Ultra Wideband Signals and Systems in Communication Engineering

Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

Recent advances in photonic integration have propelled microwave photonic technologies to new heights. The ability to interface hybrid material platforms to enhance light–matter interactions has led to the development of ultra-small and high-bandwidth electro-optic modulators, low-noise frequency synthesizers and chip signal processors with orders-of-magnitude enhanced spectral resolution. On the other hand, the maturity of high-volume semiconductor processing has finally enabled the complete integration of light sources, modulators and detectors in a single microwave photonic processor chip and has ushered the creation of a complex signal processor with multifunctionality and reconfigurability similar to electronic devices. Here, we review these recent advances and discuss the impact of these new frontiers for short- and long-term applications in communications and information processing. We also take a look at the future perspectives at the intersection of integrated microwave photonics and other fields including quantum and neuromorphic photonics. This Review discusses recent advances of microwave photonic technologies and their applications in communications and information processing, as well as their potential implementations in quantum and neuromorphic photonics.

Integrated microwave photonics

A new class of planar optics has emerged using subwavelength gratings with a large refractive index contrast, herein referred to as high-contrast gratings (HCGs). This seemingly simple structure lends itself to extraordinary properties, which can be designed top-down based on intuitive guidelines. The HCG is a single layer of high-index material that can be as thin as 15% of one wavelength. It can be designed to reflect or transmit nearly completely and with specific optical phase over a broad spectral range and/or various incident beam angles. We present a simple theory providing an intuitive phase selection rule to explain the extraordinary features. Our analytical results agree well not only with numerical simulations but also experimental data. The HCG has made easy fabrication of surface-normal optical devices possible, including vertical-cavity surface-emitting lasers (VCSELs), tunable VCSELs, and tunable filters. HCGs can be designed to result in high-quality-factor (Q) resonators with surface-normal output, which is promising for wafer-scale lasers and optical sensors. Spatially chirped HCGs are shown to be excellent focusing reflectors and lenses with very high numerical apertures. This field has seen rapid advances in experimental demonstrations and theoretical results. We provide an overview of the underlying new physics and the latest results of devices.

/pdf/high-contrast-gratings-for-integrated-optoelectronics-3ykfc99oae.pdf

High-contrast gratings for integrated optoelectronics

A vertical-cavity surface emitting laser (VCSEL) was invented 30 years ago. A lot of unique features can be expected, such as low-power consumption, wafer-level testing, small packaging capability, and so on. The market of VCSELs has been growing up rapidly in recent years, and they are now key devices in local area networks using multimode optical fibers. Also, long wavelength VCSELs are currently attracting much interest for use in single-mode fiber metropolitan area and wide area network applications. In addition, a VCSEL-based disruptive technology enables various consumer applications such as a laser mouse and laser printers. In this paper, the recent advance of VCSEL photonics will be reviewed, which include the wavelength extension of single-mode VCSELs and their wavelength integration/control. Also, this paper explores the potential and challenges for new functions of VCSELs toward optical signal processing

https://cnst.nctu.edu.tw/mbe08/abstract/6-13.30-14.00-koyama.pdf

Recent Advances of VCSEL Photonics

A novel type of photonic background-free multiband arbitrarily phase-coded microwave signal generator with power fading elimination capability is reported. An $x$ -polarized phase modulated optical signal and a $y$ -polarized radio frequency (RF) modulated harmonic single-sideband (HSSB) optical signal are produced based on a dual-polarization quadrature phase shift-keying modulator (DP-QPSKM). After polarization modulation to intensity modulation conversion, a microwave signal with arbitrarily phase encoding in multiple frequency bands is generated. Benefiting from the phase modulation state of the driven electrical coded signal, the generated arbitrarily phase-coded signal has no baseband components. Moreover, the equivalent HSSB modulation ensures the system can realize antidispersion transmission of one-to-multi base stations (BSs). The main distinct highlights of our generator are multifunction. The proposed single-modulator-based photonic scheme can achieve phase encoding in arbitrary format over multiple frequency bands and transmit over long-distance single-mode fiber with the elimination of power fading simultaneously. This work is pretty promising in multiband radar systems for one-to-multi BSs transmission and can increase the detection range, range resolution, Doppler tolerance, and sensitivity of objective recognition of radars.

Photonic Generation and Antidispersion Transmission of Background-Free Multiband Arbitrarily Phase-Coded Microwave Signals

A tunable photonic temporal integrator with ultra-long integration time windows based on Raman-gain assisted phase-shifted silicon Bragg gratings

1 × N hybrid radio frequency photonic splitter based on a dual-polarization dual-parallel Mach Zehnder modulator

In this paper, we propose an interference technique that can provide a quantitative and ultrafine-resolution spectral analysis because the optical heterodyning is performed at nonzero frequency and interfering waves propagate in optical fiber. The spectrum of a laser consists of a large number of wave trains. Our study is focused on the features of wave trains. We demonstrate that wave trains emitting simultaneously have random frequency spacings, and the probability of occurrence of two or more joint wave trains with the same frequency is high. The estimated linewidth of the wave train is narrower than 1 mHz, corresponding to a wavelength range of 10(-23) m.

Hyperfine spectral structure of semiconductor lasers

A novel technique for generating narrow-linewidth microwave or millimeter-wave signals is proposed. In this scheme, a delayed self-injected distributed Bragg reflector laser diode, which is tuned by a low-frequency square-wave voltage, is used to generate two correlated lightwaves simultaneously. Experiments show that the 10-dB linewidth of generated microwave signals is reduced from 147 MHz to 68 kHz utilizing the proposed self-injection technique.

Ninghua Zhu

Papers

Photonic Generation and Antidispersion Transmission of Background-Free Multiband Arbitrarily Phase-Coded Microwave Signals

A tunable photonic temporal integrator with ultra-long integration time windows based on Raman-gain assisted phase-shifted silicon Bragg gratings

1 × N hybrid radio frequency photonic splitter based on a dual-polarization dual-parallel Mach Zehnder modulator

Hyperfine spectral structure of semiconductor lasers

Narrow-Linewidth Microwave Generation Using a Self-Injected DBR Laser Diode