JP2003303438A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the light quantity difference of the laser beams of respective wavelengths in a 2-wavelength light source type optical pickup device. <P>SOLUTION: Though the optical axis of the laser beam L1 for a CD of 780 nm emitted from a 2-wavelength light source in the 2-wavelength light source type optical pickup device coincides with a system optical axis, since the optical axis of the other laser beam L2 for a DVD of 650 nm is shifted from the system optical axis, the optical axis is adjusted by performing diffraction by an optical axis adjusting element 10. The optical axis adjusting element 10 is provided with a binary blaze grating 11, the number of the steps is 5 and the level difference h is 780/(n-1). Thus, blaze height H is 6×650/(n-1). Zero-order diffracted light L1(0) is generated by maximum efficiency for the laser beam L1 for the CD and first-order diffracted light L2(1) is generated by the maximum efficiency for the laser beam L2 for the DVD. Since the laser beam for the CD does not receive diffraction action, light quantity is hardly lost and thus the light quantity difference from the laser beam for the DVD is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wavelength light source type optical pickup device, and more specifically, an optical axis for adjusting the optical axis of each wavelength so that light of each wavelength can be received by a common photodetector. It relates to the adjusting element.

[0002]

2. Description of the Related Art As an optical pickup device, a DVD laser light source having a wavelength of 650 nm and a wavelength of 780 nm are used for recording and / or reproducing a DVD and a CD.
There is known a two-wavelength type optical pickup device equipped with a laser light source for CD. In recent years, in order to reduce the size and size of a two-wavelength light source, it has been proposed to mount a plurality of laser diodes in a single package. For example, a monolithic twin laser light source in which two laser diodes are formed on a semiconductor substrate housed in a single package is used.

In the case of a twin laser light source, since the distance between the light emitting points of both laser diodes arranged in parallel is small (about 100 μm), they are apart from each other, so that the optical axis of one laser diode is set to the system optical axis. , The optical axis of the laser beam from the other laser diode deviates from the system optical axis. As it is, the return light emitted from both laser diodes and reflected by the optical recording medium cannot be received by the common photodetector. Therefore, one of the return lights is diffracted by using an optical axis adjusting element such as a diffraction grating or a diffraction grating called an optical path combining element so that both return lights can be received by a common photodetector.

A two-source type optical pickup device provided with such an optical axis adjusting element or an optical path synthesizing element is disclosed in Japanese Patent Application Laid-Open No.
001-143312 gazette, Unexamined-Japanese-Patent No. 2001-25667.
No. 0 publication and the like.

[0005]

In the conventional dual light source type optical pickup device, the laser diode for emitting the laser light for DVD in the twin laser light source is a CD.
Since the durability is inferior to that of the laser diode that emits the laser light for DVD, the drive power of the laser diode for DVD is reduced. As a result, the amount of emitted laser light for DVD is lower than the amount of emitted laser light for CD. Therefore, the optical axis adjusting element is designed with emphasis on the efficiency of laser light for DVD. That is, the diffraction characteristics are designed so that the 0th-order diffracted light is used for the DVD laser light and the 1st-order diffracted light is used for the CD laser light. In this way, the light amount loss of the DVD laser light passing through the optical axis adjusting element is suppressed as much as possible.

An object of the present invention is to propose an optical pickup device equipped with a new optical axis adjusting element designed with attention paid to the fact that the durability of a laser diode for emitting a laser beam for DVD is improved. .

[0007]

According to the present invention, the durability of a laser diode for emitting a laser beam for DVD is improved, and C
This is done in order to solve this problem by paying attention to a new problem that occurs when the laser light for DVD, which has the same light quantity as the laser diode for D, can be used.
That is, when the DVD laser diode and the CD laser diode have similar light intensities, the numerical aperture NA of the objective lens for DVD is 0.6, while the numerical aperture NA of the objective lens for CD is 0.45. It is as small as about 0.5. Therefore, the aperture diameter of the laser light for CD is generally narrowed through the aperture stop, so that the light amount of the laser light applied to the recording surface of the optical recording medium for reproduction of the optical recording medium is the laser light for DVD. There is a new problem that the amount of light is less than that of.

