Dual-wavelength Brillouin ring-cavity fiber laser with tunable channel spacing

We experimentally demonstrate a dual-wavelength Brillouin fiber laser configured a pre-amplified Brillouin pump and FBG filter in a ring-cavity. The Brillouin laser can generate 21 Brillouin Stokes with 0.084 nm spacing, the first-Stoke has a peak power of 2.19 dBm. By adjusting the TLS wavelength and FBG’s reflection wavelength from circulating in the ring-cavity, the generated output dual-wavelength is stabile and the channel spacing is tunable, the widest and narrowest channel spacing obtained is approximately 1.12 nm (139 GHz) and 0.084 nm (10.5 GHz).     

Effects of output coupler reflectivity on the performance of a linear cavity Brillouin/erbium fiber laser

The effect of output coupler reflectivity (or output coupling ratio) on the performance of a linear cavity Brillouin/erbium fiber laser (BEFL) is demonstrated. The operating wavelength, output laser power and number of channels vary with changes in the coupling ratio in the linear cavity system. The optimum BEFL operation is obtained with an output coupling of 40%, i.e., 60% of the laser power is allowed to oscillate in the cavity. A stable laser comb consisting of up to 40 channels with line spacings of approximately 0.09 nm are obtained at the Brillouin pump and 980 nm pump with powers of 2.5 mW and 100 mW, respectively. The linear cavity BEFL has the potential to be used in inexpensive wavelength division multiplexing system.      

Widely tunable ring-cavity tellurite fiber Raman laser

We report a widely tunable ring-cavity tellurite fiber Raman laser covering the S+C+L+U band. A tunable range (1495-1600 nm, limited by the tunable optical bandpass filter) over 100 nm is obtained by using a single-mode tellurite fiber with high Raman gain coefficients (55 W(-1)km(-1)) and large Raman shift (~22.3 THz) as the gain medium. Furthermore, the free-running 1665 nm Raman fiber laser is achieved from the ring cavity by removing the tunable optical bandpass filter, which shows that such a tellurite fiber has potential for constructing a widely tunable fiber Raman laser covering the S+C+L+U band. A high optical signal-to-noise ratio of over 60 dB for almost all of the tunable range is also demonstrated.     

激光输出功率随耦合率及放大率的变化规律

建立了涵盖稳定腔和非稳腔的激光有源理论模型和激光开式谐振腔的边界条件。根据定态薛定谔方程与亥姆霍兹方程的等价性,采用量子力学方法求解谐振腔的亥姆霍兹波动方程,得到满足方程、边界条件、矩阵光学、稳定条件的本征解和本征方程。根据本征方程推导出横模数目随耦合率变化的规律,进而推导出激光输出功率随耦合率变化公式,以及激光输出功率随放大率的变化规律。该理论模型能够从稳定腔自然过渡到非稳腔,在小耦合率情况下退化到与传统公式基本一致的形式,又能在大耦合率情形下与实验结果符合得很好。     

激光输出功率随耦合率及放大率的变化规律

建立了涵盖稳定腔和非稳腔的激光有源理论模型和激光开式谐振腔的边界条件。根据定态薛定谔方程与亥姆霍兹方程的等价性,采用量子力学方法求解谐振腔的亥姆霍兹波动方程,得到满足方程、边界条件、矩阵光学、稳定条件的本征解和本征方程。根据本征方程推导出横模数目随耦合率变化的规律,进而推导出激光输出功率随耦合率变化公式,以及激光输出功率随放大率的变化规律。该理论模型能够从稳定腔自然过渡到非稳腔,在小耦合率情况下退化到与传统公式基本一致的形式,又能在大耦合率情形下与实验结果符合得很好。     

Tunable multiwavelength Brillouin-erbium ring-cavity fiber laser with short-length photonic crystal fiber

A multi-wavelength Brillouin-erbium ring-cavity fiber laser utilizing 2-m erbium doped fiber (EDF) and 70-m high nonlinear photonic crystal fiber (PCF) is proposed and demonstrated. The output characteristics and also the impacts of pump and Brillouin pump (BP) on the output spectra are investigated in detail. The output number and wavelength location of Brillouin lines are tunable by adjusting the power of 1465 nm pump and BP, and a 5-channel output within 11 nm (1551–1562 nm) tuning range is achieved by choosing appropriate pump power.     

