Tunable Fiber Laser Research Articles

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.

Tunable spectrally-flat multi-wavelength cylindrical vector beam fiber laser by using a re-circulating frequency shifter loop with two external injections

We experimentally demonstrate a tunable spectrally -flat multi-wavelength cylindrical vector beam (CVB) fiber laser based on a two-mode long-period fiber grating (TM-LPFG) and a re-circulating frequency shifter loop with two external injections. The TM-LPFG is utilized as a mode converter in the re-circulating frequency shifter loop to excite the LP11 mode in the two-mode fiber. By adjusting the wavelength interval of the two injected seed signals, the power of the injected seed signals, and the pump power can produce a flat intensity envelope between the two injected wavelengths. Multi-wavelength CVBs of 12, 18, or 30 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.08 nm. The wavelength spacing can be adjusted by changing the frequency of the radio frequency signal. Multi-wavelength CVBs of 14 channels with a peak-to-peak power variation lower than 2 dB between the two injected wavelengths are obtained with a wavelength spacing of approximately 0.2 nm. The purity of the generated multi-wavelength CVBs is higher than 98%. Due to the absence of interference-type filter elements, the multi-wavelength CVB fiber laser exhibits excellent stability. The maximum wavelength deviation of each channel is less than 6.5 pm, and the maximum intensity fluctuation is less than 0.7 dB over a period of one hour.

Switchable and tunable orthogonal single-polarization dual wavelength SLM fiber laser based on parity-time symmetric system and PM-FBG

A dual-wavelength narrow linewidth orthogonal single polarization fiber laser based on a parity-time (PT) symmetric system is proposed and demonstrated, which achieves the function of tunable and switchable wavelength, and single longitudinal mode (SLM) operation. The PT symmetric system composes of a single physical loop, which includes two polarization controllers (PCs) and a polarization beam splitter (PBS). By modulating PCs to match gain, loss and coupling coefficient, the switchable wavelength and stable SLM laser output have been achieved. Through stretching the polarization maintaining fiber Bragg grating (PM-FBG), the wavelength adjustment range from 1549 nm to 1551 nm is obtained. In the process of tuning, the full width at half maxima (FWHM) linewidths and polarization states at each wavelength have been measured and keep basically stable. The measured FWHM linewidths are less than 13.66 kHz and 11.89 kHz. Further, the stable orthogonal single polarization state has been realized. The degree of polarization (DOP) at each wavelength exceeds 97% and basically remains unchanged during 20 min.

Tunable ultra-narrow linewidth linear-cavity fiber lasers assisted by distributed external feedback

We proposed and demonstrated a widely tunable and ultra-narrow linewidth fiber laser scheme by exploiting an original Fabry-Perot laser main cavity and a distributed external feedback structure. This was feasible with the aid of a feedback signal with distributed characteristics which is injected into the main cavity to induce an intense mode competition effect. Eventually, a single frequency fiber laser with a side mode suppression ratio of 69 dB, an output linewidth of 570 Hz, a white frequency noise of 110 Hz2/Hz at the frequency offset that is beyond 2 × 105 Hz, and a relative intensity noise less than −140 dB/Hz is successfully obtained under normal conditions. Also, the high spectral purity performance of the laser can be maintained under different pump powers for each wavelength channel. This work presents a promising method to obtain tunable ultra-narrow linewidth lasers.

Stable tunable narrow-linewidth fiber laser based on random distributed feedback

Stable narrow linewidth fiber lasers with relatively high output power have broad application prospects in optical communication, sensing and precision measurement, due to their high coherence and low noise characteristics, which are the main requirements to increase the detection range and accuracy of these systems. Obtaining narrow linewidth laser output with improved performance has been one key topic in the field of laser science and technology. Here, we propose a combination of transmission and reflection of randomly distributed Bragg grating arrays to compress the linewidth of laser emission in an Erbium-doped fiber system at the 1550 nm band, thereby providing a selective reflection-transmission channel effect without too many feedback points. A stable narrow linewidth fiber laser with a linewidth of 570 Hz (output power of 6 mW) and 830 Hz (output power amplified to 25 mW), a maximum signal-to-noise ratio (SNR) greater than 63 dB, and a wavelength adjustable in the range of 445 pm is realized.

