InP-Based photonic crystal waveguide technology for filtering and sensing applications

Abstract

EXTENDED ABSTRACTPhotonic crystal (PhC) components in InP-based materials are of practical importance not only for their unique properties but also for integration with conventional optoelectronic components on InP substrate. Several PhC devices in the substrate approach such as filters, lasers, and waveguides have been demonstrated [1,2] and this has been possible due to the development of deep etching of PhCs in InP [3].PhC waveguides have been investigated extensively for their unique waveguiding and dispersive properties [2,[4][5][6]. One such interesting property is the so-called mini-stop band (MSB) or mode-gap which originates from energy transfer between forward and backward propagating modes in 2-D PhC waveguides [7,8]. This effect has been investigated not only from a fundamental physics point of view but also for device applications such as coarse wavelength selection [9][10][11] pulse compression [12], selective mirror in photonic crystal laser [13] and fluid sensors [14]. However, the optical characteristics of the MSB have to be significantly improved [15] and new waveguide structures have to be investigated for better performances and new applications. For example, very sharp edges and high attenuation in the transmission mini-stop band could be attractive for tuneable filters and sensing applications[15,16]. Recently, a new class of photonic crystal components/structures have emerged, namely photonic crystal heterostructures [17]. While most of the work relate to high Q cavities and their applications, single heterojunction PhC waveguides have received much less attention. In multi-mode line defect waveguides the "internal" MSB effect due to mode-coupling could bring a new dimension in single junction heterostructure waveguides, both for fundamental physics and applications.In this work ГK oriented 2D-PhC waveguides (line-defects in a triangular lattice of air-holes) fabricated in InP-based materials are theoretically and experimentally investigated. Specifically we focus on the MSB effect due to the coupling between the first and fifth order modes in PhC waveguides for filter and sensing applications. The investigated waveguides include multi-mode line-defect (three-row missing) waveguides with different waveguide widths and air-fill factors, and, single-junction heterostructure waveguides. A central issue in the low-index system is the requirement of high aspect ratio etching. The quality of the etched PhC holes (shape, uniformity and depth) has a direct bearing on the optical properties of the waveguides. Here we present the stateof-the-art high aspect ratio etching of InP-PhCs highlighting the fundamental limits and how they can be overcome. Near cylindrical hole shapes together with a dramatic improvement in the hole to hole depth uniformity and reduction in shape irregularities are demonstrated. These excellent geometrical characteristics of the etched PhC result in waveguides with superior performances. In particular extremely sharp MSB edges are obtained. MSB as deep as 35 dB and with shar...