Tunable S-band erbium-doped triple-ring laser with single-longitudinal-mode operation

Expanding gain bandwidth using ion-hybridized fiber for kHz-linewidth single-frequency fiber lasers at S-, C-, and L-bands: design and performance evaluation

Single-frequency fiber lasers at S-, C-, and L-bands play a crucial role in various applications such as optical network expansion, high-precision metrology, coherent lidar, and atomic physics. However, compared to the C-band, the S- and L-bands have wavelength deviations and suffer from excited-state absorption, which limits the output performance. To address this issue, a strategy called ion hybridization has been proposed to increase the differences in site locations of rare earth (RE) ions in the laser matrix, thereby achieving a broader gain bandwidth. This strategy has been applied to an Er3+/Yb3+ co-doped modified phosphate fiber (EYMPF), resulting in gain coefficients per unit length greater than 2 dB/cm at S-, C-, and L-bands. To demonstrate its capabilities, several centimeter-long EYMPFs have been used to generate single-frequency laser outputs at S-, C- and L-bands with kHz-linewidths, high signal-to-noise ratios (>70 dB), and low relative intensity noise (<-130 dB/Hz) in a compact short linear-cavity configuration.

High-Temperature-Resistant Fiber Laser Vector Accelerometer Based on a Self-Compensated Multicore Fiber Bragg Grating

We propose and demonstrate a novel high-temperature-resistant vector accelerometer, consisting of a ring cavity laser and sensing probe (i.e., fiber Bragg gratings (FBGs)) inscribed in a seven-core fiber (SCF) by using the femtosecond laser direct writing technique. A ring cavity laser serves as a light source. Three FBGs in the outer cores of SCF, which are not aligned in a straight line, are employed to test the vibration. These three FBGs have 120° angular separation in the SCF, and hence, vibration orientation and acceleration can be measured simultaneously. Moreover, the FBG in the central core was used as a reflector in the ring cavity laser, benefiting to resist external interference factors, such as temperature and strain fluctuation. Such a proposed accelerometer exhibits a working frequency bandwidth ranging from 4 to 68 Hz, a maximum sensitivity of 54.2 mV/g, and the best azimuthal angle accuracy of 0.21° over a range of 0-360°. Furthermore, we investigated the effect of strain and temperature on the performance of this sensor. The signal-to-noise ratio (SNR) only exhibits a fluctuation of ~1 dB in the range (0, 2289 με) and (50 °C, 1050 °C). Hence, such a vector accelerometer can operate in harsh environments, such as in aerospace and a nuclear reactor.

Watt-level 1.7-μm single-frequency thulium-doped fiber oscillator

Here we demonstrated an efficient high-power single-frequency thulium-doped fiber ring laser operating at 1720 nm. Three cascaded sub-rings were inserted into the main cavity to significantly enlarge the effective free spectral range. By incorporating a fiber Bragg grating, the single longitudinal mode operation was achieved. The maximum single-frequency output power reached up to 1.11 W under 3.75-W launched pump power, while the slope efficiency with respect to the absorbed pump power was 46.4%. The laser linewidth at maximum single-frequency power was measured of 1.9 kHz. Potential power scaling of the single-frequency output power with different quantity and lengths of the sub-rings was also theoretically investigated.

Efficient multi-watt 1720 nm ring-cavity Tm-doped fiber laser

Using commercial Tm-doped silica fiber and 1570-nm in-band pump source, we demonstrated an efficient 1720-nm all-fiber laser with ring-cavity configuration. The theoretical model based on rate equations was built up to analyze the laser performance of Tm-doped fiber, which exhibits strong absorption in the 1.7-μm region. The results show that efficient laser operation can be achieved through the optimization of output coupling and the length of Tm-doped fiber. An experimental investigation was performed and agreed with the calculation. By using homemade couplers, we experimentally achieved 2.36-W laser output at 1720 nm under a 6-W launched pump. The slope efficiency with respect to the absorbed pump power and optical efficiency were 50.2% and 39.3%, respectively. Due to the employment of a ring resonator, a narrow laser linewidth of ∼4 GHz at maximum output power was observed.

