Pump reflectors for use in cladding-pumped fiber systems, such as laser or amplifier systems, are provided. The pump reflector includes an optical fiber segment having at least one core and at least one cladding. A cladding Bragg grating is written by femtosecond inscription in the optical fiber segment, and extending across at least a portion of the cladding. The cladding Bragg grating has a reflectivity profile encompassing the spectral profile of the pump and a spatial profile encompassing the pump spatial distribution in the cladding. A method of manufacturing a pump reflector using femtosecond light pulses is also provided.

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.

An optical fiber amplifier comprising a first optical fiber, a second optical fiber, a third optical fiber, and an excitation light source, is disclosed. Each optical fiber has cores and a cladding surrounding the cores. The third optical fiber transmits excitation light used for signal amplification in the second optical fiber. A rare-earth element is doped to the second optical fiber that amplifies an optical signal propagating therein by the excitation light. The third optical fiber includes a reduced-diameter portion. A distance between the cores of the third optical fiber in the reduced-diameter portion is shorter than a distance between the cores in other portion of the third optical fiber, and the excitation light entering from the excitation light source to one of the cores of the third optical fiber is mode-coupled with another core of the third optical fiber to distribute the excitation light in the reduced-diameter portion.

Apparatus and methods for generating mid-IR frequency combs using intra-pulse DFG. A mode-locked pulse generation laser generates near-IR pulses which are amplified. The amplified pulses are spectrally broadened by a nonlinear element, for example a normal dispersion highly nonlinear fiber (ND-HNLF) to generate broadened pulses. The nonlinear spectral broadening element is a transparent dielectric material having a cubic nonlinear response. Broadened pulses are temporally compressed to generate short, high-power pulses which few-cycle conditioned pulses which are ready for the intrapulse DFG process. The DFG block generates a mid-IR comb by difference frequency generation. It might comprise an orientation patterned GaP (OP-GaP) crystal or a poled lithium niobate (PPLN) crystal.

A compact diode laser achieves high-power, short duration output pulses by separating the lasing action from the pulse-generating mechanism. A diode seed source is configured for gain-switching via a variable RF source. A time lens element includes an intensity modulation device, a phase modulation device, and a pulse compressor. The intensity modulation device carves shorter pulses from the long gain-switched seed pulses, the phase modulation device adds chirp, and the pulse compressor compensates for the chirp while producing high-power short-duration output pulses.

A diamond Raman laser may include a diamond Raman oscillator (DRO) with a first diamond gain medium, a seed laser providing a seed beam at a seed wavelength, and a cavity configured to resonate at a first-Stokes wavelength, the first-Stokes wavelength corresponding to first-Stokes emission in diamond when pumped with the seed wavelength, and where the DRO outputs a first-Stokes beam at the first-Stokes wavelength. The diamond Raman laser may further include a diamond Raman amplifier (DRA) to amplify the first-Stokes beam and generate an amplified first-Stokes beam, where the DRA includes two or more diamond Raman amplification stages, each including one or more second diamond gain media, and one or more optical filters to filter light with a second-Stokes wavelength generated in at least one of the one or more second gain media.

A pulse analysis system or method includes a frequency filter that receives an ultrafast pulse under test and disperses the pulse under test over a frequency range. The frequency filter separates the pulse under test into component frequency slices and provides the frequency slices to a detector coupled to a digitizer, which processes the digitized signal and collects a sonogram characteristic of the pulse under test. The frequency slices are arranged to overlap. Ptychography is performed on the sonogram to obtain characteristics of the pulse under test.

A frequency stabilizing system for high precision single-cavity multi-frequency comb includes a single-cavity multi-comb pulse oscillator, a frequency detection system, and a frequency feedback control system. The single-cavity multi-comb pulse oscillator is configured to output mode-locked pulse trains with a certain repetition rate difference at two or more central wavelengths. The frequency detection system is configured to detect the frequency signal, and output the corresponding electrical signal. The frequency feedback control system is configured to process the electrical signal from the frequency detection system, and transmit it to the frequency response component in the single-cavity multi-comb pulse oscillator to control a strain of the frequency response component, so as to realize feedback control on the frequency (repetition rate, repetition rate difference, and carrier envelope offset frequency) of the mode-locked pulse trains.

A method of pulse shaping using spectral filtering, positive chirp, and self-phase modulation to control the accumulated higher-order phase terms of the spectral phase. This pulse shaping method has particular advantage in fiber chirped pulse amplification (FCPA) systems, where there are two effects: (1) an offsetting of the fourth order phase via nonlinear phase accumulation, allowing for a higher Strehl ratio (i.e., a cleaner pulse), higher peak power pulse and (2) enabling power scaling to higher pulse energies without the increased nonlinear phase accumulation leading to pulse breakup. This technique can be used both in a passive system with no amplification to clean up an existing pulse, and in an amplifier system to enable higher performance operation (shorter pulses, cleaner pulses, higher energy pulses).

An optical fiber filter includes a fiber core, inner cladding, and outer cladding. A refractive index of the fiber core, a refractive index of the inner cladding, and a refractive index of the outer cladding progressively decrease in sequence. The fiber core is configured to transmit at least two mutually different first optical signal modes, the inner cladding is configured to transmit at least two mutually different second optical signal modes, and at least one fiber grating is etched on the fiber core. At least part of optical power of a target first optical signal mode is coupled to only a target second optical signal mode at the fiber grating. The target first optical signal mode is one of the at least two first optical signal modes, and the target second optical signal mode is one of the at least two second optical signal modes.