Multiwavelength Thulium-doped Fiber Laser Research Articles

Michelson interferometer-based tunable multiwavelength thulium-doped fluoride fiber laser in S-band for 5 G networks

This work reported a multiwavelength thulium-doped fluoride fiber laser (TDFFL) for the S-band region using the Michelson interferometer as an optical filter. Michelson interferometer was utilized as a comb-like filter, whereas dispersion-compensated fiber (DCF) of 10 km length was used to increase the number of lasing lines and reduce mode competition. Approximately 61 lasing lines were achieved with a signal-to-noise ratio (SNR) of 40 dB in the wavelength region from 1501.36 to 1505.52 nm within 10 dB of maximum power. The stability of the multiwavelength fiber laser was also recorded for the time duration of two hours, and it was found that all lasing lines were stable and equally spaced at the free spectral range (FSR) of 0.07 nm. The variation in optical power was less than 0.5 dB; however, the wavelength shift was about 0.01 nm. Tunability of multiwavelength laser has also been observed up to the broader transmission span of 57 nm by incorporating the tunable band pass filter (TBPF). Moreover, FSR was observed to be tunable within the range of 0.02 to 0.14 nm by using the optical delay line (ODL) with a Michelson interferometer. Additionally, the proposed laser can generate frequency signals from 2.65 GHz to 18.54 GHz according to the obtained range of FSR.

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.

Selectable multiwavelength thulium-doped fiber laser based on parallel Lyot filter

This paper demonstrates a selectable wavelength spacing of thulium-doped fiber laser (TDFL) based on a parallel Lyot filter. An intensity-dependent loss (IDL) mechanism acts as an amplitude equalizer to flatten and stabilize the multiwavelength spectrum. The IDL mechanism is obtained at a specific polarization state from the combination of highly nonlinear fiber and polarizer. The wavelength spacing of the TDFL can be selected to either 0.9 nm or 1.8 nm when the polarization controllers (PCs) in each branch of the parallel Lyot filter are adjusted. The wavelength spacing is selected by adjusting PC2 and PC3 to suppress or transmit the light at each branch. Up to 4 and 9 lasing lines are generated based on wavelength spacing of 0.9 nm and 1.8 nm, respectively. Lower pump power has disappeared lasing lines, while different half-wave plate angle of PC has shown variation in the laser performances.

A Multi-Wavelength Thulium-Doped Fiber Laser Using a Photonic Crystal Fiber-Based Sagnac Loop

A multi-wavelength thulium-doped fiber laser incorporating a photonic crystal fiber (PCF) Sagnac loop was presented and experimentally demonstrated. In the laser cavity, the Sagnac loop mirror used a 0.5 m PCF as a comb filter. A nonlinear polarization rotation (NPR)-based 600 m single-mode fiber (SMF) was used to suppress the mode competition. By adjusting the polarization controllers (PCs), up to nine stable wavelength outputs near the 2 μm spectrum were obtained at room temperature with an optical signal-to-noise ratio (OSNR) of up to 30 dB. The channel spacing of this fiber laser is 4.88 nm, and the 10 dB bandwidth encompasses 1950.39 to 1989.43 nm.

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.

Wavelength-interval-switchable multi-wavelength thulium-doped fiber laser with a nonlinear dual-pass Mach-Zehnder interferometer filter in 2-μm-band

A wavelength-interval-switchable multi-wavelength thulium-doped fiber laser (MWTDFL) is proposed and demonstrated, based on a nonlinear dual-pass Mach-Zehnder interferometer (NDP-MZI) filter for the first time. We investigate the NDP-MZI filter theoretically and experimentally, which has both the transmission characteristics of a dual-pass Mach-Zehnder interferometer (DP-MZI) for wavelength selection and a nonlinear optical loop mirror (NOLM) for suppressing wavelength competition. By tuning two polarization controllers (PCs), two 20-wavelength operations with an opposite phase and a same wavelength-interval of 0.46 nm are obtained and switched between each other flexibly. The maximum power fluctuation and wavelength drift measured are 0.612 dB and 0.04 nm, respectively. In addition, due to the power-equalizing effect resulting from the NOLM, 60 lasing wavelengths within a 3-dB bandwidth with an adjacent wavelength-interval of 0.23 nm are also obtained by adjusting the PCs carefully, and the stability of the MWTDFL is measured experimentally. Furthermore, the performance of the NDP-MZI using an 80 m highly nonlinear fiber has been studied in detail as well. The proposed MWTDFL may find great applications in optical communication and optical sensing.

