Nonlinear Polarization Rotation Effect Research Articles

Observation of self-mode-locked noise-like pulses from a net normal dispersion erbium-doped fiber laser

Self-mode-locked noise-like pulses (NLPs) were experimentally investigated from a normal dispersion erbium-doped fiber laser. Different from noise-like pulses with a broadband spectrum, the self-mode-locked NLPs have a narrow optical spectrum of 1–2 nm and hundreds of nanoseconds duration. However, the intra-cavity maximum energy of NLPs is up to 560 nJ without pulse breaking. The higher pulse energy output is promising in the proposed fiber laser. To confirm whether self-mode-locked NLPs are caused by an invisible nonlinear polarization rotation (NPR) mechanism owing to slight residual polarization asymmetry of the fiber and components used, we compared the output characteristics between self-mode-locked NLPs and NPR mode-locked pulses in the same cavity. The experimental results show that the formation mechanism of such self-mode-locked NLPs could be related to a weak NPR effect.

Optically Controlled Fast Reconfigurable Microwave Photonic Dual-Band Filter Based on Nonlinear Polarization Rotation

A high-speed optically controlled microwave photonic (MWP) reconfigurable dual-band filter is presented, which is achieved using a Lyot loop filter for spectrum slicing and ultrafast nonlinear polarization rotation (NPR) effect in a semiconductor optical amplifier for high-speed tuning. Through the control of optical pump power, the MWP filter is switchable between four different operation states-all-block state, dual-band state, and single-band state with two different passband frequencies. The use of NPR greatly increases the tuning speed of the MWP filter to gigahertz range, making it capable for high-speed tuning in dynamic multiband applications. The four operation states and high-speed adjustment significantly improve operation flexibility of the filter. Furthermore, good passband quality is also obtained that the sidelobe suppressions of both passbands are over 40 dB with clean and sharp passband profiles, providing good filter selectivity.

Switchable thulium-doped fiber laser from polarization rotation vector to scalar soliton.

We experimentally demonstrate switchable temporal soliton generation from a thulium-doped fiber laser (TDFL), using carbon nanotubes as the mode-locker. With the help of residual polarization dependent loss of a wavelength division multiplexer, a weak nonlinear polarization rotation (NPR) effect can be achieved within the laser cavity, which may provide joint contribution for passive mode-locking operation. By finely adjusting the polarization to alter the strength of NPR-based saturable absorption, the TDFL either approaches the operation regime of scalar soliton with strong NPR effect, or generates polarization rotation locked vector soliton (PRLVS) with weak NPR effect. The scalar solitons and PRLVSs possess 3-dB optical spectrum bandwidth of 2.2 nm and 2 nm, pulse-width of 1.8 ps and 2 ps, respectively. Moreover, the PRLVSs demonstrate a typical energy exchange between two polarized components on optical spectra and a period-doubling feature in time domain. Such operation principle can also be used in 1550 nm band fiber lasers and other nonlinear systems.

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.

Study of all-optical sampling using a semiconductor optical amplifier

All-optical sampling is an important research content of all-optical signal processing. In recent years, the application of the semiconductor optical amplifier (SOA) in optical sampling has attracted lots of attention because of its small volume and large nonlinear coefficient. We propose an optical sampling model based on nonlinear polarization rotation effect of the SOA. The proposed scheme has the advantages of high sampling speed and small input pump power, and a transfer curve with good linearity was obtained through simulation. To evaluate the performance of sampling, we analyze the linearity and efficiency of sampling pulse considering the impact of pulse width and analog signal frequency. We achieve the sampling of analog signal to high frequency pulse and exchange the positions of probe light and pump light to study another sampling.

