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

The relation between the output wavelengths of a laser array and the injection currents of all the channels is experimentally investigated and is found to be approximately linear. Based on this, the authors propose an optimization method of adjusting the wavelength distribution of the laser array by tuning the injection currents. In the proof-of-concept experiment, the linear wavelength residual is significantly reduced.

A Method of Adjusting Wavelengths of Distributed Feedback Laser Arrays by Injection Current Tuning

An on-chip microwave photonic phase shifter based on an electrically tunable feedback-coupled microring resonator (FCMR) is proposed and experimentally demonstrated. By properly adjusting the voltage applied on the FCMR, the transmission spectrum with different optical extinction ratios is realized while the phase shift range remains almost unchanged. This proposal solves the conflict between the large range of phase shift and small radio frequency (RF) power variation in the ring-resonator-based microwave photonics phase shifter. Finally, a microwave photonic phase shifter with phase tuning of over 172 deg from 20 to 30 GHz is obtained, and the RF power variation can be compressed less than 5 dB under a certain status tuned by the bias voltage.

Broadband microwave photonic phase shifter based on a feedback-coupled microring resonator with small radio frequency power variations.

Reconfigurable microwave photonic filter with negative coefficient based on an optoelectronic oscillator

A new method for fabricating electroabsorption modulator integrated with a distributed feedback laser (EML) was proposed. With the method we fabricated a selective area growth double stack active layer EML (SAG-DSAL-EML). Through comparing with other fabrication methods of EMLs, the characters and the merits of the new method presented in this paper were discussed.

A selective area growth double stack active layer electroabsorption modulator integrated with a distributed feedback laser

Photonic integrated circuits (PICs) technologies in China have made rapid progress in the past decade. In this paper, recent advances and future prospective of PICs in China are introduced and discussed, respectively. More than nine major projects in the field of PICs have been issued. Various material platforms and technologies have been developed to realize photonic integrated devices for many applications focusing on broadband communication, such as optical and wireless network, optical interconnects, and optical coherent communication. Many research achievements and breakthrough have been made under the support of these projects, such as silicon photonics transceiver, InP-based transceiver, and optical and microwave signal processing chips. It can be expected that the PICs technology will be continuously supported in the next five years, since it has been considered as one of the key enabling technologies for supporting several national major assignments and strategies, such as broadband communication, supercomputing and datacenter.

Ninghua Zhu

Papers

A Method of Adjusting Wavelengths of Distributed Feedback Laser Arrays by Injection Current Tuning

Broadband microwave photonic phase shifter based on a feedback-coupled microring resonator with small radio frequency power variations.

Reconfigurable microwave photonic filter with negative coefficient based on an optoelectronic oscillator

A selective area growth double stack active layer electroabsorption modulator integrated with a distributed feedback laser

Photonic Integration Circuits in China