Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
2002-03-12
2004-02-24
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Modulation
C372S021000
Reexamination Certificate
active
06697395
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-074683, filed Mar. 15, 2001, 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 sum frequency light generation method and a sum frequency light generation apparatus adaptable for wide-band wavelength conversion and more particularly to a sum frequency light generation method and a sum frequency light generation apparatus for obtaining an angular frequency by summing up angular frequencies possessed by two lights projected from a pair of separate light sources.
2. Description of the Related Art
In recent years, laser lights having various kinds of angular frequencies (wavelength) depending on application purpose have been employed in respective technical fields of high density memory, optical display light source, medical instrument, color printer and the like.
The wavelength range of laser light for use has been expanding from visible lights of red, orange, green, blue and the like to ultraviolet bands.
The lights having these respective wavelengths can be generated by means of each dedicated laser light source.
However, generally, a method of converting laser light to each wavelength through a nonlinear optical crystal has been actually employed because this system can be realized at a low cost with a relatively simple configuration.
As a technology for converting the wavelength through this nonlinear optical crystal, since before, a method in which second harmonic generation is generated through a nonlinear optical crystal (hereinafter referred to as type 1 phase matching crystal) capable of matching the phase (type 1) and converted has been employed.
According to this method, basically, the angular frequency of inputted laser light is multiplied by 2 through the type 1 phase matching crystal. A first light having an angular frequency &ohgr;
1
and a second light having an angular frequency &ohgr;
2
, whose polarization directions are parallel to each other, are multiplexed through a type 1 phase matching crystal so as to convert to a light having a twofold angular frequency
2
&ohgr;
1
.
However, according to the wavelength conversion method through the type 1 phase matching crystal, if it is intended to convert two lights having each different frequency to a sum frequency generation light (SFG light) having a sum frequency of these frequencies, the first light having the angular frequency light &ohgr;
1
and the second light having the angular frequency &ohgr;
2
, whose polarization directions are parallel to each other, are inputted to the type 1 phase matching crystal.
Thus, actually, three kinds of lights each having an angular frequency
2
&ohgr;
1
,
2
&ohgr;
2
, &ohgr;
1
+&ohgr;
2
are produced.
Therefore, if the angular frequencies &ohgr;
1
and &ohgr;
2
are near each other, separation of two lights having angular frequencies
2
&ohgr;
1
and
2
&ohgr;
2
and sum frequency generation light having an angular frequency &ohgr;
1
+&ohgr;
2
becomes difficult, so that it is impossible to pick up a desired light alone, which is a problem to be solved.
Further, if looking in terms of efficiency, actual conversion efficiency for converting to the sum frequency generation light having the angular frequency &ohgr;
1
+&ohgr;
2
drops because excessive two lights having the angular frequencies
2
&ohgr;
1
and
2
&ohgr;
2
are outputted, which is another problem to be solved.
That is, the method and apparatus for generating the sum frequency generation light by wavelength conversion using the type 1 phase matching have such problems.
Thus, to solve this problem, a method of generating the sum frequency light generation using a nonlinear optical crystal (hereinafter type 2 phase matching crystal) capable of executing type 2 phase matching has been invented.
Here, the wavelength conversion based on the type 2 phase matching will be described in detail.
As described above, the wavelength conversion by type 1 phase matching multiplexes the first light having the angular frequency &ohgr;
1
and the second light having the angular frequency &ohgr;
1
, with the polarization directions thereof being parallel to each other, so as to produce the light having the angular frequency
2
&ohgr;
1
which is twofold.
Contrary to this, the wavelength conversion by type 2 phase matching multiplexes a first light having an angular frequency &ohgr;
1
and a second light having an angular frequency &ohgr;
2
, with the polarization direction thereof being perpendicular to each other, so as to produce a light having an angular frequency &ohgr;
1
+&ohgr;
2
.
Because the wavelength conversion by the type 2 phase matching is not carried out but between lights having polarization directions perpendicular to each other, even when the first light having the angular frequency &ohgr;
1
and the second light having the angular frequency &ohgr;
2
are entered, different from the wavelength conversion by the type 1 phase matching, only the light having the angular frequency &ohgr;
1
+&ohgr;
2
which is the SFG light is outputted to outside as wavelength converted light.
Further, because the wavelength conversion by the type 2 phase matching does not produce the light having the angular frequency
2
&ohgr;
1
or the light having the angular frequency
2
&ohgr;
2
, efficiency of conversion to the SFG light having the angular frequency &ohgr;
1
+&ohgr;
2
is excellent.
Thus, the wavelength conversion method which generates the SFG light using the type 2 phase matching crystal may be used for the purpose of obtaining a correlation signal between two optical signals and in recent years, an SFG light generating apparatus for that purpose has been developed.
FIG. 9
is a schematic structure diagram of a concrete apparatus based on the sum frequency light generation method using the type 2 phase matching crystal.
A first light “a” entered to an input terminal
1
from outside having a wavelength &lgr;
1
(angular frequency &ohgr;
D
) and linearly polarized, is controlled in terms of its polarization direction by a polarization direction controller
2
, so as to be directed at 90° with respect to a reference direction (0°) and after that, entered to a multiplexer
3
.
On the other hand, a second light “b” entered to an input terminal
4
from outside, having a wavelength &lgr;
2
(angular frequency &ohgr;
S
) and linearly polarized, is controlled in terms of its polarization direction by a polarization direction controller
5
, so as to be directed to, for example, the reference direction (0°) and after that, entered to the multiplexer
3
.
The multiplexer
3
composed of for example, a beam splitter and the like, reflects the first light “a” at right angle with a half mirror
3
a
while allowing the second light “b” to advance straight.
Thus, this multiplexer
3
multiplexes the entered first light “a” and the second light “b” with the polarization directions thereof being perpendicular to each other on the same optical axis.
The first light “a” and the second light “b” emitted from this multiplexer
3
with the polarization directions thereof being perpendicular to each other are entered to one face of the nonlinear optical material
6
which is cut to match with a phase matching direction corresponding to a purpose from the type 2 phase matching crystal.
This nonlinear optical material
6
emits a sum frequency light “c” having an angular frequency &ohgr;
D
+&ohgr;
D
(wavelength &lgr;
3
) which is a sum of the angular frequencies &ohgr;
D
and &ohgr;
S
possessed by each of the first light “a” and the second light “b” with the polarization directions thereof being perpendicular to each other, to an output terminal
7
from the other face.
The phase matching direction will be explained in detail hereinafter.
For the sum frequency light to be generated, the velocity (phase velocity) of each incident light within crystal of a
Kawanishi Satoki
Otani Akihito
Otsubo Toshinobu
Shake Ippei
Takara Hidehiko
Al-Nazer Leith
Anritsu Corporation
Frishauf Holtz Goodman & Chick P.C.
Ip Paul
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