Three-dimensional complete photonic bandgap materials or photonic crystals block light propagation in all directions. The rod-connected diamond structure exhibits the largest photonic bandgap known to date and supports a complete bandgap for the lowest refractive index contrast ratio down to n high /n low ∼ 1.9. We confirm this threshold by measuring a complete photonic bandgap in the infrared region in Sn-S-O (n ∼ 1.9) 1 arXiv:1905.00404v1 [physics.optics] 1 May 2019 and Ge-Sb-S-O (n ∼ 2) inverse rod-connected diamond structures. The structures were fabricated using a low-temperature chemical vapor deposition process via a singleinversion technique. This provides a reliable fabrication technique of complete photonic bandgap materials and expands the library of backfilling materials, leading to a wide range of future photonic applications. Keywordsdirect laser writing, two-photon lithography, chemical vapor deposition, chalcogenide materials, photonic bandgap, three-dimensional photonic crystals Three-dimensional (3D) complete photonic bandgap (PBG) structures have been widely studied since their invention in 1987 by John 1 and Yablonovitch. 2 A complete PBG structure can prohibit photon propagation in any direction and this strong confinement of light can be exploited for applications ranging through high precision sensing, 3 ultralow power and ultrafast optical switches, 4 low threshold nanolasers, 5 high efficiency single photon sources, 6 and integrated photonic circuits. 7 However, such 3D PBG materials are difficult to fabricate. Currently two main techniques of fabrication have been demonstrated: bottom-up and top-down. The bottom-up method refers to schemes where nano-objects self-assemble into structures that then exhibit a PBG. 8,9 The top-down approach refers to creating 3D structures using etching, ion-milling, lithography or laser writing that then produce PBGs. Many of the top-down techniques involve miscellaneous fabrication steps such as waferfusion and micromanipulation, 10,11 while others such as single prism holographic lithography 12,13 do not allow for local modification for defects or waveguides. Alternatively, direct laser writing (DLW) using two-photon polymerization (2PP) allows for a variety of high refractive index contrast (RIC) 3D photonic crystal (PhC) structures with complete PBGs in near-infrared 14 and visible 15 regions to be realized. To fulfill the high RIC (> 2 : 1) requirement high index material (silicon or titanium dioxide) needs to be deposited into 3D Engineering and Physical Sciences Research Council (EPSRC) (EP/M009033/1, EP/M008487/1, EP/M024458/1, EP/N00762X/1). Acknowledgement This work was carried out using the cleanroom fabrication facilities of the Centre for Nanoscience and Quantum Information (NSQI), University of Bristol, and the Optoelectronics Research Centre (ORC), University of Southampton, and computational facilities of the Advanced Computing Research Centre (ACRC), University of Bristol.

Gallium lanthanum sulfide glass (GLS) has been widely studied in the last 40 years for middle‐infrared applications. In this work, the results of the substitution of selenium for sulphur in GLS glass are described. The samples are prepared via melt‐quench method in an argon‐purged atmosphere. A wide range of compositional substitutions are studied to define the glass‐forming region of the modified material. The complete substitution of Ga2S3 by Ga2Se3 is achieved by involving new higher quenching rate techniques compared to those containing only sulfides. The samples exhibiting glassy characteristics are further characterized. In particular, the optical and thermal properties of the sample are investigated in order to understand the role of selenium in the formation of the glass. The addition of selenium to GLS glass generally results in a lower glass transition temperature and an extended transmission window. Particularly, the IR edge is found to be extended from about 9 µm for GLS glass to about 15 µm for Se‐added GLS glass defined by the 50% transmission point. Furthermore, the addition of selenium does not affect the UV edge dramatically. The role of selenium is hypothesized in the glass formation to explain these changes.

Spectral characterisation of Er3+ and Nd3+ doped novel GLS-Se glass showing strong green fluorescence.

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