Optical Network Unit RF Tone Injection for OBI Reduction
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Solution Overview
Problem
Conventional OFDMA-PON systems face challenges in reducing optical beat interference (OBI) due to wavelength differences between optical network units, leading to degraded signal-to-noise ratio and system performance.
Innovation Solution
An optical network unit is designed with a signal generator, RF tone generator, and photoelectric converter, where an RF tone with a sinusoidal waveform is combined with the electrical signal to generate an optical signal with a broadened spectrum, reducing OBI by increasing the linewidth of the laser diode and spreading out interference components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple laser diodes with the same wavelength are used in OFDMA-PON system, then the photoelectric converter part can be shared among optical network units, but wavelength differences between laser diodes generate optical interference noise that degrades signal-to-noise ratio
Solution Approach 1:
The invention changes the wavelength parameter of the optical carrier by introducing a frequency offset between the main carrier wavelengths of different optical network units. This parameter change allows the system to maintain photoelectric converter sharing while eliminating optical interference noise, as the frequency offset ensures that carriers from different ONUs do not coincide in the frequency domain at the OLT.
2Object-affected harmful factors
If laser diode resonator length is adjusted with high precision to achieve identical wavelengths, then optical interference noise is reduced, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The invention extracts the wavelength adjustment function from the laser diode manufacturing process and relocates it to the electrical signal processing domain. Instead of requiring precise physical adjustment of laser diode resonator lengths during manufacturing, the system uses frequency offsetting in the electrical domain to achieve the same effect of preventing optical interference, thereby simplifying manufacturing while maintaining performance.
3Stability of the object's composition
If refractive index of gain medium is kept constant to maintain stable center wavelength, then wavelength stability is improved, but the system cannot accommodate frequency offsetting for interference reduction
Solution Approach 1:
The invention replaces the mechanical/optical approach of controlling refractive index stability with an electrical signal processing approach. Instead of relying on stable refractive index to maintain fixed wavelengths, the system introduces controlled frequency offsets in the electrical domain, which then translate to controlled wavelength differences in the optical domain, effectively reducing optical interference while allowing greater flexibility in wavelength management.
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 effectively reduces OBI, improving the signal-to-noise ratio and system performance by suppressing optical interference noise, as demonstrated by simulation results showing reduced EVM and BER values within FEC limits.
Implementation Method 1
a photoelectric converter part configured to convert the combined signal of the electrical signal and RF tone into an optical signal
Implementation Method 2
an RF tone generator part configured to generate an RF tone... The RF tone may have a sinusoidal waveform... generating an RF tone; combining the electrical signal and the RF tone... generate an optical signal with a broadened spectrum, reducing OBI by increasing the linewidth of the laser diode
Data Source
AI summary
Disclosed are an optical network unit included in an OFDMA-PON system that is capable of reducing OBI (optical beat interference), and a method of controlling the optical network unit. The disclosed optical network unit includes: a signal generator part configured to generate an electrical signal carrying transmission data; an RF tone generator part configured to generate an RF tone; a combiner part configured to combine the electrical signal and the RF tone; and a photoelectric converter part configured to convert the combined signal of the electrical signal and RF tone into an optical signal.