Nonlinear Optical Loop Mirror Research Articles

Supercontinuum generation in an Er-doped figure-eight passively mode-locked fiber laser.

A supercontinuum source based on a figure-eight Er-doped fiber ring cavity has been experimentally demonstrated with low repetition rate. The proposed configuration of the experiment is a figure-eight fiber laser grounded in Nonlinear Optical Loop Mirror (NOLM) technique. A broad spectrum of approximately 410 nm spanning the range 1315-1725 nm at the level of 30 dB can be obtained at a given average power of 2.6 mW and without any amplifier. Such wide spectrum can be directly achieved in the fiber resonator, which makes the structure compact and robust. By changing the pump power, the temporal pulse width can be adjusted accordingly. The pulse width is about 4 ns at the pump power of around 240 mW. The broadband spectrum was generated directly from the fiber resonator, which can be easily applied in numerous areas, such as the optical frequency metrology, optical spectroscopy, optical coherence tomography, optical communications, and medical sciences.

2 µm high-power dissipative soliton resonance in a compact σ-shaped Tm-doped double-clad fiber laser

We report direct generation of a high-power, large-energy dissipative soliton resonance (DSR) in a 2 µm Tm-doped double-clad fiber laser. A compact σ-shaped cavity is formed by a fiber Bragg grating and a 10/90 fiber loop mirror (FLM). The 10/90 FLM is not only used as an output mirror, but also acts as a nonlinear optical loop mirror for initiating mode locking. The mode-locked laser can deliver high-power, nanosecond DSR pulses at 2005.9 nm. We further perform a comparison study of the effect of the FLM’s loop length on the mode-locking threshold, peak power, pulse energy, and optical spectrum of the DSR pulses. We achieve a maximum average output power as high as 1.4 W, a maximum pulse energy of 353 nJ, and a maximum peak power of 84 W. This is, to the best of our knowledge, the highest power for 2 µm DSR pulses obtained in a mode-locked fiber laser.

Compressibility of Dissipative Solitons in Mode-Locked All-Normal-Dispersion Fiber Lasers

We numerically investigated the compressibility of dissipative soliton pulses in an all-normal-dispersion fiber laser which was mode-locked with a nonlinear optical loop mirror. A transition state within the area between the traditional dissipative soliton regime and dissipative soliton resonance regime was revealed to have much higher dechirped peak power and shorter dechirped pulse duration than its vicinity. This phenomenon is reported for the first time to the best of our knowledge. The peak power and pulse width of the dechirped pulse were calculated using the linear compression method. The dynamics and the distribution of the transition state were systematically analyzed in laser parameter spaces. The nonlinear frequency chirp was mainly induced by self-phase modulation and the pulse formation mechanism, which influenced the linear compressibility of the dissipative. We demonstrated that there were optimal filter bandwidth values corresponding to the best pulse compressibility under different laser parameters. The simulation results indicate that dechirped pulses with a pulse peak power of 0.5–1 MW, a pulse duration of the 100-fs level, and a pulse energy of ∼100 nJ can be obtained using the optimal parameters.

An integrated nonlinear optical loop mirror in silicon photonics for all-optical signal processing

The nonlinear optical loop mirror (NOLM) has been studied for several decades and has attracted considerable attention for applications in high data rate optical communications and all-optical signal processing. The majority of NOLM research has focused on silica fiber-based implementations. While various fiber designs have been considered to increase the nonlinearity and manage dispersion, several meters to hundreds of meters of fiber are still required. On the other hand, there is increasing interest in developing photonic integrated circuits for realizing signal processing functions. In this paper, we realize the first-ever passive integrated NOLM in silicon photonics and demonstrate its application for all-optical signal processing. In particular, we show wavelength conversion of 10 Gb/s return-to-zero on-off keying (RZ-OOK) signals over a wavelength range of 30 nm with error-free operation and a power penalty of less than 2.5 dB, we achieve error-free nonreturn to zero (NRZ)-to-RZ modulation format conversion at 10 Gb/s also with a power penalty of less than 2.8 dB, and we obtain error-free all-optical time-division demultiplexing of a 40 Gb/s RZ-OOK data signal into its 10 Gb/s tributary channels with a maximum power penalty of 3.5 dB.

