Ultrashort pulse generation using fiber FM laser

Ultrashort optical pulse generation using a fiber FM laser is presented and analyzed in detail. Fiber FM laser operation is realized using a fiber ring with an internal phase modulator and an erbium-doped fiber amplifier. To compress FM laser pulses, an external dispersive single-mode fiber is employed. Furthermore, by external intensity modulation, the pulse background is removed. The background ratio of the generated ultrashort pulse is calculated and compared with the experimental results. The experimental results show an output optical pulse width of 1.77 ps and a spectral bandwidth of 0.5 THz.     

Ultrashort pulse measurements using a nonlinear mirror

The use of nonlinear optical phenomena at the boundary of a nonlinear medium for measuring the duration and the pulse shape of ultrashort light pulses are considered. Two different schemes are discussed.     

Ultrashort pulse breaking in optical fiber with third-order dispersion and quintic nonlinearity

The optical wave breaking （OWB） characteristics in terms of the pulse shape, spectrum, and frequency chirp, in the normal dispersion regime of an optical fiber with both the third-order dispersion （TOD） and quintic nonlinearity （QN） are numerically calculated. The results show that the TOD causes the asymmetry of the temporal- and spectral-domain, and the chirp characteristics. The OWB generally appears near the pulse center and at the trailing edge of the pulse, instead of at the two edges of the pulse symmetrically in the case of no TOD. With the increase of distance, the relation of OWB to the TOD near the pulse center increases quickly, leading to the generation of ultra-short pulse trains, while the OWB resulting from the case of no TOD at the trailing edge of the pulse disappears gradually. In addition, the positive （negative） QN enhances （weakens） the chirp amount and the fine structures, thereby inducing the OWB phenomena to appear earlier （later）. Thus, the TOD and the positive （negative） QN are beneficial （detrimental） to the OWB and the generation of ultra-short pulse trains.     

Ultrashort pulse propagation in multiple-grating fiber structures

We propose a multiple-grating fiber structure that decomposes an ultrashort broadband optical pulse simultaneously in both wavelength and time. As an initial demonstration, we used a transform-limited 1-ps Gaussian pulse centered at 1.55 mu;m as the ultrashort broadband input into a three-grating fiber structure and generated three output pulses separated in wavelength and time with good correlation between experimental results and simulations. This device structure can be used to generate a multiwavelength train of pulses for use in wavelength-division-multiplexed systems or to implement frequency-domain encoding of coherent pulses for optical code-division multiple access.     

High speed ultra short pulse fiber ring laser using photonic crystal fiber nonlinear optical loop mirror

A scheme to generate high speed optical pulse train with ultra short pulse width is proposed and experimentally studied. Two-step compression is used in the scheme: 20 GHz and 40 GHz pulse trains generated from a rational harmonic actively mode-locked fiber ring laser is compressed to a full width at half-maximum (FWHM) of ~ 1.5 ps using adiabatic soliton compression with dispersion shifted fibers (DSF). The pulse trains then undergo a pedestal removal process by transmission through a cascaded two photonic crystal fiber (PCF)-nonlinear optical loop mirrors (NOLM) realized using a double-ring structure. The shortest output pulse width obtained was ~ 610 fs for 20 GHz pulse train and ~ 570 fs for 40 GHz pulse train. The signal to noise ratio of the RF spectrum of the output pulse train is larger than 30 dB. Theoretical simulation of the NOLM transmission is conducted using split-step Fourier method. The results show that two cascaded NOLMs can improve the compression result compared to that for a single NOLM transmission.     

Ultra-flat and broadband two-pump optical parametric amplifiers using a single-section highly nonlinear fiber

A broadband two-pump optical parametric amplifier with ultra-flat gain spectra is proposed in a single-section highly nonlinear fiber. By elaborately setting the dispersions and pump wavelength space, a gain over 250 nm with 0.02-dB uniformity is obtained. The pump polarizations and fiber length can be changed, achieving polarization-insensitive or higher gain, while the flatness and bandwidth of gain curve remain the same.     