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.     

Ultrafine optical-frequency tunable Brillouin fiber laser based on fiber strain

We present an ultrafine tunable single-frequency Brillouin fiber laser in which the fiber Brillouin gain also acts as a high-precision tunable filter. Controlling the strain on the fiber, the Stokes frequency shift may be precisely changed, and thus the lasing frequency can be tuned. Assisted by the frequency pulling effect, this method provides continuous ultrafine tuning ability for ~30% of the free spectral range without mode hopping, and can cover 271 MHz. The experiments showed that the laser achieves tuning step of 60 kHz.     

Single-frequency Brillouin distributed feedback fiber laser

We demonstrate a single-frequency Brillouin distributed feedback laser (DFB). The DFB laser cavity was a 12.4 cm long fiber Bragg grating with a π-phase shift offset from the grating center. It exhibited a threshold of 30 mW and conversion efficiency from pump to Stokes wave as high as 27%. Higher-order Stokes waves were suppressed by more than 20 dB. The Stokes output of the laser could be obtained in either the forward or backward direction, simply by changing the orientation of the offset of the discrete phase shift with respect to the pump propagation direction. The DFB laser operated over a pump frequency range of 1.2 GHz, more than 60 times larger than the SBS gain bandwidth.     

A high-efficiency Brillouin fiber ring laser

A high-efficiency Brillouin fiber ring laser is demonstrated using the standard single-mode fiber. The laser exhibits a 3.6-mW threshold. The output power is 22 mW with 40-mW pump power, and the maximum optical-to-optical efficiency is 5570. The output is single wavelength with a 3-dB linewidth of 5 MHz, and the interval of center frequency between the laser and the pump light is 11 GHz （0.088 nm）. It is shown that the stimulated Brillouin scattering threshold of ring resonator is lower and the energy transfer efficiency is higher than those in fiber.     

Effect of Brillouin slow light on distributed Brillouin fiber sensors

The effect of Brillouin slow light on distributed Brillouin fiber sensors (DBFSs) is studied. We demonstrate Brillouin slow light for a 1.2 ns pulse with peak powers (PS) from 3.3 to 56.2 mW on depletion of the pump power (PP) ranging from 1.3 to 83.2 mW in conventional optical fibers (SMF-28). Experiments show that, when pump power depletion is not negligible, for a given PP the Brillouin gain and delay time of a pulse decrease when PS increases in a long (> or =10 km) sensing fiber. The optimum pump beam depletion resulting from strong interaction of the pump and the probe in the fiber provides accurate temperature and strain information at a high spatial resolution. Our study reveals that at low PP the spatial resolution error caused by the pulse delay for a DBFS with centimeter spatial resolution is less than 5% of the pulse length.     

Multi-wavelength Brillouin fiber laser using dual-cavity configuration

A simple technique for achieving multi-wavelength tunable multi-wavelength Brillouin fiber laser (BFL) based on dual-pass configuration is demonstrated. The BFL uses a piece of 10 km long non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium to obtain odd-order Brillouin Stokes waves as an output with the line spacing of 0.16 nm (20 GHz) between each two consecutive waves by employing even-order Brillouin Stokes to improve output performance of the laser. With a BP of 15.3 dBm, at least 15 odd-order Brillouin Stokes and anti-Stokes lines are generated. The laser is room temperature stable, tunable over 50 nm wavelength range and has an optical signal to noise ratio of more than 30 dB at 1560 nm region. This Brillouin fiber laser can operate at any wavelength depending on the Brillouin pump (BP) wavelength used.     

基于多波长布里渊光纤激光器的温度传感特性

为了在高腐蚀、高辐射和强电磁干扰等复杂环境下实现对温度的精确测量,设计并实验了一种基于传感多波长布里渊光纤激光器(MBFL)和参考MBFL的高灵敏度全光纤温度传感器。理论和实验上分析了布里渊散射光的频移与温度变化之间的关系,根据输出斯托克斯激光信号对拍频所得微波信号的频移变化,测量温度的变化。通过带宽为0.1 nm的可调谐光滤波器选择第10阶斯托克斯激光信号对输出,并对其进行拍频探测,实现对传感MBFL周围温度变化的精确测量。通过拍频探测第10阶斯托克斯激光信号对,得出其灵敏度为10.829 MHz/℃。当选用第10阶斯托克斯激光信号对进行温度测量时,温度变化40℃的测量误差约为0.138℃。     

Single-longitudinal-mode Brillouin fiber laser incorporating an unpumped erbium-doped fiber loop

A long-cavity single-longitudinal-mode (SLM) Brillouin fiber laser is firstly demonstrated by utilizing an unpumped Erbium-doped fiber (EDF) loop. The utilized EDF enables to form a self-induced ultra-narrow grating filter, and thus guarantees the SLM operation.     