Ultraviolet-enhanced supercontinuum generation with a mode-locked Yb-doped fiber laser operating in dissipative-soliton-resonance region.

We experimentally demonstrate an all-fiber, ultraviolet-enhanced, supercontinuum generation in a specifically designed seven-core photonic crystal fiber pumped by a picosecond Yb-doped master oscillator power amplifier (MOPA). The MOPA source is seeded by a giant-chirped Yb-doped mode-locked fiber laser operating in the dissipative-soliton-resonance (DSR) region. The DSR is achieved by using a nonlinear optical loop mirror (NOLM) with a fundamental repetition rate of 4.5 MHz and a central wavelength of 1035 nm. An extremely wide optical spectrum spanning from 350 nm to 2400 nm is obtained with a total output power of 6.86 W.

Cavity-birefringence-dependent h-shaped pulse generation in a thulium-holmium-doped fiber laser.

We report on a type of 2μm h-shaped pulse generation in a thulium-holmium-doped fiber laser and experimentally investigate its cavity birefringence and pump power dependences. An asymmetric nonlinear optical loop mirror is employed as an artificial saturable absorber, which incorporates ∼52.7 m dispersion-shifted fiber and ∼3.8 m ultra-high numerical aperture fiber to enhance the nonlinearity. The h-shaped pulse shows both a polarization state (PS) and pump power related evolutions, even when randomly weak birefringence fibers are employed. By further incorporating different lengths of high birefringence polarization-maintaining fiber (PMF), i.e., introducing different amounts of linear cavity birefringence, much larger pulse tuning ranges can be realized. In particular, when the PMF is lengthened to ∼2.3 m through manipulating the PS, the achieved longest pulse duration of ∼318.14 ns can almost cover the whole repetition period of ∼323.96 ns, corresponding to a pulse duty circle of ∼98.2%, the largest ever reported from a fiber laser, to the best of our knowledge. We demonstrate the related characteristics in detail.

All-polarization-maintaining figure-eight Er-fiber ultrafast laser with a bidirectional output coupler in the loss-imbalanced nonlinear optical loop mirror

In this Letter, we report on a novel architecture for a self-starting mode-locked figure-eight erbium-doped fiber laser using a loss-imbalanced nonlinear optical loop mirror (NOLM) with a bidirectional output coupler. An all-polarization-maintaining structure is adopted. A 2 × 2 optical coupler with a splitting ratio of 50:50 is used at the junction to form an NOLM. Another coupler with a splitting ratio of 10:90 is introduced at one end of the fiber loop. The 10:90 coupler plays two roles: power attenuator and bidirectional output coupler. This architecture can achieve both large modulation depth and good self-starting ability simultaneously. With this architecture, the self-starting mode-locking operation is achieved easily with pump power above the threshold. The clockwise and counter-clockwise mode-locked output powers are 10.1 and 10.3 mW, respectively, with the repetition rate of 3.63 MHz. The spectral bandwidths of the clockwise and counter-clockwise mode-locked output pulses are 7.4 and 2.9 nm, and the corresponding pulse widths of the direct outputs are 530.6 fs and 1.55 ps, respectively.

1.1-kW Peak-Power Dissipative Soliton Resonance in a Mode-Locked Yb-Fiber Laser

We report an ytterbium-doped all-fiber laser generating dissipative soliton resonance (DSR) pulses with kilowatt-level peak power. The laser cavity was constructed with all-10/125 large-mode-area fibers to alleviate excessive nonlinear effects caused by high peak power. DSR pulse breaking and Raman-induced instability are avoided by carefully placing the fiber sections. Numerical and experimental investigation of high-peak-power DSR laser mode-locked with nonlinear optical loop mirrors is presented. Up to 1.66 W, 161-nJ energetic pulses are obtained without pulse-breaking. In particular, the laser generates pulses with 48–146 ps tunable pulse duration and an almost fixed peak power as high as 1.1 kW. To the best of our knowledge, this letter presents the first demonstration of DSR pulses with kilowatt-level peak power in mode-locked fiber lasers.