Ultrashort optical pulse in a defect order-disorder ferroelectric

Physics of the Solid State - The dynamics of an ultrashort optical pulse in order—disorder ferroelectrics in the presence of defects without limitations on the pulse power is considered in...     

Low-noise and highly stable optical fiber temperature sensor using modified pulse-reference-based compensation technique

We modify the pulse-reference-based compensation technique and propose a low-noise and highly stable optical fiber temperature sensor based on a zinc telluride film-coated fiber tip. The system noise is measured to be 0.0005 dB, which makes it possible for the detection of the minor reflectivity change of the film at different temperatures. The temperature sensitivity is 0.0034 d B/℃, so the resolution can achieve 0.2℃. The maximum difference of the temperature output values of the sensor at 20℃ at different points in time is 0.39℃. The low cost, ultra-small size, high stability, and good repeatability of the sensor make it a promising temperature sensing device for practical application.     

Ultrashort pulse formation and evolution in mode-locked fiber lasers

Passive mode-locking in fiber lasers is investigated by numerical and experimental means. A non-distributed scalar model solving the nonlinear Schr?dinger equation is implemented to study the starting behavior and intra-cavity dynamics numerically. Several operation regimes at positive net-cavity dispersion are experimentally accessed and studied in different environmentally stable, linear laser configurations. In particular, pulse formation and evolution in the chirped-pulse regime at highly positive cavity dispersion is discussed. Based on the experimental results a route to highly energetic pulse solutions is shown in numerical simulations.     

Short optical pulse polarization dynamics in a nonlinear birefringent doped fiber

Numerical solutions are obtained of the full self-consistent system of equations for the counter, rotating polarization components of the field of a short optical pulse propagating in a nonlinear birefringent fiber and in the ensemble of the energy-level degenerate doped resonance atoms implanted in the fiber material. In every cross section of the fiber, the ellipticity of the polarized wave experiences a complex evolution in time accompanied by rapid changes of the azimuthal angle due to the interplay of the dispersion and the Kerr nonlinear self-and cross-phase modulation. The reciprocal effect of the impurities on the traveling pulse causes oscillations of the pulse envelope that can completely distort the shape of the input signal, while the resonance absorption can drive the birefringence process from the nonlinear regime back to the linear one.     

A tunable nonlinear optical loop mirror with feedback using linear highly birefringent fiber in the loop

The dynamics of a nonlinear optical loop mirror (NOLM) with feedback using a high birefringence fiber in the loop are investigated. The effect of rotating input polarization angle on the output power and polarization angle is numerically examined, illustrating the sensitivity of the NOLM with feedback to the input’s polarization state, as well as the polarization chaos present with sufficient input powers. The inclusion of a polarization-dependant loss in one or both arms of the coupler is also shown to change the output dynamical behaviour of the system.     

Gain characteristics and optimization of dual-pump fiber optical parametric amplifier using two-section highly nonlinear fibers

In this paper the gain characteristics of two-pump fiber optical parametric amplifiers (FOPA) with two-section highly nonlinear fibers are analyzed numerically and the parameters of the fibers are optimized to reach broad and flat gain spectra using genetic algorithm. Different from the previous methods, here the space between two pump wavelengths and the parameter β₄ of the fibers are included as a pivotal factor in the optimization. The numerical simulation shows that using two-section practical high nonlinear fibers, the amplifier may reach 110 nm bandwidth covering 1495–1605 nm with 10.5 dB average gain and gain ripple of 0.17 dB, when the total pump power is 1 W.     

Short optical pulse profile characterization using a nonlinear optical loop mirror

We propose in this work a technique for short pulse profile retrieval based on the Kerr effect in a fiber nonlinear optical loop mirror (NOLM). Under some assumptions, the profile can be determined from the energy transfer characteristic of the pulses through the NOLM, which can be measured with a low-frequency detection setup. Two numerical approaches are considered, both relying on the resolution of a system of nonlinear algebraic equations, and which differ in the way that the profiles are discretized. We show numerically that both approaches allow proper profile retrieval for a wide variety of pulse shapes. The two techniques are compared, and their advantages and drawbacks are discussed. The effect of the amplitude noise of the pulses is assessed, as well as the impact of an inaccurate knowledge of the NOLM transfer function, or of the energy transfer characteristic. The technique is demonstrated in the frame of the characterization of both ns and ps pulses.     

