TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: Future INP on IR sensors, following current ARC on Long range ISR in Degraded Visual Environments

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OBJECTIVE: Develop a capability to enable digital data reports from microwave kinetic inductance detector (MKID) arrays that are currently being read out via analog wideband frequency-division multiplexed (FDM) techniques.

DESCRIPTION: Imaging through dense fog is desirable from a continuity of operations point of view and is expected to be achievable using large arrays of highly sensitive, cryogenic photon detectors such as Microwave Kinetic Inductance Detectors (MKIDs). These detectors are typically cooled to very low (&tl; 1 K) temperatures to obtain best sensitivity. Today's most prevalent readout method is to make each detector as a micro-resonator at a unique carrier frequency. Analog multiplexing in the frequency domain is then used twice: an analog signal comprising a closely-spaced frequency comb is sent down to the array by a programmable signal generator and the comb elements are amplitude and phase modulated by transmission through the resonator array. Allowing 1 MHz wide frequency domains per sensor, a 10,000-element detector array requires 10 GHz of instantaneous bandwidth.

Such a wideband, closely spaced frequency comb emanating from low-temperature is particularly vulnerable to nonlinear distortion and noise pick-up. It must be transported up the temperature gradient and to the signal analysis system with extreme fidelity in order to retain the information while also maximizing the field of view (FOV) of the imagery. Any nonlinearity in high-gain low-noise amplifiers that are required by current analog readout systems, can compromise the signal quality by creating intermodulation products. By performing digitization as close as possible to the sensing elements of the focal plane, signal quality will be maximally preserved. Therefore, while room temperature Analog to Digital Converters (ADC) are currently used in the read-out, digitization of the wideband signal on/close to the focal plane is preferable following little or no analog amplification.

Low-power cryogenic ADCs, such as superconductor ADCs, make this possible, even convenient, given the cryogenic requirements of the MKIDs. Digital readout approaches must balance requirements on instantaneous bandwidth (scaling in number of pixels in field of view) and dynamic range (impacting image contrast), which together determine the image quality, with total power consumption (<10 kW from wall desired). Digital multiplexing approaches of either electrical or optical character that reduce the number of output lines from the cryogenic environment are also of interest. Superconductor ADCs with sample rates up to 100 GHz have been demonstrated. Such ADCs would need to be optimized for sensitivity, dynamic range, and low power consumption for the Frequency Division Multiplex Module (FDM) detector readout application while showing documented ability for co-fabrication with MKIDs. Semiconductor ADCs require demonstration of integration feasibility, including power dissipated in the cryogenic environment, and performance.

Phase I proposals need to define a definite approach to be taken and include an analysis of technical risks for this approach/application. The base period should noticeably reduce the total technical risk and produce the initial Phase II proposal. The Phase I option, if awarded, should further reduce the total technical risk. The proposed technical approaches should include all aspects of data transport, including cryogenic cables and data recovery circuits at room temperature. Approaches including standard non-proprietary interfaces are strongly preferred.

PHASE I: Develop a conceptual design through modeling and prototype circuit measurements for a complete digital readout system compatible with a large, scalable cryogenic detector arrays. Design should include quantified trade-off between ADC dynamic range and the number of pixels feasible to individually digitize. Quantify risk of non-linear distortion of array readout signal as a function of separation of frequencies in the comb.

PHASE II: Develop and demonstrate a prototype detector readout scheme and its associated components and integrate them on a cryogenic platform (consistent with that needed by MKID detector array) produced using a COTS cooler. By the end of phase II option demonstrate the operation of delivery and removal of a comb of 64 discontinuously amplitude modulated frequencies or more to a circuit with MKIDs-like output functionality. Experimentally quantify required separation of comb frequencies to achieve low bit error rate from digitizer to room temperature processors. In option II or before, replace MKIDS-like circuit with actual MKIDS linear array and prove readout circuitry can report out all elements in at least a scanning mode. Determine the range of signal pulse durations reported. Engineer a readout system suitable for cost-share source’s highest priority MKIDS system.

PHASE III DUAL USE APPLICATIONS: Build a first ever imaging system comprising a cryogenic MKIDS detector array and the readout circuit designed according to stakeholder’s requirements and demonstrated to TRL4 or above in Phase II. Private Sector Commercial Potential: Both nuclear and high energy physics research requires large area, rad hard imaging arrays to allow accurate reproduction of complex events and discovery of new physics. The materials science, and conceivably manufacturing industry, also needs this sort of detectors for compositional uniformity metrics. Many petaflop computing centers may also benefit from this work if 4K superconducting circuits are used for the raw digital processing since many bit wide results data will need to be transmitted back to room temperature at high rates.

REFERENCES:

• P.K. Day, et al., "Broadband superconducting detector suitable for large arrays," Nature 425, pp. 817-821 (2003).
• H. Leduc, et al., "Titanium Nitride Films for Ultrasensitive Kinetic Inductance Detectors", Appl. Phys. Lett., 97, 102509 (2010); available online at http://arxiv.org/abs/1003.5584.
• J.J. Baselmans, et al., "Development of high-Q superconducting resonators for use as kinetic inductance detectors", Adv. Space Research 40, pp. 706-713 (2007).
• B.A. Mazin, et al., "Digital readouts for large microwave low-temperature detector arrays", Proc. 11th Int. Workshop on Low Temp. Detectors, in Nuclear Instrum. & Methods in Phys. Research A559, pp. 799-801 (2006).

KEYWORDS: Microwave Kinetic Inductance Detectors; imaging arrays; wavelength division multiplexing; frequency division multiplexing; cryogenic detectors; thermal engineering

** TOPIC AUTHOR (TPOC) **

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