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We demonstrate a compact (40 ${\mu}$m $\times$ 260 ${\mu}$m) spectrometer based on multimode interference aided by scattering of light from random SiO$_2$-filled hole arrays on a silicon-on-insulator platform. We characterize the performance of the spectrometer for wavelengths around 1310 nm, and report that the spectrometer can reconstruct a broadband $\sim$ 67 nm source, as well as Lorentzian probes of $\sim$ 1 nm bandwidth. This compact nanometer level resolution spectrometer can be fabricated at a low cost for lab-on-a-chip sensing and imaging applications., Comment: 11 pages, 6 figures

The field of silicon photonics has experienced widespread adoption in the datacoms industry over the past decade, with a plethora of other applications emerging more recently such as light detection and ranging (LIDAR), sensing, quantum photonics, programmable photonics and artificial intelligence. As a result of this, many commercial complementary metal oxide semiconductor (CMOS) foundries have developed open access silicon photonics process lines, enabling the mass production of silicon photonics systems. On the other side of the spectrum, several research labs, typically within universities, have opened up their facilities for small scale prototyping, commonly exploiting e-beam lithography for wafer patterning. Within this ecosystem, there remains a challenge for early stage researchers to progress their novel and innovate designs from the research lab to the commercial foundries because of the lack of compatibility of the processing technologies (e-beam lithography is not an industry tool). The CORNERSTONE rapid-prototyping capability bridges this gap between research and industry by providing a rapid prototyping fabrication line based on deep-UV lithography to enable seamless scaling up of production volumes, whilst also retaining the ability for device level innovation, crucial for researchers, by offering flexibility in its process flows. This review article presents a summary of the current CORNERSTONE capabilities and an outlook for the future.

We demonstrate an on-chip Silicon-on-Insulator (SOI) axicon etched using a low resolution (200 nm feature size, 250 nm gap) deep-ultraviolet lithographic fabrication. The axicon consists of circular gratings with seven stages of 1x2 multimode interferometers. We present a technique to apodize the gratings azimuthally by breaking up the circles into arcs which successfully increased the penetration depth in the gratings from $\approx$5 $\mu$m to $\approx$55 $\mu$m. We characterize the device's performance by coupling 1300$\pm$50 nm swept source laser in to the chip from the axicon, and measuring the out-coupled light from a grating coupler. Further, we also present the implementation of balanced homodyne detection method for the spectral characterization of the device and show that the position of the output lobe of the axicon does not change significantly with wavelength.

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We investigate the membranes of cells fixed on a photonic chip using evanescent excitation and collection of Raman signals using single-mode nano-photonic waveguides. Enhancement and selectivity of the evanescent interaction allow for selectively probing the membrane with higher efficiency than confocal microscopes.