Electronic devices with relative humidity sensors

Abstract

An electronic device may include a housing and relative humidity sensor in the housing. The relative humidity sensor may include an optical layer, a relative humidity-sensitive layer coupled to a surface of the optical layer, a light emitter that emits light into the optical layer, and a light detector that detects light that has reflected within the optical layer and off of the relative humidity-sensitive layer. The relative humidity may be determined based on the light detected by the light detector. The optical layer may be a layer with angled edges, a prism, a Bragg reflector, or a waveguide. A reference light detector and/or a temperature sensor may be included in the relative humidity sensor, and measurements from these additional sensors may be used in determining the relative humidity. In this way, an optical relative humidity sensor may be formed in the electronic device.