JPH04295635A - Optical pickup apparatus - Google Patents

Abstract

PURPOSE:To achieve a stable emission control by preventing a light emitting power from varying by a return light in a semiconductor laser or the like of a tracing type optical pickup. CONSTITUTION:A phase difference plate 11 of (lambda/4)Xn is provided between semiconductor laser 1 and a polarized beam splitter 3. Light output varying portion detecting means 13 and 14 are provided which receive a laser light reflected (transmitted through) on the polarized beam splitter 3 to detect an output varying portion of the laser light. This enables monitoring with a simple construction only having a phase difference plate without altering optical characteristic of the conventional optical part thereby obtaining a stable light output regardless of the existence of the return light.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to an optical pickup device in an optical information recording/reproducing apparatus that records, reproduces, and erases information by forming a minute spot on an optical information recording medium such as an optical disk. In particular, the present invention relates to an optical pickup device that prevents fluctuations in light emission power caused by return light in a semiconductor laser or the like of a write-once optical pickup and performs stable light emission control.

0002

2. Description of the Related Art Conventionally, the Foucault method (double knife edge method) has been known as a focus detection method for focus control in an optical pickup device of an optical information recording/reproducing device. This Foucault method generally has the advantage of high sensitivity in detecting defocus on the information recording surface.

FIG. 4 is a diagram illustrating an example of the configuration of a main part of an optical system based on the Foucault method in a conventional optical information recording/reproducing apparatus. In the figure, 1 is a semiconductor laser, 2 is a collimating lens, 3 is a deflection beam splitter, 4 is a λ/4 plate, 5 is an objective lens, 6 is a disk, 7 is a detection lens, 8
9 represents a knife edge prism, 9 represents a focus signal detection light receiving element, and 10 represents a tracking signal detection light receiving element.

The light emitted from the semiconductor laser 1 is made into parallel light by a collimating lens 2, transmitted through a polarizing beam splitter 3 and a λ/4 plate 4, and the linearly polarized light is polarized into circularly polarized light, which enters an objective lens 5. Ru.

A minute light spot of about 1 μm is formed on the recording surface of the disk 6 by the objective lens 5, and information is recorded, erased, and reproduced.

The reflected light from the disk 6 becomes circularly polarized light that rotates in the opposite direction to the forward path, is again converted into parallel light by the objective lens 5, and is converted into linearly polarized light by the λ/4 plate 4.

In this case, the linearly polarized light on the return trip is orthogonal to the linearly polarized light on the outbound trip, and is entirely reflected by the polarizing beam splitter 3.

The light reflected from the polarizing beam splitter 3 is
The detection lens 7 converges the light, and a part of the light is blocked by the knife edge prism 8.

However, the light that is not blocked by the knife edge prism 8 enters the focus signal detection light receiving element 9, and the light reflected from the knife edge prism 8 enters the tracking signal detection light receiving element 10.

[0010] Usually, in conventional optical pickup devices, the so-called knife edge method is used as a focus detection method.
Further, a push-pull method is adopted as a track detection method.

The optical pickup device having the configuration shown in FIG. 4 includes a deflection beam splitter 3 and a λ/4 plate 4 on the disk 6 side as an isolated optical system.

Next, an ideal state and an actual state of the optical path of an optical pickup device including a conventional deflection beam splitter 3 and a λ/4 plate 4 on the disk 6 side will be explained.

FIG. 5 is a diagram illustrating an ideal state of the isolated optical system in the optical pickup device. The symbols in the figure are the same as in FIG. 4.

Ideally, as shown in FIG. 5, all of the reflected light from the disk 6 should be reflected off the deflection beam splitter 3 and guided to the detection system.

However, in reality, the accuracy of the components of the λ/4 plate 4 (for example, the inclination of the optical axis and the phase difference), the relative deviation of the optical axes between the deflection beam splitter 3 and the λ/4 plate 4, Due to birefringence of the disk 6, the reflected light from the disk 6 does not become circularly polarized light but becomes elliptically polarized light.

As a result, the reflected light from the disk 6 is λ
Even after passing through the /4 plate 4, the light does not become linearly polarized light that is orthogonal to the linearly polarized light on the outgoing path. This state is shown in FIG. 6 below.

