PICWave

Electrical model

PICWave has extensive capabilities for accurately modelling the electrical aspects of your active photonic components, including diode IV characteristics, current spreading, travelling wave (microstrip) effects and external electrical circuits composed of resistors, inductors and capacitors.

Current spreading and leakage

PICWave can model the current spreading within the cladding regions of gain sections based on mobility and doping, as illustrated below. The current spreading model supports near-arbitrary, rectangle-based cross-section geometry, and also allows multiple electrical contacts and insulating regions. Furthermore, it can also model the leakage of current through the left and right boundaries of the simulated region of the cross-section using an appropriate boundary condition.

PICWave can thus be used both to assess the impact of lateral current spreading/leakage on the performance of lasers, and also to simulate SOI hybrid lasers  with n and p-contacts on the same side, where lateral current flow is crucial to laser operation. 

Current density vector plot showing lateral current spreading in a ridge waveguide laser

Electrical components

Near-arbitrary electrical circuits can be constructed from inductors, capacitors, resistors, electrical nodes and electrical drives. These can be attached to active sections and the electrical-optical interaction modelled e.g. the effect of parasitics on laser operation, or the electrical response of a photo-detector etc.

The example below shows an FP laser modulated by a current data signal via a drive circuit containing an inductor and capacitor.

An LCR drive network attached to an FP laser

The effect of the capacitance and inductance on the laser output is shown in the oscilloscope plots beneath. 

Laser output for 1Gbit/s current modulation: when drive circuit has zero capacitance and zero inductance (top left); 50pF capacitance (top right), causing the longer rise/fall time; 50pH inductance (bottom left), causing ripples

Travelling Wave Electrode

Electrodes on active sections can be modelled as travelling wave electrodes with a defined inductance and capacitance per unit length. These electrodes can in turn be connected together or connected to other elements using the LCR connections described above. This enables one to model the propagation of electrical signals along the electrode and any reflections that occur due to impedance mismatches at connections or terminations.

A key application of this feature is modelling travelling wave modulators.

Propagation of voltage pulse along electrode in PICWave’s travelling electrode model

This advanced algorithm will even alter the microwave impedance as a function of bias voltage, i.e. taking into account the variation of diode impedance with diode bias voltage. 

(left) Electrodes on two sections joined together. Impedance mismatches
between the two electrodes and between the second electrode and termination gives rise to reflections (right).