OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Space Technology OBJECTIVE: The U.S. Space Force (USSF) will require high accuracy navigation attitude systems for use in proliferated constellations with smaller space vehicles. Current low mass micro electro-mechanical (MEMS) gyroscopes do not have the required performance to allow precision operation in small space vehicles. A gyroscope with MEMS size weight and power but with high navigation-grade performance would enable precision pointing of small space vehicles. Small high-grade gyros would also have applications in counterspace uses both for offensive and defensive efforts. Laser communication terminals and hosted sensor payloads would benefit from low mass rate sensors on the gimbaled assembly. DESCRIPTION: There is an ongoing effort to leverage unique advantages in gyro sensitivity versus size when an optical system is operated at what is termed an exceptional point. The exceptional point in a nanophotonic system which occurs when the gain and loss are balanced. The resulting operational singularity radically changes the behavior of the optical system and creates large changes in system response to external stimulus. A macro scale ring laser gyro (RLG) has sensitivity that is highly dependent on the optical ring resonator loss and the enclosed path length that the light travels. Operation of a nano scale RLG at an exceptional point promises to overcome the limitations of the very short optical path length. Utilization of the behavior singularity at the exceptional point is only possible due to recent developments in exploiting gain/loss properties in nano scale waveguides. To develop a nano scale RLG which operates at the exceptional point, you first need a nano scale RLG which operates in the standard regime of parity-time (PT) symmetry. Once that is achieved, the design can be manipulated to reach the point where parity-time symmetry breaks down and operation is at the exceptional point. This effort supports development of the PT-symmetry chip level RLG as well as error modeling for a future RLG operating at the exceptional point. The project will attempt to leverage advances in gyro technology to enable better than navigation grade performance from a single channel gyro with a one cubic inch volume. The final design should target 1 W per active channel for power consumption. The technology employed will need to be radiation hardened in the future. Target ARW is 0.005 deg/rt-hr. Bias stability at constant temperature target is 0.05 deg/hr at 30 minutes. The gyro dynamic range will be up to 10 deg/s. Performance must be maintained through TBD g acceleration in any orientation relative to the gyro sensing axis. Gyro scale factor nonlinearity from 1 deg/sec to 10 deg/sec magnitude will be less than 10 ppm after any compensation. The SF error of between +1 deg/sec and -1 deg/sec will be 0.036 deg/hr. The SF spec is 2-sigma. These performance goals are very challenging for the sensor size and could be reconsidered if the technology demonstrates promise in initial prototypes. PHASE I: Phase I will produce a design for a chip level phase-time (PT) symmetric ring laser gyro (RLG). Further investigation into what is required to push the design to the exceptional point will be done. While the concept of an RLG operating in the mode is still at an early stage of development, it is desired to assess the practical aspects of operational use of the device. For example, operation at the exceptional point (EP) requires high bandwidth servos to assess where is the EP is and to keep the gyro at that point. Behavior on either side of the EP is drastically different than at the singularity itself. Models should be developed to assess expected instrument output in the presence of EP control loop error. Temperature sensitivity could be quite high. Models should be developed to assess required temperature stability of the nano-optical substrate needed to maintain EP operation. Phase I will design a sensor which demonstrates 50% of the required static environment performance. Brass board electronics without flight representative size are acceptable. The sensor form factor will be flight representative. Meeting the 50% static performance goal with a 1 ci sensor volume is a challenging task and will enable assessment of the technology's suitability to meet the higher performance goals. Error models of the sensor shall be presented which show a path to the target static and dynamic performance. PHASE II: Phase II will produce a sensor which satisfies the complete performance requirement. Error models described in Phase I would be enhanced to account for measured characteristics of the functional device. The supporting electronics should be small enough at the end of Phase II to be able to be mounted on a 24 rate table platter to facilitate dynamic testing. Error models should be sufficiently developed to be able to provide a realistic prediction of gyro noise, gyro bias stability, and scale factor non-linearity. PHASE III DUAL USE APPLICATIONS: The prototype gyro and Phase II electronics will be tested in an actual dynamic environment with DC rate, AC rate, and reasonable temperature diurnal. The data will be used to validate behavioral models from Phase II. Testing of this type can be performed at The Aerospace Corporation if the small business does not have suitable facilities. REFERENCES: Mercedeh Khajavikhan, Yuzhou (Nathan) Liu & Mohammad Hokmabadi (USC), Alex Schumer (TU Wien), Ardy Winoto & Gloria Hoefler (Infinera), Demetrios Christodoulides (UCF-CREOL), Parity-Time Symmetric Ring Laser Gyroscopes ; J. Ren, H. Hodaei, G. Harari, A. U. Hassan, W. Chow, M. Soltani, D. Christodoulides, M. Khajavikhan, Ultrasensitive micro-scale parity-time-symmetric ring laser gyroscope, Optics Letters, Vol. 42, Issue 8, pp. 1556-1559, (2017), https://doi.org/10.1364/OL.42.001556; KEYWORDS: ring laser gyro; distributed constellations; nanophotonic system; precision pointing; Gyroscope, GNC (Guidance, Navigation, & Control), RLG (Ring Laser Gyro), MEMS (micro electro-mechanical), gimbal, attitude control, Sagnac effect
