A wavelength-tunable, polarization-maintaining (PM) fiber laser for use in the two micron wavelength region is based upon a ring laser geometry and includes sections of polarization-maintaining (PM) optical fiber for supporting propagation of the circulating laser radiation around the ring. At least one gain module is included in the ring and is formed of polarization-maintaining active optical fiber including a core region that is doped with either Thulium (Tm) or Holmium (Ho), or co-doped with both of these rare earth materials. In the presence of a pump beam operating at a suitable wavelength, the gain module(s) generate laser radiation at a wavelength within the two micron region. A PM-based tunable bandpass filter (BPF) is included within the ring and used to control/adjust the wavelength of the output beam provided by the fiber laser.

An optical modulator includes first and second waveguides; a first phase shifter provided in at least one of the first and second waveguides and configured to control a phase of the laser beam; a first optical element configured to combine the laser beam propagating through the first waveguide and the laser beam propagating through the second waveguide and separate the combined laser beam into two laser beams; a third (fourth) waveguide on which one (the other) of the laser beams separated by the first optical element is incident; a second phase shifter provided in at least one of the third and fourth waveguides and configured to control a phase of the laser beam; and a second optical element configured to combine the laser beam propagating through the third waveguide and the laser beam propagating through the fourth waveguide and emit the laser beam in the superposition state.

A fiber laser device includes a first optical fiber, a second optical fiber, and a third optical fiber configured by polarization maintaining fibers. The first optical fiber includes at least one first part and at least two second parts alternatively disposed with the first part. The first part and the second part adjacent to each other are connected to each other such that a fast axis of the first part coincides with a slow axis of the second part at a connection point. A total length of the first part is equal to a total length of the second parts. A mode field diameter of the first optical fiber is smaller than each of a mode field diameter of the second optical fiber and a mode field diameter of the third optical fiber.

An apparatus includes an amplified spontaneous emission source, which in turn includes an optical fiber. The optical fiber includes a solid core and a first end. The solid core includes a silica matrix. The silica matrix includes a rare-earth element and a glass co-dopant. The rare-earth element includes dysprosium or neodymium. The glass co-dopant includes Al.sub.2O.sub.3. The apparatus further includes a laser pump diode coupled to the first end of the optical fiber. The laser pump diode and the optical fiber cooperate to generate a spontaneous spectral emission confined to the solid core. The spontaneous spectral emission includes a simultaneous plurality of spectral regions.

Embodiments relate to a resonator including a graphene layer formed on a support, and a tapered fiber disposed around at least part of the support, close to the graphene layer, wherein the tapered fiber has different paths along which light travels in a region extending from one end and a region extending from the other end, and a passive-mode-locked pulse laser oscillation system including the same.

The invention discloses a multi-wavelength and single-frequency Q-switching optical fiber laser device. The laser device comprises a saturable absorber, a high gain optical fiber, a polarization-maintaining multi-wavelength narrow-band fiber Bragg grating, a resonant cavity temperature control module, a polarization-maintaining wavelength division multiplexer, a pump source and a polarization-maintaining light isolator. By taking a highly doped phosphate optical fiber as a laser gain medium, two ends of the optical fiber device are connected with the saturable absorber and the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating respectively to form a short linear laser cavity. A short cavity length of the short linear laser cavity can realize single longitudinal mode operation of laser in the resonant cavity, and meanwhile, a stable multi-wavelength and single-frequency pulse laser output is realized in the resonant cavity by combining multi-wavelength resonance caused by the polarization-maintaining multi-wavelength narrow-band fiber Bragg grating with passive Q-switching performance of the saturable absorber in the cavity. The multi-wavelength single-frequency Q-switching optical fiber laser device of the invention realizes output of a plurality of wavelength pulse laser with adjusted repeated frequency simultaneously, and the laser in each wavelength is maintained in single-frequency operation, such that the multi-wavelength single-frequency Q-switching optical fiber laser device can be widely applied to aspects of laser radar, laser sensing, gas detection and the like.

A figure-8 laser is configured in which gain in the uni-directional loop can be removed while maintaining mode-locked operation with gain only in the bi-directional nonlinear amplifying loop. Simplified self-starting and control over pulse characteristics by controlling gain in the bi-directional loop is made possible.

A laser head for a high power fiber laser system has a 5 to 10 mm high housing which is provided with a bottom. The housing encloses an input collimator assembly which collimates a single mode pump light at a fundamental frequency and maximum power of 2 kW. The housing further encases a multi-cascaded nonlinear frequency converter receiving the collimated pump light so as to convert the fundamental frequency into a higher harmonic thereof, wherein converted light at the higher frequency has a maximum power of 1 kW. Enclosed in the housing are electronic and light guiding optical components mounted in the housing. The bottom of the housing is an electro-optical printed circuit board (EO PCB) which directly supports the input collimator assembly, multi-cascaded nonlinear frequency converter, electronic and optical components at respective designated locations.

A fiber grating apparatus includes a first optical fiber, an optical wave assembly coupled to the first optical fiber and having grating function, and a second optical fiber coupled to the optical wave assembly. The optical wave assembly includes a first substrate, a metalens assembly, a filter, and a second substrate. The first optical fiber, the optical wave assembly, and the second optical fiber are arranged on a same plane.

An optical apparatus for depolarizing a laser beam within a fiber MOPA laser is disclosed. The apparatus includes a first phase modulator for spectral broadening, a linear polarizer, an optical coupler, a second phase modulator for depolarizing the laser beam, and a polarization-maintaining optical fiber. The optical coupler divides a linearly-polarized portion of the laser beam equally between fast and slow axes of the second phase modulator. The laser beam delivered by the polarization-maintaining optical fiber is truly unpolarized. The apparatus provides independent control of the spectral broadening and the depolarization to mitigate stimulated Brillouin scattering during subsequent amplification. A method for depolarizing a laser beam, using this apparatus, is also disclosed.