The low-loss wide bandwidth capability of opto-electronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper reviews the development status of microwave photonic devices, describes their systems applications, and suggests some likely areas for future development

Microwave Photonics

The two main trends in the progress of ultrawide-band/high-frequency photodetectors (PD's), improving the bandwidth-efficiency product and obtaining a high saturation current, are reviewed. With respect to achieving large bandwidth-efficiency, the limiting factors and potentials of edge-coupled (waveguide, waveguide-fed, traveling-wave, periodic-traveling-wave), resonant-cavity, and refracting-facet photodiodes, as well as the avalanche photodiode are discussed. Regarding high-saturation current, the author estimated how much the space-charge effect limits the saturation current and two ways to reduce the space-charge effect are outlined. One way is to distribute the photocarriers along the edge-coupled PD's and the other is to increase the carrier velocity using a uni-traveling carrier structure. The waveguide-photodiode-based technologies that we have developed are also presented; namely the design and fabrication of a 100-GHz waveguide photodiode (WGPD), uni-traveling carrier WGPD, 60-GHz packaging, and a 20-GHz large-core WGPD for planar lightwave circuit integration. A 50-Gb/s receiver opto-electronic integrated circuit technology based on the WGPD is also presented.

Ultrawide-band/high-frequency photodetectors

The low-loss wide-bandwidth capability of optoelectronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper describes the development of microwave photonic devices, describes their systems applications, and suggests likely areas for future development.

Microwave photonics

For high-bit-rate long-haul fiber optic communications, the avalanche photodiode (APD) is frequently the photodetector of choice owing to its internal gain, which provides a sensitivity margin relative to PIN photodiodes. APDs can achieve 5-10-dB better sensitivity than PINs, provided that the multiplication noise is low and the gain-bandwidth product is sufficiently high. In the past decade, the performance of APDs for optical fiber communication systems has improved as a result of improvements in materials and the development of advanced device structures. This paper presents a brief review of APD fundamentals and describes some of the significant advances

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Recent Advances in Telecommunications Avalanche Photodiodes

The development of high-performance optical receivers has been a primary driving force for research on III-V compound avalanche photodiodes (APDs). The evolution of fiber optic systems toward higher bit rates has pushed APD performance toward higher bandwidths, lower noise, and higher gain-bandwidth products. Utilizing thin multiplication regions has reduced the excess noise. Further noise reduction has been demonstrated by incorporating new materials and impact ionization engineering with beneficially designed heterostructures. High gain-bandwidth products have been achieved waveguide structures. Recently, imaging and sensing applications have spurred interest in low noise APDs in the infrared and the UV as well as large area APDs and arrays. This paper reviews some of the recent progress in APD technology.

Recent advances in avalanche photodiodes

A waveguide AlInAs/AlGaInAs superlattice avalanche photodiode with a record 3 dB bandwidth of >20 GHz is reported at a wavelength of 1.55 /spl mu/m. A large gain-bandwidth product of >160 GHz is obtained. These devices are suitable for 20 Gbit/s long wavelength photoreceivers.

Waveguide AlInAs/GaAlInAs avalanche photodiode with a gain-bandwidth product over 160 GHz

High speed photodetectors are needed in optical communication systems and avalanche photodiodes are essential in highly sensitive photoreceivers at the 1.55 /spl mu/m wavelength. Avalanche photodiodes (APDs), when compared to PIN photodiodes, provide higher responsivities due to their internal gain M. An improvement in the signal to noise ratio of about 10 dB is expected at 20 Gbit/s. Very good performances have already been demonstrated at 10 Gbit/s. For higher bit-rates, a side-illuminated structure has been proposed, to reach simultaneously high responsivity and high speed. The simulations allowing to design waveguide APD structures, their fabrication and their characteristics are reported in this paper.

http://ieeexplore.ieee.org/iel3/4783/13228/00600201.pdf

A. Bonzo

Papers

Waveguide AlInAs/GaAlInAs avalanche photodiode with a gain-bandwidth product over 160 GHz

Waveguide AlInAs/AlGaInAs avalanche photodiode for 20 Gbit/s photoreceivers