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

Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics1. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III–V semiconductor compounds2,3,4,5,6 and/or electro-optic materials such as lithium niobate7,8,9. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only ∼20 MHz (refs 10, 11), although it has been predicted theoretically that a ∼1-GHz modulation frequency might be achievable in some device structures12,13. Here we describe an approach based on a metal–oxide–semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.

A high-speed silicon optical modulator based on a metal–oxide–semiconductor capacitor

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

Recently reported logic style comparisons based on full-adder circuits claimed complementary pass-transistor logic (CPL) to be much more power-efficient than complementary CMOS. However, new comparisons performed on more efficient CMOS circuit realizations and a wider range of different logic cells, as well as the use of realistic circuit arrangements demonstrate CMOS to be superior to CPL in most cases with respect to speed, area, power dissipation, and power-delay products. An implemented 32-b adder using complementary CMOS has a power-delay product of less than half that of the CPL version. Robustness with respect to voltage scaling and transistor sizing, as well as generality and ease-of-use, are additional advantages of CMOS logic gates, especially when cell-based design and logic synthesis are targeted. This paper shows that complementary CMOS is the logic style of choice for the implementation of arbitrary combinational circuits if low voltage, low power, and small power-delay products are of concern.

/pdf/low-power-logic-styles-cmos-versus-pass-transistor-logic-40lwlx0imm.pdf

Low-power logic styles: CMOS versus pass-transistor logic

We demonstrate a silicon modulator with an intrinsic bandwidth of 10 GHz and data transmission from 6 Gbps to 10 Gbps Such unprecedented bandwidth performance in silicon is achieved through improvements in material quality, device design, and driver circuitry

/pdf/high-speed-silicon-mach-zehnder-modulator-2hgwixmx7l.pdf

High speed silicon Mach-Zehnder modulator

Describes circuit techniques for fabricating a high-speed adder using pass-transistor logic. Double pass-transistor logic (DPL) is shown to improve circuit performance at reduced supply voltage. Its symmetrical arrangement and double-transmission characteristics improve the gate speed without increasing the input capacitance. A carry propagation circuit technique called conditional carry selection (CCS) is shown to resolve the problem of series-connected pass transistors in the carry propagation path. By combining these techniques, the addition time of a 32-b ALU can be reduced by 30% from that of an ordinary CMOS ALU. A 32-b ALU test chip is fabricated in 0.25- mu m CMOS technology using these circuit techniques and is capable of an addition time of 1.5 ns at a supply voltage of 2.5 V. >

A 1.5-ns 32-b CMOS ALU in double pass-transistor logic

A 54/spl times/54-b multiplier using pass-transistor multiplexers has been fabricated by 0.25 /spl mu/m CMOS technology. To enhance the speed performance, a new 4-2 compressor and a carry lookahead adder (CLA), both featuring pass-transistor multiplexers, have been developed. The new circuits have a speed advantage over conventional CMOS circuits because the number of critical-path gate stages is minimized due to the high logic functionality of pass-transistor multiplexers. The active size of the 54/spl times/54-b multiplier is 3.77/spl times/3.41 mm. The multiplication time is 4.4 ns at a 3.5-V power supply. >

A 4.4 ns CMOS 54/spl times/54-b multiplier using pass-transistor multiplexer

Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

A semiconductor optical device fabricating method for easily fabricating on a single substrate a plurality of distributed feedback lasers or distributed Bragg reflector lasers with uniform static and dynamic properties and individually different oscillation wavelengths. A plurality of pairs of stripe type insulating thin film masks are formed over that region of the semiconductor substrate which has optical waveguides formed therein for the lasers. Each pair of stripe type masks has a constant gap therebetween. With the masks in place, optical waveguide layers for the lasers are grown in crystallized fashion through metal organic vapor epitaxy. The stripe type masks in pairs differ dimensionally from one another. The semiconductor optical device thus fabricated comprises on one semiconductor substrate a plurality of distributed feedback lasers or distributed Bragg reflector lasers whose optical waveguide layers differ in both film thickness and composition and whose oscillation wavelengths also differ from one another.

Semiconductor optical device and method for fabricating the same

A multiprocessor system of the present invention has an address bus, a data bus, first and second processors, four access queues, and a shared memory divided into four banks. The four access queues are constituted by first-in first-out memories for buffering a plurality of access-request addresses transmitted through the address bus. Even if continuous access requests are addressed to one bank of the shared memory, a succeeding access request need not wait for a previous access request to be finished. Accordingly, the throughput of the system can be improved greatly.

Suzuki Makoto

Papers

A 1.5-ns 32-b CMOS ALU in double pass-transistor logic

A 4.4 ns CMOS 54/spl times/54-b multiplier using pass-transistor multiplexer

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

Semiconductor optical device and method for fabricating the same

Multiprocessor system having shared memory divided into a plurality of banks with access queues corresponding to each bank