Multi-wavelength Brillouin Raman Fiber Laser Research Articles

OSNR enhancement of Rayleigh-assisted Brillouin-Raman fiber laser via double pass configuration.

We propose and demonstrate a 10 GHz spacing multi-wavelength Brillouin-Raman fiber laser (MBRFL) with wide bandwidth and an outstanding optical signal-to-noise ratio (OSNR). This is achieved by utilizing loop mirror at one end of the laser cavity through a symmetrical bi-directional Raman pumping scheme. The setup is arranged in a double pass configuration by employing different lengths of dispersion compensating fibers (DCF). The attainment of MBRFL with outstanding performance necessitates the optimization of Raman pump power, Brillouin pump wavelength, and DCF length. By employing an 11 km DCF, when setting the Brillouin pump wavelength at 1531.4 nm, 504 Stoke lines are produced with a channel spacing of 0.08 nm. All the counted laser lines have less than a 1-dB peak amplitude variation and are spread across a 40.4 nm bandwidth that covers from 1531.4 to 1571.8 nm wavelength. In this case, the Raman pump power is fixed at 900 mW which results in average OSNR and Stokes peak amplitude level of 28 dB and -7 dBm respectively. To date, this is the simplest cavity design with the widest bandwidth and flattest spectrum together with outstanding OSNR attained in 10 GHz spacing multi-wavelength fiber lasers that incorporate a single low-power Raman pump unit.

Broadband multi-wavelength Brillouin-Raman fiber laser with frequency switching

We purpose and demonstrate the switchable multi-wavelength Brillouin–Raman fiber laser (MBRFL) through a bi-directional Raman pumping scheme. The laser structure is arranged in a linear cavity by including a physical mirror at one side of the cavity. The switching operation for MBRFL with single- and double-wavelength spacing is implemented by optimizing the Raman power distribution through a variable optical coupler. This effect on feedback power of the physical mirror provides the difference between odd- and even-order Stoke lines’ maximum power on different sides of the cavity with 10 GHz and 20 GHz spacing. A 90/10 coupler is found to be the optimal. Up to 460 flat-amplitude lines within only a 0.5-dB flatness range, average −5 dBm Stokes peak power (SPP), 10 GHz frequency spacing, and an average optical signal-to-noise ratio (OSNR) of 26 dB are observed. All the counted laser lines are spread across a 37 nm bandwidth. Simultaneously, 170 Stoke lines with overall −2 dBm SPP, 28 dB OSNR, and 20 GHz frequency spacing are attained on other side of the cavity. These are achieved when the Raman pump power is set only at 900 mW. To date, this is the simplest cavity design with the flattest spectrum and highest output power for both wavelength spacing and excellent OSNR achieved in multi-wavelength fiber lasers that incorporate a single low-power Raman pump unit.

O-band tunable multiwavelength Brillouin-Raman fiber laser based on a wavelength-agile Raman pump.

Multiwavelength Brillouin-Raman fiber laser (MBRFL) features broadband multiwavelength generation with flat-amplitude and high optical signal to noise ratio (OSNR), which has great potential in optical fiber communication applications. Till now, the spectral regions of MBRFLs are mostly concentrated at conventional C- and L-band and the tunability of MBRFL is limited by using the Raman pump with fixed wavelength. Here, by utilizing wavelength-agile random fiber laser which can emit tunable lasing at 1.2 µm band as the Raman pump, we experimentally demonstrate the tunable MBRFL in the O-band for the first time, to the best of our knowledge. At Raman and Brillouin pump powers of 920 mW and -3 dBm, respectively, up to 90 Stokes lines with 0.13 nm wavelength spacing and >13 dB OSNR can be obtained when the Raman and Brillouin pump wavelength are set at 1231 nm and 1300 nm, respectively. Moreover, by tuning the wavelength of Brillouin pump from 1295 nm to 1330 nm, tunable MBRFL can be achieved with similar multiwavelength generation bandwidth by simultaneously tuning the Raman pump wavelength, and the number of Stokes lines are beyond 85 across the tuning range. The bandwidth of the demonstrated O-band MBRFL is also the widest wavelength span ever reported for multiwavelength Brillouin fiber lasers at 1.3 µm band. Our work indicates that the use of wavelength-agile random fiber laser as Raman pump in MBRFL can provide an effective way to extend the spectral regions of MBRFL and also improve the tunability performance of MBRFL.

