Liu Yan-Ge

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.

Experimental Investigation of High Power Erbium–Ytterbium Co-doped Double Clad Fibre Laser

All-fibre high power erbium–ytterbium co-doped double clad fibre lasers are proposed and demonstrated. By using different back-cavity mirrors, the different double clad fibre lasers are constructed. It is experimentally found that the output behaviour of laser can be controlled by a back-cavity mirror. The lower the reflectivity of the back-cavity mirror, the higher the output power and the high the slop efficiency. The maximum output power is about 1.6 W and the slop efficiency is 27.6%.

Transmission Bandwidth Tunability of a Liquid-Filled Photonic Bandgap Fiber

A temperature tunable photonic bandgap fiber (PBGF) is demonstrated by an index-guiding photonic crystal fiber filled with high-index liquid. The temperature tunable characteristics of the fiber are experimentally and numerically investigated. Compression of transmission bandwidth of the PBGF is demonstrated by changing the temperature of part of the fiber. The tunable transmission bandwidth with a range of 250 nm is achieved by changing the temperature from 30°C to 90°C.

Multi-wavelength fiber laser based on broadband fiber grating and HiBi fiber loop mirror

A fiber laser based on broadband C-band fiber grating (CFG) and high birefringence (HiBi) fiber loop mirror (FLM) is demonstrated, which uses the comb-like reflection performance of the HiBi FLM. Under different polarization states, different output lasers are gained by choosing the polarization states of the light in the cavity using the polarization controller. By this method, a single wavelength or dual wavelength laser beam can be output, and multi-wavelength oscillates can be achieved.

Enhancing Coherent Combining Efficiency via Choosing Appropriate Lasing Wavelength in a Michelson Compound Cavity Based on Two 3 dB Fibre Loop Mirrors and One Fibre Bragg Grating

Enhancing coherent combining efficiency via choosing appropriate lasing wavelength in a Michelson compound cavity based on two 3?dB fibre loop mirrors and one fibre Bragg grating (FBG) has been experimentally demonstrated. The FBG with 4.5% reflectivity is replaced at the cleaved facet with 4% Fresnel reflection. A high coherent combining efficiency of 93.5% is obtained when the FBG with central wavelength at 1559.845?nm is introduced into the cavity, while it is only 90.1% combining efficiency with the FBG at central wavelength 1557.830?nm. In comparison with other reports, the proposed compound-cavity laser has the advantage of needless tuning FBG to obtain the coherent condition, and it is facile to ascertain the seemly wavelength lasing for a Michelson compound cavity.