This paper is divided into two major parts. Following a brief introduction that establishes some definitions and assumptions, Section II updates our earlier study on the limits of the RF performance of optical links. Section III reviews progress since our 1997 review paper in the development of devices enabling link performance closer to these limits, including (but not limited to): 1) cascade lasers that permit broad-band direct modulation links with gain >0 dB; 2) injection-locked edge- and surface-emitting lasers at 1300 and 1550 nm with modulation frequency responses as great as 40 GHz; 3) modulators with improved performance, especially electroabsorption modulators that now have switching voltages as low as 0.36 V, or handle optical powers as great as 60 mW, or have bandwidths as great as 50 GHz (but not all three of these in one device yet); and 4) high-speed photodetectors with high saturation currents, e.g., a 20-GHz device with a saturation current of 90 mA and a 55-GHz device with saturation at 50 mA. We conclude in Section IV by summarizing the component developments necessary for higher performance RF-over-fiber links, i.e.: 1) semiconductor lasers (for direct modulation) that have higher slope efficiency and bandwidth and lower relative intensity noise (RIN) at reasonable bias current levels; 2) continuous wave (CW) lasers (for external modulation) with higher fiber-coupled power and lower RIN; 3) higher frequency lower loss external modulators with more linear transfer functions and lower V/sub /spl pi// that can withstand larger CW optical powers; and 4) photodetectors with higher responsivity and bandwidth that respond linearly even when illuminated by greater average optical powers.

Limits on the performance of RF-over-fiber links and their impact on device design

The authors correct an error in their original article (see ibid., vol.54, no.2, p.906-20, Feb. 2006).

Corrections to "Limits on the Performance of RF-Over-Fiber Links and Their Impact on Device Design"

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

/pdf/recent-advances-in-telecommunications-avalanche-photodiodes-18tsmvg7y2.pdf

Recent Advances in Telecommunications Avalanche Photodiodes

Describes the most straightforward method for accurately measuring the frequency response of optoelectronic devices. The method uses a calibrated optical reference receiver, a modulated optical source, and a calibrated electrical vector network analyzer.

Calibrated measurement of optoelectronic frequency response

Microwave photonics and optics-based analog links are technologies that are being developed for a growing number of applications. Photodetectors that operate at high power levels are key components. Additionally, it is important for many of these applications that the photodiodes have millimeter-wave bandwidths and highly linear response. This paper reviews the performance of modified uni-traveling carrier photodiodes with respect to these characteristics.

High-power, high-linearity photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

Beam propagation method simulation shows that evanescently coupled waveguide/photodiodes can be optimized to have absorption lengths as short as butt-coupled photodiodes. Efficient focalization of optical power in the absorber is achievable by appropriate choice of layer geometry and refractive index. Two AlGaInAs-GaInAs structures have been designed for ultrawide-band operation at 60 and 100 GHz: these devices exhibit internal quantum efficiency as high as 94% and 75%, respectively, at 1.55-/spl mu/m wavelength. Such promising performances are suitable for the realization of high-speed high-efficiency integrated photoreceivers with applications to millimeter-wave optical fiber links.

Optical design of evanescently coupled, waveguide-fed photodiodes for ultrawide-band applications

50 GHz bandwidth photodiodes, attaining a compression point of +12 dBm, have been fabricated. The structure design allows an almost complete absorption at 25 /spl mu/m, corresponding to 0.5 A W responsivity and gives a polarisation dependence as low as /spl plusmn/0.1 dB. These components have been realised with a low-cost technology including etched waveguide input facet antireflection coating on wafer and cleaving V-grooves.

http://ieeexplore.ieee.org/iel5/2220/19885/00919995.pdf

Low-cost, polarisation independent, tapered photodiodes with bandwidth over 50 GHz

Evanescent PIN photodiodes are fabricated using all 2"-InP processing including on-wafer mirrors and coatings. 0.73 A/W responsivity at 1.55 /spl mu/m, -1 dB vertical coupling tolerance of 2.2 /spl mu/m and 47 GHz bandwidth are simultaneously demonstrated.

New all 2-inch manufacturable high performance evanescent coupled waveguide photodiodes with etched mirrors for 40 Gb/s optical receivers

High-speed photodiodes are realized with low-cost technology including etched waveguide input facet, antireflection coating on wafer and cleaving V-grooves. 0.46A/W responsivity, 40 GHz bandwidth, 6 mA saturation current, are simultaneously achieved with less than /spl plusmn/0.1 dB polarization dependence.

S. Demiguel

Papers

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

Optical design of evanescently coupled, waveguide-fed photodiodes for ultrawide-band applications

Low-cost, polarisation independent, tapered photodiodes with bandwidth over 50 GHz

New all 2-inch manufacturable high performance evanescent coupled waveguide photodiodes with etched mirrors for 40 Gb/s optical receivers

Low-cost, polarization insensitive photodiodes integrating spot size converters for 40 Gbits/s applications