Small profile apparatus for pressure and/or temperature sensing within a wellbore are provided. The apparatus may include optical sensing assemblies designed for inclusion in traditional or coiled production tubing deployments and suitable for use in high pressure, high temperature environments. One example assembly generally includes an outer housing, an inner housing at least partially disposed in the outer housing, a port for fluid communication between an internal volume of the inner housing and a volume external to the outer housing, and a large diameter optical waveguide disposed in the internal volume of the inner housing. The waveguide includes a first portion with a first grating and a second portion with a second grating, wherein the outer diameter of the large diameter optical waveguide is at least 300 μm.