Device, light source device, and imaging apparatus using the same
A device includes a first resonating cavity and a second resonating cavity. The first resonating cavity includes a first end surface and a second end surface. The first resonating cavity has a first free spectral range. The first free spectral range is a first frequency of a wavelength dependent ripple in a gain of the device that is a function of a first distance between the first end surface and the second end surface. The second resonating cavity includes a third end surface and a fourth end surface. A second distance between the third end surface and the fourth end surface is set such that an amplitude of the wavelength dependent ripple is reduced.
1. A device comprising:
an optical resonator including an optical gain medium and an optical member which allows light to pass therethrough:
a first Fabry-Pérot resonator constructed by an end and another end of the optical gain medium; and
a second Fabry-Pérot resonator constructed by the another end of the optical gain medium and an end of the optical member facing the another end of the optical gain medium,
wherein the first Fabry-Pérot resonator provides a first ripple to an oscillation spectrum of the optical resonator,
wherein the second Fabry-Pérot resonator provides a second ripple to the oscillation spectrum of the optical resonator,
wherein a resonator length of the second Fabry-Pérot resonator is set such that an amplitude of a sum of the first ripple and the second ripple is smaller than an amplitude of the first ripple at least at one of wavelengths in an amplification frequency band of the optical gain medium, and
wherein another end of the optical member has an anti reflection coating.
2. The device according to claim 1 , wherein the optical gain medium and the optical member are arranged adjacent to each other.
3. The device according to claim 1 , wherein assuming that at least one frequency in the gain band of the optical gain medium is represented by ν 0 , a length of the first Fabry-Pérot resonator is represented by L 1 , an integer is represented by n, and the speed of light is represented by c, a length L′ of the second Fabry-Pérot resonator satisfies the following expression
L
′
=
L
1
×
v
0
v
0
±
(
n
+
1
2
)
×
c
2
L
1
,
where assuming that a width of the amplification frequency band is represented by ν G , n satisfies the following expression
-
1
2
(
v
0
2
v
G
-
1
)
≤
n
≤
1
2
(
v
0
2
v
G
-
1
)
.
4. The device according to claim 1 , wherein the optical member is formed of a second optical gain medium.
5. The device according to claim 4 , wherein assuming that a length of the first Fabry-Pérot resonator is represented by L 1 , a length of the second Fabry-Pérot resonator is represented by L′, and a length of a third Fabry-Pérot resonator defined by an end surface of the second optical gain medium and another end surface of the second optical gain medium is represented by L 2 ,
the first optical gain medium and the second optical gain medium having amplification frequency bandwidths in which at least some of the frequencies overlap, and assuming that an overall amplification frequency band for the first optical gain medium and the second optical gain medium has a low-frequency end ν GS and a high-frequency end ν GE , L 1 , L′, and L 2 satisfy the following two expressions
v
GS
≤
c
4
L
1
×
L
′
L
1
-
L
′
≤
v
GE
v
GS
≤
c
4
L
2
×
L
′
L
2
-
L
′
≤
v
GE
.
6. An optical coherence tomographic imaging apparatus comprising:
a light source unit that uses the device according to claim 1 ;
a specimen measurement unit that irradiates a specimen with light from the light source unit and that transmits reflected light from the specimen;
a reference unit that irradiates a reference mirror with light from the light source unit and that transmits reflected light from the reference mirror;
an interference unit that causes the reflected light from the specimen measurement unit and the reflected light from the reference unit to interfere with each other;
an optical detection unit that detects interference light from the interference unit; and
an image processing unit that obtains a tomographic image of the specimen on the basis of the light detected by the optical detection unit.
7. The device according to claim 1 , wherein the anti reflection coating is wedged.