A method for optically sensing a parameter of the group of temperature, humidity or mechanical stress using at least one optical sensor, (a) the at least one optical sensor comprising a chirped Bragg grating, an optical reference reflector and a probing signal port, wherein the geometrical distance between the chirped Bragg grating and the reference reflector, in order to sense the desired parameter at a respective given location of interest, is so small that both the chirped Bragg grating and the optical reference reflector are provided at or sufficiently near the respective location of interest, the method comprising the steps of (b) providing the at least one optical sensor comprising the optical reference reflector at the respective location of interest, (c) creating at least one optical probing signal (S probe) having a predetermined center wavelength and a bandwidth that lies, for the whole range of the parameter to be sensed, within the reflection bandwidth of the chirped Bragg grating, (d) feeding the at least one optical probing signal (S probe) to the probing signal port of the at least one optical sensor via an optical measurement path, (e) receiving, via the optical measurement path, at least one optical reflection signal created by the at least one optical sensor, wherein the at least one optical reflection signal comprises, for each of the at least one optical sensor, a first partial reflection signal (S r1) created by the optical reference reflector and a second partial reflection signal (S r2) created by the chirped Brag grating of the respective at least one optical sensor, (f) measuring the group delay (τ g) between the first and second partial reflection signal (S r1, S r2) created by each of the at least one optical sensor, and (g) determining, for each of the at least one optical sensors, an absolute or relative value of the at least one parameter using the group delay (τ g) measured and a reference information. (a) the at least one optical sensor comprising a chirped Bragg grating, an optical reference reflector and a probing signal port, wherein the geometrical distance between the chirped Bragg grating and the reference reflector, in order to sense the desired parameter at a respective given location of interest, is so small that both the chirped Bragg grating and the optical reference reflector are provided at or sufficiently near the respective location of interest, the method comprising the steps of (b) providing the at least one optical sensor comprising the optical reference reflector at the respective location of interest, (c) creating at least one optical probing signal (S probe) having a predetermined center wavelength and a bandwidth that lies, for the whole range of the parameter to be sensed, within the reflection bandwidth of the chirped Bragg grating, (d) feeding the at least one optical probing signal (S probe) to the probing signal port of the at least one optical sensor via an optical measurement path, (e) receiving, via the optical measurement path, at least one optical reflection signal created by the at least one optical sensor, wherein the at least one optical reflection signal comprises, for each of the at least one optical sensor, a first partial reflection signal (S r1) created by the optical reference reflector and a second partial reflection signal (S r2) created by the chirped Brag grating of the respective at least one optical sensor, (f) measuring the group delay (τ g) between the first and second partial reflection signal (S r1, S r2) created by each of the at least one optical sensor, and (g) determining, for each of the at least one optical sensors, an absolute or relative value of the at least one parameter using the group delay (τ g) measured and a reference information.