How do I calculate the link gain and noise figure of an analog photonic link?

The link gain and noise figure of an analog photonic link are determined by the optical components (laser, modulator, fiber, photodetector) and their parameters: (1) Link gain (for a directly modulated laser link): G_link = (s_laser × R_PD × Z_out / Z_in)² × 10^(-α_fiber × L / 10). Where s_laser = laser slope efficiency (W/A, the change in optical power per change in modulation current), R_PD = photodetector responsivity (A/W, the current generated per watt of received optical power), Z_in = input impedance of the laser module (typically 50 Ω), Z_out = output impedance of the photodetector module (typically 50 Ω), α_fiber = fiber attenuation (dB/km), and L = fiber length (km). For an external modulation link (Mach-Zehnder modulator): G_link = (π × P_laser × R_PD / V_π)² × Z_out / Z_in × 10^(-α_fiber × L / 10). Where V_π = half-wave voltage of the modulator (the RF voltage required to shift the optical phase by π; lower V_π = higher link gain). (2) Noise figure: NF_link = (RIN × I_PD² + 2qI_PD + k_B T/R_load) / (k_B T × G_link). Where RIN = relative intensity noise of the laser (dB/Hz, typically -155 to -165 dB/Hz), I_PD = photocurrent at the detector (A), q = electron charge (1.6 × 10^-19 C), and k_B T = thermal noise at room temperature. The three noise terms: RIN noise (laser intensity fluctuations): dominates at high optical power, shot noise (2qI_PD): fundamental quantum limit, and thermal noise (k_B T/R_load): dominates at low optical power. Typical NF: 20-40 dB for standard analog links. High-performance links (high-power laser, low V_π modulator): NF = 10-15 dB achievable. (3) Improving NF: increase optical power (higher laser power or optical amplifier). Use a modulator with lower V_π (more efficient RF-to-optical conversion). Use a higher-responsivity photodetector. Reduce fiber loss (shorter fiber length or use optical amplification).