Generation of wideband tunable femtosecond laser based on nonlinear propagation of power-scaled mode-locked femtosecond laser pulses in photonic crystal fiber

We implement an experimental study for the generation of wideband tunable femtosecond laser with a home-made power-scaled mode-locked fiber oscillator as the pump source.By coupling the sub-100 fs mode-locked pulses into a nonlinear photonic crystal fiber(NL-PCF),the exited spectra have significant nonlinear broadening and cover a spectra range of hundreds of nm.In experiment,by reasonably optimizing the structure parameters of NL-PCF and regulating the power of the incident pulses,femtosecond laser with tuning range of 900-1290 nm is realized.The research approach promotes the development of femtosecond lasers with center wavelengths out of the traditional laser gain media toward the direction of simplicity and ease of implementation.

Fiber optical parametric oscillator based on photonic crystal fiber pumped with all-normal-dispersion mode-locked Yb:fiber laser

We demonstrate a cost effective, linearly tunable fiber optical parametric oscillator based on a home-made photonic crystal fiber pumped with a mode-locked ytterbium-doped fiber laser, providing linely tuning ranges from 1018 nm to 1038 nm for the idler wavelength and from 1097 nm to 1117 nm for the signal wavelength by tuning the pump wavelength and the cavity length. In order to obtain the desired fiber with a zero dispersion wavelength around 1060 rim, eight sam- ples of photonic crystal fibers with gradually changed structural parameters are fabricated for the reason that it is difficult to accurately customize the structural dimensions during fabrication. We verify the usability of the fabricated fiber experimen- tally via optical parametric generation and conclude a successful procedure of design, fabirication, and verification. A seed source of home-made all-normal-dispersion mode-locked ytterbium-doped fiber laser with 38.57 ps pulsewidth around the 1064 nm wavelength is used to pump the fiber optical parametric oscillator. The wide picosecond pulse pump laser enables a larger walk-off tolerance between the pump light and the oscillating light as well as a longer photonic crystal fiber of 20 m superior to the femtosecond pulse lasers, resulting in a larger parametric amplification and a lower threshold pump power of 15.8 dBm of the fiber optical parametric oscillator.

Photonic crystal fiber Mach-Zehnder interferometer with microholes ablated by a femtosecond laser for refractive index sensing

A new structure of the photonic crystal fiber（PCF）based Mach-Zednder interferometer（MZI）is fabricated and presented.The structure has microholes ablated by a femtosecond laser.The fringe visibility can be enhanced more than 10 dB compared with the interferometer without a microhole.The interferometer is characterized by sodium chloride solutions for refractive index（RI）sensing.The RI sensitivities are greatly increased by the hole fabrication since it directly changes the cladding modes of the PCF.For the interferometer sensor with two holes,the RI sensitivity is 157.74 nm/RIU,which is 5 times than that of the sensor without a microhole.Microholes ablation with a femtosecond laser on PCF can increase the sensor＇s sensitivity dramatically.Femtosecond laser has a wide application prospect in the field of performance improvement of the sensors.

Stable CW Single-Mode Photonic Crystal Fiber DFB Ring Laser

We demonstrate stable single-mode CW operation of a DFB ring laser based on Er3＋ doped photonics crystal fiber （PCF）. The incorporation of a ring cavity allows one single mode to lase and also suppresses the unwanted effect of self-pulsing. Such a narrow linewidth source in PCF has great potential in spectroscopy.

Recent developments in high power near-infrared super-continuum generation based on photonic crystal fiber

High power supercontinuum generation has witnessed rapid developments during the past few years. The mecha- nism and the latest achievements in high power supercontinuum generation are reviewed both for the continuous wave pump regime and the pulsed pump regime. The challenges in scaling the average power of supereontinuum generation are analyzed. Some of our works on high power supercontinuum generation are summarized, and perspectives for the future development are discussed.

Generation of a compact high-power high-efficiency normal-dispersion pumping supercontinuum in silica photonic crystal fiber pumped with a 1064-nm picosecond pulse

Broadband normal dispersion pumping supercontinuum （SC） generation in silica photonic crystal fiber （PCF） is investigated in this paper. A 1064-nm picosecond fiber laser is used to pump silica PCF for the SC generation. The length of PCF is optimized for the most efficient stimulated Raman scattering process in the picosecond pump pulse region. The first stimulated Raman Stokes peak is located in the anomalous dispersion regime of the PCF and near the zero dispersion wavelength; thus the SC generation process can benefit from both a normal dispersion pumping scheme and an anomalous dispersion pumping scheme. The 51.7-W SC spanning from about 700 nm to beyond 1700 nm is generated with an all-fiber configuration, and the pump-to-SC conversion efficiency is up to 90%. In order to avoid the output fiber end face damage and increase the stability of the system, an improved output solution for the high power SC is proposed in our experiment. This high-efficiency near-infrared SC source is very suitable for applications in which average output power and spectral power density are firstly desirable.

