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In this paper, we propose an ultra-high speed random bit generator without the time-delay signature based on an ytterbium-doped random fiber laser (YRFL) with Rayleigh scattering feedback. The spectrum of the YRFL has a relatively broad bandwidth (0.35 nm) and the lasing temporal intensity shows random fluctuations without cavity induced time-delay signatures (TDS), which are essential for ultra-high speed random bit generation. The chaotic signal and its time-delayed signal sampling at 40 Giga samples per second (GS/s) are converted to digital 8-bit signals. By selecting 5 least significant bits from each 8-bit digital signal and using bitwise exclusive-OR operation, we experimentally achieve 200 Gbps physical random bit generation based on ytterbium-doped random fiber laser with the verified randomness. The combination of broadband emission and free of TDS makes random fiber lasers new promising sources for high performance random bit generation in a simple and compact configuration, which has a great potential in cryptography and secure communication applications.

We propose and experimentally demonstrate a centralized PON monitoring scheme using the reflection spectrum of a single fiber Bragg grating. Each fiber Bragg grating used in the scheme adopts different central reflection wavelength or 3-dB reflection bandwidth. The unique reflection spectrum is generated after each fiber Bragg grating used is interrogated by a broadband probe source. These generated reflection spectra are used to identify and distinguish the drop fiber links. The similarity analysis model is established to solve the problem of waveform superposition identification for different 3-dB reflection bandwidths with the same central reflection wavelength, which can further improve the network monitoring capacity. The proposed scheme provides a simple and effective monitoring solution for large-capacity network, especially for high-density network with small end-user distance difference.

Brillouin optical time-domain analysis (BOTDA) that operates over a long sensing fiber is prone to be affected by the detrimental non-local effects (NLE); since NLE can distort Brillouin gain spectrum (BGS), therefore correctly retrieving Brillouin frequency shift (BFS) is very challenging. Recently, the basic artificial neural networks (B-ANN) has been demonstrated to retrieve BFS effectively, in the case that a distortion-free BGS can be obtained. However, in the more general cases with NLE, a neural network for retrieving BFS in BOTDA data has not been proposed. In this paper, firstly the physical origin of NLE is analyzed theoretically and experimentally in detail. Then a specific ANN (NLE-ANN) is proposed to deal with the BOTDA data affected by NLE for the first time. The experimental verifications show that with the cooperative implementation of NLE-ANN and B-ANN, the effective retrieval of BFS along the whole fiber can be achieved, even though the BGS has been affected by NLE. This work proposes a promising approach in traditional BOTDA, because the upper limit of probe power could be raised by artificial intelligence to boost the sensing performance.

A novel concept of distributed temperature–strain sensors is proposed using inter-mode Kerr four-wave mixing of polarization-maintaining fiber (PMF), in which the dominated physical mechanism is basically different from reported Brillouin dynamic grating (BDG). The independent measurement for temperature and strain sensitivities (−0.431 MHz °C−1 and 0.067 MHz/10 με) was completed by detecting the change in birefringence under pump-Stokes frequency separation at 370 MHz. As a preliminary proof-of-concept, sensing with a spatial resolution of ∼5 m was demonstrated along ∼210 m PMF. Compared with BDG, the proposed sensor features potential of multiple parameters measurement including temperature–strain and liquid acoustic impedance.

We propose a novel method using dual pulse widths to locate the fiber break, which can share the pulse detecting source with the previous proposed passive optical network (PON) monitoring systems. The rectangular detecting pulses with two different pulse widths are sequentially injected into the faulty fiber link to generate corresponding parameters for the established model equations. We also investigate the corresponding variables (i.e., different combinations of dual pulse widths, pulse repetition frequency and accuracy of the power meter) that may affect the performance of the proposed method. The experimental results show that the fiber breakpoint can be located with little error. The simple and low-cost method provides a fault localization functionality for the PON monitoring systems.

We propose a self-match based on polling scheme for passive optical network monitoring. Each end-user is equipped with an optical matcher that exploits only the specific length patchcord and two different fiber Bragg gratings with 100% reflectivity. The simple and low-cost scheme can greatly simplify the final recognition processing of the network link status and reduce the sensitivity of the photodetector. We analyze the time-domain relation between reflected pulses and establish the calculation model to evaluate the false alarm rate. The feasibility of the proposed scheme and the validity of the time-domain relation analysis are experimentally demonstrated.

