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 demonstrate a novel scheme to generate ultra-wideband (UWB) triplet pulses based on four-wave mixing and phase-to-intensity modulation conversion. First a phase-modulated Gaussian doublet pulse is generated by four-wave mixing in a highly nonlinear fiber. Then an UWB triplet pulse is generated by generating the first-order derivative of the phase-modulated Gaussian doublet pulse using an optical filter serving as a frequency discriminator. By locating the optical signal at the linear slope of the optical filter, the phase modulated Gaussian doublet pulse is converted to an intensity-modulated UWB triplet pulse which well satisfies the Federal Communications Commission spectral mask requirements, even in the extremely power-restricted global positioning system band.

Generation of ultra-wideband triplet pulses based on four-wave mixing and phase-to-intensity modulation conversion

We experimentally demonstrate a perfectly orthogonal optical single-sideband signal generation technique using stimulated Brillouin scattering. By using both the Brillouin gain and loss, a perfectly orthogonal optical single-sideband signal is achieved. In addition, the modulation depth of the single-sideband signal is adjustable by separately tuning the gain and loss for the optical carrier.

Perfectly Orthogonal Optical Single-Sideband Signal Generation Based on Stimulated Brillouin Scattering

A directly-modulated distributed-feedback laser module has been achieved with a ridge-waveguide laser chip in our laboratory. It is packaged in butterfly housing with a K connector, and the bandwidth of the laser module is up to 24 GHz with in-band flatness of ±3 dB. It shows a high linearity with input 1-dB compression point of higher than 23 dBm and third-order intercept of 32.2 dBm at 24 GHz. Meanwhile, the packaged DFB laser module gives rather low relative intensity noise of less than -150 dB/Hz when the bias current is 75 mA and it can show a great performance in analog optical communication systems.

24-GHz Directly Modulated DFB Laser Modules for Analog Applications

We theoretically and experimentally demonstrate a novel broadband phase-to-intensity modulation conversion technique for microwave photonics processing system. The technique is based on optical carrier phase shift of a phase modulated signal using stimulated Brillouin scattering. More than 360 ° carrier phase shift can be achieved. By simply adjusting the carrier phase shift while preserving its amplitude unchanged, the phase modulation can be fully or partially converted to intensity modulation. The main advantage of the proposed method lies in its broadband nature since the SBS is only imparted on the optical carrier and the phase modulated sidebands are not affected as long as the modulating frequency is higher than the Brillouin bandwidth. In addition, as a microwave photonics processing application, we demonstrate the dispersion induced power penalty control in radio-over-fiber systems using the proposed technique. Experimental results match well with the theoretical prediction.

Broadband Phase-to-Intensity Modulation Conversion for Microwave Photonics Processing Using Brillouin-Assisted Carrier Phase Shift

A wide-spectrum, ultra-stable optical frequency comb (OFC) module with 100 GHz frequency intervals based on a quantum dot mode locked (QDML) laser is fabricated by our lab, and a scheme with 12.5 Gb/s multi-channel broadcasting transmission for free-space optical (FSO) communication is proposed based on the OFC module. The output power of the OFC is very stable, with the specially designed circuit and the flatness of the frequency comb over the span of 6 nm, which can be limited to 1.5 dB. Four channel wavelengths are chosen to demonstrate one-to-many channels for FSO communication, like optical wireless broadcast. The outdoor experiment is established to test the bit error rate (BER) and eye diagrams with 12.5 Gb/s on-off keying (OOK). The indoor experiment is used to test the highest traffic rate, which is up to 21 Gb/s for one-hop FSO communication. To the best of our knowledge, this scheme is the first to propose the realization of one-to-many broadcasting transmission for FSO communication based on the OFC module. The advantages of integration, miniaturization, channelization, low power consumption, and unlimited bandwidth of one-to-many broadcasting communication scheme, shows promising results on constructing the future space-air-ground-ocean (SAGO) FSO communication networks.

Ninghua Zhu

Papers

Generation of ultra-wideband triplet pulses based on four-wave mixing and phase-to-intensity modulation conversion

Perfectly Orthogonal Optical Single-Sideband Signal Generation Based on Stimulated Brillouin Scattering

24-GHz Directly Modulated DFB Laser Modules for Analog Applications

Broadband Phase-to-Intensity Modulation Conversion for Microwave Photonics Processing Using Brillouin-Assisted Carrier Phase Shift

12.5 Gb/s multi-channel broadcasting transmission for free-space optical communication based on the optical frequency comb module.