JP2618868B2 - Optical head unit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for recording / reproducing information on / from an optical information recording medium, and in particular, a light emitting / receiving function applicable also as a non-contact position sensor. The present invention relates to an optical head unit provided with:

2. Description of the Related Art An optical system in a recording / reproducing apparatus converges a laser beam emitted from a laser diode light source on an information recording medium via a converging optical element such as an objective lens, and converges on a surface of the information recording medium. Is known as a device for reading information stored in a storage medium or writing and storing the information on the surface of the information recording medium. Regardless of the optical reading of the information,
Regardless of the optical writing, the laser beam must be properly focused on the surface of the information recording medium by a focusing optical element such as an objective lens. Therefore, an optical head device that operates while detecting whether or not the laser beam is converged on the surface of the information recording medium by a converging optical element such as an objective lens is required.

5A and 5B are configuration diagrams illustrating a layout of an optical head device according to a conventional example. In the figure, (1) shows a laser diode serving as a light source, and (2) shows a laser beam emitted from the laser diode (1). (4) shows a parallel plate beam splitter for splitting the laser beam, (5) shows a light converging lens element such as a condenser lens for converging these beams, and (6) shows an optical card, an optical tape or a circle. An optical information recording medium such as a plate-shaped optical disk, (7) is an information track formed on the information recording surface of the information recording medium (6), and (10) is a laser reflection from the optical information recording medium (6). This is a photodetector light receiving unit that receives light (2 ').

Next, the operation will be described. Laser diode (1)
The divergent light beam (2) emitted from the optical disk is reflected by the surface (4a) of the flat plate beam splitter (4), and then converged on the optical information recording medium (6) by the converging light converging lens element (5). The reflected light beam (2 ') reflected from the optical information recording medium (6) is reflected by the back surface (4b) of the flat plate beam splitter (4), slightly shifted from the emitted light beam (2), and proceeds in the opposite traveling direction. The light is received by the photodetector light receiving section (10). In order to correctly obtain information on the optical information recording medium (6), the light converging spot (3) must be accurately illuminated on the surface of the information track (7). Since the reflected light beam (2 ') is a convergent light beam, astigmatism occurs as is well known when the light beam travels from the flat plate beam splitter (4) to the photodetector light receiving section (10). Now, assuming that the flat plate beam splitter (4) is a parallel flat plate, the thickness is t, the refractive index is n, and the incident angle on the surface (4a) is θ [rad], the astigmatic difference Δ is given by the following equation.

The reflected light beam (2 ') from the beam splitter (4) provided with the astigmatism is parallel to the light beam (2) emitted from the LD (1) and travels in the opposite direction, and is shown by a dashed line in the figure. The principal ray to be detected has a shift of 2t · tan θ ′ · cos θ (2).
(10). Here, the θ ′ is n sin θ ′ =
sin θ is satisfied.

In such an optical head device, the photodetector light receiving section (10) detects the light beam reflected from the information recording medium disk when the light converging spot on the optical disk (6) is in focus, as shown in FIG. As shown in b), it is arranged at the position in the optical axis direction where the circle of least confusion (11) occurs. The photodetector light receiving section (10) is divided into four parts, as shown, into detecting elements (10a), (10b), (10c), and (10d). Is detected.

As is well known, the output of each of these detection units is opposed in the diagonal direction because the light converging spot on the photodetector light receiving unit (10) becomes a distorted spot (12) when defocus occurs. The defocus of the light beam can be detected by calculating the sum of the photoelectric conversion outputs of the detection elements and calculating the difference output between the opposing detection units.

That is, the sum output pair difference output of the facing detection element unit is
{(10a) + (10c)}-{(10b) + (10d)}
The calculation output signal is output as a focus error signal, and the focus actuator (not shown) corrects the defocus of the light converging spot on the optical information recording medium.

On the other hand, tracking is performed as an in-plane direction adjusting means in order to properly irradiate the light convergence point (3) on the optical information recording medium (6) onto the information track. Although not specifically described here, a twin spot method, a push-pull method, or the like can be applied to the conventional apparatus.

[Problems to be Solved by the Invention] Since the conventional optical head device is configured as described above, the following problems occur.

As described above, the light emitting point of the laser diode (1) and the light converging spot (11) of the photodetector light receiving section (10) are δ = 2 · t · cos θ · tan (θ ′) in the Z direction in FIG. ). If, for example, θ = 45 ° and t = 1 mm, δ
= 0.75 mm and 1 mm or less. At this time, the shift amount in the optical axis direction (x) is as short as 1 mm or less.

