Widely tunable mid infrared radiation achievable using quantum cascade lasers (QCLs) often
requires external cavities and several QCL chips to cover a large bandwidth similar to the range
reported here (~ 1000s nm). The cost and mechanical stability of these designs leaves room for
alternative more rugged approaches, which require no cavities to achieve very broad band tunability.
While difference frequency generation (DFG) will unlikely match the power levels achievable from
QCLs, it can provide spectral brightness and extremely wide tunablity, which can be valuable for
Recently, we have demonstrated that dispersion engineering techniques can be used for phase
matching of second order nonlinearities near the bandgap in monolithic waveguides. In this work we
demonstrate an extremely simple structure to grow and fabricate, which utilizes dispersion
engineering not only to achieve phase matching but also to expand the tuning range of the frequency
conversion achieved in a waveguide through difference frequency generation. Frequency conversion
in monolithic AlGaAs single-sided Bragg reflection waveguides using<i> χ<sup>(2)</sup> </i>nonlinearities produced
widely tuneable, coherent infrared radiation between 2-3 μm and 7-9 μm. The broad tunability
afforded by dispersion engineering and possible current injection, waveguide width chirping and
temperature tuning makes it possible to produce a single multi-layer substrate to generate mid-IR
signals that span μms in wavelength.
An effective approach to achieve efficient phase matching for second order nonlinearities, in
multilayer structures will be discussed. It uses dispersion engineering in Bragg reflection waveguides
to harness parametric processes in conjunction with concomitant dispersion and birefringence
engineering in active devices. This technology enables novel coherent light sources using frequency
conversion in a self-pumped chip form factor. These sources can also provide continuous coverage of
spectral regions, which are not accessible by other technologies including quantum cascade lasers.
This approach has been recently demonstrated in multi-layer Silicon-Oxy-Nitride (SiON) waveguides.
Harnessing χ<sup>(2)</sup> in SiON offers a route for integration of broadband infrared sources using frequency
mixing with opto-fluidics. Different approaches for implementing opto-fluidic structures on Si will be
discussed, where the root cause of enhancing the retrieved Raman and infrared signals in these
structures will be explained. Recent progress in using this approach to study different nanostructures
and biological molecules will be presented.
We propose and examine single-stack matching-layer enhanced Bragg re
ection waveguides as a platform for integrated parametric devices. The proposed designed is asymmetric in geometry, where a multi-layer core is surrounded by a single-layer upper cladding and a lower quarter-wave Bragg mirror. The propagation of the Bragg mode in the new design relies on total internal reection form the upper cladding and Bragg reflectionthe lower periodic cladding. Analytical expressions for modal analysis of TE- and TM-polarized Bragg modes
are derived. An Al<sub>x</sub>Ga<sub>x</sub>As second-harmonic generation device is theoretically examined to highlight nonlinear performance of the new design and it is compared to symmetric phase-matched Bragg reflection waveguides reported to date.
An overview of recent advances in exact phase matching technologies of second order nonlinear optical processes in
compound semiconductors is reported. The technique used utilizes dispersion engineering in Bragg reflection
waveguides (BRWs) or 1-dimensoinal photonic bandgap structures to achieve phase matching between the interacting
waves. One of its distinguishing features in comparison to other techniques is that it does not involve any demanding
technological steps such as oxidation, nor does it rely on periodic modulation of the optical properties of the materials
used in the propagation direction. This in turn provides phase matching with significantly lower optical losses in
comparison to other techniques. Nonlinear conversion efficiency matching what is achievable in periodically poled
lithium niobate is obtained for ridge BRWs fabricated in GaAs/AlGaAs. Most notable applications that would benefit
from integrable ultrafast second order optical nonlinearities include monolithically integrated optical parametric
oscillators, correlated photon pair sources and monolithic tunable frequency conversion elements.