Fengping Yan

A 1.97 μm multiwavelength thulium-doped silica fiber laser based on a nonlinear amplifier loop mirror

A 1.97 μm multiwavelength Tm-doped fiber laser based on a nonlinear amplifier loop mirror (NALM) has been experimentally demonstrated. The NALM with 500 m standard single mode fiber introduces intensity-dependent gain to alleviate mode competition caused by homogeneous gain broadening in Tm-doped fibers. At room temperature, up to 42 wavelengths with a wavelength spacing of 0.33 nm oscillate within a 10-dB bandwidth simultaneously. Repeat measurement of the laser spectrum shows the wavelength drift of a multiwavelength Tm-doped fiber laser is less than 0.05 nm in 40 min.

1.94 μm switchable dual-wavelength Tm 3+ fiber laser employing high-birefringence fiber Bragg grating

A 1.94 μm switchable dual-wavelength Tm(3+) fiber laser employing two high-birefringence fiber Bragg gratings (HB-FBGs) is demonstrated. The polarization hole burning effect enhanced by the HB-FBG is first observed and adopted to guarantee stable dual-wavelength operation in the spectral region near 2 μm at room temperature. The wavelength spacing between the dual lasing wavelengths is 0.81 nm. The polarization states of the dual-output lasers are orthogonal. By adjusting a polarization controller, a single-wavelength mode operating at one of the dual wavelengths can be selected. The side-mode-suppression ratio of each laser can be greater than 60 dB. The power fluctuation measurement at both operating wavelengths shows that this Tm(3+) fiber laser has good stability.

A stable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser with superimposed FBG and an in-line two-taper MZI filter

A simple approach to fabricate a stable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser with one superimposed fiber Bragg grating (FBG) is proposed and demonstrated. The superimposed FBG is fabricated by the dual-exposure method for wavelength selection. A home-made in-line two-taper Mach?Zehnder interferometer is incorporated to balance the intra-cavity loss for the wavelengths. The SLM operation is guaranteed by a feedback fiber loop and saturable absorber. A stable dual-wavelength SLM fiber ring laser with a wavelength spacing of approximately 8.53?nm is experimentally realized. The optical signal-to-noise ratio of the laser output is over 50?dB and the linewidth of each wavelength measured by the delayed self-heterodyne method is 9.67?kHz and 9.07?kHz, respectively. The proposed scheme offers the possibility for difference frequency generation of terahertz radiation.

Switchable and tunable dual-wavelength single-longitudinal-mode erbium-doped fiber laser with special subring-cavity and superimposed fiber Bragg gratings

A switchable and tunable dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) has been proposed and demonstrated. Two superimposed fiber Bragg gratings (SI-FBG) have been used as one original wavelength selection component. A special subring-cavity was employed to select the SLM. By properly adjusting a polarization controller, single- and dual-wavelength switchable operations with high wavelength and power stability were realized experimentally. Regardless of which work mode, the signal to noise ratio was higher than 60 dB and the polarization extinction ratio was higher than 20 dB. The wavelength-spacing was 9.96 nm, indicating that it can be used to generate continuous-wave terahertz waves. The linewidth of each lasing wavelength measured by the delayed self-heterodyne method was approximately 1.25 kHz and 1 kHz, respectively. By stretching the SI-FBG, the EDFL had a wavelength-tunable range of 5.96 nm in both the single- and dual-wavelength operations.

A high stability wavelength-tunable narrow-linewidth and single-polarization erbium-doped fiber laser using a compound-cavity structure

A high stability wavelength-tunable narrow-linewidth and single-polarization erbium-doped fiber laser using a compound-cavity structure is proposed and demonstrated experimentally. The compound-cavity is composed of a main-linear-cavity and a subring-cavity. Using a pump power of 150?mW, the optical signal to noise ratio of the laser output is as high as ?67?dB; the wavelength and output power fluctuation are 0.7?pm and 0.07?dBm respectively in an experimental period of 1?h; the linewidth of the laser output is as narrow as 650?Hz; the degree of polarization of the laser output is stable at a value of 100.8% in 15?min and the polarization extinction ratio is as high as 30.57?dB; the wavelength-tunable range is as wide as ?8.1?nm. The proposed fiber laser can be used in areas where high stability, narrow-linewidth, single-polarization and wide wavelength-tunable range are needed.

