Towards lab-on-chip ultrasensitive ethanol detection using photonic crystal waveguide operating in the mid-infrared

Abstract

Thanks to the unique molecular fingerprints in the mid-infrared spectral region, absorption spectroscopy in this regime has attracted widespread attention in recent years. Contrary to commercially available infrared spectrometers, which are limited by being bulky and cost-intensive, laboratory-on-chip infrared spectrometers can offer sensor advancements including raw sensing performance in addition to use such as enhanced portability. Several platforms have been proposed in the past for on-chip ethanol detection. However, selective sensing with high sensitivity at room temperature has remained a challenge. Here, we experimentally demonstrate an on-chip ethyl alcohol sensor based on a holey photonic crystal waveguide on silicon on insulator-based photonics sensing platform offering an enhanced photoabsorption thus improving sensitivity. This is achieved by designing and engineering an optical slow-light mode with a high group-index of n g = 73 and a strong localization of modal power in analyte, enabled by the photonic crystal waveguide structure. This approach includes a codesign paradigm that uniquely features an increased effective path length traversed by the guided wave through the to-be-sensed gas analyte. This PIC-based lab-on-chip sensor is exemplary, spectrally designed to operate at the center wavelength of 3.4 μm to match the peak absorbance for ethanol. However, the slow-light enhancement concept is universal offering to cover a wide design-window and spectral ranges towards sensing a plurality of gas species. Using the holey photonic crystal waveguide, we demonstrate the capability of achieving parts per billion levels of gas detection precision. High sensitivity combined with tailorable spectral range along with a compact form-factor enables a new class of portable photonic sensor platforms when combined with integrated with quantum cascade laser and detectors.

Free-space optical multiplexed orbital angular momentum beam identification system using Fourier optical convolutional layer based on 4f system

“…Light reflected from the first DMD is naturally Fourier transformed passing through the first Fourier lens at one focal length, f, apart from the first DMD in the object plane. [103][104][105][106][107][108][109][110][111][112][113][114][115][116] The pattern in the second DMD, with particular orientation with respect to the first one, acts as a spatial mask in the Fourier plane, periodically selecting the spatial frequency components of the input image. The frequency filtered image is inverse Fourier transformed into the real space by the second Fourier lens and imaged by a high-speed camera.…”

Slow-Light Enhanced Liquid and Gas Sensing Using 2-D Photonic Crystal Line Waveguides—A Review

“…The authors reported a 11.7% of absorption drop observed on the introduction of gas in a PhCW made using SOI platform. An updated work with 250 ppb detection limit was also reported [98] A 2D rod-type PhCW was also discussed for methane (CH 4 ) detection in the Mid-IR regime [99]. The FDTD analysis was performed for gas concentration of 700 ppm.…”

Michelson interferometric methods for full optical complex convolution

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