This simulator opens a fiber-coupled laser transmitter. Choose a repeating bit pattern and bit rate, then adjust driver bandwidth, zero-bit and one-bit current, threshold, junction temperature, slope efficiency and fiber coupling to see the laser current, optical power, extinction ratio and how a slow driver rounds the bits.
• A 3D fiber-coupled transmitter with a pattern source and bit indicators, a current driver on a circuit board, a laser chip in a butterfly package, a coupling lens, a ferrule and fiber pigtail, a heat spreader with temperature stage, and an electrical and optical monitor. • Eleven controls: data pattern, bit rate, driver bandwidth, zero-bit current, extra one-bit current, threshold, junction temperature, slope efficiency, coupling efficiency, driver enable and a marker toggle. • Twelve readouts including actual laser current, threshold, facet power, fiber power, steady P0 and P1, modulation amplitude, extinction ratio and rise time. • Four guided experiments, a verification bench, Curves & measurements and a Learn & assess tab.
The commanded current is Ibias plus the bit times the swing, limited to 100 mA. A first-order driver with time constant τ = 1/(2πB) smooths it: I(t+Δt) = Icmd + [I(t) − Icmd] exp(−Δt/τ). The threshold rises with temperature, Ith(T) = Ith25 exp[(T − 25)/70], and facet power is 0.01 mW times min(I/Ith, 1) plus the slope times the current above threshold. Fiber power is coupling efficiency times facet power.
The optical modulation amplitude is P1 − P0 and the extinction ratio is 10 log10(P1/P0). A high zero-level bias lets both levels emit, which raises average power but lowers extinction ratio, and lower coupling scales P0, P1 and OMA together without changing the ratio.
This is a representative directly modulated laser with a first-order current driver, a static piecewise light-current curve and scalar fiber coupling. Temperature dependence is illustrative rather than fitted to a device, junction temperature is prescribed, and there are no carrier-photon rate equations, chirp, relaxation oscillations, laser safety classification, receiver, noise or BER calculation. P0, P1 and ER are steady predictions rather than measured eye levels.
Below threshold the chip emits only weak spontaneous light. Above it, stimulated emission dominates and optical power rises steeply with current. The model captures this with a small pre-threshold output and a linear slope above threshold.
The threshold current increases. In the simulator at high temperature the threshold rises to about 54.86 mA, above the 40 mA one-level command, so stimulated laser output disappears.
The first-order driver bandwidth. If the current cannot settle within one bit period, the optical high and low levels compress even though the steady predictions stay the same.
Raising the zero-bit current lifts P0 toward P1. Output power rises, but the ratio P1/P0 shrinks, which reduces extinction ratio.