Nanosecond Hybrid Q-Switched Er-Doped Fiber Laser With WS2Saturable Absorber

We demonstrate a stable hybrid Q-switched Er-doped fiber (EDF) laser with WS2 as the saturable absorber (SA). The SA device is obtained by depositing WS2 on a tapered fiber using the pulsed laser deposition method. The modulation depth of the SA is 8.0%, the nonsaturable loss is 30%, and the saturation intensity is 200 MW/cm2. By combining the saturable absorption of fiber-taper WS2 and the effect of nonlinear polarization rotation, the Q-switched EDF laser is achieved with a pulse duration of 443 ns and average power of 43 mW. The repetition rate can be adjustable among 235–365 KHz. To our best knowledge, both pulse duration and output power are the best results among Q-switched EDF lasers with transition mental dichalcogenide materials like SAs. These results indicate that the proposed hybrid Q-switched EDF laser performs better to achieve shorter pulses with higher power in the future.

Widely tunable multi-wavelength thulium-doped fiber laser based on nonlinear polarization rotation

A kind of widely tunable multi-wavelength thulium-doped fiber laser based on nonlinear polarization rotation (NPR) is achieved. Using a ring cavity, 1565 nm laser pump, a 3m long thulium doped fiber, and NPR effect is used as filter. By adjusting the fiber polarization controller, stable 1–5 wavelengths laser output is observed at room temperature, and the side mode suppression ratio is 40–60 dB. The measured results show that the wavelength shift is less than 0.2 nm within one hour and the output peak power fluctuation is less than ±3 dB. The wavelength spacing is about 6.75 nm and the tuning range is 33 nm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1540–1543, 2016

Generation of tunable multi-wavelength EDFL by using graphene thin film as nonlinear medium and stabilizer

The applications of graphene thin film as a nonlinear medium and stabilizer to generate a stable multi-wavelength is proposed and demonstrated. A 50m long highly nonlinear photonic crystal fiber (PCF) is incorporated into the cavity to achieve unstable multi-wavelength based on nonlinear polarization rotation (NPR) effect. By introducing the graphene thin film into the cavity, a stable multi-wavelength oscillation is obtained. The laser generates more than 7 lasings with constant spacing of 0.47nm. The output is highly stable with power fluctuation of less than 3dB within a period of 30min. The multi-wavelength EDFL exhibits a tunability from the center wavelength of 1550nm to 1560nm.

Generation of multi-wavelength erbium-doped fiber laser by using MoSe2 thin film as nonlinear medium and stabilizer

We experimentally demonstrate the application of MoSe2 thin film as a nonlinear medium and stabilizer to generate a multi-wavelength erbium-doped fiber laser. The cooperation of a photonic crystal fiber and a polarization- dependent isolator induces unstable multi-wavelength oscillations based on the nonlinear polarization rotation effect. A MoSe2 thin film is further incorporated into the cavity to achieve a stable multi-wavelength. The laser generates 7 lasings with a constant spacing of 0.47 nm at a pump power of 250 mW. The multi-wavelength erbium-doped fiber laser is stable with power fluctuations of less than 5 dB over 30 min.

Tunable multiwavelength erbium-doped fiber laser incorporating single-core comb filter at room temperature

The generation of tunable multiwavelength erbium-doped fiber laser based on an integrated structure of a single-core comb filter and nonlinear polarization rotation (NPR) is proposed and successfully demonstrated at room temperature. The NPR effect effectively induced intensity and wavelength-dependent loss to alleviate mode competition caused by homogeneous gain broadening in erbium-doped fibers. Thirty-two lasing wavelengths in a 3dB flattened spectrum with a tunable wavelength spacing of 0.9nm–1.8nm have been achieved. Good stability of the laser operating at room temperature has been verified by using an optical spectrum analyzer to measure every 10min for an hour.

