S-band multiwavelength ring Brillouin/Raman fiber laser with 20 GHz channel spacing

We propose and demonstrate a tunable S-band multiwavelength Brillouin/Raman fiber laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long dispersion compensating fiber in a simple ring configuration, acting as a nonlinear medium for the generation of multiple wavelengths from stimulated Brillouin scattering (SBS) and also as a nonlinear gain medium for stimulated Raman scattering (SRS) amplification. A laser source with a maximum power of 12 dBm acts as the Brillouin pump (BP), while two 1420 nm laser diodes with a total power of 26 dBm act as the Raman pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of even and odd Stokes at an average power of -12 dBm and -14 dBm respectively, and by separating the even and odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the four-wave mixing (FWM) effect, anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using SRS to obtain gain in the S-band region.     

Switchable multiwavelength ytterbium-doped double-clad fiber laser based on a multimode fiber grating

A simple switchable multiwavelength double-clad fiber laser using a multimode fiber Bragg grating (MMFG) as a wavelength selective component is demonstrated. The MMFG is fabricated directly in the active double-clad fiber, resulting in low splicing loss and compact configuration. By properly adjusting the polarization controller in the cavity, the double-clad fiber laser can stably operate at different multiwavelength states at room temperature. At lower pump levels, the laser can be switched between single- and dual-wavelength operations, while at higher pump levels the laser can switch between dual- and triple-wavelength operations. The slope efficiency of the system is 41% with the maximum output power of 6.2 W.     

Frequency switching multiwavelength Brillouin Raman fibre laser based on feedback power adjustment technique

A simple switchable multiwavelength Brillouin–Raman fibre laser (BRFL) was demonstrated. The laser was arranged in a half-open cavity configuration including a physical mirror device with an adjustable reflectivity at one side of the laser cavity. The impact of the feedback power adjustment on frequency switching was carried out by comparing the peak power difference between odd- and even-order Stokes lines. Up to 468 flat-amplitude lines with a 10?GHz frequency spacing and average optical signal to noise ratio (OSNR) of 33 dB were observed with mirror reflectivity values of ～15% up to 60% at a 1534?nm Brillouin pump power of 7?dBm and 0.9?W Raman pump power of 0.9?W. – Under the same pumping conditions, setting the mirror reflectivity at its OFF state (where reflectivity is nearly 0%) allows for up to 242 lines with 20?GHz spacing to be realized, with ONSR values of ～35?dB.     

Tunable optical frequency comb generation in a periodically poled lithium niobate waveguide based on stimulated Brillouin scattering

We propose and demonstrate a technique for the generation of an optical frequency comb (OFC) in a periodically poled lithium niobate (PPLN) waveguide based on stimulated Brillouin scattering. A single continuous wave laser is sent to a multi-wavelength Brillouin erbium fibre laser for generating a set of coherent and phase-locked multi-wavelength spectral lines. They are injected into a PPLN waveguide to obtain an OFC. We investigate the influence of the cavity structure on the OFC property in our two different schemes. The number of comb lines is affected by the 980 pump current and Brillouin pump power. The OFCs are tunable in a large range by changing their central wavelength.     

Bismuth-based Brillouin/erbium fiber laser

A multi-wavelength Brillouin/erbium-doped fiber laser (BEFL) operating in the 1573 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a bismuth-based erbium-doped fiber (Bi-EDF) approximately 215 cm long and a single mode fiber (SMF) of various lengths to generate an optical comb with a spacing of approximately 0.089 nm. Two 3 dB couplers were used to form a looping arm in the system in order to produce cascaded Brillouin Stokes waves as internal feedback for multi-wavelength operation. A stable output laser comb with 10 lines at more than ??13 dBm was obtained with 4.85 dBm Brillouin pump power and two 140 mW pumps at 1480 nm. The 1480 nm pumps' power and SMF length have a significant effect on the number of wavelengths and on the output power of the generated wavelength comb.     

Investigation of the effects of SOA locations in the linear cavity of an O-band Brillouin SOA fiber laser

An investigation into the effect of semiconductor optical amplifier (SOA) location in an O-band Brillouin SOA fiber laser (BSFL) was performed. Better output peak power flatness was generated by placing the SOA after the nonlinear medium, which is a 20?km true wave fiber (TWF) than placing it before the TWF. A maximum power of six flat output peaks with average power of ?22.0?dBm for a BP (Brillouin pump) wavelength of 1320?nm was obtained, generated from a BSFL with a SOA located after the TWF, compared with three flat Stokes signals with the SOA before the TWF at a BP wavelength of 1310?nm. The flat peak power output for the O-band Brillouin fiber laser is important, especially in producing a good O-band source.     

