Adjusting Polarization Controller Research Articles

Real-time transition dynamics of harmonic mode-locking states with spectral filtering effect in a hybrid mode-locked fiber laser

We experimentally investigated the transition dynamics between 2nd and 3rd harmonic mode-locking states using the dispersive Fourier transform technology in a hybrid mode-locked fiber laser. Keeping the pump power unchanged and adjusting polarization controller to change intracavity-loss-dependent gain profile and the spectral filtering effect, a set of soliton dynamics induced by soliton interaction are revealed before the soliton splitting. Solitons undergo similar oscillation behaviors during the reverse decay process of the harmonic mode-locking order until one of the solitons disappears. In these transient dynamics, a significant wavelength shift phenomenon could be observed in the transition process of harmonic orders. The numerical results further show that intracavity spectral filtering effects play key role in the harmonic order transition dynamics process, consistent with experimental results. It provides new insights into the evolution and dynamics behavior in harmonic mode-locked soliton order conversion and its potential applications.

High-power cylindrical vector beam fiber laser based on an all-polarization-maintaining structure

We propose and demonstrate an all-polarization-maintaining (PM) high-power cylindrical vector beam (CVB) fiber laser based on the principle of mode superposition. The non-degenerated LPy 11a is generated from the oscillator with the maximum power of 11.9W, whose slope efficiency is 24.4%. Then the stable single TE01 vector beam is achieved by the superposition of LPy 11a and LPx 11b in an all-PM architecture, its output power is 3.1W and mode purity of 91.2%. Due to the all-PM architecture, our configuration is free of adjusting polarization controller (PC) and reliable during long-term operation. This laser could be used as a high-power CVBs source for a wide range of applications towards scientific research and industrial field.

Passively mode-locked cascaded Raman fiber laser in a linear cavity

Passively mode-locked cascaded Raman fiber laser is proposed and demonstrated in a linear cavity. The mode-locking is based on nonlinear polarization rotation (NPR) with a polarization beam splitter (PBS) in the proposed laser. The passively mode-locked Raman fiber laser with a spectral range of 220 nm operates in a low pump power level, and up to the three orders Raman frequency shift are observed under our pump power conditions. The maximum output average power and single pulse energy of the proposed laser are 119.3 mW and 63.97 nJ with a slope efficiency of 41.7%. Multi-pulse mode-locked operation can also be generated by precisely adjusting polarization controller (PC) under suitable pump power conditions.

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 erbium-doped fiber laser based on core-offset structure and four-wave-mixing effect

Abstract A switchable multi-wavelength erbium-doped fiber laser (EDFL) based on the two-mode fiber (TMF) with core-offset structures and the four-wave-mixing effect (FWM) is experimentally demonstrated in this paper. The proposed filter is constructed by splicing a section of TMF with two segments of single-mode fiber (SMF) and the insertion loss is ~0.4 dB, which is smaller than the most of offset structures. The filter is based on the interference of the LP01 mode and the LP11 mode, which are excited by the core-offset structure. Due to the characteristics of the filter spectra and wavelength competition, the output wavelengths can be single-, dual-, and triple-wavelength by adjusting polarization controller (PC). In order to mitigate the intense gain competition, the FWM is introduced by using highly nonlinear fiber (HNLF) and SMF, respectively. Benefiting from the intensity-dependent gain caused by FWM, the number of output lasers increases and outputs are more flexible, which can be quadruple-, quintuple-, septuple- and decuple-wavelength by adjusting PC. The flatness of the wavelengths is also studied.

