Patent EP-3578946-A1 (EP)
Inventor: EISELT MICHAEL
IPC: H04B10/071
Filed: 2018-06-07
Abstract: The invention relates to a method of determining a time-of-flight of an optical signal between a starting point of an optical path and a reflection point within the optical path, especially an optical fiber, the method comprising the steps of supplying to the optical path (116) at least one binary optical probing signal (S opt ) comprising a sequence of pulses according to a binary transmit code sequence, the sequence of pules having a predetermined bit duration, phase and bit rate; detecting at least one electrical return signal (R el ) according to at least one optical return signal (R opt ) returning from the optical path (116) in response to a corresponding one of the at least one optical probing signals (S opt ) using direct detection; deriving at least one receive code sequence by sampling and slicing the at least one electrical return signal (R el ), wherein a sampling rate corresponding to the bit rate of the sequence of pulses of the at least one optical probing signal (S opt ) is used; determining a correlation function by correlating the transmit code sequence and the at least one receive code sequence; and identifying a main peak of the correlation function that corresponds to the reflection point and a time position of the main peak, and determining the time-of-flight as the time position of the main peak. According to the invention, two or more receive code sequences are derived from one or more electrical return signals (R el ), wherein at least two receive code sequences are generated by sampling and slicing the same one of the one or more electrical return signals (R el ) at different phase positions, and/or from two or more electrical return signals (R el ), wherein at least two receive code sequences are generated by sampling and slicing different ones of the two or more electrical return signals (R el ) at different phase positions. A multi-phase correlation function is determined by calculating, for each receive code sequence that has been determined for a given phase position, values of a discrete correlation function by correlating the respective receive code sequence and the transmit code sequence of the corresponding optical probing signal (S opt ), and interleaving the values of the at least two discrete correlation functions according to their respective phase position, or by, if required, interleaving the receive code sequences that have been determined for different phase positions according to their respective phase position in order to create an interleaved receive code sequence, and creating an interleaved transmit code sequence by interleaving a number of transmit code sequences that corresponds to the number of different phase positions, and correlating the interleaved receive code sequence and the interleaved transmit code sequence. According to the invention, the multi-phase correlation function is used to identify the main peak that corresponds to the reflection point. The invention further relates to a device for determining a time-of-flight of an optical signal between a starting point of an optical path and a reflection point within the optical path, especially an optical fiber, that implements this method.