Effects of different Raman pumping schemes on stimulated Brillouin scattering in a linear cavity

The effects of backward, forward, and bidirectional Raman pumping schemes on stimulated Brillouin scattering (SBS) is investigated in this study. By using a linear cavity, we utilize residual Brillouin pump (BP) and Raman pump (RP) power after each transmission through a 25 km single-mode fiber (SMF) used as a gain medium. The SBS threshold power is reduced in the forward, backward, and bidirectional Raman pumping schemes by 2.5, 1.75, and 2.75 dB, respectively when the 1480 nm RP power is fixed at 150 mW and the BP wavelength is 1580 nm. Surprisingly, it is revealed that the SBS threshold reduction depends strongly and solely on Raman gain and it is independent of the Raman pumping schemes. In addition, the effect of Raman amplification on SBS is more effective at the SBS threshold, especially in the bidirectional and forward schemes.     

Efficient Raman laser system using stimulated Brillouin scattering with different confocal parameters for CH(4)

We report the efficient Raman laser system with the wavelength of 1.54 microm from a passively Q-switched Nd:YAG laser with high-pressure methane gas. It has been known that the stimulated Brillouin scattering (SBS) prevents the Raman conversion. The efficiency of the Raman conversion, however, has been greatly enhanced with a specially designed lens to use a backward-stimulated Brillouin in our scheme. The special lens has a focal length of 12 cm, and a maximum conversion efficiency of 51% has been obtained with the first-Stokes energy of 32 mJ and the residual pump energy of 30 mJ at 1,400 psi. Comparing two resonators with different focal lengths of the lenses, we have found that backward-SBS can be greatly enhanced by use of the shorter focal length of 12 cm, and the enhanced backward-SBS helps to increase the conversion efficiency.     

Slow light generation using SBS in a liquid-core photonic crystal fiber

Based on stimulated Brillouin scattering (SBS), the slow light effect in photonic crystal fibre (PCF), which is filled with highly nonlinear liquid-carbon disuphide in the core region, is investigated. Maximum allowable pump power for undistorted output pulse, minimum value of pump power required to initiate the SBS effect, Brillouin gain and time-tonic delay experienced by the pulse in the designed liquid-core photonic crystal fibre, are all calculated numerically. We have found that the maximum time-delay up to ～134.4 ns at 1.064 μm can be obtained using 1 m long liquid-core PCF pumped with only 65.8 mW, which is lower than the value reported in the literature for achieving such a high delay time. The results indicate that liquid-core PCF is capable of generating tunable time-delay that is adjusted by the pump power and structural parameters of the proposed liquid-core PCF.     

Slow light generation in single-mode tellurite fibers

Theoretical investigations of stimulated brillouin scattering-based tunable slow light in (i) Er-doped tellurite and (ii) undoped tellurite fibers are reported. Maximum allowable pump power for undistorted output pulse, Brillouin gain, time-delay, figure-of-merit, and time-delay slop efficiency of both the fibers has been obtained. We have found that (i) Brillouin gain up to ~91 dB and time delay of 140 ns can be achieved using 1100 mW pump power in 2 m Er-doped fiber and (ii) Brillouin gain up to ~86 dB and time delay of ~227 ns using 23 mW pump power in 100 m undoped tellurite fiber can be achieved. Simulated results indicate that the time delay in fibers can be tuned with the pump power to obtain tunable slow light features in these fibers. We feel that detailed theoretical investigations and simulations carried out in the study have potential impact in the design and development of slow light-based photonic devices.     

光纤拉曼放大器中级联的受激布里渊散射

在以25kmG652单模光纤为增益介质的光纤拉曼放大器中,观察到了级联的受激布里渊散射。光纤中的双瑞利折射作用导致了二阶布里渊散射光子的出现,加快了二阶布里渊散射的出现。在拉曼增益的作用下,随着二阶布里渊散射的饱和会出现级联的多阶布里渊散射,形成梳状光谱。该梳状光谱也具有明显的阈值特性。在拉曼泵浦功率是1200mW的时候,出现梳状光谱的阈值在1.5到2.5dBm之间。在传输系统中,级联的受激布里渊散射会导致放大器的增益饱和,严重恶化系统的信噪比,因此必须采用增加信号光的带宽或者对信号光进行调制等措施加以控制。但该现象也有可能被用来制造梳状光源。     

Multiwavelength picosecond and single wavelength femtosecond pulses emission in a passively mode-locked fiber laser using a semiconductor saturable absorber mirror and a contrast ratio tunable comb filter

We propose and demonstrate a highly flexible fiber laser capable of generating stable multiwavelength picosecond and single wavelength femtosecond pulses by using a semiconductor saturable absorber mirror and a contrast ratio tunable comb filter. In the multiwavelength lasing regime, up to 11-wavelength stable mode-locked pulses in 3 dB bandwidth with a channel spacing of 0.8 nm were obtained. While in the single wavelength with broadband spectrum lasing regime, the fiber laser emitted 576 fs soliton pulse. Through changing the contrast ratio of the comb filter, the conversion between the multiwavelength picosecond and single wavelength femtosecond pulsed operations could be efficiently achieved.     