Image rejection mixer based on a bidirectional phase modulator with full-spectrum utilization

ABSTRACTAn all-optical image rejection (IR) mixer, based on a dual electrical port phase modulation (PM) in a Sagnac loop and a wavelength division multiplexer (WDM), is proposed. The radio frequency (RF) and the local oscillator signals are loaded onto the two electrical ports of the PM, respectively. The two down-conversion channels are obtained with the use of WDM. A pair of phase orthogonal down-converted intermediate frequency (IF) signals are obtained by properly adjusting polarization controller. Then an electrical low-frequency 90 hybrid coupler (90HC) combines the two IF signals to double the desired IF signal and suppress the image interference IF signal. In the simulation, a 30-GHz RF signal is successfully down-converted to 1 GHz with about 57 dB IR. Compared with the IR mixer based on two parallel PMs, conversion efficiency is improved about 6 dB.

Tunable and switchable triple-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer with a polarization-maintaining photonic crystal fiber

A tunable and switchable triple-wavelength ytterbium-doped fiber laser (YDFL) based on a polarization-maintaining photonic crystal fiber (PMPCF) Sagnac interferometer is proposed and experimentally demonstrated. Owing to the large inhomogeneity of gain profile and simple two-level system of ytterbium-doped fiber, a tunable triple-wavelength lasing output is achieved with a tuning range of 1.6 nm. At room temperature, the maximum wavelength shift and peak power fluctuation are less than 0.018 nm and 0.64 dB, respectively. Moreover, the output lasing can be switched to single-wavelength lasing or dual-wavelength lasing through adjusting polarization controller. A tunable single-wavelength lasing with the side-mode suppression ratio above 50 dB is achieved from the wavelength of 1034.276 nm to 1038.314 nm. Two kinds of tunable dual-wavelength lasing with the tuning range of 3.2 nm are obtained in our experiment. In addition, the temperature stability is discussed by constructing the YDFL with PMPCF and conventional polarization-maintaining fiber (PMF), respectively. Experimental results demonstrate that the measured temperature sensitivity for PMPCF-based YDFL is 0.014 nm/℃, which is five times lower than that for PMF-based YDFL.

Generation of mode-locked square-shaped and chair-like pulse based on reverse saturable absorption effect of nonlinear multimode interference.

In this paper, the phenomenon of reverse saturable absorption of offset-spliced graded index multimode fibers (OS-GIMF) is revealed. And based on that, the stable square-shaped and chair-like mode-locked pulses are demonstrated with the maximum pulse energy of 0.14 µJ and 23.8 nJ respectively, while the OS-GIMF acts as a saturable absorber (SA) in fiber laser. By adjusting polarization controller (PC) and the pump power, square-shaped and chair-like pulse can be switched to each other. This multimode SA could sever as high power light source owing to its high damage threshold, compact structure and low cost.

A switchable dual-wavelength fiber laser based on phase-shifted fiber Bragg grating combined with Sagnac loop

A switchable dual-wavelength erbium-doped fiber (EDF) laser is proposed and demonstrated. The interference filter is achieved by employing a phase-shifted fiber Bragg grating (PSFBG) combined with Sagnac loop structure. By adjusting polarization controller (PC) states, the birefringence effect is introduced to weaken mode competition, then stable and switchable dual-wavelength fiber laser can be realized. Based on coupled-mode theory and transmission matrix, the Sagnac loop transmission characteristics are studied. The experimental results show that the proposed fiber laser can operate in switchable dual-wavelength output mode at room temperature just by simply adjusting PC. The output wavelength range of fiber laser is 1 556.128–1 556.384 nm, the side mode suppression ratio (SMSR) is over 45 dB, and dual-wavelength spacing as small as 0.048 nm is achieved, which can be used in high-fineness dense wavelength division multiplexing (DWDM) systems and similar structures.

