Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera.

A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid's absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.

Physical model for high indium content InGaN/GaN self-assembled quantum dot ridge-waveguide lasers emitting at red wavelengths (λ ~ 630 nm).

We present a physical model for recently demonstrated high indium content self-assembled In0.4Ga0.6N/GaN quantum dot (QD)-based ridge-waveguide lasers emitting at red wavelengths. The strain distribution in the QD is calculated using linear elastic theory with the application of shrink-fit boundary condition at the InGaN/GaN material interface, and the electronic states are evaluated using a single-band effective mass Hamiltonian. A Schrödinger-Poisson self-consistent solver is used to describe the effect of charge screening under current injection. Our theoretical result shows a good match to the measured Hakki-Paoli gain spectrum. Combining the calculated gain spectrum and cavity properties, we have developed a device-level simulation to successfully explain the electrical and optical characteristics of this specific laser. Possible solutions to improving the device performance have been explored.

Detailed model for the In0.18Ga0.82N/GaN self-assembled quantum dot active material for λ = 420 nm emission.

We present a comprehensive model for In(0.18)Ga(0.82)N/GaN self-assembled quantum dot (QD) active material. The strain distribution in the QD structure is studied using linear elastic theory with the application of the shrink-fit boundary condition at the material interface. Subsequent calculations also predict the strain-induced quantum-confined Stark effect (QCSE). Under carrier injection, the overall effect of band bending and charge screening is studied by solving the Schrödinger and Poisson equations self-consistently. The optical gain spectrum of the InGaN/GaN QD active material is calculated based on the electronic states solved from the Schrödinger-Poisson equation, and both the calculated material gain peak and emission wavelength agree well with the measured experimental data.

Integrated tunable CMOS laser.

An integrated tunable CMOS laser for silicon photonics, operating at the C-band, and fabricated in a commercial CMOS foundry is presented. The III-V gain medium section is embedded in the silicon chip, and is hermetically sealed. The gain section is metal bonded to the silicon substrate creating low thermal resistance into the substrate and avoiding lattice mismatch problems. Optical characterization shows high performance in terms of side mode suppression ratio, relative intensity noise, and linewidth that is narrow enough for coherent communications.