The Compressed Baryonic Matter (CBM) is one of the leading scientific programs of the future Facility for Anti-proton and Ion Research (FAIR), Darmstadt, Germany. The Silicon Tracking
System (STS) will be the core detector system of CBM for charged-particle reconstruction and momentum measurement. It will be placed inside a 1Tm magnet and kept at an ambient temperature of about −10degC to mitigate radiation-induced bulk current in the silicon sensors. Due to the conditions inside the STS reliable monitoring and control of humidity and temperature is required to avoid icing or water condensation on the electronics or silicon sensors. Fiber Optic Sensors (FOS) based on Fiber Bragg Grating (FBG) have proven to be suitable environmental monitoring sensors due to their resilience to the magnetic field, ionizing radiation, and miniature size. In this contribution, we introduce two different approaches to implement relative humidity (RH) and temperature FBG FOS. The first approach is based on inscribing both RH and temperature FBG into one fiber and the second one features two separate FBGs arrays. In both cases, the RH-sensitive FBGs are coated with polyimide.