Therefore, there is a problem that it is very difficult to arrange the laser diode (1) and the photodetector light receiving section (10) separately as shown in the figure. The photodetector light receiving section (10) must be arranged at the position where the circle of least confusion (11) is irradiated as described above, and has an adjusting means. However, as described above, since it is adjacent to the laser diode (1), there is a problem that the configuration and arrangement of the adjusting means becomes very difficult.

In order to solve such a problem, a laser diode chip is used by utilizing the fact that the light emitting point of the laser diode (1) and the light converging spot (11) are adjacent to each other by 1 mm or less in the optical axis and a direction perpendicular to the optical axis. It is also conceivable to form the photodetector and the photodetector on the same substrate.

Since the light emitting point of the laser diode (1) and the light converging spot (11) are in a conjugate relationship, if the relative position accuracy and the parallelism of the flat plate beam splitter (4) can be ensured, the photodetector light receiving unit is calculated. It is only necessary to set the position relative to the laser diode (1) obtained by the above, and it is possible to realize the non-adjustment of the detector.

The relative positional accuracy is relatively easy if both elements are formed on the same substrate, but the allowable width of the parallelism of the flat plate beam splitter (4) is strict. For example, in FIG. 5, for example, the distance 1 from the laser diode (1) to the plate beam splitter is 15 mm, the (4a) plane incident angle of the plate beam splitter (4) is 45 °, n = 1.5, t = 1 mm, and the parallelism α [ deg], α = 0.010 ° (= 0.6 ′) is required in order to set the allowable displacement of the light converging spot (11) with respect to the photodetector light receiving section (10) to ± 10 μm. Thus, in order to integrate the photodetector light receiving section (10) and the laser diode (1) without adjustment, it is necessary to maintain the parallelism with a high precision of 1 'or less in the parallel beam splitter (4). The required effective area of the flat plate beam splitter is also large in the above example, when the numerical aperture NA of the light beam of the laser diode (the numerical aperture NA corresponds to the spread angle of the light beam) is 0.1, a circle having a diameter of about 5 mm is wide. Since flatness is required with high accuracy over the area, there is a problem that cost is increased in order to maintain such surface accuracy over a wide area.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an inexpensive and simple optical head device while realizing no adjustment of the position of a light detector light receiving unit. It is.

[Means for Solving the Problems] The optical head unit of the present invention includes a light source such as a laser,
A light detecting unit provided near the light source and a flat optical element that reflects light from the light source on the first surface and reflects a return beam from the information recording medium on the second surface include a laser beam and a return beam. It is configured to be sealed in a predetermined package having a window through which light can enter and exit. These members are arranged close to each other on the same block integrally formed, and the light source and the flat optical element are arranged so that the optical path length from the light source to the first surface of the flat optical element is about 3 mm. ing.

[Operation] Since the optical head unit according to the present invention is configured as described above, the laser diode light source, the light detecting unit, and the flat plate optical element can be arranged in the package with extremely high accuracy. It is not necessary to adjust the angle and the like. Further, by precisely arranging the distance between the light source and the flat optical element at a short distance,
The allowable range of the parallelism between the second surface and the second surface is wide, the displacement of the storage position of the return beam is small, and a high-performance and compact optical head unit can be configured. In addition, it can be configured using a practical and inexpensive flat optical element having not so high parallelism.

Furthermore, by combining the optical head unit of the present invention with, for example, a light converging lens and its position control actuator, an optical head device can be easily configured.
With the use of the optical head unit of the present invention, even when an optical head device is configured, it is possible to obtain recording information, focus information, and tracking information of an information recording medium without performing adjustment of a light detection unit and the like. In addition, other special detection means and adjustment means are not required.

Embodiment Hereinafter, the configuration of an optical head unit according to an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a laser diode (1), a beam splitter (4), and a photodetector light receiving section (10) have the same functions as those of each element of the conventional example. Laser diode (1) is PN
A semiconductor chip comprising a junction is used, and (10 ') is a photodetector light-receiving section for monitoring the output of a laser diode. (17) shows an exit window of the laser head from the optical head device.

Here, the laser diode (1), the beam splitter (4), and the photodetector light receiving section (10) are formed while being positioned with respect to the block (18). This block (18) is used for heat radiation of the laser diode. Means is also used.