Stable and widely tunable single-/dual-wavelength erbium-doped fiber laser by cascading a twin-core photonic crystal fiber based filter with Mach-Zehnder interferometer

A stable and widely tunable single-/dual-wavelength erbium-doped fiber laser (EDFL) is proposed by cascading a homemade twin-core photonic crystal fiber (TCPCF) based filter with Mach-Zehnder interferometer (MZI). By bending the TCPCF, single-wavelength lasing can be tuned from 1560.4 nm to 1583.44 nm with the tuning step of ∼0.78 nm and the widely tunable wavelength range over 23.04 nm can be achieved. Furthermore, by adjusting polarization controller, the output lasing can be switched from single-wavelength to dual-wavelength; the dual-wavelength lasing with wavelength interval of 0.78 nm can be tuned over a range of 33.82 nm from 1559.72 nm/1560.48 nm to 1593.54 nm/1594.32 nm. The tuning step and the interval of dual-wavelength is determined by the MZI. The SMSR of single- and dual-wavelength are higher than 45 dB and 42 dB, respectively. In addition, the stability of output lasing is measured experimentally. Excremental results demonstrate that the wavelength drift is less than 0.02 nm and peak power fluctuations of single-/dual-wavelengths are less than 0.47 dB and 0.8 dB, respectively. Such wide tuning range, small wavelength drift and high power stability makes this tunable EDFL have a potential application in the fields of optical fiber communication and sensing.

Tunable multi-wavelength EDF laser based on Sagnac interferometer with weakly-coupled FMF delay line

A simply manufactured and broadly tunable multi-wavelength Erbium-doped fiber (EDF) ring laser based on Sagnac interferometer with weakly-coupled few-mode fiber (FMF) delay line is proposed and experimentally demonstrated. The incorporation of FMF is realized with all-fiber mode multiplexer/demultiplexer (MUX/DEMUX) consisted of mode-selective couplers (MSC). The FMF and the mode MUX can simultaneously generate higher-order modes and fundamental mode. Single-, dual- and triple-wavelength lasing are obtained with broad tuning over 30-nm and smallest tuning step of 0.52-nm by adjusting polarization controller (PC) in the Sagnac interferometer. Optical signal-to-noise ratio (OSNR) higher than 30-dB and stability in 30-min are also measured.

Experimental Study on Soliton Rain Patterns in Yb-Doped All-Fiber Standing Wave Cavity Configuration

We demonstrate for the first time, experimental observation of soliton rain (SR) state at relatively low pumping power in Yb-doped fiber laser in all-fiber standing wave cavity configuration. SR is shown to be controllable in terms of speed, density, and direction of drifting. Other SR states, such as stationary SR, cyclic SR, and harmonic SR, were also observed by adjusting polarization controller settings. We carefully identified the portion of the spectra contributing to the SR state and correlate its influence on the speed and direction of rain drift relative to the condensed phase. Observation of SR in our cavity can help in enhancing the understanding of dissipative soliton dynamics in all normal dispersion fiber lasers.

Tunable and switchable thulium-doped fiber laser utilizing Sagnac loops incorporating two-stage polarization maintaining fibers

Abstract A ring cavity thulium-doped fiber laser incorporating a Sagnac loop is proposed and experimentally demonstrated. In the designed fiber laser, a 0.4-m-long thulium-doped fiber is selected as the gain medium; the Sagnac loop is composed of two-stage polarization maintaining fibers of lengths 1 m and 2 m, respectively; and one broadband reflection mirror is used as the wavelength reflector. In the experiment, the lasing threshold is 135 mW, and by adjusting the polarization controller, a tunable and stable single-wavelength laser can be realized. The line interval is less than 3 nm within 1832–1865 nm, the power difference of each line is less than 1.111 dB, and the side-mode suppression ratio is larger than 44.7 dB. When 1848.4 and 1846.4 nm single-wavelength lasers are realized, the peak power fluctuation is less than 0.18 dB and 0.206 dB, respectively, within 10 min of scan time. A tunable and stable dual-wavelength laser can be realized by adjusting polarization controller; the power difference is less than 3.68 dB, and the side-mode suppression ratio is more than 35.04 dB. When 1844 and 1863.2 nm lasers are obtained simultaneously, the power shift is less than 0.6 dB and 0.95 dB, respectively, at room temperature. By changing the polarization state, tunable triple-wavelength lasing can be achieved ultimately, and the side-mode suppression ratio is larger than 41 dB.

