Single Longitudinal Mode Fiber Laser Research Articles

Linewidth compression of a single longitudinal mode ytterbium-doped fiber laser based on femtosecond laser fabricated fiber Bragg gratings.

We demonstrate a single longitudinal mode distributed Bragg reflection (DBR) fiber laser by directly fabricating fiber Bragg gratings (FBGs) on an ytterbium-doped fiber (YDF) using a femtosecond laser. A simple optical self-injection feedback method was used to effectively compress the linewidth and reduce relative intensity noise (RIN) of a single longitudinal mode DBR fiber laser. Further, we investigated the effect of self-injection feedback cavity length and reflectivity on linewidth compression and determined that the linewidth tends to decrease with the increase of the external cavity photon lifetime. By a self-injection feedback, the laser linewidth was compressed from 31.8kHz to 1.4kHz. Meanwhile, the relaxation oscillation peak from -103.2d B/H z at 1.51MHz was suppressed to -122.3d B/H z at 0.16MHz. This low-noise narrow linewidth single longitudinal mode fiber laser is expected to be a promising candidate for applications such as active detection of neutral atmosphere and distributed fiber sensing.

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.

Computer analysis of three mode filters through optical couplers for single longitudinal mode fiber laser

In this paper, three basic mode filters based on optical couplers (OCs) for single longitudinal mode (SLM) fiber lasers are theoretically analyzed and compared by numerical simulation, providing a reference for the selection of filters according to the corresponding requirement. The three basic mode filters are single-coupler fiber ring (SCFR), double-coupler fiber ring (DCFR), and Mach-Zehnder filter (MZF). The three mode filters are acclaimed for the effective selection of SLM in fiber lasers. The transfer functions of the SCFR, DCFR, and MZF are derived and numerically simulated, respectively. Consequently, the bandwidths and amplitude characteristics of the three mode filters are analyzed and compared. The simulation results show that the bandwidths of DCFR and SCFR are mainly affected by the intensity coupling coefficient of the OC and the length of the ring. However, the bandwidth of MZF is hardly influenced by the intensity coupling coefficient but the difference of length between its upper and lower arm. The intensity coupling coefficient primarily impacts the amplitude of the three mode filters.

Temperature fiber sensor based on single longitudinal mode fiber laser in 2 μm band with Sagnac interferometer

Abstract A single longitudinal mode (SLM) fiber laser with a ring cavity based on Sagnac interferometer (SI) for temperature sensing in the 2-μm band is proposed and demonstrated. The simulation and experimental results show that the transmission spectrum of the SI filter is sensitive to temperature change. Based on this distinguishing feature, the correlation between the laser wavelength drift and temperature variation can be established. Experimental results show that the proposed laser operates stably at the resonant wavelength of 1988.21 nm and the optical signal-to-noise ratio is approximately 55 dB at ambient temperature. Through continuous measurement for 100 min, the fluctuation of the output laser power is lower than 0.74 dB, and the resonant wavelength shift is less than the minimum resolution of the spectrometer of 0.05 nm. This indicates that it has good stability for a certain period of time. At the same time, the laser operates stably in SLM state. A temperature sensitivity of 2.09 nm/°C is obtained in experiment. Notably, the proposed fiber laser sensor possesses the merits including high sensitivity, low cost and simple structure, which are beneficial to its practical application.

Switchable Single-Longitudinal-Mode Fiber Laser Based on $\theta$ -Shaped Microfiber Filter

In this letter, we design a wavelength-switchable single-longitudinal-mode (SLM) fiber laser based on a reflective $\theta $ -shaped microfiber resonator ( $\theta $ -MR). By cascading the $\theta $ -MR with a fiber Fabry–Perot interferometer, Vernier effect can be generated for SLM filtering. Due to the reflective nature of the $\theta $ -MR, a section of unpumped erbium-doped fiber can be directly inserted in front of the $\theta $ -MR to further suppress-mode competition. A SLM lasing spectrum with central wavelength of 1564.685nm, and sidemode suppression ratio as high as 56.6 dB is achieved. Stability test shows that the proposed fiber laser has a good long-term stability. Additionally, the lasing wavelength of the proposed laser is switched to 1564.690nm, 1559.392nm, and 1558.99nm when temperature around the $\theta $ -MR is set as 30°C, 40°C, and 50°C, respectively, verifying the wavelength switch ability of the $\theta $ -MR-based SLM fiber laser.

Switchable dual-wavelength SLM narrow linewidth fiber laser based on nonlinear amplifying loop mirror

We demonstrate a stable switchable dual-wavelength single longitudinal mode (SLM) narrow linewidth ytterbium-doped fiber (YDF) laser using a nonlinear amplifying fiber loop mirror (NALM) at 1064nm. The NALM of intensity-dependent transmission acts as a saturable absorber filter and an amplitude equalizer to suppress mode competition and the fiber Bragg grating (FBG) pair is used as one wavelength selection component. By properly adjusting the polarization controllers (PCs), the switchable dual-wavelength SLM fiber laser can be operated steadily at room temperature. The optical signal-to-noise ratio (OSNR) is better than 50dB for both lasing wavelengths. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 17.07kHz and 18.64kHz with a 20dB linewidth, which means the laser linewidth is approximate 853Hz and 932Hz FWHM. Correspondingly, the measured relative intensity noise (RIN) is less than −120dB/Hz at frequencies over 5.0MHz.

