I always used VPItransmissionMaker which is similar to Optisystem. If you have a powermeter, you could use one at Laser output and another one at the input of the photodiode. Hope helping you :)
Habib,
If you want to calculate power penalties (either in VPI or optisystem), you need to use the following procedure :
1) Draw the reference back-to-back curve with the Emitter (Tx) directly connected to the receiver (Rx), by varying the optical power incident onto the Rx (Pr) using a variable optical attenuator and measuring the Bit-error-rate (BER) as a function of Pr,
2) Insert the element or system for which you want to determine the power penalty (a fiber, a filter, a transmission system etc ...)
3) repeat operation 1, i.e. measure the BER = f(Pr) curve with the new element inserted
4) measure the power penalty as the horizontal shift between the two curves for a given reference bitrate (e.g. BER = 10^-9).
First design a transmission system with optimum BER of 1*10^-9. Now disturb the any one of the parameter in the transmission link like Bit rate, fiber length , and signal modulation then it will reduce the BER below the mentioned value. By adjusting the given input signal power once again the same BER can be reached. so, the amount of additional input power is required to reach the BER of 10E-9 after the perturbation of transmission link is called power penalty.
S. Selvendran sir but in literature the power penalty value is given in dB and received power and input signal power is given in unit dBm. Why does the both vary.
Gain or lose are calculated as a relative power (difference between two power levels), input and output are absolute power
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