Via implementing parallel tasks including Santa-Fe time series prediction and nonlinear channel equalization, we studied the characteristics of reservoir computing (RC) using two mutually-coupled semiconductor lasers (MC-SLs) with optoelectronic feedback. The influence of system parameters (injection current, coupling strength, scaling factor and coupling time-delays) on RC performance have been investigated in detail. Results show that, the optimized performance is always achieved around the edge of bifurcation points; positive feedback is more preferred when the scaling factor exceeds a certain level; under optimized parameters, both of lower normalized mean squared error (NMSE) and symbol error rate (SER) can be achieved to perform parallel tasks, due to the richer dynamics and states of virtual nodes. The effect of system parameters on RC performance was also discussed. Our study would be helpful for the design and optimization of proposed parallel RC with optoelectronic feedback.

Dissipations in the waveguide-cavity systems destroy quantum interference between the incident signal photons and the cavity photons linearly and, thus, usually limit the manipulation of the photon transport. Here, we adopt a four-mode microring cavity including both second-order (${\ensuremath{\chi}}^{(2)}$) and third-order (${\ensuremath{\chi}}^{(3)}$) nonlinearities side coupled to two different waveguides to manipulate photon transport against dissipative effects. The results show that the incident signal photons can be amplified due to the optical parametric amplification (OPA) originated from ${\ensuremath{\chi}}^{(3)}$ nonlinearities. Owing to the coherent interference between cavity photons with different frequencies, the transmission spectra of the signal field are split into two amplified peaks. The transmission intensities are not always linearly reduced by increasing the dissipations but determined by the competition between the OPA and the dissipations. It means that we can utilize the OPA process to overcome the dissipative effects to manipulate photon transport and, thus, control the transmission intensities of the incident signal photon from ${T}_{c}=0$ to ${T}_{c}g100%$. This competition can also be used to convert the signal field to the idler field with amplified efficiencies.

In order to combine the diagnosis and treatment guidelines for chronic obstructive pulmonary disease (COPD) with medical knowledge of electronic medical records, a semi-automatic construction method for knowledge maps of chronic obstructive pulmonary disease was proposed. First, the schema concept layer is designed in a top-down manner for the diagnosis and treatment of chronic obstructive pulmonary disease. Knowledge is removed from the data in the electronic medical records of the China-Japan Friendship Hospital. Knowledge extraction of unstructured data is based on the conditional random field (CRF) combined with the symptom dictionary method, through the design of the experiment to extract disease symptoms, verified the accuracy and effectiveness of the design, and stored the knowledge of chronic obstructive pulmonary disease to Neo4j.

In order to realize automatic recognition and extraction of entities in unstructured medical texts, a model combining language model conditional random field algorithm (CRF) and Bi-directional Long Short-term Memory networks (BiLSTM) is proposed. We crawled 804 drug specifications for treating asthma from the Internet, and then quantized the normalized field of drug specification word by a vector as the input of the neural network. Compared with the traditional machine learning algorithm CRF model, the system accuracy, recall and F1 value are improved by 6.18%, 5.2% and 4.87%. This model is applicable to extract named entity information from drug specification.

Distributed fiber sensors based on forward stimulated Brillouin scattering (F-SBS) have attracted special attention because of their capability to detect the acoustic impedance of liquid material outside fiber. However, the reported results were based on the extraction of a 1st-order local spectrum, causing the sensing distance to be restricted by pump depletion. Here, a novel post-processing technique was proposed for distributed acoustic impedance sensing by extracting the 2nd-order local spectrum, which is beneficial for improving the sensing signal-to-noise ratio (SNR) significantly, since its pulse energy penetrates into the fiber more deeply. As a proof-of-concept, distributed acoustic impedance sensing along ∼ 1630 m fiber under moderate spatial resolution of ∼ 20 m was demonstrated.

We proposed and demonstrated a new structure, which employs a single laser in Brillouin optical time-domain analysis sensor assisted by distributed Brillouin amplification. This structure can avoid the stability problem caused by laser frequency drift. In addition, we used an optical comb technique to suppress the distortion of pump pulse. Moreover, the feasibility of an optical pulse coding technology in this system was studied. In particular, we explored the influence of coding parameters on the transient gain saturation of the coded pulse. Results show that the coded pulse space and coding length must be optimized to suppress its transient gain saturation, by which the sensing with lower decoding error can be achieved.

