High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.Index Terms-Cavity resonators, filters, integrated optics, resonator filters, resonators, wavelength-division multiplexing (WDM).T IGHT CHANNEL spacing in wavelength-division-multiplexed (WDM) systems calls for filters that exhibit boxlike response. As channels are packed more closely together, filter specs become more demanding and tax available technologies to produce the required spectral performance. Thin-film filters (TFFs) have played a critical role in WDM systems due in part to the fidelity of their response which is achieved by the use higher order or coupled cavities. The ability to go to higher and higher orders has made resonators invaluable not only at optical frequencies but at all frequencies from kilohertz to microwaves. Significant fabrication challenges remain in TFFs as either the channel spacing decreases or the number of cavities increases. For instance, a four-cavity TFF for 25-GHz channel spacing applications requires from 200 to 400 sequentially deposited layers. In addition, as channel count increases, stack up losses in discrete TFFs mount.Microring resonators fabricated in planar technology offer significant advantages over discrete TFFs. In terms of fabrication, almost arbitrarily high orders can be produced with microring resonators, as all cavities reside in a single dielectric layer, as opposed to requiring hundreds of layers. Rings support traveling wave modes. This allows them to have four spatially separated ports which gives them unique advantages in optical circuit architectures. In this letter, we demonstrate very high-order microring cavities having commercial grade performance for 50-and 25-GHz applications.Coupled microrings have been suggested for add-drop filter applications [1]. Fig. 1 shows the schematic of such a filter having three cavities. Multiring cavities have been analyzed by matrix methods [2] as well as in the time domain [3]. The timedomain formulation yields a simple continued fraction representation of the filter response which may be written down by inspection for any th-order filter as (1a) Manuscript Fig. 1. Third-order microring resonator filter comprised of three coupled rings. The input and output bus waveguides are vertically coupled to the rings while the rings are laterally coupled to their neighbors. (1b)where all rings are identical and lossless. The frequency offset is denoted by , where is the resonant frequency. The term is related to the bus-to-ring coupling, while the terms are related to the coupling between adjacent rings [3]. The structure in Fig. 1 takes advantage of vertical coupling between the bus and outer rings for precise control of the coupling strength [4]- [8]. The rings are all mutually coupled laterally. During fabrication, all cavities are printed in the same step, unlike TF...

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In this letter, we demonstrate all-optical nonlinear switching in compact GaAs-AlGaAs microring resonators at the 1.55-m wavelength. Switching is accomplished in the pump-and-probe configuration in which the pump-and-probe signals are tuned to different resonance wavelengths of the microring. Refractive index change in the microring due to free carriers generated by two photon absorption is used to switch the probe beam in and out of resonance. Measured transient responses of the pump and probe through the microring show good agreement with theoretical predictions based on nonlinear pump-probe interaction due to two photon absorption.Index Terms-All-optical switching, microrings, photonic switching, pump and probe, semiconductor microresonators, two photon absorption.

Abstract-We present experimental and numerical studies of a novel packet-switch architecture, the data vortex, designed for large-scale photonic interconnections. The selfrouting multihop packet switch efficiently scales to large port counts ( 10 k) while maintaining low latencies, a narrow latency distribution, and high throughput. To facilitate optical implementation, the data-vortex architecture employs a novel hierarchical topology, traffic control, and synchronous timing that act to reduce the necessary routing logic operations and buffering. As a result of this architecture, all routing decisions for the data packets are based on a single logic operation at each node. The routing is further simplified by the employment of wavelength division multiplexing (WDM)-encoded header bits, which enable packet-header processing by simple wavelength filtering. The packet payload remains in the optical domain as it propagates through the data-vortex switch fabric, exploiting the transparency and high bandwidths achievable in fiber optic transmission. In this paper, we discuss numerical simulations of the data-vortex performance and report results from an experimental investigation of multihop WDM packet routing in a recirculating test bed.Index Terms-Optical networks, optical packet switch, wavelength division multiplexing (WDM) optical packet routing.

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