L-U-band multiwavelength Brillouin-Raman fiber laser assisted by a broadband pump source

L-U-band multiwavelength Brillouin-Raman fiber laser assisted by a broadband pump source

Flatness enhancement of multi-wavelength Brillouin-Raman fiber laser with 10 GHz spacing utilizing Raman pump power distribution.

A simple high flat amplitude multi-wavelength Brillouin-Raman fibre laser (MBRFL) with 10 GHz spacing and excellent optical signal-to-noise ratio (OSNR) in C-Band spectral region is demonstrated. The laser consists of a linear cavity in which 12 km dispersion compensating fiber (DCF) in addition to 49 cm Bismuth-oxide Erbium doped fiber (Bi-EDF) are employed as a gain medium for amplification. The impact of Raman pump power distribution through changes in coupling ratio on amplitude flatness is carried out by comparing the peak power discrepancy between odd- and even-order Brillouin Stoke lines. This is the main property that allows the efficient controlling of gain propagation between lasing lines that is vital for Stokes flattening initiation and other output spectra characteristics. The attainment of MBRFL with outstanding OSNR necessitates the utilizing of Bi-EDF as a noise suppressor. By utilizing a 50/50 coupler, 354 identical channels together with uniform Brillouin Stokes linewidth within only 0.3-dB maximum power difference between adjacent channels is generated. The average OSNR and Stokes power are 28 dB and -5 dBm respectively when the RPP is set at 1300 mW. To date, this is the highest flatness 10 GHz spacing MBRFL with outstanding OSNR attained in MBRFL that incorporate only a single Raman pump unit.

Ultralong wavelength operation of a tunable multiwavelength Brillouin-Raman fiber laser in 1.65 μm band

A tunable multiwavelength Brillouin-Raman fiber laser (MW-BRFL) operated at an ultralong wavelength band (U-band) is presented in this work. The MW-BRFL was configured in a full-open linear cavity consisting of 11.2 km long dispersion compensating fiber that functioned as a Brillouin frequency shifter and Raman amplification gain medium. At Raman and Brillouin pump powers of 930 mW and 11.8 dBm, respectively, a stable multiwavelength generation with wavelength spacing of 0.17 nm was generated over a wavelength span of 53 nm. The generated channels covered a spectral range of 1630–1683 nm corresponding to 314 channels. The channels could also be tuned over 10 nm with an average optical signal-to-noise ratio greater than 26 dB. The laser system exhibited power fluctuation of less than 0.25 dB over 3 h. In a nutshell, the proposed MW-BRFL is promising with respect to its performance, simplicity and flexibility.

Switchable single-double frequency multi-wavelength Brillouin Raman fiber laser based on micro-air cavity misalignment

This study experimentally demonstrates a switchable single-double frequency spacing multi-wavelength Brillouin Raman fiber laser (MW-BRFL). The switching functionality was assisted by a micro air cavity (MAC) that was constructed by lateral misalignment of two cleaved fiber facets. Experimental results indicated that the frequency spacing of the generated channels could be switched via adjusting the MAC lateral misalignment. The laser performance was evaluated by fixing the peak power flatness to 1.5 dB. For Raman pump power of 800 mW, as many as 503 channels (39.72 nm bandwidth) with single frequency spacing of 0.079 nm were obtained when the lateral misalignment was set at 0 µm. On the other hand, with MAC misalignment of 25 µm, the laser produced 235 channels (37.03 nm bandwidth) with double frequency spacing of 0.158 nm. The peak power discrepancy between the odd and even channels was 20 dB, indicating high suppression of double-frequency spacing laser. In comparison to other switchable MW-BRFLs, this proposed configuration exhibited significant improvements with respect to channel bandwidth, flatness and suppression.

