Optical Receivers

The first step in the design of an optical communication systems is to decide how the electrical signal should be converted into an bit stream. There are two typical choices for the modulation format of the signal: return-to-zero (RZ) nonreturn-to-zero (NRZ) Examples of the modulation formats are shown in Figure 1. Figure 1: Modulation Formats…

In this tutorial, we provide a basic example of Goal Attainment optimizations. In this example we will use the optimization tool in the context of parameter extraction. Thermal noise parameter of PIN will be extracted to get a receiver sensitivity of -17 dBm. The design layout is shown in Figure 1. The transmitter power is…

There are two fundamental noise mechanisms in a photodetector: shot noise thermal noise Receiver Shot and Thermal noise.osd details the signal degraded by thermal and shot noise in the PIN photodetector. The low-pass filter has a cutoff frequency with the same value as the bit rate. Figure 1: Receiver Shot and Thermal noise The upper…

Optical receivers with APD generally provide a higher SNR for the same incident optical power. The improvement in the SNR is due to the internal gain that increases the photocurrent by the multiplication factor M. Figure 1: Receiver PIN x APD The APD photodetector systems (see Figure 2) has a Q factor higher that the…

The performance criteria for digital receivers if governed by the bit-error-rate (BER), defined as the probability of incorrect identification of a bit by the decision circuit of the receiver. Receiver BER – Q factor.osd shows the BER and Q factor at the data recovery stage for different values of input power. Receiver BER – Q…

This example shows the minimum optical power that a receiver needs to operate reliably with a BER below a specific value (see Figure 1). In this example, you calculate this input power by targeting a BER of 10-9, a Q factor equal to 6 for a PIN photodetector, and an APD. Figure 1: Receiver Min.…

A simple source of power penalty is related to the energy carried by 0 bits. Some power is emitted by transmitters even in the off-state. Sensitivity Degradation – ER.osd includes an external modulated laser where you can specify the extinction ratio at the modulator (see Figure 1). Figure 1: Sensitivity Degradation – ER In this…

Jitter is defined as the short-term variations of a digital signal’s significant instants from their ideal positions in time. Significant instants could be (for example) the optimum sampling instants. Project Signal Degradation – Jitter.osd (Figure 1) demonstrates the setup for the ‘Electrical Jitter’ component. It requires an electrical signals and the clock signal from the…

The system demonstrates an electrical phase-locked loop. Sample: EPLL.osd The layout presented in the figure below is PLL system configured with a phase detector, a low pass filter and a voltage controlled oscillator. This example shows the response of a PLL to a sequence of pulses modulated in frequency to an electrical carrier at 1GHz.…