JPH0362328A - Focal position detector for optical device - Google Patents

Abstract

PURPOSE:To detect a focal position accurately with a small sized and inexpensive detector by providing a position detection means integrated with a reflecting member in an optical axis direction with free of inching and adjusting the position of a reflecting means while detecting an optical output of a semiconductor laser. CONSTITUTION:A position adjusting device 9 able to be free of inching in the optical axis direction of an optical head 4 is provided above an objective lens 6 ad a mirror piece 10 and a position detector 12 are mounted. For the adjustment of the height of a spindle motor 1, the light from the head 4 is collected to the mirror piece 10 through the objective lens 6 to form light spot thereby inching the device 9 in the optical axis direction. When the light spot of the mirror piece 10 approaches the focusing state, the detection output of the photodetector is rapidly increased and reaches a maximum when the spot on the mirror piece 10 is focused. Thus, the position of the motor 1 is adjusted by a distance in response to the detector 12 in this case. Thus, the focus of the radiating light of the optical system is detected accurately with the small sized and inexpensive device and the positioning of the motor 1 or the like is implemented with high accuracy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical system for detecting the focal position of light emitted from an optical head in assembling an optical device equipped with an optical head such as an optical recording/reproducing device. The present invention relates to a focal position detection device for an apparatus.

[Conventional technology]

An optical recording/reproducing device is equipped with an optical head that irradiates a disc with light. The optical head is usually provided with an actuator that drives the objective lens in the optical axis direction in order to focus the optical spot on the disk.

Since this actuator has a limited driving range, the optical spot cannot be focused unless the optical pickup and the disk are placed in the correct positional relationship. Therefore, when assembling an optical information recording/reproducing device, the positional relationship between the optical pickup and the disk must be strictly determined.
It is necessary to ensure that the light spot is accurately focused within the drive range of the actuator. For this reason, in the past, a method was used to determine the height of the disk for optical pickups, and in reality, this was done by highly precisely adjusting the height of the spindle motor that rotates the disk. .

As shown in FIG. 4, in adjusting the height of the spindle motor 1, the disk 3 is first fixed on the turntable 2 which is rotationally driven by the spindle motor l. Next, an optical measuring device 7 such as a laser scanning micrometer
using the scanner 7a to detect the lower end surface of the disk 3,
Light is irradiated between the optical head 4 and the upper end surface of the objective lens 6 held by the actuator 5, and the distance therebetween is measured in a non-contact manner. The difference between this measured value and the designed value is then determined, and the height of the spindle motor is adjusted to eliminate this difference.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, the working distance of the objective lens 6 actually has errors and variations with respect to the designed value, so when the distance between the disk 3 and the upper end surface of the objective lens 6 is measured, the measured value will include the above errors and variations. For this reason, the conventional techniques still have the problem of measurement reliability as described above, and are not practically satisfactory.

In addition, devices such as a laser scanning micrometer used as the optical measuring device 7 perform electrical processing on optically measured quantities to obtain measured values, so if the processing equipment is included, they are large and expensive. Become. Therefore, a large installation space is required, resulting in high assembly and adjustment costs.

[Means to solve the problem]

In order to solve the above-mentioned problems, a focal position detection device for an optical device according to the present invention is provided so as to be able to move slightly in the optical axis direction of light emitted from an optical system that condenses emitted light from a laser light source. a reflecting member that reflects the light and returns it to the laser light source via the optical system;
It is characterized by comprising a position detecting means for detecting the position of the reflecting member and a light output detecting means for detecting the light output of the laser light source.

[For production]

According to the above configuration, the light emitted from the laser light source is
The light is focused on a reflective member by an optical system to form a light spot, and is reflected by the reflective member and returned to the laser light source. When the light spot is not focused on the reflective member, the optical output of the semiconductor laser hardly changes even if the returned light is incident on the semiconductor laser. However, by slightly moving the reflecting member in the direction of the optical axis of the light, when the reflecting member approaches the focused position of the light spot, the optical output of the laser light source sharply increases due to the returned light due to the so-called three-mirror effect. . When the light spot is focused on the reflective member, the light output becomes maximum. Therefore, by adjusting the position of the reflecting member while detecting the optical output of the semiconductor laser with the optical output detection means, the focal position of the emitted light of the optical system can be easily detected. Moreover, if the position of the reflecting member at this time is detected by the position detecting means, it is possible to accurately position the members arranged around the optical component in accordance with the position of the reflecting member.

Therefore, even if the working distance of the objective lens in the optical system has an error or variation with respect to the designed value, the focal position of the light emitted from the optical system can be accurately detected without being affected by the error or variation. Further, since the emitted light of the optical system is used to detect the focal position, there is no need to use a large optical measuring device as in the past, and the focal position detection device can be constructed in a small size and at low cost.

(Embodiment) An embodiment in which the present invention is applied to the spindle motor position adjustment of an optical information recording/reproducing device will be described below based on FIGS. 1 to 3. The same reference numerals are added to the members having the same functions as those of the conventional example shown in the figures.

As shown in Figure 1, the upper part of the spindle motor l is
A turntable 2 is provided on which a disk 3 shown in FIG. 2 is placed and fixed. A reference device 8 whose upper and lower end surfaces are parallel and whose thickness is known is fixed to the upper end surface of the turntable 2. On the other hand, in the upper part of the optical head 4 as an optical system,
An actuator 5 is provided to drive the objective lens 6 in its optical axis direction and in the tracking direction of the disk 3.

