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A novel and simple photonic approach for generating symmetry-tunable full-duty triangular-shaped microwave waveforms is proposed and experimentally demonstrated. In this approach, a simple commercial single-drive Mach-Zehnder modulator (MZM) is adopted and driven by the radio frequency (RF) input. By properly presetting the RF modulation index and simply adjusting the direct current (DC) bias voltage of MZM, the full-duty triangular-shaped microwave waveforms with self-defined symmetrical coefficients can be obtained. A complete theoretical analysis on operation principle is presented and a proof-of-concept experiment is carried out. The full-duty triangular-shaped waveforms with tunable symmetrical coefficients at the repetition rate of 5 GHz are successfully generated. This approach features simple architecture, less variables, excellent reconfigurability and integrable capability, which are highly desired for the high-performance triangular-shaped waveform generator.

In this article, a photonic scheme based on dual-drive dual-parallel Mach-Zehnder modulator (DD-DPMZM) to generate switchable dual-band dual-chirp microwave waveforms is proposed and experimentally demonstrated. In the scheme, the switching among two single-band dual-chirp signals and a dual-band dual-chirp signal can be readily realized by simply adjusting the bias voltages on the modulator. Theoretical analysis on the operation of the approach is presented. Full experimental verification on the generation of switchable dual-chirp signals in the S-band and C-band has been successfully demonstrated. The presented scheme features in the simple structure, easy tunability and reconfigurability, which has potential applications in multi-band radar.

A chirped microwave waveform with a large time-bandwidth product (TBWP) can find important applications in modern radar systems and microwave imaging systems. Microwave photonics, a field that studies the generation and processing of microwave signals in the optical domain to take advantage of the ultra-wide bandwidth offered by photonics, has been considered an effective solution for high-frequency and large-bandwidth microwave waveform generation. In this paper, an overview on photonic generation of wideband chirped microwave waveforms is provided. Three major methods are discussed including chirped microwave waveform generation based on spectral shaping and frequency-to-time (SS-FTT) mapping, frequency and bandwidth multiplication, and Fourier-domain mode-locking of an optoelectronic oscillator (OEO). The performance of the techniques for chirped microwave waveform generation is studied. Techniques to generate chirped microwave waveforms based on photonic integrated circuits (PICs) are also discussed.

A novel approach to realize broadband microwave spectrum sensing based on photonic RF channelization and compressive sampling (CS) is proposed. The photonic RF channelization system is used to slice the input broadband signal into multiple sub-channel signals with narrow bandwidth in parallel and thus the rate of pseudo-random binary sequence (PRBS) and the bandwidth of the MZM for CS can be largely decreased. It is shown that a spectrally sparse signal within a wide bandwidth can be captured with a sampling rate far lower than the Nyquist rate thanks to both photonic RF channelization and CS. In addition, the influence of the non-ideal filtering of the photonic channelizer is evaluated and a novel approach based on measuring twice is proposed to overcome the problem of frequency aliasing induced by the non-ideal filtering. It is demonstrated that a system with 20 Gbit/s PRBS and 2.5 GS/s digitizer can be used to capture a signal with multiple tones within a 40 GHz bandwidth, which means a sampling rate 32 times lower than the Nyquist rate.

We propose and experimentally demonstrate a novel and simple approach to identifying both the direction and value of Doppler frequency shift (DFS) in this paper. A pair of phase modulators, as well as a dispersion medium in between them, are employed in the approach. The different dispersion-induced phase shifts of the upper and lower sidebands after passing the dispersion medium can be used to determine the direction of DFS. The value of DFS is characterized by measuring the frequency of the output signal from a low-speed photodetector. Experimental results verify the feasibility of the approach. The major advantages of the approach lie in that it can measure both the DFS direction and value while avoids the use of complicated modulators and additional reference signal, which greatly simplifies the system's architecture.

