# DESCRIPTION
# {
#     Modulation bandwidth is calculated from the transient simulation, where a numerically small step signal is applied
#     on top of the DC signal after intitial steady state is reached. To increase the accuracy of bandwidth calculation 
#     the capture/escape rate model is implemented based on 1992, Nagarajan, High speed quantum-well lasers and carrier 
#     transport effects.
#          
#     NOTES:
#       
#       1. Spontaneous emission contribution to the photon density is significantly reduced in the transient simulation 
#          as it does not affect the modulation bandwidth significantly. This agrees with the reference (1992, Nagarajan).
#          Spontaneous emission is reduced to a level just enough to spark lasing but not polute output power with noise,
#          making it challenging to extract the RF response from the time-domain output power.
#       2. The device model used in this example is our FP getting started example, modified to include a step source 
#          on top of the DC source and to reduce the spontaneous emission coupling coefficient.
#
# }

clear;

transient_bandwidth; #load custom script function that implements the time-domain output power post-processing to calculate the RF response.
load("TWLMexampleLaserFP300umCF353THzR3R3nel100_transient");
switchtolayout;
#Enable carrier capture/escape rate model and set some reasonable values (not necessarily accurate for the device in question)
setnamed('TWLM_1','enable SCH',true);
setnamed('TWLM_1','well carrier capture rate',1.42857e+10);
setnamed('TWLM_1','well carrier escape rate',7.14286e+09);
setnamed('TWLM_1','total well thickness',1e-7);
setnamed('TWLM_1','total barrier thickness',1e-7);

#Reduce spontaneous emission to a level just enough to spark lasing but not pollute output power with noise.
setnamed('TWLM_1','spontaneous emission factor 1',1e-12);
    
run;

transient_BW = rf_bandwidth_postprocess(25e-12,20e9);
?'3dB bandwidth from transient simulation is ' + num2str(transient_BW.bandwidth*1e-9) + ' GHz';
three_dB=log10(ones(length(transient_BW.rf_response))*0.001);
plot(transient_BW.freq*1e-9,transient_BW.rf_response,three_dB,"Frequency (GHz)", " Normalized response (dB)","","linewidth=2");
legend('transient RF response','3dB cut-off');