JPH03173942A - Focusing mechanism and optical head - Google Patents

Abstract

PURPOSE:To attain high speed access by providing a lens including a face of diffraction grating structure, a light source whose oscillating wavelength is varied, and an actuator moving the light source in the optical axis direction. CONSTITUTION:A micro Fresnel lens 102 is formed to the face of a lens 101 and parameters such as curvature and refractive index of the face of the lens 101 including the lens 102 are selected so that the divergence light from a wavelength variable semiconductor laser 103A is made converged to a spot 104A. A laser 103A is moved to the position 103B on the optical axis 106 and the oscillating wavelength is made longer to move the spot to the point 104B thereby suppressing the caused aberration. The laser 103A is moved by using an electromagnetic or piezoelectric actuator 105. Thus, the image spot is moved over a wide range while fixing the lens, and suppressing the caused aberration to attain high speed access, thereby allowing the head to trace a large surface waver of a recording medium.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a focusing mechanism that moves the image point of a lens in the optical axis direction while keeping it fixed, and a structure of an optical head that performs focusing using this focusing mechanism. Regarding.

[Prior Art] Conventionally, in order to move the image point of a lens in the optical axis direction, mechanical means for moving the lens in the optical axis direction using an actuator or the like has been used.

Also, in an optical head for recording and reproducing information using light, an objective lens 1 is used as shown in FIG.
302 is moved in the focus direction F by a lens actuator 1303 consisting of a magnet and a coil, and the image point 60 is moved.
6 was focused on the recording medium 607.

The optical head shown in FIG. 13 has a configuration aimed at high-speed access, including a semiconductor laser 13f0, a collimator lens 201, a beam splitter 601... lens 6
08. The housing 13 is fixed to the chassis of the optical memory device without mounting the photodiode 609 on the access means.
04, a mirror 603, an objective lens 1302,
Only the lens actuator 1303 is assembled in a housing 1305 that can be moved by a voice coil motor. arrow 61
4 indicates the moving direction of the movable housing 1305.

The lens actuator 1303 moves the objective lens 1302 in the focus direction F and in the cross-track direction T according to the focusing error signal or tracking error signal obtained from the photodiode 609, and moves the objective lens 1302 to the image point 6.
06 to a desired position on the recording medium 607.

[Problem H to be solved by the invention] However, in the conventional focusing 8N structure, especially in the focusing mechanism of an optical head, the lens actuator for moving the lens in the optical axis direction is large and heavy, and is difficult to access because it consists of a magnet and a coil. At times, the weight that must be moved by the voice coil motor becomes heavy, making it impossible to speed up access.

Therefore, the present invention aims to solve these problems.
The purpose is to provide a focusing mechanism that can move the image point over a wide range while maintaining a good point image while keeping the lens fixed, and an optical head that allows high-speed access using the focusing mechanism. It's there.

[Means for Solving the Problems] The first focusing mechanism of the present invention uses a diffraction grating jj
It is characterized by comprising a lens including a surface made of a d-shaped structure, a light source whose oscillation wavelength is variable, and an actuator that moves the light source in the optical axis direction.

The second focusing mechanism of the present invention is characterized in that a condensing point where the emitted light from the light source is condensed by the lens is movable in the optical axis direction with respect to the lens including the surface made of the diffraction grating structure. Features.

A third focusing mechanism of the present invention is characterized in that the light source includes a plurality of light sources, each of the plurality of light sources having a different center wavelength and a variable oscillation wavelength.

In the fourth focusing mechanism of the present invention, the plurality of light sources are arranged on the same substrate in a direction perpendicular to the optical axis,
The substrate is characterized in that it is movable in a direction perpendicular to the optical axis.

An optical head of the present invention is characterized in that it includes any one of the focusing mechanisms described above.

[Operation] In a lens that focuses the diverging light emitted from a point light source onto a certain image point on the optical axis, if the point light source is moved in the optical axis direction, the position of the image point also moves on the optical axis. , the sign of the spherical aberration that occurs also changes depending on the moving direction of the image point.

