The present disclosure discloses a degassing-free underwater dissolved carbon dioxide detection device and a detection method. The degassing-free underwater dissolved carbon dioxide detection device includes a computer, which is used to provide the driving signal and controlling parameters for the power tuning unit; the computer is connected with a laser driving control module and the power tuning unit, respectively; the laser driving control module is connected with a laser; the laser is connected with a photo-isolator; the photo-isolator is connected with a thulium-doped fiber vertical-cavity laser system; the thulium-doped fiber vertical-cavity laser system is connected with a photoacoustic cell system through a fiber collimator; the photoacoustic cell system is connected with a pre-amplifier circuit and a lock-in amplifier in sequence, and the lock-in amplifier is connected with the computer.

An optical semiconductor device outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The optical semiconductor device includes a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer. The optical semiconductor device further includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The quantum well active layer is doped with 0.3 to 1×10.sup.18/cm.sup.3 of n-type impurity.

An optical fiber connector includes: amplifying fibers in which an active element activated by excitation light is added to a core of each of the amplifying fibers. The amplifying fibers are connected together such that an absorption amount of excitation light per unit length increases with an increase of a distance from an incident end of the excitation light. A mode field diameter of laser light propagating through the core is same among the amplifying fibers.

Various example embodiments relate to active optical fibers and devices using active optical fibers. An active optical fiber may comprise a central part surrounded by an annular active core. The fiber may have a tapered longitudinal profile such that the fiber comprises a single-mode portion and a multimode portion. The annular core may have low birefringence, obtained for example by rotating (spinning) the fiber preform during manufacture of the fiber. Refractive index of the annular core may be higher than the refractive indices of the central part and cladding layer(s) surrounding the annular core. The active optical fiber enables selective generation or amplification of light modes with orbital angular momentum (OAM). Furthermore, the fiber has a large mode field diameter (MFD) and it is not sensitive to internal heating or environmental influences.

An optical fiber securing structure includes: an optical fiber including a coating, and a coating-removed section in which a partial section of the coating is removed from the optical fiber; a reinforcement member including main surfaces and a groove formed from one of the main surfaces toward an inside of the reinforcement member, where the groove has a pair of side walls and a bottom wall; and a resin member that secures the coating-removed section to the pair of side walls and the bottom wall. A bottom part of the groove that includes the bottom wall has a widthwise cross-sectional shape where the bottom wall constitutes a trapezoidal shape such that a distance between the pair of side walls becomes greater in a direction away from the bottom wall.

A semiconductor-fiber-laser assembly is provided that includes a pumping module, an active optical fiber and an assembling board. The active optical fiber is provided on an upper surface of the assembling board, the pumping module is provided on a surface of the assembling board that is the same as or opposite to the upper surface; and input-side and output-side optical-fiber gratings are provided at two ends of the active optical fiber, to form a laser resonator between the input-side and output-side optical-fiber gratings. The pumping module includes a plurality of semiconductor-laser single emitters, a collimating-lens group and a mirror group that are sequentially arranged, and light beams from the semiconductor-laser single emitters pass through the mirror group to realize beam combination.

A broadband optical amplifier for operation in the 2 μm visible wavelength band is based upon a single-clad Ho-doped fiber amplifier (HDFA). A compact pump source uses a combination of discrete laser diode with a fiber laser (which may be a dual-stage fiber laser) to create a pump output beam at a wavelength associated with creating gain in the presence of Ho ions (an exemplary pump wavelength being 1940 nm). The broadband optical amplifier may take the form of a single stage amplifier or a multi-stage amplifier, and may utilize a co-propagating pump and/or a counter-propagating pump arrangement.

An amplified hollow-core fiber (HCF) optical transmission system for low latency communications. The optical transmission system comprises a low-latency amplified HCF cable. The low-latency amplified HCF cable comprises multiple HCF segments (or HCF spans). Between consecutive HCF segments, the system comprises low-latency remote optically pumped amplifiers (ROPAs). Each ROPA comprises a gain fiber, a wavelength division multiplexing (WDM) coupler, and an optical isolator. Preferably, the ROPAs are integrated into the HCF cable. Each ROPA is pumped by a remote optical pump source, which provides pump light to the gain fiber. The gain fiber receives an optical transmission signal from the HCF. The WDM coupler combines the pump light with the optical transmission signal, thereby allowing the gain fiber to amplify the optical transmission signal to an amplified transmission signal. The amplified signal is transmitted to another HCF segment through the optical isolator.

A fiber laser apparatus includes: an amplification optical fiber that amplifies a laser beam; one or more pumping light sources that generate pumping light that is supplied to the amplification optical fiber; an output optical fiber including a first core that allows the laser beam amplified by the amplification optical fiber to propagate therethrough, and a first cladding having a refractive index lower than a refractive index of the first core and surrounding a circumference of the first core; a delivery fiber including a second core optically coupled to the first core of the output optical fiber, and a second cladding having a refractive index lower than a refractive index of the second core and surrounding a circumference of the second core; and a first housing unit that houses the amplification optical fiber and the output optical fiber therein.

A photonic lantern couples light from several fibers or fiber cores into one or more fibers or fiber cores. Photonic lanterns are often used to combine several lower-power beams into a single higher-power beam. They can also be used to couple light from multi-core fibers into single-mode, multi-mode, or other multi-core fibers. By modulating the phases of the input beams, the light can be switched from output to output—for example, between output cores of a multi-core output fiber. If desired, the beams can also be amplified using an active fiber in or coupled to the photonic lantern. A first photonic lantern couples signal light and pump light into the core and cladding, respectively, of an active multi-mode or multi-core fiber. And the active multi-mode or multi-core fiber couples amplified signal light into output fiber(s) via a second photonic lantern.