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.     

Tunability of the multiple-bandpass response of cascaded single-source and continuous-sample microwave photonic filters

We report a theoretical and experimental investigation on the structure and tuning capabilities of cascaded associations of microwave photonic filters composed of a single-source incoherent filter and a continuous-sample filter based on periodically-sliced broadband sources that undergo dispersion after being modulated. We derive the condition that guarantees both incoherent operation and cascading of the radio-frequency responses. This condition implies a lower bound for the ratio between resonance bandwidth (Δf) of the continuous-sample filter and the free spectral range (FSR) of the single-source filter, thus showing the possibility of cascading filters in two complementary regimes, Δf/FSR < 1 and >1. The tunability of the cascaded responses is also explored in a series of proof-of-concept experiments, where a static response of a single-tap, incoherent loop filter is reconfigured by use of a Solc filter. In particular, it is demonstrated a reconfigurable single and dual-bandpass cascaded response, which can be further modified by changes in dispersion, spectral period of the slicing filter, central wavelength or spectral width of the broadband source, and apodization of the resonance. The results are compared with the predictions of the Gaussian model for the degradation of resonances in continuous-sample filters due to second-order dispersion.     

Wide-band nulling system for antenna array based on a photonic microwave filter and optical delay lines

A nulling system for phased array antennas with broad bandwidth and reduced complexity is presented. The system is based on combining the output of an optical beamforming network with an optical transversal filter steered in the angle where a null is desired in a configuration that reduces the number of optoelectronic conversion compared to previous proposals. Preliminary experimental results to show the feasibility of the concept are provided between 2 and 6 GHz, showing null depths of 22, 10 and 19 dB at 2, 5 and 6 GHz, respectively.     

Reconfigurable photonic differentiators based on all-optical phase modulation and linear filtering

We theoretically propose a novel scheme to implement two types of optical differentiators using all-optical phase modulation and linear filtering. Differences between the two differentiators rely on whether the differentiated signals are formed on the optical intensity or optical field of the output signal, which in turns depends on the relative shift between the probe wavelength and the closest notches of a linear filter. A proof-of-concept experiment is carried out using a semiconductor optical amplifier and a fiber-based delay interferometer (DI). Both differentiators are obtained for periodical Gaussian pulses and pseudo random non-return-to-zero signals at various data rates. Defined as the mean absolute deviation of the measured waveform from the ideal one, total average errors of less than 18% are observed in all cases. The impact of probe wavelength on the total average errors is investigated. Due to periodical feature of the DI spectrum, we also demonstrate the capability of multi-channel differentiation.     

Analytical design of photonic band-gap fibers and their dispersion characteristics

The paper essentially deals with the analysis of photonic band-gap fibers in analogy with the electron wave motion in periodic crystal lattice. As such, the analyses are based on Bloch formulation. The dispersion characteristics of such fibers are presented by considering some illustrative values of design parameters. The effect of design parameters on the dispersion characteristics is also presented in terms of the variation of widths of allowed and forbidden bands of band-gap fibers. It is found that the number of allowed bands increases with the increase in difference between refractive indices of different layers. Further, widths of the allowed and forbidden bands increase with the increase in layer thickness.     

Optical clock recovery with dual-wavelength output from degraded RZ and NRZ signals

A novel scheme to implement clock recovery from degraded signals is proposed and demonstrated based on an optoelectronic oscillator and a dual-wavelength mode-locked fiber ring laser with distributed dispersion cavity. The scheme can obtain wavelength-tunable optical clocks at two wavelengths, which is highly desirable for composite optical logic gates, cascaded optical signal processing modules or optical signal processing modules that need synchronized pulses at multiple wavelengths. In addition, the scheme can operate in both RZ and NRZ systems. The feasibility of the method is demonstrated by an experiment, in which dual-wavelength 10-GHz optical clock with a timing jitter less than 170 fs is obtained from 10-Gb/s degraded RZ and NRZ signals. The optical clocks can be tuned from 1530 to 1565 nm.     

Digital synthesis of programmable photonic integrated circuits

Programmable photonic waveguide meshes can be programmed into many different circuit topologies and thereby provide a variety of functions.Due to the complexity of the signal routing in a general mesh,a particular synthesis algorithm often only accounts for a specific function with a specific cell configuration.In this paper,we try to synthesize the programmable waveguide mesh to support multiple configurations with a more general digital signal processing platform.To show the feasibility of this technique,photonic waveguide meshes in different configurations(square,triangular and hexagonal meshes)are designed to realize optical signal interleaving with arbitrary duty cycles.The digital signal processing(DSP)approach offers an effective pathway for the establishment of a general design platform for the software-defined programmable photonic integrated circuits.The use of well-developed DSP techniques and algorithms establishes a link between optical and electrical signals and makes it convenient to realize the computer-aided design of optics–electronics hybrid systems.     

