Performance of volume phase gratings manufactured using ultrafast laser inscription

摘要

Ultrafast laser inscription (ULI) is a rapidly maturing technique which uses focused ultrashort laser pulses to locallymodify the refractive index of dielectric materials in three-dimensions (3D). Recently, ULI has been applied to thefabrication of astrophotonic devices such as integrated beam combiners, 3D integrated waveguide fan-outs andmultimode-to-single mode convertors (photonic lanterns). Here, we outline our work on applying ULI to the fabricationof volume phase gratings (VPGs) in fused silica and gallium lanthanum sulphide (GLS) glasses. The VPGs we fabricatedhad a spatial frequency of 333 lines/mm. The optimum fused silica grating was found to exhibit a first order diffractionefficiency of 40 % at 633 nm, but exhibited approximately 40 % integrated scattered light. The optimum GLS gratingwas found to exhibit a first order diffraction efficiency of 71 % at 633 nm and less than 5 % integrated scattered light.Importantly for future astronomy applications, both gratings survived cooling to 20 K. This paper summarises the gratingdesign and ULI manufacturing process, and provides details of the diffraction efficiency performance and blaze curvesfor the VPGs. In contrast to conventional fabrication technologies, ULI can be used to fabricate VPGs in almost anydielectric material, including mid-IR transmitting materials such as the GLS glass used here. Furthermore, ULIpotentially provides the freedom to produce complex groove patterns or blazed gratings. For these reasons, we believethat ULI opens the way towards the development of novel VPGs for future astronomy related applications.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.