Non-polarization light source device and raman amplifier
A laser light source outputs a virtually linearly-polarized light beam that has plural mode components arranged at an interval of an almost equal angular frequency. A polarization dispersion device is connected to the laser light source in such a way that a polarization axis of the polarization dispersion device is at 45° with respect to a polarization axis of the light beam output from the laser light source. This polarization dispersion device effects on the light beam output from the laser light source a polarization mode dispersion that is not in the vicinity of (2π/Δω), where Δω is a mode interval angular frequency.
1. A non-polarized light source, comprising:
a laser light source that transmits a substantially linearly-polarized light beam, the substantially linearly-polarized light beam having plural mode components arranged at an interval Δω of substantially equal angular frequency; and
a polarization dispersion device optically coupled to the laser light source in such a way that a polarization axis of the polarization dispersion device is at 45° with respect to a polarization axis of the light beam output from the laser light source, wherein the polarization dispersion device performs a polarization mode dispersion on a spectrum of frequencies of the light beam except for frequencies substantially equal to 2π/Δω.
2. The non-polarized light source according to claim 1 , wherein the laser light source is a semiconductor laser device having a Fabry-Perot optical resonator cavity.
3. The non-polarized light source according to claim 1 , further comprising a reflector provided between the laser light source and the polarization dispersion device, wherein the reflector selectively reflects a portion of the light beam output from the laser light source and forms an external resonator.
4. A non-polarized light source, comprising:
a laser light source that transmits a substantially linearly-polarized light beam, the substantially linearly-polarized light beam having plural mode components arranged at an interval Δω of substantially equal angular frequency; and
a polarization dispersion device optically coupled to the laser light source in such a way that a polarization axis of the polarization dispersion device is at 45° with respect to a polarization axis of the light beam output from the laser light source, wherein the polarization dispersion device performs a polarization mode dispersion τ such that the degree of polarization, DOP, determined by the equality
DOP
=
1
+
∑
n
=
1
∞
{
2
A
(
n
·
Δ
ω
)
2
cos
(
n
·
Δ
ω
·
τ
)
}
1
+
∑
n
=
1
∞
{
2
A
(
n
·
Δω
)
2
}
(
8
)
is less than 0.5 for a function A(ω′) of spectral form of a relative angular frequency ω′=ω−ωc of the angular frequency ω that has a mode interval angular frequency Δω and a central angular frequency ωc as criteria.
5. The non-polarized light source according to claim 4 , wherein the laser light source is a semiconductor laser device having a Fabry-Perot optical resonator cavity.
6. The non-polarized light source according to claim 4 , further comprising a reflector provided between the laser light source and the polarization dispersion device, wherein the reflector selectively reflects a portion of the light beam output from the laser light source and forms an external resonator.
7. A Raman amplifier comprising:
an optical fiber that is a Raman-amplifying medium and that carries a light signal;
the non-polarized light source according to claim 1 ; and
an injection unit that injects into the optical fiber the pump light.
8. A Raman amplifier comprising:
an optical fiber that is a Raman-amplifying medium and that carries a light signal;
the non-polarized light source according to claim 4 ; and
an injection unit that injects into the optical fiber the pump light.
9. A non-polarized light source, comprising:
a laser light source that transmits a substantially linearly-polarized light beam, the substantially linearly-polarized light beam having plural mode components arranged at an interval Δω of substantially equal angular frequency; and
a polarization dispersion device optically coupled to the laser light source such that a polarization axis of the polarization dispersion device is at substantially a 45° angle with respect to a polarization axis of the light being output from the laser light source, wherein the polarization dispersion device performs a polarization mode dispersion such that a substantially non-polarized output is obtained even when an optical path difference between the two polarization modes of the linearly-polarized light beam is less than the coherent length of the laser light source.
10. The non-polarized light source according to claim 1 , wherein the laser light source includes a semiconductor laser and a reflector which selectively reflects a portion of the light beam output from the semiconductor laser.
11. The non-polarized light source according to claim 1 , wherein the polarization dispersion device is a polarization maintaining fiber.
12. The non-polarized light source according to claim 4 , wherein the laser light source includes,
a first laser light source that outputs a first light beam, a second laser light source that outputs a second light beam, and a polarization combining unit that polarization combines the first light beam and the second light beam.