Ultrafast mode switching based on a micro-ring laser

Injection locking and multi-mode switching characteristics of a semiconductor ring laser with the radius of 10 μm are investigated based on a nonlinear time domain multimode rate-equation model. The stable injection locking regions for different target modes are studied as the function of detuning frequency and injection power ratio. The results show that ultra-wide detuning range of ∼100 GHz wide at 5 dB injection power ratio and ultra-low switching power ratio of −27 dB can be realized for this micro-ring laser device. Optimal detuning value and high injection power lead to the minimal switching time. An ultrafast response time of 10 ps indicates that a 10 μm-radius SRL can be utilized for ultrafast all-optical scenarios and high-speed tunable lasers.     

Electroluminescence properties of light emitting devices based on silicon nanocrystals

We have fabricated MOS devices where the dielectric layer consists of a substoichiometric SiO_x (x<2) thin film, annealed at 1100°C for 1 h to induce the separation of the Si and SiO₂ phases, with the formation of silicon nanocrystals (nc) embedded in the insulating matrix. We have studied the electroluminescence (EL) properties of such devices as a function of the current density and of the temperature. We have evaluated the excitation cross section of Si nc under electrical pumping at room temperature and at low temperature (12 K). Moreover, we have used the experimental EL intensities and decay times to evaluate the radiative rate as a function of the temperature.     

Microcavity filters based on hexagonal lattice 2-D photonic crystal structures embedded in ridge waveguides

Two-dimensionally periodic photonic crystal microcavity filters in a ridge waveguide format have been designed and fabricated. Transition mode-matching features were added to increase the optical throughput by more than a factor of two. An increase of Q-factor (more than 100%) was achieved by the addition of two further rows of photonic crystal holes to the microcavity filters. Attempts have also been made to tailor the filter response by applying design concepts used in other Bragg-grating optical filter technologies.     

Generalized optical filters using a nonlinear micro ring resonator system

We present the interesting results of nonlinear behaviors of a soliton pulse within a nonlinear micro ring resonator system, where the optical filter characteristics in terms of frequency, wavelength and time can be functioned by using the chaotic filter within the micro ring resonator system. There are three forms of applications using the chaotic soliton behaviors and optical filter characteristics presented. Firstly, the simultaneous up-link and down-link frequency bands can be filtered and the required frequency bands obtained. Secondly, we propose the simple system of an extremely narrow light pulse generation over the spectrum range, where the required wavelengths can be filtered and obtained. Finally, a simple system of fast light generation by using a soliton pulse circulating in the integrated micro ring devices is proposed. Using such a system, an attosecond pulse and beyond can be easily filtered and obtained.     

Investigation of multiwavelength clock recovery based on heterodyne beats of sideband-filtered signal

We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an optical sideband-filtered signal. The oscillating clock signal is recovered when the filtered sideband is combined with a stable local oscillator. The filtering is performed with an optical resonator, which by nature provides possibility for multiwavelength operation. The local oscillator could be realized by a multiwavelength laser, whose emission wavelengths are injection seeded with carrier wavelengths of the input data. The output signal of such a configuration benefits from a reduced bit-pattern effect and a stable offset level. The sideband filtering is demonstrated for 23 simultaneous channels at 100 GHz DWDM grid, each hosting a data stream of 10 Gbit/s.     

Light emitting devices based on silicon nanostructures

In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light emitting devices based on silicon nanostructures. The performances of crystalline, amorphous and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 μm. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature EL with the advantage to be formed at a temperature of only 900 °C, remarkably lower than the temperature needed for the formation of Si nanocrystals (1100 °C or higher). To improve the extraction of the light, we coupled the emitting system with a 2D photonic crystal structure properly fabricated with ULSI technology to reduce the total internal reflection of the emitted light. We demonstrate that the extraction efficiency is increased by a factor of 4. Finally, the light emission from devices based on Er-doped Si nanoclusters has been studied and in particular we have investigated the luminescence quenching processes limiting quantum efficiency in these devices. In fact the carrier injection, that determines the excitation of Er ions through electron–hole recombination, at the same time produces an efficient non-radiative Auger de-excitation with trapped carriers. These data are presented and the implications on the device performances discussed.     