Single-longitudinal-mode broadband tunable random laser.

In this work, we demonstrate a broadband tunable single-longitudinal-mode (SLM) random laser based on Rayleigh backscattering in a standard single-mode fiber. The wide tuning range of this SLM fiber laser over 1500-1570nm is demonstrated with a linewidth of 4.5-30kHz. The tuning is achieved using a tunable bandpass Fabry-Perot filter, and a semiconductor optical amplifier is used as the wide-bandwidth gain medium. The laser is able to operate in the S + C + L band.

Stability wavelength-spacing-tunable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on nonlinear amplifying loop mirror

A simple linear cavity configuration for a stability wavelength-spacing-tunable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser based on a nonlinear amplifying loop mirror (NALM) is proposed. The gain competition in the erbium-doped fiber (EDF) has been suppressed by the intensity dependent loss introduced by the NALM. The SLM operation is guaranteed by a section of unpumped EDF as saturable absorber. A stable dual-wavelength SLM fiber laser with a wavelength-spacing of 11.35 nm is experimentally realized. The optical signal-to-noise ratio is over 47 dB and the linewidths of two wavelengths measured by delayed self-heterodyne method are 1.1 and 1.0125 kHz, respectively. The tuning range of wavelength-spacing is 9.09–11.35 nm, correspondingly, and the THz signal is from 1.235 to 1.416 THz.

Widely tunable/wavelength-swept SLM fiber laser with ultra-narrow linewidth and ultra-high OSNR

We propose and demonstrate a novel single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio (OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Perot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength- swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.

Switchable 10 nm-spaced dual-wavelength SLM fiber laser with sub-kHz linewidth and high OSNR using a novel multiple-ring configuration

A switchable dual-wavelength (10 nm spacing) single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) that uses a multiple-ring configuration was demonstrated experimentally. A novel theoretically lossless triple-ring passive secondary cavity composed of three optical couplers was utilized to select the SLM from the dense main cavity longitudinal modes for the first time. Using two superimposed fiber Bragg gratings as one compact mode-restricting element and introducing the nonlinear polarization rotation effect to alleviate the strong mode competition for the fiber laser, a highly stable dual-wavelength mode-hop-free SLM operation with sub-kHz linewidths and optical signal to noise ratios (OSNRs) of >69 dB was achieved for both lasing wavelengths. By adjusting the polarization controllers, the dual-wavelength operation could be easily switched to single-wavelength lasing with a linewidth of <1 kHz and an OSNR of >72 dB. The proposed EDFL may find many important applications, such as the generation of very pure terahertz waves.

A Broad Continuous Temperature Tunable DBR Single-Frequency Fiber Laser at 1064 nm

Based on a temperature-dependent longitudinal-mode-selection model, a broad temperature range for single-longitudinal-mode (SLM) operation of a short DBR phosphate fiber laser has been demonstrated. In order to make the variety in cavity resonance wavelength match the reflection peak changing in fiber Bragg grating (FBG) when the ambient temperature changes, the packaging materials with different coefficient of linear expansion are used for the active fiber and the FBG, respectively. The temperature variation range without mode hopping of the SLM fiber laser has been increased from about 2 °C to over 20 °C, while the continuous tunable wavelength range broadened to be > 149 pm.

SLM Fiber Laser Stabilized at High Temperature

In this letter, an annealing process of UV-written fiber Bragg gratings (FBGs) has been employed to achieve FBGs with narrower reflection spectra to be employed in fiber lasers. These FBGs have been used to design distributed Bragg relfector (DBR) laser sensors working on the single longitudinal mode (SLM) regime even at high temperatures. A fiber laser sensor working on multimode regime has been written into commercial Er-doped fiber before annealing its mirror FBGs, removing the unstable UV-induced modulation part and narrowing the FBGs’ combined response. This process obtains a DBR fiber laser sensor working on SLM regime at high temperatures ( $T=500~^{\circ }\text{C}$ ), and also exhibiting a remarkably good linearity and stability. The achieved results confirm the empirically adjusted aging model and prove its usefulness to design high precision devices able to work at high temperatures.

Dual-wavelength single longitudinal mode fiber laser for microwave generation

Abstract A simple dual-wavelength single longitudinal mode (DW SLM) fiber laser for microwave generation is proposed and demonstrated. Simultaneous oscillation of dual-wavelength with a wavelength spacing of 0.2124 nm is realized, the output peak power of the lasing dual-wavelength is equalized by adjusting polarization controller at room temperature. Birefringent fiber filter and saturable absorber are utilized to guarantee the SLM operation of dual-wavelength fiber laser. A microwave signal at 26.49 GHz is successfully obtained in the experiment, the laser is proved to be effective in the application of microwave generation.

