to the focus adjustment flowchart shown in FIG. Laser light 4 emitted from semiconductor laser 3 is converted into a parallel beam by collimator lens 5, reaches objective lens 6, and is converged by objective lens 6. Here, the main control unit 24 sends each motor control signal to the drivers 25 and 26 to drive each drive motor 15 and 14, and operates the Y-axis positioning table 13 and the X-axis positioning table 12, for example. As shown in Figure 3, the slit plate S
is moved to the right on the X-axis so that the laser beam focused by the objective lens 6 is irradiated to the left side of the slit plate S.

Now, with the slit plate S placed at this position, in step s1, the slit plate S is moved at a constant speed in the X-axis direction to cause the laser beam to pass through the slit e1. Then, the electric signals a1, a output from each light receiving element P1, P2 at this time
2 are amplified by amplifiers 19 and 20, respectively, and added by an adder 21 to become a summed electric signal as shown in FIG. 6, which is sent to a peak value detector 22.
Further, electrical signals output from each amplifier 19 and 20 are sent to a phase detector 23. Then the step
At s2, the peak value Q and phase of the added electrical signal K are determined. That is, the peak value detector 22
detects the peak value Q (Vp1) from the added electric signal K as shown in FIG.
Send to. On the other hand, the phase detector 23 detects the phase between the electrical signals a1 and a2 in the following manner.
In other words, when the focal point F is between the slit plate S and each of the light receiving elements P1 and P2 as shown in FIG. 7a, b, and c, when the slit position moves at a constant speed in the Since the laser beam is received by element P2 and gradually moves to light receiving element P1,
As shown in FIG. 8, the electric signals a1 and a2 of the respective light receiving elements P1 and P2 change rapidly in the rise of the electric signal a2. Therefore, the phase detector 23 detects this change and sets the phase detection signal H to "0".
It is sent to the main control unit 24 as a. Also, conversely, the 9th
As shown in Figures a, b, and c, when the focal point F is located in front of the slit plate S, when the slit position moves at one speed in the X-axis direction, first the light receiving element P1
Since the laser beam is received by the laser beam and gradually moves to the light receiving element P2, the electric signals a2 and a1 of each of the light receiving elements P2 and P1 become the electric signal a1 as shown in FIG.
The rise of the value changes quickly. Therefore, the phase detector 23 detects this change and sends the phase detection signal H as "1" to the main controller 24. In this embodiment, since the focal point position is in front of the slit plate S as shown in FIG. 3, a phase detection signal H of "1" is sent to the main control section 24.

Next, the main control unit 24 calculates and obtains an estimated defocus value ΔY1 in step s3. In other words, as shown in FIG. 3, the peak value Vp is calculated from the defocus information K1.
An estimated defocus value ΔY1 corresponding to 1 is determined, and from the phase detection signal H of 1, it is determined that the position is in front of the slit plate S. When the defocus estimated value ΔY1 is obtained in this manner, the main control section 24 sends a motor control signal to the driver 25 to move the slit plate S downward by this amount ΔY1. As a result, the drive motor 15 is driven and the slit plate S is moved downward by ΔY1. In addition,
Since this defocus estimated value ΔY1 includes an error, the process moves to the next step and gradually eliminates this error.

At step s5, the slit plate S is again moved in the X direction, and this time the laser beam is passed through the slit e2, which is narrower than the slit e1. Then, in steps s6 and s7, the peak value Vp2 of the added electric signal K at this time is detected, and its phase is detected in the same manner as above.
is sent to the peak value Vp by this main control unit 24.
2, the defocus estimated value ΔY2 is obtained from the defocus information K2 shown in FIG. Then, in the next step s8, the slit plate S is moved downward by the defocus estimated value ΔY2.

Furthermore, in the next step s9, the slit plate S is moved in the X direction again, and this time the slit plate S is moved in the X direction.
The laser beam is passed through the slit e3, which is even narrower than the slit e3. Then, in steps s10 and s11, the peak value Vp3 of the added electric signal K at this time is detected, and it is detected from the phase detection signal H that the focal point F is on the front side of the slit plate S in the same manner as described above. is sent to the main control unit 24, and the main control unit 24 uses the peak value Vp3 to
Defocus information K3 or defocus ΔY3 shown in the figure is obtained. Then, in the next step s12, the slit plate S is moved downward by the focus shift ΔY3.

