OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Quantum Science; Advanced Materials 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: Development of a low size, weight, and power photonically integrated laser system that includes a narrow linewidth (under 10 kilohertz) laser natively at 778.1 nanometers, specifically the rubidium two-photon transition frequency, and a non-magnetic or minimally magnetic on-chip optical isolator with at least 30 decibels of isolation. The device should be packaged in a standard enclosure such as a butterfly package with all electrical connections made, and fiber-coupled with at least 40 milliwatts out of a polarization-maintaining fiber. DESCRIPTION: Atomic clocks have seen a revolution in technology over the past decade as they have pushed towards chip-scale sizes, allowing them to be used in communications, navigation, and other defense-related technologies [1]. Future technologies such as clocks for "5G" networks and future Global Navigation Satellite System architectures could potentially incorporate more advanced clocks. Optical clocks such as the rubidium two-photon clock offers potential improvements over current chip scale clocks and surpass rubidium atomic frequency references [2]. One limiting factor in future, more advanced optical clocks is the development of the needed laser technology. Optical clocks require narrow linewidths down to kHz linewidths for the rubidium two photon optical clock, or even more narrow for other optical clocks such as strontium. These devices must be optically isolated to ensure the narrow linewidth and to avoid reflections causing unwanted lasing modes. Current systems typically employ a series of free space or fiber coupled components to achieve narrow linewidths and high optical power [2], but they can be susceptible to vibrations and shock. Furthermore, these systems typically have optical isolators with large magnetic fields, limiting the compactness of the device due to the effect of the magnetic field on the atoms. Recently, there have been advancements in each individual area such as narrow linewidth lasers [3, 4], on-chip non-magnetic isolators [5, 6], and new integration techniques [7]. The creation of such a device will not only enhance the manufacturability of the clock and lower the overall size, weight, and power, but it will also increase the environmental robustness to effects such as shock and vibration [8]. However, these devices have not been integrated into a single photonically integrated package. The DoD seeks the development of a photonically integrated circuit that includes a narrow linewidth laser and an on-chip non-magnetic optical isolator in a single package to serve the needs for next generation optical clocks. PHASE I: Initial design and simulation of a sub-10 kilohertz linewidth laser at 778.1 nanometers, specifically the rubidium two-photon transition frequency, as well as a non-magnetic or minimally magnetic on-chip optical isolator with greater than 30 decibels of isolation and a fiber-coupled output greater than 40 milliwatts. Also a method for integrating the devices into a single package, either heterogeneous or hybrid integration, that allows for mass fabrication, ideally at the foundry level. PHASE II: Packaged device with a sub-10 kilohertz linewidth laser at 778.1 nanometers, specifically the rubidium two-photon transition frequency, integrated with a non-magnetic or minimally magnetic on-chip isolator that provides at least 30 decibels of isolation, and fiber coupled. The means of integration should allow for mass fabrication, ideally at a foundry level. It should provide at least 40 milliwatts out of a polarization-maintaining fiber with greater than 25 decibels polarization extinction ratio. The packaging should contain all electrical connections and thermal control, and be mounted in a standard style enclosure, such as a butterfly package, with a polarization maintaining fiber out. At least 2 prototypes are expected to be delivered. PHASE III DUAL USE APPLICATIONS: These devices will be extremely useful for a variety of applications such as next generation optical and atomic clocks, but will require further testing for shock and vibration, acceleration sensitivity, radiation tolerance, etc. REFERENCES: Kitching, J., Chip-scale atomic devices, Appl. Phys. Rev. 5, 031302 (2018); Lemke, N., Martin, K., Beard, R., Stuhl, B., Metcalf, A., Elgin, J., Measurement of Optical Rubidium Clock Frequency Spanning 65 Days, Sensors 22, 1982 (2022); Corato-Zanarella, M., Gil-Molina, A., Ji, X. et al. Widely tunable and narrow-linewidth chip-scale lasers from near-ultraviolet to near-infrared wavelengths. Nat. Photon. 17, 157 164 (2023); Chauhan, N., Isichenko, A., Liu, K. et al. Visible light photonic integrated Brillouin laser. Nat Commun 12, 4685 (2021); Tian, H., Liu, J., Siddharth, A. et al. Magnetic-free silicon nitride integrated optical isolator. Nat. Photon. 15, 828 836 (2021); White, A.D., Ahn, G.H., Gasse, K.V. et al. Integrated passive nonlinear optical isolators. Nat. Photon. 17, 143 149 (2023); Tran, M.A., Zhang, C., Morin, T.J. et al. Extending the spectrum of fully integrated photonics to submicrometre wavelengths. Nature 610, 54 60 (2022); Niffenegger, R.J., Stuart, J., Sorace-Agaskar, C. et al. Integrated multi-wavelength control of an ion qubit. Nature 586, 538 542 (2020).; KEYWORDS: Laser; integrated photonics; optical clock; optical isolators