On the other hand, lenses with diffraction grating structures such as micro Fresnel lenses and hologram lenses have diffraction angles that change depending on the wavelength, and can move the position of the image point by changing the wavelength. The sign of the chromatic aberration changes.

Therefore, in a lens that includes a surface made of a diffraction grating structure and focuses light from a point light source onto a certain image point, the position of the point light source is moved in the optical axis direction, and the point light source is By changing the wavelength of
Focusing 1141 allows the image point to be moved over a wide range on the optical axis while maintaining a good point image.
ji4 can be configured.

An example of the effect of aberration correction will be shown using FIG. 9.

FIG. 9 is a sectional view.

Micro Fresnel lens 90 on the surface of glass substrate 902
3 is formed, and this micro Fresnel lens 90
3, the divergent light from the point light source 901 on the optical axis 106 is focused at the image point 9.
04.

The specifications are shown below.

Glass substrate thickness t=2mm refractive index
na = 1.517 Atsube number yn = 64.2 Point light source, distance between micro Fresnel lens a = 4 mm Glass, image point pressure Hb = 4 mm Micro Fresnel lens radius approximately 2 mm Design wavelength
λs=830 nm Under such a reference arrangement, the wavelength of the point light 'FA901 is kept fixed, and the point light source 901 is moved in the optical axis direction to move the image point 904 (paraxial image point in this case). FIG. 10 shows the lateral aberration that occurs in this case.

The horizontal axis is the incident height R of the light beam to the micro Fresnel lens 903, and since the micro Fresnel lens is axially symmetrical, only the radial direction is shown. The outermost circumference of the lens is 1. 0
It's Toshide. The vertical axis is the lateral aberration y.

FIG. 10(a) Movement amount of point light source 901 -58 μm Image point 904
Amount of movement of -0.1mm Fig. 10(b) Amount of movement of point light source 901 +55μm Image point 904
Amount of movement +Q, 1 mm FIG. 11 shows the lateral aberration that occurs when, conversely, the wavelength of the point light source is changed and the image point 904 is moved while the position of the point light source 901 is fixed.

Fig. 11(a) Amount of change in wavelength +e, SNM image point 904
Movement amount -0.1mm Figure 11(b) Change in wavelength ffi -6, Snm image point 9
04 movement amount +0.1 mm FIG. 12 shows the lateral aberration caused by the focusing mechanism of the present invention, that is, by changing the oscillation wavelength as well as the position of the point light source.

FIG. 12(a) Amount of movement of point light source 901 - 19 μm Amount of change in wavelength +4, Amount of movement of SNM image point 904 -
0.1 mm FIG. 12(b) Movement amount of point light source 901 +17 μm Change in wavelength fi −4.5 nm Movement fi of image point 904 +0.1 mm From the comparison from FIG. 10 to FIG. By using a combination of moving the position of the light source relative to the lens and changing the wavelength of the light source, aberrations that occur over a wider range of image point movement can be reduced compared to moving the image point by moving the light source alone or changing the wavelength of the light source alone. It can be seen that it is possible to suppress the

A semiconductor laser can be used as a point light source.

The point light source can be moved by moving the semiconductor laser with an actuator, or as shown in FIG. 2, the emitted light from the semiconductor laser 103 is once collimated and focused again by the condensing lens 202 to create an image. Point light source 203
, the lens 202 is moved by the actuator 206 (
207) to move the position of the point light source 203.

The tunable range of the oscillation wavelength of a semiconductor laser is limited, and if a wide wavelength tunable range is required, it is possible to widen the wavelength tunable range of the light source by switching and using multiple semiconductor lasers with different center wavelengths. .

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1 FIG. 1 is a main sectional view showing a first example of the focusing mechanism of the present invention.

A micro Fresnel lens 1 is provided on one surface of the lens 101.
02 is formed. Micro Fresnel lens 102
Parameters such as the curvature and refractive index of the surface of the lens 101 including the lens 101 are designed to converge the diverging light from the wavelength tunable semiconductor laser 103A to the image point 104A.

