III-V/Si Device Integration

One of the critical issues of hybrid InP/SOI lasers is to design a laser structure, able to generate light in the III-V layer and then to couple it efficiently from the III-V layer to a silicon waveguide.

III-V Lab has done the first demonstration.
As the main solution proposed up to now is based on evanescent coupling, whereby the optical mode is mainly confined in the silicon waveguide and interacts with the multi quantum wells (QW) layer, we use a tapered silicon waveguide, which allows to couple the light from a III-V waveguide to the silicon waveguide in the tapered region. The structure used is a double tapered structure, incorporating mode transformers in both the III-V and silicon waveguides. The InP waveguide is very wide (> 6 µm), leading to very high threshold current and low emission efficiency. Mode coupling occurs in the tapered region, while light generation and amplification takes place in a single mode III-V waveguide.

The structure can be divided into three parts.
  • In the center of the device there is a III-V waveguide that provides optical gain.
  • At both sides of this section there is a coupling region that couples light from one guide to the other.
  • The third part is a silicon waveguide without III-V on top.

Top view, cross sections and calculated mode profiles of the III-V/SOI laser

The mode is adiabatically transferred from the III-V waveguide to the Si waveguide and vice versa: a coupling efficiency of nearly 95% can be achieved for an InP taper width of 0.4µm.

Fiber coupled laser power as a function of drive current (L-I curve) under pulsed operation at 20°C.

Optical spectrum of the laser driven at 55mA