This paper proposes a novel linear precoder design based on the singular value decomposition (SVD) for multi-input multi-output visible light communications (MIMO VLC). We provide an analytical expression on power allocation subject to the function of maximizing the lower bound of capacity according to the optical wireless communication channel model. The expression is rather different from the radio frequency (RF) communications due to the non-negativity of the transmitted signals in VLC. Furthermore, we design an adaptive bit loading scheme for sub-streams with consideration of the tremendous gain difference among subchannels. Performances of the proposed adaptive power and bits allocation strategy are evaluated in two traditional MIMO VLC scenarios, i.e., a practical 2×2 indoor scenario and a classical 4×4 system that is generated according to the MIMO model. In simulations, the techniques of unipolar M-level pulse amplitude modulation (M-PAM) and spatial-multiplexing (SMP) are employed, and the performance comparison with other SVD-based linear precoders is also given. Simulation results show that the proposed approach can effectively improve the spectral efficiency and guarantee the bit error rate (BER) performance under the same constraints of aggregate optical power budget and non-negativity included by the intensity modulation. It indicates that the strategy of uneven bits and power allocation with full consideration of the ill-conditioned characteristics of subchannels performs better than that based on equal bits transmission in VLC systems.

The structure and electrical characteristics of a dielectric resonator (abbreviated as DR hereafter) loaded plasmonic waveguide with controllable bandwidth are investigated in the present research. By loading the high permittivity dielectric medium on a spoof surface plasmonic waveguide, the working bandwidth of the filtering structure can be regulated flexibly due to the resonant effect of the loaded cylindrical DR. The DR is home-made and possesses the permittivity of 25.66, tanδ of 5.3 × 10-5 and stable temperature coefficient of -6.3 ppm/°C in microwave region. After the DR is loaded, the filtering structure can form the transmission zero on the edge of the pass band, regulating the bandwidth as well as increasing the out-of-band rejection. By controlling the height between the loaded DR and the substrate, or adjusting the inter-distance between the DRs, the relative bandwidth of the filtering structure can be effectively tailored.

The scattered Optical Network Units (ONUs) in an optical access network have different propagation delays. In an Ethernet passive optical network (EPON) adopting the traditional Interleaved Polling with Adaptive Cycle Time (IPACT) scheme, such ONU propagation delay difference will waste network resources and will degrade both network delay performance and network energy efficiency in delivering low-latency services. In this article, to deal with the heterogeneous ONU propagation delays problem, two solutions are proposed and investigated. The first solution, namely the Upstream Postponing with ONU Dozing (UP-OD) scheme, is to properly postpone the upstream transmissions of those ONUs having relatively short propagation delays to improve channel utilization efficiency, and ONU doze mode is incorporated to enhance network energy efficiency. The second solution, namely the Identical Fiber Length with ONU Sleeping (IFL-OS) scheme, is to adopt an identical distribution fiber length for ONUs to enhance channel utilization, and ONU sleep mode is incorporated for energy consumption reduction. Simulation results show that both the UP-OD scheme and the IFL-OS scheme reduce network delay and improve network energy efficiency in delivering low-latency (

The major limitation of the photonic digitization schemes based on the phase-shifting of modulation transfer function lies in its relatively low bit resolution, which is log2(2N ), where N is the number of optical channels or modulators. In this paper, we propose a novel photonic digitization scheme based on hierarchical quantization, which could greatly improve the system resolution with a relatively simple configuration. It is shown that 6N quantization levels, can be realized by using only three Mach-Zehnder modulators (MZMs) and a hierarchical quantization module (HQM) in the proposed scheme. By adjusting the fine quantization module inside HQM, the system resolution can be enhanced greatly. A proof-of-concept experiment is implemented, which fully verifies the correctness of the approach. Since simpler configuration and higher resolution are achieved, the proposed scheme provides a promising solution for high-performance photonic analog-to-digital conversion.

