Optical Transmitter Differential Modulation for Burst Signal Stability
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Solution Overview
Problem
In optical transmitters with capacitively coupled modulation circuits, differential electric signals cause transient state fluctuations in optical signal output due to uneven average potential fluctuations at normal and reverse phase input terminals, leading to waveform deformation and instability.
Innovation Solution
A control circuit equalizes the transient states of average potential fluctuations at both terminals by adjusting the modulation circuit to cancel in-phase components of the differential electric signal, ensuring stable optical signal transmission before stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the LDD and LD are capacitively coupled to use differential electric signals, then the modulation circuit can suppress electric crosstalk and achieve high-speed transmission, but transient state fluctuations occur in the optical signal output due to uneven average potential fluctuations at the terminals
Solution Approach 1:
The patent applies equipotentiality by introducing a dummy terminal connected through a capacitor to ground, which equalizes the average potential fluctuations between the normal phase and reverse phase terminals. This ensures that both terminals experience identical transient state fluctuations, causing them to cancel each other out in the differential signal, thereby maintaining optical signal stability while preserving the benefits of capacitive coupling for crosstalk suppression.
2Productivity
If the LDD intermittently outputs electric signals for burst transmission, then the optical transmitter can stop output during other ONU transmissions, but the average potential at each terminal fluctuates depending on the time constant, generating transient state fluctuations
Solution Approach 1:
The dummy terminal provides a reference path that equalizes the potential fluctuation characteristics during burst transmission intervals. By matching the time constant of the dummy terminal capacitor with that of the LD capacitor, the system ensures that both terminals experience identical potential transients during intermittent operation, allowing the differential signaling to reject these fluctuations and maintain stable optical output during burst mode transmission.
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 enables normal optical signal transmission from the light source even before average potentials at the input terminals are stabilized, maintaining signal integrity and reducing transient state fluctuations.
Implementation Method 1
a light source 320 that emits an optical signal in accordance with a drive current
Implementation Method 2
a modulation circuit 11-1 that passes a bias current through a capacitively-coupled light source 320
Data Source
AI summary
A modulation method according to the invention is applied to a modulation device in which a light source is driven by a differential signal while a modulation circuit and the light source are capacitively coupled. In the modulation method of the invention, when an average potential fluctuates at an input terminal of the light source, a potential fluctuation is externally provided using a control circuit such that a normal phase side and a reverse phase side become equal to each other in a time constant of the fluctuation in average potential, and transient states of the average potentials at the normal phase side and reverse phase side are equalized and cancel each other as in-phase components of a signal input to the light source, which allows an optical signal to be normally transmitted from the light source. The optical signal can normally be transmitted from the light source even before the average potentials at a normal phase input terminal and a reverse phase input terminal of the light source are stabilized.