Compact In-Line Thin-Core Fiber Filter at C-Band for a Dual- and Triple-Wavelength Fiber Laser

.A triple-wavelength erbium-doped compound ring fiber laser using the fiber-based triple-ring filter (TRF) is proposed and experimentally investigated. Using the fiber-based TRF laser scheme, the proposed laser can lase three wavelengths simultaneously. The fiber laser retrieve the optical side-mode suppression ratios (SMSRs) of 40.2, 40.4 and 41.6 dB and the output powers of -9, -8.8 and -7.6 dBm at the wavelengths 1555.89, 1556.77 and 1557.66 nm, respectively. The mode spacing of the triple-wavelength fiber laser is nearly 0.9 nm. Moreover, the output power stability of the ring laser has also been measured and analyzed.

A multi-wavelength tunable fiber laser is constructed for a wavelength-division multiplexed (WDM) fiber Bragg grating (FBG) sensor array in which simultaneous detection of multipoint vibrations and temperature stabilization of the sensor outputs are achieved. The laser consists of a semiconductor optical amplifier (SOA) as a gain medium and of FBGs as wavelength selection components. Since the SOA is an inhomogeneous broadening gain medium, stable multi-wavelength oscillation at the Bragg wavelengths of the FBGs can be realized. In addition, the oscillation wavelengths of the laser can be tuned by applying strain to the FBGs used. In the sensor scheme, triple wavelength fiber laser is fabricated, in which the three wavelength components provide narrowband light sources for arrayed WDM FBG sensors and the wavelength tuning enables temperature compensation for the vibration detection. In the experiment, simultaneous three-point vibration detection with temperature stabilization has been successfully demonstrated.

A simple switchable microwave frequency generator based on a multi-wavelength fiber grating laser is proposed and demonstrated. Microwave signal of 10.4 GHz, 21.2 GHz, and 31.6 GHz can be obtained by simple adjustment of a polarization controller. (2 pages)

We report on supercontinuum generation in a highly nonlinear fiber (HNLF) pumped by noise-like pulses (NLPs) emitted from a compact fiber ring laser. The compact erbium-doped fiber ring laser is constructed by using an optical integrated component and mode-locked by the nonlinear polarization rotation technique. The laser produces NLPs with a 3-dB spectral bandwidth of 60.2 nm, repetition rate of 9.36 MHz, and pulse energy of 2.8 nJ. Numerical simulations reproduce the generation of NLPs in the experiment. The NLPs are then launched into a 110-m-long HNLF and a supercontinuum with a 20-dB spectral width over 500 nm is obtained. Such a simple and inexpensive supercontinuum-generation system is a potential alternative for various practical applications.

A compact optical fiber reflective index sensor is proposed and experimentally demonstrated. It is based on the tilted fiber Bragg grating (TFBG) inscribed in the thin-core fiber that is downstream spliced to the conventional single mode fiber (SMF). Thanks to the core dismatch between the SMF and the thin-core fiber, more cladding modes can be recoupled back into the SMF .The sensor can be used to detect the change of surroundings refractive index (SRI). Besides, the sensor can solve the problem of cross-sensitivity between SRI and temperature.

We developed a compact and high-power mode-locked fiber laser for three-dimensional optical memory. Fiber lasers have the potential to be compact and stable light sources that can replace bulk solid-state lasers. To generate high-power pulses, we used stretched-pulse mode locking. The average power and pulse width of the output pulse from the fiber laser that we developed were 109 mW and 2.1 ps, respectively. The dispersion of the output pulse was compensated with an external single-mode fiber of 2.5 m length. The pulse was compressed from 2.1 ps to 93 fs by dispersion compensation. The pulse emitted from this fiber laser has a sufficient energy to generate two-photon recording effectively, so the fiber laser we have developed is possible to use as a light source of three-dimensional optical memory. We also propose an all-fiber recording and readout system for multilayered memories.

We report a compact all-fiber high-energy fiber laser that consists of a laser oscillator and a compression section. The laser oscillator generates the pulses with high energy and large chirp. The compression section is made of a piece of standard single-mode fiber that dechirps the chirped pulses. The compact all-fiber fiber laser produces pulses with 8 nJ of the pulse energy and 290 fs of the pulse duration.