According to the present invention, a DVD light source for generating light of wavelength λ1 is provided in order to make the light amounts of the CD laser light and the DVD laser light radiated as a light spot on the recording surface of the optical recording medium to be approximately the same. A light source for CD that emits light of wavelength λ2, a photodetector for receiving each return light emitted from these light sources and reflected by an optical recording medium, and each return light is received by the photodetector. In an optical pickup device having an optical axis adjusting element for adjusting the optical axis of one of the returned lights, the optical axis adjusting element is a diffractive element having a binary blazed grating, and the diffractive element is a light of wavelength λ1. On the other hand, the binary blazed grating is formed so that the 1st-order diffracted light becomes maximum and the 0th-order diffracted light becomes maximum with respect to the light of wavelength λ2.

The binary blaze-shaped (binary optics) diffraction grating has a structure in which the blaze grating surface formed on the light incident surface or the light emitting surface is stepped, and does not generate unnecessary light and diffracts light. It has the advantage of high efficiency.

In the optical pickup device of the present invention, an optical axis adjusting element having a binary blazed grating having a high diffraction efficiency is used, and the optical axis adjusting element is used to enhance the utilization efficiency of the light for CD having a small numerical aperture. Let the element pass through,
The light for DVD having a large numerical aperture is diffracted and the first-order diffracted light is used. Therefore, according to the present invention,
The light amount difference between the DVD light and the CD light due to the difference in numerical aperture can be reduced by diffracting the DVD light for adjusting the optical axis.

Here, in order to maximize the first-order diffraction efficiency for the DVD light and the zero-order diffraction efficiency for the CD light, the step height of the binary blazed grating and the refractive index of the diffraction grating are n. Then, λ2 / (n-1) may be set.

Further, the number of levels of the binary blazed lattice is D if 5x levels, where x is a positive integer.
Since the diffraction efficiency of the first-order diffracted light with respect to the VD light can be maximized, it is possible to suppress the light amount loss of the DVD light.

In practice, the number of levels of the binary blazed grating may be 5 or 10.

That is, the wavelength λ1 of the DVD light source is 65
Since the wavelength of the light source for CD is 0 nm and the wavelength λ2 of the light source for CD is 780 nm, the wavelength of the light for CD is 1.
It is double. Therefore, the blaze height of the binary blazed grating corresponding to 6 wavelengths of light for DVD corresponds to 5 wavelengths of light for CD. Therefore, if the blaze height of the binary blazed grating for the light for DVD is set to a dimension corresponding to 6 wavelengths or an integral multiple thereof, it is possible to form a binary blazed grating of 5 levels (the number of steps is 4 steps) or an integral multiple thereof. For example, the height dimension of one stage of the binary blazed grating corresponds to the dimension of one wavelength of the light for CD.

As a result, when the CD light is incident on the optical axis adjusting element in which the binary blazed grating is formed, the CD light does not have a phase difference due to the step, so that it is not substantially diffracted. To Penetrate. In other words, the 0th order diffracted light is generated with maximum efficiency. On the other hand, when the DVD light is incident, the first-order diffracted light is generated with the maximum efficiency. As described above, the 780 nm laser diode for CD is narrowed down by the aperture stop, and the light amount is reduced. But the CD
The optical axis of the light source for CD is made to coincide with the system optical axis of the optical pickup device, and the light from the light source for CD is passed through the optical axis adjusting element, so that the loss of light emitted from the light source for CD is minimized. Can be suppressed to Also, DVD
The light for use can also be diffracted and guided to the photodetector in a state where the light utilization efficiency is high.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a two-wavelength light source type optical pickup device including an optical element to which the present invention is applied will be described below with reference to the drawings.

(Optical System of Optical Pickup Device) FIG.
It is a schematic block diagram which shows the optical system of the optical pickup apparatus of this example. The optical system of the optical pickup device 1 of the present example is made into a parallel light through the two-wavelength light source 2, the half mirror 4 that reflects the laser light emitted from the light source 2 and guides it to the collimator lens 3, and the collimator lens 3. A laser beam is used as the optical recording medium 5
And a bifocal objective lens 6 for converging the light. Further, it has a photodetector 7 which receives the return light of the laser light reflected by the optical recording medium 5 via the objective lens 6, the collimator lens 3 and the half mirror 4. A diffraction grating 8 is arranged between the two-wavelength light source 2 and the half mirror 4, and the laser light from the two-wavelength light source 2 is diffracted into three beams toward the optical recording medium 5, and the photodetector 7 is An error signal is detected based on the amount of the returned light of each beam reflected by the recording medium 5.

