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In multi-chip integrated photonic micro-systems, it is important to protect the laser source from reflection because the semiconductor laser is sensitive to the back reflection induced by the roughness of the waveguide sidewall or other on-chip optical structures. In order to maintain the stable operation of the light source, an additional micro-ring resonator coupled with the laser source is design before the optical circuit which enables the laser diode to enter a self-injection locking state and improves the reflection tolerance. It is experimentally demonstrated in the hybrid system that by tuning the phase shifter and the micro-ring resonate wavelength, the distributed feedback (DFB) laser enters a self-injection locking state, resulting significant improvement of the critical reflection ratio from −18.69 dB to −4.31 dB. The method can isolate the external reflection of laser diode without using heterogeneous integration, which provides a new idea for on-chip source isolation. The parameters design of the micro-ring and the coupling method with the laser are also introduced in the letter.

The dynamic properties of one kind of Inter-Connected Hydro-Pneumatic Struts (IC HPS), which is designed based on the developed double-gas-chamber compacted Hydro-Pneumatic Struts (HPS) integrating double inner gas chambers, will be investigated in this research. Comparing with the traditional IC HPS designs based on single gas chamber compacted HPS, the proposed IC HPS can postpone the force distortion, and then increase the working envelop, provide good stiffness performance and be stable in both In-Phase and Out-of-Phase working condition. The equation of motion of the proposed IC HPS will be derived firstly. And then based on the established dynamic model, the related simulating model will be established utilizing the AMEsim software, and the validity of the established simulating model will be verified on the basis of experimental data and available literatures. The validity and performance of the proposed IC HPS will be verified and investigated through comprehensive comparison with traditional IC HPS designs. Finally, the detailed sensitivity analysis of the essential design parameter of the proposed IC HPS will be presented to illustrate the advantage of the proposed IC HPS design.

Ghost imaging is a fascinating framework which constructs the image of an object by correlating measurements between received beams and reference beams, none of which carries the structure information of the object independently. Recently, by taking into account spacetime duality in optics, computational temporal ghost imaging has attracted attention. Here, we propose a novel Fourier temporal ghost imaging (FTGI) scheme to achieve single-shot nonreproducible temporal signals. By sinusoidal coded modulation, ghost images are obtained and recovered by applying Fourier transformation. For demonstration, non-repeating events are detected with single-shot exposure architecture. It is shown in experimental results that the peak signal-to-noise ratio (PSNR) of FTGI is significantly better (13 dB increase) than traditional temporal ghost imaging in the same condition. In addition, by using the obvious physical meaning of the Fourier spectrum, we show some potential applications of FTGI, such as frequency division multiplexing demodulation in the visible light communications.

We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with the method of zero-pole theory. As a proof of concept, the proposed structure is fabricated on the Si3 N4 waveguide platform. In the experiment, the 3-dB bandwidth of the proposed filter can be continuously tuned from 14.1 GHz to 4.1 GHz, maintaining a rectangular transmission response, and the wavelength can also be continuously tuned. This reconfigurable rectangular optical lattice filter shows the potential in many practical applications for reconfigurable optical signal processing due to flexibility and reconfigurability.

Higher dimensional optical imaging has seen remarkable growth in the past decade. As a representative method, multiplexed structured illumination (MSI) has been widely introduced for its ultra-high resolution of high-dimensional information. In this letter, an imaging framework for recovering higher dimensional image data, which terms quadrature multiplexed structured illumination (QMSI), is proposed and demonstrated. QMSI incorporates the illumination pattern spatial phase information as a new parameter into the encoding process. This strategy can double the frequency spectrum utilization without any overhead compared to MSI, which means it can double the image sequence depth or image spatial resolution. As a proof of concept, we demonstrate the performance of QMSI by experiments on multispectral imaging.

