Optical CPFSK Transmission With Intensity Component Cancellation
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Solution Overview
Problem
Existing optical transmission methods face challenges in increasing transmission speed while maintaining signal quality, particularly due to the degradation of signal-to-noise ratio (SNR) caused by intensity modulation components in continuous phase frequency shift keying (CPFSK) signals.
Innovation Solution
An optical transmission device that generates both intensity modulation and CPFSK signals, with an intensity modulation unit to cancel intensity modulation components, and an optical reception device for polarization and phase separation to decode these signals, enhancing signal quality and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high multilevel degree is set in CPFSK signal to increase transmission speed, then the transmission speed increases, but the distance between signal points decreases causing SNR degradation
Solution Approach 1:
The patent changes the modulation parameters by applying different modulation indices to different frequency components. Specifically, it uses a first modulation index for a first frequency component and a second modulation index for a second frequency component, where the ratio between these indices is optimized to maintain signal point separation while enabling high-order modulation. This parameter optimization allows achieving high transmission speed without excessive SNR degradation.
2Reliability
If M-QAM scheme is used to prevent SNR degradation, then signal quality is maintained, but intensity modulation component degrades SNR because frequency modulation signal is generated by direct modulation laser
Solution Approach 1:
The patent segments the modulation process by separating the frequency modulation and intensity modulation components. It applies frequency modulation through direct laser modulation and separately applies intensity modulation through an external modulator. This segmentation allows the system to use the frequency modulation for basic signal generation while using the external intensity modulation to compensate for SNR degradation without being constrained by the limitations of direct modulation alone.
Solution Approach 2:
The patent introduces an external modulator as an intermediary device between the direct modulation laser and the final transmitted signal. This external modulator serves as a mediator that performs additional intensity modulation to compensate for the SNR degradation caused by the direct modulation process, thereby maintaining signal quality while enabling frequency modulation.
3Device complexity
If direct modulation laser is used for CPFSK signal generation, then device complexity is reduced, but intensity modulation component degrades SNR
Solution Approach 1:
The patent merges two modulation approaches: direct frequency modulation using a simple direct modulation laser and external intensity modulation using an external modulator. By combining these two methods, the system maintains the simplicity of direct modulation for frequency control while adding external intensity modulation to compensate for SNR degradation, achieving a balance between device complexity and signal quality.
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
The solution reduces CPFSK signal degradation, thereby increasing transmission speed and maintaining signal quality by utilizing both intensity and frequency modulation components effectively.
Implementation Method 1
a light source that outputs a signal modulated by the CPFSK signal
Implementation Method 2
an intensity modulation unit that performs intensity modulation for canceling an intensity modulation component generated by modulation by the CPFSK signal, and intensity modulation by the intensity modulation signal, on the signal output from the light source
Data Source
AI summary
Provided is an optical transmission device including: a modulation signal generation unit that generates an intensity modulation signal and a continuous phase frequency shift keying (CPFSK) signal; a light source that outputs a signal modulated by the CPFSK signal; and an intensity modulation unit that performs intensity modulation for canceling an intensity modulation component generated by modulation by the CPFSK signal, and intensity modulation by the intensity modulation signal, on the signal output from the light source.