Research Progress in Tunable Fiber Lasers Based on Multimode Interference Filters.

Tunable fiber lasers have the advantages of good beam quality, high integration, and adjustable output wavelength, and they are widely used in fields such as optical fiber communication and optical fiber sensing. The fiber filter is one of the key components of tunable fiber lasers. Among the various filters currently used, multimode interference filters have the advantages of simple structure, convenient implementation, flexible tuning methods, and convenient spectral range design. The structures of multimode interference filters based on multimode fibers, no-core fibers, multi-core fibers, tapered fibers, and other special fibers are introduced in this paper. The working principles and tuning methods are analyzed and the research progress of tunable fiber lasers based on these filters is summarized. Finally, the development trend of tunable fiber lasers based on multimode interference filters is discussed. The rapid development and applications of multimode interference filters can help improve the performance of continuous and pulse lasers as well as promote the practicality of tunable fiber lasers.

All-normal dispersion widely tunable dual-wavelength mode-locked fiber laser based on NALM.

We experimentally and numerically demonstrate the all-normal dispersion (ANDi) ytterbium (Yb)-doped fiber laser based on nonlinear amplifying loop mirror (NALM) mode-locked, which allows tunable single-wavelength and dual-wavelength outputs. The pulses tuning ranges of the dual-wavelength are from 1032.24 nm to 1053.13 nm and from 1047.94 nm to 1069.05 nm, and the repetition frequency difference varies from 1766Hz to 1834Hz. To our knowledge, this is the widest dual-wavelength tuning range of Yb-doped fiber lasers based on NALM mode-locked. We test for 90 minutes and have high stability in both single-wavelength and dual-wavelength. In addition, the pulsed collision dynamics between two solitons at different wavelengths are numerically studied. Numerical results show that during the pulse collision, the two solitons pass through each other and maintain their properties, which also confirms the particle nature of the isolated wave. Our research contributes to the dynamics of dual-wavelength solitons collision in NALM mode-locked fiber laser and provides what we believe to be is a new idea for tunable Yb-doped dual-comb sources.

Controllable and abundant soliton states from an all-fiber laser based on a ZrGeTe4 saturable absorber

With many applications increasing expectations for the tunability of coherent pulses, the demand for tunable soliton fiber lasers (TSFLs) is growing. Two-dimensional ternary zirconium germanium telluride (ZrGeTe4) nanomaterials provide an opportunity to obtain high-performance TSFLs. In this research, we developed a TSFL with ZrGeTe4-based saturable absorber (SA). Employing a strategy of constant pump power, tunable soliton states were acquired. The 1st to 5th order harmonic mode-locking were obtained sequentially. The shortest pulse able to obtain was 1.05 ps. Furthermore, the soliton molecule was also obtained. The results suggest that ZrGeTe4-SA may provide an effective route for photonics research.

Plasmonic structure assisted all-optical tunable fiber laser

In this paper, we proposed and demonstrated a tunable fiber laser using all-optical plasmonic modulation, where the localized surface plasmon resonance effect of gold nanobipyramids (GNBPs) and polarization maintaining thin-cladding photonic crystal fiber were utilized to realize tunable output wavelength controlled by the 980 nm pump light. The laser achieves a tunability of 2.21 nm in C-band, with a side mode suppression ratio of 27 dB and the peak intensity can also be tuned continuously. The proposed tunable laser shows an average power fluctuation of less than 1 dB and the output wavelength and the power intensity both exhibit high stability. Therefore, the proposed plasmonic structure assisted all-optical tunable laser has advantages such as compact structure, good reproducibility, continuous tuning, and simple operation, which indicates great potential in future all-optical applications.

