Single Sideband Optical Modulation for Fiber Dispersion
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Solution Overview
Problem
Existing optical mm-wave generation techniques face limitations such as laser chirp, lower frequency response, fiber dispersion, and restricted transmission distances due to coherence issues and modulation format limitations, particularly in radio-over-fiber systems.
Innovation Solution
An optical wireless network employing an optical coupler to split millimeter-wave signals into multiple paths, using a single sideband modulation scheme with an optical filter and intensity modulator to generate and transmit mm-wave signals, allowing for efficient conversion to electrical signals and modulation for broadcast and upstream transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct modulation is used to generate optical mm-wave signals, then the transmitter structure is simplified, but the signal quality is limited by laser chirp
Solution Approach 1:
The patent replaces direct electrical modulation of the laser (which suffers from chirp effects) with an optical modulation approach using an optical modulator driven by an electrical signal. This substitution of the modulation mechanism eliminates laser chirp limitations while maintaining transmitter simplicity.
2Speed
If optical heterodyne technique is used to generate mm-wave signals, then the frequency response is improved, but the signal quality deteriorates due to lower coherence requirements
Solution Approach 1:
The patent extracts and utilizes only the necessary sideband components from the optical heterodyne spectrum while suppressing the carrier and unwanted sidebands. By taking out only the essential frequency components through optical filtering, the system achieves good frequency response while maintaining signal quality through coherent detection.
3Length of stationary object
If DSB modulation is used to overcome fiber dispersion, then the transmission distance is improved, but the performance deteriorates due to fading problems
Solution Approach 1:
The patent extracts only the single sideband component from the double sideband modulation spectrum, eliminating the carrier and the other sideband. This extraction of the essential frequency component allows the system to overcome fiber dispersion effects while avoiding the performance fading problems associated with DSB modulation.
4Length of stationary object
If OCS modulation is used to generate mm-wave signals, then the transmission distance is extended, but the bandwidth is limited to shorter than 60 km
Solution Approach 1:
The patent changes the modulation parameter from optical carrier suppression (OCS) to single sideband (SSB) modulation. This parameter change in the modulation scheme allows the system to achieve both extended transmission distance and maintained bandwidth capability, overcoming the limitations of OCS modulation.
5Length of stationary object
If SSB modulation is used to overcome fiber dispersion, then the transmission distance is extended, but the system complexity increases
Solution Approach 1:
The patent introduces an optical modulator as an intermediary device that converts electrical mm-wave signals to optical domain for transmission, and an optical filter as another intermediary that selects the desired sideband. These intermediary optical components enable SSB modulation to overcome fiber dispersion while managing system complexity through standardized optical processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach overcomes fiber dispersion and bandwidth limitations, enabling longer transmission distances and reduced costs by using a low LO frequency and bandwidth for modulators, while maintaining signal quality and mobility in optical wireless networks.
Implementation Method 1
an optical modulator which modulates the optical carrier with an electrical signal to generate millimeter-wave optical signals
Implementation Method 2
an optical filter which filters the optical signals to pass only the optical carrier and first order sidebands
Implementation Method 3
an optical coupler for splitting received millimeter-wave signals comprised of an optical carrier and second order sidebands into multiple transmission paths
Implementation Method 4
a converter for converting the optical carrier and single sideband to a corresponding electrical signal for amplification
Data Source
AI summary
An optical wireless network includes an optical coupler for diverting received millimeter-wave signals comprised of an optical carrier and second order sidebands into multiple transmission paths; a downstream optical path being one of the multiple transmission paths and including an optical filter for filtering passing through the optical carrier with a single sideband, a converter for converting the optical carrier and single sideband to a corresponding electrical signal for amplification and broadcast transmission from an antenna; and an upstream path being one of the multiple transmission paths and having a filter for passing through the optical carrier only from the mm-wave signals and an intensity modulator driven by data received over the antenna to modulate the optical carrier for optical transmission to a receiving destination.