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

The silicon chip has been the mainstay of the electronics industry for the last 40 years and has revolutionized the way the world operates. Today, a silicon chip the size of a fingernail contains nearly 1 billion transistors and has the computing power that only a decade ago would take up an entire room of servers. As the relentless pursuit of Moore's law continues, and Internet-based communication continues to grow, the bandwidth demands needed to feed these devices will continue to increase and push the limits of copper-based signaling technologies. These signaling limitations will necessitate optical-based solutions. However, any optical solution must be based on low-cost technologies if it is to be applied to the mass market. Silicon photonics, mainly based on SOI technology, has recently attracted a great deal of attention. Recent advances and breakthroughs in silicon photonic device performance have shown that silicon can be considered a material onto which one can build optical devices. While significant efforts are needed to improve device performance and commercialize these technologies, progress is moving at a rapid rate. More research in the area of integration, both photonic and electronic, is needed. The future is looking bright. Silicon photonics could provide low-cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects, as well as emerging areas such as optical sensing technology and biomedical applications. The ability to utilize existing CMOS infrastructure and manufacture these silicon photonic devices in the same facilities that today produce electronics could enable low-cost optical devices, and in the future, revolutionize optical communications

http://ieeexplore.ieee.org/iel5/6668/34347/01638290.pdf

Silicon photonics

An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

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

The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

/pdf/rationale-and-challenges-for-optical-interconnects-to-5clh2238g9.pdf

Rationale and challenges for optical interconnects to electronic chips

Recent developments in silicon based optoelectronics relevant to fiber optical communication are reviewed. Silicon-on-insulator photonic integrated circuits represent a powerful platform that is truly compatible with standard CMOS processing. Progress in epitaxial growth of silicon alloys has created the potential for silicon based devices with tailored optical response in the near infrared. The deep submicrometer CMOS process can produce gigabits-per-second low-noise lightwave electronics. These trends combined with economical incentives will ensure that silicon-based optoelectronics will be a player in future fiber optical networks and systems.

Advances in silicon-on-insulator optoelectronics

We demonstrate a new concept for analog-to-digital (A/D) conversion based on photonic time stretch. The analog electrical signal is intensity modulated on a chirp optical waveform generated by dispersing an ultrashort pulse. The modulated chirped waveform is dispersed in an optical fiber, leading to the stretching of its envelope. We have derived analytical expressions for the stretch factor and the resolution of the system. An analog-to-digital converter (ADC) consisting of the photonic time-stretch preprocessor and a 1-Gsample/s electronic ADC is demonstrated. This technique is promising for A/D conversion of ultrafast signals and, hence, for realization of the digital receiver.

/pdf/photonic-time-stretch-and-its-application-to-analog-to-35j9tdz3w6.pdf

Photonic time stretch and its application to analog-to-digital conversion

A new concept for analogue-to-digital (ADC) conversion is proposed and demonstrated. The analogue signal is stretched in time prior to sampling and quantisation. Time stretching increases the input bandwidth and sampling rate of the ADC and is best implemented using optoelectronic techniques.

Time-stretched analogue-to-digital conversion

We demonstrate the first phased-array wavelength multiplexer fabricated in the silicon-on-insulator (SOI) waveguide technology. The four-channel wavelength division multiplexer (WDM) has a channel spacing of 1.9 nm centered at 1550-nm wavelength and a 3-dB channel bandwidth of 0.72 nm. The crosstalk to neighboring channels is less than -22 dB and the on-chip insertion loss is below 6 dB for all channels. The TE-TM shift is less than 0.04 nm which is the smallest attained without compensation techniques in any integrated optic technology.

Silicon-on-insulator (SOI) phased-array wavelength multi/demultiplexer with extremely low-polarization sensitivity

We present an all optical delay-line radio-frequency (RF) notch filter. The filter exploits cross-gain modulation in a homogeneously broadened laser medium to obtain a negative tap in an optically incoherent system. Applications including moving-target indication (MTI) in optically controlled radars are discussed.

F. Coppinger

Papers

Advances in silicon-on-insulator optoelectronics

Photonic time stretch and its application to analog-to-digital conversion

Time-stretched analogue-to-digital conversion

Silicon-on-insulator (SOI) phased-array wavelength multi/demultiplexer with extremely low-polarization sensitivity

All-optical RF filter using amplitude inversion in a semiconductor optical amplifier