Andrea Melloni

Dual-Mode Coupled-Resonator Integrated Optical Filters

A photonic integrated architecture realizing the concept of coupled-resonator dual-mode optical filters is presented. The proposed structure consists of a chain of directly coupled microring resonators with a partial reflector embedded in the last resonator. The contradirectional coupling induced by the reflector makes the effective order of the filter double with respect to the number of coupled resonators. Since the counterpropagating modes share the same physical cavity, the resonant frequencies are intrinsically aligned, sensitivity of the filter to fabrication tolerances is reduced, and control of the structure is eased with respect to coupled resonator filters of the same order. Second- and fourth-order dual-mode filters made of microring resonators loaded with a Bragg grating are experimentally demonstrated on a silicon-on-insulator photonic platform.

An effective method for the analysis of bent dielectric waveguides

We have developed a simple but efficient algorithm for the calculation of the modes of a bent rectangular waveguide. The method is simple to use, and permit to obtain in a single calculation step all the modes of the bend. The results are in good agreement with those found with the traditional methods.

Switching characteristics of the resonant-ring based router

The Resonant Router (ReR) is an integrated optical crossbar matrix based on the ring resonator. The ReR can operate as cross connect or wavelength router depending on the FSR and bandwidth of each node. In this contribution the cross connect characteristics are investigated, focusing on the characteristics of the single nodes, the necessaries technologies and the impact on WDM systems. An effective method for the BER estimation of the ReR is presented.

Synthesis of direct-coupled-resonators bandpass photonic filters

We propose a simple technique for the exact synthesis of bandpass photonic filters realized with direct-coupled-resonators. The synthesis technique is derived by modifying a classical synthesis method used for microwave filters and it is suitable for the design of bandpass filters of any order with Butterworth, Chebyshev or other all-pole characteristics.

A generic design platform for generic photonic foundries

A software platform able to fulfill the requirements of the new approach in photonic integration through the establishment of generic foundries is presented. The kernel is a circuit simulator able to combine the foundry building blocks described by accurate models to design and analyze complex circuits in the spectral domain.

Direct electrostriction measurement in optical fibers

We report the direct measurement of the electrostrictive contribution to the nonlinear refractive index n/sub 2/ in standard optical fibers for telecommunications. The fiber under test (FUT) is inserted between two flat electrodes to induce a quasi-static intense electric field in the fiber core. The FUT is kept in a straight line to preserve the polarization, controlled by a polarizer. Because of the Kerr effect and the electrostriction, the refractive index slightly changed, and the phase shift induced on the probe light is measured by means of an interferometric technique. To minimize acoustical and mechanical noises, the whole interferometer was kept in a vacuum, and a feedback control was added to the reference arm of the interferometer. This technique has several advantages, leading to a reliable measurement of n/sub 2/: the applied electric field is uniform over the fiber cross section, its intensity can be accurately calculated from the applied voltage, and the field direction is exactly known. Moreover, by controlling the polarization state of the light propagating in the FUT, the electrostriction effect can be discriminated from the Kerr effect.

Automatic hitless reconfiguration of silicon photonics microring filters (Conference Presentation)

Photonic integrated circuits (PICs) have been demonstrated as a promising technology to implement flexible and hitless reconfigurable devices for telecom, datacom and optical interconnect applications. However, the complexity scaling of such devices is raising novel needs related to their control systems, and the automatic calibration, reconfiguration and operation of these complex architectures both during manufacturing and in service is still an open issue. In this contribution, we report our recent achievements on the automatic hitless tuning of a telecommunication-graded filter operating in the L band, fabricated on a commercial foundry Silicon Photonics (SiP) run. A novel channel labeling strategy is used to automatically identify the desired channel within a Dense Wavelength Division Multiplexing (DWDM) through a FPGA-embedded closed-loop control algorithm. The photonic architecture consists of a hitless third order Micro Ring Resonator (MRR) filter with 8 nm Free Spectral Range (FSR), integrating transparent detectors (ContactLess Integrated Photonic Probes - CLIPP) as power monitors and thermooptic actuators. Transparent detectors enable to control the input/output port of the filter without introducing any loss to the WDM channel comb. Hitless operation is achieved through a pair of switchable Mach-Zehnder interferometers used as input/output couplers of the MRR filter. The fabricated device has a 3 dB bandwidth of 40.7 GHz and provides a through-port in-band isolation of 23 dB and a drop port isolation of 25 dB at 50 GHz spacing from the dropped channel. Hitless reconfiguration is achieved with more than 30 dB isolation during channel selection. The automatic tuning and locking technique is based on the use of a pilot tone generated locally at the node site and applied as a low frequency (few kHz), small modulation index (< 8%), amplitude modulation on the channel to be added to the network. The effectiveness and robustness of the automatic controller for tuning and stabilization of the filter is demonstrated by showing that no significant bit-error rate (BER) degradation is observed in an adjacent channel while the filter is being reconfigured. In addition, the convergence of the algorithm is shown to require only few tens of iterations, each one requiring a few milliseconds. The FPGA-embedded control technique together with the compactness provided by SiP meets the integration requirements for high capacity networks and pluggable modules. In addition, the filter unit can be cascaded with other units to realize a multichannel reconfigurable add-drop architecture operating on several wavelengths at the same time with complete independency.

Travelling-wave resonant four-wave mixing on a silicon chip

We demonstrate that travelling-wave four-wave mixing in coupled resonators overcomes the bandwidth limitations of wavelength conversion in single resonators, preserving the efficiency enhancement: 28-dB gain over silicon waveguides of the same length is here achieved.

Visible light trimming of chalcogenide-assisted photonic integrated circuits

Visible light trimming of As2S3-assisted optical waveguides is exploited to compensate for fabrication tolerances and to demonstrate permanent reconfiguration of photonic integrated circuits. Applications to ring-resonator filters and variable delay lines are presented.

Visible light trimming of coupled ring-resonator filters in As 2 S 3 chalcogenide glass technology

Photosensitivity in chalcogenide glass waveguide allows for a permanent refractive index change by means of light exposure [1]. This property can be usefully exploited for post-fabrication trimming of integrated optical devices in order to compensate for fabrication imperfections and alleviate the need for restrictively tight fabrication tolerances [2]. In this work, visible light trimming is exploited to optimize the performance of coupled resonator filters realized by cascading micro-ring resonators in As2S3 glass technology.