Coupled Resonator Structure Research Articles

Optical gyroscope based on a coupled resonator with the all-optical analogous property of electromagnetically induced transparency

The electromagnetically induced transparency- (EIT)-like phenomenon, called coupled-resonator-induced transparency (CRIT), could occur through a classical mean in a coupled resonator structure, due to classical destructive interference. We propose to utilize this property to construct a miniature highly sensitive gyroscope. We analyze the Sagnac effect in the CRIT structure and point out that the Sagnac phase shift contributed by the whole structure is notably enhanced due to its highly dispersive property. An explicit expression of the phase shift is derived and discussed. To realize the implementation of the CRIT-structure-based gyroscope, issues that ought to be considered are fully discussed here, such as the fabrication possibility, linewidth, shot-noise-limit sensitivity, and integration.

Dispersion and loss limitations on the performance of optical delay lines based on coupled resonant structures

The relative importance of group-velocity dispersion and loss-induced distortion in limiting the performance of optical delay lines based on coupled resonator structures is investigated. It is shown that for the current state of the quality of fabrication both factors play roughly comparable roles for bit rates of 2.5-40 Gbits/s and that as the storage capacity grows, the relative weight of loss-imposed limitation increases.

Optical buffers based on slow light in electromagnetically induced transparent media and coupled resonator structures: comparative analysis

The optical buffer is a key component in all-optical information processing systems. Recently a number of schemes that use slow light propagation in various media and structures have been proposed as means toward implementation of all-optical buffers. We rigorously analyze the similarities and differences in approaches that use electromagnetically induced transparency (EIT) and coupled resonant structures (CRS). We introduce the figure of merit, finesse, that is common to both approaches and obtain fundamental limitations on bit rates and storage capacities of optical buffers. We show that at very low bit rates and storage capacities EIT outperforms CRS, but at rates of 10 Mbits/s and above the EIT medium becomes quite inefficient, and the situation is reversed. Two types of CRS based on high-index-contrast fiber gratings and high-index semiconductor-air photonic crystals and (or) microring resonators are found to hold promise for applications in the 1-1000-Gbits/s range, but only if the losses can be drastically reduced.

Coupled-resonator-induced transparency

We demonstrate that a cancellation of absorption occurs on resonance for two (or any even number of) coupled optical resonators, due to mode splitting and classical destructive interference, particularly when the resonator finesse is large and the loss in the resonator farthest from the excitation waveguide is small. The linewidth and group velocity of a collection of such coupled-resonator structures may be decreased by using larger resonators of equal size, by using larger resonators of unequal size where the optical path length of the larger resonator is an integer multiple of that of the smaller one, or by using a larger number of resonators per structure. We explore the analogy between these effects and electromagnetically-induced transparency in an atomic system.

Porous silicon multilayers for sensing by tuneable IR-transmission filtering

The suitability of porous silicon multilayer (PSM) structures in sensing applications has been investigated. Bragg-filters as well as Fabry–Perot interference structures were prepared using controlled anodisation of silicon in an HF electrolyte by a tight control of structural parameters. The relationship between process parameters (current density and etching time) and final structural parameters (porosity and layers thickness) was established earlier by means of spectroscopic ellipsometry and optical modelling. Transmission filtering in the NIR range as well as reflective type operation in wet ambient was demonstrated in the visible range. On the example of coupled resonator structures we proved the slightly increasing porosity developed in the multilayer during subsequent anodisation steps. The shifting of the resonant peak positions by incorporated liquid in the pores can be monitored in situ enabling the dynamic, spatial analysis of pore filling or drying.

Q-switched operation of a coupled-resonator vertical-cavity laser diode

We report Q-switched operation from an electrically injected monolithic coupled-resonator structure which consists of an active cavity with InGaAs quantum wells optically coupled to a passive cavity. The passive cavity contains a bulk GaAs region which is reverse biased to provide variable absorption at the lasing wavelength of 990 nm. Cavity coupling is utilized to effect large changes in output intensity with only very small changes in passive cavity absorption. The device is shown to produce pulses as short as 150 ps at repetition rates as high as 4 GHz. A rate equation approach is used to model the Q-switched operation yielding good agreement between the experimental and theoretical pulse shape. Small-signal frequency response measurements also show a transition from a slower (∼300 MHz) forward-biased modulation regime to a faster (∼2 GHz) modulation regime under reverse-bias operation.

Vibration transmission through symmetric resonant couplings

The transmission of vibration through a symmetric junction is considered. The problem is introduced using a stretched string with a general point attachment, and then a result is derived which encapsulates the important aspects of the transmission behaviour for a wider class of systems. These are systems that consist of two semi-infinite sections of identical, one-dimensional structure having only one propagating wavetype (but any number of evanescent ones), joined through any linear system that satisfies a condition of symmetry. For such systems, it is shown that there will in general be a set of frequencies of perfect transmission and perfect reflection, in a number and pattern which can be described in terms of the behaviour of the junction alone. Representative examples are presented, based on the behaviour of bending beams and thin circular cylinders with attached structures providing wave reflection. The implications of this result are explored for SEA coupling loss factors, and for the interpretation of SEA model predictions when such resonant coupling structures are present.

Optimum dielectric overlay thickness for equal even- and odd-mode phase velocities in coupled microstrip circuits

An optimum dielectric overlay thickness was found for achieving the equal even- and odd-mode phase velocities in coupled microstrip lines. The theoretical results were calculated based on a variational method. Coupled linear resonator structures were used to measure both the even- and odd-mode effective dielectric constants and the results agree very well with the theory. A directional coupler, built with overlay, has greater than 60 dB isolation as compared with 20 dB isolation for an uncompensated coupler.

Electrical Behavior of Long Linac Tanks and a New Tank-Coupling Scheme

The electrical behavior of long linac tanks can be represented by the behavior of a finite chain of coupled harmonic oscillators.1 A theory is given of chains of oscillators of two kinds, which is appropriate for semi-resonant or resonant coupling structures.2 The perturbation theory given previously is extended to predict the effects of errors in the coupling cells and in the main cells.2 Some advantages of ?/2 mode operation of the double chain are discussed. A new accelerating scheme is presented in which the coupling structures are resonant and the tanks are resonantly coupled. The theory, numerical calculations, and measurements on laboratory models3 all indicate that tolerances on power amplifier voltage and phase can be relaxed by as much as a factor of five.