This paper is concerned with the local synchronization problem for the interconnected Boolean networks (BNs) without and with stochastic disturbances. For the case without stochastic disturbances, first, the limit set and the transient period of the interconnected BNs are discussed by resorting to the properties of the reachable set for the global initial states set. Second, in terms of logical submatrices of a certain Boolean vector, a compact algebraic expression is presented for the limit set of the given initial states set. Based on it, several necessary and sufficient conditions are derived assuring the local synchronization of the interconnected BNs. Subsequently, an efficient algorithm is developed to calculate the largest domain of attraction. As for the interconnected BNs with stochastic disturbances, first, mutually independent two-valued random logical variables are introduced to describe the stochastic disturbances. Then, the corresponding local synchronization criteria are also established, and the algorithm to calculate the largest domain of attraction is designed. Finally, numerical examples are employed to illustrate the effectiveness of the obtained results/ algorithms.

The resolution of analog to digital converter (ADC) and the power consumption of digital signal processing (DSP) are becoming the bottleneck of optical communication system. To acquire and recover signals with low resolution ADCs, we propose a binarized coherent optical receiver based on opto-electronic neural network, which consists of three layers, the broadcast layer, the optical neural layer, and the electronic neural layer. The broadcast layer that composed of Mach–Zehnder interferometers (MZIs) is to duplicate and select the input optical signal into the opto-electronic neural network. The optical neural layer is constituted by specially designed structures to map the binarized weights into optical domain, which can be integrated on silicon together with the broadcast layer. The one-bit vertical resolution ADCs act as the binarized activation after the optical neural layer. This binarized coherent optical receiver is demonstrated in simulation of 50-Gb/s single polarization (SP) QPSK system and 100-Gb/s polarization multiplexing (PDM) QPSK system. The one-bit vertical resolution ADCs can be utilized to recover the complex modulation format signal successfully. The broadcast layer and the optical neural layer can be integrated based on silicon, which could increase the calculation speed and reduce the energy consumption of the total system.

A fiber optical parametric oscillator (FOPO) is an effective way of generating new wavelength lasers in non-conventional wavelength bands, but the complex nature behind it is challenging for both theoretical and experimental studies. Luckily, dispersive Fourier transformation, which has been emerging in recent years, provides us with a good method of demystifying this complexity. In this letter, we capture and report, for the first time, the instantaneous dynamics of the initiating process in a fiber optical parametric oscillator. We directly observe that the initiating process experiences three stages. The FOPO fully establishes the parametric oscillation during nearly 2000 round-trips, i.e., nearly 93 $\mu \text{s}$ . In the meantime, the spectrum of the amplifier spontaneous emission noise gradually narrows down and evolves into the characteristic spectrum of the parametric oscillation. In order to start parametric oscillation, the pump power needs to exceed a certain threshold, after reaching which the power of the residual pump decreases while the signal and idle light grow. As we expect, due to the four-wave mixing effect, the signal and idle light are completely synchronous. Moreover, the stability of the oscillation is very sensitive to a slight fluctuation of the pumping pulses.

The fast-growing fields of coherent optical communications, light detection and ranging (LIDAR), etc., have huge demand for narrow linewidth lasers. While laboratory-scale lasers have high stability with narrow linewidth down to few Hz, they are usually in large size and unable to be integrated with chip-scale optical systems. In this paper, we develop a new on-chip semiconductor laser by introducing the Vernier effect and the self-injection locking effect simultaneously between a Fabry–Perot diode laser and an external microresonator on silicon chip. The proposed laser is demonstrated with a narrow linewidth of 8 kHz and wide switchable range of 17 nm. This paper explores a new scheme to realize narrow linewidth with wide tunability for on-chip semiconductor lasers.

This paper investigates the synchronization problem for the realization-dependent probabilistic Boolean networks (PBNs) coupled unidirectionally in the drive-response configuration. The realization of the response PBN is assumed to be uniquely determined by the realization signal generated by the drive PBN at each discrete time instant. First, the drive-response PBNs are expressed in their algebraic forms based on the semitensor product method, and then, a necessary and sufficient condition is presented for the synchronization of the PBNs. Second, by resorting to a newly defined matrix operator, the reachable set from any initial state is expressed by a column vector. Consequently, an easily computable algebraic criterion is derived assuring the synchronization of the drive-response PBNs. Finally, three illustrative examples are employed to demonstrate the applicability and usefulness of the developed theoretical results.