AMPLIFICATION AND LASING CHARACTERISTICS OF THULIUM YTTERBIUM CO-DOPED FIBER

The amplification and lasing characteristics of the newly developed Thulium-Ytterbium co-doped fiber (TYDF) are investigated. It is obtained that both TYDF amplifier and laser operate at 1950 nm region. The maximum gain of 22.4 dB is obtained for 1942 nm signal when the 980 nm multimode pump power, TYDF length and input signal power are fixed at 1.2 W, 5 m and -20 dBm, respectively. At 5 m long of TYDF, the laser produces two prominent lines at 1960 nm and 1965 nm with peak powers of 2.8 dBm and 3.1 dBm, respectively due to the nonlinear polarization rotation (NPR) effect in the cavity.

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and graphene – Polyethylene oxide saturable absorber

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser is demonstrated using graphene based saturable absorber, which is prepared using polyethylene oxide as a host polymer. The multi-wavelength operation is achieved based on nonlinear polarization rotation effect by incorporating 50m long photonic crystal fiber in the ring cavity. The Erbium-doped fiber laser produces a stable wavelength oscillation for more than 10 lines and fixed spacing of 0.46nm. The Erbium-doped fiber laser also demonstrates a stable pulse train with the repetition rate increases from 14.6 to 16.3kHz as the pump power increases from the threshold power of 39.6mW to the maximum pump power of 46.8mW. The minimum pulse width of 1.2μs was obtained at the maximum pump power of 46.8mW while the highest energy of 1.57nJ was obtained at pump power of 39.6mW.

Flexible rectangular wave-breaking-free pulse generation in actively mode-locked ytterbium-doped fiber laser.

We demonstrate nanosecond scale rectangular wave-breaking-free pulse generation in an actively mode locked Yb-doped fiber laser based on a combined action of active periodic cavity loss modulation and nonlinear polarization rotation effect. The pulse width of the laser can be controlled in the range of 890 ps to above 124 ns instantaneously by adjusting the electrical signal applied on the modulator. As high as 19.8 nJ wave-breaking-free pulse is achieved with maximum available pump power. The output pulse temporal dynamics exhibit various distinct characteristics under different modulation and polarization control. The laser presents unusually flexible tunabilities in pulse width, pulse energy and pulse shape.

Stable multi-wavelength fiber laser based on a compounded nonlinear polarization rotation effect

A stable multi-wavelength polarization-maintaining erbium-doped fiber (PM-EDF) laser with high signal-to-noise ratio (SNR) based on a compounded nonlinear polarization rotation effect (CNPRE) is proposed and demonstrated. In order to effectively reduce homogeneous broadening of EDF and then to the alleviate mode competition, two sandwich configurations formed by a polarization dependent isolator (PDI) or a segment of single-mode fiber sandwiched between two polarization controllers (PC), are introduced into the ring cavity to generate the CNPRE. A home-made asymmetry twin-core fiber (ATCF) is also incorporated in the ring cavity as a comb filter. With only 150 mW pump power, there are up to 45-wavelengths lasing with the approximate amplitude in a 3 dB bandwidth generated at room temperature. The wavelength spacing between the adjacent peaks is 0.29 nm and the highest SNRs reach 41.5 dB by optimizing the state of polarization of PCs. The power fluctuation and wavelength shift for each lasing wavelength are less than 0.05 dB and 0.02 nm, respectively. This indicates that the proposed multi-wavelength fiber laser can be stably operated at room temperature.

Photonic generation of triangular pulses based on nonlinear polarization rotation in a highly nonlinear fiber.

We propose a novel method to generate triangular pulses based on the nonlinear polarization rotation (NPR) effect in a highly nonlinear fiber. A continuous wave probe beam is polarization-rotated by an intensity-modulated control beam via the NPR effect. A polarization-division-multiplexing emulator is exploited to split the probe beam into two orthogonally polarized states with imbalanced time delay. After detection by a photodetector, a 90° microwave phase shifter is used to compensate the phases of the fundamental and the third-order harmonic components in order to generate triangular pulses. Triangular pulses at 5 and 6 GHz with full duty cycles are experimentally generated. The root mean square errors between the generated and the simulated waveforms are 3.6e-4 and 1e-4 for triangular pulses at 5 and 6 GHz, respectively.