Each important optical element in these optical head units is
As shown in the figure, it is configured and sealed in one package, and the relative position of each optical element is set with high precision.

In the case of this embodiment, as in the conventional example, for example, t = 1 mm,
Assuming that the numerical aperture NA is 0.1, the relative positional accuracy of the laser diode (1) with respect to the light receiving unit (10) of the photodetector or other important optical elements (for example, the beam splitter (4)) is in the optical axis direction. It is adjusted to ± 25 μm and ± 5 μm in the direction perpendicular to the optical axis. It is preferable that the overall shape of the package that can determine the relative position of such important optical elements has a cylindrical shape, and the outer diameter is not more than 10 mm even if it is large. Although it is difficult to make a circular tube package with a very small diameter theoretically or practically, it is also possible in principle to make an optical head unit (13) having a package with a diameter of 5 mm.

Optical head unit (13) according to an embodiment of the present invention
Is a laser diode (1) and a beam splitter (4)
Is set very short, for example, if l = 3 mm, the parallelism of the beam splitter (4) should be about 3 'at the worst. The adjustment of) is not necessary.

In addition, the above-described embodiment of the present invention is advantageous in that the effective area of the beam splitter (4) can be reduced, thereby maintaining surface accuracy, which is an important factor, and contributing to an inexpensive beam splitter. Can be. And
The relative positional relationship is 1 and the thickness t of the plate beam splitter,
If the inclination = θ is determined, it is a value automatically determined by the equation (2). Specifically, in order to assemble the relative distance in the optical unit, the block (18) has marks for positioning the laser diode (1) and the photodetector (10),
For example, if a groove or the like is formed, positioning can be performed sufficiently with a mechanical accuracy of ± 5 μm.

2A, 2B and 2C show an embodiment in which the optical head unit (13) of the present invention is applied to an optical head device. No.
2A, 2B and 2C, (14) is an optical lens barrel, (1)
Reference numeral 5) denotes an actuator related to focus and tracking for feedback driving control of the light converging lens element.

The operation of the optical head unit (13) of the embodiment of the present invention is basically the same as the operation of the conventional example, but the convergence of the optical head unit (13) and the objective lens etc. An actuator (1) that operates the optical element (5)
The signal of the information recording medium disk (6) and the convergent light spot position information can be caught by the optical head unit (13) only by adding the item (5). In addition, there is an operation that does not require adjustment work of the photodetector light receiving unit and the like at the time of assembly.

By using the present optical device, various types of optical head devices can be configured. FIG. 2B shows an example of the optical head device. (16) is a reflection mirror. Since the reflection mirror (16) is formed such that the optical path is bent and then incident on a converging optical element such as an objective lens, a large volume and an occupied optical path space are usually compressed. By doing so, a thinner optical head device can be easily provided.

2A and 2B, as described above, the optical head unit (13) of the present invention is configured so that the center axis of the package and the optical axis of the emitted light coincide with each other, as shown in FIG. 2C. In addition, the central axis of the package and the optical axis of the emitted light do not overlap, and a thinner optical head can be achieved.

Although the tracking method was not particularly mentioned in the description of the conventional example, by forming a diffraction grating on the surface (4a) of the beam splitter (4) in the optical head unit (13), it is possible to increase the number of new optical components without increasing the number of new optical components. Tracking by the twin spot method can be performed. The twin spot method itself is well known and will not be described. When the twin spot method is adopted, the focal point on the optical disc (6) of the three beams emitted from the (4a) plane is
Information track (7) based on zero-order light converging point (3)
In some cases, it is necessary to adjust the rotation of the diffraction grating so as to be slightly tilted. In FIG. 3, (3a) and (3b) denote ± first order light,
Assuming that the track pitch is P and the interval between the ± 1st order light and the 0th order light is d, When θ is rotationally adjusted so as to obtain, the largest tracking signal can be obtained.

In this case, it is advantageous that the center of the package of the optical head unit (13) coincides with the optical axis of the emitted light, and the rotation of the entire optical head unit (13) can be adjusted by the mounting portion of the optical barrel (14). Since the optical axis does not deviate even when rotated, good light convergence characteristics can be maintained without generating an image height for the convergence optical element (5) such as an objective lens. At this time, it is clear that the focus signal is not affected at all, and it is not necessary to adjust the photodetector.

However, the photodetector light receiving section (10) requires a detecting section having at least a six-part configuration.

