Aspects of the present disclosure describe physical layer security in optical telecommunications networks wherein a filtering-based physical security is provided by a wavelength tunable distributed fiber optical sensing (DFOS) system operating simultaneously on the telecommunications network.

In order to readily carry out communication between terminal stations, a submarine optical communication system includes a first terminal station including a first monitoring means for monitoring the signal quality of dummy light a first dummy light source that outputs dummy light to the second terminal station, and a first light transmitting means for transmitting an optical signal to the second terminal station, the optical signal including a first signal quality of the dummy light; and the second terminal station including a second dummy light source that outputs dummy light to the first monitoring means, a second monitoring means for monitoring the signal quality of the dummy light, and a light receiving means for receiving the optical signal.

The present application provides a method for transmitting performance parameters of a far-end optical module of a far-end node, a detection method for detecting performance of a far-end optical module, a method for transmitting control parameters for controlling a far-end optical module of a far-end node, a method for controlling a far-end optical module of a far-end node, a far-end optical module, a near-end optical module, and a fronthaul system. The method for transmitting performance parameters includes: generating, in response to at least one of a plurality of registers of the far-end optical module becoming a first source register, an uplink optical signal according to ID information and a register value of the first source register, where the first source register is a register having a changed register value of the plurality of registers, and register values of the registers have a mapping relationship with performance parameters of the far-end optical module; and transmitting the uplink optical signal to a near-end optical module of a near-end node.

There is provided a method, apparatus and system for determining multipath interference (MPI) in optical communications. It is object of embodiments of the present disclosure to provide an effective, low-cost way of detecting or measuring MPI. To effectively detect and measure the MPI, multiple zero-power gaps are inserted into the transmission signal (optical signal) in time domain. In some embodiments, at least some of the zero-power gaps inserted in the main signal do not overlap the zero-power gaps of the reflection of the main signal. Using the zero-power gaps contained the main signal and the reflection (where applicable), power inside and outside the zero-power gaps are determined. Then, the strength of the MPI is determined based on the determined power inside and outside the zero-power gaps.

A system for testing line attenuation defects includes a data transmission line configured to transmit a forward signal in a first direction, at least one reflection point at a first location along the data transmission line, a test probe configured to (i) electrically contact a center conductor at a second location along the data transmission line, (ii) introduce a broadband data signal onto the data transmission line, and (iii) measure, at the second location, a return signal from the reflection point, and a spectrum capturing device in operable contact with the test probe. The spectrum capturing device is configured to (i) collect and arrange frequency data measured by the test probe for the test signal, the return signal, and a standing wave created by the sum of the broadband data signal and the return signal, (ii) determine the voltage VSWR of the standing wave, and (iii) calculate a line loss from the VSWR.

The disclosure is directed at a method and system for optical telecommunications performance monitoring via a dual frequency pilot tone. By applying a dual frequency pilot tone, with a first pilot tone frequency selected from a low frequency band and a second pilot tone frequency selected from a high frequency band, either simultaneously or alternatively, to a wavelength channel, one of the pilot tone frequencies may be adaptively selected to improve wavelength channel monitoring. More specifically, stimulated Raman scattering (SRS) caused crosstalk and chromatic dispersion (CD) caused pilot fading which adversely affect performance monitoring of the wavelength channel may be reduced.

An aspect of the disclosure provides methods and systems for encoding a data bit stream onto a pilot tone signal. Another aspect of the disclosure provides method and systems for pilot tone detection. In both, a coded pilot tone signal is encoded using a code sequence m.sub.1 for each bit value of 1 (b.sub.1) and a code sequence m.sub.0 for each bit value of 0 (b.sub.0) of a data bit stream including pilot tone data bit values of 1 (b.sub.1) and bit values of 0 (b.sub.0), with each code sequence having multiple coding bits in the duration of each bit. Pilot tone detection can further include decoding each code sequence of the coded pilot tone signal using a plurality of successive overlapping measurement windows. In some embodiments each measurement window is of the same duration, being of the duration of each code sequence, and detecting each code sequence comprises selecting one of the plurality of measurement windows to represent a complete code sequence.

An apparatus includes: a laser driver configured to output a laser diode current in accordance with a transmit data, a bias control code, and a modulation control code, a laser diode configured to receive the laser diode current and output a light signal, a photodiode configured to receive the light signal and output a photodiode current, a reference driver configured to output a reference current in accordance with the transmit data, the transmit enable signal, a reference bias code, and a reference modulation code, a two-fold comparison circuit configured to compare the photodiode current and the reference current and output a first decision and a second decision, and a DSP configured to adjust the bias control code and the modulation control code in accordance with the first decision and a second decision. A method provides reliable light output using the described apparatus.

A reception apparatus includes: a receiving unit configured to coherently detect an optical signal and output an electrical signal containing a modulated signal and a pilot signal; a first compensating unit configured to detect a frequency of the pilot signal by performing a DFT of the electrical signal, and determine and compensate for frequency error in the electrical signal based on a reference frequency; a frequency converting unit configured to convert the frequency of the pilot signal after the compensating such that the frequency of the pilot signal is lowered by the reference frequency; and a second compensating unit configured to determine frequency error in the modulated signal after the compensating by performing a DFT on the pilot signal after the frequency converting and detecting a frequency of the pilot signal after the frequency converting.

Disclosed are methods for monitoring and measuring Optical Signal-To-Noise Ratios in optical communications systems. One exemplary method involves intentionally inserting zero power symbols into an optical signal stream such that those periods of time in which only zero power symbols are transmitted may be detected and compared with periods of time in which signals modulated with information including both signal and noise are detected such that the OSNR may be determined.