Abstract: A time-domain or frequency domain including a sample light path between a source interface and a detector interface, a reference light path between the source interface and the detector interface, and a photonic integrated circuit, wherein the reference light path is at least partially separate from the sample light path, wherein the sample light path comprises a forward sample light path between the source interface and a sample interface, and a backward sample light path between the sample interface and the detector interface, wherein the forward sample light path and the backward sample light path are at least partially provided by the photonic integrated circuit, and wherein the photonic integrated circuit comprises an integrated sample-side polarization beam splitter arranged in the forward sample light path and the backward sample light path.

Abstract: Since the magnitude of a nonlinear effect depends on the nonlinearity coefficient of the microstructured fiber and the intensity of pump light, either the nonlinearity coefficient or the intensity of pump light are adjusted. The nonlinearity coefficient is modified by introducing a nonlinear refractive index profile that has the inverse characteristic of the intensity distribution of either the pump or the signal light. The intensity of the pump light is adjusted by an optical amplifier, an optical attenuator, or a pre-emphasizing filter under the control of a control unit. The control unit controls the intensity of the pump light based on a look-up table which is prepared in advance by experiment or calculation, or based on a function of the pump and signal wavelength.

Abstract: In an optical fiber communication system, the input power to an all-optical nonlinear device in an optical regenerator is monitored and adjusted such that the regenerator operates at an optimized operation point.

Abstract: Higher-order Raman pumping is combined with pump modulation in a Raman amplified optical communication system. First- and second-order Raman pumps are both modulated and launched in opposite direction to signals in an optical fiber. Relative timing of the pumps is controlled to optimize lateral signal power distribution along the fiber.

Abstract: A nonlinear birefringent waveguide is used for four wave mixing, wavelength conversion, Raman amplification, etc. In order to adjust the polarization of the input light to such waveguide 14, a polarization controller 10 is provided. And at the output side of the waveguide 14, a polarization beam splitter is provided. The polarization beam splitter splits one of orthogonal polarizations which is not desired to be passed through. The power of the split light is detected at photodiode 13. The detection signal of the photodiode 13 is fed back to the polarization controller 10. The polarization controller 10 controls the polarization of input light so that the power of light detected at the photodiode 13 is minimized.

Abstract: An optical fiber cable including first, second and third optical fibers connected together so that light traveling through the cable travels through the first optical fiber, then through the second optical fiber and then through the third optical fiber. The second optical fiber has a negative dispersion value. The first and third optical fibers each have a positive dispersion value. The cable optically connects together two optical repeater stations, or an optical repeater station and an end station. Lengths of the first, second and third optical fibers are set so that loss in the first, second and third optical fibers of light transmitted through the first, second and third optical fibers is compensated by Raman amplification occurring in the first, second and third optical fibers.

Abstract: In a WDM transmission system employing a plurality of short wavelength bands having great attenuation due to optical fiber transmission, an optical repeater is constructed of a first multiplexing section and a second multiplexing section. The first multiplexing section is used for wavelength-multiplexing both the excitation light from a first Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The second multiplexing section is used for wavelength-multiplexing both the excitation light from a second Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The first and second multiplexing sections are provided between the optical fibers disposed between end offices. Thus an equal and satisfactory optical SN ratio even at any band are obtained.

Abstract: All-optical polarization rotation switch is disclosed. A linearly polarized probe light is split by a polarization beam splitter (PBS) into two orthogonal linear polarization components, which are coupled with respective ends of a nonlinear optical fiber in loop configuration. A linearly polarized control pump light is launched into one direction of the fiber. The probe light component co-propagating with the control light pulse undergoes a nonlinear phase shift due to cross phase modulation (XPM). The phase shift of the light co-propagating with the control pulse thus causes a rotation of the recombined light output from the PBS. The rotation is detected by using a polarizer. Exploiting XPM instead of the nonlinear birefringence enables the use of highly nonlinear PM fiber.

Abstract: In an optical fiber communication system, the input power to an all-optical nonlinear device in an optical regenerator is monitored and adjusted such that the regenerator operates at an optimized operation point.

