Dual-Pulse DAS Laser Frequency Control Without AOM Insertion Loss
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Solution Overview
Problem
Existing distributed acoustic sensing (DAS) systems rely on acousto-optic modulators (AOM) for pulsing and frequency shifting, which have limited bandwidth and introduce extra insertion loss, and electro-optic modulators (EOM) require additional gating, leading to inefficiencies and limitations in frequency control and signal quality.
Innovation Solution
A direct control method using semiconductor optical amplifiers (SOA) to generate dual-pulse pairs by applying small current changes, eliminating the need for AOMs and EOMs, and enabling precise frequency and phase control through mini-steps, allowing for RF beat techniques and wide frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acousto-optic modulators (AOM) are used for pulsing and frequency shifting, then frequency control is achieved, but bandwidth is limited and insertion loss increases
Solution Approach 1:
The patent extracts and removes the AOM component from the system entirely. Instead of using AOM for pulsing and frequency shifting, the invention directly modulates the laser diode current to generate pulse pairs with controlled frequency and phase differences, eliminating the insertion loss and bandwidth limitations associated with AOM while maintaining precise frequency control capability
Solution Approach 2:
The patent replaces the mechanical acousto-optic modulation system with an electrical direct modulation approach. By applying voltage or current directly to the laser diode, the system achieves pulsing and frequency shifting without mechanical moving parts or acoustic wave interactions, thereby eliminating insertion loss and expanding bandwidth while preserving frequency control precision
2Measurement precision
If electro-optic modulators (EOM) are used for frequency shifting, then frequency control is achieved, but additional gating is required reducing efficiency
Solution Approach 1:
The patent removes the EOM component and its associated gating mechanism from the system. Direct laser diode modulation eliminates the need for separate gating operations, allowing continuous frequency control without the efficiency losses inherent in EOM-based approaches that require additional synchronization and gating steps
Solution Approach 2:
The laser diode performs both pulsing and frequency shifting functions through its own direct electrical modulation, making the system self-sufficient. The laser diode inherently responds to current changes with both amplitude and frequency modulation, eliminating the need for external EOM gating mechanisms and improving overall system efficiency while maintaining precise frequency control
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 signal quality by removing tailing effects, reduces bandwidth limitations, and enables high-frequency acoustic sampling and encoding, improving spatial resolution and signal accuracy in DAS systems.
Implementation Method 1
A semiconductor optical amplifier (SOA) may be operatively connected to the at least one laser to generate a plurality of pulses
Implementation Method 2
applying, by a laser signal controller that is executed by at least one hardware processor, between two pulses of the plurality of pulses, a relatively small-step to obtain laser signal emitted changes of optical frequency
Data Source
AI summary
In some examples, a direct control on laser frequency for dual-pulse distributed acoustic sensing (DAS) apparatus may include at least one laser to transmit a laser signal. A semiconductor optical amplifier (SOA) may be operatively connected to the at least one laser to generate a plurality of pulses. A laser signal controller that is executed by at least one hardware processor may apply, between two pulses of the plurality of pulses, a relatively small-step to obtain laser signal emitted changes of optical frequency.