A position adjustment device 9 is provided above the objective lens 6 and is movable slightly in the direction of the optical axis of the light emitted from the optical head 4 . This position adjustment device 9 has a mirror piece 10 serving as a reflecting member attached to its lower end surface, and its position is adjusted by slightly moving the mirror piece 10 in the optical axis direction. The ξ radius piece 10 reflects the light emitted from the objective lens 6 and returns it to the objective lens 6.

Further, a position detector 12 is attached to the position adjustment device 9 via a connecting portion 11, and the position detector 12 can be slightly moved integrally with the position adjustment device 9. A position detector 12 as a position detection means has a detection section 1 at its lower end.
2a is provided, and the height of the lower end surface of the mirror piece 10 from the upper end surface of the turntable 2 is detected by detecting the position of the detection part 12a from the upper end surface of the reference device 8 in a non-contact manner. ing. Therefore, the detection value of the position detector 12 is determined from the difference between the position detection value of the detection part I2a from the upper end surface of the reference device 8, the thickness of the reference device 8, and the height of the detection part 12a from the mirror piece 10. The distance in the vertical direction between the upper end surface of the turntable 2 and the lower end surface of the ξ roller piece 1o is added and output. Note that, as the position detector 12, a capacitance type minute displacement meter, a laser displacement meter, or the like is used as an instrument that performs position detection in a non-contact manner as described above.

As shown in FIG. 2, in the optical head 4, light emitted from a semiconductor laser 13 as a laser light source is converted into a parallel beam by a collimating lens 14, shaped into a circular beam by a shaping prism 15, and then polarized. It passes through a beam splitter 16 and is guided to an objective lens 6 by a 45° ξ coupe. The light focused on the disk 3 by the objective lens 6 and reflected passes through the objective lens 6 and the 45'' mirror 17, and is separated into two different polarized lights by the polarization beam splitter 16, one of which is sent to a photodetector for detecting the reproduced signal. 18, and the other is guided to a 45° prism 19.
The light deflected by the prism 19 is separated into three beams by the modified Wollaston prism 2o, and then passed through the spot lens 21 and the cylindrical lens 22.
The light is focused on a six-divided photodetector 23 for detecting focus error signals and tracking error signals. Further, a monitor diode 24 as a light output detection means is provided inside the semiconductor laser 13 to detect the light output of the semiconductor laser 13.

In the above configuration, in order to adjust the height of the spindle motor 1, light is emitted from the semiconductor laser 13, and this light is focused on the mirror piece 10 by the objective lens 6 to form a light spot. When the light spot is not focused on the mirror piece 10 and the light returned via the optical system between the objective lens 6 and the semiconductor laser 13 is incident on the semiconductor laser 13, as shown in FIG. , monitor diode 2
The optical output of the semiconductor laser 13 detected by the semiconductor laser 4 is approximately constant. Here, by slightly moving the position adjustment device 9 in the direction of the optical axis of the light emitted from the optical head 4, when the light spot on the mirror piece lo approaches a focused state, as shown in FIG. The optical output of the diode 24 increases sharply. Then, as shown in FIG. 1, when the light spot is focused on the mirror piece 10, the light output of the monitor diode 24 becomes maximum.

Therefore, by adjusting the position of the spindle motor I by a distance corresponding to the detected value of the position detector 12 at this time, the spindle motor 1 can be accurately positioned.

It goes without saying that the present invention can also be applied to optical devices equipped with optical systems other than the optical head 4.

〔Effect of the invention〕

As described above, the focal position detection device of the optical device according to the present invention is provided so as to be able to move slightly in the optical axis direction of the light emitted from the optical system that condenses the emitted light of the laser light source, and reflects the light. a reflective member that returns to the laser light source via the optical system;
This configuration includes a position detection means that is provided integrally with the reflection member so as to be freely movable and detects the position of the reflection member, and an optical output detection means that detects the light output of the laser light source.

As a result, since the reflecting member is provided to be able to move slightly in the direction of the optical axis of the light emitted from the optical system, the light spot formed by the light on the reflecting member is focused by moving the reflecting member slightly. be able to. Furthermore, when the optical output of the semiconductor laser reaches its maximum upon receiving the returned light, the light spot is focused on the reflective member, so by detecting the position of the reflective member at this time using the position detection means, the optical system The focal position of the light emitted from the can be accurately detected.

Therefore, even if the working distance of the objective lens in the optical system has errors or variations with respect to the design value, the focal position can be accurately detected without being affected by it. The height of the spindle motor of the recording/reproducing device can be adjusted with high precision. Furthermore, since the emitted light from the optical system is used to detect the focal position, there is no need to use an optical measuring device as in the past, and the focal position detection device can be constructed in a small size and at low cost.

[Brief explanation of drawings]

1 to 3 show one embodiment of the present invention. FIG. 1 is an explanatory diagram showing a configuration when a focal position detection device of an optical device is used for adjusting the height of a spindle motor. FIG. 2 is an explanatory diagram showing the configuration of the optical head. FIG. 3 is a graph showing the relationship between the position of the mirror piece and the optical output. FIG. 4 shows a conventional example, and is an explanatory diagram showing a configuration for measuring the height of a spindle motor. 4 is an optical head (optical system), 9 is a position adjustment device, IO is a mirror piece (reflection member), 12 is a position detector (position detection means), 13 is a semiconductor laser (laser light source), 24 is a monitor diode (light source) output detection means).

Claims (1)

[Claims] 1. A reflecting member that is provided to be able to move slightly in the optical axis direction of the light emitted from an optical system that condenses the emitted light of the laser light source, and that reflects the light and returns it to the laser light source via the optical system; What is claimed is: 1. A focal position detecting device for an optical device, comprising: a position detecting means for detecting the position of a reflecting member; and a light output detecting means for detecting a light output of a laser light source.