Investigation of hybrid modulator based on nonlinear optical loop mirror and single-walled carbone nanotubes for mode-locking in Yb-doped ultrafast fiber laser

Algorithm for the mathematical modelling of a fiber oscillator with a hybrid modulator based on a nonlinear fiber mirror and single-walled carbon nanotubes is suggested. It is based on a numerical solution of the nonlinear Schrödinger equation. Using numerical simulation, optimum NOLM coupler ratio, laser spot diameter on the sample preventing sample degradation and high modulator effect are determined.It is shown that hybrid modulator accelerates the self-starting process and decreases the output pulse duration up to 10%.

All-Optical Actively Mode-Locked Fiber Laser at 2-μm Based on Interband Modulation

In this paper, we have achieved a high repetition rate and tunable pulse generation near ∼2 μm through an all-optical actively mode-locked fiber laser. The performances of the fiber laser have been systematically investigated through numerical simulations. The thulium-doped fiber laser cavity is modulated by the optical injection at 1.55 μ m via a nonlinear optical loop mirror in which a specially-designed group-velocity-matching highly nonlinear fiber is incorporated. According to the simulation results, up to 40-GHz pulse train with picosecond tunable pulse width and peak power can be produced. Moreover, the repetition rate can be further enlarged with the help of higher gain. The impacts of gain coefficient, cavity length, and repetition rate on the output are studied in details. The proposed mode-locked fiber laser can be potentially used for future 2- μ m fiber communication.

Elimination of continuous-wave component in a figure-eight fiber laser based on a polarization asymmetrical NOLM

The operation of a nonlinear optical loop mirror (NOLM) with polarization-dependent transmission was analyzed to perform high-quality ultrashort optical pulses in a figure-eight fiber laser configuration. The design of the NOLM is based on a symmetrical coupler, a loop of highly twisted low-birefringence fiber and a quarter-wave retarder (QWR) to provide polarization asymmetry. Pedestal-free optical pulses were obtained by careful adjustment of the NOLM low-power transmission, which is easily realized in our setup by rotation of the QWR. The laser is capable of operating in both the conventional soliton and the noise-like pulse regimes. Optical pulses as short as 1.39 ps were observed at the fundamental repetition frequency of 0.8 MHz. The effectiveness of the proposed scheme is demonstrated by the elimination of low-intensity radiation at the laser output.

Single-polarization noise-like pulse generation from a hybrid mode-locked thulium-doped fiber laser

A hybrid mode-locked thulium-doped fiber laser incorporating a nonlinear optical loop mirror and a nonlinear polarization rotation effect is proposed in the 2 μm band for the first time. By adjusting two polarization controllers, a stable single-polarization noise-like (SPNL) pulse operation is obtained. The SPNL pulse could work steadily for at least 400 min. At a launched pump power of 3.52 W, the hybrid mode-locked SPNL pulse centers at 2007 nm with an optical full width at half maximum of 20 nm, a polarization extinction ratio of 26.3 dB, a coherence spike width of 258 fs and a pulse energy of 42.11 nJ, respectively.

State distributions in two-dimensional parameter spaces of a nonlinear optical loop mirror-based, mode-locked, all-normal-dispersion fiber laser.

