We report measurements characterizing the performance of a kinetic inductance detector array designed for a wavelength of 25 microns and very low optical background level suitable for applications such as a far-infrared instrument on a cryogenically cooled space telescope. In a pulse-counting mode of operation at low optical flux, the detectors can resolve individual 25-micron photons. In an integrating mode, the detectors remain photon noise limited over more than 6 orders of magnitude in absorbed power from 70 zW to 200 fW, with a limiting noise equivalent power of 4.6×10-20 W Hz-1 at 1 Hz. In addition, the detectors are highly stable with flat power spectra under optical load down to 1 mHz. Operational parameters of the detector are determined including the efficiency of conversion of the incident optical power into quasiparticles in the aluminum absorbing element and the quasiparticle self-recombination constant.

Context. Integrated superconducting spectrometers (ISSs) for wide-band submillimeter (submm) astronomy use quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires an accurate alignment of the laser to the submm beam from the instrument, which is not always guaranteed to a sufficient accuracy. Aims. We develop an alignment strategy for wide-band ISSs that directly uses the submm beam of the wide-band ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wide-band ISS. Methods. We measured the misalignment in a quasi-optical system operating at submm wavelengths using a novel phase and amplitude measurement scheme that is capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the microwave kinetic inductance detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we followed a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns were taken across a harmonic range between 205 and 391 GHz and were simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Results. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the submm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.

Large format focal plane arrays (FPAs) of dielectric lenses are promising candidates for wide field-of-view submillimeter imagers. In this work, we optimize the scanning gain of such imagers via shaping lens surfaces. We develop an optimization procedure using a field correlation technique between the fields generated by a reflector on the top of the lenses and those generated by the lens feeds. Based on this procedure, an FPA of quartz lens antennas combined with leaky-wave feeds is designed to efficiently illuminate the reflector, achieving a directivity of 50.5 dBi up to scanning 20.3°. The obtained scanning gain loss of 2.6 dB is much lower than that associated with the direct fields coming from the reflector (about 6 dB). The proposed FPA is validated by full-wave simulations with excellent agreement. We have fabricated and measured an example shaped quartz lens optimized for the scanning angle of 20.3° at 180 GHz. The comparison between the simulations and the measurements also shows excellent agreement.

A system concept for online alignment verification of millimeter-wave, corneal reflectometry is presented. The system utilizes beam scanning to generate magnitude-only reflectivity maps of the cornea at 650 GHz and compares these images to a precomputed/measured template map to confirm/reject sufficient alignment. A system utilizing five off-axis parabolic mirrors, a thin film beam splitter, and two-axis galvanometric mirror was designed, simulated, and evaluated with geometric and physical optics. Simulation results informed the construction of a demonstrator system which was tested with a reference reflector. Similarity metrics computed with the aligned template and 26 misaligned positions, distributed on a 0.5 mm x 0.5 mm x 0.5 mm mesh, demonstrated sufficient misalignment detection sensitivity in 23 out of 26 positions. The results show that positional accuracy on the order of 0.5 mm is possible using 0.462 mm wavelength radiation due to the perturbation of coupling efficiency via beam distortion and beam walk-off.

This article presents a feasibility study of single feed per beam quasi-optical (QO) antennas for enabling incoherent multiple-input multiple-output (MIMO) array front-end architectures at 270 GHz. The objective is to reach ultrafast and radiated energy efficient point-to-point (PtP) wireless links by exploiting the multimode capacity of radiative (Fresnel region) near-field links. In this article, we present a feasibility study of the number of independent links achievable with QO MIMO incoherent arrays. For this purpose, we present theoretical curves of the level of EM co-coupling and interference between the multiple modes versus the link distance. The study focuses at the 252-325 GHz spectral bandwidth defined by the new IEEE 802.15.3d standard. A specific and new MIMO array architecture operating at 270 GHz based on a 2 × 2 array of parabolic reflectors is proposed for a link distance of 100 m. The proposed PtP MIMO system is capable of generating 16 dual-polarized modes in a 70 GHz bandwidth with signal-to-interference ratio >17 dB and a power co-coupling coefficient of -3 dB without the need for interference cancelation techniques. Combining this architecture with wideband front ends could potentially lead to an aggregated data rate in the order of terabit per second in a PtP wireless line-of-sight link, not previously achieved experimentally to the best of authors' knowledge.

Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here, we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220–440 GHz band in a single shot, corresponding to a redshift range of z = 3.3–7.6 for the ionized carbon emission ([C II] 158 μ m). The first-light experiment of DESHIMA 1.0, using the 332–377 GHz band, has shown an excellent agreement among the on-sky measurements, the laboratory measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign.

An efficient method for rapid, non-contact scanning of human cornea is presented. The optics utilize two, 101.6-mm diameter off-axis parabolic mirrors fed by a goniometrically scanned, planar mirror. An evaluation system at 650 GHz was built and demonstrated ~ 1.5 mm beam radius on target and ~ 30 ^o x 30 ^o field of view. The system was inspired by confocal laser scanning principles and represents a system design where image acquisition time is limited by SNR, not mechanical translation.

We present a freely accessible graphical user interface (GUI) for analyzing antenna-fed quasi-optical (QO) systems in reception (Rx). This analysis is presented here for four widely used canonical QO components: parabolic reflectors and elliptical, extended hemispherical, and hyperbolic lenses. The employed methods are geometrical optics (GO) and Fourier optics (FO). Specifically, QO components are illuminated by incident plane waves. By using a GO-based propagation code, the scattered fields are evaluated at an equivalent sphere centered on the primary focus of the component. The FO methodology is then used to represent the scattered fields over the focal plane as plane wave spectrum. A field correlation between this spectrum and the antenna feed radiating without the QO component is implemented to evaluate the induced open-circuit voltage on the feed in Rx. By performing a field matching between these two spectral fields, feed designers can optimize the broadside and/or steering aperture efficiencies of QO systems in a fast manner. The tool is packaged into a MATLAB GUI, which reports the efficiency terms, directivity, and gain patterns of antenna-coupled QO systems. The described tool is validated via full-wave simulations with excellent agreement.

DESHIMA 2.0 is a spectrometer for astronomical applications targeting sources at sub-mm wavelengths from 240GHz to 720GHz. The design for its wide band Quasi-Optical system was presented in the previous works. In this work, the experimental validation of the beam pattern of the system at the lower end of its frequency band is presented. The measurement for the complete frequency band of the system is ongoing and will be presented at the conference.