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50 m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48 nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4 kHz as the pump power increases from the threshold power of 69.0 mW to the maximum pump power of 133.8 mW. The minimum pulse width of 4.4 μs was obtained at the maximum pump power of 133.8 mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0 mW.

A multiwavelength thulium-doped silica fiber laser incorporating a highly nonlinear fiber

A multiwavelength Tm3+-doped silica fiber laser incorporating a highly nonlinear fiber is presented. In the laser cavity, a nonlinear polarization rotation (NPR) based fiber loop mirror is used to overcome the mode competition and a polarization-maintaining fiber Sagnac loop mirror is used as the filter. The 150 m highly nonlinear fiber can improve the NPR effect in the laser cavity, which can increase the number of output channels. By adjusting the polarization state of the polarization controllers properly, stable multiwavelength operation at the 2 μm spectrum can be obtained at room temperature. It can achieve 15 output channels within a 10 dB bandwidth from 1990 to 2007.5 nm. The channel spacing of the multiwavelength Tm3+-doped silica fiber laser is 1.22 nm. Moreover, the performance of the laser is investigated for different pump powers and fibers.

A stable and uniform-amplitude multi-wavelength erbium-doped fiber laser based on nonlinear polarization rotation and a polarization-maintaining fiber loop mirror

We propose and demonstrate a stable and uniform-amplitude multi-wavelength erbium-doped fiber laser based on nonlinear polarization rotation and a polarization-maintaining fiber (PMF) loop mirror. The nonlinear polarization rotation (NPR) effect induces an intensity-dependent loss (IDL) to alleviate mode competition caused by homogeneous gain broadening of erbium-doped fiber (EDF) at room temperature. By adjusting the polarization controllers (PCs) carefully, up to twelve stable wavelengths with a side mode suppression ratio (SMSR) of 28.8 dB are achieved. The outputs have uniform amplitudes and the power fluctuation and wavelength shift for each lasing wavelength are smaller than 0.1 dB and 0.02 nm, respectively, in an hour.

Multiwavelength Brillouin-Thulium Fiber Laser

We demonstrate the first multiwavelength Brillouin-thulium fiber laser (BTFL) with wavelengths near 1.97 μm. The multiwavelength fiber laser was realized based on stimulated Brillouin scattering and nonlinear polarization rotation effects. The laser can generate five Brillouin wavelengths with spacing of about 0.105 nm, which is identical with the wavelength spacing of adjacent Brillouin Stokes lines. The peak power fluctuations of the multiwavelength BTFL were less than 0.5 dB, and the wavelength shifts were less than 0.01 nm in 20 min.

A switchable dual-wavelength erbium-doped fiber laser based on Sagnac loop inserted with two FBGs

A novel switchable dual-wavelength erbium-doped fiber (EDF) laser is demonstrated. The wavelength selection element consists of two fiber Bragg gratings (FBGs), a polarization controller (PC) and a 3 dB coupler forming a Sagnac loop inserted with two FBGs. We study the effect of coupling ratio on filtering performance in this paper. By adjusting PC, we can change the wavelength-dependent loss, and then using nonlinear polarization rotation effect to suppress the mode competition caused by the homogeneous broadening of EDF, we obtain single- and double-wavelength laser outputs. At room temperature, under 200 mW pump power, dual-wavelength laser is achieved, and the center wavelengths are 1545.34 nm and 1548.20 nm, respectively. The peak power values are −13.36 dBm and −14.58 dBm, and side mode suppression ratios (SMSRs) are 41.10 dB and 39.88 dB, respectively. Within two hours, the maximum fluctuation of peak power is less than 0.7 dB, which shows that the demonstrated fiber laser is stable. Moreover, by adjusting PC, singel-wavelength laser output is obtained, the peak power is −6.27 dBm or −5.45 dBm, and SMSR is 40.03 dB or 39.96 dB at 1545.34 nm or 1548.20 nm, respectively.