Multimode FMCW Lidar Laser System with Frequency Tuning
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Solution Overview
Problem
Current FMCW lidar systems face challenges in achieving high optical output power using single mode lasers, which are costly and inefficient, while multimode lasers offer a cost-effective solution but require complex grating structures and precise temperature control.
Innovation Solution
A laser system utilizing multimode semiconductor lasers with varying angular frequencies, emitting radiation at multiple modes, which are guided through a beam splitter to both a detector and an object, allowing for efficient detection without the need for expensive gratings or precise temperature control, achieving high optical power without additional amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single mode lasers are used to achieve high optical output power, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent segments the laser emission into multiple discrete longitudinal modes (at least two modes with different angular frequencies) rather than using a single continuous spectrum. This segmentation allows the system to achieve high optical power through multi-mode operation while maintaining sufficient frequency discrimination for accurate lidar measurements, thereby reducing device complexity compared to single-mode laser requirements
Solution Approach 2:
The patent applies partial action by using only the necessary minimum number of longitudinal modes (at least two) rather than requiring full single-mode precision. The frequency difference between modes is designed to be greater than the detector's upper cutoff frequency, which is sufficient for FMCW lidar operation without needing the complete spectral purity of single-mode lasers, thus simplifying the system while maintaining measurement capability
2Ease of manufacture
If multimode lasers are used to reduce cost, then manufacturing cost decreases, but manufacturing precision requirements increase due to grating structures
Solution Approach 1:
The patent extracts and eliminates the complex grating structures from the laser system by using a semiconductor laser that naturally operates in multiple longitudinal modes without requiring external diffraction gratings. This removal of the grating component directly reduces both manufacturing cost and the associated precision requirements for grating fabrication and alignment
Solution Approach 2:
The patent employs standard semiconductor laser diodes that are inexpensive and widely available, rather than costly specialized single-mode lasers or systems requiring precision-grated components. These conventional semiconductor lasers, while producing multiple modes, are sufficiently robust and cost-effective for lidar applications when combined with the frequency-based detection method described
3Power
If multimode lasers are used to achieve high optical power, then power output increases, but temperature control precision requirements increase
Solution Approach 1:
The patent employs dynamic frequency tuning of the semiconductor laser, periodically varying the angular frequencies of the longitudinal modes over time (frequency sweeping). This dynamic operation allows the laser to operate at higher powers across multiple modes without requiring precise static temperature control, as the frequency modulation enables FMCW lidar functionality while the laser temperature can vary within a broader range
Solution Approach 2:
The patent changes the operating parameters of the semiconductor laser by intentionally modulating the frequency of multiple longitudinal modes over time rather than maintaining a fixed frequency. This parameter change approach allows the system to achieve high optical power output while being less sensitive to temperature variations, as the frequency sweeping technique compensates for thermal drift and enables operation without precision temperature control
4Reliability
If detector bandwidth is reduced to filter high frequency noise, then measurement reliability improves, but frequency resolution decreases
Solution Approach 1:
The patent applies preliminary action by designing the frequency modulation sweep range and detector bandwidth in advance such that the beat frequencies generated by the frequency-modulated continuous wave (FMCW) operation fall within the detector's limited bandwidth. The frequency sweep is configured so that the difference frequencies between modes and reflected signals are lowered to ranges detectable by bandwidth-limited detectors, enabling reliable detection without requiring high bandwidth while maintaining sufficient frequency resolution for distance and velocity measurement
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 system achieves high optical powers exceeding 100 mW with reduced manufacturing costs and increased efficiency, enabling a cost-effective and scalable FMCW lidar system that can operate over a wide temperature range.
Implementation Method 1
The at least one semiconductor laser is configured to emit laser radiation
Implementation Method 2
The at least one detector is in particular a detector diode, for example a photodiode
Data Source
AI summary
A laser system may include a semiconductor laser configured to emit laser radiation in continuous wave operation at M modes having differing angular frequencies, where 2 ≤ M and where n ∈ [1; M]ℕ. A tuning apparatus may periodically modify the angular frequencies where a variation of each angular frequency is smaller by at least a factor of 2 than a mode distance between the relevant adjacent angular frequencies. A detector has an upper cutoff frequency which is smaller by at least a factor of 10 than the smallest of the mode distances. A beam splitter may guide the M modes each to the detector and to an object, such that the detector may detect, for each of the M modes, portions of the laser radiation reflected by the object and portions of the laser radiation which come optically directly from the semiconductor laser.