Multi-wavelength Thulium-Doped Fiber Laser Via a Polarization-Maintaining Sagnac loop Mirror With a Theta-Shaped Configuration

A modified polarization-maintaining Sagnac loop mirror is proposed, and the simulated transmission spectrum of the proposed filter is in accordance with experimental transmission spectrum. Based on the proposed filter, a multi-wavelength thulium-doped fiber laser is constructed and experimentally demonstrated. The stable multi-wavelength oscillation within 60 minutes is achieved through the nonlinear polarization rotation effect enhanced by the highly nonlinear fiber. By fine tuning the polarization state, up to 35 lasing lines are obtained within a 10-dB bandwidth with wavelength separation of ~1.38 nm at room temperature. The wavelength shift and the output power fluctuation are less than 0.04 nm and 1.69 dB, respectively. In addition, by changing the optical coupling ratio in the Sagnac loop mirror, different outputs with 7, 8, 16 lasing lines are also obtained.

Tunable Multiwavelength Thulium-Doped Fiber Laser Based on Parallel Lyot Filter

This paper demonstrates a tunable wavelength spacing of thulium-doped fiber laser (TDFL) based on a parallel Lyot filter. An intensity-dependent loss (IDL) mechanism acts as an amplitude equalizer to flatten and stabilize the multiwavelength spectrum. The IDL mechanism is obtained at a certain polarization state from the combination of highly nonlinear fiber and polarizer. The wavelength spacing of the TDFL can be tuned to either 0.9 nm or 1.8 nm when the polarization controllers (PCs) in each branch of the parallel Lyot filter are adjusted. The wavelength spacing is tuned by adjusting both PC2 and PC3 to suppress or transmit the light at each branch. Up to 4 and 9 lasing lines are generated based on wavelength spacing of 0.9 nm and 1.8 nm, respectively. Lower pump power has disappeared lasing lines, while different half-wave plate angle of PC has shown variation the laser performances.

Stable Multi-Wavelength Thulium-Doped Fiber Laser With Two Cascaded Single-Mode-Four-Mode-Single-Mode Fiber Interferometers

We propose and experimentally demonstrate a multi-wavelength thulium-doped fiber laser using two cascaded single-mode-four-mode-single-mode (SFS) fiber interferometers and a 150-m-long highly nonlinear fiber. The transmission properties of SFS fiber interferometers with two different four-mode fiber (FMF) lengths are analyzed theoretically. The interferometer with a longer FMF is used to select specific wavelengths, and the one with a shorter FMF is used to stimulate more laser lines. By adjusting the polarization controller and increasing the pump power, the number of output laser channels and the wavelength spacings can be changed and switched. By selecting the proper length of the FMFs, 31 lasing lines are achieved with covering a wavelength range of $\sim 22$ nm. The power fluctuation and the wavelength drift of the 31-wavelength operation for the proposed fiber laser are within 0.706 dB and 0.02 nm, respectively.