Reseach Progress of Photonic Crystal Fibers in China

Photonic Crystal Fibers have attracted worldwideinterest within the last decade due to their uniqueoptical properties and because they exhibit a muchhigher degree of design freedom compared to conventionaloptical fibers.In this article, the fabricationtechnologies of photonic crystal fibers and theirapplications at home and abroad were formulated atlength, especially in the following fields, such aslarge mode area active photonic crystal fibers andfiber lasers, birefringence fibers and sensors, highnonlinear photonic crystal fibers and frequencytransformation, dispersion compensation PCFs anddispersion compensation for telecommunicationsystems, and photonic band-gap fibers. Finally, accordingto the above analysis, the prospects anddeveloping trends of photonic crystal fibers in thefuture were presented.

Development of Fiber Lasers and Their Applications

Development of fiber lasers, especially the latest progress in high power fiber lasers, and the problems of the commercialization of high power fiber lasers, are discussed. Research on other kinds of fiber lasers, such as microstructure fiber laser, ultrashort pulse fiber lasers, Raman fiber lasers are also involved.

All-fiber laser amplification at 1948 nm based on doublecladding Tm/Al co-doped photonic crystal fiber fabricated by laser additive manufacturing

In this work,we demonstrated the double-cladding Tm/Al co-doped photonic crystal fiber(PCF)by laser additive manufacturing.The measurements show that the fiber was heavily doped with a Tm^(3+)concentration of 2.13%(mass fraction)without any crystallization.The splicing property of PCF was studied,and the integrity of the PCF air holes was maintained during the splicing process.The PCF with combiner pigtail has a splice loss of 0.23 d B.The all-fiber Tm/Al co-doped PCF amplifier system achieves a slope efficiency of 13%at 1948 nm with an output laser power of nearly 1.59 W.An upconversion process was also observed under laser excitation with a 1064 nm pulse.This method provides a new idea to deal with Tmdoped PCF fabrication and promotes the promising application of 2μm fiber lasers.

Compact pulsed thulium‐doped fiber laser for topographical patterning of hydrogels

We report the generation of high energy 2μm picosecond pulses from a thulium-doped fiber master oscillator power amplifier system.The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber(LMA-PCF).The amplifier output is a linearly-polarized 1.5 ns,100 kHz pulse train with a pulse energy of up to 250μJ.Pulse compression was achieved with(2+2)-pass chirped volume Bragg grating(CVBG)to obtain a 2.8 ps pulse width with a total pulse energy of 46μJ.The overall system compactness was enabled by the all-fiber amplifier design and the multi-pass CVBG-based compressor.The laser output was then used to demonstrate high-speed direct-writing capability on a temperature-sensitive biomaterial to change its topography(i.e.fabricate microchannels,foams and pores).The topographical modifications of biomaterials are known to influence cell behavior and fate which is potentially useful in many cell and tissue engineering applications.

Ultrahigh resolution optical coherence tomography with femtosecond Ti:sapphire laser and photonic crystal fiber

Optical coherence tomography (OCT) with ultrahigh axial resolution was achieved by the super-contin-uum generated by coupling femtosecond pulses from a commercial Ti:sapphire laser into an air-silica microstructure fiber. The visible spectrum of the super-continuum from 450 to 700 nm centered at 540 nm can be generated. A free-space axial OCT resolution of 0.64 μm was achieved. The sensitivity of OCT system was 108 dB with incident light power 3 mW at sample,only 7dB below the theoretical limit. Subcellular OCT imaging was also demonstrated,showing great potential for biomedical application.

Switchable dual-wavelength fiber ring laser featuring twin-core photonic crystal fiber-based filter

A simple configuration for the generation of a switchable dual-wavelength fiber ring laser is presented.The proposed configuration employs a short twin-core photonic crystal fiber acting as a Mach–Zehnder interferometer at room temperature.A polarization controller is further utilized to enable switchable dualwavelength operation.

