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Hybrid Silicon Tapered Laser Diode (SOI)

Simulation with PICWave software

PICWave’s current spreading model allows the simulation of hybrid silicon laser diodes (or hybrid SOI laser diodes), where both n and p-contacts are on top, with lateral current flow from the central contact to those on the sides.

Hybrid silicon laser

A hybrid silicon laser - the red arrow shows the current spreading

Hybrid silicon laser diode

The figure below shows the setup of a hybrid silicon laser device in PICWave. The gain curves of the hybrid laser were generated using Harold and fitted in PICWave.

SOI hybrid laser defined in PICWave

SOI hybrid laser device built in PICWave

In this example, the silicon-on-insulator (SOI) waveguide has a central silicon rib with air channels on each side. PICWave’s FDM mode solver can find the proper mushroom-shaped mode of the SOI waveguide mode, shown below, where the bottom part lies in the rib and the upper part in the centre of the active layer.

SOI waveguide mode

SOI waveguide mode found by PICWave’s FDM solver

A material resistivity is assigned to each material used in the waveguide. PICWave can then automatically generate a resistive mesh to model current spreading in the simulation. The current flows down the central conductive channel, through the active layer, then laterally outwards to the ground contacts on each side. This is illustrated in the figure below.

Current density showing lateral current flow

Vector plot of the current density in the vertical-horizontal plane. The arrows indicate the magnitude and direction
of the current density. The active layer lies above of the lateral contacts; beneath it the current flows out
laterally and then up to the contacts on either side.

Tapered SOI laser diode

Light is commonly coupled out of such SOI hybrid lasers by linearly narrowing the III-V mesa region above the silicon waveguide. This adiabatically transforms the mode from the hybrid waveguide to the passive silicon waveguide.

Current density showing lateral current flow

3D view of one half of the the tapered active section; the intensity distribution is shown in the central section.

This can be modelled in PICWave using active taper sections. The example below shows a hybrid DBR laser with a central straight gain region and tapered regions connecting to a DBR grating at each end, formed in passive silicon waveguides.  

Tapered silicon laser diode circuit

The optical mode at various points in the laser are shown below. 

Tapered silicon laser diode circuit

Optical mode in (a) straight gain section – distributed between III-V mesa ridge and silicon waveguide beneath,
(b) end of taper – now largely confined to silicon waveguide, (c) silicon waveguide grating section;
(d) shows the longitudinal profile of quantum well confinement factor along entire length of electrically pumped region.