Generation of multiorder Stokes and anti-Stokes lines in a Brillouin erbium-fiber laser with a Sagnac loop mirror

Fiber-optic frequency comb generation using low-seed power FWM and Brillouin-assisted power equalization

In this paper, we experimentally demonstrate an all-fiber broadband tunable optical frequency comb (OFC) operating in the C-band. The OFC is generated by broadening a power-equalized stimulated Brillouin scattering (SBS)-based seed comb (SBS-OFC) using four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). The seed SBS-OFC is obtained from a pump and Stokes power recycling cavity, which yields ≈15 comb lines with 10.8 GHz line spacing having 16 dBm average power. The seed SBS-OFC is further power-equalized by a Brillouin-assisted power equalization (BAPE) technique to minimize the high pump contribution at the recycling cavity output. The power-equalized seed SBS-OFC, which has low-power of -4.5d B m at the BAPE cavity output, is propagated down a dual-pass 200 m dispersion flattened HNLF. At the HNLF output, we obtain ≈140 comb lines within a 12 nm bandwidth having 10.8 GHz line spacing. We demonstrate wavelength tunability over a span of 35 nm by using a tunable laser source as the Brillouin pump. We also observe and measure a secondary OFC generated during the power-equalization process by placing a 10% coupler inside the BAPE cavity. Our experimental results closely match the trends obtained in the simulation.

Relative intensity noise in a multi-Stokes Brillouin laser

We investigate the relative intensity noise (RIN) properties of a multi-Stokes Brillouin fiber ring laser. We experimentally analyse the intensity noise of each Stokes wave and study the noise dynamics of the cascaded Brillouin scattering process. We observe up to 20 dB/Hz intensity noise reduction compared to that of the RIN input pump laser. We examine the impact of the fiber ring quality factor on the laser RIN features such as amplitude reduction and relaxation frequency. We also investigate the influence of the Brillouin gain detuning on the RIN reduction. A numerical model based on a set of coupled-mode equations replicates the experimental observations. Our study enables us to determine the optimal parameter values to operate the multi-Stokes laserin the low noise regime.

Wide tuning range and high OSNR self-seeded multi-wavelength Brillouin-erbium fiber laser based on a Lyot filter

A tunable self-seeded multi-wavelength Brillouin-erbium fiber laser (BEFL) based on a Lyot filter is experimentally demonstrated in this paper. The Lyot filter is constructed by a polarization-dependent isolator (PDI), two polarization controllers (PCs), and a 20-cm-length polarization-maintaining fiber. In this proposed structure, the PDI is used as a polarizer. Due to the periodic filtering characteristics of the Lyot filter, the multi-wavelength output of the laser shows different Brillouin bands by adjusting the PCs. In the experiment, a single Brillouin band can be produced with the tuning range of 30 nm, from 1527.8 to 1557.8 nm. The optical signal-to-noise ratio (OSNR) of the output wavelengths is ∼20  dB. Dual Brillouin bands are observed.

S-band multiwavelength Brillouin/Raman distributed Bragg reflector fiber lasers

A multiwavelength Brillouin/Raman distributed Bragg reflector fiber laser operating in the S-band region is proposed and demonstrated. The laser uses a 7.7 km long dispersion-shifted fiber with an effective mode area of 15 μm(2) as the Brillouin and Raman gain media simultaneously. Two 1420 nm laser diodes with a combined power of 372 mW are used as pump sources, while a fiber Bragg grating with a center wavelength of 1500 nm is used as a reflector in the cavity. The setup is capable of generating 6 clearly defined Stokes lines at the highest pump power, spanning from 1499.8 to 1500.3 nm with the even Stokes having relatively higher peak powers, between 1.4 and 3.5 dBm as compared to the odd Stokes, which have peak powers between -4.7 and -5.0 dBm. The output of the laser is very stable and shows little to no fluctuations over a monitoring period of 50 min.

Broadly tunable L-band multiwavelength BEFL utilizing nonlinear amplified loop mirror filter

We demonstrate a widely tunable L-band multiwavelength Brillouin-erbium fiber laser utilizing a nonlinear amplified fiber loop mirror filter (AFLMF). By manipulating polarization controllers placed in the fiber loop, the erbium peak gain spectrum is able to be shifted. The nonlinear AFLMF induces wavelength-dependent cavity loss and serves as an amplitude equalizer. In addition, it provides flexibility on controlling the amount of light reflected and transmitted into and out of the laser's cavity. By utilizing 100 mW 1480 nm pump and 1.1 mW Brillouin pump power, an average of 24 stable output channels are generated by the proposed structure that could all be tuned over the whole L-band window from 1570 nm to 1610 nm.

