Dong Xiao-yi

Generation of wavelength-switched optical pulse from a fiber ring laser with an F-P semiconductor modulator and a HiBi fiber loop mirror

A simple configuration to perform wavelength switching in an actively mode-locked fiber ring laser is demonstrated. A Fabry-Perot laser diode was used as a modulator and a HiBi fiber loop mirror was used as a periodic multichannel wavelength filter in the cavity. By setting the channel spacing of nm can be achieved by tuning the fiber loop mirror filter. In the wavelength-switched process, the modulation frequency was not required to be changed.

High extinction ratio Mach–Zehnder interferometer filter and implementation of single-channel optical switch

Abstract A novel structure of high extinction ratio filter based on a Mach–Zehnder (M–Z) interferometer and a standard single-mode fiber loop mirror (SMFLM) is proposed for the first to our knowledge. The numerical simulation and experimental results show that the extinction ratio can be improved greatly in comparison with the conventional M–Z interferometer in the same parameters. The improvement of the extinction ratio depends on mainly the difference between the two arms and the measuring resolution. A single-channel optical switch is also demonstrated by using a fiber Bragg grating (FBG) instead of the SMFLM. The dynamic range of greater than 37.4 dB at wavelength-selective port is obtained.

Tunable dual-wavelength actively mode-locked fiber laser with an F-P semiconductor modulator

A novel actively mode-locked fiber laser for generating dual-wavelength picosecond pulses is proposed by using a Fabry-Perot laser diode as the modulator in the ring cavity. A linear chirped fiber grating was used as a wavelength selector and produces temporal-spectral multiplexing of the pulses in the gain medium to reduce gain cross-saturation effects. About 2-GHz stable dual-wavelength pulses with a wavelength spacing of 0.92 nm at room temperature were experimentally demonstrated and the wavelengths could be tuned in a range of about 3 nm.

Pulse-amplitude equalization in a rational harmonic mode-locked fiber ring laser by using modulator as both mode locker and equalizer

A simple method, by letting the pulses pass through an electrooptic intensity modulator twice, for the amplitude equalization of high repetition rate pulses generated from a p-order rational harmonic mode-locked fiber ring laser when p<5 was proposed. The modulator was used as both a mode locker and a pulse-amplitude equalizer in the cavity. A theoretical explanation based on time-domain analysis was used to find appropriate parameters to obtain an equalized pulse train and the experimental results agree with the theory.

Switchable dual-wavelength erbium-doped fiber laser with a tilted fiber grating

A dual-wavelength erbium doped fiber laser with a tilted fiber Bragg grating and photonic crystal fiber is proposed and demonstrated. In the laser, a 2W EDFA provides gain for all the laser lines; the highly nonlinear photonic crystal fiber introduces dynamic energy transfer between the two wavelengths caused by four wave mixing effect, so that a stable dual-wavelength oscillation at room temperature is implemented. Different switching modes can be achieved by adjusting the lateral offset between the fiber grating and the guiding single mode fiber or by varying the state of polarization in the laser cavity. The maximum of output power of the laser has reached 314mW.

A Room-Temperature Multiwavelength Erbium-Doped Fibre Laser by Exploiting Polarization Hole Burning

Multiwavelength operation of a linear cavity erbium-doped fibre laser (EDFL) is proposed and demonstrated. A 3-dB fibre loop mirror and a high birefringence (HiBi) fibre loop mirror are utilized as the cavity reflectors. By utilizing the wavelength-dependent polarization rotation induced by the HiBi fibre loop mirror and by using a fibre polarizer to control the intracavity polarization state, the polarization states of different wavelengths are diversified. Therefore, the polarization hole burning (PHB) effect has been greatly enhanced and the homogeneous broadening of erbium-doped fibre is suppressed to a large extent. By simply tuning a polarization controller, we experimentally obtained simultaneous lasing of four and five wavelengths with wavelength spacing of ~1.8 nm and less than 2 nm at room temperature, respectively. The repeated scans show that all of these lasers have good stability.

Mode Exciting Properties of Photonic Crystal Fibres with the Optical Field Incident from a Single Mode Fibre

We numerically investigate the mode exciting properties of photonic crystal fibres by using the beam propagation method when the optical field is input from a traditional single mode fibre. The results show that both the excited mode spectrum and the coupling-efficiency of each excited mode depend on the normalized pitch ?/? and the normalized hole-size ?/?. Furthermore, we obtain the boundary profile of the optimizing coupling-efficiency for the excited fundamental mode: the boundary (?/?)* is linear to the boundary (d/?)*. All of these will pave the way for smoothing applications of photonic-crystal fibres, such as splicing and designing photonic-crystal-fibre functional devices.

Principles and realizations of FBG wavelength tuning with elastic beams

The general principles and realizations of FBG wavelength tuning with elastic beams are proposed and demonstrated. Theories and experiments show that when displacement at the center point of simple beams, deflection of cantilever beams and torsion strain of torsion beams are relatively small, Bragg wavelength shifts of sensing FBGs have linear relationship with applied external stress, lateral displacement, torque and torsional angles, respectively. The experimental results indicate that the curvature sensitivity of the simple beam is 1.65 nm/m−1, the displacement sensitivity of the equivalent-strain cantilever beam is 4.4 cm/kg and the torque and torsional angle sensitivities of the torsion beam are 6.27 nm/Nm and 0.0867 nm/degree, respectively.

Realization of Stable Narrow Linewidth Dual-Wavelength Lasing in an Erbium-Doped Fibre Laser by Cleaving the Wavelength-Selective Filter Spectrum

We propose and demonstrate a new concept of stable narrow-line-width and close wavelength spacing dual-wavelength lasing in an Er-doped fibre ring laser (EDFRL) by cleaving the spectrum with a wavelength-selective component in the EDFRL. A fibre loop mirror (FLM) combining with a polarization controller (PC) acts as the cleaver. The cleaver can produce a fine pectinate spectrum. By adjusting the PC, the fine pectinate spectrum can be so changeable that cleaving the spectrum of a fibre Bragg grating (FBG) into two parts. As a result, we obtain the dual-wavelength fibre lasering with a bandwidth of only 0.03 nm and a wavelength spacing of only 0.07 nm. Furthermore, the laser can also perform stable switchable single wavelength or stable different-bandwidth dual-wavelength by carefully adjusting the PC at room temperature.

Simulations of Effect of High-Index Materials on Highly Birefringent Photonic Crystal Fibres

Novel highly birefringent photonic bandgap fibres (PBGFs) are obtained by filling of a high index material in the air holes of total internal reflection birefringent photonic crystal fibres. The effect of the filling high index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using plane-wave method. Moreover, the phase and group modal birefringence have been studied by a full-vector finite-element method. Numerical results show that very high group and phase modal birefringence with magnitude of order of 10−2 and 10−3 has been respectively acquired, which is much higher than those of the non-filled fibres. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs, whose effect on the birefringence and confinement loss has also been discussed.