Interleaver Transfer Function Compensation for Optical Subcarriers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current optical fibre networks face challenges in achieving high transmission speeds without incurring hardware issues and spectral inefficiencies when using a single carrier, particularly at 1Tb/s transmission rates, due to sensitivity and phase noise problems, which are exacerbated by the need for sophisticated modulation schemes.
Innovation Solution
The system employs multiple subcarriers spaced closely together to form a 'superchannel', with digital signal processing units pre-emphasizing modulation signals to compensate for wavelength-dependent power transfer functions in Mach-Zehnder interleavers, allowing for efficient interleaving and de-interleaving within photonic integrated circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single carrier is used for very high transmission speeds (1Tb/s), then transmission rate is improved, but sensitivity and phase noise issues worsen
Solution Approach 1:
The invention segments the single high-rate carrier into multiple lower-rate subcarriers (e.g., four 256-Gbaud subcarriers instead of one 1Tb/s carrier). Each subcarrier can be transmitted with better sensitivity and lower phase noise, while collectively achieving the high transmission rate through spatial or spectral multiplexing
2Speed
If sophisticated quadrature amplitude modulation (PM-1024QAM) is used for 1Tb/s transmission, then transmission rate is improved, but hardware problems and non-linearity impact worsen
Solution Approach 1:
The system divides the high-order modulation into multiple lower-order modulations on separate subcarriers. Instead of implementing complex PM-1024QAM on a single carrier, the invention uses multiple subcarriers with lower modulation orders (e.g., DP-16QAM or DP-64QAM), reducing hardware complexity and non-linearity effects while maintaining aggregate throughput
Solution Approach 2:
The invention replaces the mechanical/electronic complexity of high-order modulation hardware with a parallel structure of multiple lower-order modulators, shifting the complexity from individual component performance to system-level coordination and signal processing
3Device complexity
If passive splitters/combiners are used for multiplexing subcarriers, then device complexity is reduced, but transmission loss increases
Solution Approach 1:
The invention replaces passive optical splitters/combiners with active electro-optic modulators that perform multiplexing through electrical signal combining before optical modulation. This substitution eliminates insertion losses associated with passive splitting while integrating the multiplexing function directly into the modulator chip
4Loss of energy
If external multiplexers/demultiplexers are used, then transmission loss is reduced, but footprint increases
Solution Approach 1:
The invention merges the multiplexing/demultiplexing functions with the modulator/detector circuits by integrating multiple modulators and detectors on a single photonic integrated circuit chip. This consolidation eliminates the need for external multiplexers while maintaining low loss through direct optical coupling between integrated components
Solution Approach 2:
The system implements a hierarchical integration where multiple subcarrier modulators are nested within a single photonic chip, which itself is nested within the overall transmitter system. This nested architecture allows compact packaging of multiple functional elements without requiring external bulk optical components
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 enhances channel density and transmission capacity by optimizing subcarrier distribution and processing, reducing hardware complexity and costs while maintaining spectral efficiency.
Implementation Method 1
The interleaver may be a Mach-Zehnder interleaver, and may have a sinusoidal (e.g. raised cosine) power transfer function
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
There is described a transmitter device for transmitting an optical signal in the form of a plurality of subcarrier channels having different wavelengths. The device comprises first and second optical carrier emitters for emitting light in first and second subcarriers at first and second frequencies or polarisations respectively. First and second modulators are provided for modulating the first and second subcarriers with first and second modulation signals. An interleaver is provided for interleaving the first and second modulated subcarriers into the optical signal. First and second digital signal processing units are configured to pre-emphasise the first and second modulation signals to compensate for a wavelength-dependent power transfer function of the interleaver.