Simultaneous bandwidth (BW) enhancement and time-delay signature (TDS) suppression of chaotic lasing over a wide range of parameters by mutually coupled semiconductor lasers (MCSLs) with random optical injection are proposed and numerically investigated. The influences of system parameters on TDS suppression (characterized by autocorrelation function (ACF) and permutation entropy (PE) around characteristic time) and chaos BW are investigated. The results show that, with the increasing bias current, the ranges of parameters (detuning and injection strength) for the larger BW (> 20 GHz) are broadened considerably, while the parameter range for optimized TDS (< 0.1) is not shrunk obviously. Under optimized parameters, the system can simultaneously achieve two chaos outputs with enhanced BW (> 20 GHz) and perfect TDS suppression. In addition, the system can generate two-channel high-speed truly physical random number sequences at 200 Gbits/s for each channel.

We experimentally study a dual-sideband Brillouin optical time-domain analyzer (BOTDA) with balanced detection. The amplification regime is simple (only bi-directional first-order Raman amplification); however, taking advantage of the balanced detection, 200 km fiber-loop sensing system is achieved (half of the whole length is used for sensing). Before the balanced detector, a FBG is used to separate the anti-Stokes and the Stokes components of the probe light, and the optical source׳s wavelength with regard to the given FBG׳s Bragg wavelength is shown to be highly relevant to the system׳s performance.

In this paper, we make a comprehensive study on a highly efficient half-open cavity design for high power random fiber laser (RFL). With the theoretical analysis, we optimize the cavity's fiber length for getting higher output power within the scheme, i.e., shorter fiber length is preferred for efficiently harvesting the first order random lasing at the open end of the cavity. As the verification of the theory, we experimentally demonstrate a high output power (7 W), highly efficient (70% optical conversion efficiency) RFL working at 1140 nm, using 10 W 1090 nm laser as the pump source and only 1 km standard single-mode fiber as the distributed cavity.

Random distributed feedback fiber laser (RDF-FL) based on combination of Er-doped fiber (EDF) and single-mode fiber (SMF) is proposed in this paper. Through pumping of both the EDF (i.e., 1480 nm pump) and the SMF (i.e., 1455 nm pump), random lasing is obtained. With increase of pump powers, different transitions between chaotic and stable status of the output spectrum are observed. Especially, single-peak random lasing can be obtained under the stable operation regime.

Distributed fiber-optic sensing (DFOS) has drawn great attention in both academic research and industrial applications due to its unique advantages. Recent progress at University of Electronic Science and Technology of China (UESTC) in DFOS, mainly on ultra-long-distance Brillouin optical time-domain analysis (BOTDA) and phase-sensitive optical timedomain reflectometry (Φ-OTDR), is discussed in this paper, including research progress and real-life applications.

In this paper, the regions of spreading of partially coherent beams propagating through non-Kolmogorov turbulence are examined by using the turbulence distances zT and zTT. The spreading is less affected by atmospheric turbulence (AT) when z zTT. The dependence of zT and zTT on the turbulence parameters and the beam parameters is studied in detail. It is found that both zT and zTT reach their minimums when the fractal constant of the atmospheric power spectrum is equal to 3.11. However, the dependence of zTT on turbulence parameters and beam parameters is much larger than that of zT. There exists a minimum of zT versus the waist width, but zTT decreases monotonically as the waist width increases. On the other hand, the relation between the turbulence distance zT and the Rayleigh range zR is investigated. It is shown that zT=zR may appear when a suitable waist width or a suitable coherent parameter is chosen. For the small free-space diffraction (FD) case zT zR. Some physical explanations for the results obtained in this paper are also given.

A distributed Brillouin optical time-domain analysis (BOTDA) sensor enhanced by forward stimulated Brillouin scattering (FSBS) based distributed Brillouin amplification (DBA) was proposed and presented. Due to co-propagating of pump and Stokes lights, the Stokes pulse is effectively amplified in front segment of fiber, resulting in flatter gain distribution. As a proof-of-concept, FSBS-DBA based BOTDA sensing with distance of ~74.2 km, Brillouin frequency shift standard deviation of less than ~2 MHz and spatial resolution of ~10 m was demonstrated. This method is compatible and complementary with backward SBS-based DBA, and features better pumping efficiency than Raman amplification.

