Nonlinear Optical Processes in Micro- and Nanostructures

**109**

**Chapter 7**

**Abstract**

coupling

**1. Introduction**

Heterostructure

*Ivan Favero and Giuseppe Leo*

*Alice Bernard, Jean-Michel Gérard,* 

distributed Bragg reflectors (DBRs) are used.

Widely Tunable Quantum-Well

Laser: OPO Diode Around 2 μm

Based on a Coupled Waveguide

We present the design of a widely tunable monolithic source on GaAs/AlGaAs. It consists of a quantum-well distributed feedback (DFB) laser vertically coupled with a waveguide engineered for nonlinear frequency conversion. No regrowth or alignment is necessary, and all the structure stems from a single epitaxy step. Light is emitted by the 0.98 μm DFB laser and transmitted to the underlying waveguide by an adiabatic taper, where it can undergo parametric down-conversion, providing signal and idler beams around 2 μm. Transfer rates and tolerances for transfer and conversion efficiency are calculated to be compatible with the tolerances of current fabrication processes. We estimate that an OPO threshold can be reached in the underlying waveguide for a laser emitted power of 20–100 mW, if high-reflectivity

**Keywords:** quantum well, laser diode, near infrared, AlGaAs, tunable source, optical parametric oscillator (OPO), active-passive integration, adiabatic coupling, vertical

Five decades after the first demonstrations of a laser diode [1, 2], current integrated laser sources include diodes, quantum cascade lasers, and interband cascade lasers. These sources span a wide range from the visible spectrum to the far infrared. However, they present to this day a limited tunability, up to a few tens of nm at the most excluding external cavity setups. This is a limitation in particular in the field of spectroscopy, in demand of coherent and widely tunable sources. In parallel to the development of integrated lasers, optical parametric oscillators (OPOs) have undergone a wide progress, spanning the electromagnetic spectrum from ultraviolet to infrared and providing largely tunable outputs, but they are not yet widely adopted on integrated platforms. This is mostly due to the difficulty of adjusting the phase mismatch in situ and historically to the lack of nonlinear materials in semiconductor platforms. However, GaAs/AlGaAs provides high nonlinear conversion efficiencies, and fabrication efforts have resulted in a diminution of losses in this material system [3, 4]. Optically, pumped OPOs have been demonstrated
