Optical: systems and elements – Lens – With support
Reexamination Certificate
1999-08-03
2001-01-30
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C250S201500, C369S044110, C369S044210, C369S044230
Reexamination Certificate
active
06181491
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical head device for positioning an information head device when information is recorded on an information recording medium such as a high density floppy disk or an optical disk, etc., or reproducing the information recorded on the information recording medium, an information recording and reproducing apparatus, for example, a floppy disk drive, an optical disk drive, etc., provided with the aforementioned optical head device, and an optical system capable of obtaining light beam having a desired wave surface and useful for the optical head device and information recording and reproducing apparatus.
BACKGROUND OF THE INVENTION
When information is recorded on a floppy disk at high density, the positioning of an information head device in the direction perpendicular to a track is required. In this case, if the positioning of the information head device is mechanically conducted, sufficient positioning accuracy cannot be secured. Therefore, recently, the positioning of the information head device has mainly been conducted by using light beam.
Hereinafter, a conventional optical head device in which the positioning of the information head device is conducted by using a light beam will be described with reference to FIG.
20
.
As shown in
FIG. 20
, a light beam emitted from a semiconductor laser
101
serving as a light source is divided into a zero-order light beam and a ±first order diffracted light beam (±first order diffracted light beam is not shown) by a diffraction grating
152
provided on the surface of a diffraction element
150
at the side of the light source. Hereinafter, the zero-order light beam will be referred to as “the main beam” and the ±first order diffracted light beam will be referred to as “the sub-beam”.
The main beam and sub-beam pass through a diffraction grating
151
provided on the surface of the diffraction element
150
at the side of a lens
102
and are converged by the lens
102
serving as an converging optical system. The main beam and sub-beam converged by the lens
102
are limited to the desired numerical aperture NA by an aperture stop
103
and irradiate a disk
104
serving as an information recording medium. On the disk
104
, a line connecting the main beam spot and two sub-beam spots is arranged so as to have a predetermined angle with respect to a track. Moreover, the disk
104
is sandwiched by magnetic heads
201
being attached to an arm
211
and serving as the information head device, and thus the position of the disk
104
in the direction of the z-axis is regulated. Furthermore, each member of the optical system and the magnetic heads
201
are fixed in a frame
210
. Thus, the distance between the optical system and the disk
104
always remains constant (20 mm in this case).
The light beam reflected from the disk
104
passes through the aperture stop
103
and the lens
102
again, is diffracted at the diffraction grating
151
provided on the surface of the diffraction element
150
at the side of the lens
102
, and then enters the photo detectors
105
R and
105
L.
Each of the photo detector
105
R and
105
L consists of three detecting regions respectively, receives the main beam and two sub-beams separately and outputs signal in accordance with the quantity of the received light.
On the disk
104
, three beam spots irradiate the different positions in the direction perpendicular to the track. Therefore, the modulation degrees of signals obtained by the three detecting regions are different from each other. The modulation degree of signal is sequentially changed as these beam spots cross the track. Therefore, by calculating these signals, the relative position relationship between the track and the beam irradiation position can be detected.
Namely, first, an envelope detection of these signals is conducted and the obtained envelope signals are defined as M, S
1
and S
2
. Next, by using these envelope signals M, S
1
and S
2
, the calculation of A=M−S
1
and B=S
2
−M are conducted so as to generate signals A and B. By multiplying the signals A and B by an appropriate factor k
1
, tracking error signals k
1
·A and k
1
·B, which zero-cross in optional phases, are obtained. By using these tracking error signals k
1
·A and k
1
·B, the relative position relationship between the track and the beam irradiation position can be detected. Herein, the factor k
1
is initially learned so that the magnetic head
201
is positioned on the track for recording and reproducing information. Moreover, both the magnetic head
201
and the optical system move in the radius direction of the disk
104
by a moving means
203
shown in FIG.
7
.
In the above-mentioned conventional optical head device, the lens
102
having a focal length f of 10 mm is used. When the optical system of single magnification is constructed as in
FIG. 20
, the distance between the semiconductor laser
101
serving as the light source and a light converging point of the disk
104
serving as an information recording medium (the distance between an object point and an image point) is about 40 mm, and the distance L
2
between the lens
102
and a geometrical optical converging point is 20 mm. Furthermore, when the numerical aperture NA is 0.04, the radius a of the opening in which the aperture stop
103
having the opening of radius a′ is projected on the principal plane of the disk side of the lens
102
is 800 &mgr;m. Furthermore, when the wavelength &lgr; of the light beam emitted from the semiconductor laser
101
serving as the light source is 800 nm, a spot diameter d=&lgr;/NA on the disk
104
is 20 &mgr;m, and the Fresnel number N=(a×a)/(&lgr;×L
2
) is 40. In addition, the positional difference between the geometrical optical converging point and a point in which the intensity of the converged light is maximum is about 20 &mgr;m. Since the focal depth &Dgr;z that is a distance between the point in which the intensity of the converged light is maximum and the point in which the intensity of the converged light is 80% of the maximum is about 80 &mgr;m, this positional difference is substantially negligible.
However, in the above-mentioned conventional optical head device, it is necessary to increase the distance between the object point and the image point so that the positional difference between the geometrical optical converging point and the point in which the intensity of the converged light is maximum is substantially negligible. Accordingly, it is impossible to miniaturize the optical head device. Furthermore, when the distance between the object point and the image point is longer, the light beam emitted from the light source of the optical head device is susceptible to environmental changes such as change of temperature or vibration. Thus, a stable positioning of the information head device cannot be conducted.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical head device capable of stably positioning an information head device even if a distance between an object point and an image point is small so as to miniaturize the device, and an information recording and reproducing device including this optical head device and an optical system useful for the optical head device or the information recording and reproducing device.
In order to achieve the above-mentioned object, an optical head device of the present invention comprises a light source emitting a light beam, a converging optical system converging the light beam emitted from the light source to an information recording medium on which information is recorded, and a holding means maintaining a distance between the information recording medium and the converging optical system constant. The optical head device satisfies the following equations 9 and 10:
L
2
=
f×L
1
/(
L
1
−
f
) (equation 9)
h<L
2
(equation 10)
wherein f denotes a focal length of the converging optical
Kadowaki Shin-ichi
Sano Kousei
Epps Georgia
Matsushita Electric - Industrial Co., Ltd.
Rosenthal & Osha L.L.P.
Thompson Tim
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