Switchable Multi-wavelength Fiber Laser Research Articles

Tunable and switchable multi-wavelength mode-locked fiber lasers induced by an optimized hybrid mode-locked composite filtering effect

A multi-wavelength mode-locked fiber laser can generate different wavelengths from a single laser cavity, offering potential as a dual-frequency comb and serving as an ideal light source for terahertz wave generation. We present an optimized hybrid mode-locked Er-doped fiber laser with flexible outputs: switchable and tunable dual-wavelength mode-locking, along with stable tri-wavelength mode-locking, which is achieved by introducing 0.69 m polarization-maintaining fiber and bent 200 m single-mode fiber to enhance intra-cavity birefringence and nonlinear effect to optimize the hybrid mode-locking effect, that is, build the composite filter effect. The dual-wavelength mode-locking not only covers a tunable wavelength range of 5 nm but also provides tunable wavelength intervals of 4-26 nm due to the composite filter effect. The formation dynamics of the tri-wavelength mode-locking can be switched either pair-by-pair or one-by-one. This approach enables the realization of wavelength interval tunable dual-wavelength mode-locking in mode-locked fiber lasers simply by introducing fiber without additional actions. Such a simple, compact fiber laser with tunable wavelength capabilities holds significant potential for diverse applications.

Tunable and switchable multi-wavelength random fiber laser based on random distributed feedback and improved Lyot filter

Tunable and switchable multi-wavelength random fiber laser based on random distributed feedback and improved Lyot filter

Tunable and switchable multiwavelength fiber laser incorporating tapered few-mode fiber Bragg gratings

A tunable and switchable multiwavelength Erbium-doped fiber laser (MWFL) is proposed and demonstrated based on tapered few-mode fiber Bragg gratings (TFMFBG). Optical modes inside TFMFBG have extensive evanescent tails that are sensitive to changes in the external medium. The MWFL can be tuned in the 1.5 µm wavelength region when temperature and refractive index variations are applied to the TFMFBG. The temperature and refractive index sensitivities range from 11.5 pm/⁰C to 14.6 pm/⁰C and 3.10 nm/RIU to 3.93 nm/RIU, respectively. Additionally, due to the polarization dependency of TFMFBG, single-, dual-, and triple-wavelength lasing lines can be switched within the MWFL cavity. The stable triple-wavelength lasing was generated at peak wavelengths of 1533.04 nm, 1532.35 nm, and 1531.71 nm for λ1, λ2, and λ3, respectively. The developed triple-wavelength laser corresponded to a specific guided mode inside the few-mode FBG, including fundamental LP01 mode, higher-order LP11 mode, and mode coupling between LP01 and LP11 (LP01-LP11).

Tunable and switchable multi-wavelength pulsed fiber laser based on a nonlinear optical loop mirror and an improved Sagnac filter.

We propose and experimentally demonstrate a tunable and switchable multi-wavelength erbium-doped fiber ring pulsed laser based on a nonlinear optical loop mirror (NOLM) and an improved Sagnac filter. To achieve multi-wavelength pulsed laser output, we adopt a NOLM as a quasi-saturable absorber and an improved Sagnac loop as a wavelength selected filter. The constructed laser has a maximum output wavelength number of five with a pulse repetition frequency of 40.45kHz and pulse duration of 108ns. The laser can output single-wavelength and dual-wavelength pulsed lasers within a certain wavelength tuning range and a five-wavelength pulsed laser with a constant wavelength interval of 3nm by adjusting the polarization controller. Dual-wavelength, three-wavelength, and four-wavelength pulsed lasers with various wavelength intervals are also obtained. The output performance of the constructed laser is tested with a maximum average output power of 127.45µW and minimum pulse duration of 52ns, and the stability of the laser output is also tested with a maximum power fluctuation of 0.62dB and minimum wavelength drift of 0.51nm with pump power of 350mW.