FIG. 6 is a diagram illustrating the actual state of an isolated optical system in a conventional optical pickup device. The symbols in the figure are the same as in FIG. 5.

As shown in FIG. 6, the actual optical path is λ
The reflected light from the disk 6 that has passed through the /4 plate 4 is not entirely reflected by the polarizing beam splitter 3, but a portion thereof is transmitted to the semiconductor laser 1 side.

The light returned to the semiconductor laser 1 side is condensed by the collimator lens 2 and enters the semiconductor laser 1, so that the emission power of the semiconductor laser 1 changes.

That is, this semiconductor laser 1 is
(Auto power control) When driving, the emission power of the semiconductor laser 1 decreases.

Therefore, when the semiconductor laser 1 is driven by ACC (auto current control), the light emission power increases.

[0022] As a result, reading and writing cannot be performed using appropriate laser power, resulting in a disadvantage that the characteristics of the optical disc drive deteriorate.

[0023]

[Problems to be Solved by the Invention] In the present invention, such inconveniences that occur in conventional optical pickup devices,
In other words, this solves the problem of the light emitting power changing due to the return light to the semiconductor laser side, which causes deterioration of the characteristics of the optical disk drive.Even if there is light returning to the semiconductor laser side, the semiconductor laser always emits light at a predetermined power. Lead with proper laser power,
An object of the present invention is to provide an optical pickup device that prevents deterioration of characteristics of an optical disk drive by enabling writing.

[0024]

[Means for solving the problems] In this invention, firstly,
The light beam from the semiconductor laser is focused by an objective lens,
In an optical pickup device of an optical information recording and reproducing device that records, reproduces, and erases information by forming a minute spot on an optical information recording medium such as an optical disk, the optical pickup device is arranged between the semiconductor laser and the deflection beam splitter. (λ/4)
xn (n=an integer of 1 to n) phase difference plate, and an optical output variation detection means for receiving the laser light reflected (or transmitted) by the deflection beam splitter and detecting the output variation of the laser light. , and is configured to control the optical output of the semiconductor laser based on the output fluctuation of the laser beam detected by the optical output fluctuation detecting means.

Second, in the first optical pickup device, the retardation plate is a λ/2 plate.

Thirdly, in the first or second optical pickup device, the retardation plate is provided with means for rotating it around the optical axis of a light source such as a conductive laser.

[0027]

[Function] The optical pickup device of the present invention has a simple configuration in which a retardation plate is placed between a light source such as a semiconductor laser and a polarizing beam splitter, without changing the optical characteristics of conventional optical components. By controlling the light emission based on the monitor output, stable light output can be obtained even if there is light returning to the light source such as a semiconductor laser.

[0028]

[Embodiment 1] Next, an embodiment of the optical pickup device of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the optical pickup device of the present invention.
FIG. 2 is a diagram showing an example of the configuration of main parts of the optical system. The symbols in the figure are the same as those in FIG. 4, and 11 is a retardation plate, 12 is a condensing lens, 13 is a light receiving element for LD (semiconductor laser) power monitoring, and 14 is an APC (auto power control) circuit. show.

In the optical pickup device of the present invention shown in FIG. 1, a retardation plate 11 is added in order to change the state of linearly polarized light. This retardation plate 11 is λ/
It is a two-plate or λ/4 plate, and the state of linearly polarized light transmitted through it is changed.

In addition, for APC control, the condenser lens 1
2, LD (semiconductor laser) power monitor light receiving element 13, and APC (auto power control)
A circuit 14 is provided, but in this respect, the configuration is basically the same as that of a conventional optical pickup device. Note that the polarization beam splitter 3 separates the P-polarized component of the light incident from the collimating lens 2 (light emitted from the semiconductor laser 1) and the light incident from the objective lens 5 (light reflected from the disk 6). The light is transmitted and reflected, respectively, and the S-polarized light component is almost completely reflected.

The light emitted from the semiconductor laser 1 is made into parallel light by the collimating lens 2, and is transmitted through the retardation plate 11 to change the state of the linearly polarized light. for example,
When the retardation plate 11 is a λ/2 plate, the polarization direction is rotated (see Figure 2, described later), and when it is a λ/4 plate, it becomes elliptically polarized light including a circle (see Figure 3, described later). .

When the light transmitted through this phase difference plate 11 reaches the polarization beam splitter 3, the light beam of the P polarization component is transmitted as is (the transmitted light follows the same path as in the case of the prior art). , S-polarized components are reflected and converted into convergent light by a condenser lens 12, and reach a light receiving element 13 for LD (semiconductor laser) power monitoring.

Therefore, if the semiconductor laser 1 is driven so that the output of the light receiving element 13 is constant, the output power of the semiconductor laser 1 is always constant, and the power of the disk 6 surface is also controlled to a constant value. .

As explained in detail above, in the optical pickup device of the present invention, there is a (λ/4)×n (n=1 to n
A retardation plate (an integer of It detects fluctuations in light output and controls the emitted light to maintain it at a constant level.

[0035]

[Embodiment 2] Next, another embodiment of the present invention will be described. This embodiment corresponds to the invention of claim 2.

FIG. 2 is a diagram illustrating the rotation state of the polarization direction when the retardation plate 11 is a λ/2 plate in the optical pickup device of the present invention. 2) is the light after passing through the λ/2 plate, (3) is the light transmitted through the polarizing beam splitter 3, and (4) is the light reflected from the polarizing beam splitter 3. The horizontal axis of the figure shows the P polarized light component, the vertical axis shows the S polarized light component, and A shows the amplitude.

In FIG. 2, it is assumed that the light emitted from the semiconductor laser 1 is polarized as shown in (1). Here, the amplitude is A and the light intensity is A2. When this light passes through the λ/2 plate of the retardation plate 11, it is polarized as shown in FIG. 2(2). Here, θ is the tilt angle of the optical axis of the λ/2 plate, the amplitude is A, and the light intensity is A2.

If the optical axis of the λ/2 plate is tilted by an angle θ with respect to the polarization direction of the incident light in the optical axis direction of the λ/2 plate, then The deflection direction is tilted by 2θ.

Therefore, when this transmitted light is incident on the polarizing beam splitter 3 from the λ/2 plate, transmitted light as shown in FIG. 2(3) is obtained. That is, its amplitude is
Acos 2θ, the light intensity is A2cos2 2θ.

The light shown in FIG. 2(3)
Head to The reflected light from the disk 6 enters the polarizing beam splitter 3 again. This deflection beam splitter 3
The reflected light is polarized as shown in FIG. 2(4).

That is, the amplitude is Asin 2θ,
The light intensity is A2sin22θ. This figure 2 (4
The light shown in ) reaches the light receiving element 13 for LD power monitoring. In this way, by using a λ/2 plate as the retardation plate 11, it is possible to make the light beam of the S polarization component enter the light receiving element 13 for LD power monitoring.

If the emission of the semiconductor laser 1 is controlled so that the output of the light receiving element 13 is constant, the output power can be kept constant at all times.

[0043]

[Embodiment 3] Next, a third embodiment of the present invention will be described. This embodiment corresponds to the invention of claim 3.

FIG. 3 is a diagram illustrating the rotation state of the polarization direction when the retardation plate 11 is a λ/4 plate in the optical pickup device of the present invention. 2) is the light after passing through the λ/2 plate, (3) is the light transmitted through the polarizing beam splitter 3, and (4) is the light reflected from the polarizing beam splitter 3. The horizontal axis of the figure shows the P polarized light component, the vertical axis shows the S polarized light component, and A shows the amplitude.

Also in FIG. 3, it is assumed that the light emitted from the semiconductor laser 1 is polarized as shown in (1). Here, the amplitude is A and the light intensity is A2.

When this light passes through the λ/4 plate of the retardation plate 11, it is polarized as shown in FIG. 3(2). Here, the amplitude is A and the light intensity is A2. Also, the dashed line is λ
The fast axis and slow axis of the /4 plate are shown.