40 GHz narrow linewidth frequency-switched microwave signal generation based on a single-longitudinal-mode double-Brillouin-frequency spaced Brillouin fiber laser

A novel approach to generating 40 GHz narrow linewidth frequency-switched microwave signals is proposed and demonstrated. In this scheme, a single-longitudinal-mode (SLM) double-Brillouin-frequency spaced Brillouin fiber laser with dual-ring configuration and unpumped erbium-doped fiber (EDF) is used to generate dual-wavelength lasers, and a fiber Bragg grating is used to select the laser for different Brillouin frequency spacings. Dual-ring configuration and unpumped EDF are designed to select the mode for the SLM laser. Dual-wavelength lasers are inserted into a photodetector, and microwave signals at 10.66, 21.39, 32.12, or 42.85 GHz can be obtained. The linewidth of the generated microwave signals is less than 69 kHz. The frequency drift at each frequency is less than 0.83 MHz. The frequency noise and linewidth of Stokes signals are measured, and the linewidth broadening effect of microwave signals is analyzed.

Tunable single frequency fiber laser based on FP-LD injection locking

We propose and demonstrate a tunable single frequency fiber laser based on Fabry Pérot laser diode (FP-LD) injection locking. The single frequency operation principle is based on the fact that the output from a FP-LD injection locked by a multi-longitudinal-mode (MLM) light can have fewer longitudinal-modes number and narrower linewidth. By inserting a FP-LD in a fiber ring laser cavity, single frequency operation can be possibly achieved when stable laser oscillation established after many roundtrips through the FP-LD. Wavelength switchable single frequency lasing can be achieved by adjusting the tunable optical filter (TOF) in the cavity to coincide with different mode of the FP-LD. By adjustment of the drive current of the FP-LD, the lasing modes would shift and wavelength tunable operation can be obtained. In experiment, a wavelength tunable range of 32.4 nm has been obtained by adjustment of the drive current of the FP-LD and a tunable filter in the ring cavity. Each wavelength has a side-mode suppression ratio (SMSR) of at least 41 dB and a linewidth of about 13 kHz.

Stable and wavelength-tunable silicon-micro-ring-resonator based erbium-doped fiber laser

In this work, we propose and demonstrate a stable and wavelength-tunable erbium-doped fiber (EDF) ring laser. Here, a silicon-on-insulator (SOI)-based silicon-micro-ring-resonator (SMRR) is used as the wavelength selective element inside the fiber ring cavity. A uniform period grating coupler (GC) is used to couple between the SMRR and single mode fiber (SMF) and serves also as a polarization dependent element in the cavity. The output lasing wavelength of the proposed fiber laser can be tuned at a tuning step of 2 nm (defined by the free spectral range (FSR) of the SMRR) in a bandwidth of 35.2 nm (1532.00 to 1567.20 nm), which is defined by the gain of the EDF. The optical-signal-to-noise-ratio (OSNR) of each lasing wavelength is larger than 42.0 dB. In addition, the output stabilities of power and wavelength are also discussed.

Tunable graphene Q-switched erbium-doped fiber laser with suppressed self-mode locking effect

Self-mode locking effect in a wideband tunable graphene-based passively Q-switched erbium-doped fiber laser has been observed experimentally. Q-switching is achieved by using graphene as a saturable absorber, while a tunable bandpass filter with a narrow bandwidth is used to obtain wideband tunability. We propose to suppress the modulation on each pulse from self-mode locking by introducing three subring resonators constructed with three 3 dB couplers into the laser ring cavity. Moreover, the laser output characteristics with respect to pump power are studied in detail. A stable Q-switched erbium-doped fiber laser with a tunable range from 1522 nm to 1568 nm is demonstrated experimentally.

Tunable Er-doped fiber ring laser with single longitudinal mode operation based on Rayleigh backscattering in single mode fiber

A tunable and single longitudinal mode Er-doped fiber ring laser (SLM-EDFRL) is proposed and demonstrated based on Rayleigh backscattering (RBS) in single mode fiber-28e (SMF-28e). Theory and experimental study on formation of SLM from normal multi-mode ring laser is demonstrated. The RBS feedback in 660 m SMF-28e is the key to ensure SLM laser oscillation. This tunable SLM laser can be tuned over 1549.7-1550.18 nm with a linewidth of 2.5-3.0 kHz and a side mode suppression ratio (SMSR) of ~72 dB for electrical signal power. The tuning range is determined by the bandpass filter and gain medium used in the experiment. The laser is able to operate at S+C+L band.

