Wavelength-spacing tunable multiwavelength erbium-doped fiber laser based on four-wave mixing of dispersion-shifted fiber

We experimentally demonstrate a wavelength-spacing tunable multiwavelength erbium-doped fiber laser based on degenerate four-wave mixing in a dispersion-shifted fiber incorporating multiple-fiber Bragg gratings. We have achieved stable operation of the multiwavelength erbium-doped fiber laser, which has 0.8 nm spacing ten-channel lasing wavelengths and a high extinction ratio of more than approximately 45 dB, at room temperature. The output power of the multiwavelength erbium-doped fiber laser is stable, so the peak fluctuation is less than approximately 0.2 dB. By changing the properties such as loss and polarization state of multiple fiber Bragg grating cavities, we can exercise flexible control of the wavelength spacing of the multiwavelength output. We can also obtain switchable multiwavelength lasing operation by elimination of the effects of alternate single-fiber Bragg gratings.     

Broadly tunable multiwavelength Brillouin-erbium fiber laser using a twin-core fiber coupler

A tunable multiwavelength Brillouin-erbium fiber laser (MW-BEFL) using a twin-core fiber (TCF) coupler is proposed and demonstrated. The TCF coupler is formed by splicing a section of TCF between two single-mode fibers. By simply applying bending curvature on the TCF coupler, the peak net gain is shifted close to the Brillouin pump (BP), which has advantage for suppressing self-lasing cavity modes with low-BP-power injection. In this work, the dependency of the Stokes signals tuning range on the free spectral range (FSR) of TCF coupler is studied. It is also found that the tuning range of MW-BEFL can exceed the FSR of TCF coupler by adopting proper BP power and 980-nm pump power. Up to 40 nm tuning range of MW-BEFL in the absence of self-lasing cavity modes is achieved.     

Widely tunable linear-cavity multiwavelength fiber laser with distributed Brillouin scattering

We demonstrate a multiple wavelength Brillouin/erbium fiber laser in a linear cavity configuration.The laser cavity is made up of a fiber loop mirror on one end of the resonator and a virtual mirror generated from the distributed stimulated Brillouin scattering effect on the other end.Due to the weak reflectivity provided by the virtual mirror,self-lasing cavity modes are completely suppressed from the laser cavity.At Brillouin pump and 1480-nm pump powers of 2 and 130 mW,respectively,11 channels of the demonstrated laser with an average total power of 7.13 dBm can freely be tuned over a span of 37-nm wavelength from 1530 to 1567 nm.     

Multi-wavelength erbium-doped fiber laser using four-wave mixing effect in doped fiber

We demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) using erbium gain and four-wave mixing (FWM) effect in a piece of erbium-doped fiber (EDF) with high erbium ion concentration. The EDF has a pump absorption rate of 24.6 dB/m at 979 nm and is bi-directionally pumped by 980-nm laser diodes. FWM effect redistributes the energy of different oscillating lines and causes multi-wavelength operation. The laser generates more than 22 lines of optical comb with a line spacing of approximately 0.10 nm at the 1569-nm region using only 1.5-m-long EDF.     

Simple tunable multiwavelength Brillouin/Erbium fiber laser utilizing short-length photonic crystal fiber

We have demonstrated a simple ring cavity tunable multiwavelength Brillouin/Erbium fiber laser (MWBEFL), in which 70 m highly nonlinear photonic crystal fiber (HNL-PCF) is used as the Brillouin gain medium. The fiber laser utilizes recycling mechanism to enhance stimulated Brillouin scattering (SBS). The configuration that consists of only 3 optical components is easy to be integrated and improves the practicality. At the maximum 1480 nm pump power of 110 mW and the Brillouin pump power of 3 dBm, 10 stable output channels with more than 10 dB optical signal to noise ratio (OSNR) and 0.078 nm channel spacing could achieve 10 nm tuning ranges.     

Broadly tunable multiwavelength fiber laser with bismuth-oxide EDF using large effective area fiber

A multiwavelength laser comb using 2.49 m Bismuth-oxide erbium-doped fiber (Bi-EDF) with different lengths of large effective area fiber (LEAF) in a ring cavity configuration is realized. The Bi-EDF is used as the linear gain medium and LEAF is used as the non-linear gain medium for stimulated Brillouin scattering. Out of the four different lengths, the longest length of 25 km LEAF exhibits the widest tuning range of 44 nm (1576 to 1620 nm) in the L-band at 264 mW pump power and 5 mW Brillouin pump power. In addition, a total of 15 output channels are achieved with total average output power of −8 dBm from this laser structure. All Brillouin Stokes signals exhibit high peak power of above −20 dBm per signal and their optical signal-to-noise ratio of greater than 15 dB.     