In this paper, the effects of atmospheric turbulence, initial field amplitude, optical system and thermal blooming on the centroid position of laser beams propagating through the atmosphere are studied in detail. With the average over the ensemble of the turbulent medium, the centroid position is independent of turbulence. However, the centroid position depends on the centroid positions at the source plane and in the far-field, and the elements of ray-transfer-matrix. The physical reason why the centroid position changes on propagation is that the far-field centroid position is not located on the propagation z-axis due to the field phase distortion and the decentred intensity. The centroid position of laser beams with the spherical aberration and the decentred intensity is examined analytically. When laser beams with the decentred intensity propagate through the atmosphere, the effect of thermal blooming on the centroid position is investigated by using the four-dimensional (4D) computer code of the time-dependent propagation of high power laser beams through the atmosphere.

Taking the mean-squared beam width, the angular spread, the Rayleigh range and the turbulence distance as characteristic parameters, the spreading of partially coherent polychromatic decentered laser beams propagating through non-Kolmogorov turbulence is studied. The influence of the bandwidth Ω of spectrum, the beam decentered parameter β , and the fractal constant α of the atmospheric power spectrum on the beam spreading is examined in detail. It is found that polychromatic laser beams are less sensitive to turbulence than monochromatic ones, and decentered laser beams are less sensitive to turbulence than centered ones. The larger the Ω and β are, the larger the beam spreading is in free space, but the less the beam spreading is affected by turbulence. In turbulence laser beams with different values of β will have the same directionality if the angular spread is chosen as the characteristic parameter of beam directionality, which is quite different from the behavior in free space. The beam spreading is largest and the influence of turbulence on the beam spreading is also largest when α is in a region about 3.1. In addition, the dependence of the turbulence distance on Ω and β is also investigated, and some interesting results are obtained.

In this paper, we experimentally demonstrate a novel configuration of multiwavelength Brillouin–Raman random fiber laser (MBRRFL) utilizing a half-open cavity. The laser resonator is formed by fiber loop mirror at the Brillouin pump (BP) side and random distributed Rayleigh backscattering in a 10 km dispersion compensating fiber. As a result, we are able to obtain a flat amplitude bandwidth of 16.8 nm from 1,550.0 to 1,566.8 nm built-in 210 uniform Brillouin Stokes lines with 0.08 nm spacing and an average OSNR of 13.5 dB. We also studied the influence of BP power and wavelength on the MBRRFL’s performance. Furthermore, comparing with the open cavity configuration, the discrepancies in power level and linewidth between neighboring channels are overcome by using the half-open cavity.

Flattened gain was experimentally demonstrated for enhancing the performance of Brillouin optical time-domain analysis (BOTDA) sensors based on distributed Brillouin amplification (DBA) using intensity-compensated optical-comb pump.

A novel approach for long-distance sensing through Brillouin optical time-domain analysis (BOTDA) assisted by second-order distributed Brillouin amplification (DBA) was proposed and experimentally demonstrated. To the best of our knowledge, this is the first BOTDA study that used second-order DBA. Compared with BOTDA assisted by first-order DBA, the proposed approach enhanced the signal-to-noise ratio of the Brillouin trace by ~3 dB for a range featuring minimum sensing intensity. Long-distance sensing with ~5 m spatial resolution and ± 1.6°C measurement uncertainty over ~99 km fiber was successfully realized by employing high-efficiency pumping using ~6 dBm second-order and ~1.5 dBm first-order pumps.

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20 dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.

For Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA), constant Brillouin response achieved by the exponentially variable bandwidth/intensity pump modulation suffers from the much lower pumping efficiency for long-range sensing, which counterbalances the merit of DBA. In this Letter, pump modulation by multiple constant bandwidths was proposed and demonstrated. The ∼98.9 km sensing with ∼5 m spatial resolution and no use of optical pulse coding (OPC) was achieved by ∼8 dBm Brillouin pump, which is lower by ∼9 dB in theory by comparison with exponentially increased bandwidth modulation. Compared with traditional DBA-BOTDA, signal-to-noise ratio (SNR) enhancement with >4.6 dB was obtained. The flattened standard deviation (STD) of Brillouin frequency shift (BFS) (less than ∼2 MHz) along the whole fiber was demonstrated.

