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

We propose and experimentally verify an approach to generate pulsed microwave signal with continuously tunable phase and discrete tuning in microwave frequency based on phase shifted Lyot optical filter in conjunction with wavelength-to-time mapping technology. The Lyot optical filter with the discretely tunable spectral spacing is realized by changing the state of polarization of the bidirectionally propagated optical signals. The frequency response of the filter is continuously tuned over a full free-spectral range (FSR) keeping its shape and FSR unchanged by simple adjusting the bias voltage of the phase modulator. The proposed approach could also obtain pulsed microwave frequency multiplication with a discretely tunable multiplication factor by simply cascading multiple Lyot optical filters in the form of series. The proposed scheme is theoretically analyzed and experimentally demonstrated.

Photonic Generation of Pulsed Microwave Signal Based on Phase Shifted Lyot Optical Filter

Parity-time (PT) symmetry is a new method to get single mode operation in lasers, mostly, micro-ring lasers. In this study, we propose and experimentally demonstrate an electrically pumped PT symmetric Fabry-Perot (FP) laser which can work with a mode selection. The proposed laser could achieve the PT symmetric condition by an electrical manipulation of the interplay between gain and loss in two FP resonators. The single mode lasing is demonstrated at 1574.6nm with a 20.81dB sidemode suppression ratio.

Observation of parity-time symmetry in electrically pumped FP laser

The invention belongs to the technical field of optical communication and discloses a time domain Talbot effect based time domain stealth system. The time domain stealth system comprises a signal generating device and a stealth device, the signal generating device is used for generating optical pulses and modulating signals, and the stealth device is used for realizing time domain stealth throughintroduction of a chromatic dispersion value according with an equation as shown in the specification. By introduction of a time domain average effect of the time domain Talbot effect to a time domainstealth conception, energy of pulse sequences with modulated intensity information is redistributed to realize average in a certain time range, and thus, obtained output light looks the same as output light of a light source, and time domain stealth is realized.

Time domain Talbot effect based time domain stealth system

To overcome the beam squint in wide instantaneous frequency, we review a number of system-level optical controlled phase array antennas for beam forming. The optical delay network based on a fiber device in terms of topological structure of an N-bit optical switch, fiber grating, high-dispersion fiber, and vector-sum technology is discussed, respectively. Lastly, an integrated circuit is simply summarized.

Optically controlled phase array antenna [Invited]

In modern radar system, pulse compression technique has been widely used to increase the detection distance and range resolution. To enlarge the pulse compression ratio, the microwave signals are often phase modulated, such as phase-coded or frequency chirped. Conventionally, the phase-modulated microwave signals generated by electrical methods suffer from low microwave carrier frequency, limited bandwidth, low data rate and high transmission loss. Photonic-assisted generation and transmission of phase-modulated signals is a promising candidate to overcome these limitations In this paper, we review our recent works about the photonic generation and transmission of phase-modulated microwave signals, including the simultaneously frequency up-conversion and phase-coding, background-free frequency-doubled phase-coded microwave signal generation, phase-coded microwave pulse generator by optoelectronic oscillation (OEO), as well as transmission of dual-chirped microwave signals with chromatic-dispersion-induced power fading (CDIP) compensation and elimination technology. These works represent the new progresses in photonic approaches to generate and transmit phase-modulated microwave signals, which has great potential in the modern radar system.

Ninghua Zhu

Papers

Photonic Generation of Pulsed Microwave Signal Based on Phase Shifted Lyot Optical Filter

Observation of parity-time symmetry in electrically pumped FP laser

Time domain Talbot effect based time domain stealth system

Optically controlled phase array antenna [Invited]

Photonic generation and transmission of phase-modulated microwave signals