An example optical module includes: an optical splitter configured to split a received incident optical signal into a first optical signal and a second optical signal; a wavelength filter sheet configured to receive the second optical signal to reflect a first part of the second optical signal to generate reflected light, and to transmit a second part of that to generate transmitted light; a first photo detector configured to convert the reflected light into an electric signal; a second photo detector configured to convert the transmitted light into an electric signal; and an MCU configured to obtain the first detected signal and the second detected signal, to determine the difference in optical power between the reflected light and the transmitted light, and to determine from the difference in optical power and a specified standard difference in optical power whether the wavelength of the second optical signal is shifted.