We report on an efficient wavelength-tunable gain-switched and gain-switched mode-locked Er3+-doped double-clad fiber laser with a linear cavity. Stable gain-switching and gain-switched mode-locking were achieved with slope efficiencies of 28.6% and 34.5% with respect to launched pump power, respectively. The gain-switched laser pulses were generated with a maximum average output power of around 110 mW, pulse width of 661.2 ns, and calculated peak power of ~16.5 W at a repetition rate of 10 kHz. At the same repetition, the gain-switched mode-locked laser pulses were generated with a maximum average output power of around 514 mW, subpulse repetition rate of ~30.7 MHz, and peak power of higher than 154 W at a repetition rate of 10 kHz when the wavelength was tuned to 2.78 μm. This is, to the best of our knowledge, the first demonstration of a gain-switched self-started mode-locked fiber laser near 3 μm.

We propose an adaptive three-dimensional (3-D) optimization including bit loading, power loading, and trellis-coded modulation for optical direct-detection orthogonal frequency division multiplexing (OFDM) in the fading channel. This approach could improve the bandwidth of the various devices such as electro-optical components, digital to analog convertors (DACs), and analog to digital convertors (ADCs) effectively. We conduct experiments to verify this 3-D optimization and compare the performance with that of 2-D optimization, i.e., bit loading and power loading only. Our experimental results show that the receiver sensitivity of 3-D optimization can be improved by 2 dB at the BER of 10 –3 compared with that of 2-D optimization in the fading channel. With the simple scheme we present of realizing the optimum 3-D optimization adaptively, the data rate is improved by 32% compared with using adaptive 2-D optimization in the fading channel. With the adaptive 3-D optimization, we also transmit a 16-GHz optical OFDM signal using a 10-GHz Mach–Zehnder (MZ) intensity modulator over a 20-km standard single-mode fiber link successfully. The modulation bandwidth of the MZ modulator is improved by 60% and the data rate is improved by 40%.

This paper investigates the complete synchronization problem for the drive-response switched Boolean networks (SBNs) under arbitrary switching signals, where the switching signals of the response SBN follow those generated by the drive SBN at each time instant. First, the definition of complete synchronization is introduced for the drive-response SBNs under arbitrary switching signals. Second, the concept of switching reachable set starting from a given initial state set is put forward. Based on it, a necessary and sufficient condition is derived for the complete synchronization of the drive-response SBNs. Last, we give a simple algebraic expression for the switching reachable set in a given number of time steps, and two computable algebraic criteria are obtained for the complete synchronization of the SBNs. A biological example is given to demonstrate the effectiveness of the obtained main results.

Single-pixel imaging (SPI) exploits the sparsity structure of natural images and enables image acquisition with far fewer measurements than the number of pixels. However, current SPI devices suffer from low imaging speed and an extremely time-consuming image reconstruction operation. Photonic time-stretch (PTS) technique is demonstrated to enable high-speed structured-illumination pattern generation, which significantly accelerates the imaging speed of conventional SPI devices. Meanwhile, to achieve fast image reconstruction, phase-shifted sinusoidal illumination patterns are used to acquire the Fourier spectrum of images and then a simple inverse fast Fourier transform (IFFT) operation is required for image reconstruction, which is quite computationally efficient. This paper presents a high-speed real-time compressive imaging system and its applications to imaging flow cytometry. Not only is a 625-kHz frame rate demonstrated, which is three orders of magnitude higher than that of a conventional SPI device, but the reconstruction process is remarkably accelerated as well, which enables our prototype system to operate in real time.