In this paper a novel photonic digitization scheme with differential encoding based on orthogonal vector superposition (OVS) is proposed and demonstrated. A phase modulator (PM) and two delay-line interferometers (DLIs) with π/2 difference in bias phase are employed to generate two orthogonal modulated signals. By adjusting and combining the intensity of two orthogonal signals with an OVS module, the desired phase shifts among different transfer functions can be obtained. The proposed scheme can differentially encode the input signal with enhanced bit resolution. Compared with the existing photonic digitization schemes based on modulators, this scheme features its simple configuration, because only a single PM, two DLIs and an OVS module are required; moreover, since the desired phase shifts of transfer functions are realized by attenuating the signal intensities, the proposed scheme can effectively alleviate the problem of phase bias drift induced by modulators. Proof-of-concept experiments of 3- and 4-bit photonic digitization systems based on OVS are successfully carried out, which demonstrate the feasibility of the approach.

Compressive sensing (CS) with photonic technologies provides a promising way to acquire information with reduced measurement. Photonic CS with pulse stretch and compression has been proved to be capable of capturing wideband time-domain signals at extremely high equivalent sampling rate or images at high frame rate. In this approach, an input short pulse is first stretched by propagating through a dispersive medium and then the stretched pulse is modulated by a signal to be measured and a pseudorandom bit sequence (PRBS). The stretched pulse encoded with the signal and the PRBS is compressed in the time domain after passing a second dispersive medium with an opposite dispersion value. The time-domain compression of the stretched pulse was regarded as the integration function in the CS process (but it has never been proved), which is a key to realize time-domain downsampling or single-pixel imaging. In this paper, we fully investigate the theoretical framework of the photonic CS with optical pulse stretch and compression, and present an analytical model of the CS measurement matrix based on the analysis of the pulse stretch, modulation and compression, for the first time to our knowledge. Moreover, we prove the equivalence between the peak value of the compressed pulse and the integral value of the mixed signal, which is the basis of the analytical model. In addition, we further discuss the impact of the limited bandwidth of the employed photodetector on the measurement and the performance of signal reconstruction.

The crosstalk suppression of multichannel coupled drivelines is studied for high-performance integration of micro-electro-mechanical system arrays. By using traditional drivelines, for example, microstrip lines, the distance between adjacent drivelines should be large enough to reduce the multichannel coupling effects. As a result, the size and the area of ultra-low crosstalk and closed-packaged driveline become an issue for design. To address it, we proposed a new scheme of multichannel spoof surface plasmon polaritons (SSPP)-based drivelines. The new drivelines consist of multiple parallel planar corrugated metallic strips. Thanks to the strong field confinement and localization characteristics of the SSPPs, the coupling effects between drivelines in different channels can be significantly suppressed with no need of any other coupling suppression circuits. For demonstration and investigation, both simulation and measurement are carried out up to 20 GHz. The results show that the crosstalk by using the proposed new drivelines can be reduced by about 10 dB on average. Therefore, the SSPP-based multichannel drivelines would be a good candidate for large-scale advanced integrated devices and systems with requirements of both miniaturization and coupling suppression.

Temporal Talbot phenomena occur when a periodic optical pulse train propagates through a dispersive medium with a proper dispersion amount, which includes integer and fractional orders depending on the dispersion amount. The fractional temporal Talbot (FTT) effect has attracted great interest because of its potentials in repetition rate multiplication of optical pulse train and passive amplification of short pulses. In this paper, we investigate the evolution of amplitude fluctuation in FTT systems from the viewpoint of the frequency-dependent fading of pulse train envelope. It is found that the envelope frequency response of FTT is different from that of integer orders since there is waveform-to-waveform phase profile in the output pulse train in FTT systems. The noise reduction phenomenon in FTT systems is analyzed based on the derived frequency response. A closed-form expression of the noise reduction ratio is derived for the first time based on the analysis of the noise power spectral density. With the given model, we are able to predict the fluctuation suppression effect in FTT systems more precisely.

