Introduction
This receiver’s clean responses and 35-ps rise times make the product well-suited for a time-domain characterization of 10-Gbit/s signals. Using the scope's built in parametric measurements and math functions we are able to perform the dark calibration and measure extinction ratio.
Set-Up
Figure 1 below shows the set up of the 1554-B and other devices. In this example, the 1554-B was powered by +/- 15 V DC power supply. Our electrical binary data source (10-Gb/s PRBS7) was connected to the Lightwave Transmitter that modulated a laser source to the 1554-B to create an optical serial data signal.
Procedure
First, connect the 1554-B output to Ch2 of the oscilloscope using the DC50ohm input coupling mode (see Figure1) for the connection layout. Then set up the Math channel F1 and F2 as rescale functions of Ch2 to convert the voltage waveform to a power waveform. The trace F1 shows the photo receiver output before the dark calibration and the trace F2 shows it after the dark calibration. From the 1554-B receiver specification, we know the peak conversion gain for the 1554-B is -600V/W.
Therefore, both F1 and F2 are rescaled by multiplying by -1.667E-3 (1/600 V/W) with the output unit set to Watts. The negative multiplication for the rescaling is because the receiver inverts the input signal. The optical input to the 1554-B is covered so as to measure the mean value of the receiver output (Figure 2). This is the “dark” output power. In this particular receiver it was measured as -11.03μW.
Now, the dark calibration adjustment can be done by adding 11.03μW to the rescale trace F2 (Figure 3). As a result of this action the mean value measurement on trace F2 (P2) is compensated to near zero.
With the dark calibration done, we can now measure Extinction Ratio from the rescaled waveform (F2) using LeCroy’s SDAII software eye measurement parameters.
Reconnect the optical input and adjust the vertical gain of the Ch2 and F2 traces to fill approximately 6 out of 8 vertical divisions of the grid (Figure 4). In this example the data input used is a 10.699Gb/s PRBS serial data signal from a BERT.
Setup the SDAII software for eye diagram testing (Figure 5). Select the input source to be F2 in signal input dialog box. This is the dark calibrated input signal. Press “Find Rate” in the Clock Recovery dialog box to find the right bit rate from the F2. In this example it found the bit rate as 10.699Gb/s. There are several eye related parameters under the Eye Parameters setup screen including “Ext Ratio”. In this example we measured the Extinction Ratio as 16.92dB as shown in Figure 5.
