Microring Resonator Devices Research Articles

Modeling Photobleaching of Optical Chromophores: Light-Intensity Effects in Precise Trimming of Integrated Polymer Devices

We present a model for the photobleaching of nonlinear optical (NLO) chromophores, via photo-oxidation, using either high-intensity or low-intensity light sources. A closed-form expression is derived for calculating the temporal evolution of bleaching-induced refractive index change, averaged over the thin-film depth. The averaged values are appropriate for analytically calculating corresponding changes in the effective index of optical waveguides. This applies to precise trimming of the resonant wavelength and coupling in chromophore-doped polymer microring resonator (MRR) devices. In high-intensity (few kW/cm2) laser photobleaching experiments for trimming of MRR coupling, the observed refractive index changes are nearly 1 order of magnitude less than those predicted by low-intensity bleaching curves, for the same total exposure energy. An in-depth review of the photophysics and photochemistry of photo-oxidation of aromatic molecules is presented here, revealing that a high-intensity excitation source is likely to cause chromophore ground-state depopulation, due to the long lifetime of the triplet state. This theory also explains why photobleaching efficiency can be increased by pulsing the excitation, because the chromophore ground-state is allowed to replenish between bleaching pulses. For the first time, to our knowledge, the concept of saturated absorption is applied to model the effect that high-intensity light has on photobleaching-induced index change. The values of the photostability figure-of-merit and saturation intensity for π-conjugated NLO chromophores, such as CLD-1, are obtained here by fitting experimental data. We also note that light-intensity is known to affect the rate of varied photoreactions, such as laser ablation of polymers and human tissue and plant photosynthesis, which share striking photophysical similarities with photobleaching.

Design of single-mode vertically coupled microring resonators

In this work we have studied the possibility of obtaining a single-mode operating vertically coupled microring resonator that can be obtained by wafer bonding. A single-mode operation regime for these types of microring resonator is important since AIIIBV ring waveguides have a highly multimodal behaviour which can affect the functionality of microring resonator based devices. We have found that this problem can be solved by imposing a lateral offset (a misalignment between the ring and the bus waveguide) that allows the radiation carried in the bus waveguide to be coupled predominantly into the ring waveguide's fundamental mode. The coupling coefficient variation with the lateral offset is useful for assessing the fabrication tolerance. We have concluded that the use of the offset is effective for obtaining single-mode operating microring resonator devices.

Microring Resonators Made in Poled and Unpoled Chromophore-Containing Polymers for Optical Communication and Sensors

Poled and unpoled chromophore-containing polymers offer some unique advantages in device functionality and fabrication. UV light and electron beam (e-beam) can bleach out the color of chromophores and reduce the index of refraction of the polymer. The photobleaching and e-beam bleaching methods form optical waveguides in a single step and do not involve solvents or wet chemicals, and can be applied to polymers that are not compatible with other waveguide fabrication techniques. A variety of microring resonator devices for fiber-optic telecommunication and sensors have been realized with chromophore-containing polymers. A novel broadband fiber-optic electric field sensor is presented as an example. The sensor uses a polymer with chromophores preferentially aligned after electric poling, and the microring resonator is directly coupled to the core of optical fiber. The feasibility of vertical integration of a poled electrooptic polymer waveguide device interfaced with silicon microelectronic circuits is also demonstrated.

Multiple-wavelength integrated photonic networks based on microring resonator devices

Feature Issue on Nanoscale Integrated Photonics for Optical Networks Microring resonator devices implemented on silicon and silicon-on-insulator substrates have a unique potential to be used in high-bandwidth multiple-wavelength integrated photonic networks. A scheme for the wavelength allocation is proposed, and its feasibility is verified experimentally. The important system-level trade-offs that result from the proposed scheme, including those among bandwidth, device footprint, and electrical power consumption, are discussed as well.

Highly dispersive micro-ring resonator based on one dimensional photonic crystal waveguide design and analysis

We propose and analyze a novel design of a hybrid micro-ring resonator and photonic crystal device. The proposed device is based on a micro-ring resonator with the addition of a series of periodic defects that are introduced to the microring. When the wavelength of operation approaches the band-gap of the periodic structure, the modal dispersion is significantly increased. The huge dispersion leads to narrowing of the spectral linewidth of the resonator. We predict an order of magnitude linewidth narrowing for a microring radius of the order of 10mum. The proposed hybrid device is analyzed theoretically and numerically using finite-elements calculations and finite-difference-time-domain calculations. We also present as well as the design and analysis of add-drop and notch filters based on the highly dispersive ring resonator.

On cascades of resonators for high-bandwidth integrated optical interconnection networks

The power penalty characteristics of high-speed optical signals transmitted through a variety of filters based on multiple microring resonator devices are analyzed by numerical simulation. The technique used here has been verified with single-ring experimental measurements. Butterworth and Chebyshev filters are investigated, as are serial cascades of resonant devices. Although the power penalty is generally not prohibitive, it is a parameter which cannot be ignored for the design of complex high-bandwidth photonic interconnect systems that utilize microring resonators as filters and switches.

POLYMER-BASED OPTICAL PRINTED CIRCUIT BOARD (O-PCB) AS A POTENTIAL PLATFORM FOR VLSI MICROPHOTONIC INTEGRATION

We introduce the concept of optical printed circuit board (O-PCB) and discuss the issues regarding the miniaturization, interconnection, and integration of polymer-based photonic devices with a view to using it as a potential platform for VLSI microphotonic integration. We present new approaches to miniaturize and integrate some examples of microphotonic devices and examine the considerations regarding the design, fabrication, and characterization for miniaturization and integration for O-PCB application. Devices that we have used for our study include mode conversion adaptors, micro-ring resonator devices, multimode interference devices, arrayed waveguide gratings. Scaling rules are also discussed.