We report about optical spectrometry using gold nanostructures printed on top of an integrated optical waveguide. The optical waveguide is a single-mode buried waveguide made from a combination of photo-polymerizable materials and is fabricated by photolithography on a glass substrate. To detect the electric field inside the waveguide, a gold nanocoupler array of thin lines (50 nm thick and 8 μm in length) is embedded on top of the aforementioned waveguide. They are produced by e-beam lithography. Both waveguide ports are polished, and the output port, in particular, is coated with a thin gold layer to assimilate a mirror and hence, it enables the creation of stationary waves inside the structure. Stationary waves generated inside the guide constitute a spatial interferogram. Locally, light is out-coupled using the nanocouplers and allows measuring the interferogram structure. The resulting pattern is imaged by a vision system involving an optical microscope with the objective lenses of different magnifications and a digital camera mounted on top of the microscope. The 5× objective lens demonstrates a superior performance in retrieving the investigated spectrum compared to 20× and 100× objectives. Fast Fourier transform is performed on the captured signal to extract the spectral content of the measured signal.
We present an aspheric collimating lens for mid-infrared (4-14 μm) quantum cascade lasers. The lenses were
etched into silicon by an inductively coupled plasma reactive ion etching system on wafer level. The high
refractive index of silicon reduces the height of the lens profile resulting in a simple element working at high
numerical aperture (up to 0.82). Wafer level processes enable the fabrication of about 5000 lenses in parallel.
Such cost-effective collimating lens is a step towards the adoption of quantum cascade lasers for all its potential
Since the operating mode of 1.55 μm AlN/GaN-based intersubband photodetectors is based on optical rectification, both
the excited state lifetime and the lateral displacement of the carriers play an important role for performance optimization.
We thus show here results of an improved detector generation based on a novel type of active region. Thanks to the use
of quantum dots instead of quantum wells, a factor of 60 could be gained in terms of maximum responsivity. In addition,
the maximum performance was achieved at a considerably higher temperature of 160 K instead of 80 K as typically seen
for quantum wells.
We present our evaluation of a compact laser system made of a 795 nm VCSEL locked to the Rubidium absorption line
of a micro-fabricated absorption cell. The spectrum of the VCSEL was characterised, including its RIN, FM noise and
line-width. We optimised the signal-to-noise ratio and determined the frequency shifts versus the cell temperature and
the incident optical power. The frequency stability of the laser (Allan deviation) was measured using a high-resolution
wavemeter and an ECDL-based reference. Our results show that a fractional instability of ≤ 10-9 may be reached at any
timescale between 1 and 100'000 s. The MEMS cell was realised by dispensing the Rubidium in a glass-Silicon preform
which was then, sealed by anodic bonding. The overall thickness of the reference cell is 1.5 mm. No buffer gas was
added. The potential applications of this compact and low-consumption system range from optical interferometers to
basic laser spectroscopy. It is particularly attractive for mobile and space instruments where stable and accurate
wavelength references are needed.