Accelerated Optical Keying Beyond 3 dB Bandwidth
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Solution Overview
Problem
Optical communication systems, particularly those using LEDs or laser diodes, face bandwidth limitations due to low-pass filtering effects, leading to inter-symbol interference and reduced bit rates, especially when operating above the 3 dB bandwidth, which complicates data transmission.
Innovation Solution
A driving scheme for semiconductor radiation sources that modulates the driving current between discrete radiation output levels within a reduced range, using feedback to adjust the upper and lower target levels, allowing faster modulation and reducing inter-symbol interference by controlling the current beyond the 3 dB bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the driving current is modulated at high rates beyond the 3 dB bandwidth, then the bit rate is improved, but inter-symbol interference increases and transmission quality deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-charging the junction capacitance during a first sub-bit period before the actual data transition. This advance preparation ensures that when the driving current switches direction, the capacitance is already in a favorable state, enabling faster and more accurate transitions without excessive inter-symbol interference, thus resolving the contradiction between high bit rate and transmission quality
Solution Approach 2:
The patent implements periodic action by dividing each bit period into multiple sub-bit periods with specific charging and discharging phases. The junction capacitance is periodically charged during first sub-bit periods and discharged during second sub-bit periods, creating a rhythmic pattern that enables high-speed modulation while maintaining signal integrity and reducing inter-symbol interference
2Speed
If the driving current switches rapidly between levels, then the modulation speed is improved, but the junction capacitance charge state becomes insufficient, degrading signal accuracy
Solution Approach 1:
The patent applies preliminary action by initiating the charging of the junction capacitance during the first sub-bit period before the main data transition occurs. This advance charging ensures that when the driving current switches rapidly, the capacitance is already partially charged, providing a smoother transition and more accurate signal levels while maintaining high modulation speed
Solution Approach 2:
The patent segments each bit period into multiple sub-bit periods, with specific segments dedicated to charging and discharging the junction capacitance. This segmentation allows the rapid switching to occur during optimized time windows when the capacitance is in the desired charge state, achieving both high speed and signal accuracy
3Reliability
If the radiation output range is reduced to a subset of the full range, then the error rate is reduced, but the available bandwidth is reduced
Solution Approach 1:
The patent applies preliminary action by pre-charging the junction capacitance before the main modulation signal is applied. This advance preparation allows the system to operate with a reduced radiation output range (subset of full range) while maintaining high bandwidth, because the pre-charged capacitance enables faster and more accurate transitions within the limited range, reducing errors without sacrificing bandwidth
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 enables higher bit rates with reduced error rates by exploiting the bandwidth above the 3 dB attenuation frequency, maintaining transmission quality despite low-pass filtering, and ensuring the radiation output levels can be accurately distinguished at the receiver.
Implementation Method 1
semiconductor radiation source... generate at least two levels of a driving current through the radiation source that define a radiation output range
Implementation Method 2
The junction capacitance acts as a low pass filter
Data Source
AI summary
This invention relates to a binary signaling scheme for use in a transmitter comprising a semiconductor radiation source where the driving current and thus also the radiation output level is modulated by switching the driving current on and off. However, the modulation of the driving current is adapted to not wait for the radiation response to follow the complete rise or fall curve but to switch between two (or a larger number of) selected radiation output levels. During prolonged sequences of zeros (or ones), the driving current is switched to keep the radiation output level between a certain minimum and maximum level. This range of radiation output levels is adaptively selected in accordance with characteristics of the driving current, the optical transmission channel, the radiation source and/or the radiation detector.