Nonlinear Polarization Rotation Effect Research Articles

200-Gb/s wavelength conversion using a delayed-interference all-optical semiconductor gate assisted by nonlinear polarization rotation

The pattern-induced intensity fluctuation (PIF) of output signals with a bit-rate above 160Gb/s has been one of the major issues regarding all-optical semiconductor gates. We have demonstrated that the nonlinear polarization rotation (NPR) in the semiconductor optical amplifier (SOA) plays a significant role in the high-frequency operation of a delayed-interference signal-wavelength converter (DISC). We did this using a cross-correlation system whose temporal resolution is 1.5ps which was developed to monitor our 200-Gb/s, 4992-bit-long binary-patterned waveforms. When we experimentally optimized the NPR effect inside our DISC specially for our 200-Gb/s wavelength conversion, the PIF was significantly improved (from 5.0 to 1.5, for example). Our systematically measured dependence of the PIF on the polarization settings was qualitatively explained with the new gate model that we developed earlier in this work.

A Tunable Lyot Birefringent Filter With Variable Channel Spacing and Wavelength Using Nonlinear Polarization Rotation in an SOA

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We experimentally demonstrate a tunable fiber-optical Lyot birefringent comb filter with independent tuning of the channel spacing and wavelength. The filter configuration is based on sandwiching a fiber-optic programmable differential group delay line (DGDL) and a semiconductor optical amplifier (SOA) between two polarizers. The channel spacing of the filter can be tuned by adjusting the programmable DGDL. Using the nonlinear polarization rotation effect in the SOA, the phase shift between the transverse electric and the transverse magnetic components of the input probe beam can be adjusted by varying the power of the pump light, and hence fast and continuously wavelength tuning of the filter can also be achieved. The wavelength tuning range is up to 50% of the channel spacing when the pump power is increased from <emphasis><formula formulatype="inline"><tex>${-}$</tex></formula></emphasis>10 to 17 dBm. </para>

Passively Q‐switched erbium‐doped fiber laser based on nonlinear polarization rotation

AbstractWe have experimentally demonstrated an all‐fiber passively Q‐switched Erbium‐doped fiber (EDF) ring laser based on nonlinear polarization rotation. By incorporating a long section of single‐mode fiber and a polarization‐dependent isolator into the EDF ring laser, the intensity‐dependent transmission due to the effect of nonlinear polarization rotation can be implemented, which can act as an artificial saturable absorber for Q‐switching. Such a passively Q‐switched ring laser has the simple and all‐fiber configuration. In addition, passively harmonic mode‐locking and chaotic pulses are also generated from the EDF ring laser. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 694–696, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23185

基于非线性偏振旋转效应的多波长光纤激光器

Multiwavelength fiber laser is a perfect light source for future wavelength-division-multiplexing optical communication systems. A multiwavelength fiber laser based on nonlinear polarization rotation with up to 18 wavelengths has been proposed and demonstrated. The intensity- and wavelength-dependent loss induced by nonlinear polarization rotation effect is used to alleviate the mode competition in the homogeneous broadening gain medium of erbium-doped fiber. Instead of traditional filters, a polarization-maintaining fiber is inserted into the laser cavity, with which the polarization-dependent isolator composes an equivalent Lyot birefringent fiber filter. The in-line birefringence fiber filter is used to simplify the laser configuration, which benefits systematic integration. The effect of the 980 nm pump power on the multiwavelength generation is investigated. It is shown that the pump power contributes a lot to the evenness of the multiwavelength spectra due to the intensity dependence of nonlinear polarization rotation effect.

All-Optical NRZ-OOK to BPSK Format Conversion in an SOA-Based Nonlinear Polarization Switch

All-optical format conversion from nonreturn-to-zero on-off keying to binary phase-shift keying is demonstrated in a semiconductor optical amplifier-based nonlinear polarization switch. This conversion is realized by cross-phase modulation effect for phase encoding and nonlinear polarization rotation effect for amplitude equalization. In the experiment, error-free operation at 10 Gb/s is achieved with a receiver sensitivity penalty of 1.3 dB after single-ended detection.

Interaction of polarization mode dispersion and nonlinearity in optical fiber transmission systems

Aspects of the interaction of the Kerr nonlinearity and polarization mode dispersion (PMD) are reviewed. The basic equation that governs this interaction on the length scale of interest in optical fiber communications systems is the Manakov-PMD equation. This equation is derived using multiple-length-scale techniques. The focus of the derivation is the elucidation of common misunderstandings and pitfalls rather than mathematical rigor. It is shown that the scalar nonlinear Schro/spl uml/dinger equation is valid when PMD is absent and the signal is initially in a single polarization state. Two examples are then presented that illustrate the complexity of the interaction between nonlinearity and PMD. The first example considers the interaction of a nonlinearly induced chirp with PMD. As the power increases, one can obtain an improved eye opening relative to the case when PMD is absent. The second example considers the effect of nonlinear polarization rotation in a wavelength-division-multiplexed system. When nonlinear polarization rotation is important, the principal states of polarization become time dependent and PMD compensation becomes ineffective. This problem can be mitigated through the use of line codes.