Efficient Raman conversion through backward stimulated Brillouin scattering

We report a new scheme for efficient Raman conversion in high-pressure CH(4) gas. Through the use of backward stimulated Brillouin scattering as a resonator mirror for the pump wave at a wavelength of 1.06 μm, Raman laser generation at the eye-safe wavelength of 1.54 μm has been obtained from a passively Q-switched Nd:YAG laser. At a pressure of 600 psi, we obtained Raman conversion efficiencies of up to 48%.     

Tunable multiwavelength fiber laser based on a double Sagnac HiBi fiber loop

A tunable multiwavelength fiber laser based on double Sagnac loops is proposed and demonstrated. Comb filter characteristics of single and double Sagnac loops are analyzed by Jones matrix. Simulated results show that there are better tunability and controllability with double loops than with a single loop, and this also has been confirmed by experimental results. By adjusting the polarization controller and the length of the polarization maintaining fiber the wavelength range, wavelength spacing, and laser linewidth can be tuned. Experimental results indicate that the linewidth of the multiwavelength fiber laser was 0.0187 nm and the optical sidemode suppression ratio was 50 dB.     

Bulk acousto-optic wavelength agile filter module for a wavelength-multiplexed optical scanner

An acousto-optic tunable filter-based wavelength-selection module with features optimized for a wavelength-multiplexed optical scanner (W-MOS) is proposed and demonstrated. The W-MOS produces high-speed multiple scan beams if it is engaged with an agile tunable source with multiwavelength generation capability. In particular, the proposed fiber-connected module features high-speed, low-loss, narrow-linewidth, and single-multiple wavelength selection by means of radio frequency drive signal control for single- or multiple-beam scan operations. The unique module offers input laser beam power control that in turn delivers the desired scanned laser beam power shaping. Experimental results match module design theory and demonstrate a fast 5.4-micros wavelength selection speed, a low (1.53-dB) fiber-to-fiber optical insertion loss, a 5.55-nm 3-dB spectral width, and a 1500-1600-nm agile wavelength operational band.     

Photonic generation of tunable microwave signal using Brillouin fiber laser

A simple approach to generate two bands of tunable microwave signal is proposed and demonstrated. In this scheme, two single-mode fibers with optimized Brillouin frequency shift spacing have been chosen as the scattering medium in two cascaded ring cavities. Two bands of tunable microwave signal from 390 to 453 MHz and 10.863 to 11.076 GHz can be obtained through adjusting the temperature of the fiber and the pump wavelength. The tunable frequency range can be further expanded by using a temperature controller with a wider adjustment range. The generated microwave signal exhibits high stability on frequency.     

分立式光纤拉曼放大器泵浦方式的实验研究

对分立式光纤拉曼放大器的前向、后向泵浦方式进行了实验研究。拉曼增益介质为10km的色散补偿光纤。分别测量了前、后向泵浦的分立式FRA的增益、噪声指数和动态范围。实验结果表明,当泵浦功率小于500mW时,前、后向泵浦的分立式FRA的增益几乎相等。当泵浦功率大于500mW时,在前向泵浦的分立式FRA中发生了受激布里渊散射,前向泵浦的FRA的增益小于后向泵浦的FRA的增益,前者的噪声大于后者的噪声;前向泵浦的FRA不再具有增益保持特性,而后向泵浦的FRA仍具有增益保持特性。当泵浦功率大于500mW时,分立式FRA应该采用后向泵浦的方式。     

Self-seeded multi-wavelength Brillouin–erbium fibre laser with 20 GHz frequency gap

We demonstrate a self-seeded multi-wavelength Brillouin–erbium fibre laser with double Brillouin frequency gap. The twice channel gap is induced by the gain difference in different directions. Thirty-six stable output channels with 20?GHz frequency gap are obtained when the 980?nm pump power is 300?mW. The factor that induces the double frequency gap is investigated and proved.     

10 Gbit/s optical wavelength converter with a Brillouin scattering-based spectral filter

For the first time, to our knowledge, a highly robust, high-bit-rate (10 Gbit/s) wavelength converter that is based on a narrow Brillouin filter is reported. The conversion takes place in a semiconductor optical amplifier (SOA) in a cross-gain-phase process. The SOA operates in a weak-modulation mode, and the exiting signal undergoes a dc reduction with a narrow spectral filter. In our system we perform spectrally narrow filtering by using a long Brillouin grating.     

光纤中基于SBS实现慢光的数值研究

通过运用带有预测.校正的隐格式有限差分法对基于光纤的受激布里渊散射耦合方程组进行了数值求解.在增益0～16范围内考察了布里渊增益系数、增益带宽以及有效模面积对时间延迟和脉冲展宽的影响.结果表明,较小的增益系数和增益带宽、较大的有效模面积使得Stokes信号具有更大的饱和增益值,相应的时间延迟也较大.在固定泵浦功率并保证增益参数在小信号范围的情况下,时间延迟及脉冲展宽因子随着增益系数的增加而增加,但随着增益带宽以及有效模面积的增加而减少.