Sensing in downhole environment can be considered as one of the toughest working conditions on earth. Typical temperature and pressure condition in a well can rise to hundreds of degrees in Celsius and hundreds of bars. However, current solutions on the market have the difficulty in dealing with cross-sensitivity between temperature and pressure in a rapid temperature transient. While at the same time, fiber optic sensing technologies have demonstrated their adaptability, reliability and accuracy in sensing different critical parameters in downhole applications. For example, fiber optic has long operating life time as it is completely passive, and it benefits from its low attenuation which allows the possibility to have a measurement over kilometers long distances from the field side. By combining different gratings writing technologies and specialty optical fibers one can fabricate pressure sensors with unique sensing capabilities to eliminate the cross-sensitivity over a wide temperature and pressure working ranges.