In such an arrangement, by moving the wavelength tunable semiconductor laser along the optical axis 106 to the position 103B and lengthening the oscillation wavelength, the image point is moved to the position 104B as explained in the operation section. At the same time, it is possible to suppress aberrations that occur at that time.

Tunable wavelength semiconductor lasers include those with a structure in which the wavelength control region is monolithically integrated with the light emitting region, those with a structure that controls a diffraction grating or mirror provided outside the semiconductor laser chip, and those with a structure that controls the injection current or temperature of the laser. It is possible to use an F14 type control device. Further, the light source is not limited to a semiconductor laser, and any light source whose wavelength is variable may be used.

As the lens 101, a combination lens consisting of a plurality of lenses, an aspherical surface, a lens including a refractive index distribution, etc. can be used.

The lens having a diffraction grating structure is not limited to a micro Fresnel lens, but a hologram lens, a zone plate, etc. can be used, and it may also be formed on the spherical surface of the lens.

The wavelength tunable semiconductor laser is moved by an actuator 105.
It is done by As the actuator 105, an electromagnetic type consisting of a magnet and a coil, or a piezoelectric actuator can be used. Embodiment 2 FIG. 2 is a main sectional view showing a second embodiment of the focusing mechanism of the present invention.

Emitted light from the wavelength tunable semiconductor laser 103 is made into parallel light by a collimator lens 201, and then once condensed by a condenser lens 202, and then becomes diverging light again and enters a lens 204 including a micro Fresnel lens 205. An image is formed at an image point 104.

The first image point focused by the condenser lens 202 is the lens 20
4 becomes a point light source 203.

The point light source 203 is moved by moving the condensing lens 202 in the optical axis direction using the actuator 206 (207).

Embodiment 3 FIG. 3 is a main sectional view of a third embodiment of the focusing mechanism of the present invention.

The emitted light from the wavelength tunable semiconductor laser 103 is collimated by a collimator lens 201 and then condensed by a condensing lens 202 to become a point light source 203.
The light diverging from the lens 3 is made into parallel light again by the collimator lens 301, and is focused on the image point 104 by the lens 302 including the micro Fresnel lens 303.

The point light source 203 is moved by moving the condenser lens 202 in the optical axis direction using the actuator 206 (207), but focusing can also be performed by moving the collimator lens 301 in the optical axis direction.

Embodiment 4 FIG. 4 is a main sectional view of a fourth embodiment of the focusing mechanism of the present invention. Light emitted from the wavelength tunable semiconductor lasers 103a, 103b, and 103c, each having a different center wavelength, passes through a prism 401, is made into parallel light by a collimator lens 402, and is condensed by a condensing lens 202 to form a point light M.
Forms 2O3. The prism 401 has a function of converting the light from the wavelength tunable semiconductor lasers 103b and 103C so that it also follows the optical axis 106.

When the actuator 206 moves the condensing lens 202 in the optical axis direction (207), a point light J! X2O3 also moves on the optical axis 1, so the image point 104 formed by the lens 403 including the micro Fresnel lens 404 also moves on the optical axis. Tunable semiconductor lasers 103a and 103b that can oscillate the wavelength necessary to correct the aberrations that occur at this time are used.
, 103c, and correct aberrations by changing the wavelength.

81 as the center wavelength of each wavelength tunable semiconductor laser.
If you select 0nm, 830nm, 840nm, 800nm
It becomes possible to change the oscillation wavelength over about 50 nm from 850 nm to 850 nm. On the other hand, the center wavelength is 830
In the case of a single wavelength tunable semiconductor laser, the oscillation wavelength can only be changed within a range of approximately 20 nm. Therefore, by combining a plurality of wavelength tunable semiconductor lasers, a focusing mechanism (111) capable of correcting aberrations over a wide focusing range can be constructed.

The number of wavelength tunable semiconductor lasers is not limited to three.

Note that the prism 401 and the plurality of wavelength tunable semiconductor lasers 103a, 103b, 10 as used in this example
3c is placed in place of the wavelength tunable semiconductor laser 103A and the actuator 105 in the optical system as shown in FIG. Focusing is also possible by changing the distance of the wavelength tunable semiconductor laser from the lens 101 in the optical axis direction and the oscillation wavelength.

