1、PDF外文：http:/ Performance 10 Gb/s PIN and APD Optical Receivers Abstract The increasing market demand for high-speed optical- transmission systems at rates of 10 Gb/s has resulted in technical challenges for suppliers of high-performance, manufacturable opto-electronic components and syst
2、ems. In particular, the performance of the InP semiconductor devices, integrated circuits (ICs) and hybrid IC modules strongly influences the achievable transmission capability. Anopticalreceiverdesignispresented which incorporates anInP-based p-i-n (positive-intrinsic-negative) photodet
3、ecto(PD) or avalanche photodetector (APD) and aGaAs high electron mobility transistor (HEMT) pre-amplifier integratedcircuit. Several aspects of the receiver design are presented, including thep-i-nPD and APD structures and performance, pre-amplifier performance, hybrid module layout and elect
4、rical simulation and results. The useof analytical techniques and theory commonly used in the design ofmicrowave amplifiers and circuits is emphasized. Receivertest results are included which are in close agreement withpredicted theoretical performance. Introduction Over the past 15 year
5、s the demand has continued to increase for higher speed and higher performing opto- electronic components. Components designed to operate at data rates of 155 Mb/s through 1 Gb/s are now used in high volume, are manufactured with high yields, and are available from several suppliers. Component
6、s designed for 2.5 Gb/s are fast approaching this manufacturing status as well. The emphasis now for new opto-electronic product development centers around performance requirements at transmission rates of 10 Gb/s and higher. The optical receiver represents one of the key componentsin optical-fiber
7、based communication systems, and isgenerally considered as a component, or module, which isavailable with specified levels of electrical functionality orintegration. The basic elementsof an optical receiver moduleare a photodetector, pre-amplifier, limiting or AGC(automatic gain control) amplifier,
8、and clock and data recovery circuitry. At data rates of 2.5 Gb/s and below, thesystem designer can currently purchase the optical receiver elements in various levels of integration, from a discretephotodetector module to a fully integrated clockand data recovery module. In many multi-ele
9、ment systems and circuits the performance is strongly influenced by those elements which are located near the input of the system or circuit. This is certainly true in a digital optical receiver where the performance of the photodetector and pre-amplifier elementswill have a strong impact on r
10、eceiver and system performance. In addition to the individual performance of these two elements, the electrical and physical design of the interface between them is equally critical. At speeds of 10 Gb/s, the current focus for suppliers of optical receivers is the development of modules, which
11、 incorporate the photodetector and pre-amplifier elements. Naturally as time progresses, the additional electrical functions will be incorporated into the modules as well. This paper focuses on the design and characterization of 10Gb/s optical receiver modules that incorporate the photodetector and
12、pre-amplifier elements. Optical Receiver Basics Before considering 10 Gb/s receiver design a brief review is presented of optical receivers for digital applications. A basic schematic of an optical receiver front-end is shown in Figure I. The schematic includes the photodetector and pre-
13、 amplifier elements. The key perfomance requirements of an optical receiverare high sensitivity, wide dynamic range and adequate bandwidth for the intended application. The purpose of the PD is to convert the incident optical signal to an electricalcurrent. The photodiode should have the follo
14、wing performance characteristics: high responsivity (quantum efficiency), low dark current, low capacitance and wide bandwidth. For applications at optical wavelengths of 1310nm and 1550 nm, high quantum efficiency InGaAs / InP type photodetectors are commonly selected. The purpose of th
15、e pre-amplifier is to convert the photocurrent from the PD into a usable voltage that can be further processed. The common pre-amplifier technology used in optical receivers is transimpedance amplification, (TIA) due to its optimum trade-off between noise, dynamic range and bandwidth. Other types of
16、 pre-amplifiers include high-impedance and low-impedance (e.g. 50 ) designs. p-i-n Photodetectors Our p-i-n photodiode is a double-heterojunction structure grown on an n+-InPsubstrate and consists of an n+-1nP bufferlayer, an n-InGaAs active layer, and ann InP cap layer. The buffer growth prec
17、edes the active layer growth to provide a surface with fewer defects than exist on the bare substrate surface. The In0.53Ga0 .47As active layer is lattice-matched to InP and, with a bandgap g 0.75 eV, is sensitive to light with wavelengths shorter than 1.65m. The device exhibits a short-
18、wavelength cutoff at 0.90m since more energetic short-wavelength light is absorbed in the InP ( g1.35 eV) before it reaches the InGaAs. The larger-bandgap InP cap layer reduces surface leakage (relative to InGaAs) and is passivated using Si3N4. Using etched patterns in the Si3N4as a mask, high-relia
19、bility planar diodes are created by diffusing a p-type dopant (Zn) to form one-sided p+-n-junctions just below the InP-InGaAs (cap-active) heterojunction (see Fig. 5a). Contact metallization alloyed to the diffused junction allows electrical contact to the p-side of the junction. After thinnin
20、g the substrate to 120 m, the back side of the wafer is metallized to provide electrical connection to the n-side of the junction. Apertures in the backside metallization allow optical coupling to the active region in aback-illuminated geometry, and an anti-reflecting (AR) Si3N4coating is present in
21、 the aperture to eliminate reflection from the air-InP interface. Several of the critical device characteristics pose conflicting design constraints that must be optimized for good high frequency performance. Of primary importance is the ability to achieve sufficient 3-dB bandwidth. The standard p-
22、i-n diode has two fundamental bandwidth limitations: (i) finite carrier transit time and (ii) RC roll-off. The finite transit time taken by photon-induced carriers to traverse the active region can be shortened by reducing the thickness of the active region, but only at the expense of increase
23、d capacitance per unit area and lower quantum efficiency (which results in lower responsivity). The tendency towards increased capacitance for thinner active layers can be offset by reducing the total junction area, but this leads to greater difficulties in achieving high optical coupling efficiency and reliable electrical connections (e.g., by wire bonding). For 10Gb/s performance, the conflicting requirements just described can be adequately resolved using a device diameter of 30 um. In this case, an active layer width Wa 2.3 um gives