Brillouin-Raman fiber laser with switchable wavelength spacing based on Brillouin pump distribution

A switchable multi-wavelength Brillouin-Raman fiber laser (MW-BRFL) is presented in this work. The MW-BRFL consists of a full-open linear cavity in which dispersion compensating fiber is employed as the gain medium for Brillouin and Raman amplification. The switching operation for single- and double-wavelength spacing MW-BRFL can be implemented by controlling Brillouin pump (BP) power distribution and direction that enters the laser cavity via two fiber-entry points. This is achievable by optimizing the splitting ratio of an optical coupler and the initial BP power. For the proposed laser setup, a 30/70 optical coupler was found to be the optimum. By setting the initial BP power at −3.0 dBm, 246 laser lines with 20-GHz frequency spacing were observed. The transformation to 10-GHz frequency spacing was attained by increasing the BP power to 11.8 dBm that resulted in 483 laser lines. All the counted laser lines had 3 dB peak power variation and were spread across a 38 nm bandwidth. In a nutshell, the proposed MW-BRFL is promising with respect to its performance, simplicity and flexibility.

Full-Open Cavity Multi-Wavelength Random Fiber Laser With Double Brillouin Frequency Spacing

A multi-wavelength Brillouin-Raman random fiber laser (BRRFL) with wavelength spacing of double Brillouin frequency shift (BFS) has been proposed for the first time, to the best of our knowledge. This BRRFL has an extremely simple full-open cavity configuration made up of only one roll of fiber, where bidirectional stimulated Raman/Brillouin scattering (SRS/SBS) and Rayleigh scattering based random distributed feedback coexist. In order to further enhance the performance of the BRRFL, a combination of erbium-doped fiber amplifier and single-mode fiber is incorporated into one side for random lasing regeneration. Both the side-mode suppression ratio (SSR) and order number of generated Brillouin Stokes lines (BSLs) show some improvements. A total of 66 BSLs with double BFS spacing has been obtained. Furthermore, the demonstrated laser system offers a wide tunable range with excellent flatness of spectral envelope. The proposed laser featuring simple structure and double BFS spacing would enable promising potentials in optical communication and sensing systems.

Wide multiwavelength Brillouin-Raman fiber laser assisted by an arc-shaped fiber attenuator.

A wide bandwidth, single-spacing half-open-cavity multiwavelength Brillouin-Raman fiber laser (MWBRFL) is demonstrated. The laser cavity contains a fiber loop mirror (FLM) with an arc-shaped optical fiber attenuator that is used to control the mirror reflectivity, thereby suppressing gain competition from longitudinal cavity modes. A tuning range of 45 nm with 632 lines at Raman and 1525 nm Brillouin pump powers of 1.2 W and 12 dBm can be achieved using the 10 dB arc-shaped optical fiber attenuator in the cavity. This is in comparison to 433 Stokes lines obtained over a 31 nm tuning range for the half-open MWBRFL cavity without any feedback power optimization. The MWBRFL has low power fluctuations of less than 0.1 dB over a 1 h test period. The inclusion of the arc-shaped optical fiber attenuator in the MWBRFL provides substantial control over the reflectivity of the FLM as well as improving the laser's tuning range to generate a high number of Brillouin Stokes signals.

Wide-band multiwavelength Brillouin–Raman fiber laser based on feedback optimization

A multiwavelength Brillouin–Raman fiber laser (BRFL) with a 51-nm wide bandwidth is proposed and demonstrated. The BRFL is configured in a half-open cavity (HOC) design with a variable optical attenuator in the cavity. The BRFL exhibits a 60 % improvement in tunability as compared to a conventional half-open BRFL structure. At a Raman pump power of 1.2 W and 1525 nm Brillouin pump power of 12 dBm, 652 uniform Stokes lines with an average optical signal to noise ratio (OSNR) higher than 40 dB are produced. The generated channels have a total output power of 14.5 dBm and a power fluctuation of 0.5 dB over a period of one hour. In contrast, the conventional HOC shows a lower performance in terms of tuning range, OSNR and Stokes lines count. The 51 nm bandwidth using a single Raman pump laser is, to the best of our knowledge, the widest yet reported.

Erbium-Doped Fiber Amplification Assisted Multi-Wavelength Brillouin-Raman Fiber Laser

Multi-wavelength fiber laser based on Brillouin scattering in optical fiber has the potential of application in dense wavelength division multiplexing (DWDM) system. To enhance the performance of the fiber lasers, researchers proposed usages of erbium, or Raman amplification techniques. In an earlier work, it was reported that extracting residual Raman pump out of the laser cavity improves the performance of a multi-wavelength Raman fiber laser. In this paper, we proposed a setup utilizing the residual Raman pump to pump an erbium-doped fiber in multi-wavelength Brillouin-Raman fiber laser. Results show that the additional erbium-doped fiber is capable of amplifying the propagating Brillouin Stokes by more than 15-dB. This in turn helps in achieving lower stimulated Brillouin threshold and subsequently allow for higher number of Brillouin Stokes lines to be generated.