Stable Single-Longitudinal-Mode Fiber Ring Laser Using Topological Insulator-Based Saturable Absorber

A single-longitudinal-mode (SLM) fiber ring laser based on topological insulator (TI) Bi2Te3 saturable absorber (SA) had been experimentally demonstrated. The TI: Bi2Te3 nanosheets, which were fabricated through the bottom-up approach, were coated onto the microfiber as an efficient saturable absorber device to ensure the SLM operation. Combined with fiber Bragg grating, the output wavelength can be continuously tuned about 1 nm. Without any accurate cavity control, stable SLM operation without mode hopping had been conveniently achieved. Based on the Lorentzian fitting, the line-width was measured to be less than 10 kHz. The output power of SLM fiber laser can reach up to 23 mW, indicating that the proposed TI-based SA may be suitable for high-optical power SLM operation in the future.

Widely Tunable Single Longitudinal Mode Fiber Laser With Cascaded Fiber-Ring Secondary Cavity

A widely tunable single longitudinal mode (SLM) fiber laser with cascaded Type I and Type II fiber ring secondary cavities, which uses a tunable fiber Bragg grating (FBG) as the mode-restricting and wavelength-tuning element, is proposed and demonstrated. Since the cascaded fiber rings can effectively expand the pass-band spacing to make the mode selection with the FBG easier, the stability of SLM oscillation can be improved by suitably optimizing the coupling ratio of optical couplers in Type II fiber ring to ensure that at least one and only one longitudinal mode dominates in the selected pass-band. When the fiber ring lengths are designed to make their expanded pass-band spacing be a value from 0.5 to 1 times of the 3-dB bandwidth of the FBG, the mode competitions between both neighboring pass-bands and main cavity modes, may be effectively eliminated, making the laser maintain mode-hop-free SLM oscillations while it is widely tuned.

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.

Stable and High OSNR Compound Linear-Cavity Single-Longitudinal-Mode Erbium-Doped Silica Fiber Laser Based on an Asymmetric Four-Cavity Structure

We propose a stable and high optical signal-to-noise ratio (OSNR) compound linear-cavity single-longitudinal-mode (SLM) erbium-doped silica fiber laser. It consists of three uniform fiber Bragg gratings (FBGs) and two fiber couplers to form a simple asymmetric four-cavity structure to select the longitudinal mode. The stable SLM operation at the wavelength of 1544.053 nm with a 3 dB bandwidth of 0.014 nm and an OSNR of ∼60 dB was verified experimentally. Under laboratory conditions, a power fluctuation performance of less than 0.05 dB for 5 h and wavelength variation of less than 0.01 nm for about 150 min is demonstrated. Finally, the characteristic of laser output power as a function of pump power is investigated. The proposed system provides a simple and cost-effective approach to realize a stable SLM fiber laser.

Photonic generation of microwave signal using a dual-wavelength erbium-doped fiber ring laser with CMFBG filter and saturable absorber

A simple approach for photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time as we know, a chirped moiré fiber Bragg grating (CMFBG) filter with ultra-narrow transmission band and a chirped fiber Bragg grating (FBG) are used to select the laser longitudinal mode. The stable SLM operation of the fiber laser is guaranteed by the combination of the CMFBG filter and 3m unpumped EDF acting as a saturable absorber. Stable dual-wavelength SLM fiber laser with a wavelength spacing of approximately 0.140nm is experimentally realized. By beating the dual-wavelength fiber laser at a photodetector, photonic generation of microwave signal at 17.682GHz is successfully obtained.

Tunable single longitudinal mode S-band fiber laser using a 3 m length of erbium-doped fiber

In this paper a tunable single-longitudinal mode (SLM), short-wavelength band (S-band) fiber laser using a conventional erbium-doped fiber (EDF) with a length of 3 m and a step index erbium dopant profile as opposed to the commonly used depressed cladding erbium-doped fiber (DC-EDF) is proposed and demonstrated. The proposed SLM fiber laser has a tuning range of 1496 to 1507 nm in a ring configuration using two 0.15 m of EDF which acts as saturable absorbers (SAs). The highest peak power measured is about −0.6 dBm at a wavelength range of 1502 to 1507 nm. The measured signal-to-noise ratio (SNR) is approximately 74 dB for the same wavelength range. The line-width of the SLM output is measured to be 140 kHz.

A Stabilized Fiber Laser for High-Resolution Low-Frequency Strain Sensing

We frequency stabilize a fiber laser for use in low-frequency sensing applications. Using a radio frequency locking technique, an Erbium-doped single longitudinal mode fiber laser is stabilized to a Mach-Zehnder interferometer. The low-frequency fiber laser noise was suppressed by more than 1.5 orders of magnitude at frequencies below 300 Hz reaching a minimum of 2 Hz/radicHz between 60 and 250 Hz. The corresponding strain sensitivities are 2 pepsiv/radicHz at 1 Hz and 15 fepsiv/radicHz from 60 to 250 Hz.