Photonic multi-shape UWB pulse generation using a semiconductor optical amplifier-based nonlinear optical loop mirror

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband(UWB) signal generation using a semiconductor optical amplifier(SOA) based nonlinear optical loop mirror(NOLM).By employing the cross phase modulation(XPM) effect,cross gain modulation(XGM),or both,multi-shape UWB waveforms are generated including monocycle,doublet,triplet,and quadruplet pulses.Both the shapes and polarities of the generated pulses are flexible to adjust,which may be very useful in UWB pulse shape modulation and pulse polarity modulation.     

Optical ultrawideband monocycle pulse generation based on cross-gain modulation in a semiconductor optical amplifier

A novel method for generating ultrawideband (UWB) monocycle pulses based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. Thanks to the XGM in the SOA, a pair of polarity-reversed optical Gaussian pulses is generated at the output of the SOA, to which a Gaussian pulse pump and a continuous-wave probe are applied. The two polarity-reversed optical pulses are then time delayed by two cascaded fiber Bragg gratings to introduce a time delay difference. A UWB monocycle pulse with a full width at half-maximum of 48 ps and a fractional bandwidth of 188% is generated at the output of a high-speed photodetector.     

All-optical switchable UWB pulses generation,modulation and transmission

We proposed and demonstrated all-optical polarity- and shape-switchable ultrawideband (UWB) Gaussian pulses generation schemes using a single polarization interferometer (PI) or a semiconductor optical amplifier (SOA) cascaded by a PI. When an optical signal with dark return-to-zero (RZ) format propagates directly through a single PI, a pair of polarity-reversed UWB monocycle pulses and a positive UWB doublet pulse is acquired respectively only by adjusting the polarization controllers, without changing the bias of the intensity modulator. If a SOA is connected at the input of the PI to firstly implement the first-order differential function to the input dark RZ pulse utilizing gain saturation effect of the SOA, both polarity- and shape-switchable UWB Gaussian monocycle and doublet pulses are all acquired from the cascaded system. Moreover, if a nonreturn-to-zero control signal is introduced into the SOA, utilizing the cross-gain modulation (XGM) effect of the SOA and the differential characteristic of PI, all-optical shape modulation to UWB signals can be realized, and the polarity of the modulated UWB pulses can also be switched. Also, UWB signal transmission characteristics in fiber link were investigated.     

All-optical ultrawideband monocycle generation utilizing gain saturation of a dark return-to-zero signal in a semiconductor optical amplifier

We demonstrate a simple and compact scheme to generate ultrawideband (UWB) monocycle pulses utilizing gain saturation of a dark return-to-zero (RZ) signal in a semiconductor optical amplifier (SOA). When optical pulses with a dark RZ format propagate through the SOA, the output power at the rising edge will be overamplified compared with that at other durations due to the gain unsaturation. As a result, the output pulses are monocyclelike. The UWB frequency spectra at different injected currents, different input pulse widths, and different input wavelengths are analyzed. Our experiments show that the monocycle generation has good tolerance to the SOA bias current and the input signal wavelength.     

Filter-free ultrawideband generation based on semiconductor optical amplifier nonlinearities

A filter-free scheme for ultrawideband (UWB) generation with single semiconductor optical amplifier (SOA) is proposed and demonstrated. A pair of polarity-reversed optical pulses is generated due to cross gain modulation (XGM) in the pump-probe scheme, whereas the amplified pump pulse becomes sharp at its leading edge such that the power peak is shifted forward. Hence, the combination of the pump and probe signals at the SOA output is quasi-monocycle shape. Our scheme is an improved scheme to avoid exploiting optical filters and time-delay devices. The generated UWB radio frequency spectrum shows good stability when the input probe power varies from −10 dBm to 6 dBm, the probe wavelength varies in the whole C-band, and the bias current varies from 100 mA to 240 mA. Although the generated quasi-monocycle deviates from a standard Gauss monocycle to some extent, the frequency spectrum conforms to the UWB regulation. Two SOAs with different XGM dynamics are compared in generating UWB signals.     

Photonic ultra-wideband monocycle pulses generation using semiconductor optical amplifier and electro-absorber in parallel

A scheme for photonic generation of ultra-wideband （UWB） pulses using a semiconductor optical amplifier （SOA） and an electro-absorber （EA） in parallel is proposed and numerically demonstrated. By adjusting the time delay between two pump signals incident into the SOA and the EA, we can obtain monocycle pulses with reversed polarities and different bandwidths. The proposed method is flexible in pulse shaping and easy in practical optimization.     

UWB monocycle pulse generation based on optical cross-polarization modulation

A novel all-optical method for ultra-wideband （UWB） monocycle pulses generation based on cross polarization modulation （CPM） effect in highly nonlinear photonic crystal fiber is proposed and demonstrated. Due to the CPM effect between the probe light and the pump pulse, a pair of polarity-reversed Gaussian pulses is produced. After proper differential delay, an UWB monocycle pulse with 84-ps width and the fractional bandwidth of 153% is generated after photodetection.     