Linear cavity Brillouin fiber laser with improved characteristics

A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.     

Switchable Brillouin frequency multiwavelength and pulsed fiber laser

Switchable single and double Brillouin multiwavelength and pulsed laser is successfully demonstrated. Brillouin spacing can be switched from single(0.08 nm) to double spacing(0.16 nm) or vice versa by swapping the ports of the coupler in the proposed configuration. The proposed configuration can also be used to produce pulsed laser by inserting a home-made carbon nanotubes saturable absorber into the laser cavity. The proposed system is very versatile and flexible as it can be used as a multiwavelength laser or pulsed laser to cater for different types of applications.     

Multi-wavelength Brillouin fiber laser generation using dual-pass approach

A simple and compact multi-wavelength tunable Brillouin fiber laser (BFL) in conjunction with dual-pass approach is proposed and experimentally compared with the output of a conventional single ring cavity architecture. This BFL source is demonstrated using 10 km long non-zero dispersion shifted fiber (NZ-DSF) as a Brillouin gain medium. By single ring cavity configuration, odd-order Brillouin Stokes lines appear in the backward direction with the line spacing 0.16 nm (∼20 GHz) between each two consecutive waves. However, this single ring cavity in conjunction with dual-pass configuration is able to generate Brillouin Stokes lines with 0.08 nm spacing by providing bi-directional oscillations of Brillouin waves in both forward and backward directions. With a Brillouin pump power of 15.3 dBm, approximately up to 17 Brillouin Stokes lines are generated which is tunable over 40 nm tuning range.     

CW-pumped polarization-maintaining Brillouin fiber ring laser: I. Self-structuration of Brillouin solitons

Stimulated Brillouin scattering (SBS) of a cw-pump in a long optical fiber ring cavity generates for a given gain G, below a critical feedback R_crit, a backward soliton Stokes pulse at the roundtrip repetition rate, through resonant three-wave interaction between the optical pump wave and backward Stokes wave, and a high frequency (GHz) axial acoustic wave. In Part I, we perform a systematic experimental and numerical exploration of the whole soliton localisation domain for a large set of (G, R) parameters, in a polarization-maintaining Brillouin fiber ring laser in the best conditions of stability and coherence, and we confirm the excellent quantitative agreement of the coherent three-wave model and the experiments.     

Weak laser pulse signal amplification based on a fiber Brillouin amplifier

We propose a high-gain and frequency-selective amplifier for a weak optical signal based on stimulated Brillouin scattering in a single mode fiber. To be able to satisfy the needs of high gain and high signal-to-noise ratio laser pulse amplification, different fiber lengths and core diameters are used to fulfill this experiment. In the experiment, a 430 nW(peak power) pulsed signal is amplified by 70 dB with a signal-to-noise ratio of 14 dB. The small size, high gain, low cost, and low noise of the fiber Brillouin amplifier make it a promising weak signal amplification method for practical applications such as lidar.     

A low-threshold multiwavelength Brillouin fiber laser with double-frequency spacing based on a small-core fiber

We demonstrate multiwavelength Brillouin fiber lasers (MWBFLs) with double-frequency spacing based on a small-core fiber (SCF) and a standard single-mode fiber (SMF), which have core diameters of 5 and 8.8 μm, respectively. Experimental results show that the SCF-based MWBFL exhibits a higher laser output power and a lower pump threshold. The output powers of the SCF-based MWBFL are > 1.4 times those of the SMF-based MWBFL. Moreover, the threshold power required to generate each channel of the SCF-based MWBFL is 59% that of the SMF-based MWBFL. When the same pump power of 180 mW is injected, the number of laser channels generated for the SCF-based MWBFL is 13, which is twice that generated for the SMF-based MWBFL. In addition, the SCF-based MWBFL exhibits good wavelength tunability from 1535 to 1565 nm and temporal stability over an hour.