Then, in the next step s13, the slit plate S is moved in the X-axis direction to allow the laser beam to pass through the center of the slit s4. In other words, it is installed at a position corresponding to the peak value of the added electrical signal K, and then
In s14, the slit plate S is placed at a position corresponding to the peak value when the slit plate S is moved in the Y-axis direction. Due to the above action, the slit plate S is placed at the focal point of the objective lens 6. Therefore, this state is the position of the slit plate S that makes up the laser optical system 2.

When inspecting the laser optical system 2,
From this state, by moving the slit plate S by a small distance in the X-axis direction, the irradiation position of the laser beam is changed to the Cr vapor deposited film g2 of the slit plate S, and the laser beam is reflected. As a result, the reflected laser light is transferred to the objective lens 6.
The beam is converted into a parallel beam by the (1/4) wavelength plate 7 and the beam splitter 8, bent by 90 degrees, and sent to the condenser lens 9 where it is condensed and sent to the detector 10.
is irradiated. Then, depending on the output signal of the detector 10 and the state of other parts at this time, the laser optical system 2
Inspections, etc. will be conducted.

In this way, in the above embodiment, the slit plate S having the slits e1 to e4 formed therein, and the first and second light receiving elements that receive the laser beams that have passed through these slits e1 to e4 are provided. A laser beam is sequentially passed through the slit, and the peak value and the phase between each electric signal are determined from each electric signal a1, a2 from the first and second light receiving elements P1, P2 at that time, and the focal shift is determined. Since the configuration is such that the slit width is sequentially narrowed and the slit plate S is moved to the focal position F for adjustment, the focal position F
Detection and placement of the slit plate S at the focal position F can be performed automatically and accurately using a luminous flux. Therefore, when inspecting the laser optical system 2, etc., the slit plate S can be placed at the focal position as soon as possible, so that the efficiency of inspection, etc. is improved.

Note that the present invention is not limited to the above-mentioned embodiment, and can be modified without departing from the spirit thereof. For example, in the above embodiment, the slit plate S is moved in the X-Y axis direction, but the slit plate S may be fixed and the laser optical system 2 is moved in the X-Y axis direction. Furthermore, the number of slits is not limited to four, but may be formed in order of desired width. Note that in the above embodiment, the steps
The functions of s13 and s14 can be omitted and the focus can be adjusted using the peak value of the added electric signal K and the phase between the electric signals.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a focus adjustment device that can detect the focal position of a laser optical system and adjust to this position automatically and with high efficiency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the focus adjusting device according to the present invention, FIGS. 2 a and b are block diagrams of a slit plate used in the device of the present invention, and FIG. 3 is a defocus detection function of the device of the present invention. FIG. 4 is a diagram for explaining the function of obtaining defocus information.
FIG. 5 is a focus adjustment flowchart of the device of the present invention;
FIG. 6 is a diagram showing the added electric signal peak value in the apparatus of the present invention, and FIGS. 7 to 10 are diagrams for explaining the effect of phase detection between electric signals. 2... Laser optical system, 3... Semiconductor laser, 5
...Collimator lens, 6...Objective lens, 7...
...(1/4) Wave plate, 8... Beam splitter, 9
... Condenser lens, 10 ... Detector, 11 ... Positioning mechanism, 12 ... X-axis positioning table, 13
... Y-axis positioning table, 14, 15 ... Motor, 18 ... Focus detection circuit, 19, 20 ... Amplifier, 21 ... Adder, 22 ... Peak value detector,
23... Phase detector, 24... Main control section, S...
Slit plate, P1, P2... Light receiving element.

Claims (1)

[Claims] 1. In a focus adjustment device used for inspection of a laser optical system, etc., which has the function of receiving laser light, converging it with an objective lens, reflecting the converged light, guiding it to a photoelectric conversion element, and converting it into an electrical signal, the convergent light is a slit plate in which a plurality of slits are formed and have different widths, and a positioning mechanism that moves the laser optical system or the slit plate in the optical axis direction of the laser beam and in a direction perpendicular to the optical axis direction. and first and second light-receiving elements disposed close to each other for photoelectrically converting the laser light that has passed through each of the slits, and receiving the first and second electric signals from the first and second light-receiving elements to determine the peak value. and a focus detection means for detecting the phase between the first and second electric signals, and passing the laser beam in order from the widest one of the slits to detect the peak value and the signal at that time. 1. A focus adjustment device, characterized in that the slit plate is adjusted to the focal position of the objective lens for each slit by determining a focus shift from an interphase phase.