We present the results of numerical simulations of dissipative soliton generation using nonlinear Schrödinger equations in an all-normal-dispersion (ANDi) mode-locked fiber laser based on a nonlinear optical loop mirror (NOLM). Firstly, systematic and computationally intensive analysis of the pulse state distributions in two-dimensional parameter spaces of an ANDi fiber laser was conducted. In addition, we determined that unstable non-vanishing regions including pulsation and noise-like pulses are directly related to the saturable absorptions of NOLMs and that two critical filter bandwidths separate those regions from stable ones. Finally, we found that the multi-pulsing power threshold can be maximized by using an optimal optical filter bandwidth.

Tunable Multiwavelength Er-Doped Fiber Laser With a Two-Stage Lyot Filter

A switchable and tunable multiwavelength erbium-doped fiber laser is proposed and demonstrated based on a two-stage Lyot filter and intensity-dependent loss (IDL) effect induced by a nonlinear optical loop mirror (NOLM). The proposed laser can achieve multi-parameter individually tuning functions, such as adjusting the channel-spacing, number, and spectral-range of lasing line. The channel spacing can be switched via adjusting the beam's polarization in the Lyot filter among 0.53, 0.78, and 1.56 nm. Meanwhile, the number and the spectral range of the multiwavelength lasing line can be independently controlled by IDL modulation through the combination of adjusting pump power and the birefringence in the loop of the NOLM. The individual tuning method of the proposed laser on each specific output characteristic provides more convenience and practicality to the applications.

1.2-W average-power, 700-W peak-power, 100-ps dissipative soliton resonance in a compact Er:Yb co-doped double-clad fiber laser.

Mode-locked pulses in the dissipative soliton resonance (DSR) regime enable extremely high pulse energy, but typically have the limited peak power of <100 W and a nanosecond-long pulse duration. In this Letter, we demonstrate high-peak-power, ultrashort DSR pulses in a compact Er:Yb co-doped double-clad fiber laser. The linear cavity is simply formed by two fiber loop mirrors (FLMs) using a 50/50 optical coupler (OC) and a 5/95 OC. The 5/95 FLM with a short loop length of 3 m is not only used as the output mirror, but also acts as a nonlinear optical loop mirror for initiating high-peak-power DSR. In particular, the mode-locked laser can deliver ∼100 ps DSR pulses with a maximum average power of 1.2 W and a peak power as high as ∼700 W. This is, to the best of our knowledge, the highest peak power of DSR pulses obtained in mode-locked fiber lasers.

All polarization-maintaining fiber laser architecture for robust femtosecond pulse generation

We report on a novel architecture for robust mode-locked femtosecond fiber lasers using a nonlinear optical loop mirror with all polarization-maintaining fibers. Due to a nonreciprocal phase shift, the loop mirror can be operated in a compact and efficient reflection mode, offering the possibility to reach high repetition rates and easy implementation of tuning elements. In particular, longitudinal mode spacing and carrier-envelope offset frequency may be controlled in order to operate the laser as an optical frequency comb. We demonstrate femtosecond pulse generation at three different wavelengths (1030, 1565, and 2050 nm) using Ytterbium, Erbium, and co-doped Thulium–Holmium as gain media, respectively. Robust operation is achieved for a wide range of parameters, including repetition rates from 10 to 250 MHz.

Group Delay measurements of ultrabroadband pulses generated in highly nonlinear fibers