High pulse energy femtosecond large-mode-area photonic crystal fiber laser

A high pulse energy femtosecond fiber laser based on a large-mode-area photonic crystal fiber is demonstrated. A segment of Yb-doped single-polarization large-mode-area photonic crystal fiber with extremely low nonlinearity is explored as gain media of this fiber laser, resulting in intrinsically environmentally stability. The fiber laser is based on a linear cavity with dispersion compensation free configuration, and the stable mode-locking is obtained by a semiconductor saturable absorber mirror (SESAM). The fiber laser directly generates 2.5 W of average power at a repetition rate of 51.4 MHz, corresponding to a single pulse energy of 50 nJ. The output pulse duration is 4.2 ps, which is dechirped to 410 fs after extracavity dispersion compensation. The nonlinear absorption of SESAM determines the pulse shaping at low output power, while the mode-locking mechanism is under the balance between spectrum broadening from self-phase-modulation and gain filtering at the high output power.

Blue light generation in photonic crystal fibers with 1-μm femtosecond laser pulses

Using 300-fs 1039-nm Yb-doped fiber laser, we experimentally demonstrate blue light generation in a high- Δ and high nonlinear photonic crystal fiber （PCF）. The zero dispersion wavelength of PCF is 793 nm, detuning 245.8 nm from the pump wavelength. PCF allows a frequency conversion exceeding the octave of pump wavelength. The visible component of the measured output spectrum occurs in the fundamental mode and spans from 391.3 to 492.3 nm. The peak wavelength of 441.8 nm has a frequency detuning of 390 THz from the pump wavelength of 1039 nm.

Strain and Temperature Characterization of LPGs Written by CO2 Laser in Pure Silica LMA Photonic Crystal Fibers

This paper reports on the writing of long period gratings （LPGs） in a six-ring pure silica solid core, and large mode area photonic crystal fiber （fiber core diameter p = 10.1 μm） using a CO2 laser system, and the characterization of their strain and temperature sensitivities. Temperature and strain sensitivities in the order of-19.6pm/℃ and -88 pm/με, respectively, were obtained, which were comparable or surpassed values of the similar photonic crystal fiber （PCF）-based LPG or sensor configurations found in the literature.

Splicing on Condensed Photonic Crystal Fiber Using CO_2 Laser

Condensation in the air-holes of photonic crystal fiber results in bubble development during the electric arc splicing is first reported. The condensation can be removed by laser splicing; and 1.4dB splice loss has been achieved.

Three-channel dual-wavelength fiber laser based on a digital micromirror-device processor and photonic crystal fiber

A stable three-channel dual-wavelength fiber ring laser is proposed and experimentally demonstrated. The dig- ital mieromirror-deviee （DMD） processor can select and reeirculate any dual waveband from the gain spectrum of the erbium-doped fiber at each channel. The uniform and stable dual-wavelength oscillation is obtained by a highly nonlinear photonic crystal fiber, which causes two degenerate the four-wave-mixing processes. By loading different reproducibility diffraction gratings on the optoelectronic DMD processor, the laser can be operated stably in a three-channel dual-wavelength scheme at room temperature. The power fluctuation of each laser channel is less than -0.02 dB.

Yb^(3+)-doped large-mode-area photonic crystal fiber laser with 210 W continuous-wave output power

An Yb3+-doped double-clad large-mode-area photonic crystal fiber(LMA PCF) laser with up to 210 W of continuous-wave output power centered at 1.05 μm is demonstrated.The length of the fiber used is 2 m and the produced laser power per meter can attain 105 W.The PCF is pumped by two diode lasers with central wavelength of 976 nm.The slope efficiency is 76%,and the beam quality factor M2 at x and y axes are measured to be 1.06 and 1.08,respectively.No thermo-optical problems and other roll-over even are observed at the highest output power.

Sensing Properties of Femtosecond Laser-Inscribed Long Period Gratings in Photonic Crystal Fiber

为在 photonic 水晶纤维的长时期纤维栅栏的铭文的近红外线的、高紧张 femtosecond 激光脉搏的使用被报导。在 photonic 水晶纤维的栅栏结构的形成由允许波浪指导，但是损害并且散布 femtosecond 铭文横梁的纤维结构是复杂的。对称、不对称的 femtosecond 激光铭文的效果被比较，到外部不安的长时期栅栏和他们的回答的极化特征被报导。