Embodiment 5 FIG. 5 is a main sectional view showing a fifth embodiment of the focusing mechanism of the present invention.

Tunable semiconductor lasers 501a and 50 with different center wavelengths
1b and 501c are arranged on the same substrate 502 in a line perpendicular to the optical axis 106.

Separately produced laser chips may be lined up and mounted, or lasers with different center wavelengths may be monolithically formed on a compound semiconductor substrate.

The substrate 502 is aligned with the optical axis 1 by the piezoelectric actuator 503.
06 in the vertical direction, a semiconductor laser capable of emitting the required wavelength is aligned with the optical axis, and oscillated at the required wavelength. In the fourth embodiment, the semiconductor lasers were switched electrically, but in this embodiment, they were switched mechanically. The configuration after the collimator lens 201 is the same as the configuration after the collimator lens 402 in FIG. 4 showing the fourth embodiment.

Note that it is also possible to arrange the plurality of light sources of this embodiment at the positions of the respective semiconductor lasers of embodiment 4 shown in FIG.

Further, a substrate 502 on which a plurality of wavelength tunable semiconductor lasers 501a, 501b, and 501c as used in this embodiment are arranged side by side can be wavelength tunable using an optical system as shown in FIG. The substrate 5.2 is placed in place of the semiconductor laser 103A and the actuator 1.5, and the substrate 5.2 is moved in a direction perpendicular to the optical axis so that the position of the selected wavelength tunable semiconductor laser coincides with the optical axis, and the oscillation wavelength is changed. Focusing is also possible by moving the substrate 502 in the optical axis direction.

Embodiment 6 FIG. 6 is a main configuration diagram showing a first embodiment of the optical head of the present invention.

The light emitted from the wavelength tunable semiconductor laser 103 passes through a collimator lens 201, a beam splitter 601, a galvanometer mirror 602, and is moved by a voice coil motor (614).
The light is reflected by a mirror 603 fixed in a housing 611 that is capable of moving, and is focused by an objective lens 604 to form an image point 606 on a recording medium 607 . Objective lens 604 includes a surface consisting of a micro Fresnel lens 605.

The wavelength tunable semiconductor laser 103 is connected to the actuator 105.
can be moved in the optical axis direction.

The reflected light containing information from the recording medium 607 is reflected by the objective lens 6.
04, after passing through the mirror 603 and galvano mirror 602,
The beam splitter 601 bends the optical path, and the lens 60
8 and enters the photodiode 609.

The photodiode 609 detects information on the recording medium, and also detects a focusing error signal indicating the deviation of the image point 606 from the recording medium surface and a tracking error signal indicating the deviation from the desired track.

The focusing error signal is generated by the wavelength tunable semiconductor laser 10.
3 and the actuator 105, and as explained in the operation section, the wavelength tunable semiconductor laser 103
is moved in the optical axis direction (612), and the oscillation wavelength is changed to move the image point 606 in the focus direction F to focus on the recording medium surface.

The tracking error signal is fed back to the galvano mirror 602, and by shaking the galvano mirror 602 by a small angle (613), the image point 606 is moved in the track transverse direction T to perform tracking.

Elements other than the mirror 603 and objective lens 604 included in the movable housing 611 are assembled into the housing 610 and fixed to the chassis of the optical memory device. Therefore, the only weights that need to be moved by the voice coil motor during access to send the image point 606 to a desired position on the recording medium are the mirror 603, the objective lens 604, and the housing 611, and a conventional lens actuator is not included. This makes it lighter and faster to access.

Embodiment 7 FIG. 7 is a main configuration diagram showing a second embodiment of the optical head of the present invention.

The light emitted from the wavelength tunable semiconductor laser 103 passes through a collimator lens 201, a beam splitter 601, and a condenser lens 20.
2 to form a point light source 203, and the collimator lens 3
It is made into parallel light by 01 and the optical path is bent by mirror 603.
An image point 606 is formed on the recording medium 607 by the objective lens 302 . Objective lens 302 includes a surface consisting of a micro Fresnel lens 303.

