**Figure 1.**

*Nonlinear Optics - Novel Results in Theory and Applications*

**NL waveguide on top**

**112**

**Laser on top**

> Contacts

Thermal control

Laser

multimodality

Effective indices

**Table 1.**

*Advantages and drawbacks of different coupling geometries.*

Transition from a high index in the laser to a low index in the NL guide

down in the transfer zone (longer total length)

Epi-up and epi-down possible

The laser must start in single-mode operation in a zone in shallow etching; then, it should taper

Lateral contacts necessary

Lateral contacts not necessary

Epi-down impossible

The laser is buried, and single-mode emission is easily achieved

The laser index should be lower than the indices in the NL waveguide,

which are already low (∼3.2)

Single-mode operation of the laser is hindered

*General view of the proposed coupled-cavity design.*

laser in order to provide longitudinal as well as transversal single-mode operation. The upper waveguide narrows in the transfer region, where the mode moves to the bottom waveguide. On the right, parametric conversion takes place in the bottom waveguide, where distributed Bragg reflectors (DBRs) provide a high reflectivity at the signal and idler wavelengths. We will describe the device step-by-step, starting from the end because the zone of parametric conversion is the most sensitive to geometry variations.