Ultra broadband supercontinuum pulses are commonly used as a source of different wavelengths from a wide spectral bandwidth or as a source of very short pulses. However the processes responsible for wide spectral broadening are still under investigation. In this paper we examine the temporal and spectral characteristics of the pulses broadened upon propagation in the highly nonlinear photonics crystal fibers with different dispersion profiles. Generated supercontinuum pulses were experimentally characterized using cross-correlation frequency resolved optical gating technique. Full Text: PDF ReferencesM. Bradler, P. Baum, and E. Riedle, "Femtosecond continuum generation in bulk laser host materials with sub-?J pump pulses", Appl. Phys. B 97, 561 (2009). CrossRef T. M. Kardas, B. Ratajska-Gadomska, W. Gadomski, A. Lapini, and R. Righini, "The role of stimulated Raman scattering in supercontinuum generation in bulk diamond", Opt. Express 21, 24201 (2013). CrossRef A. Brodeur and S. L. Chin, "Band-Gap Dependence of the Ultrafast White-Light Continuum", Phys. Rev. Lett. 80, 4406 (1998). CrossRef R. R. Alfano, ed., The Supercontinuum Laser Source: Fundamentals with Updated References, 2nd ed (Springer, 2006). DirectLink A. L. Gaeta, Phys. "Catastrophic Collapse of Ultrashort Pulses", Rev. Lett. 84, 3582 (2000). CrossRef J. M. Dudley, G. Genty, and S. Coen, "Supercontinuum generation in photonic crystal fiber", Rev. Mod. Phys. 78, 1135 (2006). CrossRef M. Klimczak, B. Siwicki, P. Skibinski, D. Pysz, R. Stepien, A. Heidt, C. Radzewicz, and R. Buczynski, "Coherent supercontinuum generation up to 2.3 ?m in all-solid soft-glass photonic crystal fibers with flat all-normal dispersion", Opt. Express 22, 18824 (2014). CrossRef D. J. Kane and R. Trebino, "Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating", IEEE J. Quantum Electron. 29, 571 (1993). CrossRef J. Dudley, X. Gu, L. Xu, M. Kimmel, E. Zeek, P. O'Shea, R. Trebino, S. Coen, and R. Windeler, "Cross-correlation frequency resolved optical gating analysis of broadband continuum generation in photonic crystal fiber: simulations and experiments", Opt. Express 10, 1215 (2002). CrossRef N. Nishizawa and T. Goto, "Experimental analysis of ultrashort pulse propagation in optical fibers around zero-dispersion region using cross-correlation frequency resolved optical gating", Opt. Express 8, 328 (2001). CrossRef X. Gu, L. Xu, M. Kimmel, E. Zeek, P. O'Shea, A. P. Shreenath, R. Trebino, and R. S. Windeler, "Frequency-resolved optical gating and single-shot spectral measurements reveal fine structure in microstructure-fiber continuum", Opt. Lett. 27, 1174 (2002). CrossRef S. Roy, S. K. Bhadra, and G. P. Agrawal, "Effects of higher-order dispersion on resonant dispersive waves emitted by solitons", Opt. Lett. 34, 2072?2074 (2009). CrossRef S. Bose, S. Roy, R. Chattopadhyay, M. Pal, and S. K. Bhadra, "Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman soliton", J. Opt. 17, 105506 (2015). CrossRef T. Roger, M. F. Saleh, S. Roy, F. Biancalana, C. Li, and D. Faccio, "High-energy, shock-front-assisted resonant radiation in the normal dispersion regime", Phys. Rev. A 88, (2013). CrossRef G. P. Agrawal, Nonlinear Fiber Optics, Fifth edition (Elsevier/Academic Press, 2013). DirectLink J. Szczepanek, T. Kardas, M. Nejbauer, C. Radzewicz, and Y. Stepanenko, "Simple all-PM-fiber laser system seeded by an all-normal-dispersion oscillator mode-locked with a nonlinear optical loop mirror", Proc. SPIE 9728, 972827 (2016). CrossRef C. Iaconis and I. A. Walmsley, "Self-referencing spectral interferometry for measuring ultrashort optical pulses", IEEE J. Quantum Electron. 35, 501 (1999). CrossRef L. E. Hooper, P. J. Mosley, A. C. Muir, W. J. Wadsworth, and J. C. Knight, "Coherent supercontinuum generation in photonic crystal fiber with all-normal group velocity dispersion", Opt. Express 19, 4902 (2011). CrossRef J. Szczepanek, T. M. Kardas, and Y. Stepanenko, "Sub-160-fs pulses dechriped to its Fourier transform limit generated from the all-normal dispersion fiber oscillator", Optical Society of America Frontiers in Optics conference, FTu3C?2 (2016). CrossRef G. Genty, M. Lehtonen, and H. Ludvigsen, "Effect of cross-phase modulation on supercontinuum generated in microstructured fibers with sub-30 fs pulses", Opt. Express 12, 4614 (2004). CrossRef S. Roy, S. K. Bhadra, K. Saitoh, M. Koshiba, and G. P. Agrawal, "Dynamics of Raman soliton during supercontinuum generation near the zero-dispersion wavelength of optical fibers", Opt. Express 19, 10443 (2011). CrossRef Y. Liu, Y. Zhao, J. Lyngso, S. You, W. L. Wilson, H. Tu, and S. A. Boppart, "Suppressing Short-Term Polarization Noise and Related Spectral Decoherence in All-Normal Dispersion Fiber Supercontinuum Generation", J. Light. Technol. 33, 1814 (2015). CrossRef