A compact femtosecond ytterbium-doped fiber laser has been developed with integrated optical components. The femtosecond fiber laser oscillator was miniaturized by integrating the intracavity wavelength division multiplexer and optical isolator with collimators, and placing a quarter-wave plate before a transmission grating pair to get light retroflection from the intracavity dispersive delay line. Stretched-pulse mode-locking could be self-started at a repetition rate of 65 MHz with pump power as low as 100 mW. The compact femtosecond fiber laser oscillator could be optimized to generate 86 fs pulse duration and 0.5 nJ pulse energy.

A simple and compact thin-core fiber (TCF)-based Mach-Zehnder interferometer (MZI) is proposed for curvature measurement. The sensor head is composed by a short section of TCF embedded between two single-mode fibers. The MZI works on the basis of interference between the core mode and cladding mode in TCF. The transmission spectrum of the sensor is analyzed by the fast Fourier transform, which indicates that the interference mainly occurs between LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">018</sub> modes propagating in TCF. The experimental results show that the dip wavelengths in transmission spectrum decrease linearly as the curvature increase with a sensitivity of -13.53 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The high curvature sensitivity makes this sensor a candidate for curvature discrimination and measurement in the field of structural deformation, intelligent artificial limb, and mechanical engineering.

We developed a compact and high-power mode-locked fiber laser for three-dimensional optical memory. Fiber lasers have the potential to be compact and stable light sources that can replace bulk solid-state lasers. To generate high-power pulses, we used stretched-pulse mode locking. The average power and pulse width of the output pulse from the fiber laser that we developed were 109 mW and 2.1 ps, respectively. The dispersion of the output pulse was compensated with an external single-mode fiber of 2.5 m length. The pulse was compressed from 2.1 ps to 93 fs by dispersion compensation. The pulse emitted from this fiber laser has an energy sufficient to generate two photon recording effectively, so the fiber laser we have developed is possible to use as a light source of three-dimensional optical memory.

An inline Mach-Zehnder interferometer for simultaneously measuring liquid level and temperature

We report a compact, robust, and cost-effective ultra-short pulse fiber laser incorporating a NALM-based all-PM modelocked Yb fiber laser oscillator and an Yb-doped fiber amplifier. The Yb-doped fibers are pumped with a low-power laser diode. The laser generates 12 ps pulses at a repetition rate of 20 MHz, center wavelength of 1040 nm, spectral width of 20 nm and average power of 128 mW. We believe that this type of fiber laser is an ideal seed source for further high-power femtosecond fiber laser.

Core–cladding mode recoupling based fiber optic refractive index sensor

We present a compact simultaneous strain and high-temperature measurement scheme using dual fiber Bragg gratings (FBGs) written in single mode fiber (SMF) and thin-core fiber (TCF). The different effective refractive indexes between the cores of SMF and TCF are the key point because such FBGs support two separate resonances in the reflection spectrum for sensing measurement. These two resonances have different optical parameters, elastic-optic coefficient, and thermal-optic coefficient, they shift with different sensitivities under axial strain and temperature variations. The etching process is utilized on the grating of TCF to increase the sensitivity differences of the dual FBGs. In the experiment, simultaneous measurement of strain and temperature with the high strain sensitivity of 3.25 pm/ $\mu \varepsilon $ and high temperature up to 800 °C is realized respectively. This sensor scheme suits the practical application for strain and high-temperature measurement simultaneously.

An ytterbium-doped, single-stage, double-pass nonlinear fiber amplification system was fabricated for amplifying an 1100-nm mode-locking fiber laser. Pre-chirp managed amplification (PCMA) was applied in realizing the nonlinear amplification process with an all-polarization-maintaining (PM) fiber construction. The system can deliver 19.8-nJ, 58.7-fs, 24.4-MHz amplified signal pulses with a 10-dB spectral range spanning from 1049 nm to 1130 nm. Further experimental investigations were conducted in exploring the dynamics of the double-pass nonlinear amplification process. This compact 1100-nm ultrafast fiber laser can be implemented for multi-photon microscopy (MPM) with deep penetration depth.