Switchable multi-wavelength fiber lasers based on asymmetric biconical fiber tapers

In this paper, switchable multi-wavelength erbium-doped fiber lasers (MW-EDFLs) are proposed and experimentally demonstrated. An in-fiber Mach–Zehnder interferometer (IFMZI) composed of asymmetric biconical fiber taper (ABFT) pairs is integrated into the all-fiber ring cavity for multi-wavelength filtering. This laser can stably emit single-, dual-, or triple-wavelength outputs by fine-tuning the polarization controller. A high optical signal to noise ratio of 58.5 dB is obtained for the output spectra. The maximum wavelength shift is 0.08 nm and the power fluctuation in all laser emissions is recorded at 1.64 dB.

A switchable multi-wavelength mode-locked fiber laser based on a multi-mode interference device

A switchable multi-wavelength, passively mode-locked fiber laser in the 1 μm regime is demonstrated in this paper. The key principles of working include the nonlinear polarization rotation (NPR) mechanism for the mode-locked pulse generation and a single mode-multimode-single mode (SMS) structure as the spectral filter. The SMS structure is coiled on the paddles of a polarization controller (PC). Stable mode-locking operation is achieved at the fundamental repetition rate of 7.97 MHz. The pulse duration is 429 ps at the pump level of 216 mW, with the dual-wavelength laser emitting at 1037.86 nm and 1045.72 nm. By properly tuning the paddles of PCs, multi-wavelength mode-locked laser spectra can be observed switching from triple- to sextuple-wavelength, with the emission bandwidth of 27.6 nm from 1035.6 nm to 1063.2 nm.

Vernier effect based on hybrid fiber interferometers: a new tool for wavelength switchability and adjustable free spectral range fiber lasing

In optical communications systems, the used filter and/or demultiplexer needs to have a broad free spectral range (FSR) in order to accommodate more channels and have acceptable interchannel crosstalk. The Vernier effect applied to fiber filters is a recent effective tool to enlarge the FSR. Here, by harnessing the Vernier effect of a hybrid interferometer consisting of a Mach–Zehnder interferometer (MZI) and Sagnac interferometer (SI), we proposed and experimentally demonstrated a new kind of comb filter for a switchable and interval adjustable multi-wavelength C-band erbium-doped fiber laser (EDFL) application. In the designed comb filter, the MZI is composed of bi-tapered polarization-maintaining fibers (PMFs) fabricated by fusion splicing and has the function of achieving the switchability of the proposed dual-wavelength EDFL. The SI configured by nesting tapered PMF is employed as a switchable and wavelength-spacing tuning component of triple-wavelength EDFL. In this experiment, the FSR of the MZI and the SI is designed to be close but not equal, which could be achieved by properly adjusting the length of the employed PMF, so the Vernier effect can exist and a comb spectrum with an obvious envelope is obtained. Through the adjustment of the polarization controller (PC1) and (PC2) inside the cavity, a switchable and interval-adjustable multi-wavelength EDFL was achieved. To the best of the authors’ knowledge, this is the first time that an all-fiber hybrid filter based on the Vernier effect has been used to manipulate the spectral output characteristic of an EDFL and achieve a switchable multi-wavelength fiber laser.

Switchable multi-wavelength fiber laser based on a taper-coupled microbottle resonator

A multi-wavelength erbium-doped fiber laser (EDFL) based on a taper-coupled microbottle resonator is proposed and investigated experimentally. The taper-coupled microbottle resonator has the comb filter characteristics with Q factor 2.9 × 104, which is integrated into an EDFL system. The taper-coupled microbottle resonator was packaged by ultraviolet glue, which has excellent stability of output power and wavelength at room temperature. Then, switchable dual-, triple-, quad- and quint-wavelength fiber laser states can be achieved by adjusting the polarization controller (PC). Furthermore, for dual-wavelength and triple-wavelength laser state, the position of output wavelengths also can be precisely modulated with the PC. The developed multi-wavelength EDFL has the optical signal to noise ratio as high as 40 dBm, and the wavelength shift and peak power fluctuation are less than 0.03 nm and 6 dBm.