In the above embodiment, the external shape of the optical head unit (13) is shown as a cylindrical shape. However, for example, a rectangular package can be used, and the external shape can be appropriately selected for each usage.

The optical head unit (13) of the present invention can be applied not only to the optical head device as described above, but also to various uses such as a position sensor as a light emitting / receiving element.

An example will be described with reference to FIG. (19) is a sample, and the optical head unit (13) and the objective lens (5) of the present invention are fixed to a lens barrel (14). At this time, if the sample (19) is placed near the focusing position, the focus error signal is zero when the sample surface is focused, but when the sample (19) is moved in the direction A, the surface has irregularities. If so, the focus error signal changes. By calibrating the amount of unevenness and the focus error signal, the surface shape can be checked.
And a light converging numerical aperture of a converging optical element such as an objective lens.
By selecting NA, it is possible to function as a sensor for detecting a change in the position from the converging optical element such as the objective lens to the surface of the light converging spot in a wide range of measurement accuracy and measurement range.

[Effects of the Invention] As described above, according to the present invention, the light source, the light detection unit, and the flat optical element are arranged close to each other on the same block integrally formed, and from the light source to the first surface of the flat optical element. Since the optical head unit is configured by arranging the light source and the flat plate optical element so that the optical path length becomes about 3 mm, there is no need to adjust the position and angle of the light detection unit and the like after the arrangement. Further, since the allowable range of the parallelism of the flat optical element is wide, a high-performance and small-sized unit can be provided by using an inexpensive element. When applied to an optical head device, there is no need to adjust the arrangement and angle of the individual components of the optical head unit, such as a laser diode light source, a light detection unit, and a flat optical element. Focusing on information recording media etc. can be performed only by adjusting the position of
It is not necessary to adjust the position of the light detection unit and the like at the time of assembling the optical head device, and the workability is remarkably improved.

In addition, since the optical head unit is independent of the converging optical element, the optical path can be set freely according to the allowable space without adjusting the inclination of the laser diode light source, the light detecting unit, the flat optical element, and the like. . As a result, the degree of freedom in device design is improved, and the size and thickness of the optical head device can be reduced.

Further, when performing tracking adjustment of an information recording medium by utilizing the diffraction effect of a laser beam, since the optical head unit is configured to be sealed in a package, a laser diode light source, a flat plate optical element, a light detection It is also possible to adjust the tracking simply by rotating the entire optical head unit, for example, about the center axis of the package without changing the position of each part.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head unit according to an embodiment of the present invention, FIGS. 2A, 2B, and 2C are configuration diagrams of an optical head device to which the optical head unit of the embodiment of the present invention is applied, and FIG. FIG. 4 is an explanatory view of an adjustment method by a twin spot method according to an embodiment of the invention, FIG. 4 is a configuration diagram showing a modified example of the position sensor of the embodiment of the invention, and FIGS. 5A and 5B are configurations showing an optical head device according to a conventional example. FIG. In the figure, (1) is a laser diode, (4) is a flat plate beam splitter, (10) is a photodetector light receiving section, and (13) is an optical head unit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Continuation of the front page (56) References JP-A-56-57013 (JP, A) JP-A-54-76177 (JP, A) JP-A-59-33641 (JP, A) JP-A-61-170126 (JP, A) , U)

Claims (3)

(57) [Claims] A laser diode light source; a return beam converging at a position adjacent to the laser diode light source; and based on the return beam, record information of an information recording medium, focus information, tracking information, And a laser beam from the laser diode light source is reflected and emitted by the first surface, which is the front surface, and the return beam that returns via the same optical path as the reflected laser beam is emitted. A flat optical element that reflects on a second surface, which is a back surface facing the first surface, and emits the light to the light detection unit, wherein the light detection unit is divided into at least four parts. The laser diode light source, the light detection unit, and the flat plate light. A first element of the flat optical element from the laser diode light source.
The laser diode light source and the flat optical element are arranged so that the optical path length to the surface is about 3 mm, and the laser diode light source, the light detection unit, the flat optical element, the laser beam and The optical head unit is sealed in a predetermined package having a window through which the return beam can enter and exit. 2. A first optical element according to claim 1, wherein a diffraction grating is arranged on a first surface of said flat optical element.
An optical head unit according to the item. 3. The package has a cylindrical shape, and a center line of the package is substantially equal to an optical axis of a laser beam emitted from a window of the package and reflected by a first surface of the flat optical element. The optical head unit according to claim 1, wherein the optical head unit comprises: