JP4356963B2 - Optical device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a countermeasure against stray light in an optical device using a hologram.
[0002]
[Prior art]
A configuration of a simple optical device using a hologram will be described with reference to FIG. In FIG. 11, light (outward path) emitted from a light source 1 such as a semiconductor laser element passes through a collimator lens 3 and an optical component 7, and is collected by an objective lens 4 onto an information recording medium 5 such as an optical disk device. The signal light (return path) reflected (diffracted) from the information recording medium 5 passes through the objective lens 4, is reflected by the reflection surface 7 a of the optical component 7, and is condensed by the detection lens 8 on the light receiving element 6. In such an optical device, the outgoing light is reflected by the reflecting surface 7 a of the optical component 7 in the middle before being condensed on the information recording medium 5, and returns to the light source 1. Due to this stray light, the light source 1 may not be able to output stably. For this measure, various types of optical devices have been proposed as disclosed in Japanese Patent Laid-Open No. 6-36330. On the other hand, an optical system using diffraction of a hologram is often used.
[0003]
For example, a hologram unit is an example. The optical device using the hologram will be described with reference to FIG. 12. Light (outward path) emitted from the light source 1 passes through the hologram 2, the collimator lens 3, and the optical component 7, and is condensed on the information recording medium 5 by the objective lens 4. Is done. The signal light (return path) reflected (diffracted) from the information recording medium 5 passes through the objective lens 4 and the collimator lens (also serving as a detection lens) 3, is diffracted by the hologram 2, and is detected by the light receiving element 6. Such an optical device has been widely used in recent years because its shape can be easily reduced in size and can be configured at low cost.
[0004]
[Problems to be solved by the invention]
However, in an optical system using a hologram, the reflected light from the optical component of the forward light follows the same path as the signal light (return light) and enters the light receiving element. At this time, the signal light detected by the light receiving element is offset by stray light, which causes problems in various control signals. In addition, in a finite (divergent) optical device that does not use parallel light due to a collimating lens, the reflected light from the optical component diverges without condensing, so that not only stray light enters the light receiving element. , The light returns to the light source. Further, since the multiplication factor of the light receiving element also varies depending on the control signal of the optical device, there is a problem that the direction in which stray light is escaped must be limited according to the function of the optical device.
[0005]
An object of the present invention is to provide an apparatus capable of preventing signal characteristics due to stray light from being deteriorated and obtaining a signal with less noise in an optical apparatus using the hologram.
[0006]
[Means for Solving the Problems]
The present invention relates to a light source that emits a light beam, a hologram for dividing the beam into a forward path and a return path, a collimator lens that changes the numerical aperture of the beam, and an objective that focuses the beam on an information recording medium having a certain substrate thickness. In an optical apparatus having a lens and a light receiving element that is arbitrarily divided to receive a return beam, the hologram is divided into a focus error detection area by a knife edge method and a track deviation detection area with a dividing line as a boundary. An optical component is installed in the optical path of the hologram and the information recording medium, and the optical component is arranged so that stray light reflected by the surface of the optical component is incident in a direction orthogonal to the dividing line. It is characterized by being inclined.
[0007]
In one embodiment, the optical component is tilted so that stray light reflected by the surface of the optical component is incident on the focus error detection region on the hologram surface. Then, a difference signal is generated from the light diffracted in the focus error detection region on the hologram surface, a sum signal is generated from the light diffracted in the track deviation detection region , and the difference signal is divided by the sum signal. An error signal is generated.
In another embodiment, the optical component is tilted so that stray light reflected on the surface of the optical component is incident on the track deviation detection region on the hologram surface. Then, a difference signal is generated from the light diffracted in the track deviation detection area on the hologram surface, a sum signal is generated from the light diffracted in the focus error detection area , and the difference signal is divided by the sum signal to generate a track. An error signal is generated.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the optical apparatus according to the present invention will be described with reference to the illustrated example. The example shown in FIG. 1 explains the relationship between the light source 1, the hologram 2, and the light receiving element 6 in the optical apparatus as shown in FIG. As shown in FIG. 1, in the optical apparatus using the hologram 2 having an incident angle of 0 °, the hologram exit angle θ1 is set to the diffraction width p of the hologram, and is expressed by the following equation when expressed by the wavelength of light λ. I can express.
sin θ1 = mλ / pm where the distance x between the integer light source and the spot transmitted through the hologram can be expressed as follows using the distance L between the diffraction grating and the light receiving element. (X << L)
x = Lsin θ1 = L (λ / p)
In the optical apparatus using the hologram, a light receiving element is provided at this position to detect signal light.
[0009]
On the other hand, when the optical component is tilted at an arbitrary angle φ, the hologram incident angle of the light reflected by the optical component is also tilted by the angle φ. For this reason, the hologram exit angle θ2 is
sin θ2 = (mλ / p) −sin2φ (m is an integer) (Equation 1)
Thus, the reflected light from the optical component is shifted by x + Δx with respect to the light source.
x + Δx = Lsin θ 2
= L [(λ / p) −sin2φ]
= X-Lsin2φ
That is, by tilting the optical component by the angle φ, the return position of the Lsin 2φ reflected light is shifted with respect to the light receiving element, so that stray light entering the light receiving element can be reduced. Then, by tilting the hologram and the optical component in the information recording medium, the reflected return light from the optical component is tilted and stray light is reduced, so that a good signal with little noise can be obtained.
[0010]
When the optical device is a finite device configured as an optical system in which collimated lens transmission light is not parallel light but is divergent light, reflected light from the optical component diverges at the position of the light receiving element. Therefore, as shown in FIG. 2, when the optical component 7 is tilted by an angle θ1 so that the reflected light of the optical component comes to the light source side, the hologram emission angle θ becomes smaller from the above equation 1, so that at the light receiving element position. The spread of the reflected light of the optical component is small. Therefore, stray light entering the light receiving element can be reduced. That is, the stray light entering the light receiving element is reduced by tilting the hologram and the optical component in the information recording medium so that the stray light on the hologram surface becomes (light source side)> (light receiving element side). The offset to the signal can be reduced.
[0011]
Similarly, in an optical device that is a finite system, for example, when a light source such as a laser whose output light intensity is disturbed by return light is used, the optical component tilt direction is tilted at an angle θ2 toward the light receiving element as shown in FIG. Let With this configuration, since the optical component reflected light is collected on the light receiving element side with respect to the light source, stray light to the light receiving element can be reduced while suppressing the return light to the light source. That is, the stray light entering the light source is reduced by tilting the hologram and the optical components in the information recording medium so that the stray light on the hologram surface becomes (light source side) <(light receiving element side). A stable beam can be obtained.
[0012]
In general, in order to follow a minute spot on an information recording medium 5 such as an optical disc, a focus error detecting means for tracking a focal error with respect to a surface blur of the disc and tracking detection for tracking a spot on a disc groove. Means are used. In such an optical apparatus, a divided light receiving element is used as a light receiving element for signal detection. Therefore, as shown in FIG. 4, by detecting the reflected light from the optical component 7 and stray light F on the hologram 2 in a direction to go to the focus error detection side X, the tracking detection of the light receiving element 6 is detected. The stray light F1 entering the side Z can be reduced. In FIG. 4, 6-1 is a focus error detection light receiving element, and 6-2 is a tracking detection light receiving element. That is, the tracking detection light receiving element 6-2 is entered by tilting the hologram and the optical components in the information recording medium so that stray light on the hologram surface satisfies (focus error detection side)> (tracking detection side). Since the stray light is reduced, the offset to the track error signal can be reduced.
[0013]
FIG. 5 shows the hologram 2 when the knife edge method is used for the focus error detection means. In FIG. 5, areas A and B are the focus error detection side (focus error detection area), and areas C and D are the tracking detection side (track deviation detection area). Since the optical component is inclined so that the reflected light goes to the hologram focus error detection side, stray light F offset by j is formed in the regions A and B by the stray light 2j. The focus error signal FE and the track error signal TE at this time are expressed as follows.
FE = [(A + j) − (B−j)] / A + j + B + j
= (A−B) / (A + B + 2j)
TE = (C−D) / (C + D)
Here, if the signal light is adjusted so that A + B = C + D,
FE = (A−B) / (C + D)
And the effect of offset can be eliminated. By tilting the hologram and the optical component in the information recording medium so that the stray light from the optical component comes to the focus error detection side of the hologram 2 surface, a good signal with less noise can be obtained. Since the inclination angle of the optical component is reduced, the occurrence of aberrations in the optical path can be suppressed.
[0014]
This effect is particularly exerted when a differential push-pull is used for the tracking detection means. The differential push-pull method is a technique for removing a track offset by generating three spots on the surface of the information recording medium 5 and taking the difference between the track signals. In order to generate these three spots, as shown in FIG. 6, a grating 9 is arranged between the light source and the hologram, and is changed according to the diffraction efficiency of the grating 9. In this example, a focus error light receiving element 6-1 and a tracking detection light receiving element 6-2 are disposed in the light receiving element 6, and the main beam tracking detection light receiving element 6-2-1 is disposed in the light receiving element 6-2. The sub-beam tracking detection light-receiving element 6-2-2 and the sub-beam tracking detection light-receiving element 6-2-3 are arranged so that the stray light F1 is detected by each element.
[0015]
Therefore, if the ratio of main beam: sub beam (1 + 2) is k,
TE = X / Z
Here, X = C−D−k [(E−F) + (G−H)]
Z = C + D + k (E + F + G + H). At this time, if an equal amount of stray light enters each of the tracking detection light receiving elements 6-2 , the sub stray light becomes k times that of the main, and the track error signal is offset, causing a decrease in amplitude. Even in this case, as in the case of FIGS. 4 and 5 , the deterioration of the track signal due to the stray light can be prevented by inclining the optical component so that the stray light on the hologram surface approaches the focus error detection side.
[0016]
On the other hand, as shown in FIG. 7, stray light entering the focus error detection side X of the light receiving element 6 by tilting the optical component 7 in a direction in which the reflected light from the optical component 7 goes to the tracking detection side Z on the hologram 2. F can be reduced. In FIG. 7, 6-1 is a focus error detection light receiving element, and 6-2 is a tracking detection light receiving element. That is, the stray light F on the surface of the hologram 2 enters the focus error detection light receiving element by tilting the hologram and the optical components in the information recording medium so that (focus error detection side) <(tracking detection side). Since the stray light F1 is reduced, the offset to the focus error signal can be reduced.
[0017]
As in FIG. 5, the hologram 2 when the knife edge method is used for the focus error detection means is shown in FIG. In FIG. 8, areas A and B are the focus error detection side (focus error detection area), and areas C and D are the tracking detection side (track detection area). Since the optical component is tilted so that the reflected light goes to the hologram tracking detection side Z, the regions C and D are offset by i by stray light 2i. The focus error signal FE and the track error signal TE at this time are expressed as follows.
FE = (A−B) / A + B)
TE = [C + i) −D−i)] / (C + i + D−i)
= (C−D) / (C + D + 2i)
Here, if the signal light is adjusted so that A + B = C + D,
TE = (C−D) / (A + B)
And the effect of offset can be eliminated. Therefore, by tilting the hologram and the optical component in the information recording medium so that stray light from the optical component comes to the tracking detection side of the hologram surface, a good signal with less noise can be obtained, and the optical Since the inclination angle of the parts becomes small, the occurrence of aberrations in the optical path can be suppressed.
[0018]
As in the examples shown in the above embodiments, a light source that emits a light beam, a hologram that divides the beam into the forward path and the return path, and a light receiving element that is arbitrarily divided to receive the return path beam are integrated. An example of the configuration of the hologram laser unit is shown in FIG. Even in such an apparatus, it is possible to obtain a good signal by inclining the optical component as in the above-described embodiment. In addition, since the apparatus can be simplified, the degree of freedom in design increases.
[0019]
The example shown in FIG. 9 shows the configuration of the hologram laser unit 10. The unit 10 includes a light source 1 that emits a light beam, a hologram 2 for dividing the beam into a forward path and a return path, and a return beam. In order to receive light, a hologram laser 6 in which arbitrarily divided light receiving elements are integrated is provided. By using the hologram laser unit 10, the same effects as those of the above embodiments can be obtained, and the apparatus can be miniaturized. When the optical device is configured as shown in FIG. 10 using the unit 10 shown in FIG. 9, since the light source and the light receiving element are provided integrally, reflected light from the optical component is received on the light receiving element or the light source. Since it does not enter, an optical pickup with a stable signal or a stable light source output can be provided. Further, by using the optical pickup, it is possible to provide a disk drive with a stable signal.
[0020]
【The invention's effect】
According to the optical device of the present invention, it is possible to prevent deterioration of signal characteristics due to stray light and to obtain a signal with less noise. Specifically, the offset to the track error signal or the focus error signal can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a positional relationship between a light source and a light receiving element.
FIG. 2 is an explanatory diagram when optical component reflected light escapes to the light source side.
FIG. 3 is an explanatory diagram when optical component reflected light escapes to the light receiving element side.
FIG. 4 is an explanatory diagram in a case where reflected light from an optical component is released to the hologram focus error detection side.
FIG. 5 is an explanatory diagram in a case where reflected light from an optical component is escaped to the hologram focus error detection side.
FIG. 6 is an explanatory diagram in a case where reflected light from an optical component escapes to the hologram focus error detection side.
FIG. 7 is an explanatory diagram in a case where reflected light from an optical component escapes to the hologram tracking detection side.
FIG. 8 is an explanatory diagram in a case where reflected light from an optical component escapes to the hologram tracking detection side.
FIG. 9 is an explanatory diagram of a hologram laser unit.
FIG. 10 is an explanatory diagram of an optical device using a hologram laser unit.
FIG. 11 is an explanatory diagram of a conventional optical device.
FIG. 12 is an explanatory diagram of an optical device using a hologram.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Hologram 3 Collimator lens 4 Objective lens 5 Information recording medium 6 Light receiving element (divided light receiving element)
7 Optical parts 8 Grating 10 Hologram laser unit 6-1 Focus error detection light receiving element 6-2 Tracking detection light receiving element 6-2-1, 6-2-2, 6-2-3 Tracking detection light receiving element

Claims (2)

A light source that emits a light beam, a hologram that divides the beam into an outward path and a return path, a collimator lens that changes the numerical aperture of the beam, an objective lens that focuses the beam on an information recording medium having a certain substrate thickness, and a return path In an optical device having an arbitrarily divided light receiving element for receiving a beam,
The hologram is divided into two with a dividing line as a boundary between a focus error detection region by a knife edge method and a track deviation detection region,
Optical components are installed in the optical path of the hologram and the information recording medium,
The optical component is tilted so that stray light reflected by the surface of the optical component is incident on the focus error detection region on the hologram surface,
A difference signal is generated from light diffracted in the focus error detection area on the hologram surface, a sum signal is generated from light diffracted in the track deviation detection area, and the difference signal is divided by the sum signal to generate a focus error signal. Generating an optical device. A light source that emits a light beam, a hologram that divides the beam into an outward path and a return path, a collimator lens that changes the numerical aperture of the beam, an objective lens that focuses the beam on an information recording medium having a certain substrate thickness, and a return path In an optical device having an arbitrarily divided light receiving element for receiving a beam,
The hologram is divided into two with a dividing line as a boundary between a focus error detection region by a knife edge method and a track deviation detection region,
Optical components are installed in the optical path of the hologram and the information recording medium,
The optical component is tilted so that stray light reflected on the surface of the optical component is incident on the track deviation detection region on the hologram surface ,
A difference signal is generated from the light diffracted in the track deviation detection region on the hologram surface, a sum signal is generated from the light diffracted in the focus error detection region, and the difference signal is divided by the sum signal to generate a track error signal. Generating an optical device.

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