An optical amplifier of the present disclosure includes an optical resonator that includes an amplification fiber capable of amplifying signal light having one or more propagation modes and resonates at least one propagation mode of the signal light amplified by the amplification fiber; an excitation light source that outputs excitation light for exciting the amplification fiber; and a multiplexer that multiplexes the signal light and the excitation light, in which the optical resonator includes a gain clamp setting unit which sets gain clamp for at least one propagation mode out of a plurality of propagation modes resonating in the optical resonator.

Techniques for improving gain equalization in C- and L-band (“C+L”) erbium-doped fiber amplifier (EDFAs) are provided. For example, the C- and L-band amplification sections of a C+L EDFA may be separated and configured in a parallel arrangement or a serial arrangement. For both the parallel and serial arrangements, the C- and L-band amplification sections may share a common gain flattening filter (GFF) or each amplification section may include and employ a separate GFF. Moreover, in some examples, an “interstage” L-band GFF may be located before or upstream of the L-band amplification section such that the L-band optical signal is gain-equalized or flattened prior to the L-band amplification section amplifying the L-band.

The technology of this application relates to the field of communication technologies, and an optical fiber raw material composition, an optical fiber, and an optical fiber product. The optical fiber raw material composition includes components of the following molar percentages: AlF.sub.3 10%-50%, BaF.sub.2 3%-20%, CaF.sub.2 3%-20%, YF.sub.3 1%-15%, SrF.sub.2 3%-20%, MgF.sub.2 3%-20%, and TeO.sub.2 1%-35%. The optical fiber prepared by using the optical fiber raw material composition provided in this disclosure can be used in aspects such as a mid-infrared band transmission optical fiber, an optical fiber amplifier, a fiber laser, and an optical fiber sensor.

An amplification fiber includes a core which is doped with an erbium ion and a cladding which surrounds the core and has a refractive index lower than a refractive index of the core, and a relative refractive index difference Δn.sub.51 between the core and the cladding is not more than a smaller one of values of a relative refractive index difference Δn.sub.1 expressed as a predetermined expression related to a radius a of the core and a relative refractive index difference Δn.sub.2 expressed as a predetermined expression related to the radius a of the core.

In some implementations, an amplifier device may include a first amplifier configured to amplify signals in a first range of optical wavelengths. The first amplifier may include a first portion that includes one or more first optical gain components, and a second portion that includes one or more second optical gain components and a variable optical attenuator. The amplifier device may include a second amplifier configured to amplify signals in a second range of optical wavelengths. The amplifier device may include a filter for the first range of optical wavelengths and the second range of optical wavelengths. The filter may be located between the first portion and the second portion of the first amplifier.

Systems and methods are provided for amplifying optical signals within one of two optical bands, such as C-band and L-band. An optical amplifying device, according to one implementation, may include a shared optical coil configured to propagate an optical signal. The optical amplifying device may further include a first junction configured to separate the shared optical coil into a first-band optical fiber and a second-band optical coil and a pump device configured to amplify the optical signal in the shared optical coil and the second-band optical coil. The first-band optical fiber may be configured to propagate the optical signal when the optical signal resides in a channel of a first plurality of channels within a first optical band. The second-band optical coil may be configured to propagate the optical signal when the optical signal resides in a channel of a second plurality of channels within a second optical band.

To limit the number of excitation laser diodes (LDs) in an optical amplification device provided with a redundant excitation LD configuration, the optical amplification device is provided with: an excitation unit which outputs a plurality of excitation lights generated by a plurality of excitation light sources; a first distributing unit of which inputs are connected to the plurality of excitation light sources and which branches input lights and then outputs branched lights as a plurality of first distributed lights; a plurality of second distributing units of which inputs are connected to the first distributing unit and which combines and branches input lights and then outputs branched lights as a plurality of second distributed lights; and a plurality of gain mediums which are respectively excited by the plurality of second distributed lights.

An optical amplifier includes two amplifier stages, a circulator and an output stage. The first amplifier stage amplifies an input optical signal, and provides a first-stage amplified optical signal that is to be outputted via the circulator to the second amplifier stage. The second amplifier stage amplifies the first-stage amplified optical signal, and outputs a second-stage amplified optical signal to the output stage. The output stage outputs a returned optical signal to the second amplifier stage, so that the second amplifier stage amplifies the returned optical signal, and provides a third-stage amplified optical signal that is to be outputted via the circulator and the output stage to serve as an output optical signal.

In some implementations, an amplifier device may include a first amplifier configured to amplify signals in a first range of optical wavelengths. The first amplifier may include a first portion that includes one or more first optical gain components, and a second portion that includes one or more second optical gain components and a variable optical attenuator. The amplifier device may include a second amplifier configured to amplify signals in a second range of optical wavelengths. The amplifier device may include a filter for the first range of optical wavelengths and the second range of optical wavelengths. The filter may be located between the first portion and the second portion of the first amplifier.

[Problem] To accommodate single-band signal processing devices in a high-density manner. [Solution] Provided is a system including: a first signal cable; a second signal cable; a third signal cable; a fourth signal cable; a first multi-band signal processing device that processes a first signal input from the first signal cable and outputs a resultant second signal to the second signal cable; a second multi-band signal processing device that processes a third signal input from the third signal cable and outputs a resultant fourth signal to the fourth signal cable; a first joint box that accommodates the first signal cable, the first multi-band signal processing device, the second signal cable, and the fourth signal cable; and a second joint box that accommodates the second signal cable, the third signal cable, the second multi-band signal processing device, and the fourth signal cable.