A low-noise amplifier includes a gain medium and two or more amplifier stages. Each amplifier stage includes an optical filter to pass all wavelengths of a respective input optical signal in a given propagation direction over the gain medium and reflect wavelengths above a respective threshold wavelength received in the opposite direction, and a respective Raman pump to inject a pump light centered at a wavelength lower than the threshold wavelength onto the gain medium for transmission in the given direction. A first amplifier stage outputs a first combined optical signal including all wavelengths of the respective input optical signal and a pump light injected by the respective Raman pump. The second amplifier stage receives the first combined optical signal as its input and outputs a second combined optical signal including all wavelengths of the first combined optical signal and a pump light injected by the respective Raman pump.

The present application 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 application is also directed to methods of signal transmission using the unrepeatered systems.

The present invention is to provide a backscattered light amplification device, an optical pulse test apparatus, a backscattered light amplification method, and an optical pulse test method for amplifying a desired propagation mode of Rayleigh backscattered light with a desired gain by stimulated Raman scattering in a fiber under test having the plurality of propagation modes. The backscattered light amplification device according to the present invention is configured to control individually power, incident timing, and pulse width of a pump pulse for each propagation mode when the pump pulse is incident in a plurality of propagation modes after the probe pulse is input to the fiber under test in any propagation mode.

Disclosed are a method, device and system for dynamically controlling a gain of a Raman optical fiber amplifier. The method comprises: determining whether a target gain falls within a gain mask range; if the target gain falls within the gain mask range, directly locking a gain to the target gain; and if the target gain falls outside the gain mask range, locking the gain to a corresponding maximum gain in the gain mask range, and gradually increasing the locked gain according to a preset first step length until the target gain is reached or until at least one pump laser reaches a maximum output power. The invention enables an optical fiber amplifier to respond quickly to a change in an input optical signal, ensures gain stability, and ensures that no power overshoot or undershoot occurs in the non-switched optical channels in an optical path. Moreover, the invention minimizes an amount of time required to complete switching between gains.

An excitation light source apparatus includes: an excitation light source to generate Raman excitation light in a drive state and to stop generating the Raman excitation light in a stop state; a light source controller to control the intensity of the Raman excitation light in the drive state; a light level measuring instrument to measure the light level of signal light; a logarithmic converter to convert at least one measurement result of measuring by the light level measuring instrument to a logarithmic value; and a main controller to decide a correction value based on the logarithmic value of the at least one measurement result in the stop state. The main controller controls the light source controller by using the correction value and a preset gain control target value.

According to an aspect of an embodiment, an optical amplification system may include a broadband pump source and an optical fiber doped with phosphorus. The broadband pump source may be configured to generate a pumping beam. The pumping beam may include a pumping wavelength range between 1330 nm and 1400 nm. The optical fiber may be configured to receive the pumping beam and an input optical signal. The input optical signal may include a first component that may correspond to a first wavelength range and a second component that may correspond to a second wavelength range. The pumping beam may cause Raman amplification to the first component and the pumping beam may cause Raman amplification to the second component. The amplification of the first component and the second component by the pumping beam may produce an amplified optical signal.

Systems and methods are provided for creating a sequence of turn-up processes for amplifiers. A method, according to one implementation, includes determining when a fiber span is initially installed in an optical line system or when an Optical Line Failure (OLF) in the fiber span has recovered. The optical line system includes a first set of amplifiers deployed at an upstream node and a second set of amplifiers deployed at a downstream node, the upstream node connected to the downstream node via the fiber span. In response to determining that the fiber span is initially installed in the optical line system or that an ORL in the fiber span has recovered, the method also includes sending a flag from the upstream node to the downstream node to allow the first set of amplifiers to perform a first turn-up process before the second set of amplifiers perform a second turn-up process.

A smart spool is configured to be optically coupled between a pumping light source and optical point-loss sources in an optical fiber transmission line. The smart spool comprises a probe signal transmitter that transmits an optical probe signal into the transmission line. An optical detector receives probe signals scattered in the transmission line. A loss-measuring device is coupled to the optical detector and operable to measure aggregate losses in the transmission line and report the aggregate losses to a network manager. The spool comprises a fiber of sufficient length to offset the aggregated losses to enable a distributed Raman amplifier to pump the transmission line. The smart spool prevents the distributed Raman amplifier from shutting down and allows the distributed Raman amplifier to achieve entitled gain by pumping the fiber in the spool.

A transmission device including: a signal power detection circuit that detects signal power of a wavelength-division-multiplexed optical signal to be transmitted to a transmission line into which pumping light is inputted from a Raman amplifier; a variable optical attenuator that attenuates the wavelength-division-multiplexed optical signal; and a control circuit that reduces an attenuation amount of the variable optical attenuator depending on an increase in the signal power.

The present invention relates to a method for optimizing performance of a multi-span optical fiber network. Each span has an associated optical transmission fiber connected to an associated optical amplifier. Gain and output power of the associated optical amplifier are respectively controlled independently. An amplifier noise figure respectively depends on the gain of the associated optical amplifier, with each associated optical amplifier further connected to launch optical signals into a remainder of a corresponding optical transmission line. The method includes the steps of for each span, computing the amplifier noise figure and a non-linear noise generated in the span based on information about the span and using the computed amplifier noise figure and the computed non-linear noise to compute an optimum launch power, and optimizing performance of the multi-span optical fiber network based on the computed optimum launch powers of all spans.