Optics: measuring and testing – By light interference – Having polarization
Reexamination Certificate
2001-12-21
2004-02-24
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
Having polarization
C356S453000
Reexamination Certificate
active
06697160
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-402120, filed Dec. 28, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light wavelength measuring apparatus that uses a two-beam interferometer and a measuring method therefor. Particularly, the present invention relates to a light wavelength measuring apparatus that measures a wavelength of an incident light to be measured by using a two-beam interferometer, wherein the wavelength of the subject light is measured with high speed and a method therefor.
2. Description of the Related Art
FIG. 22A
shows a configuration of a principal portion of a prior-art light wavelength measuring apparatus which uses a two-beam interferometer, which is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-279824.
FIGS. 22B and 22C
show waveforms of a reference light R and a subject light S coming out of a beam splitter
1102
in FIG.
22
A.
Specifically, a light wavelength measuring apparatus
1101
as shown in
FIG. 22A
is mainly configured by a two-beam interferometer which comprises: a beam splitter
1102
disposed on an optical path to which a subject light and a reference light having a known wavelength are incident; a fixed mirror
1103
serving as a reflection optical system disposed on an optical path of one of the two beams split by the beam splitter
1102
; and a movable mirror
1104
serving as another reflection optical system disposed on an optical path of the other of the two beams split by the beam splitter
1102
.
According to the light wavelength measuring apparatus
1101
which uses the two-beam interferometer of the above configuration, the subject light, and the reference light having a known wavelength are introduced into the beam splitter
1102
. The beam splitter
1102
splits each of the lights for reflection by the fixed mirror
1103
and the movable mirror
1104
.
Then, the beams incident on the fixed mirror
1103
and the movable mirror
1104
are reflected back to the beam splitter
1102
, combined together by the beam splitter
1102
into respective single beams, and then come out as the reference light R and the subject light S.
In the above, the movable mirror
1104
is moved by a predetermined distance. This causes, as shown in
FIGS. 22B and 22C
respectively, a power shift or a shift of sine wave in each of the reference light R and the subject light S that are combined and come out by the beam splitter
1102
.
In the above, assuming that an optical path difference between the reference light R and the subject light S (a difference in distance between the two optical paths from the point of splitting by the beam splitter
1102
to the combining thereby) is x, an index of refraction is n, and a wavelength of the incident light is &lgr;, there is generated an interference light component of cos (nx/&lgr;) in the combined light power.
In order to obtain the wavelength of the subject light, as shown in
FIG. 23
, a calculation is performed to obtain a wave number k which crosses a reference level L in the combined light power, for each of the reference light R and the subject light S.
Then, calculating means (not shown) calculates the wavelength &lgr; of the subject light, based on a ratio of the wave numbers in the reference light R and the subject light S, and on a value of the known wavelength of the reference light as follows:
nx=k·&lgr;
&lgr;=nx/k
The result of the calculation is outputted.
According to the light wavelength measuring apparatus
1101
which uses the conventional two-beam interferometer as described above, in order to obtain the wavelength of the subject light, it is necessary to move the movable mirror
1104
by a predetermined distance and to obtain the wave number ratio of the interference fringe between the reference light and the subject light. For this reason, it is only after the movable mirror
1104
has been moved that the measurement result can be obtained.
Therefore, according to the light wavelength measuring apparatus
1101
which uses the conventional two-beam interferometer, a certain time must be used for moving the movable mirror
1104
. This poses a problem that it is impossible to shorten a measuring time.
Now, the sine curve shift in the output beam power from the two-beam interferometer occurs not only when the movable mirror
1104
is moved but also when there is a change in the wavelength of the incident light, as shown in FIG.
24
.
This relationship can be utilized in order to improve the light wavelength measuring apparatus
1101
which uses the conventional two-beam interferometer, thereby achieving a reduction in the measuring time. Specifically, the movable mirror
1104
is fixed, and change in the interference light power caused by the wavelength change in the incident light is detected, so that an amount of change in the wavelength of the incident light can be measured.
However, as shown in
FIG. 24
, at a point A on the wavelength, the power decreases in each of the case where the wavelength changes in the short wavelength direction and the case where the wavelength changes in the long wavelength direction.
On the contrary, at a point B on the wavelength, the power increases in each of the case where the wavelength changes in the short wavelength direction and the case where the wavelength changes in the long wavelength direction.
As a result, according to the attempt for the improvement described above, when detecting the power change in the interference beam, associating with the wavelength change of the incident light, it is impossible to know in which direction the wavelength is changed to increase or decrease the wavelength. This poses a problem that the amount of wavelength change in the incident light cannot be measured accurately.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration to the problems described above, and it is therefore an object of the present invention to provide a light wavelength measuring apparatus capable of performing a quick measurement of the wavelength of the subject light, by using a two-beam interferometer which does not require the movement of the movable mirror when measuring the amount wavelength change of the incident light, is capable of properly measuring the amount of wavelength change of the incident light through real-time measurement of how much and in which of the increasing or decreasing directions the wavelength has changed.
Another object of the present invention is to provide a light wavelength measuring apparatus and a method therefor, capable of solving various problems in the course of achieving the above object.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a light wavelength measuring apparatus comprising:
a two-beam interferometer which splits an incident light in two optical paths, combines and outputs split lights together again, the two-beam interferometer being configured to generate at least one or more combined light made from two beams having polarization states different from each other;
a polarization state detector which detects a variation in the polarization state of the combined light generated by the two-beam interferometer; and
an electric circuit which calculates a wavelength of the incident light based on the variation in the polarization state of the combined light detected by the polarization state detector,
wherein a difference in length between the two optical paths of the two-beam interferometer of a point of splitting the incident light and a point of combining the split lights is fixed, for a detection of polarization variation in the combined light according to a wavelength variation of the incident light by the polarization state detector.
Further, according to a second aspect of the present invention, there is provided the light wavelength measu
Anritsu Corporation
Font Frank G.
Frishauf Holtz Goodman & Chick P.C.
Lee Andrew H.
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