Enhanced flatness of 20 GHz channel spacing multiwavelength Brillouin-Raman fiber laser with sub-millimeter air gap.

We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation. When setting the Brillouin pump wavelength at 1529 nm and the air-gap distance to 0.4 mm, 296 Stokes lines are produced with a channel spacing of 0.158 nm. The lasing bandwidth is 46.60 nm that covers from 1529.16 to 1575.76 nm wavelength. In this case at Raman power of 950 mW, the intense Brillouin pump power of 2 dBm saturates the cascaded higher-orders lasing lines. As a result, the overall peak power discrepancy is maintained at just 1.8 dB where an average optical-signal-to-noise ratio of 20 dB is realized. To date, this is the widest bandwidth with the flattest spectrum attained in multiwavelength fiber lasers that incorporate a single Raman pump unit.

Switchable Multiwavelength Brillouin–Raman Fiber Laser Utilizing an Enhanced Nonlinear Amplifying Fiber Loop Design

We propose and demonstrate a new multiwavelength Brillouin–Raman fiber laser with switchable 10 and 20 GHz spacing. This is achieved by proper adjustments of optical coupling ratios that are incorporated in the design that consists of an enhanced nonlinear amplifying fiber loop. By utilizing a 50/50 coupler, 443 flat amplitude channels with 10 GHz spacing is realized. On the other hand, a 99/1 coupler is feasible for 20 GHz spacing that yields 215 lasing lines. In both cases, the average optical signal-to-noise ratios (OSNR) are 16.5 dB (50/50 coupler) and 24 dB (99/1 coupler). Wide multiwavelength bandwidth, flexible wavelength spacing, and high number of channels with excellent OSNRs are achieved using only a single Raman pump unit through a simple construction.

Tunable multiwavelength Brillouin-Raman fiber laser in a linear cavity with spectrum reshaped by Rayleigh scattering

Abstract In this paper, we propose and experimentally study a simple linear cavity multiwavelength Brillouin-Raman fiber laser (MBRFL). The fiber feedback loop which consists of an optical circulator is placed at the end of the dispersion compensating fiber (DCF) to enhance the reflectivity of the Brillouin Stokes waves. As a result, 245 Brillouin Stokes lines with 0.072 nm channel-spacing are generated across the wavelength range of 18.6 nm from 1544.98 to 1563.58 nm when Brillouin pump (BP) is fixed to 1545 nm/−2.94 dBm and a single Raman pump (RP) laser power is set to 718 mW. The output spectrum is reshaped based on Rayleigh scattering by adding 45 km single mode fiber (SMF) in the cavity. The average optical signal to noise ratio (OSNR) about 18 dB has been measured in this structure. A tunable multiwavelength range of 20 nm from 1545 to 1565 nm is obtained. We also demonstrate the influence of BP wavelength and power on MBRFL.

S-band multiwavelength Brillouin-Raman fiber laser utilizing an optical reflector

This paper reports on the performance of multi-wavelength Brillouin-Raman fiber laser exploiting an optical reflector. The ring-cavity multi-wavelength Brillouin-Raman fiber laser is based on hybrid Brillouin-Raman gain supported by SBS and SRS. The multiwavelength Brillouin-Raman fiber laser is systematically analyzed at different values of Raman pump powers, Brillouin pump powers, and categorically based on single mode fiber length, and Raman fiber length which operated from 1460nm to 1430nm of BP wavelengths. The optical reflector at 90% of reflectivity acts as an optical mirror is used in this structure. There are 5 channels at 1500nm, and 1510nm of BP wavelengths observed at Raman pump power of 30dBm, 8km of Raman fiber and 4km of single mode fiber. In addition, the Raman pump power of 30dBm is able to produce high gain value and subsequently generate a large number of channels across S-band region.