We experimentally demonstrated an integrated spatial heterodyne spectrometer fabricated on double-strip TriPleX waveguide technology. The TriPleX waveguide has a very low loss and tight bend so that the spectrometer realizes a high resolution of 0.023 nm across a wavelength range of 0.184 nm at 1550 nm in a small footprint of 4 mm × 8 mm. Moreover, the proposed integrated spectrometer combines the advantages of the planar lightwave circuit waveguide technology-based spectrometer and silicon-on-insulator technology-based spectrometer. The former has a very high resolution and relative high temperature stability while the latter can be implemented into a compact size based on CMOS-compatible standard technology. Besides, the wide transparency waveband of TriPleX waveguide platform makes it possible for the spatial heterodyne spectrometer to extend the working wavelength to the waveband of visible light and near infrared.

In current metro and access optical networks, the frequency band beyond the bandwidth of the electro-optical components is always deprecated due to the fading frequency response. On the other hand, an orthogonal frequency division multiplexing (OFDM) system is managed on individual subcarrier and can adapt to the varied channel frequency response by optimally allocating different modulation formats and powers across different subcarriers. Therefore, to reuse the commercial low bandwidth components in high speed networks, we design modified OFDM signals, which are with adaptive power and bit allocation, to improve the bandwidth utilization and maximize the data rate. We successfully transmit 16-GHz optical OFDM signals over a 20-km standard single mode fiber link with a 10-GHz commercial Mach–Zehnder (MZ) intensity modulator and direct detection. Eleven modulation formats are used for bit loading and the maximum data rate can reach 88.8 Gb/s. The modulation bandwidth utilization of the MZ modulator is increased by 60%.

In an optical orthogonal frequency division multiplexing (OFDM) system, channel impairments, such as residual chromatic dispersion, residual synchronization error, and clock frequency offset, induce phase shifts over subcarriers. We propose a method of using image processing for phase channel estimation with negligible overhead, which is applicable to various subcarrier modulation formats. We conduct the experiment of 32-, 40-, and 48-Gbit/s direct detection optical OFDM with 16QAM, 32QAM, and 64QAM subcarrier modulation and simulation of 112-Gb/s coherent optical OFDM to verify this method and compare the results with those of the conventional method. Then, we investigate the effects of the numbers of required test phases and OFDM symbols with experimental data. We also present an approach of removing the inner part of constellation points to reduce the complexity.

A stable nanosecond chirp-free pulse generation with ultra-narrow bandwidth is established from a passively mode-locked erbium-doped fiber laser with a homemade fiber Bragg grating as the intra-cavity filter and careful intra-cavity dispersion management introduced. The laser generates nearly chirp-free pulse that is close to the Fourier transform-limited condition. The measured pulsewidth is 2 ns and the spectral width is only 192 MHz. The measured time jitter is below 1%. The pulse repetition rate is 982 kHz, which reveals there are only 195 oscillating longitudinal modes. This is the longest duration of single stable chirp-free pulse in passively continuous-wave mode-locked fiber lasers to our best knowledge.

An all-optical orthogonal frequency-division multiplexing (OFDM) demultiplexer based on silicon-on-insulator (SOI) waveguide technology is proposed and experimentally demonstrated. Such an integrated structure performing a discrete Fourier transform (DFT) not only has the advantages of a smaller volume and better stability but can also handle more optical subcarriers by increasing the number of the cascaded Mach-Zehnder interferometer (MZI) stages. An SOI-based eight-channel OFDM demultiplexer has been successfully fabricated with a free spectrum range (FSR) of approximately 64 GHz. Eight-subcarrier optical OFDM signals with non-return-to-zero (NRZ) formats are successfully detected by the proposed demultiplexer after a 30-km fiber-link transmission. The total modulation speed is 64 Gbaud, and the bit error rate (BER) performance of each subcarrier is also measured.