Tunable Fabry-Perot filter using hollow-core photonic bandgap fiber and micro-fiber for a narrow-linewidth laser

A novel tunable fiber Fabry-Perot (FP) filter is proposed and demonstrated by using a hollow-core photonic bandgap fiber (HC-PBF) and a micro-fiber. The interference cavity is a hollow core of HC-PBF. One of the reflection mirrors is the splicing point between a section of HC-PBF and a single mode fiber. The other reflection mirror is a gold-coated end of micro-fiber that uses chemical etching process to obtain the similar diameter as the core of HC-PBF. Hence the movable mirror can be adjusted with long distance inside the hollow core of HC-PBF. Tunable FP filter is used as a mode selecting component in the reflection mode to implement stable single longitudinal mode (SLM) operation in a ring laser. With FP cavity length of 0.25 ± 0.14 mm, the wavelength of SLM laser can be tuned over 1554-1562 nm with a tuning step of 0.2-0.3 nm, a side-mode suppression ratio (SMSR) of 32-36 dB and a linewidth of 3.0-5.1 kHz. With FP cavity length of 2.37 ± 0.37 mm, the SLM laser can be tuned over 1557.3-1560.2 nm with a tuning step of 0.06-0.1 nm, a SMSR of 44-51 dB and a linewidth of 1.8-3.0 kHz.

C-band single-longitudinal mode lanthanum co-doped bismuth based erbium doped fiber ring laser

We propose and demonstrate a stable, tunable and narrow linewidth C-band lanthanum co-doped bismuth based erbium doped fiber (EDF) ring laser with single longitudinal mode (SLM) operation. A free space thin film filter acts as a wavelength discriminative component selecting a few oscillating modes while a Lyot filter formed by a polarization maintaining (PM) fiber and a linear polarizer further discriminates and selects SLM efficiently. A power stability of < or = 0.05 dB, central wavelength variation of < or = 0.02 nm, a side-mode suppression ratio (SMSR) of at least > 43 dB, and a linewidth of about 1.3 kHz have been experimentally demonstrated.

Dual Sagnac loop mirror SOA-based widely tunable dual-output port fiber laser

A widely tunable (30 nm) fiber laser based on a double Sagnac loop mirror configuration is proposed and demonstrated. A semiconductor optical amplifier (SOA) placed between the two loop mirrors acts as the gain medium. The fiber laser has two output ports with adjustable optical power outputs. Wavelength tunability is obtained through the use of a thin film tunable filter, while optical power adjustability is accomplished by proper adjustment of each of the loop mirror reflectivity via a polarization controller. A total output power of + 9 dBm is measured and the potential for higher output powers is discussed. Optical power stability of better than +/- 0.15 dB is measured for 6 hours.

Single-frequency 1060 nm semiconductor-optical-amplifier-based fiber laser with 40 nm tuning range

A compact single-frequency 1060 nm fiber laser based on a high-power semiconductor optical amplifier (SOA) has been proposed and demonstrated with over 40 nm wavelength tuning range. The inhomogeneous gain-broadening feature of the SOA and the unpumped ytterbium-doped fiber-based saturable absorber contribute to the single longitudinal mode lasing of the fiber laser. The maximum 3 dBm output power can be obtained with the optical signal to noise ratio larger than 50 dB. Stable single-frequency operation can be maintained more than 1 h with negligible power fluctuations and low relative intensity noise.

Frequency-switchable microwave generation based on a dual-wavelength single-longitudinal-mode fiber laser incorporating a high-finesse ring filter

A wavelength-switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser (EDFL) incorporating a novel high-finesse ring filter is proposed and demonstrated. The ring filter consists of two optical couplers and a section of pumped erbium-doped fiber (EDF). Thanks to the gain generated by the EDF, the ring filter has spectral response with a high finesse. The incorporation of the ring filter leads to the suppression of undesirable modes in the dual-wavelength EDFL. An experiment is carried out. Two SLM wavelengths are generated. The side mode suppression ratio is greater than 50 dB. The wavelength spacing of the two wavelengths is tunable with a tuning step of approximately 10 GHz. A frequency switchable microwave signal from approximately 10 to approximately 40 GHz is thus generated by beating the two wavelengths at a photodetector (PD). The spectral width of the generated microwave signal is measured to be less than 5 kHz.

C-band wavelength-swept single-longitudinalmode erbium-doped fiber ring laser

A wavelength-swept single-longitudinal-mode erbium-doped fiber ring laser capable of operating at sweeping frequency in the order of a few kHz is designed and demonstrated by using a fiber Fabry-Perot tunable filter and a Sagnac loop incorporated with a 3.5-meter unpumped erbium-doped fiber. The laser operates in continuous-wave (CW) mode and can sweep approximately 45 nm over the entire C-band (1520nm-1570nm) window with linewidth less than 0.7 kHz. The optimum wavelength sweeping frequency in order to achieve the best output power stability was found to be approximately20Hz with sweeping-induced power fluctuation of only 0.1%.