Single Brillouin frequency shifted S-band multi-wavelength Brillouin-Raman fiber laser utilizing fiber Bragg grating and Raman amplifier in ring cavity

This paper is focusing on simulation and analyzing of S-band multi-wavelength Brillouin–Raman fiber laser performance utilizing fiber Bragg grating and Raman amplifier in ring cavity. Raman amplifier-average power model is employed for signal amplification. This laser system is operates in S-band wavelength region due to vast demanding on transmitting the information. Multi-wavelength fiber lasers based on hybrid Brillouin–Raman gain configuration supported by Raman scattering effect have attracted significant research interest due to its ability to produced multi-wavelength signals from a single light source. In multi-wavelength Brillouin–Raman fiber, single mode fiber is utilized as the nonlinear gain medium. From output results, 90% output coupling ratio has ability to provide the maximum average output power of 43 dBm at Brillouin pump power of 20 dBm and Raman pump power of 14 dBm. Furthermore, multi-wavelength Brillouin–Raman fiber laser utilizing fiber Bragg grating and Raman amplifier is capable of generated 7 Brillouin Stokes signals at 1480 nm, 1510 nm and 1530 nm.

Effect of large effective area fiber length on the performance of forward-backward scattering combination multiwavelength Brillouin-Raman fiber laser

In this paper we experimentally demonstrate the effect of large effective area fiber length on the performance of a multiwavelength Brillouin–Raman fiber laser in which the forward and backward generated Stokes lines due to Brillouin scattering are combined together through a 3 dB coupler. Thus, the demonstrated laser is dubbed a forward–backward scattering combination multiwavelength Brillouin–Raman fiber laser (FBSC-MBRFL). This laser system utilizes a large effective area fiber and a dispersion compensating fiber that act as Brillouin and Raman gain media, respectively. It is demonstrated that by employing forward pumping schemes, the demonstrated laser system is capable of generating a good flat amplitude Brillouin Stokes line with an average optical to noise ratio of 17 dB along the spectral spans. However, the backward pumping scheme is able to produced high bandwidth spans. At the optimal large effective area fiber length of 50 km, a Raman pump power of 1100 mW at Brillouin pump wavelengths of 1550 mm and 1560 nm is identified to produce the maximum bandwidth with values of approximately 28.45 nm and 24.08 nm, respectively.

Effects of Raman pump power distribution on output spectrum in a multi-wavelength BRFL.

This paper aims to investigate changes in multi-wavelength Brillouin-Raman fiber laser (MBRFL) spectra characteristics that are influenced by variation of Raman pump power distribution along the two fiber-entry points. This is carried out by incorporating a Raman pump source with a set of couplers with various ratios. In this arrangement, the optimization of pumping ratio is properly carried out to achieve high number of lasing lines with 20 GHz spacing which yield the highest peak power discrepancy between odd- and even-order lasing lines and an excellent Stokes optical signal-to-noise ratio (S-OSNR). Employment of 50/50 coupler offers 212 flat amplitude channels with an average 27.5 dB S-OSNR and -10 dBm Stokes peak power when the Brillouin pump wavelength is set at 1543 nm. Achievements such flat and wide bandwidth MBRFL spectrum with 20 GHz spacing and excellent S-OSNR utilizing just a single pump source is significant in terms of simplicity and flexibility.

Pump power optimization for linear cavity multiwavelength Brillouin–Raman fiber laser

The optimization of the pump power of L-band multiwavelength Brillouin–Raman fiber laser utilizing a linear cavity is experimentally demonstrated. We determine the optimum Raman pump power (RPP) in which the maximum number of Brillouin Stokes lines, a wide tuning range, and a high optical signal-to-noise ratio (OSNR) can be obtained. Two different dispersion compensating fiber lengths (1.18 and 7.1km) are used in this work. The number of Brillouin Stokes lines is saturated in the moderate Raman pump region, and both the tuning range and OSNR decrease with increasing RPP. The tuning range decreases from 20nm to 13nm and from 27nm to 16.5nm and the OSNR decreases from 18.6dB to 15.3dB and from 19.3dB to 16.6dB for the 1.18 and 7.1km fiber lengths, respectively. The optimum RPP is identified at 500mW for the 1.18km fiber length and at 325mW for the 7.1km fiber length.