Improved 2∼5 μm mid-infrared fluorescence through energy transfer processes in Er3+/Ho3+ co-doped fluoride glasses

In this paper, Er3+/Ho3+ co-doped fluoride glasses were prepared by the high temperature melt-quenching technique. Pumped by the 980 nm LD, as a result of the emission spectra overlapping of Er3+ and Ho3+ ions, a broadband mid-infrared emission band from 2530 to 2950 nm with a full width at half maximum of the synthetic fluoride glasses near 231 nm was obtained, which exist latent application in wide band tunable mid-infrared fiber laser. Furthermore, the intense 4.1 μm mid-infrared fluorescence (3600–4400 nm) was obtained and the FWHM was 320 nm. The up-conversion emission peaks around 525, 546 and 660 nm, near-infrared emissions at 1.2 and 1.5 μm together with mid-infrared fluorescence around 2.0 μm was observed in Er3+/Ho3+ co-doped fluoride glass. Moreover, the relevant energy transfer processes were discussed in detail based on the emission spectrum and the energy level transition processes. The results indicate that the fabricated Er3+/Ho3+ co-doped fluoride glasses exist prominent emission features for fiber laser gain medium.

C + L band ultra-widely tunable SOA hybrid fiber laser based on acousto-optic add-drop filter induced by polarization conversion

Scientific and industrial applications have put forward new requirements for the wavelength tuning range of continuous-wave lasers. Herein, the constructed filter based on the acoustically-induced polarization conversion in single-mode fiber (SMF) covers the wavelength from 1464.2–1640.8 nm, and the tuning range is about ∼176.6 nm. The lasing wavelength is managed by the acousto-optical interaction in the SMF. Moreover, the gain spectrum of semiconductor optical amplifier (SOA) is flat and wide, which can achieve a wide range of laser tuning. Hence, we propose and demonstrate an ultra-widely tuning range ring cavity C + L tunable SOA hybrid fiber laser. Eventually, the tuning channel of the fiber laser is from 1527.3–1613 nm with the tuning range of about ∼85.7 nm, and its tuning range is determined by the gain bandwidth of SOA. The measured output power and center wavelength variations of the proposed fiber laser over a long-term observation are less than 0.11 mW and 0.44 nm, respectively. This work opens up a new way to expand the tuning range of other types of lasers.

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

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.

Wavelength tunable Raman fiber laser based on Raman gain spectrum control

Wavelength tunable Raman fiber laser based on Raman gain spectrum control

Broadband tunable Raman fiber laser with monochromatic pump.

Raman fiber laser (RFL) has been widely adopted in astronomy, optical sensing, imaging, and communication due to its unique advantages of flexible wavelength and broadband gain spectrum. Conventional RFLs are generally based on silica fiber. Here, we demonstrate that the phosphosilicate fiber has a broader Raman gain spectrum as compared to the common silica fiber, making it a better choice for broadband Raman conversion. By using the phosphosilicate fiber as gain medium, we propose and build a tunable RFL, and compare its operation bandwidth with a silica fiber-based RFL. The silica fiber-based RFL can operate within the Raman shift range of 4.9 THz (9.8-14.7 THz), whereas in the phosphosilicate fiber-based RFL, efficient lasing is achieved over the Raman shift range of 13.7 THz (3.5-17.2 THz). The operation bandwidths of the two RFLs are also calculated theoretically. The simulation results agree well with experimental data, where the operation bandwidth of the phosphosilicate fiber-based RFL is more than twice of that of the silica fiber-based RFL. This work reveals the phosphosilicate fiber's unique advantage in broadband Raman conversion, which has great potential in increasing the reach and capacity of optical communication systems.

