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

Deep learning is able to functionally simulate the human brain and thus, it has attracted considerable interest. Optics-assisted deep learning is a promising approach to improve the forward-propagation speed and reduce the power consumption. However, present methods are based on a parallel processing approach that is inherently ineffective in dealing with serial data signals at the core of information and communication technologies. Here, we propose and demonstrate a serial optical deep learning concept that is specifically designed to directly process high-speed temporal data. By utilizing ultra-short coherent optical pulses as the information carriers, the neurons are distributed at different time slots in a serial pattern, and interconnected to each other through group delay dispersion. A 4-layer serial optical neural network (SONN) was constructed and trained for classification of both analog and digital signals with simulated accuracy rates of over 90% with proper individuality variance rates. Furthermore, we performed a proof-of-concept experiment of a pseudo-3-layer SONN to successfully recognize the ASCII (American Standard Code for Information Interchange) codes of English letters at a data rate of 12 Gbps. This concept represents a novel one-dimensional realization of artificial neural networks, enabling an efficient application of optical deep learning methods to the analysis and processing of serial data signals, while offering a new overall perspective for the temporal signal processing.

Temporal optical neurons for serial deep learning

Recently, external-cavity tunable lasers (ECTLs) have been widely used in WDM systems for their excellent characteristics, such as high side-mode suppression ratio (SMSR), low relative intensity noise (RIN) and narrow line width. In this paper, we propose an analytical model for external-cavity lasers using tunable etalons and elaborate on the selection of key parameters in the design scheme, which is rarely discussed in detail in previous researches. By numerically solving the model based on the rate equation and the transmission matrix, we analyzed the effects of different end-facet reflectivity on the SMSR, PI curves, electron and photon concentration distributions. In addition, By choosing appropriate physical parameters, we theoretically demonstrate an ECTL with a single wavelength tuning range of 1570.5–1603.6 nm (186.95–190.9 THz), and a power efficiency of 0.673 W/A, as well as an SMSR exceeds 50 dB.

Analytical Models for External Cavity Lasers Using Tunable Etalons

Optical spectral relation between the master and the frequency-locked slave lasers

Soliton molecules are the manifestation of attractive and repulsive interaction between optical pulses mediated by a nonlinear medium. However, the formation and breakup of soliton molecules are difficult to observe due to the transient nature of the process. Using the time stretch technique, we have been able to track the real-time evolution of the bound state formation in a femtosecond fiber laser and unveil different evolution paths towards a stable bound state. A non-stationary Q-switched mode-locking regime consisting of various transient solitons is observed in this transition period. We also observe additional dynamics including soliton molecule vibrations, collision and decay. Our findings uncover a diverse set of soliton dynamics in an optical nonlinear system and provide valuable data for further theoretical studies.

Time-Stretch Probing of Ultrafast Soliton Molecule Dynamics

The invention discloses a Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering. The Fourier domain mode-locked photoelectric oscillator comprises a tunable laser, a phase modulator, an optical fiber, a circulator, a photoelectric detector, an electric amplifier, a power divider and a pump laser, wherein the tunable laser, the phase modulator, the pump laser,the optical fiber and the photoelectric detector form a microwave photon filter together, and the transmission band of the microwave photon filter is determined by the wavelength difference between the tunable laser and a gain spectrum. By periodically adjusting the transmission band of the microwave photonic filter and synchronizing the change period of the filter with the delay of a signal transmitted for a circle in a photoelectric oscillator loop, the Fourier domain mode locking can be realized, and a swept-frequency microwave signal with adjustable center frequency and bandwidth broadband can be generated.

Ninghua Zhu

Papers

Temporal optical neurons for serial deep learning

Analytical Models for External Cavity Lasers Using Tunable Etalons

Optical spectral relation between the master and the frequency-locked slave lasers

Time-Stretch Probing of Ultrafast Soliton Molecule Dynamics

Fourier domain mode-locked photoelectric oscillator based on stimulated Brillouin scattering