Random lasing (RL) characteristics of second-order random fiber laser formed solo by dispersion compensated fiber are studied. It is found that the threshold of first-order RL is only 0.45 W. In addition, a special route to stable second-order lasing is revealed, i.e., a special arc-shape output spectrum of second-order RL and three chaotic regimes during evolution from the first RL to the second-order one with increased pump power.

The Raman amplification can be employed to obtain the enhanced sensing performance in long-distance Brillouin optical time-domain analyzer (BOTDA) with higher temperature measurement accuracy over the whole sensing fiber. Theoretical investigation on the detected probe waveshape has been performed by using the probe-pump coupled equations combined with Raman amplification. The experimental characterization has been demonstrated to validate the theoretical prediction. The results show that, the 75 Km sensing distance can be achieved by utilizing the bi-directional Raman amplification with measurement accuracy of ±0.6°C over the whole sensing fiber. The larger Raman power and Brillouin pump power are helpful to improve the sensing signal-noise ratio (SNR). There exists an optimum range for the input probe power and the extinction ratio (ER) of input Brillouin pump pulse. The BOTDA with Raman amplification has considerable potentials to realize long- distance strain and temperature measurement for structural health monitoring and fire alarming, etc.

Based on the SFM model [M. San Miguel, Q. Feng, J.V. Moloney, Phys. Rev. A. 52 (1995) 1728.], complete chaotic synchronization characteristics of linear-polarization (LP) Mode of the vertical-cavity surface-emitting semiconductor lasers (VCSELs) with isotropic optical feedback are numerically investigated. When the propagation time τ c of light from the transmitter to the receiver equals to the external cavity round-trip time τ , and the central frequency of the T_VCSEL matches that of the R_VCSEL, in large scale region of the feedback coefficient and the injection current where the x -polarization mode as well as the y -polarization mode obtains high synchronization quality at the same time. However, in the central frequency mismatch regions where the x - and y -polarization mode can obtain inferior synchronization quality at same time. But for τ c ≠ τ , each LP mode of the mixed polarization modes achieved inferior synchronization quality at the same time. Besides, with big enough injection current, the output of the system with the same central frequency in two lasers is entirely governed by the y -polarization mode when the feedback coefficient and Δ τ (= τ c − τ ) fixed at a certain value. So the system can realize steadily good synchronization of the completely dominant y -polarization mode. But the synchronization quality of the completely dominated y -polarization mode can be deteriorated by increasing absolute frequency detuning value. Besides, in positive frequency mismatch regions where the influence of the same frequency detuning value on the synchronization quality of the entirely governed y -polarization mode becomes smaller than in negative frequency detuning regions. At last, when τ is given and the central frequency of the T_VCSEL matches that of the R_VCSEL, the influence of the τ c is not a simple time-shift in the time-evolution of the receiver VCSEL, which has serious influence on the complete synchronization quality of each LP mode.

Simultaneous non-local effect suppression and sweeping time reduction was achieved experimentally over ~50km time-division-multiplexing (TDM) based Brillouin optical time domain analysis (BOTDA) sensors using pump-probe frequency comb pairs.

We experimentally demonstrated the long-distance Brillouin optical time-domain analysis (BOTDA) sensing with high-efficiency 1st-order (~50km) and 2nd-order (~99km) distributed Brillouin amplification.

The passive mode-locked semiconductor laser (PMLL) can realize terahertz (THz) four-wave mixing (FWM) with high conversion efficiency and no need for pump input. Theoretical investigation on its FWM characteristics has been carried out by using the traveling wave and carrier rate equations combined with nonlinear dynamics of carrier density pulsation (CDP), carrier heating (CH), and spectral-hole burning (SHB). The stable mode-locked conjugate pulse with short-duration high-repetition frequency can be obtained by the PMLL. The pedestal-free conjugate pulse has narrower width and larger amplitude jitter compared with the pump wave. Smaller absorption recovery time is helpful to extend the stable conjugate output regime. There exists a down-limit for absorption recovery time to avoid self-pulsation (SP) instability. The larger injection current is required for smaller absorption recovery time to reach the given conversion efficiency. The larger conversion efficiency and narrower conjugate pulse can be obtained by proper design of distributed Bragg reflector (DBR) coupling strength. The DBR bandwidth must be designed to be within signal-pump detuning to avoid resonance-induced conjugate pulse distortion. The FWM in PMLL has considerable potential such as demultiplexing in optical time-division multiplexing systems.

