An optical amplifier repeater system includes an optical fiber propagating a light beam in a plurality of propagation modes and an optical amplifier repeater amplifying the light beam propagated through the optical fiber. The optical amplifier repeater includes an optical demultiplexer demultiplexing the light beam in the plurality of propagation modes propagated through the optical fiber into a plurality of single-mode light beams, an optical amplifier amplifying, by simultaneous pumping, intensities of the plurality of single-mode light beams using a light beam generated by one pumping light source, an optical multiplexer multiplexing the plurality of single-mode light beams amplified by the optical amplifier into a light beam in the plurality of propagation modes, and an optical intensity adjusting unit adjusting the intensity of each of the plurality of single-mode light beams at least one of before or after the amplification by the optical amplifier. The optical intensity adjusting unit performs the adjustment by amplifying or attenuating the optical intensity of each of the plurality of single-mode light beams in an individual optical path through which the single-mode light beam is propagated.

The present invention is directed to techniques and systems for extension of unrepeatered submarine fiber links to provide an increase in reach of unrepeatered fiber transmission. Both single channel unrepeatered systems and multiple channel unrepeatered systems can be used. The multiple channel unrepeatered systems can further employ nonlinearity compensation. The present invention is also directed to methods of signal transmission using the unrepeatered systems.

A method of providing in-line Raman amplification in an optical fiber sensing system, including the procedures of generating a probe light having a probe wavelength, transmitting the probe light into an optical fiber, generating at least one Raman pump light at a respective pump wavelength, the pump wavelength being shorter than the probe wavelength, generating at least one Raman seed light at a respective seed wavelength, the seed wavelength being between the pump and probe wavelengths, transmitting the Raman pump light into the optical fiber, transmitting the Raman seed light into the optical fiber and propagating the Raman pump light, the Raman seed light and the probe light along the optical fiber to achieve distributed Raman amplification of signal light produced by the probe light as it propagates along the optical fiber.

Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

An optical system including a transmission fiber to transmit a WDM input optical signal between first and second points; a second order forward Raman pump module positioned along a first region of the transmission fiber proximate to the first point; a first order backward Raman pump module positioned along a second region of the transmission fiber proximate to the second point, the first order backward Raman pump module is configured to generate a first pumping light along the transmission fiber to amplify the WDM input optical signal at the second region of the transmission fiber, wherein the second order forward Raman pump module is configured to generate a second pumping light along the transmission fiber to amplify the first pumping light generated by the first order backward Raman pump module, wherein the amplified first pumping light amplifies the WDM input optical signal at the first region of the transmission fiber.

An optical system including a forward and a backward Raman pump module positioned along a transmission fiber; a noise matrix computing module configured to: determine, for first gains of the optical signal, a first noise associated with the first gain of the forward Raman pump; determine, for second gains of the optical signal, a second noise associated with the second gain of the backward Raman pump module; generate a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and ii) the second noise for each second gain of the backward Raman pump module; identify a span loss of the optical signal as the optical signal is transmitted along the transmission fiber; identify a combination of a particular first gain of the forward Raman pump module and a particular second gain of the backward Raman pump module.

Embodiments of this disclosure provide a method and apparatus for establishing a transmission impairment decomposition model for a Raman amplified system and a system. The method includes: converting a Jones vector of a test signal after passing through a Raman amplified system into a Stokes vector; calculating transmission impairments to which the test signal is subjected by using the Stokes vector according to a pre-established transmission impairment decomposition model; and substituting values of the transmission impairments into the pre-established transmission impairment decomposition model to obtain a complete transmission impairment decomposition model used for estimating transmission impairments.

An optical amplifier includes a light source that generates excitation light in a wavelength band for Raman-amplifying signal light, an input unit that inputs the signal light and the excitation light to an optical fiber, and a processor connected to the light source. The processor executes a process including: acquiring a gain reduction amount of Raman amplification according to power of the signal light input to the optical fiber; determining a target gain based on the gain reduction amount acquired; judging whether a Raman gain corresponding to power of spontaneous emission light generated when the signal light is Raman-amplified in the optical fiber achieves the target gain determined; and setting power of the excitation light according to a judging result at the judging.

Systems and methods for remotely turning on and turning up a Raman amplifier are provided. In one embodiment, a method includes the step of turning on one or more Raman pumps of a Raman amplifier to a predetermined safe gain or power level. The method also includes determining an estimated loss along a fiber optic span of a link between adjacent nodes of an optical network. Responsive to the estimated loss being greater than a reach of an Optical Supervisory Channel (OSC) signal along the link, the method includes the step of adjusting the gain or power level of the one or more Raman pumps.

Disclosed are fiber amplifiers with multiple pumping sources including multiple optical sources or an optical comb source with multiple spectral lines. A comb source may include generating a plurality of evenly spaced or nearly evenly spaced spectral lines. The optical comb source may pump a fiber by propagating optical energy at the multiple spectral lines through the fiber. The comb source may cause gain in the fiber at in a band of wavelengths different from the spectral lines of the comb source. A weak signal injected into the fiber that propagates in the fiber will experience optical gain in the fiber producing an amplified signal at the wavelength within a band of wavelengths different from the comb source wavelengths. When the bandwidth of the multiple bands of gain is wide, the amplifier may be referred to as an ultra-wideband amplifier.