Single-Core Bidirectional Optics With Raman Crosstalk Suppression
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Solution Overview
Problem
In same wavelength single-core bidirectional optical transmission systems, return light due to Fresnel reflection and Rayleigh scattering superimposes as noise on signal light, degrading signal quality and causing OSNR penalties due to excessive crosstalk.
Innovation Solution
Employing a Raman amplifier with forward- and backward-pumped Raman amplification using incoherent and coherent pump lights to suppress return light noise, particularly through optical circulators and multiple pump light sources to manage signal power and reduce crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bidirectional transmission is implemented using a single-core optical fiber, then fiber utilization efficiency is improved, but return light from Fresnel reflection and Rayleigh scattering superimposes as noise on signal light, degrading signal quality
Solution Approach 1:
The patent applies Raman amplification, which utilizes the harmful Rayleigh scattering effect to generate useful pump light for signal amplification. By converting the scattering process from a noise source into a beneficial amplification mechanism, the system simultaneously addresses the harmful return light issue while improving signal quality through distributed Raman gain.
Solution Approach 2:
The patent introduces an optical circulator as an intermediary device to manage the bidirectional signal paths. The circulator directs signals in specific directions, separating the forward and backward transmission paths and preventing direct interference between them, thereby reducing the impact of return light noise on the received signal.
2Power
If Raman amplification is used to amplify signal light, then signal power is enhanced, but pump light at the same wavelength as signal light causes excessive crosstalk and OSNR penalties
Solution Approach 1:
The patent segments the pump light into multiple wavelength components, using different wavelengths for forward and backward Raman amplification. This segmentation prevents the pump light from interfering with the signal light at the same wavelength, thereby reducing crosstalk while maintaining effective signal amplification.
Solution Approach 2:
The patent applies different Raman amplification characteristics to different directions (forward and backward) by using separate pump light sources with different wavelengths. This local differentiation ensures that each direction receives appropriate amplification without experiencing excessive crosstalk from the opposite direction's pump light.
3Ease of operation
If optical circulators are used to guide signals in bidirectional transmission, then signal routing is improved, but device complexity increases
Solution Approach 1:
The patent employs optical circulators that serve multiple functions: signal routing, isolation, and protection against return light noise. By making these components multi-functional, the system achieves improved signal routing capability without proportionally increasing overall system complexity, as the same components perform multiple protective and directing roles.
Data Source
AI summary
An optical transmission apparatus is disposed at an end of a single-core optical fiber and is used when signal light is transmitted bidirectionally by the optical fiber. The optical transmission apparatus includes an optical transmitter that transmits a first signal light in one direction belonging to the signal light, an optical receiver that receives a second signal light in an opposite direction belonging to the signal light, an optical circulator that guides the first signal light transmitted from the optical transmitter to the optical fiber and guides the second signal light from the optical fiber to the optical receiver, and a light source that outputs, to the optical fiber, pump light for Raman-amplifying the second signal light to a second optical power higher than a first optical power of the first signal light.