Example fiber amplifiers and gain adjustment methods for the fiber amplifiers are described. One example fiber amplifier includes a first power amplifier, a wavelength level adjuster, and a controller, where the first power amplifier is connected to the wavelength level adjuster. The controller includes a first input end and a control output end. The first input end is configured to receive an input optical signal, and the control output end is configured to output a first amplification control signal to the first power amplifier, and output an adjustment control signal to the wavelength level adjuster. The wavelength level adjuster is configured to perform power adjustment on each wavelength in a separate manner based on the adjustment control signal.

A hybrid optical amplifier is proposed that includes a preamplifier element formed of single-clad Ho-doped optical fiber and a power amplifier element formed of single-clad Tm-doped (or Tm—Ho co-doped) optical fiber. The preamplifier is used to impart gain to an input signal propagating at a wavelength λ.sub.S in the presence of a first pump beam operating at λ.sub.P1, creating an amplified output over a defined transmission bandwidth. The power amplifier element is disposed at the output of the preamplifier element and provides an additional level of gain to the output of the preamplifier element in the presence of a second pump beam operating at λ.sub.P2. A passband filter may be used between the preamplifier and the power amplifier to ensure that only wavelength components within the defined transmission bandwidth are applied as an output to the power amplifier.

A multi-stage optical amplifier has an input port for receiving an optical signal and a relatively short erbium doped optical fiber is coupled to the input port. Complex costly pump feedback is not required as a constant non-varying saturation pump is configured to provide non varying output power pump light of a predetermined wavelength suitable for excitation and full saturation of the erbium ions such that a full population inversion occurs. The length of the short erbium doped fiber and rare earth doping concentration of the erbium doped fiber is such that when pumped by said pump provides amplification of the optical signal of less than 15 dB. Locating a gain flattening filter after the short erbium doped optical fiber provides a relatively flat amplified output signal. Multi-stages of similar short erbium doped fibers pumped and saturated by the same pump signal economically provide increased amplification of the signal and filters after each state flatten the gain.

The present invention relates to the field of optical communication, and particularly to a balanced pumping L-band optical fiber amplifier comprising a first erbium-doped optical fiber, a second erbium-doped optical fiber, an absorbing erbium-doped optical fiber and at least two pumping lasers, the first erbium-doped optical fiber, the second erbium-doped optical fiber and the absorbing erbium-doped optical fiber being sequentially arranged in this order, and the at least two pumping lasers providing pumping light; wherein the first erbium-doped optical fiber and the second erbium-doped optical fiber both are injected with forward pumping light and backward pumping light, and the absorbing erbium-doped fiber is arranged downstream of the second erbium-doped optical fiber to absorb amplified spontaneous emission (ASE) generated in the amplifier. In the present invention, bidirectional pumping 1s applied in the first and last erbium-doped fibers in the optical path, and an erbium-doped optical fiber that has no pumping injection is added to absorb the ASE. Thus, the pumping conversion efficiency is greatly improved, the nonlinear four-wave mixing effect is reduced, and the problem that the L-band optical fiber amplifier has a high noise when utilizing the backward pumping 1s solved. Meanwhile, the noise figure and the manufacturing cost of the amplifier are reduced.

The subject invention includes a semiconductor laser with the laser having a DBR mirror on a substrate, a quantum well on the DBR mirror, and an interior CGH with a back propagated output for emitting a large sized Gaussian and encircling high energy. The DBR mirror has a plurality of GaAs/AlGaAs layers, while the quantum well is composed of AlGaAs/InGaAs. The CGH is composed of AlGaAs.

A method for realizing precise gain control for a hybrid fibre amplifier, and a hybrid fibre amplifier, in which by an erbium-doped fibre amplifier firstly outputting a constant power, a comparable source signal optical power is provided for a raman fibre amplifier of a next stage. A feedback for the gain control may be formed by comparing a source signal optical power calculated after starting pumping of the Raman fibre amplifier and a source signal optical power detected after pumping stops, thereby greatly improving gain control precision of the Raman fibre amplifier. Moreover, the erbium-doped fibre amplifier parts of all the hybrid fibre amplifiers may simultaneously output a constant optical power, and the Raman amplifier parts of all the hybrid fibre amplifiers may simultaneously start calibration, so that the time for starting operation of the entire system may be improved greatly.

A hybrid fiber amplifier and method of adjusting gain and gain slope of thereof. The hybrid fiber amplifier comprises: RFA and EDFA that does not comprise variable optical attenuator. The RFA comprises pump signal combiner, pump laser group, out-of-band narrow-band filter, and photodetector. The EDFA comprises input coupler, erbium-doped fiber, output coupler, input photodetector, and output photodetector that are connected in sequence. The hybrid fiber amplifier also comprises control module that coordinates and controls EDFA and/or RFA to adjust gain and/or the gain slope based on desired amplification requirements. The EDFA and/or RFA can be coordinated and controlled by using the control module to achieve desired amplification effect. In addition, the EDFA does not comprise the variable optical attenuator, which avoids problems caused by the variable optical attenuator. The hybrid fiber amplifier and method of adjusting gain and gain slope thereof are applicable to technical field of optical communications.

A multi-core optical amplifying fiber device includes a plurality of multi-core optical amplifying fibers including a plurality of core portions doped with amplification medium and a cladding portion formed at outer peripheries of the plurality of core portions; and a connection portion connecting the core portions of the plurality of multi-core optical amplifying fibers to one another. The connection portion connects the core portions to restrain deviation, between every connected core portions, of amplification gain for a total length of the core portions connected one another.

The present disclosure relates to a technical field of optical communication, and provides a method and an apparatus for determining maximum gain of Raman fiber amplifier. Wherein the method includes obtaining transmission performance parameters of a current optical fiber transmission line; respectively obtaining impact factors A.sub.1, A.sub.2, A.sub.4 according to a distance between a joint and a pump source, a fiber loss coefficient, and a fiber length included in the transmission performance parameters; calculating a joint loss value Att.sub.Aeff according to a distance between a joint and a pump source, a fiber loss coefficient, and looking up impact factor A.sub.3 according to Att.sub.Aeff; determining an actual maximum gain which may actually be achieved by the Raman fiber amplifier according to A.sub.1, A.sub.2, A.sub.3, A.sub.4. The actual maximum gain obtained in the present disclosure is the maximum gain that may be achieved over all input power ranges, and the original signal in system is kept to operate at a fixed gain, such that a gain locking effect is realized, and fluctuation of existing transmission signal power caused by signal change in transmission fiber link is avoided.

A method of spectrally multiplexing diode pump modules to increase brightness includes generating one or more pump beams from respective diode lasers at a first wavelength in a diode laser package, generating one or more pump beams from respective diode lasers at a second wavelength different from the first wavelength in the diode laser package, wavelength combining at least one of the pump beams at the first wavelength with at least one of the pump beams at the second wavelength to form one or more combined pump beams, and receiving the combined pump beams in a pump fiber coupled to the diode laser package. Laser systems can include multi-wavelength pump modules and a gain fiber having a core actively doped so as to have an absorption spectrum corresponding to the multiple wavelength, the gain fiber situated to receive the pump light and to produce an output beam at an output wavelength.