Indistinguishable sub-nanosecond pulse generator

The indistinguishable laser pulse is predominant in the realization of qubits in decoy state-based quantum cryptography. Such cryptography in an automotive framework needs to be compact and inexpensive. However, their implementation is cumbrous and uneconomical. Significant effort has been put into reducing the form factor of quantum cryptography implementation. We report a compact, low-cost, indistinguishable, sub-nanosecond pulse generator with adjusted delay and amplitude using a Fabry–Perot laser diode. The approach was derived based on algebraic topology formulation of the electrical network, and the implementation involves time-dependent perturbation of a constant current node to generate tunable, sub-nanosecond excitation with a constant pre-bias. The simulation model of the laser diode accounted for effects of spontaneous emission and relaxation oscillation. The shortest excitation pulse thus generated was measured to have FWHM of 496 ps. Further, the indistinguishability of two laser pulses is statistically evaluated.