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 present a method to realize a single-notch microwave photonic filter (MPF) based on interferometry of a single, low-coherence broadband optical source (BOS). Normally, a notch MPF based on low-coherence interferometry requires independent control of two optical sources located in different wavebands. In this work, we use a single BOS to accurately perform destructive interference between a bandpass and an all-pass MPF. A frequency and bandwidth freely tunable single-notch MPF can thus be realized. The proposed method is theoretically analyzed and experimentally demonstrated. A notch depth of more than 30 dB and a continuously tunable frequency range from 2 to 18 GHz was demonstrated in the proof-of-concept experiment.

Tunable notch microwave photonic filter based on interferometry of a single low-incoherence source.

Coplanar electrode directly modulated lasers with different cavity length

In wireless communication networks, the amplitude, phase, and frequency of a radio-frequency (RF) carrier is modulated to carry data signals. Generally, amplitude-shift keying (ASK), phase-shift keying (PSK) and frequency-shift keying (FSK) are served as the basic digital modulation formats. They are also the fundamental modulation schemes to form advanced modulation formats such as quadrature amplitude modulation (QAM) and quaternary phase-shift keying (QPSK). In order to extend the transmission distance of RF signals, radio-over-fiber technique has been proposed. In this context, it is highly desirable to generate ASK, PSK and FSK RF signals directly in the optical domain. In this paper, we report our recent works on the all-optical generation of ASK, PSK, and FSK RF signals based on cross polarization modulation (XPM) effect in nonlinear devices. For the generation of ASK RF signal, single-sideband (SSB) modulation and SSB upconversion is proposed to overcome the fiber chromatic dispersion induced power fading. Moreover, binary PSK RF signal is generated using XPM effect in a highly nonlinear fiber (HNLF). The precise phase shift of the PSK RF signal is independent of the optical power of the control beam. In addition, all-optical FSK RF signal is generated based on ASK to FSK modulation in an HNLF. The significant merit of this all-optical scheme is that the electrical bottleneck can be overcome thanks to the ultra-fast response of the nonlinear media. Thus, the carrier frequency of the phase-coded microwave signal is widely tunable. We have examined our schemes theoretically and experimentally. The proposed all-optical approach has the potential to realize uninterrupted transmission of the RF signals over fiber across different networks to the remote locations.

All-optical generation of ASK, PSK, and FSK radio-frequency signals

The invention discloses an integrated Fourier domain mode-locked photoelectric oscillator, an application and a communication system, and relates to the technical field of microwave photonics. The integrated Fourier domain mode-locked photoelectric oscillator comprises a photoelectric chip and an electronic chip; the photoelectric chip comprises a laser, a modulator, an optical notch filter and aphotoelectric detector which are connected through optical waveguides; the electronic chip comprises an electric amplifier and a power divider which are connected through a coplanar microwave waveguide. All devices needed by a Fourier domain mode-locked photoelectric oscillator are integrated on the chips, so that the size, the weight and the power consumption of the Fourier domain mode-locked photoelectric oscillator are greatly reduced; the tunable frequency sweeping microwave signal output can be realized; the frequency sweeping speed of an output signal is increased; and the integrated Fourier domain mode-locked photoelectric oscillator can be applied to a radar and the communication system.

Integrated fourier domain mode-locked optoelectronic oscillator, application and communication system

We observe the optical phase matching between a fiber taper and a high-order azimuthal whispering gallery mode (WGM) in a water droplet for the first time. The eccentricity of the droplet separates the wavelength of azimuthal modes. We evaluate the optical phase matching between the fiber taper mode and different azimuthal modes. In the experiments, the phase matching of a high-order azimuthal WGM (l-|m|=6) is realized around 1550 nm. The lifted azimuthal modes make high-efficient coupling easier for a probing light with narrow spectral range. They also have potential applications in detecting the shape fluctuation and eccentricity of water droplets.

Ninghua Zhu

Papers

Tunable notch microwave photonic filter based on interferometry of a single low-incoherence source.

Coplanar electrode directly modulated lasers with different cavity length

All-optical generation of ASK, PSK, and FSK radio-frequency signals

Integrated fourier domain mode-locked optoelectronic oscillator, application and communication system

Optical phase matching of high-order azimuthal WGM in a water droplet resonator