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 a new scheme of microwave photonic filter (MPF) based on the polarization processing of a broadband optical source (BOS), which features single-bandpass response and a wide span of operation bandwidth. The BOS is orthogonally polarized by a polarization division multiplexing emulator (PDME) with a tunable time delay between the two polarization states and incident at ±45° to one principle axis of a polarization modulator (PolM). The PDME cascades a PolM, and a polarizer realizes a microwave modulation making the phase of the carrier able to be tuned while ±1st sidebands remain unchanged, which after propagating in a dispersive medium results in a tunable single-bandpass response in the RF domain. We experimentally verify the MPF. By adjusting the time delay and the optical spectrum bandwidth, the passband center frequency is continuously tuned from DC to 20 GHz and the 3 dB passband bandwidth changes while the optical spectrum bandwidth ranges from 1 to 4 nm.

Widely tunable single-bandpass microwave photonic filter based on polarization processing of a nonsliced broadband optical source

A scheme to perform ultrahigh-Q and single passband microwave photonic filter (MPF) with tunability is proposed and experimentally demonstrated. The single passband of the MPF is implemented by the stimulated Brillouin scattering (SBS) in an optical fiber. The ultrahigh-Q of the MPF is realized due to the ultra-narrow resonant linewidth of the fiber ring resonator, which compresses the bandwidth of the SBS dramatically. A MPF with a single passband and an ultra-narrow 3 dB bandwidth of 825±125  kHz over the wide center frequency tuning range of 2-16 GHz are achieved. The MPF also shows high out-of-band suppression exceeding 25 dB and small amplitude fluctuation of ±1.8  dB within the tuning range. The maximum Q-factor of the MPF is 17778. To the best of our knowledge, this is the highest Q single-passband MPF reported to date, with wide tunability, high out-of-band suppression, and a simple structure.

Ultrahigh-Q and tunable single-passband microwave photonic filter based on stimulated Brillouin scattering and a fiber ring resonator

We present a novel microwave photonic single-passband filter based on polarization control through simulated Brillouin scattering (SBS). The principle of the filter is based on a vector SBS process, which is different from the previously reported scalar SBS technique. For a radio-frequency (RF) modulated signal launched to the proposed processor, the state of polarization (SOP) of the optical carrier is rotated by 90° through a two-step SBS process. As a result, the RF signals cannot be recovered in the photodetector (PD). To recover the desirable RF signal, the SOP of the RF modulated sideband is rotated by another pump wave. Since the orthogonal polarization condition between the optical carrier and the sideband is destroyed, the desirable RF signal can be recovered. By adjusting the wavelength of the pump wave, the frequency response of the filter is tunable in a frequency range from ~2 to 20 GHz with out-of-band rejection of ~30 dB and -3 dB bandwidth of ~20 MHz. In addition, for any modulation format, it is converted to the single-sideband (SSB) modulation by the proposed filter. Therefore, the system is expected to be immune to the fiber dispersion-induced power fading. Moreover, it is independent of the modulation formats of the incoming signal wave. The filter structure can be inserted anywhere in conventional fiber-optic links without the need for modifying the link configuration and the transmitter.

All-Optical Microwave Photonic Single-Passband Filter Based on Polarization Control Through Stimulated Brillouin Scattering

We report a photonic approach to simultaneously realize frequency upconversion and phase coding of a radio-frequency (RF) signal based on polarization manipulation of optical signals An intermediate frequency (IF) signal is upconverted to the local frequency (LO) band using a dual-polarization dual-parallel Mach-Zehnder modulator, while a high-speed polarization modulator is used to realize high-speed phase coding of the upconverted signal The key advantage of the proposed method is that no optical or electrical filters are required to remove the residual IF, LO, and undesired downconverted signals, which ensures a broad operation bandwidth, excellent isolation, and wide tunability The proposed scheme is theoretically analyzed and experimentally verified

Ninghua Zhu

Papers

Widely tunable single-bandpass microwave photonic filter based on polarization processing of a nonsliced broadband optical source

Ultrahigh-Q and tunable single-passband microwave photonic filter based on stimulated Brillouin scattering and a fiber ring resonator

All-Optical Microwave Photonic Single-Passband Filter Based on Polarization Control Through Stimulated Brillouin Scattering

Simultaneous frequency upconversion and phase coding of a radio-frequency signal for photonic radars

Reconfigurable microwave photonic mixer based on dual-polarization dual-parallel Mach–Zehnder modulator