High-Order Ultrawideband Pulse Generation from NRZ-DPSK Signals

A simple method to generate ultrawideband （UWB） doublet and triplet from nonreturn-to-zero （NRZ） differential phase shift keying （DPSK） signals is proposed and experimentally demonstrated. The proposed configuration consists of a Mach-Zehnder modulator （MZM） to generate NRZ-DPSK signals, a section of single-mode fibre to form a microwave bandpass filter, which is used to generate doublet pulses, and a Gaussian optical bandpass filter （OBF）, which serves as a frequency discriminator to generate higher-order UWB pulses. A pair of polarity- reversed triplet pulses is achieved by locating the optical carrier at the positive and negative linear Mopes of the OBF, where the OBF detuning is 0.12nm and -0.2 nm, respectively. The spectra of the pair of UWB triplets have a central frequency of 5 GHz and 5.6 GHz, and have a -10 dB bandwidth of 6.9 GHz and 8.1 GHz, respectively. The UWB pulses remain doublet shape when the light wavelength is located at the peak of the OBF. The spectrum of the doublet has a central frequency of 5.6 GHz and a -10 dB bandwidth of 6.9 GHz.     

Photonic generation of millimeter-wave ultra-wideband signal using phase modulation to intensity modulation conversion and frequency up-conversion

We propose and experimentally demonstrate the generation of a pair of polarity-reversed 24 GHz millimeter-wave (MMW) ultra-wideband (UWB) monocycles. The scheme is realized by using delay interferometer (DI) based phase modulation to intensity modulation (PM–IM) conversion and carrier suppression modulation (CSM) based frequency up-conversion. The phase modulation is realized by using either electro-optic phase modulator (EOPM) or cross phase modulation (XPM) in semiconductor optical amplifier (SOA), which is an all-optical approach to obtaining baseband UWB signals, respectively. After frequency up-converted by using CSM in a Mach–Zehnder modulator (MZM), a pair of polarity-reversed 24 GHz MMW-UWB signals complying with the Federal Communication Committee (FCC) requirements is generated. The bi-phase modulation (BPM) of 24 GHz MMW-UWB signals can also be realized by electrically switching the bias voltage of delay interferometer.     

Suppression of Nonlinear Patterning Effect in Wavelength Conversion Based on Transient Cross-Phase Modulation in Semiconductor Optical Amplifier Assisted with a Detuning Filter

Nonlinear patterning （NLP） effect in wavelength conversion based on transient cross-phase modulation （XPM） in semiconductor optical amplifier （SOA） assisted with a detuning filter is theoretically investigated. A non- adiabatic model is used to estimate the ultrafast dynamics of gain, phase and electron temperature in the SOA. Simulation results show that the NLP can be greatly suppressed by introducing an assist light, especially for the probe wavelength distant from gain peak. Furthermore, the results also indicate that the improvement is more evident for long wavelength probe light and assist light in counter-propagating configuration.     

基于频域相位共轭技术的交叉相位调制所致失真的复原

理论分析和讨论了基于频域相位共轭技术的交叉相位调制所致信号失真的复原和补偿机理，数值模拟了在交叉相位调制作用下，高斯脉冲在中距相位共轭光纤系统中的传输演化过程.结果表明，频域相位共轭技术能够抑制交叉相位调制对光纤系统中传输信号的损害，复原其所导致的信号失真，并能够同步补偿群速度色散和自相位调制非线性效应所导致的信号失真.合适的初始脉冲时延和初始脉冲啁啾有利于频域相位共轭技术对交叉相位调制所致信号失真的抑制. 关键词： 频域相位共轭 交叉相位调制 色散 自相位调制     

Novel 160-GHz wavelength converter based on a SOA and a long period grating

The proposed converter is based on cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). The predominantly phase-encoded signal at the SOA output is converted to a purely amplitude-modulated signal using a long period grating. First, we design the converter in terms of power conversion efficiency and pulse pedestal suppression. Subsequent analysis for the delayed-interference signal-wavelength converter (DISC) revealed that our device offers 5 dB higher power conversion efficiency and gives shorter pulses at the converter output. In the proof-of-principle experiment, good agreement with the theoretical predictions is obtained.     

All optical wavelength converters based on cross phase modulation in SOA-MZI configuration

Wavelength converter plays an important role for increasing the capacity and flexibility of future broadcast network. The cross phase modulation (XPM) based converter has high conversion efficiency at low input power. In order to improve the efficiency and wideband conversion range, the XPM is increase by optimizing the semiconductor optical amplifiers-Mach–Zehnder interferometer (SOA-MZI) configuration. The XPM is improved by increasing the active region length and bias current of the SOA.     

Study on the dynamic range of input power for wavelength converter based on cross-phase modulation in SOAs

In this paper, the dynamic range of input power for wavelength converter based on cross-phase modulation (XPM) in semiconductor optical amplifier (SOA) is studied. The dynamic range of input power is associated with the linewidth enhancement factor , which is influenced by optical wavelength and power. Shorter wavelength and larger power can induce smaller and lead to a larger dynamic range, while the gain modulation is more severe. Through dynamically controlling the current of the phase arm of the XPM wavelength converter by the detection of the input signal power level, the dynamic range of input power can be increased from 2 to 17 dB.     

