Monostatic Laser Rangefinder Duplexer With Angled Fiber End
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Solution Overview
Problem
Monostatic laser rangefinders suffer from light leakage between the transmitting and receiving paths due to Fresnel reflection, leading to glare on the photodetector, saturation, and limited signal-to-noise ratio, which restricts their range and reliability.
Innovation Solution
A monostatic laser rangefinding device with a double-clad optical fiber having an angled end and a duplexer that separates emitted and received light effectively, using a beveled end and anti-reflective treatment to minimize light reflection, coupled with a photodetector and optical amplifier for enhanced signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the power of the light source is increased to improve the signal-to-noise ratio and detection range, then the maximum signal-to-noise ratio and range are improved, but the glare on the photodetector increases causing saturation and potential destruction
Solution Approach 1:
The harmful reflected light is extracted and redirected away from the detection path by introducing an angled interface (cleaved or beveled end) between the transmitting and receiving paths. This physical separation removes the glare problem from the detection path while allowing high power light source operation.
Solution Approach 2:
An angled interface (cleaved or beveled end) is introduced as an intermediary element between the transmitting and receiving paths. This interface acts as a mediator that redirects the harmful reflected light away from the photodetector, enabling high power operation without saturation.
2Object-affected harmful factors
If the end of the double-clad optical fiber is cleaved at an angle greater than 1° to reduce reflection, then the glare on the photodetector is reduced, but a significant fraction of the optical beam is coupled into the inner cladding and can still damage the detector
Solution Approach 1:
The numerical aperture of the light guide is optimized to a specific range (0.1 to 0.5) to control the acceptance angle of reflected light. By changing this parameter, the system ensures that reflected light at the angled interface is redirected away from both the core and inner cladding, preventing detector damage while maintaining low glare.
Solution Approach 2:
The optical fiber structure is modified with specific local properties: the numerical aperture of the light guide is locally optimized in the range of 0.1 to 0.5, and the end face is given a specific angle (greater than or equal to half the arcsine of the numerical aperture). These local quality changes ensure proper redirection of reflected light.
3Weight of stationary object
If a duplexer is used to combine transmitting and receiving paths in a monostatic configuration, then the device becomes lighter and easier to adjust, but light leakage between paths causes glare and saturation
Solution Approach 1:
The Fresnel reflection, which was previously a harmful cause of glare, is converted into a useful separation mechanism. By introducing an angled interface, the reflected light is redirected away from the detection path, transforming the harmful reflection into a beneficial path separation mechanism that enables the compact monostatic design to operate reliably.
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 device achieves a high extinction rate of up to 31 dB and a signal-to-noise ratio greater than 60 dB, enabling reliable detection of objects up to 4 kilometers with improved power efficiency and reduced cost.
Implementation Method 1
light leakage between the transmitting and receiving paths, generated primarily by Fresnel reflection, on the order of 4%, on the output face of the duplexer's double-clad optical fiber
Implementation Method 2
a double-clad optical fiber coupled to an optical device for collimating an outgoing beam and focusing an incoming beam
Implementation Method 3
a double-clad optical fiber coupled to an optical device for collimating an outgoing beam and focusing an incoming beam
Data Source
Figure 1
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Figure 4
AI summary
The invention relates to a monostatic laser rangefinding device comprising: - a laser light source; - a photodetector; - a double-sheathed optical fiber coupled to a collimation and focusing device;- an optical fiber duplexer, comprising: - a first optical fiber forming an input port of said duplexer, - a second optical fiber forming a first output port of said duplexer, said second optical fiber being multimode, said first optical fiber coupled to said laser source and said second optical fiber being coupled to said photodetector and said double-sheathed optical fiber forming a second output port of said duplexer, - means for processing the current generated by said photodiode. According to the invention, the numerical aperture of the light guide formed by the inner and outer sheaths of the double-sheathed fiber is less than or equal to 0.5 and greater than 0.1 and the end of said double-sheathed fiber facing said collimation device has a face inclined with respect to an axis perpendicular to the axis of the fiber by an angle greater than or equal to half the arcsine of said numerical aperture.