Techniques are described for implementing an out-of-band communication channel used to exchange control channel information in sub-carrier-based optical communication systems. In an example implementation, an optical communication system includes a primary transceiver, a component, and secondary transceivers. The primary transceiver is operable to supply first optical subcarriers to an optical communication path, the first optical subcarriers being amplitude modulated at a first frequency to carry first control information and amplitude modulated at a second frequency to carry second control information. The component is operable to be coupled to the optical communication path and includes circuitry operable to detect the first control information. The secondary transceivers are coupled to a terminal end of the optical communication path. At least one of the secondary transceivers is operable to detect the second control information and block the first control information.

An object of the present disclosure is to allow gain compensation with a simple configuration without adding a new device to the outside. The present disclosure discloses a rare earth doped fiber including a core doped with a rare earth and a cladding region around the core, wherein one or more cavities are provided inside the core, and at least one of the cavities are provided along a longitudinal direction of the rare earth doped fiber.

An optical fiber amplification apparatus is disclosed, including an optical receiving port, a first optical output port, a second optical output port, a gain medium, a pump laser, reflection films, and a transmission-reflection film. The pump laser activates a function of the gain medium to amplify an optical signal. A multiplexed optical signal including a first-waveband optical signal and a second-waveband optical signal is incident onto the gain medium. The reflection films enable the multiplexed optical signal to be reflected back and forth in the gain medium. After the first-waveband optical signal reaches a first target gain, the first-waveband optical signal is output from the gain medium to the first optical output port. The second-waveband optical signal is amplified in the gain medium. After the second-waveband optical signal reaches a second target gain, the second-waveband optical signal is output from the gain medium to the second optical output port.

A method of marking an optical fiber that includes directing a laser beam onto a first colored layer of an optical fiber. The optical fiber includes a core and a cladding surrounding the core, the first colored layer surrounds the cladding, and the laser beam modifies the first colored layer to form one or more laser-modified regions along an outer surface of the first colored layer.

The present disclosure discloses an optical device structure including an optical fiber including a core part, a clad part, and a three-dimensional micro hole structure in the clad part, wherein a surface of the three-dimensional micro hole structure is provided with at least a non-flat surface, and a conformal graphene layer is formed on the surface of the three-dimensional micro hole structure, and a method of manufacturing the same.

A multi-stage thulium-doped (Tm-doped) fiber amplifiers (TDFA) is based on the use of single-clad Tm-doped optical fiber and includes a wavelength conditioning element to compensate for the nonuniform spectral response of the initial stage(s) prior to providing power boosting in the output stage. The wavelength conditioning element, which may comprise a gain shaping filter, exhibits a wavelength-dependent response that flattens the gain profile and output power distribution of the amplified signal prior to reaching the output stage of the multi-stage TDFA. The inclusion of the wavelength conditioning element allows the operating bandwidth of the amplifier to be extended so as to encompass a large portion of the eye-safe 2 μm wavelength region.

A measurement device includes: an optical gain unit for generating and amplifying light; a transmission optical band variation unit for selecting a specific optical frequency band from the light generated by the optical gain unit, and varying the selected specific optical frequency band to transmit light; a resonant optical frequency variation unit for performing a frequency variation so that multiple resonant optical frequency orders within the specific optical frequency band vary over a variation range narrower than intervals between the respective orders; resonance induction units forming an optical resonance unit which includes the optical gain unit, the transmission optical band variation unit, and the resonant optical frequency variation unit and causes selective oscillation of light having a specific resonant optical frequency within a specific transmission optical band; and a control signal unit for varying each of the transmission optical band variation unit and the resonant optical frequency variation unit.

An end-firing surgical laser fiber suitable for Thulium Laser Fiber lithotripsy applications includes an internally reflective tube that extends beyond the distal end surface of the fiber to provide a standoff sleeve, and that is welded or otherwise fixed to an end section of the fiber. The standoff sleeve may be made of silica glass or sapphire, a reflective metal, and/or may include a reflectivity-enhancing coating or structure on an inner surface of the tube. In addition, the reflective standoff sleeve may be tapered to increase or decrease a diameter of a distal end of the sleeve to control output power density, and may include index matched fillers or structures that absorb, transmit, or scatter energy away from the fiber cladding, and/or an energy blocking or absorbing structure positioned at an upstream end of the sleeve. Still further, the laser output may be modified by adding relatively low power, extended duration pulses to a high frequency pulse train in order to clear suspended dust particles from an interior of the sleeve during a lithotripsy procedure, and prevent buildup of the particles on the inside diameter of the sleeve.

An optical fiber includes a core and a cladding. An effective area A.sub.eff of light of a fundamental mode, having a wavelength of 1070 nm and propagating through the core, is 500 μm.sup.2 or more. A numerical aperture NA of the core satisfies the following formula:

NA≥(1.3×10.sup.−11×a.sup.4/b.sup.6).sup.1/6

where a (m) is a radius of the core and b (m) is a radius of the cladding. A V value, that is a waveguide parameter of the optical fiber, satisfies the following formula:

V≤1.3583×b.sup.−0.2555.

An objective of the present invention is to provide an amplification fiber having a cladding excitation configuration that improves amplification efficiency and an optical amplifier. An amplification fiber (10) according to the present invention is a multi-core amplification fiber having, from one end (E1) to the other end (EE), a plurality of cores (11b) in a cladding (11a), and a total distance from the one end (E1) to the other end (EE) in which rare earth ions are doped differs depending on the types of cores (11b). The cores (11b) are preferably disposed such that the cores of the same type are not adjacent to each other. By arranging the types of the cores in this manner, requirements for inter-core crosstalk can be mitigated since the bands of signal light in the adjacent cores are different. As a result, a density of cladding excitation light can be increased by shortening the inter-core distance, and thus the amplification efficiency can be improved.