The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Electronics based on two-dimensional materials

We review the current status of single-photon-source and single-photon-detector technologies operating at wavelengths from the ultraviolet to the infrared. We discuss applications of these technologies to quantum communication, a field currently driving much of the development of single-photon sources and detectors.

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Invited review article: Single-photon sources and detectors

The current status of lithium-niobate external-modulator technology is reviewed with emphasis on design, fabrication, system requirements, performance, and reliability. The technology meets the performance and reliability requirements of current 2.5-, 10-, and 40-Gb/s digital communication systems, as well as CATV analog systems. The current trend in device topology is toward higher data rates and increased levels of integration. In particular, multiple high-speed modulation functions, such as 10-Gb/s return-to-zero pulse generation plus data modulation, have been achieved in a single device.

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A review of lithium niobate modulators for fiber-optic communications systems

Digital filters underpin the performance of coherent optical receivers which exploit digital signal processing (DSP) to mitigate transmission impairments. We outline the principles of such receivers and review our experimental investigations into compensation of polarization mode dispersion. We then consider the details of the digital filtering employed and present an analytical solution to the design of a chromatic dispersion compensating filter. Using the analytical solution an upper bound on the number of taps required to compensate chromatic dispersion is obtained, with simulation revealing an improved bound of 2.2 taps per 1000ps/nm for 10.7GBaud data. Finally the principles of digital polarization tracking are outlined and through simulation, it is demonstrated that 100krad/s polarization rotations could be tracked using DSP with a clock frequency of less than 500MHz.

Digital filters for coherent optical receivers.

Optical fiber transmission is impacted by linear and nonlinear impairments. We study the use of digital backpropagation (BP) in conjunction with coherent detection to jointly mitigate dispersion and fiber nonlinearity. We propose a noniterative asymmetric split-step Fourier method (SSFM) for solving the inverse nonlinear Schrodinger equation (NLSE). Using simulation results for RZ-QPSK transmitted over terrestrial systems with inline amplification and dispersion compensation, we obtain heuristics for the step size and sampling rate requirements, as well as the optimal dispersion map.

Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation

We show that modulational instability may arise even in the normal group-velocity dispersion regime of an optical fiber when the fiber loss (gain) varies depending on the wavelength. A simple analytical expression for the instability gain is obtained, which reveals that the odd-order terms of the loss dispersion are responsible for this phenomenon. The instability gain is measured experimentally in an optical-parametric-amplification configuration. Large parametric gain is induced in a non-phase-matched regime as we apply narrow band loss at the idler wavelength.

Modulational Instability and Parametric Amplification Induced by Loss Dispersion in Optical Fibers

We propose a novel structure of fiber laser to achieve single-frequency and polarization-stable oscillation without using a polarization-maintaining (PM) active fiber. The proposed structure has two stabilization mechanisms. First, the laser has a Fabry-Perot cavity composed of Faraday-rotator mirrors (FRMs) to stabilize the polarization-mode competition. We make comparison of polarization-mode stability in various types of cavity structure, and confirm that the Fabry-Perot cavity composed of a non-PM fiber and FRMs has ideal stability similar to the ring cavity composed of a PM fiber and a polarizer. Second, in order to stabilize the longitudinal mode, the laser has an intracavity etalon specially designed to maximize its finesse by removing undesired reflections from the etalon. In the experiment, we construct a fiber laser composed of a non-PM erbium-doped fiber (EDF), FRMs, and an intracavity Fabry-Perot etalon. The polarization-stable and single-frequency operation of the laser is demonstrated.

Polarization-stable and single-frequency fiber lasers

A single‐photon detector using a Si avalanche photodiode (APD) has been constructed. A trans‐impedance type front‐end circuit was employed in order to achieve a high signal‐to‐noise ratio. The APD and front‐end circuit were cooled in liquid nitrogen to reduce dark count rate and circuit noise. The system performances were measured, and the achieved dark count rate and total quantum efficiency were 0.08 count/s and 5%, respectively. The sensitivity was evaluated to be of the order of 10−19 W. The APD single‐photon detector was demonstrated to be available for measurement of the ultraweak biochemiluminescence at the order of 10−19 W/mm2 from brain slices, i.e., hippocampal slices. It was shown that the addition of tetrodotoxin to the hippocampal slice caused a decrease in the intensity of biochemiluminescence.

Ultrahigh sensitivity single‐photon detector using a Si avalanche photodiode for the measurement of ultraweak biochemiluminescence

We present a design guideline for ultrafast wavelength conversion using a nonlinear optical loop mirror (NOLM) composed of a dispersion-shifted fiber (DSF). By using the guideline, the wavelength allocation, the loop length, and the signal peak pourer are optimized for given values of the nonlinear coefficient and dispersion slope of the DSF. We actually construct a NOLM wavelength converter composed of a 50-m-long highly nonlinear DSF, and demonstrate 26-nm wavelength conversion of 500-fs pulse trains with a relatively low peak power of 4 W.

All-optical wavelength conversion of 500-fs pulse trains by using a nonlinear-optical loop mirror composed of a highly nonlinear DSF

The unique and practical benefits of the use of bismuth-oxide-based nonlinear fiber (Bi-NLF) in implementing a four-wave-mixing (FWM)-based wavelength converter for fiber-optic-communication-system applications are experimentally demonstrated. First, the Kerr-nonlinearity and stimulated-Brillouin-scattering (SBS) characteristics of our fabricated Bi-NLF are experimentally investigated. The Bi-NLF is found to have the superior advantage of a significantly high SBS threshold in addition to its ultrahigh Kerr nonlinearity /spl gamma/ of /spl sim/1100 W/sup -1//spl middot/km/sup -1/, compared to the conventional silica-based highly nonlinear fiber. Next, the authors perform an experiment for the FWM-based wavelength conversion of a non-return-to-zero (NRZ) signal within a 40-cm length of the Bi-NLF fusion spliced to standard silica fibers by using a continuous-wave (CW) high-power pump beam. Error-free tunable wavelength conversion over a 10-nm bandwidth is readily achieved. No SBS-suppression scheme is employed for the pump due to the high SBS threshold, which simplifies the system configuration and improves the quality of the wavelength-converted signal.

Bismuth-oxide-based nonlinear fiber with a high SBS threshold and its application to four-wave-mixing wavelength conversion using a pure continuous-wave pump

Kazuro Kikuchi

Papers

Modulational Instability and Parametric Amplification Induced by Loss Dispersion in Optical Fibers

Polarization-stable and single-frequency fiber lasers

Ultrahigh sensitivity single‐photon detector using a Si avalanche photodiode for the measurement of ultraweak biochemiluminescence

All-optical wavelength conversion of 500-fs pulse trains by using a nonlinear-optical loop mirror composed of a highly nonlinear DSF

Bismuth-oxide-based nonlinear fiber with a high SBS threshold and its application to four-wave-mixing wavelength conversion using a pure continuous-wave pump