Abstract: A nonlinear birefringent waveguide is used for four wave mixing, wavelength conversion, Raman amplification, etc. In order to adjust the polarization of the input light to such waveguide 14, a polarization controller 10 is provided. And at the output side of the waveguide 14, a polarization beam splitter is provided. The polarization beam splitter splits one of orthogonal polarizations which is not desired to be passed through. The power of the split light is detected at photodiode 13. The detection signal of the photodiode 13 is fed back to the polarization controller 10. The polarization controller 10 controls the polarization of input light so that the power of light detected at the photodiode 13 is minimized.

Abstract: An optical fiber cable including first, second and third optical fibers connected together so that light traveling through the cable travels through the first optical fiber, then through the second optical fiber and then through the third optical fiber. The second optical fiber has a negative dispersion value. The first and third optical fibers each have a positive dispersion value. The cable optically connects together two optical repeater stations, or an optical repeater station and an end station. Lengths of the first, second and third optical fibers are set so that loss in the first, second and third optical fibers of light transmitted through the first, second and third optical fibers is compensated by Raman amplification occurring in the first, second and third optical fibers.

Abstract: An optical fiber cable including a plurality of optical fibers, each optical fiber having a characteristic value in a middle field which is larger than characteristic values in fields other than the middle field of the optical fiber. The characteristic value in a respective field is a nonlinear refractive index of the optical fiber in the field divided by an effective cross section of the optical fiber in the field. The middle field and the characteristic value in the middle field are set as a combination to suppress a nonlinear phase shift generated in light transmitted through the plurality of optical fibers.

Abstract: In a WDM transmission system employing a plurality of short wavelength bands having great attenuation due to optical fiber transmission, an optical repeater is constructed of a first multiplexing section and a second multiplexing section. The first multiplexing section is used for wavelength-multiplexing both the excitation light from a first Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The second multiplexing section is used for wavelength-multiplexing both the excitation light from a second Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The first and second multiplexing sections are provided between the optical fibers disposed between end offices. Thus an equal and satisfactory optical SN ratio even at any band are obtained.

Abstract: In a WDM transmission system employing a plurality of short wavelength bands having great attenuation due to optical fiber transmission, an optical repeater is constructed of a first multiplexing section and a second multiplexing section. The first multiplexing section is used for wavelength-multiplexing both the excitation light from a first Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The second multiplexing section is used for wavelength-multiplexing both the excitation light from a second Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The first and second multiplexing sections are provided between the optical fibers disposed between end offices. Thus an equal and satisfactory optical SN ratio even at any band are obtained.

Abstract: In an optical transmission system utilizing bi-directional Raman amplification, propagation directions and wavelengths of Raman pumps are chosen such that four-wave mixing products among the pump wavelengths are minimized in a signal wavelength region.

Abstract: Higher-order Raman pumping is combined with pump modulation in a Raman amplified optical communication system. First- and second-order Raman pumps are both modulated and launched in opposite direction to signals in an optical fiber. Relative timing of the pumps is controlled to optimize lateral signal power distribution along the fiber.

Abstract: Since the magnitude of a nonlinear effect depends on the nonlinearity coefficient of the microstructured fiber and the intensity of pump light, either the nonlinearity coefficient or the intensity of pump light are adjusted. The nonlinearity coefficient is modified by introducing a nonlinear refractive index profile that has the inverse characteristic of the intensity distribution of either the pump or the signal light. The intensity of the pump light is adjusted by an optical amplifier, an optical attenuator, or a pre-emphasizing filter under the control of a control unit. The control unit controls the intensity of the pump light based on a look-up table which is prepared in advance by experiment or calculation, or based on a function of the pump and signal wavelength.

Abstract: Different bands (C-band and L-band) are allotted respectively to an upstream optical signal and a downstream optical signal. In a transmission-path optical fiber for Raman amplification, the C-band optical signal is amplified by pumping light from a C-band pumping light source, and the L-band optical signal is amplified by pumping light from an L-band pumping light source. As a result of this configuration, the optical signals are Raman-amplified through backward pumping in both upstream and downstream directions, whereby negative effects, which could be exerted on the optical signals by forward pumping, can be avoided.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.