Broad spectral sliced multiwavelength source with a mode locked fiber laser

A simple multi-wavelength source is demonstrated based on spectral slicing of supercontinuum (SC) light using a Sagnac loop mirror. A mode locked fiber laser with pulse width of 800 fs is employed to generate the SC in photonic crystal fiber (PCF). The SC light extending from 1200 nm up to the wavelength region above 1750 nm is obtained at the amplified pulse pump power of 30 dBm. By slicing the SC with a loop mirror, a multiwavelength comb spectrum is obtained with different channel spacing for different operating wavelength region. Spacings of 1.5, 2.3, and 2.9 nm are shown at wavelength regions of 1220, 1450, and 1730 nm, respectively. It is also observed that the signal to noise ratio (SNR) increases from 15 to 20 dB as the operating wavelength increases from 1220 to 1730 nm region.     

Wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator based on multiple four-wave mixing

We propose a wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator (MW-FOPO) with a simple line cavity and one pump source based on multiple four-wave mixing (MFWM). Stable multi-wavelength lasing at room temperature is achieved due to the four-wave mixing effect and the broadband gain of the fiber optical parametric amplifier based on a highly nonlinear fiber. The wavelength spacing of the proposed MW-FOPO can be tuned by adjusting the wavelength of the pump light or the central wavelength of the fiber Bragg grating. Seventeen lasing lines with a wavelength spacing of 2.89 nm and an extinction ratio larger than 10 dB, which covers the wavelength region from 1540 to 1568 nm is demonstrated.     

Flattening effect of four wave mixing on multiwavelength Brillouin-erbium fiber laser

A multiwavelength Brillouin-erbium fiber laser with enhanced output uniformity is demonstrated and its performance with and without the assistance of four wave mixing (FWM) is compared. The presence of FWM effect is proven by the generation of anti-Stokes wave and higher-order Stokes wave. This scheme is successful in flattening the multiwavelength output. At Brillouin pump wavelength of 1,550 nm, between the first and the last output channel, peak power differences of 4.59 and 8.32 dB are recorded for the scheme with and without the assistance of FWM, respectively. This represents 3.73 dB improvement in the multiwavelength output power uniformity.     

Spatiotemporal mode-locked multimode fiber laser with dissipative four-wave mixing effect

The high degree of freedom and novel nonlinear phenomena of multimode fiber are attracting attention. In this work, we demonstrate a spatiotemporal mode-locked multimode fiber laser, which relies on microfiber knot resonance (MKR) via dissipative four-wave-mixing (DFMW) to achieve high-repetition-rate pulses. Apart from that, DFMW mode locking with switchable central wavelengths can also be obtained. It was further found that high pulse energy induced nonlinear effect of the dominant mode-locking mechanism transforming from DFMW to nonlinear Kerr beam cleaning effect (NL-KBC). The experimental results are valuable for further comprehending the dynamic characteristics of spatiotemporal mode-locked multimode fiber lasers, facilitating them much more accessible for applications.     

A reconfigurable multiwavelength fiber laser with switchable wavelength channels and tunable wavelength spacing

We report the experimental demonstration of a reconfigurable multiwavelength fiber laser source with switchable wavelength channels and tunable wavelength spacing by spectrum slicing a broadband light source using a tunable comb filter. The tunable comb filter is based on a thermally-induced linearly-chirped fiber Bragg grating (LCFBG). As an example to demonstrate the effectiveness of the method, two wavelength channels with various wavelength spacings and eight wavelength channels with ∼1.6 nm wavelength spacing were experimentally demonstrated. All the wavelength channels have rejection ratios of greater than 20 dB, and very small 3-dB linewidths of ∼10 pm. The multiwavelength optical source has such unique advantages as simple all-fiber structure, switchable wavelength channels, tunable wavelength spacing, very narrow linewidths, and stable room-temperature operation.     

High-order dispersion-resulted tunable multiwavelength femtosecond laser

Resonant dispersive waves generated by high-order dispersion in a Ti:sapphire mode-locked solitary laser are investigated and experiments are found to be in good agreement with theoretical analysis. Both theory and experiment show that the wavelength differences can be tuned in a large range via changing the cavity dispersion. This simple technique can be applied to the fields where tunable femtosecond pulses at multiple wavelengths are needed. The described mechanism may be applied in other systems where solitons are known to exist.     

