"Introduction". In: Fiber-Optic Communication Systems

142 CHAPTER 4. OPTICAL RECEIVERS Figure 4.7: Impact-ionization coefficients of several semiconductors as a function of the elec- ...

4.2. COMMON PHOTODETECTORS 143 Figure 4.8: (a) An APD together with the electric-field distribution inside various layers under ...

144 CHAPTER 4. OPTICAL RECEIVERS remains constant at every point inside the multiplication region. If we replaceihin Eq. (4.2.3) ...

4.2. COMMON PHOTODETECTORS 145 Table 4.2 Characteristics of common APDs Parameter Symbol Unit Si Ge InGaAs Wavelength λ μm 0.4–1 ...

146 CHAPTER 4. OPTICAL RECEIVERS Figure 4.9: Design of (a) SAM and (b) SAGM APDs containing separate absorption, multipli- catio ...

4.2. COMMON PHOTODETECTORS 147 (a) (b) Figure 4.10: (a) Device structure and (b) measured 3-dB bandwidth as a function ofMfor a ...

148 CHAPTER 4. OPTICAL RECEIVERS quantum efficiency can be maintained. Two approaches have been used to meet these somewhat conf ...

4.3. RECEIVER DESIGN 149 Figure 4.11: Diagram of a digital optical receiver showing various components. Vertical dashed lines gr ...

150 CHAPTER 4. OPTICAL RECEIVERS Figure 4.12: Equivalent circuit for (a) high-impedance and (b) transimpedance front ends in opt ...

4.3. RECEIVER DESIGN 151 interference(ISI). As discussed in Section 4.4, the receiver noise is proportional to the receiver band ...

152 CHAPTER 4. OPTICAL RECEIVERS Figure 4.13: Ideal and degraded eye patterns for the NRZ format. signal is maximum. At the same ...

4.3. RECEIVER DESIGN 153 can be determined from theeye diagramformed by superposing 2–3-bit-long electrical sequences in the bit ...

154 CHAPTER 4. OPTICAL RECEIVERS Figure 4.14: Flip-chip OEIC technology for integrated receivers. The InGaAs photodiode is fabri ...

4.4. RECEIVER NOISE 155 (a) (b) Figure 4.15: (a) Epitaxial-layer structure and (b) frequency response of an OEIC receiver mod- u ...

156 CHAPTER 4. OPTICAL RECEIVERS 4.4.1 Noise Mechanisms The shot noise and thermal noise are the two fundamental noise mechanism ...

4.4. RECEIVER NOISE 157 The quantityσsis the root-mean-square (RMS) value of the noise current induced by shot noise. Thermal No ...

158 CHAPTER 4. OPTICAL RECEIVERS with approximately Gaussian statistics, the total variance of current fluctuations,∆I= I−Ip=is+ ...

4.4. RECEIVER NOISE 159 Shot-Noise Limit Consider the opposite limit in which the receiver performance is dominated by shot nois ...

160 CHAPTER 4. OPTICAL RECEIVERS Figure 4.16: Excess noise factorFAas a function of the average APD gainMfor several values of t ...

4.4. RECEIVER NOISE 161 Figure 4.17: Optimum APD gainMoptas a function of the incident optical powerPinfor several values ofkA. ...