Optical Frequency Comb Sources for Reliable Transmission
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Solution Overview
Problem
Passive optical networks using unpowered splitters suffer from signal attenuation and noise interference, limiting the distance and reliability of optical signal transmission, while active networks with OADMs require complex wavelength switching and amplification.
Innovation Solution
Employing optical frequency comb light sources with a primary and backup source, locked together for reliable transmission, and a high-speed optical switch for seamless switching in case of failure, along with coherent receivers and DSP for accurate nonlinear compensation, enhancing signal-to-noise ratio and allowing longer fiber spans without additional amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If unpowered optical splitters are used in passive optical networks, then device complexity is reduced, but signal attenuation increases and transmission distance is limited
Solution Approach 1:
The patent applies preliminary action by implementing forward error correction (FEC) encoding at the transmitter before signal transmission. The FEC encoder pre-processes the data signal with error correction codes, enabling the receiver to correct errors that occur during transmission through attenuated signals from unpowered splitters, thus maintaining reliability without adding active components in the field.
Solution Approach 2:
The patent uses an intermediary approach by introducing optical amplifiers at central offices to boost signals after they have been attenuated by unpowered splitters. The amplifier acts as an intermediary element that compensates for signal loss without requiring active components at customer premises, maintaining network simplicity while improving transmission reliability.
2Length of stationary object
If optical amplifiers are added to compensate for signal attenuation, then transmission distance increases, but device complexity and cost increase
Solution Approach 1:
The patent applies universality by implementing digital signal processing (DSP) at the receiver that performs multiple functions: equalization to compensate for frequency-dependent attenuation, chromatic dispersion compensation, and error correction. This multi-functional DSP approach extends transmission distance without requiring multiple separate active components, reducing overall system complexity.
Solution Approach 2:
The patent uses parameter changes by optimizing the optical budget through careful selection of transmitter power, receiver sensitivity, and FEC overhead. By adjusting these parameters and using advanced modulation formats, the system achieves extended transmission distances without proportionally increasing the number of amplifiers or other active components.
3Device complexity
If traditional single-frequency sources are used, then device complexity is low, but channel power and signal-to-noise ratio are insufficient for long-distance transmission
Solution Approach 1:
The patent applies segmentation by using optical frequency combs that generate multiple equally-spaced optical frequencies from a single source. Each comb line acts as a separate channel with adequate power, enabling wavelength division multiplexing to transmit multiple high-power channels simultaneously without requiring multiple independent high-power laser sources, thus maintaining low transmitter complexity while achieving high channel power.
Data Source
AI summary
A system includes an optical transmitter and an optical receiver. The optical transmitter includes a first comb light source, a second comb light source, an optical switch configured to selectively switch either the first comb light source or the second comb light source through to an output of the optical switch, and optical modulators configured to apply differential phase modulation, to channels associated with the switched first comb light source or with the second comb light source, to generate modulated light output signals. The optical receiver includes coherent receivers configured to receive the modulated light output signals from the optical transmitter, and detect and process the received, modulated light output signals to generate corresponding digital signals. The optical receiver further includes a digital signal processor configured to apply forward error correction to the digital signals to generate forward error corrected digital signals.