For the future high-speed next-generation Ethernet passive optical network (NG-EPON) system, the low-cost system could be kept by adopting low bandwidth devices. To compensate for the signal distortion and improve the performance of high-speed bandwidth limited system, we propose a special feature vector construction to achieve a new equalizer scheme based on support vector machines (SVM) classifier. For the first time, we mathematically analyze the model of the bandwidth-limited optical transmission system and theoretically derive the linear separability of the proposed feature vector formed linear hyperplane in 100-Gb/s NG-EPON system. Furthermore, 4 × 25-Gb/s non-return to zero (NRZ) and 2 × 50-Gb/s four-level pulse amplitude modulation (PAM-4) per wavelength transmission experiments with 10-G class optics system are demonstrated to prove the feasibility of our scheme. The experimental results show that, for 25-Gb/s/λ NRZ transmission, compared to the decision feedback equalizer (DFE) and feed-forward equalizer (FFE), the receiver sensitivity achieved by our scheme can be improved by about 0.5-dB @BER=3.8e-3 with limited training sequence. For the 50-Gb/s/λ PAM-4 case, the SVM-based equalization method improves the receiver sensitivity for about 1-dB.

The plasmonic surface is made of metallic surface with deep sub-wavelength decorations, which are designed to mimic the surface plasmon polaritons at lower frequency. Recently, high-order modes in some special structures are analyzed. In order to analyze the dispersion problem of high-order modes of complex lossless structures faster and simpler, a convenient and simple method using the average input wave impedance obtained by a field-network joint solution is proposed. Meanwhile, based on Forster's reactance theorem, high-order modes of the complex structure always exist. Then, the dispersion curves of the high-order modes calculated using proposed method are in perfect match with the simulated results, which can verify the effectiveness and correctness of the proposed method. Additionally, the simulated and experimentally measured electric field distribution of high-order modes have great agreement. Using the proposed method, one can quickly obtain dispersion curve of a plasmonic structure to verify or estimate structure design. Hence, the proposed method may make a big step forward for obtaining the special dispersion relations.

The performances of plane spiral orbital angular moment (OAM)-based MIMO (PSOAM-MIMO) systems are investigated in a non-line-of-sight (NLoS) channel. Two analytical models, known as specular reflection model and circular scattering model, are applied to evaluate the reflection and scattering effects of wave propagating in the NLoS channels. The performances of the PSOAM-MIMO system in the NLoS channel are compared with those of the conventional MIMO system and in LoS channel. It is found that the capacity gain of the PSOAM-MIMO over MIMO is mainly determined by a direct path. In the NLoS channel, the capacity gain of PSOAM-MIMO over MIMO decreases compared with that in LoS, however, the multi-path effects improve the absolute capacity of PSOAM-MIMO system, and the worst case are comparable with those in an MIMO system. As a result, the PSOAM-MIMO system demonstrates the strong robustness in wireless communications.

Due to the unique properties of field confinement and enhancement, spoof surface plasmon polaritons (SPPs) are considered as special modes to break many challenges in traditional electronic and microwave engineering. Ultrathin corrugated metallic structure offers an easy fabrication method to realize spoof SPP waveguides on substrate, and has been proved to have many merits in recent years. Lately, a programmable and coding spoof SPP waveguide loaded by active elements was presented, which makes it possible to control SPPs in real time. However, this programmable SPPs waveguide suffers from the limited loadable space and hence can hardly achieve more complex controlling functions. On the other hand, the existing methods to excite spoof SPPs require large conversion structures, which are unadoptable in modern integrated circuits. In this paper, we propose a new type of spoof SPP waveguide composed of a metallic strip and corrugated ground with an open loadable space for large-scale and complex controlling networks. A new conversion structure is presented to achieve high-efficiency transition from the traditional microstrip to the SPP waveguide without using extra space. Both numerical simulations and experiments indicate the outstanding performance of the new spoof SPP waveguide. The proposed structure is also convenient to connect with active devices due to its multi-conductor nature. Hence, the proposed structure may find wide applications in SPP-based integrated circuits and systems in the future.

