Power meter showing less power than expected



Here is a simple simulation test: a CW laser + a lossless waveguide + a power meter.
power_meter.icp (107.2 KB)
I expect that the power meter should return the same power as the laser source, i.e., 0 dBm, since the waveguide is lossless. But it seems like there is always some loss for some reason…


Hi @xwang, the “loss” is caused by the delay of the waveguide element. If you may notice, the group index of the waveguide is not 0, which will cause some value of delay to the time domain signal. The following figure is plotted by an oscilloscope at the end of the waveguide, it shows that the time domain signal doesn’t start from time 0.

The Optical Power Meter collects the power of the signal for the entire time window and averages it with respect to the time window. Because of the delay, the result will be slightly less than 0 dBm.

In this example file power_meter_2.icp (222.4 KB), the circuit at the bottom is a duplication of the circuit at the top except that the group index of the waveguide is set to 0. In this case, you will be able to see that the Optical Power Meter measures the power as 0 dBm.