Ultra-broadband radiofrequency (RF) receivers are required in higher frequency-band wireless communications, radar communications or multi-band applications in radio telescopes. Such ultra-broadband receivers are inherently difficult to establish with electronics because of limits in the bandwidth of the devices. Photonic means of RF photonic receivers/frontends can overcome the bandwidth limitation in electrical receivers. One aspect that should be considered is the precise signal processing in the optical domain. Here, a full-band (from the L-band to the W-band) all-optical RF receiver based on the Si3N4 microring filter is proposed and experimentally demonstrated. The resolution and processing range of the filter are lower than 420 MHz and larger than 112.9 GHz (FSR larger than 225.78 GHz), respectively, and the out-band suppression of this filter is greater than 40 dB. The center frequency of the filter can be altered for more than one FSR by tuning the phase-shifter on top of the ring. The performance of the full-band all-optical RF-receiver has been discussed, and the spurious free dynamic range of the receiver from the L-band to the Ka-band (limited by the bandwidth of the modulator in our experiment) has been measured to be larger than 111.6 dB·Hz2/3.

A novel approach to achieving ultrafast three-dimensional (3-D) imaging based on space-to-wavelength-to-time mapping and short-time Fourier transform (STFT) is proposed and experimentally demonstrated. The fundamental concept to achieve 3-D imaging is to encode the depth information of a sample by interfering two delayed pulses that are reflected from the surface of the sample and an additional reference plane on the top of the sample. The interference pattern that contains the depth information in the frequency domain is converted into the time domain based on dispersive Fourier transform and then analyzed based on STFT. Thus, ultrafast 3-D imaging is achieved. The proposed approach is experimentally evaluated. The imaging of a sample with a depth of 1.5 mm using an ultrafast pulse laser source with a beam width of $\sim 2$ mm at a repetition rate of 48.8 MHz is demonstrated.

A linearized photonic radio frequency (RF)-to-intermediate frequency (IF) conversion system is proposed and experimentally demonstrated based on balanced detection and digital signal postcompensation. The optical carrier suppression and remodulation scheme is employed to significantly reduce the local oscillator frequency requirements and common mode optical phase noises. Photonic IF downconversion is enabled by using a reconfigurable multiport optical processor and balanced coherent detection of the spectrally separated lower and upper first-order sidebands of the phase modulated signals. Moreover, the digital linearization technique is used to suppress the third-order intermodulation components by more than 21 dB and an improvement of the spurious free dynamic range as large as 7 dB for RF signals ranging from 8–20 GHz is also achieved.

Digital signal processing has achieved great success in the field of signal processing over the past several decades. However, as the bandwidth requirement increases, the power consumption and effective number of bits (ENOB) of the analog-to-digital convertor (ADC) have become bottlenecks. One solution is returning to analog and applying microwave photonic technologies, which shows potential for multiband signal processing. In this paper, a programmable integrated analog photonic signal processor based on cascaded Mach-Zehnder interferometers (MZIs) and a channelized filter has been proposed. Different shapes of the signal processor can be acquired for different applications. The highest processing resolution is 143 MHz, and the processing range of the signal processor can be higher than 112.5 GHz. An application of the signal processor for the signal extraction in a radio frequency (RF) photonic frontend operating from L-band to K-band is presented.

We report all-fiber tunable ultrahigh-repetition-rate sub-picosecond pulse sources around 1550 nm. The sources are based on cascaded four wave mixing in an erbium-ytterbium co-doped fiber without extra nonlinear fiber. They are seeded by a spacing-tunable phase conjugated dual-wavelength parametric light source centered at 1550 nm. The repetition rate of the pulse sources can be tuned continuously in the range of 0.75-2.75 THz by adjusting the wavelength spacing of the dual-wavelength light source. We use auto-correlator to measure the waveform of the pulses. The duration of the pulses is about 100 fs.