飞秒激光作用下全向高反膜破坏的激发过程

设计和制备了全向高反膜SiO₂/TiO₂，研究了它在不同脉冲宽度、不同脉冲能量的飞秒激光作用下的破坏阈值和烧蚀深度.利用发展的抽运-探针方法，研究了抽运脉冲作用下材料中导带电子的超快激发和能量沉积过程，建立并求解了飞秒激光激发材料和材料的激发对抽运光自身反作用的耦合动力学模型.模型较好地揭示了材料破坏的激发过程. 关键词： 飞秒激光 全向高反膜 激发过程 破坏机制     

Analysis of bit rate dependence up to 80 Gbit/s of a simple wavelength converter based on XPM in a SOA and a shifted filtering

This paper provides the analysis of wavelength converted pulses obtained with a simple semiconductor optical amplifier (SOA)-based wavelength conversion scheme, which exploits cross phase modulation (XPM) in an SOA in conjunction with shifted filtering. The analysis includes experimental measurements of the back-to-back system performances as well as frequency-resolved optical gating (FROG) characterisations of the wavelength converted pulses. These measurements are implemented at different bit rates up to 80 Gbit/s and for both red and blue-shifted filtering, particularly showing different patterning effect dependencies of red and blue-shifting techniques. This analysis is developed by the addition of a numerical study which corroborates the experimental results. A further understanding of the different performances of red and blue filtering techniques, presented in the literature, can thus be proposed. The placement of the filter to undertake red-shifted filtering (RSF) allows us to achieve very short pulse widths but high bit rate operation is limited by pattern effects. The blue-shifted filtering (BSF) technique shows optimum performance as regards to patterning effects even if the wavelength converted pulses can be larger.     

Photonic generation of ultrawideband signals by exploiting gain saturation of dark pump pulse with double undershoots in a highly nonlinear fiber

We have proposed and theoretically demonstrated an alternative photonic scheme to generate ultrawideband (UWB) doublet pulses based on gain saturation effect in one piece of highly nonlinear fiber (HNLF). A flexible format swap between UWB doublet and monocycle pulses can be successfully realized by properly tuning the optical tunable delay line (ODL). Moreover, the key parameters for UWB pulse, including the center frequency (Fc), 10 dB bandwidth (BW_10dB), and fractional bandwidth (FBW), are also investigated with Fc being Einstein shift when the doublet pulse transforms into the monocycle pulse. Finally, our proposed scheme exhibits good performance that the obtained UWB pulse can have a FBW of > 100% at the Fc of ~ 7 GHz and UWB-over-fiber technology is also implemented without dispersion management.     

光子晶体光纤中交叉相位调制光谱展宽特性研究

实验研究了超高速时分复用信号与探测光同向传输,在色散平坦高非线性光子晶体光纤中的交叉相位调制光谱展宽特性,从光谱学的角度分析了信号光波长漂移,泵浦光与信号光总功率及功率比,二者偏振态失配对交叉相位调制光谱展宽效应的影响,探讨了实现偏振不敏感交叉相位调制效应的可行性。研究发现,在36 nm波长范围,总功率大于23 dBm,泵浦光与信号光功率比合理,二者偏振态匹配时交叉相位调制效果最好,交叉相位调制的偏振相关性为11 dB,指出利用色散平坦高非线性光子晶体光纤中的残余双折射,调节泵浦光与光纤双折射主轴成45°,可以实现偏振不敏感交叉相位调制效应,随后的理论模拟和实验结果相一致。研究结果为实现基于交叉相位调制原理工作的超快全光信号处理器件作了充分准备。     

基于单模光纤的交叉相位调制型频率分辨光学开关超短脉冲测量

利用单模光纤中的光弹效应和交叉相位调制(XPM)效应,提出了一种频率分辨光学开关法测量超短脉冲的新方案.在本方案中,单模光纤的前一部分产生可变延迟,后一部分作为非线性介质产生非线性效应.该方案只需一根单模光纤,无须复杂的光路校准,结构简单,损耗低;光纤中的XPM效应易发生,无须相位匹配.对提出的方案进行了数值模拟,采用基于矩阵的主元素广义投影算法,恢复出待测脉冲的幅度和相位信息,并研究了光纤长度和待测超短脉冲的脉冲宽度对测量结果的影响.结果表明:测量准确度随着光纤长度的增加而提高,选取长度为2 km的光纤,就可以实现对超短脉冲的准确测量;本文方案适用于脉冲宽度不小于80 fs的超短光脉冲的测量.     

Measurement of cross-phase modulation in optical materials through the direct measurement of the optical phase change

We measure the cross-phase modulation (XPM) nonlinear indices of optical materials resulting from the interaction of an ultrashort pump pulse at 800 nm with a weak ultrashort probe pulse at 400 nm through the direct measurement of the optical phase change, using frequency-resolved optical gating. The materials studied include fused silica (SiO(2)) , borosilicate glass (BK-7), beta-BBO , and KD(*)P . This method results in a XPM nonlinear index that is in agreement with calculations based on nonlinear indices from previous self-phase modulation measurements.