The reflected light containing information from the recording medium 607 is reflected by the objective lens 3.
02, after passing through the mirror 603, the beam splitter 601
The optical path of the light is bent, and the light passes through a lens 608 and enters a photodiode 609 .

The photodiode 609 detects information on the recording medium, and also detects a focusing error signal indicating the deviation of the image point 606 from the recording medium surface and a tracking error signal indicating the deviation from the desired track.

The focusing error signal is generated by the wavelength tunable semiconductor laser 10.
3 and the actuator 701, and as explained in the operation section, the wavelength tunable semiconductor laser 103
5'f! In addition to changing the oscillation wavelength, the condensing lens 202
By moving the point light source 203 in the optical axis direction (F) using the actuator 701, the image point 606 is moved in the focus direction and focused on the recording medium surface.

The tracking error signal is fed back to the actuator 701 which can also move in a direction perpendicular to the optical axis, and by moving the condenser lens 202 in the direction (T) perpendicular to the optical axis, the image point 606 is moved in the cross-track direction. and perform tracking.

Elements included in the movable housing 703 other than the mirror 603 and the objective lens 302 are assembled into the housing 702 and fixed to the chassis of the optical memory device. Therefore, the only weights that need to be moved by the voice coil motor during access to send the image point 606 to a desired position on the recording medium are the mirror 603, the objective lens 302, and the housing 703, and a conventional lens actuator is not included. This makes it lighter and faster to access.

Embodiment 8 FIG. 8 is a main configuration diagram showing a third embodiment of the optical head of the present invention.

Tunable semiconductor lasers 103a and 10 with different center wavelengths
The light emitted from 3b and 103c passes through a prism 401, is made into parallel light by a collimator lens 402, passes through a beam splitter 601, and is converted into a point light source 20 by a condensing lens 202.
3 is formed. The center wavelengths of each wavelength tunable semiconductor laser are 810 nm, 8'30 nm, and 840 nm.
If m is selected, it will be about 50nm from 800nm to 850nm.
over a range of g! The wavelength of vibration can be changed. A point light source 203 formed by the condenser lens 202 serves as a point light source for the objective lens 302. The light diverged again from the point light source 203 is made into parallel light by a collimator lens 301, reflected by a rotatable galvanometer mirror 602 and a mirror 603, and condensed onto a recording medium 607 by an objective lens 302 to form an image point 606.

The condenser lens 202 is movable in the optical axis direction by an actuator 206. Objective lens 302 includes a surface made of micro Fresnel lens 303 .

The reflected light containing information from the recording medium 607 is reflected by the objective lens 3.
02, after passing through a mirror 603, a galvanometer mirror 602, a collimator lens 301, and a condensing lens 202, the optical path is bent by a beam splitter 601, passes through a lens 608, and enters a photodiode 609.

The photodiode 609 detects information on the recording medium, and also detects a focusing error signal indicating the deviation of the image point 606 from the recording medium surface and a tracking error signal indicating the deviation from the desired track.

According to the focusing error signal, the focusing lens 202
is moved (207) in the optical axis direction by the actuator 206 to move the position of the point light source 203 with respect to the objective lens 302, and at the same time, a tunable semiconductor laser capable of emitting the required wavelength is selected and the oscillation wavelength is controlled to the required wavelength. By doing so, the image point 606 can be focused on the recording medium surface as explained in the section of the operation.

The tracking error signal is fed back to the galvano mirror 602, and by shaking the galvano mirror 602 by a small angle (613), the image point 606 is moved in the track cross direction to perform tracking.

Elements included in the movable housing 611 other than the mirror 603 and the objective lens 302 are assembled into the housing 801 and fixed to the chassis of the optical memory device. Therefore, the weights that need to be moved by the voice coil motor during access to send the image point 606 to a desired position on the recording medium are only the mirror 603, the objective lens 302, and the housing all, and the conventional lens actuator is not included. This makes it lighter and faster to access.