In this letter, time-interleaved multiwavelength pseudorandom binary sequence (PRBS) optical pulses are utilized to significantly increase the instantaneous bandwidth of the modulated wideband converter (MWC). A four-channel MWC with a bandwidth of 20 GHz is proposed for the first time, where four-wavelength optical pulse trains modulated by a 10.16-Gb/s PRBS signal are interleaved temporally after going through four sections of fibers with different lengths in parallel. The flat and ultrawide spectrum of the PRBS-modulated pulse train guarantees a uniform SNR and recovery probability. Sparse radio frequency signals ranging from 0.5 to 20 GHz are reconstructed faithfully from four-channel samples with only 360-MHz bandwidth.

Optical time stretch has been employed for ultrafast optical imaging based on space-to-wavelength-to-time mapping. However, temporal overlap between two adjacent time-stretched pulses is a disadvantageous factor that limits the spatial resolution, or the frame rate has to be reduced by reducing the pulse repetition rate to avoid the temporal overlap. To increase the spatial resolution without reducing the frame rate, we propose a novel technique based on polarization-division multiplexing, using a polarization modulator to generate two polarization interleaved pulse trains. Since two adjacent optical pulses are orthogonally polarized, the spacing between two adjacent pulses for one polarization direction is doubled, and the spatial resolution is doubled by using a dispersive element with two times the dispersion. The proposed approach is experimentally evaluated. An imaging system with an increased spatial resolution is demonstrated.

Based on serial channelization and coherent detection, a radio-frequency (RF) measurement scheme with a Nyquist-bandwidth detector is proposed and experimentally demonstrated. With a wavelength scanning structure, multiple RF channels serial in the time domain are implemented. A coherent receiving module based on an optical hybrid and balanced photodetectors (BPDs) is constructed to reduce the receiver bandwidth and the bandwidth of the follow-up electronic devices. In this paper, a six-channel 3-GHz-spacing channelizer, with 18-GHz receiving bandwidth and 1.5-GHz BPD, is demonstrated. In addition, multifrequency signals and a linear frequency modulation signal with the slope of 4.53 MHz/ $\mu\hbox{s}$ are tested.

We report a fiber optical parametric amplifier (FOPA) based on a photonic crystal fiber (PCF) with optimized dispersion and nonlinear properties pumped by a mode-locked ytterbium-doped fiber laser. Wavelength-tunable parametric gain bands can be obtained by adjusting the pump wavelength from the anomalous to the normal dispersion regime. By utilizing the PCF-based FOPA, weak signals located in the parametric gain bands can be amplified. Wavelength-tunable picosecond pulses can be generated at the signal and idler wavelengths. A 58-dB maximum gain and a wide gain bandwidth from 999 to 1139 nm have been achieved by pumping near the zero-dispersion wavelength. When the FOPA is pumped at 1062.5 nm in the normal dispersion regime of the PCF, the 974-nm weak continuous-wave signal is significantly amplified, and the idler pulse is generated at 1168 nm.

The obstacles of power scaling the supercontinuum (SC) source based on single-core photonic crystal fiber (PCF) are analyzed. The combination of high-power fiber lasers and multi-core PCFs would be a feasible method to obtain an all-fiber-integrated high-power broadband SC source (covering visible range). In this paper, we present a comprehensive study of high-power SC generation in multi-core PCFs. Comparative experiments are performed by using a high-power pulse-repetition-rate-tunable picosecond fiber laser to pump two kinds of home-made seven-core PCFs. The influences of PCF structure (fiber dispersion property) and pulse repetition rate (pulse peak power) on the SC generation in multi-core PCFs are investigated in detail. When the picosecond fiber laser at a pulse repetition rate of 1.9 GHz is adopted as the pump, 116 W SC spanning from 800 to 1700 nm is generated in 1# seven-core PCF. Also 64 W visible SC spanning at least 500-1700 nm is demonstrated in 2# seven-core PCF at a pump pulse repetition rate of 480 MHz. The potential of extending the spectral range and scaling the output power for the SC source based on multi-core PCFs are analyzed and discussed.

