OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy; Hypersonics
OBJECTIVE: This topic seeks to develop wafer scale processes to produce compact and robust low loss, magnetless, magneto-optic isolators. This technology should show a path towards compatibility with commercial silicon photonics foundries (preferably AIM Photonics), either through homogeneous, hybrid, or heterogeneous integration. These isolators should target isolation of 780 nm optical wavelength for quantum applications, and have an optical loss of < 3 dB, and an isolation ratio of > 20 dB. Due to the 780 nm wavelength, it is anticipated that integration with the semiconductor photonics platform may be through an intermediate dielectric waveguide layer such as silicon nitride. However, other approaches may be proposed, provided the optical loss specification can be met. Optical loss is of critical importance in single photon quantum systems. Judicious selection of the magneto-optic material or device structure, low scatter loss waveguides, design of mode matching device structures will be an important aspect of the isolator integration development process.
DESCRIPTION: Optical isolators are a key element in preventing the deleterious effects of back reflections and standing waves in integrated photonic circuits. Quantum technologies are especially susceptible to these effects since they are inherently highly coherent systems operating at extremely small photon counts, with a high integration density on a single compact chip. The most common type of optical isolator is based on the Faraday magneto-optic effect, of which bulk isolators are currently available that are based on externally applied magnetic fields. Fiber-connectorized isolator components are available, but are still based on discrete free space coupled bulk elements within the component package. Demonstrations of quantum key distribution and sensing have been done at the benchtop level using such discrete parts. The challenge now is to implement these circuits in a chip-scale integrated photonic form-factor such that they are robust and compact enough to place on airborne and space platforms. While integrated magneto-optic isolators have been realized, they typically rely on external magnets, either from a permanent magnet or from an electromagnet. An important requirement for quantum technologies is that the isolator element be magnetless since the presence of a magnetic field in a high density photonic circuit can disrupt single photon quantum entanglement processes. Additionally, it is also anticipated that such magnetless integration will reduce the size and cost of these circuits through wafer scale production and economies of scale. Significant strides have been made in developing magnetless integrated isolators that operate at telecommunications wavelengths, and other efforts have scaled the technology to operate at the 780nm wavelength targeting quantum applications. These works have typically relied on the use of latched magneto-optic films or through resonant acousto-optic effects.
PHASE I: This topic is intended for technology proven ready to move directly into a Phase II. Therefore, a Phase I award is not required. The offeror is required to provide detail and documentation in the Direct to Phase II proposal which demonstrates accomplishment of a “Phase I-type” effort, including a feasibility study. This includes determining, insofar as possible, the scientific and technical merit and feasibility of ideas appearing to have commercial potential. Device designs demonstrating the ability for magnetless optical isolation must be provided either through simulation, or preferably, previously-fabricated and tested devices. While operation at 780nm and integration within a commercial foundry-like platform are not required for the proposal, a realistic plan to take the previously designed device to this point must be provided.
PHASE II: Eligibility for D2P2 is predicated on the offeror having performed a “Phase I-like” effort predominantly separate from the SBIR Programs. Under the phase II effort, the offeror shall sufficiently develop the device design and fabrication process for the 780nanometer isolator structure. This device will then be fabricated and characterized, with the intended performance meeting the required specifications. This device structure must then be adapted to a platform compatible with commercial integrated photonics foundries (preferably AIM Photonics). Ideally, work with the commercial foundry will begin and proposer will demonstrate preliminary integration of the device design with the foundry itself (for example, successful integration and characterization of a magneto-optic material bonded to the AIM Photonics interposer platform). At the end of the effort, reports and characterization results will be provided to AFRL, as well as a fabricated device for independent test verification in AFRL’s laboratories. These Phase II awards are intended to provide a path to commercialization, not the final step for the proposed solution.
PHASE III DUAL USE APPLICATIONS: The contractor will pursue commercialization of the device design developed in Phase II for transitioning expanded mission capability to a broad range of potential government and civilian users and alternate mission applications through a commercial integrated photonics foundry. Direct access with end users and government customers will be provided with opportunities to receive Phase III awards for providing the government additional research & development, or direct procurement of products and services developed in coordination with the program. This work should meet at least Technology Readiness Level 4 before entry into Phase III, and a specific foundry for which the technology will be inserted must be identified. The foundry must be accessible by the DAF for DoD applications (this will place limitations on overseas foundries), and will be preferably domestic.
REFERENCES: 1. E. Kesto, V. Stenger, A. Pollick, S. Nelson, M. Levy. (2022) Bias-Magnet-Free Optical Isolating Ridge Waveguide Operating at 780 nm. Journal of Lightwave Technology 40:18, 6207-6212, (2022);
2. Sohn, D.B., Örsel, O.E. & Bahl, G. Electrically driven optical isolation through phonon-mediated photonic Autler–Townes splitting. Nat. Photon. 15, 822–827 (2021);
3. M. Serrano, Y. Shoji, T. Mizumoto, “Small magnetless integrated optical isolator using a magnetized cobalt ferrite film. IEICE Electronics Express. 19. 10.1587/elex.18.20210500. 2021;
4. G. Portela, M. Levy, H.E. Hernandez “Magnetless Optical Circulator Based on an Iron Garnet with Reduced Magnetization Saturation,” Molecules (Basel, Switzerland) vol. 26, 15 4692, (2021);
KEYWORDS: isolator; magneto-optic; integrated photonics; quantum