In millimeter-wave astronomy, there is a need for innovative focal plane arrays that facilitate observations with low to medium spectral resolution and allow astronomers to identify a set of potentially interesting sources, such as high-redshift galaxies with moderate mapping speed. These spectrally-resolving arrays can also support the Line Intensity Mapping (LIM) technique, which can help researchers disentangle the emission lines as a function of redshift. To achieve the intermediate spectral resolution (i.e. 100-1000) while preserving the high sensitivity, there are recent developments in designing multiple on-chip spectrometers based on kinetic inductance detectors (KIDs) like DESHIMA, SuperSpec, μ-Spec, etc.
In this presentation, we will discuss the simulation, design, fabrication, and optical characterization of focal-plane on-chip spectrometers of two different types, On-chip spectrometer using Microstrip based Kinetic Inductance Detector (OMKID)[1], and HYPer-spectral device with Kinetic Inductance Detector (HYPKID)[2], both are sensitive in the 75-110 GHz range. These are prototype designs where the incoming signal is split over different sub-bands using filters and each filter is capacitively coupled to a lumped-element kinetic inductance detector (LEKID) to identify the spectral responses. Both devices are designed based on microstrip configuration which provides the benefit of low loss, due to the mono-crystalline substrate.
The prototype spectrometers exhibit spectral resolution (R) of 200 - 1000. The optical noise equivalent power is around 10^-17 W/rt(Hz) which is in the range of an incoming power of pW per channel, confirming the gain in quantum efficiency as predicted by the electromagnetic simulations.This work affirms the reliability of both the proposed on-chip spectrometer designs while keeping an open possibility of significant improvement of the overall efficiency in the future iterations of these devices.

References :
1. U. Chowdhury, F. Levy-Bertrand, M. Calvo, J. Goupy and A. Monfardini, A horn-coupled millimetre-wave on-chip spectrometer based on lumped-element kinetic inductance detectors, A&A, 672 (2023) A7, DOI : https://doi.org/10.1051/0004-6361/202244887
2. U Chowdhury, M Calvo, J Goupy, F Levy-Bertrand, A Monfardini, A millimetre-wave superconducting hyper-spectral device, RAS Techniques and Instruments, Volume 2, Issue 1, January 2023, Pages 562–566, https://doi.org/10.1093/rasti/rzad038