DFB laser based on single mode large effective area heavy concentration EDF

A π phase shifted distributed feedback (DFB) laser based on single mode large effective area heavy concentration erbium-doped fiber (EDF) has been demonstrated. The homemade EDF was fabricated by the modified chemical-vapor deposition (MCVD) technique, and the 13cm long π phase shifted fiber grating was written in the intracore of the EDF. The erbium-doped concentration is 4.19 × 10(25) ions/m(3), the mode field diameter of the fiber is 12.2801 um at 1550 nm, the absorption coefficients of the fiber are 34.534 dB/m at 980 nm and 84.253 dB/m at 1530 nm. The threshold of the DFB laser is 66 mW, and the measured maximum output power is 43.5 mW at 450 mW pump power that corresponding to the slope efficiency of 11.5%. The signal-to-noise ratio (SNR) of the operating laser at 200 mW input power is 55 dB, and the DFB laser has a Lorentz linewidth of 9.8 kHz at the same input pump power.

Mode interference in dual-core photonic crystal fibers

The modal characteristics of dual-core photonic crystal fibers are analyzed by a full vector supercell method. The fundamental and second order modes of dual-core PCF consist of a pair of even and odd modes with different polarization, the parity properties of the modal electric field are illuminated. Based on the analysis of parity of modal electric fields, we investigated the vector modal interference in dual-core PCF. The power transfer induced by interference of different mode pair is investigated. It is the interference between two same polarized modes that contribute to the inter-core coupling of power. It is shown that the optical power will oscillate from one core to the other. The dependence of the coupling coefficients on wavelength and structural parameter for different polarization is discussed.

Widely tunable single-/dual-wavelength fiber lasers with ultra-narrow linewidth and high OSNR using high quality passive subring cavity and novel tuning method

High stability single- and dual-wavelength compound cavity erbium-doped fiber lasers (EDFLs) with ultra-narrow linewidth, high optical signal to noise ratio (OSNR) and widely tunable range are demonstrated. Different from using traditional cascaded Type-1/Type-2 fiber rings as secondary cavities, we nest a Type-1 ring inside a Type-2 ring to form a passive subring cavity to achieve single-longitudinal-mode (SLM) lasing with ultra-narrow linewidth for the first time. We also show that the SLM lasing stability can be further improved by inserting a length of polarization maintaining fiber in the Type-2 ring. Using a uniform fiber Bragg grating (FBG) and two superimposed FBGs as mode restricting elements, respectively, we obtain a single-wavelength EDFL with a linewidth as narrow as 715 Hz and an OSNR as high as 73 dB, and a dual-wavelength EDFL with linewidths less than 1 kHz and OSNRs higher than 68 dB for both lasing wavelengths. Finally, by employing a novel self-designed strain adjustment device capable of applying both the compression and tension forces to the FBGs for wavelength tuning, we achieve the tuning range larger than 10 nm for both of the EDFLs.

A switchable and wavelength-spacing tunable single-frequency and single-polarization dual-wavelength erbium-doped fiber laser based on a compound-cavity structure

A switchable and wavelength-spacing tunable single-frequency and single-polarization dual-wavelength erbium-doped fiber laser is proposed and demonstrated experimentally. The fiber laser is composed of a main linear cavity and two subring cavities. In dual-wavelength operation, the wavelength spacing can be tuned from 0.430?nm to 4.487?nm, showing that the fiber laser can be used for photonic generation of a microwave signal with a tunable frequency range from 54?GHz to 563?GHz; in single-wavelength operation, the fiber laser can either work at a fixed wavelength of 1544.108?nm or work at a wavelength with a tunable range of 4.057?nm, from 1544.538?nm to 1548.595?nm. The linewidths of two wavelengths are approximately 760?Hz and 810?Hz respectively. The polarization-extinction ratios of the laser outputs, both in dual- and single-wavelength operation, are higher than 30?dB.

An Orthogonal-Polarization Dual-Wavelength Fiber Laser with Stable Output

A new orthogonal-polarization dual-wavelength fiber laser by fabricating a uniform FBG and a chirped FBG in a polarization-maintaining erbium-doped fiber (PM-EDF) is proposed and demonstrated. The wavelength space is 0.18nm and the optical signal-to-noise ratio is greater than 50 dB with pump power of 246-mW. Chirped FBG is used to make the reflectivity wavelengths match between two PM-FBGs much easier. Since both EDF and FBGs are polarization-maintaining without splices and the two wavelengths operate with two orthogonal polarizations, the maximum amplitude variation and wavelength shifts for both lasing wavelength with 3-min intervals over a period of six hours were less than 0.2 dB and 0.005 nm, which shows stable dual-wavelength output.