Apparatus for measuring slant angle of solid immersion lens

Details Apparatus for measuring slant angle of solid immersion lens Apparatus for measuring slant angle of solid immersion lens

2002-06-04

2004-02-17

Stafira, Michael P. (Department: 2877)

Optics: measuring and testing

Lens or reflective image former testing

C356S614000

Reexamination Certificate

active

06693705

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to an apparatus for measuring a slant angle in a solid immersion lens, and more particularly to, an apparatus for measuring a slant angle in a solid immersion lens capable of measuring an inclination of the solid immersion lens which is a core element in a near-field optical data storage head for storing/reading data using the immersion lens.
2. Description of the Prior Art
A focusing control unit in a near-field data storage unit using a conventional solid immersion lens obtains a focus signal by comparing the light internally totally reflected from the plane of the solid immersion lens and the intensity of the reference light. In case that the solid immersion lens is inclined against an optical axis, however, it may occur an error in detected focus signals since the location where the internally total reflection occurs is changed. Therefore, it is essential to detect whether the solid immersion lens is inclined against the optical axis and then the signal detection against the inclination and the focus signal should be detected.
FIG. 1
shows a focusing control unit in a near-field data storage head using a solid immersion lens.
Referring now to
FIG. 1
, a focusing control unit in a near-field data storage unit using an solid immersion lens includes a solid immersion lens
104
, a polarized light splitter
101
for generating a reference light
111
and a signal light
112
from an incident light
110
, a first photodetector
107
for measuring the intensity of the reference light
111
, and a second photodetector
109
for measuring the intensity of the signal light
112
totally reflected from an internal side of the solid immersion lens
104
.
Further, a first focusing lens
106
is installed between the polarized light splitter
101
and a first photodetector
107
, and a second focusing lens
108
is also installed between the polarized light splitter
101
and the second photodetector
109
. A ¼ wave plate
102
and a third focusing lens
103
are sequentially installed between the polarized light splitter
101
and the solid immersion lens
104
.
If the incident light
110
is incident to the polarized light splitter
101
, the polarized light splitter
101
generates the reference light
111
and the signal light
112
. The reference light
111
is incident to the first photodetector
107
via the first focusing lens
106
and the first photodetector
107
detects the intensity of the reference light
111
. Meanwhile, the signal light
112
is incident to the solid immersion lens
104
via the ¼ wave plate
102
and the third focusing lens
103
. The incident signal light
112
is then totally reflected within the solid immersion lens
104
and then returns to the polarized light splitter
101
via the third focusing lens
103
and the ¼ wave plate
102
. The totally reflected signal light
112
a
is incident to the second photodetector
109
via the second focusing lens
108
and the second photodetector
109
detects the intensity of the totally reflected signal light
112
a.
As such, the reference light
111
and the totally reflected signal light
112
a
are compared to produce a focus signal. At this time, the value of the focus signal can be obtained based on below mathematical equation 1:
x=p/q
  [Equation 1]
where p indicates the intensity of the reference light and q indicates the intensity of the totally reflected signal light.
However, if the solid immersion lens
104
is inclined against to the optical axis, the location of the focus is varied and it thus occurs an error in an erroneous focus signal.
SUMMARY OF THE INVENTION
The present invention is contrived to solve the above problems and an object of the present invention is to provide an apparatus for measuring a slant angle in an solid immersion lens capable of preventing generation of an error in the focus signal by statistically measuring the inclination degree of the solid immersion lens based on the bottom using the principle of an autocollimator.
In order to accomplish the above-mentioned object, an apparatus for measuring a slant angle in an solid immersion lens according to the present invention, is characterized in that it comprises an optical generating unit for generating light to be incident to a solid immersion lens made of a hemispherical shape; a focusing lens for focusing the light reflected from a reflecting face below the solid immersion lens; and a detecting means for measuring the inclination of the solid immersion lens depending on a focus of the light focused by the focusing lens.
Further, the apparatus for measuring the slant angle in the solid immersion lens further includes an optical splitter for making incident the light generated from the optical generating unit to the focusing lens and making parallel the light within the solid immersion lens.


REFERENCES:
patent: 5553052 (1996-09-01), Oono et al.
patent: 5917599 (1999-06-01), Nishikawa et al.
patent: 6292442 (2001-09-01), Kasono
patent: 6373578 (2002-04-01), Nishikawa
patent: 6606159 (2003-08-01), Hill
patent: 2002/0113958 (2002-08-01), Wilsher et al.
patent: 1052627 (2000-11-01), None
1994 American Institute of Physics, “Near-field optical data storage using a solid immersion lens”, B, D. Terris, et al., 3 pages.

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