Christopher J. Kaalund

Pole-zero diagram approach to the design of ring resonator-based filters for photonic applications

The pole-zero diagram is a tool that has been widely employed in digital and electronic filter design. It greatly facilitates filter design by producing a simple and direct visualization of parametrical behaviors and general spectral characteristics. In this paper, we propose new methods of applying pole-zero diagrams to photonic filter design, aimed at tailoring spectral characteristics. In particular, we demonstrate the effectiveness of this method in designing ring resonator-based filters for application to optical wavelength interleavers and deinterleavers. We show that there exist close relations between the pole-zero diagram of an optical filter and its wavelength response, and derive pole-zero diagrams for filters with various ring resonator configurations. Further, we propose a novel graphical technique using pole-zero diagrams for optimizing filter performance. As a practical example to demonstrate the effectiveness of the pole-zero approach, we present a new wavelength interleaver design with low crosstalk. This design was realized by superimposing the pole-zero diagrams of parallel and series-coupled ring resonator arrays.

Novel approach to design high-performance large-port-count switches in low-index-contrast materials based on cascaded multimode interference couplers

Using a novel design approach, high-performance large-port-count switches based on cascaded multimode interference (MMI) couplers are shown to be feasible in low-index-contrast materials. This approach combines the transfer matrix method, optimization of the MMI dimensions, and mode propagation analysis (MPA) for calculation of phase shifts. 1/spl times/4, 1/spl times/8, 1/spl times/16, and 1/spl times/32 switches are designed, with insertion losses of 1 dB and crosstalk as low as -31.7 dB. Also, it is shown that this approach can balance the losses for different switch states.

Novel optical wavelength interleaver based on symmetrically parallel-coupled and apodized ring resonator arrays

Optical ring-resonators could be used to synthesize filters with low crosstalk and flat passbands. Their application to DWDM interleaving has been proposed and investigated previously. However, a number of important factors related to this topic have not yet been considered and appropriately addressed. In this paper, we propose a novel scheme of a symmetrically parallel-coupled ring resonator array with coupling apodisation. We show that it can be used to construct a wavelength interleaver with remarkably improved performance. Various design factors have been considered. An optimization procedure was developed based on minimizing the channel crosstalk in the through and drop ports simultaneously by adjusting the ring-bus coupling coefficients. We show that apodisation in coupling could suppress channel crosstalk effectively, by choosing the optimal coupling coefficients. We also introduced the equalization of both the input and output coupling coefficients to minimise passband ripple. For a 50 - 100 GHz DWDM applications, four rings is found to be the best choice for array size. A four-ring filter achieves crosstalk -24 dB, insertion loss at resonance <1 dB, and good passband flatness (shape factor >0.6).

Processing of Diamond: Towards All-Diamond Integrated Optics

Diamond photonic devices present a range of opportunities due to their unique properties. This paper presents progress in the fabrication of diamond waveguides using reactive ion etching (RIE), as a step towards all-diamond optics.

A novel out-of-plane micro-mirror actuator

A novel micro-bridge actuator that can satisfy the important requirements for optical switching has been designed, fabricated and tested. These important properties of the actuator include bi-stability, large out-of-plane movement, bi-directionality and electro-thermal actuation. The monolithic integration of a micro-mirror with this actuator is critical to demonstrate its application for optical switching in planar light circuits. In this paper, the design, simulation, fabrication and testing of the integrated system will be presented. The design and simulation issues include (i)the design of the micro-mirror that can be integrated and yet maintain the bi-stability behavior of the micro-bridge (ii) ANSYS simulations to substantiate the design (iii) the design of the dimensions of the mask lay-out of the micro-mirror to provide the desired micro-mirror size on the micro-bridge. The integrated system was fabricated on (110) oriented wafer. A vertical flat mirror, with verticality of 89.5° and a roughness of about 10nm has been obtained. The fabricated optical switch is laser diced, packaged, wire-bonded and tested. A free space optical path is established by micro-positioning optical fibers on the surface of the wafer in etched grooves to demonstrate optical switching. The optical system is actuated between the ON and OFF positions by driving 16mA and 10mA currents through the legs and bridge parts of the micro-bridge for respectively.

Pole-zero diagram approach to the design of coupled ring resonator arrays for photonic applications

Pole-zero diagrams are often employed in electronic filter design because of their simple and direct visualization of spectral characteristics. This paper proposes the use of pole-zero diagrams for tailoring the spectral response of ring resonator array filters for photonic applications. We show that there exist close relations between the pole-zero diagram features of the resonator array and its wavelength response characteristics, and demonstrate that the pole-zero diagram approach could be a very useful tool in the design of photonic devices based on resonator filters. In particular, we employ the pole-zero diagram approach for the case of a parallel-coupled ring resonator array for interleaving, and use this method to produce a new low crosstalk design.