The optical pickup device 1 of this example is for performing recording and / or reproducing of DVD and CD as the optical recording medium 5, and the two-wavelength light source 2 is, for example, D.
A laser diode that emits a laser beam with a wavelength of 650 nm for VD and a laser diode that emits a laser beam with a wavelength of 780 nm for CD are built on a common semiconductor substrate in the package. There is. Also,
The optical axis of the laser light for CD emitted from the laser diode for CD coincides with the optical axis of the system (objective lens optical axis), and the optical axis of the laser light for DVD slightly deviates from the optical axis of the system. There is.

A binary blazed grating is provided between the half mirror 4 and the photodetector 7 so that the return light of each laser beam can be received by the common photodetector 7 by adjusting the deviation of the optical axis. The optical axis adjusting element 10 is arranged. The optical axis adjusting element 10 of this example generates the 0th-order diffracted light with the maximum efficiency for the laser light of 780 nm wavelength (that is, the light component that goes straight without diffracting is maximized), and becomes the laser light of 650 nm wavelength. On the other hand, the binary blazed grating is formed so as to generate the first-order diffracted light with maximum efficiency.
By appropriately setting the diffraction direction of the first-order diffracted light, the optical axis shift of the DVD laser light can be adjusted and the return light of the laser light can be guided to the light receiving surface of the photodetector 7.

Here, in the case where the optical recording medium 5 is a DVD 51 and the case where it is a CD 52, the numerical aperture NA of the objective lens 6 for these is different due to the difference in their substrate thickness, and NA = DVD for DVD. 0.6 and NA = 0.4-0.5 for CD. Because of this, the CD
The aperture stop 9 is used to reduce the effective aperture diameter of the laser light when reproducing the data. Therefore, the light amount of the laser light for CD tends to be insufficient as compared with the light amount of the laser light for DVD.

However, in this example, the optical axis adjusting element 10 is used.
By doing so, the laser light for DVD, which tends to lack the light quantity, is diffracted, and the laser light for DVD is diffracted. Therefore, the shortage of the light quantity of the laser light for CD can be alleviated or eliminated.

(Optical Axis Adjustment Element) FIG. 2A shows a sectional shape of the optical axis adjustment element 10 of this example. Explaining with reference to this figure, a binary blazed grating 11 is formed on a light incident surface of an optical axis adjusting element 10 of this example, and a light emitting surface is a flat surface orthogonal to the optical axis. . The binary blazed grating 11 has a structure in which stair-like gratings of the same number of steps inclined in the same direction are periodically arranged on the light incident surface. In this example, five-level (four-step) step-like gratings for many cycles are arranged. Are formed (only three cycles are shown in the figure). The step height h is 780 / (n-1) (nm), where n is the refractive index of the element.

The diffraction action of the optical axis adjusting element 10 of this example will be described. Since the wavelength λ1 of the laser light for DVD is 650 nm and the wavelength λ2 of the laser light for CD is 780 nm, the wavelength of the laser light for CD is 1.2 times the wavelength of the laser light for DVD. Therefore, as shown in FIG. 2B, the blaze height H (= 6λ1 / (n−) of the binary blazed grating 11 corresponding to the six wavelengths of the DVD laser light.
1) = 6 × 650 / (n-1)) is 5 of the laser light for CD
Wavelength component (5λ2 / (n-1) = 5 × 780 / (n-
1)).

Therefore, when the step height (blaze height) H for one cycle of the binary blazed grating 11 with respect to the DVD laser light is set to a dimension corresponding to 6 wavelengths or an integral multiple thereof, the number of levels is 5 levels ( If a binary blazed grating having a number of steps of 4 steps or an integer multiple thereof is formed, the step height h for one step of the binary blazed grating 11 is C.
This corresponds to the size of one wavelength of the D laser light.