Numerical Investigation of Polarization-Dependent Ultrashort Pulse Amplification in Erbium-Doped Fluoride Fibers

We have theoretically investigated the polarization-dependent ultrashort pulse amplification in erbium-doped fluoride fibers. The numerical model is based on the coupled generalized nonlinear Schrödinger equations and the rate equations. It is found that the Raman effect can be weakened by converting the seed polarization from linear to circular. Compared with the linearly polarized seed pulses, amplification of the circularly polarized seed pulses can generate Raman solitons with a larger pulse energy of the same central wavelength, although more pump power is needed. Furthermore, the amplification dynamics when no pulse splitting occurs have also been investigated. We demonstrate that amplification of the circularly polarized seed pulses allows the main pulse to accumulate more energy while maintaining a single-pulse profile. It is predicted that sub-two-cycle laser pulses at 2.8 μm with megawatt peak power and hundreds of nanojoules pulse energy can be directly generated from the erbium-doped fluoride fiber amplifiers. The investigations conducted in this paper can provide guidelines for the design of Raman-soliton-based tunable fiber laser systems and high-power few-cycle fiber laser systems.

All-polarization-maintaining, efficiently wavelength-tunable, Er-doped mode-locked fiber laser with a compact reflective Lyot filter.

Wavelength tunable mode-locked fiber lasers have highly potential applications in precision spectroscopy, nonlinear microscopy and photonic sensing. Here, we present a compact and thermal-sensitive reflective Lyot filter and utilize it for all-polarization-maintaining efficiently wavelength-tunable Er-doped carbon-nanotube-mode-locked laser for the first time, to the best of our knowledge. The output wavelength of the laser can be tuned from 1544.46 nm to 1572.71 nm, with a wide tuning range of 28.25 nm, and a remarkable tuning efficiency of 0.589 nm/°C, when the angle-spliced fiber is only 8.2 cm and the free spectral range of the filter is 31.32 nm. Dual-wavelength mode-locking is also achieved at boundary temperatures when increasing the pump power. Due to its compact size and reflection configuration, the proposed reflective Lyot filter is promising for realizing highly efficient wavelength tuning and multiwavelength generation in all-polarization-maintaining fiber lasers where reflective filters are needed.

Tunable Multiwavelength SOA-Based Fiber Laser

Tunable multiwavelength fiber lasers based on semiconductor optical amplifiers (SOA) have received attracting interest due to their wide prospective applications in dense division multiplexing (DWDM) systems and optical sensing. Using an SOA in a nonlinear optical loop mirror (NOLM), we demonstrate up to 13 lasing peaks by controlling the pump current and the polarization controller. At maximum pump current (450 mA), the emitted multiwavelength is between 1550 nm and 1572 nm with a wavelength spacing of 1.87 nm and 3 dB output linewidth of 0.8 nm with an output power of −7 dBm and 27 dB optical signal-to-noise ratio (OSNR). The multiwavelength output power and multiwavelength peak stability are investigated, and it was found that the power fluctuation of each multiwavelength line is less than 0.2 dB. In addition, by adjusting the polarization controllers (PCs) and SOA temperature, we obtained a tunable multiwavelength emission. The proposed fiber laser offers advantages such as simple structure, low loss, and long-time stable and multiwavelength emission.

Widely-tunable all-fiber Tm doped MOPA with > 1 kW of output power.

In this paper, we report on a high-power and widely tunable thulium-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system. The master oscillator is a Tm fiber ring laser incorporating a tunable bandpass filter to realize narrow linewidth and wavelength tunable operation. The MOPA generated 1010 W ∼1039 W of output power over a tuning range of 107 nm from 1943 to 2050nm with slope efficiencies of more than 51% and spectra linewidth of ∼0.5 nm. Power stability (RMS) in ∼10 min scale is measured to be ∼0.52%. A diffraction-limited beam quality factor M2 of ∼1.18 is measured at 920 W of laser output. Output power is pump-limited without the onset of parasitic oscillation or amplified spontaneous emission (ASE) even at the maximum power level. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-tunable TDFL at 2 µm with output power exceeding 1 kW.