Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1998-03-12
2000-12-19
Pascal, Leslie
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359161, 359180, H04B 1002
Patent
active
06163395&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The cable television (CATV) industry currently transmits video signals over networks which combine fiber optic transmission and coaxial cable. In the typical network architecture, baseband video signals from a number of sources are combined into specific RF frequencies as amplitude modulated vestigial sideband video subcarriers (AM-VSB) and then modulated onto a laser transmitter located at a headend. The fiber optic transmission systems employed for CATV applications today use internally modulated diode lasers. The internal modulation varies the drive current to the diode laser to produce approximately 10 mW of output power. Typically, the 10 mW output is then optically split into three or four outputs and distributed on fiber into the cable feeder plant to three or four nodes as shown in FIG. 1. Each node converts the optical signal to an electrical signal which is then further distributed over a standard tree and branch coaxial cable network to reach approximately 500 homes per node. This network architecture effectively divides the bandwidth of a single laser transmitter between 1500 to 2000 homes, thus limiting the bandwidth per home.
Increased demand for bandwidth to provide new services such as enhanced pay per view, interactive video, and video on demand requires a larger number of channels per node. A desirable network architecture would include the following characteristics:
A continuing need exists for further improvements in fiber optic transmission systems that will accommodate these various objectives.
SUMMARY OF THE INVENTION
A fully interactive architecture with the ability to target each individual subscriber may require at least one dedicated video channel per subscriber. One could use a dedicated 2 mW internally modulated laser transmitter, but this would increase the cost per subscriber since the number of internally modulated 2 mW lasers necessary to accommodate larger bandwidths is prohibitively expensive. The present invention provides a linear multi-output optical transmitter system having multi-octave bandwidth multiplication. The solution provided by the present invention allows the full bandwidth to be transmitted so that bandwidth per subscriber is increased. The system takes advantage of optical splitting of a high energy source, external modulation, predistortion, and multi-chip fabrication techniques to provide multiple transmitters having minimized second and third order distortion characteristics for use in fiber optic communication systems such as personal communication networks, telephone systems, computer and/or interactive communication networks and cable television.
The approach to the modulation scheme for the present invention is to minimize distortion over a wide bandwidth while providing multiple transmission systems. To minimize the second and third order distortion products, the invention employs a multi-chip module arrangement comprising dual parallel traveling wave Mach-Zehnder interferometers. The dual parallel Mach-Zehnder modulators are combined with a co-located multi-chip electronic driver circuit having a feed-forward amplifier design which provides pre-distortion shaping to minimize the second and third order distortion residue and enhance performance.
Accordingly, an optical transmission system having reduced second and third order distortion products is provided which includes a continuous wave laser source, having an output power range between about 50 and 500 mW, and preferably in a range between about 100 and 350 mW, (e.g., a 300 mW YAG laser), for producing an optical carrier signal, an optical splitter coupled to the laser source for splitting the optical carrier signal to a plurality of splitter outputs, and a plurality of transmitters coupled to respective splitter outputs. The high power laser source can also include an optical amplifier to provide an optical output within the desired range above at least 100 mW and preferably over 200 mW. Optical amplifiers operating at either about 1320 nm or about 1550 nm can
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Mahapatra Amaresh
Nemecek Joseph E.
Noonan Michael J.
Fiber Optics Network Solutions Corp.
Pascal Leslie
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