In the present example, as described above, the step height h for one step is 780 / (n-1), and the step height H for one cycle.
Is 6 × 650 / (n−1). Therefore, FIG.
As shown in (a), when the return light of the CD laser light L1 is incident on the optical axis adjusting element 10 in which the binary blazed grating 11 is formed, the CD laser light L1 does not have a phase difference due to a step, and thus is substantially The light directly passes through without being diffracted. In other words, the 0th-order diffracted light L1 (0) is generated with maximum efficiency. On the other hand, laser light L for DVD
When two lights are incident, the first-order diffracted light L2 (1) is generated with maximum efficiency.

In this example, the diffraction direction of the first-order diffracted light L2 (1) is set appropriately, so that the optical axis of the DVD laser light emitted from the two-wavelength laser light source 2 is made to coincide with the system optical axis. You can adjust it. Further, in the optical axis adjusting element 10, since the 0th-order diffracted light L1 (0) and the 1st-order diffracted light L2 (1) are set to be generated with the maximum efficiency, the utilization efficiency of the laser light of each wavelength is improved. You can

Although the level of the binary blazed grating of this example is 5 levels, the same effect can be obtained when a binary blazed grating of an integer multiple level is manufactured. It is practical to make a binary blazed lattice.

[0028]

As described above, according to the present invention, in the two-wavelength light source type optical pickup device, the light amount of the CD laser light and the DVD laser light irradiated as a light spot on the recording surface of the optical recording medium is adjusted. In order to achieve the same level, the diffraction characteristics of the optical axis adjusting element are set so that the laser return light for DVD is guided to the photodetector and the laser light for CD is passed as it is and guided to the photodetector. is doing.
Also, as an optical axis adjusting element, unnecessary light is not generated, and
A diffraction grating with a binary blazed grating with high diffraction efficiency is used.

Therefore, according to the present invention, it is possible to enhance the utilization efficiency of both laser lights and reduce or suppress the difference in the light amounts of the two laser lights due to the difference in the numerical aperture.

Further, in the present invention, the light for DVD is used.
In order to maximize the 1st-order diffraction efficiency and the 0th-order diffraction efficiency with respect to the light for CD, the step height of the binary blazed grating is assumed to be λ2 for the wavelength of the laser light for CD and n for the refractive index of the diffraction grating. , Λ2 / (n-1). Further, the number of levels of the binary blazed lattice is set to 5x level, where x is a positive integer. Therefore, according to the present invention,
0 for the CD laser light in the optical axis adjusting element
The second-order diffraction efficiency can be maximized, and at the same time, the first-order diffraction efficiency for the laser light for DVD can be maximized. Therefore, the light utilization efficiency of both lights can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an optical system of a dual wavelength light source type optical pickup device to which the present invention is applied.

2A is a sectional view showing the optical axis adjusting element of FIG. 1, and FIG. 2B is an explanatory view showing a step height and a blaze height of the binary blazed grating.

[Explanation of symbols]

1 Optical pickup device 2 2 wavelength light source 3 Collimating lens 4 half mirror 5 Optical recording media 6 Objective lens 7 Photodetector 8 diffraction grating 9 Aperture stop 10 Optical axis adjustment element 11 Binary Blazed Lattice

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D119 AA05 AA20 AA41 AA43 BA01                       BB01 BB02 BB03 DA05 EC45                       EC47 FA05 FA08 FA28 JA27                 5D789 AA05 AA20 AA41 AA43 BA01                       BB01 BB02 BB03 DA05 EC45                       EC47 FA05 FA08 FA28 JA27

Claims (4)

[Claims] 1. A light source for DVD that emits light of wavelength λ1, a light source for CD that emits light of wavelength λ2, and light for receiving each return light emitted from these light sources and reflected by an optical recording medium. In an optical pickup device having a detector and an optical axis adjusting element for adjusting the optical axis of one returning light so that each returning light is received by the photodetector, the optical axis adjusting element is a binary blaze. A diffractive element having a grating, wherein the binary blazed grating is configured such that the 1st-order diffracted light becomes maximum for light of wavelength λ1 and the 0th-order diffracted light becomes maximum for light of wavelength λ2. An optical pickup device characterized by being formed. 2. The optical pickup device according to claim 1, wherein the step height of the binary blazed grating is λ2 / (n−1), where n is the refractive index of the diffraction grating. 3. The optical pickup device according to claim 1, wherein the number of levels of the binary blazed grating is 5x, where x is a positive integer. 4. The number of levels of the binary blaze lattice according to claim 3,
An optical pickup device characterized by being 0.