An efficient approach that combines the coupled volume surface integral equation (VSIE) accelerated by multilevel fast multipole algorithm (MLFMA) and the modified surface integration (MSI) method is proposed to analyze the antenna-radome structures (ARS) in receiving mode. The hybrid method not only reduces the computational time and memory requirement as compared to the purely full-wave solutions, but also more importantly overcomes the difficulties in conventional high-frequency approximate methods for analyzing the properties of the radome-enclosed receiving antennas or arrays. Numerical results are shown to illustrate the validity, efficiency, and accuracy of the proposed method.

A novel large-tap and tunable microwave photonics (MWPs) filter based on a recirculating frequency shifting loop has been proposed and experimentally demonstrated. To improve the Q -factor value of the MWP filter, we used a simple recirculation loop to economically generate a large-tone optical frequency comb in this scheme. In addition, the cumulative effect in loop structure, which affects the characteristics of the generated taps significantly, is analyzed to predict the performance of the proposed filter. In experiments, we realized a 70-tap filter at 4.5 GHz with the Q -factor value exceeding 70. Also, a filter with center frequency tunable from 1 to 8 GHz is demonstrated.

A picosecond photonic crystal fiber-based doubly resonant optical parametric oscillator is demonstrated. A four-wavelength oscillator can be obtained by selecting a wavelength in signal cavity and a wavelength in idler cavity phase-mismatched with the one in signal cavity to oscillate simultaneously. The output light beams are improved significantly when the signal wavelength and the phase-matched idler wavelength are selected to oscillate simultaneously in the two cavities. In particular, the peak intensities of the output signal and idler are increased by 2.53-5.77 dB, the 3-dB bandwidths of the signal and idler are narrowed by 0.05-2.98 nm, and the pump-to-idler conversion efficiencies are improved by 2.2-3.8 times.

In this paper, we analyze waveform generation using a single-stage dual-drive Mach-Zehnder modulator and a dispersive fiber. We derive a mathematical expression for the waveform generation process in the time domain and use this to propose a waveform generation algorithm. Furthermore, versatile waveforms, such as short pulse, trapezoidal, triangular and sawtooth waveforms and doublet pulse, are theoretically generated under different combinations of the four variables. The generated waveforms are analyzed in terms of the gradient and the instantaneous frequency. Finally, the waveform generation is experimentally demonstrated at the repetition rate of 10 GHz.

A novel high spectral efficiency all-optical sampling orthogonal frequency-division multiplexing (AOS-OFDM) scheme with optical cyclic postfixes (OCPs) inserted is proposed. Ultrashort pulses are used as optical samples and processed by all optical discrete Fourier transformers based on fiber Bragg gratings (FBGs) technique. This scheme includes five subcarrier channels with 20 Gb/s differential quadrature phase-shift keying (DQPSK) modulation of each channel. So, the total bit rate is 100 Gb/s. The spectral efficiency is higher than 1.4. Furthermore, with the help of OCPs, the dispersion tolerance of this 100 Gb/s AOS-OFDM system increases to more than 300 ps/nm, which is much higher than a traditional 100 Gb/s DQPSK system.

As an alternative to label swapping, an all-optical label stripping scheme based on SOA-MZI is proposed. The stripping process is self-controlled without any synchronization process. Simulation results show that high-quality stripping can be achieved, with no more than 0.09 dB of power fluctuation and 0.05 dB of phase fluctuation in stripped and remaining label. A power contrast ratio of 28 dB between the remaining and residual stripped label, and 30-dB signal-to-noise ratio can be reached, respectively. Parameters tolerance analysis shows that the stripping performance deteriorates little when considering the devices' imperfection in practice. The multihop simulation results also show that our scheme is applicable to large-scale optical packet switching networks.

