Narrative Summary. Application of standard theoretical approach to ring lasers does not give a clear quantitative answer on the magnitude of the Sagnac effect in a medium with substantial dispersion (such as in semiconductor materials). Generally, the influence of the medium is accounted for through the refractive index and the drag coefficient ad given by the Fresnel-Fizeau formula. In most laser gyros, the active medium of the ring has negligible material dispersion. In contrast, dispersion effects are expected to be substantial in compact monolithically integrated gyros based on semiconductor media.
The essence of the problem of the drag coefficient is its questionable modification for rotational motion. The drag coefficient in the Fresnel-Lorentz treatment contains a dispersion-related contribution lnn/lnl. In gas or solid-state media, it gives a very small correction to the observable optical dragging. In semiconductors, the dispersion term lnn/lnl is large enough to influence not only the magnitude, but even the sign of the net drag effect. However, when this term is included in modeling of the ring laser, the gyroscopic response becomes sensitive to translational motion, in contradiction with Einstein's relativity principle. The problem was first noted in 1967 by E. Post, who somewhat arbitrarily excluded the dispersion term from the drag coefficient in order to comply with the relativity principle. Until now, no experimental verification of Post's approach was attempted.
Recently, the PI has succeeded in development of monolithically integrated semiconductor ring lasers (SRLs) with relatively large (~1 cm) cavity and were able to observe the mode beating spectra from independent lasers. This opens up a possibility to perform experimental investigation of the question about contribution of dispersion term into the Sagnac effect. Experiments will be performed for precise determination of the gyroscopic coefficient in SRLs and the results will be compared with various theoretical predictions. Without these tests, the fundamental gyroscopic ratio (the ratio of Sagnac-related frequency splitting to the angular rotation rate) cannot be reliably calculated.
Intellectual Merit Criterion. In spite of their promising compactness and low power consumption, SRLs have not yet been used for gyro applications, primarily due to flaws in previous designs. This project will provide scientific base for ultimate elaboration of rotation sensing problem using SRLs: how to avoid the frequency lock-in, enhance the gyro-factor, exclude excess noise, and apply novel approaches such as slow/fast light concept.
The University of New Mexico (UNM) group led by Prof. Osinski has the best experience and numerous results in physics and technology of semiconductor ring lasers. The proposed work holds promise of overcoming the current limitations for integrated optoelectronic devices. The results will be important for fundamental physics of rotational motion (non-inertial frames and systems) and also for applied physics of rotation sensors and navigation gyroscopes. The results from this project are expected to lead to a new generation of rotation sensors based on slow/fast light.
Broader Impacts Criterion. First demonstration of Sagnac effect in monolithically integrated SRLs coupled with conclusive studies of dispersion contribution to the magnitude of the effect will open up new opportunities for high performance, small size, low cost rotation sensors with a wide range of novel applications, ranging from robotics and toy industry to high-accuracy navigation-grade gyros. UNM has a dual commitment to excellence in research and to education opportunities for minorities and diverse society. UNM is Carnegie Doctoral/Research - Extensive and Hispanic Serving Minority Institution (37.5% of main campus enrollment are minority students). Emphasis will be placed on education and human resource development via involvement of graduate and undergraduate students in the project, and incorporation of the new knowledge gained during this project into graduate-level courses directly related to the subject of this proposal. Efforts will be made to engage members of minority groups as well as women in this project. The proposed project will create an attractive environment for students supported by other major programs already in existence at UNM that target minority students and are devoted to training of a new generation of research scientists and engineers.
