A method for detecting the absolute temperature or temperature changes and/or the absolute wavelength or wavelength changes of an optical probe signal using an optical detection device (100; 200; 300) comprising an optical waveguide structure (102; 202; 302) defining an optical input port (102a; 202a; 302a) adapted to receive the optical probe signal (S probe) and a first and a second optical output port (102b, 102c; 202b, 202c; 302b, 302c) adapted to output a first and a second optical detection signal (S d1,opt, S d2,opt), respectively, as a response to the optical probe signal (S probe), the optical waveguide structure (102; 202; 302) being configured in such a way that a first power transfer function (F 1 (λ,T)) characterizing the transmission of the optical probe signal (S probe) from the optical input port (102a; 202a; 302a) to the first optical output port (102b; 202b; 302b) differs, with respect to its wavelength and temperature dependency, from a second power transfer function F 2 (λ,T) characterizing the transmission of the optical probe signal (S probe) from the optical input port (102a; 202a; 302a) to the second optical output port (102c; 202c; 302c), wherein the optical waveguide structure comprises an optical mode splitter that is configured to split an optical input path between the optical input port and a common port of the optical mode splitter into a first and a second optical splitting path (316, 318) between a first and a second optical splitting port of the optical mode splitter and the first and the second optical output port (302b, 302c), wherein a single optical resonator is provided within the optical input path, wherein the optical input path is configured to guide, at least within the optical path portion between an input port of the optical resonator and the common port of the optical mode splitter, a first and a second optical mode having differing propagation properties and wherein the optical mode splitter is configured to direct the optical power portion of the optical signal fed to the common port of the optical mode splitter that is comprised by the first optical mode to the first optical splitting path and the optical power portion that is comprised by the second optical mode to the second optical splitting path, the method comprising the steps of (a) transmitting the optical probe (S probe) signal having a predetermined - not necessarily constant - wavelength to the optical input port (102a; 202a; 302a), (b) detecting the first and second optical detection signal (S d1,opt, S d2,opt) at the first and second optical output port by means of a first and a second opto-electrical converter (106, 108) which create a first and second electrical signal (S d1,el, S d2,el) corresponding to the optical power of the respective first and second optical detection signal (S d1,opt, S d2,opt), (c) measuring values of the first and second electrical signal (S d1,el, S d2,el) and (d) determining an absolute temperature value or a value of a temperature change of the optical waveguide structure (S d1,el, S d2,el) and/or an absolute wavelength value or a value of a wavelength change of the optical probe signal (S probe) by using the values measured of the first and second electrical signal (S d1,el, S d2,el) and a first and a second previously determined wavelength and temperature dependency of both the first and second power transfer function (F 1 (λ,T), F 2 (λ,T)). (a) transmitting the optical probe (S probe) signal having a predetermined - not necessarily constant - wavelength to the optical input port (102a; 202a; 302a), (b) detecting the first and second optical detection signal (S d1,opt, S d2,opt) at the first and second optical output port by means of a first and a second opto-electrical converter (106, 108) which create a first and second electrical signal (S d1,el, S d2,el) corresponding to the optical power of the respective first and second optical detection signal (S d1,opt, S d2,opt), (c) measuring values of the first and second electrical signal (S d1,el, S d2,el) and (d) determining an absolute temperature value or a value of a temperature change of the optical waveguide structure (S d1,el, S d2,el) and/or an absolute wavelength value or a value of a wavelength change of the optical probe signal (S probe) by using the values measured of the first and second electrical signal (S d1,el, S d2,el) and a first and a second previously determined wavelength and temperature dependency of both the first and second power transfer function (F 1 (λ,T), F 2 (λ,T)).