Digital optical transmitter
View Patent ↗A cable television system ( 100 ) having forward and reverse paths includes, in the reverse path, a digital optical transmitter ( 200 ) for receiving an RF signal, converting it to a digital signal, and adding a digital pilot tone thereto. A laser is driven in accordance with the summed digital signal to generate a digital optical signal representative of the pilot tone and the RF signal. The cable television system ( 100 ) also includes an optical receiver ( 305 ) for receiving the digital optical signal and recovering therefrom the RF signal and the pilot tone. The optical transmitter ( 200 ) and receiver ( 305 ) are coupled by fiber optic communication media ( 110 ).
1. A method for providing a digital return path in a hybrid fiber coax cable television system using broadband serial optical transport, in which a return path signal from a fiber optic node to a headend is represented by encoding it entirely as ones and zeroes, comprising the steps of:
converting, at the fiber optic node a composite return path waveform to a sequence of digital words whose value represent analog signal samples;
arranging, at the fiber optic node, said digital words into a serial stream with appropriate synchronization information to identify the boundaries between words and to recover timing of the bits themselves;
converting, at the fiber optic node, the electrical digital signal to an optical digital signal, and transmitting the optical ones and zeroes across an optical fiber to the headend; and
inverting the foregoing steps at the headend.
2. A system for providing a digital return path in a hybrid fiber coax cable television system using baseband serial optical transport, in which a return path signal from a fiber optic node to a headend is represented by encoding it entirely as ones and zeroes, the fiber optic node comprising:
conversion means for converting a composite return path waveform to a sequence of digital words whose value represent analog signal samples;
means for arranging said digital words into a serial stream with appropriate synchronization information to identify the boundaries between words and to recover timing of the bits themselves;
conversion/transmission means for converting the electrical digital signal to an optical digital signal, and transmitting the optical ones and zeroes across an optical fiber.
3. A system according to claim 2 , the headend comprising:
conversion/receiver means for receiving the optical ones and zeroes from the optical fiber and converting the optical digital signal to an electrical digital signal; and
means for deserializing the serial stream of digital words and synchronization information.
4. A system according to claim 3 , further comprising conversion means for converting the sequence of digital words to analog signal samples.
5. A system for providing a digital return path in a hybrid fiber coax cable television system using baseband serial optical transport, in which a return path signal from a fiber optic node to a headend is represented by encoding it entirely as ones and zeroes, the fiber optic node comprising:
an A/D converter for converting a composite return path waveform to a sequence of digital words whose value represent analog signal samples;
a SERDES for arranging said digital words into a serial stream with appropriate synchronization information to identify the boundaries between words and to recover timing of the bits themselves; and
an optical transmitter for converting the electrical digital signal to an optical digital signal, and transmitting the optical ones and zeroes across an optical fiber,
the headend comprising:
an optical receiver for receiving the optical ones and zeroes from the optical fiber and converting the optical digital signal to an electrical digital signal; and
a SERDES for deserializing the serial stream of digital words and synchronization information.
6. The system according to claim 5 , further comprising an D/A converter for converting the sequence of digital words to analog signal samples.