Enhanced rotation sensing by nonlinear interactions in silicon microresonators.

We analyze the effect of the nonlinear Kerr index of refraction and two-photon absorption (TPA) in a rotating silicon microring resonator coupled to waveguides in an add-drop configuration. The nonlinear index of refraction leads to a bifurcation of the intensities of two counterpropagating modes in the nonrotating state. This bifurcation also significantly enhances the intensity difference between these modes due to the Sagnac-induced frequency splitting of the modes in the rotating resonator. Although silicon resonators have a very large Kerr index, they also suffer from large TPA at telecom wavelengths. It is shown that despite TPA, the Kerr nonlinear enhancement to the rotation sensitivity is still of the order of 104. An analysis of typical detector noise indicates that a detection limit of <1 deg/h in a 1.4 mm radius resonator is achievable.

Effect of resonator losses on the sensitivity of coupled resonator optical waveguide gyroscopes.

Recently there has been a growing interest in microphotonic integrated optical gyroscopes. Here, we analyze the effect of resonator losses on the rotational sensitivity of a coupled resonator optical waveguide (CROW) gyroscope in comparison to a single passive resonator gyroscope of the same size. We show that the CROW gyro offers a superior sensitivity only for very low propagation losses. Moreover, the single ring resonator gyro is found to have a sensitivity that is stable over wide range of resonator losses as well as boasting greater sensitivities than the CROW gyro for propagation losses in the resonators exceeding 10⁻¹ dB/cm.

Nonlinearly enhanced refractive index sensing in coupled optical microresonators.

We study the use of nonlinear self-phase modulation (SPM) in coupled optical microresonators for ultrasensitive refractive index sensing. SPM leads to a positive feedback enhancement of the resonance frequency shift caused by a perturbation of the index of refraction in a resonator. Moreover, the use of two resonators coupled through input and output waveguides leads to a further improvement in the sensitivity owing to constructive interference and feedback via the waveguides. For parameters based on Si microresonators, the sensitivity is more than 10(2) larger than a single resonator without SPM leading to a minimum detectable index change of 10(-11) RIU with resonator Q-factors of ~10(4). We show that the nonlinearly enhanced system is robust with respect to laser noise when operated at input powers below the onset of bistability.

Ultra-sensitive chip scale Sagnac gyroscope based on periodically modulated coupling of a coupled resonator optical waveguide.

We analyze the sensitivity to inertial rotations Ω of a micron scale integrated gyroscope consisting of a coupled resonator optical waveguide (CROW). We show here that by periodic modulation of the evanescent coupling between resonators, the sensitivity to rotations can be enhanced by a factor up to 10(9) in comparison to a conventional CROW with uniform coupling between resonators. Moreover, the overall shape of the transmission through this CROW superlattice is qualitatively changed resulting in a single sharp transmission resonance located at Ω = 0s-1 instead of a broad transmission band. The modulated coupling therefore allows the CROW gyroscope to operate without phase biasing and with sensitivities suitable for inertial navigation even with the inclusion of resonator losses.

Index of refraction engineering in five-level dressed interacting ground states atoms.

We present a five-level atomic system in which the index of refraction of a probe laser can be enhanced or reduced below unity with vanishing absorption in the region between pairs of absorption and gain lines formed by dressing of the atoms with a control laser and rf/microwave fields. By weak incoherent pumping of the population into a single metastable state, one can create several narrow amplifying resonances. At frequencies between these gain lines and additional absorption lines, there exist regions of vanishing absorption but resonantly enhanced index of refraction. In Rb vapors with density N in units of cm(-3), we predict an index of refraction up to n≈√(1+1.2×10(-14)N) for the D1 line, which is more than an order of magnitude larger than other proposals for index of refraction enhancement. Furthermore, the index can be readily reduced below 1 by simply changing the sign of the probe or rf field detunings. This enhancement is robust with respect to homogeneous and inhomogeneous broadening.

Chirped area coupled resonator optical waveguide gyroscope.

We study the transmission of an optical field through a rotating coupled resonator optical waveguide (CROW) in which the size of the ring resonators changes from one ring to the next. We focus on symmetric integer wavelength chirps of the circumference of the rings relative to the central ring in the array. The transfer matrix method is used to obtain the transmission as a function of the inertial rotation rate Ω resulting from the Sagnac effect. Chirping increases the slope of the oscillations in the transmission as a function of Ω, which can be exploited to further enhance the rotation sensitivity beyond that of a CROW with uniform resonators.

Quantum inductance and high frequency oscillators in graphene nanoribbons.

Here we investigate high frequency AC transport through narrow graphene nanoribbons with top-gate potentials that form a localized quantum dot. We show that as a consequence of the finite dwell time of an electron inside the quantum dot (QD), the QD behaves like a classical inductor at sufficiently high frequencies ω ≥ GHz. When the geometric capacitance of the top-gate and the quantum capacitance of the nanoribbon are accounted for, the admittance of the device behaves like a classical serial RLC circuit with resonant frequencies ω ∼ 100-900 GHz and Q-factors greater than 10(6). These results indicate that graphene nanoribbons can serve as all-electronic ultra-high frequency oscillators and filters, thereby extending the reach of high frequency electronics into new domains.