TECHNOLOGY AREA(S): Chemical/Biological Defense, Sensors

ACQUISITION PROGRAM: EMW-FY14-01, Compact Wide Area Reconnaissance and Spectral Sensor

OBJECTIVE: Develop a fully-packaged short-wave infrared (SWIR, 900-1600 nm) spectrometer that uses photonic integrated circuit (PIC) technology and meets these requirements:� compact (handheld, < 0.5 kg), compatible with a single-mode optical source, broadband (>200 nm, >128 channels), precise (<1 nm resol.), efficient, and fabricated using a PIC foundry.

DESCRIPTION: PICs are emerging as low-cost replacements for fiber-optic systems that use many individual fiber components, as well as a number of bulk optical systems. The DoD is developing sensors based on Raman, fluorescence, and absorption spectroscopies for areas such as chemical warfare agent detection, in situ warfighter health analysis, and environmental monitoring. However, the critical part of PIC spectroscopy, the spectrometer, does not currently meet the needs of DoD spectroscopic sensors. Successful demonstrations of critical PIC components, such as arrayed waveguide gratings (AWGs), detectors, or edge couplers have not been integrated into a single fully-packaged SWIR spectrometer using a PIC foundry. A suitable PIC will have: total package size (target: < 100 cm3); PIC area (target: < 4 cm2); and efficiency (target: > 10% quantum efficiency). Such a PIC spectrometer could then be integrated with PIC transducers and on-chip sources for a fully integrated biological or chemical detector.

PHASE I: Design and analyze a proposed approach for a PIC-based SWIR spectrometer based on a center wavelength between 1150 nm and 1250 nm. Important design criteria are optical bandwidth (target: > 200nm); channels (target: >128); channel-to-channel extinction ratio (target: >30 dB); operation temperature (target: -10 deg C); resolution (target: < 1.5 nm full width at half maximum or FWHM). Demonstrate feasibility of the concept with S-parameter circuit (or equivalent) analysis based on Process Design Kit (PDK) component and/or custom component specifications for a specific PIC foundry. Ensure that the proposed device uses single-mode waveguide as optical input. Electronic detection can be done either with on-chip photodetectors (�active� PIC) with appropriate complementary metal-oxide-semiconductor (CMOS) backplane for readout, or with off-chip detection (�passive� PIC) with detector array optically coupled to PIC. Develop a Phase II plan.

PHASE II: Fabricate, assemble, package, and test the proposed approach described in Phase I. Final packaging should be clearly described and should include fiber-coupling to input waveguide for optical testing. Test the prototype first with a polarized white light source coupled to a single-mode optical fiber; and second with a polarized pump at 1064 nm co-propagating with simulated (or real) Raman signal approximately 10^8 times weaker, also in a single-mode optical fiber. Evaluate the prototype against the criteria listed in the Phase I description. If the prototype fails to meet the targets listed above, perform a root cause analysis, and describe/report design trade-offs necessary to reach all of the performance targets. Analyze the prototype design and packaging to determine additional engineering steps required to achieve (i) lower temperature operation (dual-stage thermoelectric cooler (TEC) down to -40 deg C); (ii) wider wavelength range (target 400 nm) and/or a center wavelength near 950 nm (instead of ~1200 nm); (iii) more output channels (512 channels); (iv) and lower resolution (< 0.25 nm). Describe a realistic path for the integration of this component into the component library PDK for a PIC foundry, and provide realistic estimates of the total cost to manufacture this component.

PHASE III DUAL USE APPLICATIONS: Integrate a PIC spectrometer with a PIC laser source and a PIC transducer for chemical or biological agent detection to create a chip-scale detection system that can be deployed to virtually every warfighter or unmanned detection platform in the DoD. This deployment can be done with the assistance of the contractor via the design of the full PIC system, the submission of the design to the PIC foundry, and the test and evaluation of the manufactured system.

A PIC spectrometer is an essential component of a PIC-based sensor. While small Size, Weight, and Power (SWaP) sensors for trace concentrations of chemical warfare agents or dilute bioagents have important applications for the DoD, the technology has many commercial applications as well. Many health science sensors, such as breath analysis or illicit drug screening can benefit from the same sensing technology. Also, environmental applications such as methane leak detection or air quality monitoring could also benefit from this low SWaP sensing platform.

REFERENCES:

1. Subramanian, A.Z. et al. �Silicon and silicon nitride photonic circuits for spectroscopic sensing on-a-chip.� Photonics Research 3, October 2015, B47-59. doi: 10.1364/PRJ.3.000B47

2. Wang, R. et al. �III-V-on-silicon photonic integrated circuits for spectroscopic sensing in the 2-4 um wavelength range.� Sensors 17, 1788 (2017). doi: 10.3390/s17081788

3. Stievater, T.H. et al. �Chemical sensors fabricated by a photonic integrated circuit foundry.� SPIE 10510, 1051001 (2018). doi: 10.1117/12.2294059

KEYWORDS: Photonic Integrated Circuit; Spectrometer; Spectroscopy; Infrared; Foundry; Detector