Monolithic photonics architectures which enable the generation and processing of quantum states of light will be discussed. Some architectures are shown to exhibit characteristics that are unique to integrated architectures over their bulk-optics counterparts.
If we use on-chip quantum interference as an example, one find it is often assumed that the 2x2 mode coupler maintains a 50:50 splitting ratio over the twin-photons’ entire joint spectrum. However, this is not necessarily the only case possible for integrated devices. For some designs the interferometer behaves as an ideal 50:50 beamsplitter (BS), while for others it behaves as an ideal wavelength de-multiplexer (WD). This interesting ramifications for two-photon interference, where dispersion can allow integrated 2x2 couplers to play a far more versatile role in quantum circuits than their bulk-optics counterparts.
Generating entangled photons on monolithic chips is a significant progress towards real-life applications of optical quantum information processing such as quantum key distribution and quantum computing. Here we present our recent achievements in generating polarization entangled photons on monolithic III-V semiconductor chips without any off-chip component. We demonstrate the direct generation of broadband polarization entangled photons from a semiconductor chip for the first time with a record degree of entanglement. We also show an alternative approach for polarization entangled photon generation on the same epitaxial structure, which enabled a single chip generating both co-polarized and cross-polarized entangled photons. With recent progress on pump laser integration, our results pave the way for fully integrated entangled photon sources in the foreseeable future.
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 demonstrate efficient photon pair generation for quantum communication using an all-semiconductor approach. In an AlGaAs Bragg-reflection waveguide we employ spontaneous parametric down-conversion to produce photon pairs at telecommunication wavelengths. The various phase-matching solutions present in our device can be used to create timebin or polarization entanglement. This approach can to lead to a fully integrated photon pair source with the pump laser, active and passive optical devices all on a single semiconductor chip.