We propose a dual circularly polarized (CP) substrate integrated waveguide (SIW) cavity-backed antenna with wide axial ratio (AR) beamwidth, which can generate the right-hand CP (RHCP) or left-hand CP (LHCP) radiation through exciting different ports. Dual CP radiations are accomplished by an SIW directional coupler (DC) in the bottom layer, which provides the desired amplitude and phase conditions for two orthogonal slots. By superposing phase centers of linearly polarized (LP) electric field elements, the proposed antenna achieves a good performance of 3 dB AR beamwidth of 165° in the desired azimuth cut plane. Furthermore, an eight-element dual CP linear phased array with a wide-angle beam scanning ability is comprised by this antenna prototype. Numerical and measured results show that the array antenna can scan its main lobe from – 59° to 58°. In general, the proposed antenna array fed by the SIW structure satisfies the requirement of a multipolarization wireless communication system for low profile, simple structure, and easy integration with planar circuits. [ABSTRACT FROM AUTHOR]

The effort to confine the electromagnetic field by silicon passive metadevices has made the design of an on-chip wideband sub-terahertz (sub-THz) I/O redriver feasible, paving a new way toward energy-efficient and crosstalk-immune ON–OFF keying (OOK) communications. Two metadevices, namely spoof surface plasmon polaritons (SPPs) metawaveguide and split-ring resonator (SRR), are exploited to build the sub-THz low-crosstalk silicon channel and high-ON–OFF-ratio modulator, respectively. A sub-THz signal source combining the merit of spoof SPPs and SRR is introduced. A 140-GHz dual-channel redriver composed of these metadevices is fully integrated in a 65-nm CMOS technology. The redriver realizes both 27–1 and 231–1 13.5 Gb/s/lane for dual-channel OOK modulation. The measured energy efficiency is 2.6 pJ/bit/lane and the bit error rate (BER) is ≤10−12, demonstrating a crosstalk-immune sub-THz I/O system. The power consumption is 35.1 mW/lane and the active area of the redriver is 0.23 mm2. [ABSTRACT FROM AUTHOR]

Deep-subwavelength periodic metallic structures, which are also called plasmonic metamaterials, have received much attention due to their ability of supporting spoof surface plasmons polariton (SPP) modes. However, it is still difficult to obtain the dispersion relations of different modes for complicated plasmonic metamaterials with finite thickness. To solve the problem, we make further development of a field-network joint dispersion analysis method that was proposed recently so that the method can be used to analyze the spoof SPP structures with a certain thickness. The developed method not only allows us to predict the dispersion relations of complicated spoof SPP structures with finite thickness but also can be used to find a series of intrinsic high-order modes of the periodic metallic structures. As an example, we present the theoretical dispersion curves of the fundamental and high-order modes for a complicated spoof SPP structure, which have good agreements with the simulated results. Meanwhile, the calculated near fields also match the simulated and measured results well. [ABSTRACT FROM AUTHOR]

We propose to suppress high-power microwave pulses (HPMPs) using nonlinear dispersion and filtering natures of spoof surface plasmon polaritons (SSPPs). Frequency components of a short HPMP are distributed in time domain due to different group velocities and partly cutoff on SSPP transmission lines (TLs), leading to peak suppression of HPMP. To illustrate the protection mechanism in real microwave engineering, an SSPP mono-pulse antenna is designed. Sum and difference beam functions of the antenna are demonstrated by both simulations and experiments. For easy comparison, a microstrip mono-pulse antenna is also fabricated. HPMP incidences from the main lobe directions of the sum beam and difference beam are considered. Compared to the microstrip antenna, obvious suppression of HPMPs is observed in the SSPP mono-pulse antenna in different cases, which verifies the better performance to prevent HPMP damages by SSPPs. The proposed technology to suppress HPMPs by using SSPPs can find wide applications in radar and communication systems in the electronic warfare environment. [ABSTRACT FROM AUTHOR]