All-fiber theta cavity multi-wavelength Tm-doped fiber laser based on a dual biconical taper filter

We report experimentally a multi-wavelength Thulium-doped fiber (TDF) laser based on all-fiber theta cavity and a dual biconical taper filter without isolator. The dual biconical taper with waist of 50 μm and length of 188.05 mm is implemented as a narrow band filter. Three stable laser output states are successfully obtained with one, two or three wavelengths by increasing the pump power and properly adjusting the polarization controller. For single-wavelength output at 1978.80 nm, the full width at half maximum (FWHM) is 0.23 nm with optical signal-to-noise ratios (OSNRs) larger than 19 dB. For dual-wavelength output at 1978.80 nm and 1991.80 nm, the FWHMs are 0.24 nm and 0.19 nm with OSNRs of 30 dB and 19 dB, respectively. For triple-wavelength operation at 1978.8 nm, 1990.80 nm and 1991.60 nm, the FWHMs are 0.2 ~ 0.26 nm and OSNRs of 27 dB, 20 dB and 22 dB, respectively. The stable multiple wavelengths laser emission output with maximal (minimal) interval of 13 nm (1 nm) is achieved at 2 μm region. There is negligible wavelength shift for over one hour. It can be verified that this scheme using a dual biconical fiber taper filter is feasible and can be an alternative solution for all-fiberized stable narrow-bandwidth multi-wavelength TDF laser.

Investigation of a multiwavelength thulium-doped fiber laser incorporating a two-mode fiber filter

A multiwavelength, thulium-doped, ring fiber laser was proposed and experimentally demonstrated. The laser was realized exploiting the cooperative effects of a two-mode fiber filter, nonlinear polarization rotation and the four-wave mixing induced by a section of a highly nonlinear fiber with a length of 150 m. By fine-tuning the polarization controllers, stable multiwavelength outputs with 11 lasing lines within the bandwidth of 10 dB were obtained in 60 min. The maximum wavelength shift and optical power fluctuation of the eleven-wavelength operation for the laser are 0.08 nm and 1.86 dB, respectively, and the wavelength interval and the number of lasing lines can be changed by adjusting the length of the two-mode fiber. Furthermore, the effects of the different experimental parameters such as the pump power, output coupling ratio, nonlinear phase shift and the extinction ratio of the filter on the output performance have also been carefully investigated.

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.

Switchable multiwavelength thulium-doped fiber laser with cylindrical vector beam emission

We experimentally demonstrate a switchable multiwavelength thulium-doped fiber laser with cylindrical vector beam (CVB) emission, which is the first report, to our best knowledge, on the generation of CVBs in a 2 µm wavelength band. The Sagnac loop filter, made up of a 50:50 coupler, a section of polarization-maintaining fiber and a polarization controller, serves as a periodical filter and accounts for the excitation of multiwavelength channels. The mode-selective coupler consisting of both tapered single-mode and four-mode fibers has been designed and fabricated as a mode converter from LP01 to LP11 mode with a purity of >80%. By adjusting the polarization controllers, laser outputs with 1–3 switchable wavelengths have been realized in the spectrum ranging from 1988–1998 nm. The laser could find miscellaneous applications in wavelength/mode-division multiplexing system, etc.

Switchable Multi-Wavelength Thulium-Doped Fiber Laser Employing a Polarization-Maintaining Sampled Fiber Bragg Grating

A continuous wave, switchable multi-wavelength, thulium-doped fiber laser (TDFL) with a polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated for the first time. A length of 150 m highly-nonlinear fiber (HNLF) was used to introduce the four-wave mixing effect for the efficient suppression of the wavelength competition existing in the gain medium of thulium-doped fiber. By adjusting the state of polarization (SOP) of light in the laser cavity, two six-wavelength operations at two orthogonal SOPs and a ten-wavelength operation were obtained. When the TDFL ran at the six-wavelength operation mode with a pump power of 4.11 W, there were at least four lasing wavelengths with an optical signal-to-noise ratio (OSNR) higher than 30 dB, and when it ran at the ten-wavelength operation mode with a pump power of 4.60 W, there were nine lasing wavelengths with an OSNR higher than 30 dB. Regardless of the operation mode, the TDFL exhibited high stability.