Spacing-tunable multi-wavelength fiber laser based on cascaded four-wave mixing in highly nonlinear photonic-crystal fiber

A multi-wavelength fiber laser based on the cascaded four-wave mixing in highly-nonlinear photonic-crystal fiber is proposed and investigated. The cascade operation is initiated by two strong pump waves boosted by multi-mode pumping erbium/ytterbium co-doped double-cladding fiber amplification technique. A segment of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber is employed to induce highly efficient cascaded four-wave mixing. The wavelength spacing can be continuously tunable by stretching the fiber Bragg grating. Experimental results show that multiple wavelengths with a high optical side-mode suppression-ratio of >30 dB are achieved. Furthermore, the proposed multi-wavelength fiber laser exhibits an excellent stability at room temperature.     

Multi-wavelength bismuth-based erbium-doped fiber laser based on four-wave mixing effect in photonic crystal fiber

A stable multi-wavelength erbium-doped fiber laser based on four-wave mixing (FWM) in a photonic crystal fiber (PCF) is demonstrated in this paper. The phase matching condition for four-wave mixing in the photonic crystal fiber has been enhanced using a seed signal and a polarisation controller to control the states of polarisation in the ring laser cavity. At a maximum pump power of 1480 nm, 5 lines are observed with nearly 2.15 nm spacing between the lines, and with a signal to noise ratio of more than 20 dB. The number of channels and wavelength spacing can be controlled by varying the output coupler ratio.     

Self-seeded multiwavelength Brillouin-erbium fiber laser

We propose and demonstrate a self-seeded multiwavelength Brillouin-erbium fiber laser with an internally self-excited Brillouin pump, which is achieved by incorporation of a length of single-mode fiber together with a Sagnac loop mirror into a fiber ring cavity. In this simple scheme the Brillouin pump is self-excited in the fiber ring cavity and then used to seed the Brillouin multiwavelength comb in the single-mode fiber. Stable generation of more than 120 Brillouin Stokes wavelengths with relatively uniform amplitudes is demonstrated with this scheme. It is also shown that such a self-seeded Brillouin laser has good stability and repeatability.     

Influence of degenerate four-wave mixing on the performance of supercontinuum-based multiwavelength optical source

The influence of degenerate four-wave mixing (FWM) on the performance of supercontinuum-based multiwavelength optical source has been investigated in detail experimentally and theoretically. Numerical simulation results show that the degenerate FWM effect has a deteriorative influence on the spectral uniformity and the optical signal-to-noise ratio (OSNR) of supercontinuum-based optical source, and by suppressing degenerate FWM effect the performance enhancement of the supercontinuum can be achieved successfully. These results are also confirmed by our experiments. Experimentally, by suppressing degenerate FWM the crosstalk of adjacent channels to the filtered channel can be reduced by as much as 15 dB, and consequently the measured receiver sensitivity at 10 Gbit/s for the filtered optical source is improved from $-1.7$ to $-17.8$~dBm.     

Phase-sensitive four-wave mixing and Raman suppression in a microstructure fiber with dual laser pumps

On coupling two phase-coherent frequency-conjugate laser pulses into a microstructure fiber, we observe phase-sensitive photon generation via four-wave mixing, and suppression of Raman emission at the middle frequency.     

Nondegenerate four-wave mixing in a birefringent optical fiber pumped by a dye laser

An efficient nondegenerate four-wave-mixing process in a highly birefringent optical fiber pumped by a dye laser is reported. The output beam from a dye laser (at ~610 nm) was found to mix with the accompanying superfluorescent light (from 575 to 600 nm) in a birefringent fiber to generate a distinct frequency-shifted beam, which could be Stokes or anti-Stokes radiation, depending on which mode of the fiber was excited. The frequency shift was comparable with that observed in the well-known pump-divided degenerate process, as confirmed by the theory.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

L-band tunable multiwavelength fiber laser using an unpumped polarization maintaining an erbium-ytterbium double-clad fiber-loop mirror

An L-band tunable multiwavelength source is newly proposed and demonstrated employing an unpumped polarization maintaining an erbium-ytterbium codoped double-clad fiber (PM-EYDF) loop mirror in a semiconductor optical amplifier-based fiber-ring laser. This is achieved by only adjusting the polarization controller in the loop mirror for the birefringence of the PM-EYDF, which is polarization dependent, and which originates from the fact that the traversing signal with a different polarization state absorbed by the PM-EYDF changes its effective birefringence. A similar behavior also happens when the traversing signal power is varied. The multiwavelength operation with the tunable range as large as the comb spacing of the transmission spectrum of the PM-EYDF loop mirror is successfully accomplished.