Chair-like pulses in an all-normal dispersion Ytterbium-doped mode-locked fiber laser.

We report, for what we believe is the first time, generation of stable chair-like pulses (a pulse shape with an initial long flat portion followed by a short high peak power portion resembling the shape of a chair) by mode locking of a Ytterbium (Yb)-doped fiber laser. Chair-like pulse shapes are achieved by implementing dual saturable absorbers, one based on a nonlinear optical loop mirror (NOLM) and the other based on nonlinear polarization rotation (NPR) inside the cavity. The transmission characteristics of the NOLM-NPR pair leading to the formation of chair-like pulses are numerically investigated. We also report the amplification characteristics of chair-like pulses in an external multistage Yb-doped fiber amplifier setup at different repetition rates of the pulse train. It was found that the chair-like pulses are suitable for amplification, and more than 10 W of average power at 460 kHz repetition rate have been obtained at total pump power of ∼20 W coupled to the power amplifier. At a lower repetition rate (115 kHz), ∼8 W of average power were obtained corresponding to ∼70 μJ of pulse energy with negligible contribution from amplified spontaneous emission or stimulated Raman scattering. We believe that such an oscillator-amplifier system could serve as an attractive tool for micromachining applications.

All-Optical Wavelength Preserved Modulation Format Conversion From PDM-QPSK to PDM-BPSK Using FWM and Interference

Flexible conversion between multi-level modulation formats is one of the key processing functions to realize adaptive modulation techniques for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors have proposed an all-optical format conversion systems from binary phase-shift keying (BPSK) to quadrature PSK (QPSK) and its reverse conversion from QPSK to BPSK. The latter had an advantage of wavelength-shift-free conversion from an incident QPSK to simultaneous two BPSK outputs without loss of the transmitting data. However, it was limited only for a single polarization signal. In this paper, we propose a novel method of wavelength preserved conversion for polarization division multiplexed QPSK signal with arbitrary polarization rotation angle to the x-axis on the x-y polarization plane which is orthogonal to the propagation axis. The method is based on the orthogonal dual-pump four-wave-mixing (FWM) in the highly nonlinear fiber with a nonlinear optical loop mirror configuration, which has advantages that it separately outputs the original signal and the phase conjugate signal and has independent FWM efficiency of the signal polarization angle. We show the system performances such as bit-error-rate and optical signal-to-noise ratio penalty evaluated by numerical simulations.

6.5 µJ pulses from a compact dissipative soliton resonance mode-locked erbium–ytterbium double clad (DC) laser

The feasibility of constructing a compact, all-fiber, dissipative soliton resonance (DSR) mode-locked erbium–ytterbium double clad laser emitting 6.517 µJ pulses directly from the cavity is presented. The laser was built in a figure-8 configuration and mode-locked using a nonlinear optical loop mirror. A DSR regime of operation was enforced in the cavity by large net-anomalous dispersion (−21.431 ps2), obtained by incorporating 1 km of SMF28 fiber in the resonator. The laser operated at a 201 kHz repetition rate, with maximum average output power of 1.31 W at 7.2 W of pump power, yielding an impressive 20% slope efficiency.