Square Wave Digital Chirp Signal for Optical Range Detection
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Solution Overview
Problem
Conventional RF sources in chirped LIDAR systems have limitations such as bandwidth constraints, bulkiness, and high costs, which affect the range accuracy and sensitivity of the systems.
Innovation Solution
The use of a Field Programmable Gate Array (FPGA) transceiver for digitized chirp generation in chirped LIDAR systems, employing a square wave digital chirp signal to modulate the optical carrier, which increases bandwidth and reduces signal processing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional RF sources (DAC or DDS devices) are used to generate the chirp signal, then the system is easier to manufacture and operate, but the bandwidth is limited to about 4 GHz which reduces range accuracy
Solution Approach 1:
The patent replaces conventional RF signal generation devices (DAC or DDS) with an FPGA-based direct digital synthesis system. This substitution enables generation of chirp signals with bandwidth exceeding 10 GHz while integrating the signal generation functionality directly into the optical modulation path, thereby achieving higher range accuracy without proportionally increasing system complexity.
2Measurement precision
If conventional RF sources with increased bandwidth (about 10 GHz) are used, then range accuracy improves, but additional steps (RF multiplying, optical multiplying) are required which increase device complexity and cost
Solution Approach 1:
The patent extracts and eliminates the need for separate RF multiplying and optical multiplying stages by implementing direct digital chirp generation within the FPGA. This extraction of unnecessary intermediate steps simplifies the overall signal processing chain while maintaining the required 10 GHz+ bandwidth for high-range-accuracy measurements.
Solution Approach 2:
The patent merges the chirp signal generation and optical modulation functions into a single integrated FPGA-based system. By combining these functions, the system achieves high bandwidth signal generation without requiring separate RF and optical multiplication stages, thereby reducing device complexity and cost while maintaining high range accuracy.
3Device complexity
If conventional RF sources are used, then the system structure is simpler, but the size and cost are larger and higher
Solution Approach 1:
The patent implements a universal FPGA-based platform that performs multiple functions: chirp signal generation, optical modulation control, and range calculation. This multi-functional integration replaces multiple separate conventional RF components with a single compact device, thereby simplifying the system structure while reducing overall size and cost.
Solution Approach 2:
The patent uses digital copying of the chirp signal waveform within the FPGA memory and logic structures, replacing the need for large conventional RF signal storage and generation hardware. This digital approach significantly reduces the physical size of the system while maintaining signal fidelity and enabling high bandwidth operation.
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 the range accuracy and sensitivity of LIDAR systems by overcoming the limitations of conventional RF sources, enabling higher bandwidth and more efficient signal processing, while reducing the size and cost of the system.
Implementation Method 1
a modulator for modulating a frequency of the optical signal based on the input digital chirp signal
Implementation Method 2
an optical signal split from the transmitted optical signal... This arrangement is called homodyne detection
Implementation Method 3
a detector to combine the reference optical signal and a return optical signal based on the transmit optical signal backscattered off an object
Implementation Method 4
chirped detection based on a frequency difference between a transmitted chirped optical signal and a returned signal scattered from a target
Data Source
AI summary
An apparatus is provided for using a square wave digital chirp signal for optical chirp range detection. A laser source emits an optical signal and a RF waveform generator generates an input digital chirp signal based on the square wave digital chirp signal. A frequency of the optical signal is modulated based on the input digital chirp signal. A splitter divides the optical signal into a transmit optical signal and a reference optical signal. A detector combines the reference optical signal and a return optical signal from an object. The detector generates an electrical output signal based on the combined reference optical signal and the return optical signal. A processor determines a range to the object based on a characteristic of a Fourier transform the electrical output signal. A method is also provided for using the square wave digital chirp signal for optical chirp range detection.