Mid‐infrared suspended waveguide platform and building blocks

Abstract

In this work we present our recent progress in the development of a platform for the mid-infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch-step and can be designed for strong light-matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 μm and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides.

High performance silicon photonic devices based on practical metamaterials

“…(b) A subwavelength waveguide loaded with subwavelength Bragg segments enables measured bandwidths down to 150 pm [10], [11]. (c) Waveguides with subwavelength cladding allow for suspended waveguide which exhibit low losses in the mid-infrared [14], [15]. (d) Tilting of subwavelength segments provides fine control over waveguide birefringence; the insets show the field propagation of the TE and TM modes [16].…”

“…2(c), enables the penetration of hydrofluoric acid to remove the silicon dioxide layer, requiring only one etch step. Using this approach, we have demonstrated waveguides with subdecibel per centimeter losses near 3.8μm wavelength, 3 dB/cm losses near 7.7μm [14], and suspended MMIs [15].…”

CORNERSTONE’s Silicon Photonics Rapid Prototyping Platforms: Current Status and Future Outlook

“…Air-clad Si structures offer an alternative to germanium-based material platforms (see Section 3.2) for extending the usable wavelength range beyond that of SOI by elevating a Si waveguide so the propagating mode does not interact with the substrate material. Such structures are implemented in one of two ways: pedestal-type structures [145], which are supported by a thin rib of Si, or suspended structures, where the region under the waveguide is completely removed and the waveguide is supported by lateral bars or membranes [146][147][148]. Such air-clad platforms avoid using a new material platform and thereby allow the full range of established SOI fabrication techniques to be used.…”

“…This limits the degree of longitudinal patterning that can be achieved underneath the waveguide, for example in the pedestal. Conversely, the lateral supports of a suspended Si can be periodically structured to form a grating [148]. This enables the mode confinement in the waveguide to be optimized so that the sample-light interaction and therefore sensitivity can be adjusted for a particular application.…”

“…Second, suspended Si membrane rib waveguides were fusion-bonded to a Si substrate, which had prepatterned air trenches, to provide more support to the waveguide and improve stability [147]. Third, we have demonstrated a method where a subwavelength grating is used to suspend a waveguide core [148]. The grating is etched through the entire upper Si layer to expose the BOX for removal with HF acid.…”