Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1998-08-04
2001-03-13
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S216000, C359S719000
Reexamination Certificate
active
06201229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light intensity converter capable of converting the light intensity distribution of an incident light and emitting the converted light. The present invention also relates to an optical device and an optical disk drive using such a light intensity converter.
The present invention provides an optical element in which a laser beam having a light intensity distribution in the direction perpendicular to the optical axis is converted into a laser beam having a uniform wavefront intensity in a given aperture and the transmission wavefront aberration (RMS) is reduced to 0.07 &lgr; or less, thereby making is possible to improve the beam diameter and the beam shape in a laser beam processing system, a microscope optical system and an information recording medium optical system, used in various fields.
2. Description of the Related Art
The conventional method of changing the beam intensity distribution uses a diffraction grating with the diffraction efficiency changed from one position to another, a concentration filter having a transmission distribution inversely proportional to the intensity distribution, and a slit for taking out an area of small beam intensity distribution. Various other methods have also been proposed, including a method for superposing laser beams by a half mirror or the like, a method for generating a secondary light source by a diffraction grating or the like, a method for replacing inner and outer intensity distributions with each other by refraction through a prism or the like, and a method for utilizing a blooming of a zoom lens.
Japanese Unexamined Patent Publications No. 3-75612 and No. 3-92815, for example, disclose a method for converting an incident light having a Gaussian intensity distribution into an exiting light having a substantially uniform intensity distribution, using first and second lens groups lenses with each group including two lenses.
The above-mentioned methods using the diffraction grating, the concentration filter or the slit cannot basically attain the light utilization rate of 100% and are always accompanied by an optical loss. Also, the method of superposing laser beams and the method of generating a secondary light source cause a wavefront aberration and cannot reduce the laser beam to the limit of diffraction.
In the method using refraction, on the other hand, the light paths are crossed on inner and outer sides, so the light paths are different and a wavefront aberration is developed. Also, the method using the zoom lens attains a uniform intensity at the sacrifice of an increased wavefront aberration. The conventional technologies described in JP-A-3-75612 and JP-A-3-92815 use at least four lenses while retaining the zooming function.
In the prior art, therefore, emphasis is placed on securing a predetermined intensity distribution of a beam spot rather than reducing the beam spot size. The above-mentioned methods could be used for a laser machining equipment or the like for which a spot size of about several &mgr;m is allowable and the light amount loss poses no problem. The above-mentioned methods, however, cannot be used for an optical system including a low-output light source for reading data from an information recording medium because of the wavefront aberration and the light utilization rate.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a light intensity converter having a small thickness and a simple configuration capable of emerging a light beam while changing the light intensity distribution, and an optical device and an optical disk drive using such a light intensity converter.
A light intensity converter according to the present invention comprises a body having a center axis, a first curved surface extending transversely to the center axis, a second curved surface extending transversely to the center axis, and an outer peripheral surface extending between the first curved surface and the second curved surface, and wherein said body is constructed such that a light having first light intensity distribution is made incident to said body at said first curved surface, the incident light diverges in a first area in said body and converges in a second area in the body, by refraction, when the light enters said body from said first curved surface, and the light emerges from said body at said second curved surface, the emerging light having a second light intensity distribution different from said first light intensity distribution.
This light intensity converter can be formed as a thin body and can positively convert the light intensity distribution of the incident light into a uniform light intensity distribution.
Preferably, the incident light entering from the first curved surface diverges in the central area around the center axis of the body and converges at the peripheral area in the body.
Preferably, the amount of inclination of the outermost peripheral portion of the first and second curved surfaces and the amount of inclination at a point where the inclination changes from ascendance to descendance or from descendance to ascendance have opposite signs and substantially the same absolute value.
Preferably, the thickness of the body is such that the RMS value of wavefront aberration of the exiting light with respect to the incident light is not more than 0.07 &lgr;.
Preferably, the shape of the first and second curved surfaces of said body is determined in the following manner, where a light ray is made incident to the body at an incident point (A) with a first distance (r
1
) from the optical axis and emerges from body at an exit point (B), with the second distance (r
2
) from the optical axis:
the second distance (r
2
) is determined by dividing the amount P
1
of the light existing in the range from the optical axis to said first distance (r
1
) by the intensity I which is obtained by dividing the total amount of the incident light by a predetermined area of the emerging light;
the linear distance between the incident point (A) and the exit point (B) is hypothetically given thereby to determine the direction of deflection of the light ray passing through the incident point (A);
the inclinations of the planes passing through the incident point (A) and the exit point (B) are determined according to the law of refraction;
the inclinations of the planes passing through the incident point (A) and the exit point (B) thus determined are integrated by the radial distance from said center axis thereby to determine the curved surfaces on the incident and exit sides;
the curved surface on the exit side is determined from the curved surface on the incident side, the direction of deflection at each arbitrary distance (r
1
) and the hypothetically-determined distance (L);
the distance (L) associated with each arbitrary distance (r
1
) is changed in such a manner that the curved surface on the exit side determined by integration coincides with the curved surface on the exit side determined from the incident surface; and
the inclinations of the incident and exit surfaces are determined repeatedly so as to converge the distance (L).
According to the present invention, there is further provided an optical device and an optical disk drive, using the above-mentioned light intensity converter.
REFERENCES:
patent: 5467335 (1995-11-01), Braat
patent: 5553174 (1996-09-01), Snyder
patent: 5898167 (1999-04-01), Musha et al.
patent: 4212892A1 (1992-04-01), None
patent: 0455249A2 (1991-11-01), None
patent: 3-75612 (1991-03-01), None
patent: 3-92815 (1991-04-01), None
patent: 6-223401 (1994-08-01), None
patent: 2900648 (1999-03-01), None
Hasegawa Shin-ya
Tawa Fumihiro
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Le Que T.
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