Switchable multi-wavelength thulium-doped fiber laser using a two-taper fiber filter

An individually switchable and tunable multiwavelength thulium-doped fiber laser (TDFL) is proposed and experimentally demonstrated. The key component of the laser is a comb filter composed of two fiber tapers separated by a short middle section. A nonlinear loop mirror (NOLM) is inserted into the laser cavity to suppress the intense gain competition. By properly adjusting the polarization controllers (PCs) in the cavity, the laser can operate in at most sextuple wavelength state. In addition to these laser output characteristics, the experiment result also shows that single wavelength tuning can be achieved, and the tuning range is 1952.06 nm to 1975.62 nm. This multi-wavelength TDFL may be useful in optical fiber sensing or other fields desiring flexible optical source.

Multi-wavelength thulium-doped fiber laser at 2.05 μm incorporating a superimposed polarization-maintaining fiber Bragg grating

A switchable multi-wavelength thulium-doped fiber laser with a high optical signal-to-noise ratio (OSNR) and stability is proposed and experimentally demonstrated at 2.05 μm. For the first time, a superimposed polarization-maintaining fiber Bragg grating (SI-PM-FBG) was utilized as a multi-channel narrow bandwidth filter to select the lasing wavelengths in the laser cavity in the 2-μm band. It also introduced polarization hole burning (PHB) to inhibit the strong wavelength competition induced by homogeneous gain broadening in the thulium-doped fiber. By adjusting the two polarization controllers (PCs), four stable switchable single-wavelength operations were obtained. The OSNR reached 72 dB at a pump power of 2.89 W, and the maximum wavelength and power fluctuations were 0.01 nm and 0.162 dB, respectively. Four combinations of dual-wavelength operations were obtained by adjusting the PCs. The polarization states between each dual-wavelength lasing were orthogonal. The stability of the dual-wavelength operation was investigated in detail. The proposed laser also has the capability for three- or four-wavelength operation. The excellent performance enables this fiber laser to be used in atmospheric sensing and free-space optical communication.

Switchable Multi-Wavelength Thulium-Doped Fiber Laser Using a Cascaded or Two-Segment Sagnac Loop Filter

A switchable multi-wavelength thulium-doped fiber laser (TDFL) using either two-stage cascaded or two-segment Sagnac loop filters are proposed and analyzed. Both filters incorporate a 3-m and 1.7-m long polarization-maintaining fiber, which acts as a comb filter. By adjusting two polarization controllers, when the TDFL used a cascaded Sagnac loop filter, eight stable single-wavelength operations were obtained with easy switching among them. The wavelength range was 16.36 nm during the single-wavelength switchable operation, with the optical signal-to-noise ratio up to 55 dB. This TDFL can achieve at most quintuple-wavelength operation. When the TDFL used a two-segment Sagnac loop filter, we achieved single-wavelength and dual-wavelength switchable. This TDFL can achieve at most stable quadruple-wavelength operation. In dual-wavelength switchable operation, the maximum and minimum wavelength spacings were 21.78 nm and 1.50 nm. Due to its abundant range of wavelengths, the proposed TDFLs has great potential in wavelength-division multiplexing.

Switchable multi-wavelength mode-locked linear-cavity fiber laser of cylindrical vector beam

We have proposed and demonstrated a switchable multi-wavelength passively mode-locked linear-cavity fiber laser to generate cylindrical vector beam (CVB) pulses by using a semiconductor saturable absorption mirror (SESAM). A home-made broadband long-period fiber grating (LPFG) and two cascaded polarization-maintaining fiber Bragg gratings (PMFBGs) are used as mode converter and wavelength selectors, respectively. This fiber laser can be switched among four different single-wavelength and two different dual-wavelength lasing oscillations with CVB output. The laser has a mode-locking threshold value of 33.55 mW and delivers CVB pulses with duration of hundreds of picoseconds. The purity of the CVB is measured to be 94.1%. This laser can have some important applications in mode division multiplexed (MDM) systems and wavelength division multiplexed (WDM) systems in the future.

