There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Microwave photonics, which brings together the worlds of radiofrequency engineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years and is set to have a bright future. The technology makes it possible to have functions in microwave systems that are complex or even not directly possible in the radiofrequency domain and also creates new opportunities for telecommunication networks. Here we introduce the technology to the photonics community and summarize recent research and important applications.

Microwave photonics combines two worlds

Course Description This is an advanced course in which we explore the field of Statistical Optics. Topics covered include such subjects as the statistical properties of natural (thermal) and laser light, spatial and temporal coherence, effects of partial coherence on optical imaging instruments, effects on imaging due to randomly inhomogeneous media, and a statistical treatment of the detection of light. Development of this more comprehensive model of the behavior of light draws upon the use of tools traditionally available to the electrical engineer, such as linear system theory and the theory of stochastic processes.

http://ieeexplore.ieee.org/iel5/3/23094/01073023.pdf

Statistical optics

Broadband and low loss capability of photonics has led to an ever-increasing interest in its use for the generation, processing, control and distribution of microwave and millimeter-wave signals for applications such as broadband wireless access networks, sensor networks, radar, satellite communitarians, instrumentation and warfare systems. In this tutorial, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion. Challenges in system implementation for practical applications and new areas of research in microwave photonics are also discussed.

Microwave Photonics

A new photonic-based beamforming network that can realize a large number of simultaneous and independent beams in a wide-band phased-array antenna, and which eliminates optical beat-noise interference is presented. It is based on discrete and chirped Bragg-grating true-time delay elements and photodetector arrays at each beam port. This achieves a highly parallel delay-processing structure for signal equalization and eliminates the fundamental optical beat-noise limitation to the realization of large array sizes. Results show a very substantial reduction in the number of interconnects required of 98.4% for a 512-beam array and 99.2% for a 1024-beam array, in comparison to conventional beamforming techniques.

Optical-fiber grating-based beamforming network for microwave phased arrays

A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.

Photonic bandpass filters with high skirt selectivity and stopband attenuation

Photonic signal processing offers the prospect of realising extremely high multi-GHz sampling frequencies, overcoming inherent electronic limitations. These processors provide new capabilities for realising high time-bandwidth operation and high-resolution performance. In-fibre signal processors are inherently compatible with fibre optic microwave systems, and can provide connectivity with in-built signal conditioning. Recent new methods in wideband signal processors including high-resolution, arbitrary response, low noise, programmable processing, beamforming, and ultra-wide continuous filter tunability, are presented.

Microwave photonic signal processing

A new microwave photonic filter structure that realizes both a multitap, flat-top radio-frequency bandpass filter and bipolar taps, while also exhibiting low-noise operation, is presented. It is based on using a phase-modulated laser signal propagating through a novel sinusoidal group delay grating, which induces tailored phase shifts to the carrier and sidebands. The filter integrates tap weighting and delays simultaneously in one unit, which enables multiple-tap low-noise signal processing together with negative coefficients. Experimental results demonstrate the realization of a flat-top bandpass filter response with 7.8-GHz free spectral range and more than 45-dB rejection ratio. Extensions to this concept by connecting additional sinusoidal group delay gratings in cascade, to provide enhanced signal processing functions, are also described.

Novel Multitap, Flat-Top Microwave Photonic Filter Based on Sinusoidal Group Delay Gratings

New photonic filter structures for interference mitigation of microwave signals are presented. These fiber filters have a parallel topology, and comprise a grating based photonic bandpass filter, or a dual offset cavity structure based on a new noncommensurate delay-line approach. The new topologies overcome the problem of synthesizing both a narrow stopband and a very-wide and flat passband, to simultaneously excise interference with minimal impact on the wanted signal over a wide microwave range. Results demonstrate stopbands of around 1% of center frequency, wide-band flat transmission, and a shape factor of 10.5 that is the lowest reported for a photonic notch filter, in excellent agreement with predictions.

Robert A. Minasian

Papers

Optical-fiber grating-based beamforming network for microwave phased arrays

Photonic bandpass filters with high skirt selectivity and stopband attenuation

Microwave photonic signal processing

Novel Multitap, Flat-Top Microwave Photonic Filter Based on Sinusoidal Group Delay Gratings

Photonics-based interference mitigation filters