Cavity enhanced stimulated Brillouin scattering in an optical chip for multiorder Stokes generation

We report the first demonstration of on-chip cascaded stimulated Brillouin scattering (SBS). Cascaded SBS is characterized in a 4 cm long chalcogenide (As₂S₃) rib waveguide where the end facet reflections provide a monolithic Fabry-Perot (FP) resonator. The presence of the FP cavity reduces the Brillouin gain threshold, which enables observation of cascaded SBS at reduced pump powers. We observe up to three orders of Stokes waves in the backscattered signal at a coupled peak power of 1.34 W. Anti-Stokes waves due to four-wave mixing between the pump and the Stokes wave were observed in the forward spectrum.

Tunable multiwavelength generation based on Brillouin-erbium comb fiber laser assisted by multiple four-wave mixing processes

A tunable multiwavelength Brillouin-erbium comb fiber laser with ultra-narrow wavelength spacing and a large wavelength number, employing a 135-m highly nonlinear fiber, has been experimentally demonstrated. The simultaneous presence of Brillouin pump and Stokes lines within the ring cavity initiate higher-order Stokes and anti-Stokes lines via multiple four-wave mixing processes. The experiment demonstrates that this is an effective solution of increasing the number of lasing lines. Up to 150 lasing lines in single-longitudinal-mode operation with a rigid wavelength spacing of 0.075 nm have been achieved at 1480 nm pump powers of 165 mW and Brillouin pump power of 12.0 dBm. The multiwavelength source exhibits a good stability on both the operating wavelengths and the output powers, and a 6-nm tuning range from 1562 nm to 1568 nm is obtained.

Multiwavelength Brillouin-erbium fiber laser with double-Brillouin-frequency spacing

We demonstrate a multiwavelength Brillouin-erbium fiber laser with double-Brillouin-frequency spacing. The wider channel spacing is realized by circulating the odd-order Stokes signals in the Brillouin gain medium through a four-port circulator. The circulated odd-order Stokes signals are amplified by the Brillouin gain and thus produce even-order Stokes signals at the output. These signals are then amplified by erbium gain block to form a ring-cavity laser. Ten channels with 0.174 nm spacing that are generated at 0.5 mW Brillouin pump power and 150 mW pump power at 1480 nm can be tuned from 1556 nm to 1564 nm. The minimum optical signal-to-noise ratio of the generated output channels is 30 dB with maximum power fluctuations of ±0.5 dB.

Double Brillouin frequency shift through circulation of odd-order Stokes signal

We demonstrate a simple configuration for generating a double Brillouin frequency shift through the circulation of an odd-order Brillouin Stokes signal. It is operated based on cascaded Brillouin scattering in single-mode optical fibers that behave as the Brillouin gain media. A four-port circulator is incorporated into the setup to circulate the odd-order Brillouin Stokes signal in the fiber. It thus initiates a higher order Brillouin Stokes signal, which is double Brillouin frequency downshifted from the input signal. For the 5 km long fiber, the Brillouin pump power at 23 mW gives a clean output spectrum with 30 dB sideband suppression ratio. The output signal is 0.174 nm or approximately 21.7 GHz downshifted from the input signal.

Theory and experiment of a fiber loop mirror filter of two-stage polarization-maintaining fibers and polarization controllers for multiwavelength fiber ring laser

A fiber loop mirror (FLM) filter with two-stage polarization-maintaining fibers (PMFs) and polarization controllers (PCs) is presented. The transmission function of this FLM is calculated in detail by Jones matrix. The wavelength interval depends on both the PMFs and the PCs. The side frequencies can be restrained by choosing appropriate length of the PMFs. Furthermore, an erbium-doped fiber ring laser based on this FLM filter is proposed and demonstrated. Stable single-, double- and triple-wavelength are achieved respectively. The 3 dB line-width is less than 0.03 nm, and the fluctuation of wavelength and peak power is less than 0.05 nm and 0.1 dB in 30 minutes.

Tunable range enhancement of Brillouin-erbium fiber laser utilizing Brillouin pump pre-amplification technique

We demonstrate an enhanced multiwavelength L-band Brillouin-erbium fiber laser (BEFL), in which the Brillouin pump is pre-amplified before entering the single-mode fiber. The Brillouin pump pre-amplification provided by the Erbium-doped fiber has created higher intensity of Brillouin Stokes line generated in the single-mode fiber that leads to the homogenous gain saturation. Thus the built-up of self-lasing cavity modes is suppressed in a wider wavelength range. In contrary to the conventional linear-cavity BEFL, the number of output channels is enhanced within the same tuning range.

Brillouin amplification and lasing in a single-mode As2Se3 chalcogenide fiber

Brillouin amplification and lasing are demonstrated in a single-mode As2Se3 chalcogenide fiber. A Brillouin gain of 42 dB was measured in a 4.9 m long fiber for a pump power of 68 mW at a 1.56 mum wavelength. In addition, a compact As2Se3 fiber-based Brillouin laser with a threshold power of 35 mW and a slope efficiency of 38% for nonresonant pumping is demonstrated.

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.