N242-100 TITLE: Photonics-Based Optical Frequency Shifter in the Near-Infrared (NIR)

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics; Quantum Science; Space Technology

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a technology that shifts the frequency of near-infrared (NIR) light in a waveguide while suppressing undesirable sidebands.

DESCRIPTION: Atomic accelerometers and clocks are important elements of advanced inertial navigation and timing systems. In recent years, there has been significant effort to reduce the size, weight and power (SWaP) of various subsystems. For the laser subsystem in particular, this is typically anticipated to be accomplished by a transition from bulk optics to photonic integrated circuits (PICs).

One of the challenging aspects of this transition is redesigning the laser architecture to be compatible with PICs. Some capabilities that are straightforward to achieve in a bulk system either do not have a direct analog in PICs or do not have a proven solution for the NIR wavelengths that are relevant for atomic sensors (e.g., rubidium at 780 nm and cesium at 852 nm).

Here we focus on acousto-optic modulation as a component that is often found in atomic system architectures. A bulk-crystal acousto-optic modulator can serve multiple functions:

1. A pure frequency shift, typically in the 10MHz-1GHz range

2. Optical pulse generation with sub-microsecond rise/fall time

3. Optical switching capability with low cross-talk between spatially-separated channels

4. Variable optical attenuation capability exceeding 20 dB

The goal of this SBIR topic is focused on the first function: the development a high-quality frequency shifter (i.e., one where spurious frequency contributions are highly suppressed) that is compatible with on-chip photonics integration. Current approaches include In-Phase/Quadrature (IQ) modulation [Ref 1] and acousto-optic modulation [Ref 2], among others [Ref 3]. All these components, however, are fabricated for primarily C-band laser systems. Although it is possible to frequency double a 1560 nm laser to produce 780 nm to satisfy a rubidium-based system, a natively NIR solution would be a valuable addition to PIC capability for multiple atomic species.

Technical requirements for the frequency shifter are below:

• Operating wavelength: 780 nm [threshold], devices compatible (not necessarily tunable) with 400-900 nm [objective]

• Optical power handling (at waveguide input): > 50 mW [threshold], > 300 mW [objective]

• Electrical power draw: < 1 W [threshold], < 100 mW [objective]

• Modulation 3dB bandwidth (without regard to modulation center frequency): > 1 MHz [threshold], > 5 GHz [objective]

• Spurious sideband suppression: < 20 dB [threshold], < 30 dB [objective]

Proposed technologies do not need to provide any of the additional capabilities 2-4 listed above. If the proposed approach happens to enable any of those functions, this fact should be described with enough detail to provide a sense for the scale of the changes required to achieve that functionality. The capability does not need to be proven experimentally.

PHASE I: Perform a design and materials study to assess the feasibility of the selected technology and its ability to meet the goals above. The final report will include:

• A discussion of how the technological approach will satisfy the requirements of the frequency shift function.

• An evaluation of the technology’s SWaP for the component that would be built in Phase II.

• A discussion of the fabrication process including an assessment of risks and risk mitigation strategies.

• A discussion of the technology’s compatibility with photonic integrated circuits.

• If applicable, a brief discussion of alternate capabilities enabled by the technological approach.

The Phase I Option, if exercised, will include the initial design specifications and description to build a prototype solution in Phase II.

PHASE II: Fabricate, test, and deliver three (3) prototypes of the design developed in Phase I. The completed prototypes shall be tested against the performance goals listed above. The final report shall include an assessment of potential near-term and long-term development efforts that would improve the technology’s technical performance, SWaP, and ease of fabrication. It shall also include an evaluation of the cost of fabrication and how that might be reduced in the future. The prototypes shall be delivered by the end of Phase II.

PHASE III DUAL USE APPLICATIONS: Based on the prototypes developed in Phase II, continue development to assist the Government in integrating the technology with other PIC components.

In addition to advancing a quantum sensing capability for military/strategic applications, this technology will improve the SWaP and lower the cost of hyperspectral imagers and near infrared spectrometers useful for environmental monitoring, biomedical imaging, and film/coating characterization.

REFERENCES:

1. Templier, S., et al. "Carrier-suppressed multiple-single-sideband laser source for atom cooling and interferometry." Physical Review Applied 16.4 (2021): 044018. https://arxiv.org/abs/2107.06258
2. Sarabalis, Christopher J., et al. "Acousto-optic modulation of a wavelength-scale waveguide." Optica 8.4 (2021), pp. 477-483. https://doi.org/10.1364/OPTICA.413401
3. Bo, Tianwai, et al. "Optical Single-Sideband Transmitters." Journal of Lightwave Technology 41.4 (2023): pp. 1163-1174. https://doi.org/10.1109/JLT.2022.3212473

KEYWORDS: Photonic integrated circuits; optical frequency control; inertial sensors; atomic clocks; atomic accelerometers

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