The dynamic single-mode and modulation performance of λ/4 phase-shifted distributed feedback laser diode with chirped grating (QWS-CG-DFB) are analyzed theoretically. The numerical simulation shows that, in contrast to purely QWS-DFB laser, the enhanced dynamic single-mode suppression ratio (SMSR) can be reached by QWS-CG-DFB laser. Under the smaller biasing current, the modulation band-width in presence of chirped grating is narrower, this difference shrinks for larger biasing current. For large signal modulation, the chirped grating is helpful to increase the output extinction ratio, but worsens the frequency chirping. The good dynamic characteristic can be obtained by selecting system parameters reasonably.

By using the coupled mode equations, the dynamic characteristics of λ /4 phase-shifted distributed feedback laser diode with distributed coupling coefficient (QWS-DCC-DFB) is analyzed. The numerical simulation indicates that, compared with purely QWS-DFB laser, the better dynamic single-mode can be achieved by QWS-DCC-DFB laser; Under the smaller biasing current, the modulation band-width is narrower, this difference shrinks for larger biasing current; For large-signal modulation, the distributed coupling coefficient is helpful to increase the output extinction ratio, but worsens the wavelength chirping. The good dynamic characteristic can be obtained by selecting system parameters reasonably. QWS-DCC-DFB laser would have potentials in optics communications because of better dynamic SMSR.

By using coupled mode equations, the characteristic of terahertz wavelength converter based on four-wave mixing in lambda/4-shifted distributed feedback lasers is analyzed. The numerical simulation indicates that, the larger biasing current and smaller detuning can expand the dynamic range of conversion efficiency and extinction ratio, but worsen the frequency chirp. Due to the lasing effect, the peak modulation frequency of extinction ratio and frequency chirp occurs at relaxation oscillation frequency. The good conversion characteristic can be obtained by selecting system parameters reasonably. This configuration could have potentials in optical communications because of wideband, high-speed, and no need for pump input

It is well known that the gain-clamped semiconductor optical amplifier (GC-SOA) based on lasing effect is subject to transmission rate restriction because of relaxation oscillation. The GC-SOA based on compensating effect between signal light and amplified spontaneous emission by combined SOA and fiber Bragg grating (FBG) can be used to overcome this problem. In this paper, the theoretical model on GC-SOA based on compensating light has been constructed. The numerical simulations demonstrate that good gain and noise figure characteristics can be realized by selecting reasonably the FBG insertion position, the peak reflectivity of FBG and the biasing current of GC-SOA.

Theoretical investigations on commanding the bistability and self-pulsation characteristics of two-segment bistable semiconductor laser diode (TBLD) using delayed optoelectronic feedback have been carried out in this paper. The effects of feedback gain and delayed time have been simulated numerically based on the rate equations. The results show that the stable region of TBLD varies periodically with delayed time, the bistable region shrinks with the increase of delayed time, stability can be enhanced for certain values of delayed time, and instability can be reached easily for negative delayed optoelectronic feedback. These conclusions establish the theoretical foundation to optimize and control the TBLD and may have potential applications in bistable switching and self-pulsation generation.

Starting from the coupled-mode equation and carrier rate equation, this paper has analyzed numerically the bistable dynamic characteristics of phased-shifted and chirped distributed-feedback semiconductor optical amplifiers (DFB-SOAs). The results show that phase shift first worsens the shape distortion of the falling edge of the output pulse and then alleviates it with the decreased initial detuning. This tendency can be suppressed by introducing chirp. We also proposed a novel configuration based on linearly variable current injection, which not only enhances the on-off switching ratio, but also has a similar transmission spectrum with phase-shift effects and similar bistable features, such as the wide frequency band and the flat upper branch of the hysteresis, with chirp effects.

It is well known that the pulse compressed by the high-order soliton effect in dispersion-shifted fiber (DSF) is accompanied with undesired pedestals. In this paper, based on the optical bistability effect of the nonlinear Fabry–Perot cavity (NLFPC), a novel method by combined NLFPC and EDFA is proposed for pedestal reduction. The numerical simulations demonstrate that obvious pedestal reduction can be realized by selecting reasonably the facet reflectivity of the NLFPC, and the detuning between the central frequency of the input pulse and the resonant frequency of the NLFPC.