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.

(INVITED)Switchable multi-wavelength mode-locked Yb-doped fiber laser using a polarization maintaining 45°-tilted fiber gratings based Lyot filter

We demonstrate a multi-wavelength mode-locked Yb-doped fiber laser by incorporating a pair of polarization maintaining 45° tilted fiber gratings (PM-45°TFG) based Lyot filter. Thanks to the functions of the polarizer and the comb filtering introduced by the Lyot filter, dissipative soliton (DS) pulses centered at 1035.26 nm, 1044.93 nm, 1055.62 nm, 1066.11 nm and 1076.63 nm can be generated respectively by finely tuning the intracavity polarization controllers (PCs). Moreover, the laser also can operate in a multi-wavelength regime via appropriately adjusting the pump power and polarization orientation. The high nonlinearity induced by the long cavity length leads to the generation of h-shaped mode-locked pulse with a repetition rate of 566.27 kHz. In the absence of any disturbance, the laser can operate steadily, that can potentially be used in various fields including wavelength division multiplexing systems etc.

Switchable multi-wavelength and tunable waveband fiber laser based on a thermal sensitive filter

In this work, a waveband tunable and switchable multi-line ring-cavity fiber laser is presented. Here, the losses of the cavity are controlled by means of a variable optical attenuator (VOA) and a thermal sensitive interferometric filter, which was formed by a stack of 3 layers at the tip of an optical fiber and a long thermal sensitive sleeve. Thus, the laser can emit single–, dual–, triple–, quadruple–, quintuple–and sextuple–wavelength emissions which can be switched by adjusting the VOA. Moreover, the laser waveband can be tuned by varying the temperature of the filter. Here, it is shown that with this setup a waveband tuning resolution of ∼1.37 nm ∘C−1 within the range from 1527.52 to 1534.40 nm can be achieved.

Switchable multi-wavelength erbium-doped random distributed feedback fiber laser incorporating two-stage Sagnac filter

A low-threshold and simple structure switchable multi-wavelength fiber laser based on random distributed feedback (RDFB) is presented. The experiment setup incorporates a two-stage Sagnac fiber loop mirror, an 8 m long erbium-doped fiber (EDF), and a 25 km long single-mode fiber (SMF). The SMF provides RDFB via Rayleigh scattering. Due to the implementation of the half-open cavity structure and the gain generated by the EDF, the laser threshold can be significantly suppressed to 60 mW, and the slope efficiency of output lasing power against pump power is ∼0.9%. By adjusting the polarization controllers of the proposed two-stage Sagnac loop mirror, single-, double-, triple-, and quadruple-wavelength lasing channels in the range of 1527–1534 nm are achieved. In the case of quadruple-wavelength channel lasing, the optical signal noise ratio is up to 33 dB under the 180 mW pump power. The proposed random fiber laser can be applied in distributed sensing systems and biomedical imaging.

Tunable and switchable multi-wavelength fiber laser based on polarization hole burning effect and Sagnac loop mirrors

In this paper, a stable highly tunable and switchable multi-wavelength fiber laser is presented. It is based on the filtering characteristics of the Sagnac loop mirror and the polarization-dependent devices, the polarization hole burning effect is induced to generate multi-wavelength output with high optical signal-to-noise ratio and narrow 3 dB linewidth, optical signal-to-noise ratio is about 50 dB and linewidth is less than 0.02 nm. The tunable bandwidth is about 30 nm, which covers almost the entire C-band. By the adjusting polarization controller, the number and wavelength spacing of laser emissions can be controlled and switched. The single-wavelength exhibits good power and wavelength stability, the peak power fluctuation is less than 0.04 dB and the wavelength drift is less than 0.04 nm, and the wavelength spacing of the dual-wavelength can be tuned from 0.67 to 27.4 nm. In the proposed structure, multi-wavelength up to 6 laser emissions can be obtained span from 1528 to 1562 nm.