Multiwavelength Thulium-Doped Fiber Laser Using a Micro Fiber-Optic Fabry–Perot Interferometer

A compact, all-fiberized multiwavelength thulium-doped fiber laser based on a micro fiber-optic Fabry–Perot interferometer (FPI) and a nonlinear optical loop mirror (NOLM) has been demonstrated. The FPI with a free spectral range of ∼26 nm was used as an effective wavelength selective filter, which was constructed by splicing a ∼71.4- μ m long air-filled hollow-core fiber with single-mode fibers at both ends. An NOLM, served as an amplitude equalizer, was used for stabilizing multiwavelength laser operation. Besides switchable single-wavelength operations (1948.00 and 1972.24 nm), stable dual-wavelength operations (1948.02/1974.25 and 1974.16/1975.30 nm) and triwavelength operation (1947.94/1973.03/1974.14 nm) have been obtained. The optical signal-to-noise ratio of each emission laser line is larger than ∼47 dB.

All-fiber multimode interferometer for the generation of a switchable multi-wavelength thulium-doped fiber laser.

A compact all-fiber multimode interferometer (MMI) designed to produce a switchable multi-wavelength thulium-doped fiber laser (TDFL) is proposed and demonstrated. The TDFL fiber ring cavity employs a 60-cm-long multimode fiber into the cavity to induce multimode interference and provide intensity-dependent loss in order to generate a multi-wavelength output. The suppression of mode competition and the overall stability of the TDFL are further improved by exploiting the filtering capability of a Sagnac loop. By increasing the pump power, a switchable wavelength output is allowed with a wavelength spacing of ∼1.8 nm. At 361 mW input pump power, nine laser lines are generated, with a maximum signal-to-noise ratio value of ∼36 dB and an output power of 3.3 mW. The multi-wavelength TDFL also exhibits great stability in one-hour operation with a wavelength drift of 0.2 nm. The proposed multi-wavelength TDFL has potential to be employed in future thulium-doped fiber amplifier-based telecommunication infrastructure and also may be applicable in areas such as sensing and spectroscopy, largely associated with its 2 μm wavelength output.

Highly Nonlinear Fiber-Assisted Multiwavelength Generation in Linear Cavity Thulium-Doped Fiber Laser

We propose a multiwavelength thulium-doped fiber laser in a linear cavity stabilized by a highly nonlinear fiber (HNLF). Stable multiwavelength operation at 2 μm was obtained by introducing a 500-m HNLF within the cavity to alleviate mode competition caused by homogeneous gain broadening of the thulium gain medium. The presence of HNLF-induced spectral broadening through the FWM effect helped to increase the number of output channels, with 22 lasing lines observed within a 10-dB bandwidth and optical signal-to-noise ratio as high as 30 dB. The laser exhibited power fluctuations of less than 1.325 dB with maximum wavelength dithering of 0.12 nm. This work has demonstrated the use of simple HNLF-integrated linear cavity architecture to generate multiwavelength output without complex nonlinear-based structure.

A 1.8-µm multiwavelength thulium-doped fiber laser based on a hybrid interference filter

ABSTRACTA 1.8-µm tunable multiwavelength thulium-doped fiber laser based on a hybrid filter is proposed. In the designed ring-cavity fiber laser, the filter consists of one Sagnac loop and one dual-pass Mach–Zehnder filter. In the experiment, the lasing threshold is 155 mW, and a continuously tunable and stable single-wavelength laser could be realized with a minimum tuning interval of 2.1 nm within a scope of 22.5 nm. When an 1858-nm laser is obtained, the peak power fluctuation is less than 0.83 dB within 20 minutes at room temperature. By adjusting the polarization controller, stable dual-wavelength lasers are simultaneously achieved, and the peak power shift is less than 1.24 dB within a scan time of 20 minutes at room temperature. By changing the polarization state, stable triple-wavelength lasing is obtained, and the power fluctuation is less than 1.95 nm. In the experiment, the 3-dB linewidth of the laser is less than 0.4 nm.

Tunable multi-wavelength thulium-doped fiber laser incorporating two-stage cascaded Sagnac loop comb filter

A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873–1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.