In this paper, novel approaches for millimeter-wave signal generation using double-sideband suppressed-carrier modulation and four-wave mixing are proposed and demonstrated. The millimeter-wave signal is generated at a photodetector by beating the optical sidebands, which are gained from intensity modulation and after semiconductor optical amplifiers. In the proposed methods, the generated millimeter-wave signal has a frequency that is double, quadruple, sextuple, 12 times, or even 18 times higher than the microwave drive signal. And, it has quite good gain flatness with extremely high-spectral-purity and stability. The phase noise performance of the generated millimeter wave is investigated. The 3-dB linewidth of the millimeter wave has no broadening after propagating through 20-km standard single-mode fiber.

Optical methods for different type ultra-wideband (UWB) pulse generation based on cross-polarization modulation (CPM) are proposed and demonstrated in this paper. Two polarity-reverse pulses can be obtained by CPM and birefringence time delay to form a monocycle pulse. A semiconductor optical amplifier (SOA) is placed after the monocycle pulse process for doublet pulse generation. These two kinds of pulses can be employed in single-band impulse radio UWB (IR-UWB) systems. Two kinds of multi-band UWB pulses can be generated based on monocycle pulse train with proper apodization profiles, realized by hybrid photonic microwave filter and synchronous polarization modulation respectively. Experimental results show that these pulses can be used in multi-band UWB (MB-UWB) over fiber systems.

A novel vestigial-sideband (VSB) payload scheme is proposed for high-speed all-optical label-switching (AOLS) networks. The combination and separation of the VSB payload and the optical label is experimentally demonstrated, and the influences of the power-split ratio, time-delay interference, interferometric noise (IN), and wavelength difference between the payload and the label are analyzed. Simulation and experiment results show that this VSB payload scheme can highly reduce the channel bandwidth and it is easy to realize by using optical filters, so it is a potential technique to be used in optical networks with bit rate of 40 Gb/s.

A high-κ LaLuO3 (LLO) thin film is successfully incorporated into AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) as the gate dielectric. The LLO-AlGaN/GaN MISHEMTs fabricated with a planar process exhibit a high ION/IOFF of 109, a maximum drain current of 820 mA/mm at VGS = 3 V, a peak transconductance (Gm) of ~ 192 mS/mm, and a steep subthreshold slope (SS) of ~ 73 mV/dec.

In this letter, we present the deployment of Schottky source/drain (SSD) in InAlN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) for off-state breakdown voltage improvement. The improved breakdown voltage relies on the suppression of electron injection into the buffer under the Schottky source contact. A VBD of 460 V is obtained in an SSD MISHEMT with an LGD = 10nμm, at a 170% improvement compared with that of the control MISHEMT featuring ohmic source/drain. Despite the SSD contacts, an SSD MISHEMT with a gate length of 1 μm exhibits a respectable drain current density of 416 mA/mm and a transconductance of 113 mS/mm.

The Schottky-source forward current-voltage characteristics were measured and analyzed in a recently reported AlGaN/GaN metal-2-D-electron-gas tunnel junction field-effect transistor (FET) (TJ-FET) in order to characterize the effective Schottky barrier height (SBH) and its gate bias dependence. The SBHs were extracted and found to be gate bias dependent, varying from 0.57 eV at VGS = -0.5 V to 0.3 eV at VGS = 1 V. This gate-induced Schottky barrier lowering (SBL) effect is explained by the image-charge effect. A 2-D device simulation is carried out to analyze the SBL effect and is shown to be in good agreement with the experiment results. The larger SBH at lower gate voltage enables off -state blocking, while the lower SBH at higher gate voltage leads to high on -state current driving capability in the AlGaN/GaN TJ-FETs.

A simple code switching scheme for security enhancement of an optical code-division multiple-access (OCDMA) communication system is proposed. The scheme avoids the replacement of all the encoders and decoders in the system and all users' codes are changed by only tuning the center wavelength of the laser source. Each en/decoder contains multiple codes which are nonoverlapping in the spectrum. The scheme is demonstrated in a proof-of-principle transmission experiment. There are three codes on the encoder and decoder pairs, one 2-D code and two 1-D bipolar gold codes with chip number of 63 and 127, respectively. All three codes are decoded successfully after 12.7-km single-mode fiber link.