Wavelength converter and optical transmission system

1 . A wavelength converter comprising:

a first multiplexer that combines signal light input to the wavelength converter and wavelength-conversion excitation light;

a second multiplexer that combines the signal light and Raman excitation light;

a first nonlinear optical medium that generates wavelength-converted light of the signal light, based on a nonlinear optical effect;

a second nonlinear optical medium that amplifies the wavelength-converted light of the signal light output from the first nonlinear optical medium,

a first polarization beam splitter disposed upstream to the first nonlinear optical medium, the first polarization beam splitter performing polarization-splitting to the signal light; and

a second polarization beam splitter disposed downstream to the first nonlinear optical medium, the second polarization beam splitter performing polarization-combining to the signal light, wherein

a wavelength of the Raman excitation light is a wavelength within an amplification band that allows Raman amplification of the wavelength-converted light.

2 . The wavelength converter according to claim 1 , wherein the second nonlinear optical medium has a zero-dispersion wavelength greater than that of the first nonlinear optical medium in chromatic dispersion absolute value within wavelength bands of the signal light and the wavelength-converted light.

3 . The wavelength converter according to claim 2 , wherein the first nonlinear optical medium has a zero-dispersion wavelength that is a wavelength between wavelengths of the signal light input and the wavelength-converted light, with a chromatic dispersion absolute value of less than 3 ps/nm/km, and

the second nonlinear optical medium has a zero-dispersion wavelength that is longer than that of the first nonlinear optical medium, with a chromatic dispersion absolute value of 3 ps/nm/km or more.

4 . The wavelength converter according to claim 1 , further comprising an optical filter that is disposed upstream to the second nonlinear optical medium and rejects passage of a wavelength of the wavelength-conversion excitation light.

5 . The wavelength converter according to claim 1 , further comprising an optical filter that is disposed downstream to the second nonlinear optical medium and extracts a wavelength of the wavelength-converted light.

6 . The wavelength converter according to claim 1 , wherein the second multiplexer is disposed upstream to the first nonlinear optical medium and provides forward excitation by the Raman excitation light, or the second multiplexer is disposed downstream to the second nonlinear optical medium and provides backward excitation by the Raman excitation light, or both.

7 . The wavelength converter according to claim 1 , wherein the first nonlinear optical medium and the second nonlinear optical medium are an optical fiber or a planar optical waveguide.

8 . An optical transmission system, comprising:

a transmitting device that transmits signal light; and

a receiving device that receives the signal light via a transmission path, wherein

the transmitting device includes:

a plurality of transmitters that convert an electrical signal input thereto into a plurality of first signal light components within a first wavelength band;

a first wavelength converter that converts the plurality of first signal light components output from a portion of the plurality of transmitters, into a plurality of second signal light components within a second wavelength band; and

a multiplexer that combines the plurality of first signal light components output from the portion of the plurality of transmitters and the plurality of second signal light components output from the first wavelength converter,

the receiving device includes:

a demultiplexer that splits the signal light received from the transmission path into the plurality of first signal light components within the first wavelength band and the plurality of second signal light components within the second wavelength band;

a second wavelength converter that converts the split plurality of second signal light components within the second wavelength band into the plurality of first signal light components within the first wavelength band; and

a plurality of receivers that convert the plurality of first signal light components within the first wavelength band output from the demultiplexer and the second wavelength converter into electric signals,

the first and second wavelength converters each includes:

a first multiplexer that combines the input signal light with wavelength-conversion excitation light;

a second multiplexer that combines the signal light with Raman excitation light;

a first nonlinear optical medium that generates wavelength-converted light of the signal light, based on nonlinear optical effect; and

a second nonlinear optical medium that amplifies the wavelength-converted light of the signal light output from the first nonlinear optical medium, wherein the wavelength of the Raman excitation light is within an amplification band that allows Raman amplification of the wavelength-converted light.

9 . A wavelength converter comprising:

a first multiplexer that combines signal light input to the wavelength converter and wavelength-conversion excitation light;

a second multiplexer that combines the signal light output from the first multiplexer and Raman excitation light;

a first nonlinear optical medium that generates wavelength-converted light of the signal light output from the second multiplexer, based on a nonlinear optical effect;

a second nonlinear optical medium that amplifies the wavelength-converted light output from the first nonlinear optical medium;

a polarization beam splitter that performs polarization splitting and polarization combining of the signal light input to the wavelength converter;

a polarization controller that variably controls the polarization beam splitter; and

a polarization diversity loop circuit that is connected to the polarization beam splitter and includes the first nonlinear optical medium, wherein

a wavelength of the Raman excitation light is a wavelength within an amplification band that allows Raman amplification of the wavelength-converted light.

10 . The wavelength converter according to claim 9 , further comprising an optical filter that is disposed upstream to the second nonlinear optical medium and rejects passage of a wavelength of the wavelength-conversion excitation light.

11 . The wavelength converter according to claim 9 , further comprising an optical filter that is disposed downstream to the second nonlinear optical medium and extracts a wavelength of the wavelength-converted light.

12 . A wavelength converter comprising:

a first multiplexer that combines signal light input to the wavelength converter and wavelength-conversion excitation light;

a second multiplexer that combines the signal light output from the first multiplexer and Raman excitation light;

a first nonlinear optical medium that generates wavelength-converted light of the signal light output from the second multiplexer, based on a nonlinear optical effect; and

a second nonlinear optical medium that amplifies the wavelength-converted light output from the first nonlinear optical medium, wherein

a wavelength of the Raman excitation light is a wavelength within an amplification band that allows Raman amplification of the wavelength-converted light, and

the wavelength converter further includes an optical filter that is disposed upstream to the second nonlinear optical medium and rejects passage of a wavelength of the wavelength-conversion excitation light, or that is disposed downstream to the second nonlinear optical medium and extracts a wavelength of the wavelength-converted light.