Qinghe Mao

Switchable multiwavelength erbium-doped fiber laser with cascaded fiber grating cavities

We propose a new concept to produce switchable multiwavelength oscillations with a cascaded fiber Bragg grating overlapping cavity erbium-doped fiber laser. The laser can be designed to operate in multiwavelength or in wavelength switching modes. The different lines have different thresholds. For three-wavelength oscillation, the output powers are linear or piecewise linear functions of the input pump power. An output with a variation of only 1.5 dB has been achieved with an input pump power of 100 mW. For wavelength switching, three single-wavelength and two dual-wavelength operation regions have been obtained toy adjusting the input pump levels.

Multiwavelength erbium-doped fiber lasers with active overlapping linear cavities

Multiwavelength oscillations in erbium-doped fiber (EDF) lasers with active overlapping linear cavities are investigated in detail. The laser can be designed to produce multiwavelength oscillations in the C-band and in the L-band. With a C-band three-wavelength laser, experiments show that the output powers of the lasing lines increase linearly or piecewise linearly with pump input. Any one lasing wavelength can be tuned over several nanometers depending on the gain tilt in the vicinity of the lasing wavelength while multiwavelength oscillation is still being maintained. The output power of any specific lasing line can be adjusted by suitably designing the EDF sections. This property also allows the laser to operate in multiwavelength switching mode. The laser exhibits a novel multiwavelength optical bistable behavior in the L-band. With an L-band dual-wavelength laser, the bistable input-output hysteresis behaviors of the two L-band wavelengths evolve in antiphase with respect to each other. The width of the bistable region has been increased to several tens of mW. It can be controlled and adjusted by the cavity loss and the EDF length. It is found that simultaneous L-band dual-wavelength oscillations can be obtained when part of the EDF, which functions as a saturable absorber, has been bleached. Moreover, simultaneous multiwavelength oscillations in both C-band and L-band have also been successfully demonstrated with the laser.

Optical bistability in an L-band dual-wavelength erbium-doped fiber laser with overlapping cavities

The authors investigate the optical bistability in an L-band dual-wavelength erbium-doped fiber (EDF) laser with overlapping cavities. The bistable input-output hysteresis behavior of the two lasing wavelengths evolves in antiphase. The bistable region is tens of milliwatts wide. The bistability is essentially due to the homogeneous saturable absorption of EDF. The cross-gain saturation causes the bistabilities of the two lasing lines to evolve in antiphase with respect to each other. The gain clamping effect helps to widen the bistable region, which may be controlled by the cavity loss and by the EDF length.

L-band fiber laser with wide tuning range based on dual-wavelength optical bistability in linear overlapping grating cavities

A new mechanism to tune an erbium-doped fiber laser in the L-band is presented. The technique is based on the dual-wavelength bistability in overlapping linear cavities, which allows two lasing lines to be switched from one to another by a triggering pulse superimposed to the dc bias current applied to the pump source. The two wavelengths can be independently tuned to give the laser a total tuning range of 33 nm that covers the whole L-band, while the tuning range of either of the tunable fiber Bragg gratings (FBGs) used is only half of that range. An output dynamic range of 7 dB, and a maximum output power of up to 11 dBm with high optical signal-to-noise ratios are obtained. A study of the switching transient responses shows that the typical switching time is about 4 to 12 ms, depending on the dc bias current applied to the pump source. Moreover, our wide tuning technique is implemented by only applying ordinary commercial tunable FBGs which normally would have given rise to only about half of the tuning range; no additional filtering mechanisms are required to achieve almost uniform outputs.

Amplification enhancement of L-band erbium-doped fiber amplifiers by reflection scheme

Abstract A reflection L-band erbium-doped fiber amplifier (EDFA), which can effectively suppress and completely exploit the backward C-band amplified spontaneous emission (ASE) with a feedback reflection loop, is presented in this paper. The mechanism of the backward ASE secondary pumping effect is experimentally investigated in detail. Our experimental results have shown that, for a given input pump power, compared to the end-pumped EDFA, the gain and output power of the reflection EDFA can be improved considerably without paying much noise penalty. When the EDFA operates with flattened gain spectra, the gain is improved by about 7 dB with an extra noise penalty of about 1.2 dB, where the saturation output power is increased by 2.5–3.2 dB and which may also be made independent of the input signal power.

Widely tunable L-band erbium-doped fiber laser with fiber Bragg gratings based on optical bistability

We propose and demonstrate a mechanism to widely tune L-band erbium-doped fiber lasers with ordinary commercial tunable fiber Bragg gratings. The function is based on the dual-wavelength bistability in linear overlapping laser cavities. The laser may be switched between two wavelengths located, respectively, in the short- and long-wavelength regions of the L-band by triggering the pump with a typical switching time of about 11 ms. The two wavelengths can be independently tuned to give the laser a total tuning range of 33 nm and an output dynamic range of 7 dB. Nearly constant output powers with high optical signal-to-noise ratios are achieved across the whole tuning range.

Multiwavelength erbium-doped fiber lasers with active coupling cavities

Erbium-doped fiber (EDF) lasers with active coupling cavities have recently shown to enable the production of multiwavelength oscillations with various novel functions. This paper reviews the advances of such lasers. The lasers may be designed to produce multiwavelength oscillations in both C and L bands, either as a combined band or as two separate bands. In the C band, the laser can operate in a multiwavelength regime with controllable output powers and tunable wavelengths for any one individual lasing line. Wavelength-switching is also possible; switching responses of about 100 Hz are typical. In the L band, the laser exhibits multiwavelength bistable phenomena. The bistable hysterisis behaviors for a dual-wavelength laser evolve in antiphase with respect to each other. The width of the bistable region can be controlled; it could be designed to be as wide as a few hundred milliwatts. The two wavelengths can be switched from one to the other, with typical switching times of 4 to 15 ms. By suitably controlling the bistability, simultaneous multiwavelength oscillations in the L band alone, or in combination with the C band, can be obtained. A new wavelength-tuning and switching mechanism can be achieved by using such bistabilities. With this scheme, widely tunable and switchable lasers in fiber ring and linear configurations have been constructed with two commercially available tunable ordinary fiber Bragg gratings (FBGs). The lasers can be tuned over the whole L-band although the tunable range of each of the FBGs is only about 15 nm.

Optical bistability in a linear L-band fiber laser

Optical bistability in an L-band dual-wavelength erbium-doped fiber laser with linear overlapping cavities is investigated. The hysterisis bistabilities of the two lasing wavelengths evolve in antiphase. It has a large bistable region which may be controlled and adjusted by the EDF length and the cavity losses. Simultaneous dual-wavelength oscillations in the L-band are also achieved.