Realization of optical coupling based on semi-circular photonic crystals

In this paper, a new structure used to realize optical coupling is proposed. This structure is made up of half of a two-dimensional circular photonic crystal and a photonic crystal waveguide. It is shown that the peak value of the transmissivity shifts by choosing appropriate parameters of SCPC. This structure has great potential in optical integration and other areas.     

O波段8通道硅基二氧化硅平坦化阵列波导光栅的设计及制备

设计并制作了一款应用于IEEE 200/400GbE标准802.3bs的阵列波导光栅.该阵列波导光栅使用2.0%的超高折射率差硅基二氧化硅材料,使得芯片尺寸及损耗较小.为了获得平坦化的接收光谱,将输出波导进行展宽,采用多模波导结构,激发若干个高阶模,数个模式叠加使得原本高斯状的光谱顶部产生平坦化,形成箱形接收光谱.设计的阵列波导光栅的中心波长为1 291.10nm,通道间隔为800GHz,芯片尺寸为11mm×4mm.经过等离子增强化学气相沉积和感应耦合等离子刻蚀工艺制备了芯片,测试结果表明最小的插入损耗为-3.3dB,相邻通道间串扰小于-20dB,单通道1dB带宽在2.12~3.06nm范围,实现了良好的解复用和平坦化效果,在实际光通信系统中有一定的实用价值.     

Novel tunable microwave photonic notch filter using a 3 × 3 coupler based Sagnac loop

We propose a simple and stable structure to realize a tunable negative coefficients microwave photonic notch filter. A 3 × 3 coupler based Sagnac loop interferometer with an asymmetrically placed phase modulator is used to acquire the notches. Our system is simply implemented and with good stability. Theoretical analysis and experimental results are presented and show a good agreement. The structure is proved to be a robust filter with more than 35 dB rejection deep notches.     

Novel single-mode and polarization maintaining photonic crystal fiber

In this paper, we present and propose a novel structure for improved birefringence and single-mode propagation condition photonic crystal fiber (PCF) in a broad range of wavelength. The birefringence of the fundamental mode and single mode property in such a PCF is numerically estimated by employing full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). The simulation results illustrate that we can achieve a high birefringence and perfect single-mode condition by employing silica-filled into one-line elliptical air holes parallel to x-axis and rotated by an angle. Obviously, the proposed PCF is quite useful for optical devices.     

Wide-field-of-view narrow-band spectral filters based on photonic crystal nanocavities

We describe a novel approach to implementing wide-field-of-view narrow-band spectral filters, using an array of resonant nanocavities consisting of periodic defects in a two-dimensional three-material photonic-crystal nanostructure. We analyze the transmissivity of this type of filter for a range of wavelengths and in-plane incidence angles as a function of the defect's refractive index, the number of layers in the photonic-crystal reflectors, and the period of the defects and find that this structure diminishes the angular sensitivity of the resonance condition relative to that of a standard multilayer filter.     

Analysis and experiment of all-optical time-interleaved multi-channel regeneration based on higher-order four-wave mixing in a fiber

Simultaneous all-optical multi-channel regeneration based on second-order four-wave mixing (FWM) in a single highly nonlinear fiber (HNLF) is studied. Interchannel crosstalk, especially cross gain saturation and generation of interchannel FWM, is avoided by properly time-interleaved channels. Preliminary experiment of 2 ch × 10 Gbit/s operation shows simultaneous noise reduction of the two channels and good agreement with numerical analysis. Numerical investigation on 2 ch × 40 Gbit/s operation using the same parameters as the experiment shows that the regeneration can improve qualities of both channels. For more number of channels and higher speed of operation, several parameters need to be adjusted to avoid interchannel crosstalks. Time synchronization techniques for the input channels are also discussed.     

High quality factor polychromatic filters based on hybrid photonic structures

In this work, we have investigated theoretically the transmission properties of a hybrid quasi-periodic photonic system, which is a combination of a periodic H(LH)⁵ and a quasi-periodic multilayer structure(QPMS)^P: H(LH)⁵(QPMS)^PH(LH)⁵, where P is the repetitive number of QPMS. Simulation results showed that the number, position and the quality factor of the transmission peaks depend on the repetitive number (P) and the incident angle for both the (TE) and (TM) polarizations. Furthermore, we have studied the influence of two air layers (A) inside the previous structures at the 12^th and 29^th positions:H(LH)⁵A (QPMS)²A H(LH)⁵. The results illustrate that the introducing of the defect layers in our system provides a possible mechanism for optimizing the parameters of the transmission peaks, thus the obtaining of polychromatic filters with a high quality factor (Q) and with a minimum of layers and thickness.