When transmitted through the λ/4 plate, this figure 3 (2)
As shown in , the transmitted light becomes elliptically polarized light whose major and minor axes are in the directions of the fast and slow axes, respectively. When this transmitted light is incident on the polarization beam splitter 3 from the λ/4 plate, the transmitted light is polarized as shown in FIG. 3(3).

That is, the amplitude is Acos θ, the light intensity is A2cos2 θ, and this light heads toward the disk 6.

When the reflected light from the disk 6 enters the deflection beam splitter 3 again, as shown in FIG. 3(4), its amplitude is A sin θ and the light intensity is A2si
n2 θ. The light shown in Figure 3 (4) is
It reaches the light receiving element 13 for power monitoring.

As already mentioned, the polarizing beam splitter 3 transmits and reflects the P-polarized light component, respectively, and almost totally reflects the S-polarized light component.

Therefore, by using a λ/4 plate as the retardation plate 11 and adjusting its mounting position, the amount of light incident on the LD power monitor light receiving element 13 can be selected to an arbitrary value.

[0052]

Effects of the Invention According to the optical pickup device of the present invention, fluctuations in the power of light emission due to return light to a light source such as a semiconductor laser, which has been a problem with write-once optical pickups, can be solved by combining the light source such as a semiconductor laser and a polarizing beam splitter. By simply arranging a retardation plate in between, it becomes possible to monitor without changing the optical characteristics of conventional optical components, and light emission can be controlled based on the output of this monitor. Therefore, even if there is returned light, stable light output can be obtained (effect corresponding to the invention of claim 1).
.

Furthermore, by using a λ/2 plate as a retardation plate, the polarization direction is rotated and it becomes possible to take out only the S-polarized component of the light beam, so that the return light for the LD power monitor is similarly Even if there is a problem, a stable optical output can be obtained (an effect corresponding to the invention of claim 2).

Furthermore, by rotating the retardation plate, it is possible to set the amount of light incident on the light receiving element for monitoring the amount of light from a light source such as a semiconductor laser to an arbitrary value, so stable light emission can be achieved. Many excellent effects such as being able to control the output (an effect corresponding to the invention of claim 3) can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating an embodiment of the configuration of essential parts of an optical system of an optical pickup device of the present invention.

FIG. 2 is a diagram illustrating the rotation state of the polarization direction when the retardation plate 11 is a λ/2 plate in the optical pickup device of the present invention.

FIG. 3 is a diagram illustrating the rotation state of the polarization direction when the retardation plate 11 is a λ/4 plate in the optical pickup device of the present invention.

FIG. 4 is a diagram showing an example of the main part configuration of an optical system based on the Foucault method in a conventional optical information recording/reproducing device.

FIG. 5 is a diagram illustrating an ideal state of an isolated optical system in an optical pickup device.

FIG. 6 is a diagram illustrating the actual state of the isolated optical system in the optical pickup device.

[Explanation of symbols]

1 Semiconductor laser 2 Collimating lens 3 Polarizing beam splitter 4 λ/4 plate 5 Objective lens 6 Disk 7 Detection lens 8 Knife edge prism 9 Focus signal detection light receiving element 10 Tracking signal detection light receiving element 11 Retardation plate 12 Condensing lens 13 LD power Monitor light receiving element 14 APC circuit

Claims (3)

[Claims] Claim 1: Light of an optical information recording and reproducing device that records, reproduces, and erases information by condensing a beam from a semiconductor laser using an objective lens and forming a minute spot on an optical information recording medium such as an optical disk. In the pickup device, a (λ/4)×n (n=an integer of 1 to n) phase difference plate disposed between the semiconductor laser and the polarizing beam splitter and reflecting (or transmitting) the polarizing beam splitter. and a light output variation detection means for receiving the laser light and detecting the output variation of the laser light, and based on the output variation of the laser light detected by the light output variation detection means, An optical pickup device characterized by controlling the optical output of a semiconductor laser. 2. The optical pickup device according to claim 1, wherein the retardation plate is a λ/2 plate. 3. The optical pickup device according to claim 1, wherein the retardation plate is provided with means for rotating the retardation plate around the optical axis of a light source such as a conductive laser.