Stationary rescaled pulse in dispersion-managed comblike profiled fiber for highly efficient and high-quality optical pulse compression

A stationary rescaled pulse (SRP) exists in a dispersion-managed comblike profiled fiber (DM-CPF) that consists of alternate concatenations of normal-dispersion highly nonlinear fiber and single-mode fiber. Numerical analysis reveals that the newly found SRP exhibits a nearly Gaussian temporal profile with a small amount of pedestal in spite of a relatively large compression ratio. We apply the SRP propagation to optical pulse compression based on DM-CPF and demonstrate highly efficient and high-quality optical pulse compression. Using a three-step DM-CPF, we experimentally show that a 2.6 ps width input pulse is successfully compressed to a nearly Gaussian pulse having the width of 0.39 ps and the peak-to-pedestal ratio of 19.3 dB.     

Ultrashort pulse generation in the medium with induced optical anisotropy

Abilities of the method of accumulation of coherent unstable response of a medium for amplification of the rotated component of the probe wave’s polarization in the atomic medium of three-level atoms are studied. Probe wave is examined in frames of the perturbation theory and its frequency is considered near to one photon resonance from the ground to the first excited level. The intense monochromatic pump field connects two excited energy levels and propagates through the medium without a change. The broadening of spectral lines caused by the relaxation processes and the Doppler broadening are included into the calculations. It is shown that by multiple consistent instantaneous change of input probe field’s phase from 0 to π and back, it is possible to obtain, in the tail part of the rotated component of the probe field, a separate narrowed light pulse along with the increase in intensity by more than an order of magnitude with respect to the input field.     

Widely tunable Raman ring laser using highly nonlinear fiber

An all-optical widely tunable Raman fiber laser has been realized by incorporating a highly nonlinear fiber in a ring cavity. By feedback a portion of Raman Stokes wave back into the highly nonlinear gain medium, a Raman fiber laser is generated. We found that the lasing wavelength of Raman fiber laser can be tuned from 1537 to 1568 nm with peak power fluctuation within 1 dB, giving a total wavelength tunability of 31 nm. The optical signal-to-noise ratio is found to be wavelength dependent, and the highest optical signal-to-noise ratio of about 59 dB is recorded. The lasing threshold of the Raman fiber laser with this configuration is found to be as low as 300 mW.     

Ultrashort optical pulse shaper based on complex-modulated long-period-grating coupler

In this paper,we present a novel ultrashort pulse shaper based on complex-modulated long-period-grating coupler(CM-LPGC).Temporal rectangular waveform with 2-ps full width at half maximum(FWHM) is obtained by transforming the input Gaussian pulse.Tolerances of the CM-LPGC-based shaper to various non-ideal excitation conditions and fabricating errors are investigated.Results confirm that CM-LPGC is stable and suitable for optical pulse shaping operation.     

Quantitative monitoring of relative clock wander between signal and sampling sources in asynchronous optical under-sampling system

Optical performance monitoring using asynchronous optical or electrical sampling has gained considerable attention. Relative clock wander between data signal and sampling source is a typical occurrence in such systems. A method for the quantitative monitoring of the relative clock wander in asynchronous optical undersampling system is presented. With a series of simulations, the clock wanders recovered using this method are in good agreement with the preset clock wanders of different amounts and frequencies for both RZ and NRZ signals. Hence, the reliability and robustness of the method are proven.     

Multicore, tapered optical fiber for nonlinear pulse reshaping and saturable absorption

We present a new method to create a coupled waveguide array via tapering a seven-core telecommunications fiber. The fiber based waveguide array is demonstrated to exhibit the novel physics associated with coupled waveguide arrays, such as discrete diffraction and discrete self-focusing. The saturable absorber characteristics of the device are characterized and an autocorrelation measurement reveals significant single-pass pulse reshaping.