Although the embodiments have been described above, the present invention can be applied not only to the above embodiments but also to systems that require focusing.

[Effects of the Invention] As described above, according to the present invention, a lens made of a diffraction grating structure is used, and by combining the movement of the light source and the change in the wavelength of the light source, the lens can be fixed while suppressing the aberrations that occur. This has the effect that the image point can be moved over a wide range.

Also, is the light source +1 with multiple wavelength tunable light sources? By forming a J lens, it becomes possible to widen the range in which generated aberrations can be suppressed, and this has the effect of widening the focusing range.

Further, by applying the focusing mechanism of the present invention to an optical head, it is possible to construct an optical head that is capable of high-speed access and can follow large surface runout of a recording medium.

[Brief explanation of the drawing]

FIG. 1 is a main sectional view showing a first embodiment of a focusing 81 structure of the present invention. FIG. 2 is a main sectional view showing a second embodiment of the focusing device 01 of the present invention. FIG. 3 is a main sectional view showing a third embodiment of the focusing mechanism of the present invention. FIG. 4 is a main sectional view showing a fourth embodiment of the focusing mechanism of the present invention. FIG. 5 is a main sectional view showing a fifth embodiment of the focusing mechanism of the present invention. FIG. 6 is a main configuration diagram showing a first embodiment of the optical head of the present invention. FIG. 7 is a main configuration diagram showing a second embodiment of the optical head of the present invention. FIG. 8 is a main configuration diagram showing a third embodiment of the optical head of the present invention. FIG. 9 is a main sectional view of the optical system for explaining the function of the focusing mechanism of the present invention. 10 to 12 are lateral aberration diagrams for explaining the action of the focusing mechanism of the present invention. FIG. 13 is a main configuration diagram of an optical head showing one example of a conventional focusing mechanism and optical head. 01 102 ... 103 ... 103A, 1 0 3 a. 104... 1 04A, 105... 106... 201... Lens Micro Fresnel lens Tunable wavelength semiconductor laser 103B... Tunable semiconductor laser 103b, 103c Tunable semiconductor laser image point 104B... Image point Actuator optical axis collimator lens 202 ... 203 ... 04 205 ... 206 ... 207 ... 301 ... 302 ... 303 ... 401 ... 402 ... 403 ... 404...501 a. 5' O2 03 01 02 03 Condensing lens Point light source lens Micro Fresnel lens actuator Condensing lens Moving direction Collimator lens lens Micro Fresnel lens Prism Collimator lens lens Micro Fresnel lens 501b, 5010 Tunable semiconductor laser substrate Piezoelectric actuator Beam splitter Galvano mirror Mira 604 ... Objective lens 605 ... Micro Fresnel lens 606 ...
Image point 607... Recording medium 608... Lens 609... Photodiode 610... Housing 611... Movable housing 612... Semiconductor laser moving direction 613... Galvano mirror rotation direction 614...
Housing movement direction 701 Actuator 702 Housing 703 Movable housing 801 Housing 901 Point light source 902 Glass substrate 903 Micro Fresnel lens 904 ...
Image point 1301...Semiconductor laser 1302 1303 1304 1305...Objective lens actuator...Movable housing

Claims (5)

[Claims] (1) A focusing mechanism comprising a lens including a surface made of a diffraction grating structure, a light source whose oscillation wavelength is variable, and an actuator that moves the light source in the optical axis direction. (2) A focusing mechanism characterized in that a condensing point where the emitted light from the light source is condensed by a lens is movable in the optical axis direction with respect to the lens including a surface made of the diffraction grating structure. (3) The focusing mechanism according to claim 1 or 2, wherein the light source comprises a plurality of light sources, each of the plurality of light sources having a different center wavelength and a variable oscillation wavelength. (4) The plurality of light sources are arranged on the same substrate in a direction perpendicular to the optical axis, and the substrate is movable in the direction perpendicular to the optical axis. Focusing mechanism. (5) An optical head comprising the focusing mechanism according to any one of claims 1, 2, 3, and 4.