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.

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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

Microwave photonic systems process the electrical signal in optical domain so that the characteristics of the output optical signals include the transfer function of the signal processing link. In this paper, we review our recent works about a microwave photonic repeater, self-interference cancellation, and microwave signal coupling techniques. First, based on a photonic repeater consisting of a dual-polarized dual-parallel Mach-Zehnder modulator (DP-DPMZM) and a Polarization Controller (PC), four different down-conversion states can be performed. Two separate Local Oscillator signals (LO) also enable frequency down-conversion of microwave signals in different frequency bands. Secondly, a Dual-Parallel Dual-Drive Mach-Zehnder Modulator (DP-DDMZM) and a low-frequency LO signal source are used to achieve Self-Interference Cancellation and Harmonic Down-Conversion (SIC+HDC) for an In-Band Full-Duplex (IBFD) system. Finally, for the microwave photonic coupling technique, a Photonic Microwave Hybrid Splitter (PMHS) and a Photonic Microwave Hybrid Combiner (PMHC) are proposed, respectively. The PMHS and PMHC individually controls the amplitude and phase of the two signals by adjusting the Direct Current (DC) biases of modulators. Our proposed signal processing techniques are very promising for flexible microwave signal processing, radars, and wireless communications.

Optical domain controlled microwave signal processing technology

We presented a novel technique of generating arbitrary waveforms based on wavelength-to-time mapping (WTTM) without any dispersion. A variety of waveforms has been generated, including Gaussian, square, and other specific waveforms, is demonstrated experimentally. The arbitrary waveform generator feathers superior advantages such as low power loss, simple structure, and high reconfiguration.

Dispersion-free wavelength-to-time mapping method for optical arbitrary waveform generation

Multiple nonlinear states of a Fabry-Perot (FP) laser under external optical injection and their applications are
experimentally studied. The intensity noise of the FP laser has been demonstrated to be optimally suppressed under
injection locking state, and the comparison between stable locking range and noise suppression range at different
injection powers has been made. Photonic microwaves can be acquired at both period-one and period-two states. When
an external RF signal is added to the FP laser operated at period-one state, its nonlinear state is switched to period-two
state, which indicates the equivalence between external optical and electrical modulation added to the FP laser. At the
same time, the photonic microwave linewidth can be obviously narrowed as an effect of external RF modulation.

The nonlinear dynamics of an FP laser under external optical injection

We propose a technique to simultaneously realize microwave frequency conversion and idler filtering by polarization manipulating of an amplified spontaneous emission (ASE) source By simply adjusting the tunable differential group delay (DGD) introduced by a polarization division multiplexed (PDM) emulator, switchable and idler-free frequency conversion can be implemented Thanks to the intrinsic frequency selection of the dispersive delay structure, no electrical filter is involved to remove the mixing idlers, which ensures a broad operation bandwidth and flexible tunability In addition, the dispersion-induced mixing power fading and the environmental vibration sensitivity that exist in previous approaches are both avoided owing to the PDM optical paths The proposed method is theoretically and experimentally verified

Simultaneous microwave frequency conversion and idler filtering based on polarization manipulating of an amplified spontaneous emission source

In this paper, we review our recent works about optical domain modulation modulated microwave signal generation. A multi-format switchable microwave signal generator using a single dual-polarization dual-parallel Mach-Zehnder modulator is proposed and demonstrated. By changing the modulation state of the modulator, background-free amplitude shift keying (ASK), phase shift keying (PSK), and frequency shift keying (FSK) microwave signals can be generated. The background-free arbitrarily PSK microwave signals can be transmitted over long distances without power degradation. This work holds great promise for multifunctional radar and communication systems.

Ninghua Zhu

Papers

Optical domain controlled microwave signal processing technology

Dispersion-free wavelength-to-time mapping method for optical arbitrary waveform generation

The nonlinear dynamics of an FP laser under external optical injection

Simultaneous microwave frequency conversion and idler filtering based on polarization manipulating of an amplified spontaneous emission source

Multi-Format switchable microwave signal generation based on optical domain modulation