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 invention discloses a non-linear gain based active photonic integrator The non-linear gain based active photonic integrator comprises a phase-shift Bragg grating on a silicon-based ridge waveguide as well as a p type heavily doped region and an n type heavily doped region which are located on two sides of the grating, wherein the phase-shift Bragg grating works in a transmission mode According to the non-linear gain based active photonic integrator, integral operation can be performed on arbitrary input signals, power loss in an integrating process of the input signals is compensated through stimulated Raman scattering in the silicon waveguide, and an ultra-long integration time window is realized; the integration time window can be adjusted in a large range through control of pump light power, and the flexibility of the integrator is greatly improved; meanwhile, the silicon-based grating structure can be compatible with a CMOS (complementary metal oxide semiconductor) technology very well, on-chip integration and large-scale production are facilitated, and the non-linear gain based active photonic integrator has great application potential

Non-linear gain based active photonic integrator and method

We first report and numerically investigate sampled Brillouin dynamic gratings (SDBG) realized in optical fibers. The introduction of sample as an extra degree of freedom opens up possibilities for frequency control of stimulated Brillouin scattering.

Proposal of Sampled Brillouin Dynamic Gratings

The invention discloses a narrow-ridge distributed feedback laser with a mode field diffusion structure and application thereof. The distributed feedback laser comprises an N-surface electrode layer,a substrate layer, a buffer layer, a first waveguide layer, a multiple quantum well active layer, a second waveguide layer, a grating layer, an etching self-stop layer, a cladding layer, an ohmic contact layer, and a P-plane electrode layer; and the cladding layer and the ohmic contact layer are etched to form a ridge waveguide, and the ridge waveguide comprises a straight waveguide and a mode field diffusion structure. The ridge width in the horizontal direction is shrunk, disconnection of the end face ridges and deposition of a layer of low-refractive-index material film on the end face arerealized, the mode field area of output laser can be effectively increased, the power density of the end face of the laser is reduced, the damage threshold of the end face of the laser is improved, the maximum injection current is increased, the bandwidth is increased, the stray-free dynamic range is enlarged, the high-frequency response characteristic of the laser is improved, and the modulationrate is increased.

Narrow-ridge distributed feedback laser with mode field diffusion structure and application thereof

Experimental demonstration of filter parameters’ effect on the performance of all-optical thresholding

A photonic-assisted frequency downconverter with self-interference cancellation and fiber dispersion elimination is proposed for in-band full-duplex (IBFD) radio-over-fiber (ROF) systems based on stimulated Brillouin scattering. In this work, a dual-polarization Mach-Zehnder modulator (DPol-MZM) is employed to cancel the self-interference signal in the optical domain, thus the proposed system has a large operation bandwidth without the limitation of the electrical bottleneck. Meanwhile, a widely tunable microwave photonic filter (MPF) based on stimulated Brillouin scattering (SBS) is constructed to perform carrier-suppressed single-sideband modulation of LO. Therefore, the proposed photonic frequency downconverter is naturally free from fiber dispersion. Furthermore, thanks to the characteristics of the SBS-based MPF, such as large out-of-band rejection ratio, high resolution and wideband tunability, the proposed system has a high flexibility and downconversion efficiency, which is of great significance for IBFD ROF systems.

Photonic-assisted frequency downconverter with self-interference cancellation and fiber dispersion elimination based on stimulated Brillouin scattering.

Ninghua Zhu

Papers

Non-linear gain based active photonic integrator and method

Proposal of Sampled Brillouin Dynamic Gratings

Narrow-ridge distributed feedback laser with mode field diffusion structure and application thereof

Experimental demonstration of filter parameters’ effect on the performance of all-optical thresholding

Photonic-assisted frequency downconverter with self-interference cancellation and fiber dispersion elimination based on stimulated Brillouin scattering.