Switchable dual-wavelength all-fiber laser mode-locked by carbon nanotubes

We have proposed a compact dual-wavelength all-fiber pulse laser based on a single-walled carbon nanotube and chirped fiber Bragg gratings (CFBGs). A transmission filter is composed of a circulator and two CFBGs and is capable of controlling the operation of the proposed fiber laser. Mode-locking operations can be switched between 1551.2 and 1548.6 nm with the appropriate adjustment of polarization controller. Our laser delivers the pulses with the spectral bandwidth of about 0.6 nm and the pulse duration of about 7 ps. This work provides a low-cost, stable, and dual-wavelength ultrafast-pulsed laser source suitable for practical applications.

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.

12 GHz passive harmonic mode-locking in a 106 μm semiconductor optical amplifier-based fiber laser with figure-eight cavity configuration

We report the generation of passively harmonic mode-locked pulses using a 1.06 μm semiconductor optical amplifier (SOA) in a figure-eight laser configuration operated in the all-normal-dispersion regime. Different orders of harmonic mode-locking can be obtained from 30 MHz to 12.02 GHz by changing the injection current of the SOA from 80 to 660 mA together with the adjustment of polarization controllers. The highest pulse repetition rate increases almost linearly with the SOA current. As SOA current is set to 660 mA, we obtain the intracavity power of 46 mW at the highest repetition rate of 12.02 GHz, corresponding to the 1202th harmonic of the fundamental mode-locking frequency. To our best knowledge, this is the lowest intracavity power to generate the highest repetition rate with a passively mode-locked laser in the all-normal-dispersion regime.

All-optical clock recovery of 20 Gbit/s NRZ-DPSK signals using polarization-maintaining fiber loop mirror filter and semiconductor optical amplifier fiber ring laser

All-optical clock recovery (CR) from 20 Gbit/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signals are demonstrated experimentally by using a polarization-maintaining fiber loop mirror filter (PMF-LMF) and a semiconductor optical amplifier (SOA) fiber ring laser. Only by adjusting polarization controller (PC), NRZ-DPSK signals were conveniently and fast converted to pseudo return-to-zero (PRZ) signal via PMF-LMF. Then the PRZ signals are injected into the SOA fiber laser for CR. The recovered clock signals is with the extinction ratio (ER) of 10 dB and the root-mean-square (RMS) timing jitter of 750 fs in 2 31 − 1 long pseudorandom binary sequence (PRBS) NRZ-DPSK signals measurement. Moreover, the broad wavelength tunability of recovered clock stemmed from the use of SOAs as modulator and the gain medium are shown too.

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.

Single frequency 1083nm ytterbium doped fiber master oscillator power amplifier laser

Single frequency 1083nm ytterbium fiber master oscillator power amplifier system was demonstrated. The oscillator was a linear fiber cavity with loop mirror filter and polarization controller. The loop mirror with unpumped ytterbium fiber as a narrow bandwidth filter discriminated and selected laser longitudinal modes efficiently. Spatial hole burning effect was restrained by adjusting polarization controller appropriately in the linear cavity. The amplifier was 5 m ytterbium doped fiber pumped by 976nm pigtail coupled laser diode. The linewidth of the single frequency laser was about 2 KHz. Output power up to 177 mW was produced under the launched pump power of 332 mW.

Multi-wavelength lasing oscillations in an erbium-doped fiber laser using few-mode fiber Bragg grating

We propose a simple erbium-doped fiber laser configuration for obtaining multi-wavelength oscillation at room temperature, in which a few-mode fiber Bragg grating was used as the wavelength-selective component. An amplitude variation of 1.6 dB over 120 second period was obtained for three-wavelength oscillation at room temperature, which demonstrates stability of the output power. This multi-wavelength laser can be switched between dual- and triple-wavelength operations by properly adjusting polarization controller in the cavity. This multi-wavelength laser has the advantage of simple configuration, high stability, low cost and stable operation at room temperature.