Stable multiwavelength dispersion-tuned actively mode-locked erbium-doped fiber ring laser using nonlinear polarization rotation

We demonstrate a stable multiwavelength actively mode-locked erbium-doped fiber laser at 10 GHz based on a dispersion cavity and nonlinear polarization rotation (NPR) effect. The dispersion cavity allows simultaneous multiple wavelengths to satisfy the round-trip condition and smooth wavelength tuning, while the NPR ensures the stable operation and supermode noise suppression. A simple model is developed to explore the optimal setting of the cavity. Simultaneous dual- and five-wavelength operation is experimentally investigated

Stable and uniform multiwavelength erbium-doped fiber laser using nonlinear polarization rotation

A novel and simple technique, based on nonlinear polarization rotation (NPR) effect, to generate stable multiwavelength oscillations in an erbium-doped fiber laser is proposed and successfully demonstrated. The NPR effect effectively induced intensity- and wavelength-dependent loss to alleviate mode competition caused by homogeneous gain broadening in erbium-doped fibers. Up to 28-wavelength lasing operation with wavelength spacing of 0.8 nm has been achieved. The outputs had uniform power distributions, and the power fluctuation in each wavelength is smaller than 0.2 dB within a period of an hour.

Ultrashort pulse Yb3+-doped fiber ring laser with all-fiber structure

Theory of the self-starting passive mode-locked Yb3+-doped fiber ring laser generating short pulses is presented. The ultrashort pulse Yb3+-doped fiber ring laser with all-fiber structure has been designed and turned out. Two 976nm LD pumped lasers are used as the pump sources and high concentration Yb3+-doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained. The mode-locked threshold power of the laser is 260mW and the output power is 25mW. The center wavelength of the mode-locked pulse is 1056nm with 3dB bandwidth of 11.7nm at repetition rate of 20MHz. Comparing with the other structures of the fiber lasers, the structure we adopted is more efficient and has better stability.

High Concentration Yb3+-doped Passive Mode-locked Fiber Ring Laser

Theory and experimental results on the self-starting passive mode-locked Yb fiber ring laser generating short pulse are reported. The relations between the laser cavity parameters and mode-locked pulse characters are discussed. 980 nm LD pumped laser is used as the pump source and high concentration Yb 3+ -doped fiber is adopted as gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, self-starting stable mode-locked pulse is obtained, with center wavelength of 1046nm, 3 dB bandwidth of 6.01 nm and 20 dB bandwidth of 16 nm. The mode-locked threshold power is 150 mW and output power is 26 mW with 50 MHz repetition rate.

Research on highly Yb3+‐doped passive mode‐locked fiber ring laser

AbstractTheoretical and experimental results on the self‐starting passive mode‐locked Yb fiber‐ring laser generating short pulse are reported. The relations between the laser‐cavity parameters and mode‐locked pulse characteristics are discussed. 980‐nm LD‐pumped laser is used as the pump source and high‐concentration Yb3+‐doped fiber is adopted as the gain medium. Using the nonlinear polarization rotation (NPR) effect of the fiber, a self‐starting stable mode‐locked pulse is obtained, with a center wavelength of 1046 nm, a 3‐dB bandwidth of 6.01 nm, and a 20‐dB bandwidth of 16 nm. The mode‐locked threshold power is 150 mW and output power is 26 mW with a 20‐MHz repetition rate. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 269–270, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20792

Low repetition rate of a mode locked Nd:YAG laser using quadratic polarization switching

We present the performances of a low repetition rate (4.5 MHz) mode locked Nd:YAG laser using a nonlinear polarization rotation effect in a type II crystal cut for second harmonic generation. We compared their performances in term of peak power, pulse duration and cavity losses with a standard resonator operating at high repetition rate (125 MHz). A gain of 10.8 and 7.3 was obtained on the energy per pulse and on the output peak power between the two lasers.

Short pulse generation and control in Er-doped frequency-shifted-feedback fibre lasers

Novel features of frequency-shifted-feedback (FSF) fibre lasers are demonstrated. Dual-wavelength-switching FSF Q-switching and picosecond pulse fibre laser is reported by exploiting bandwidth of erbium fibre amplifier for pulse trapping. Wavelength switching between the states that have the spectra stably trapped by edges of the gain spectrum was accomplished by modulating the RF power applied to the acousto-optic frequency shifter. Also, a FSF fibre laser is demonstrated that utilizes a Michelson interferometer for pulse repetition rate control. The laser enables obtaining 1.64 ps pulses with a repetition rate up to 150 GHz. Finally we report the generation of 620 fs full-width at half-maximum pulses from a Ti:sapphire pumped Er-doped FSF fibre laser by exploiting nonlinear polarization rotation effects. We believe that this correspond to the shortest pulse ever obtained with a FSF fibre laser.

Experimental studies of self-starting passive mode locking Er3+ -doped fiber ring soliton laser

The mechanism of femtosecond optical pulse generation in a self-starting Er3+-doped fiber ring soliton laser and experimental research results are discussed. Using the nonlinear polarization rotation effect of the fiber for sat-urable absorbers (and then self-amplitude modulation) which acts as the mode locking mechanism in an Er3+-doped fiber ring cavity laser, stable self-starting mode locking pulses have been generated. The shortest output pulse is 269 fs, with the central wavelength of 1,531 pm at the repetition rate of 21.37 MHz. The average output powen of the two terminators of the laser are 0.25 mW and 0.08 mW respectively. The threshold pump power which sustains the mode locking is 15 mW. Under high pump power, the laser works in a high order harmonic mode locking state. The mode locking pulse durations vs different cavity lengths are also studied.

Nonlinear optical loop mirror using the nonlinear polarization rotation effect

The effect of nonlinear polarization rotation in a fiber loop mirror constricted from a low-birefringent fiber was numerically examined. We have shown that it provides in itself the intensity variation of the transmission coefficient from 1 to 0 in the configuration with a 0.5 0.5 coupler and a birefringent bias rotating polarization by π 2 at one end of the fiber. By appropriate choice of the fiber parameters both normal and inverted characteristics of the interferometer can be achieved.