Passive optical network optical network terminal apparatus and configuration method

An optical network terminal for a wavelength division multiplexed passive optical network, the optical network terminal comprising:

• an optical receiver configured to detect a downstream optical signal;
• an optical transmitter configured to generate and transmit an upstream optical signal;
• a tunable optical filter having a tunable transmission wavelength and being configured to receive a downstream optical signal and to transmit to the optical receiver any said received downstream optical signal at a selected said transmission wavelength;
• and
• a controller configured to:
• a. sequentially generate and transmit one or more wavelength control signals arranged to set the transmission wavelength of the tunable optical filter to a respective one or more wavelengths of a pre-selected plurality of transmission wavelengths until a said wavelength is identified for which no downstream optical signal is detected;
• b. determine whether a transmitter operable at said identified transmission wavelength is present at an optical line terminal of the wavelength division multiplexed passive optical network and is available to be assigned to communicate with the optical network terminal;
• c. if a said transmitter is determined to be present and available, maintain the transmission wavelength of the tunable optical filter at said identified transmission wavelength;
• and
• d. if a said transmitter is determined to be one of not present and not available, recommence step a. for one or more further wavelengths of said pre-selected plurality of wavelengths.

A passive optical network comprising:

• an optical network terminal comprising:
• an optical receiver configured to detect a downstream optical signal;
• an optical transmitter configured to generate and transmit an upstream optical signal;
• a tunable optical filter having a tunable transmission wavelength and being configured to receive a downstream optical signal and to transmit to the optical receiver any said received downstream optical signal at a selected said transmission wavelength;
• and
• a controller configured to:
• a. sequentially generate and transmit one or more wavelength control signals arranged to set the transmission wavelength of the tunable optical filter to a respective one or more wavelengths of a pre-selected plurality of transmission wavelengths until a said wavelength is identified for which no downstream optical signal is detected;
• b. determine whether a transmitter operable at said identified transmission wavelength is present at an optical line terminal of the wavelength division multiplexed passive optical network and is available to be assigned to communicate with the optical network terminal;
• c. if a said transmitter is determined to be present and available, maintain the transmission wavelength of the tunable optical filter at said identified transmission wavelength;
• and
• d. if a said transmitter is determined to be one of not present and not available, recommence step a. for one or more further wavelengths of said pre-selected plurality of wavelengths;
• an optical line terminal comprising:
• an optical receiver configured to detect an upstream optical signal;
• an optical transmitter configured to generate and transmit a downstream optical signal;
• and
• a further controller configured to:
• determine whether an upstream optical signal from the optical network terminal has been detected;
• if a said upstream optical signal has been detected, generate a further downstream optical signal and transmit the further downstream optical signal to the optical network terminal;
• wait for a time at least as long as a round trip time from the optical line terminal to the optical network terminal and back, and determine whether a further upstream optical signal has been received;
• and
• if a said further upstream optical signal is determined to have been received, generate and transmit an optical line terminal control signal configured to cause the optical line terminal to commence transmission at the transmission wavelength of the optical network terminal;
• and
• an optical transmission network connecting the optical network terminal to the optical line terminal.