Optical Short Pulse Generator for Consistent Pulse Width and Chirp
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Solution Overview
Problem
Existing optical pulse generators using MZ type optical intensity modulators suffer from inconsistent pulse width and chirp due to residual chirp variations, leading to phase modulation differences in each optical pulse.
Innovation Solution
The optical short pulse generator employs a first optical intensity modulator, a delay unit, and a second optical intensity modulator to generate optical short pulses with uniform pulse width and chirp by modulating signal intensity with drive signals around operation bias points, using a second drive signal delayed by a half cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a rectangular wave drive signal is applied to an MZ type optical intensity modulator to generate optical pulses, then the pulse generation speed is improved, but the pulse width and chirp become inconsistent due to waveform blunting and residual chirp variations
Solution Approach 1:
The patent divides a single modulator into two separate MZ type optical intensity modulators connected in series. Each modulator performs a portion of the intensity modulation process, with the first modulator receiving the rectangular wave drive signal and the second modulator receiving a phase-inverted version of the same signal. This segmentation allows each modulator to handle smaller modulation tasks, reducing the impact of waveform blunting and residual chirp variations on the final pulse characteristics.
Solution Approach 2:
The patent applies asymmetric drive signals to the two modulators - the first modulator receives a rectangular wave drive signal while the second modulator receives a phase-inverted rectangular wave drive signal. This asymmetric approach compensates for the residual chirp variations by ensuring that the chirp introduced by one modulator is counteracted by the other, thereby maintaining consistent pulse width and chirp characteristics across generated pulses.
2Reliability
If push-pull intensity modulation is used to suppress frequency chirp, then the phase modulation is improved, but residual chirp variations still occur due to coupler branching ratio variations and phase modulation amount differences
Solution Approach 1:
The patent merges two push-pull intensity modulators in series to achieve comprehensive chirp suppression. The first modulator suppresses chirp in one direction while the second modulator suppresses chirp in the opposite direction. By combining the effects of both modulators with phase-inverted drive signals, the system achieves superior chirp consistency that overcomes the limitations of individual modulator variations in coupler branching ratios and phase modulation amounts.
3Productivity
If the operation bias point is set to maximize transmittance and 2Vπ drive signal is applied, then the pulse generation efficiency is improved, but high-frequency components cause electric waveform blunting and pulse interval inconsistency
Solution Approach 1:
The patent dynamically distributes the modulation task across two modulators instead of overloading a single modulator with the full 2Vπ rectangular wave drive signal. Each modulator handles a portion of the intensity modulation, which reduces the impact of high-frequency component blunting on the electric waveform. This dynamic distribution maintains pulse generation efficiency while improving pulse interval consistency.
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 configuration enables the generation of optical short pulses with minimal variations in pulse width, chirp, and phase modulation amount, ensuring consistent optical output.
Implementation Method 1
as an external modulation method using an electro-optical effect, there are an electro-absorption type optical intensity modulator and a Mach-Zehnder type optical intensity modulator
Data Source
AI summary
It includes a first optical intensity modulator (2) that outputs an optical pulse in which the signal intensity of photocarriers output from a light source (1) is modulated in accordance with the magnitude of a first drive signal around an operation bias point α, a delay unit (3) that generates a second drive signal obtained by delaying the first drive signal by a half cycle, and a second optical intensity modulator (4) that outputs an optical short pulse in which the signal intensity of the optical pulse is modulated in accordance with the magnitude of the second drive signal around an operation bias point.