Switchable Multi-Wavelength Thulium-Doped Fiber Laser Using Four-Mode Fiber Based Sagnac Loop Filter

A switchable multi-wavelength thulium-doped fiber laser (TDFL) using a four-mode fiber based Sagnac loop filter was proposed and demonstrated. The Sagnac loop, incorporating a 4.8 m long four-mode step-index fiber, acting as a comb filter was analyzed theoretically and experimentally. By adjusting two polarization controllers, eight stable single-wavelength operations and five stable dual-wavelength operations were obtained with easy switching between the different operation modes. The wavelength range covered during the single-wavelength switchable operation with a signal-to-noise ratio of up to 55 dB was ∼28.51 nm. In dual-wavelength switchable operation, the maximum and minimum wavelength spacings were ∼21.78 nm and ∼1.50 nm, respectively. Due to the abundant wavelength resources, the proposed TDFL has great potential in wavelength division multiplexing free-space optical communications, optical fiber sensing, and photonic generation of microwave signals.

Adaptive fiber-ring lasers based on an optical fiber Fabry-Perot cavity for high-frequency dynamic strain sensing.

A fiber-optic Fabry-Perot (FP) interferometer integrated with an adaptive fiber-ring laser is configured as a switchable multi-wavelength fiber laser that can be utilized for ultrasound detection. Because the FP sensor acts as a wavelength filter and a reflector of the fiber-ring laser, the reflective spectrum of the FP sensor changes due to static/dynamic strains, and the wavelength of the laser output shifts accordingly, which is subsequently converted into a corresponding phase shift and demodulated by an unbalanced interferometer. By carefully controlling the polarization of the system, the lasing outputs with a side-mode suppression ratio higher than 30 dB can be obtained, and the lasing linewidth is much narrower than that of the spectrum of the FP sensor. The experiments show that the proposed sensing system has high sensitivity for ultrasound detection and can be adaptive to the low-frequency drifts due to environmental noise.

Tunable and Switchable Multi-wavelength Erbium-Brillouin Random Fiber Laser Incorporating a Highly Nonlinear Fiber

A tunable and switchable multi-wavelength Erbium–Brillouin random fiber laser (MW-EBRFL) with a half-open cavity structure and incorporating a segment of highly nonlinear fiber (HNLF) is proposed and experimentally demonstrated. Due to HNLF being with high nonlinear coefficient, high Brillouin gain coefficient and high Rayleigh scattering (RS) coefficient, a reduced length of HNLF can provide a strong random distributed feedback (RDFB) and high stimulated Brillouin scattering (SBS) gain. In addition, an optical fiber amplify loop (OFAL) including a high-power erbium-doped fiber amplifier (HP-EDFA) and an optical attenuator (ATT) is constructed to provide a strong Brillouin pump (BP) and controllable optical feedback. Using the presented MW-EBRFL, up to 11 orders of stable Stokes laser lines with a wavelength spacing of 0.074 nm and the minimum optical signal-to-noise ratio (OSNR) of 41.22 dB are obtained. System parameters including BP power and HP-EDFA pump power influence on output of MW-EBRFL are also investigated. By adjusting BP wavelength, multi-wavelength output with 6–11 channel numbers can be tuned in a wide wavelength range spanning 36 nm. The proposed MW-EBRFL also can realize switchable multi-wavelength generation of 1 ∼ 11 order Stokes with an increasing wavelength number in turn, only by simply adjusting HP-EDFA pump power. Furthermore, when a polarization-maintaining fiber loop mirror filter (PMF-LMF) is cascaded with output port of the cavity, it can be very convenient to achieve wavelength switching between single- and double-Brillouin frequency spacing (BFS), only by tuning polarization controller in PMF-LMF.