Multimode Fiber Bessel Beam Generation via Mode Coupling
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Solution Overview
Problem
Existing methods for generating non-diffracting optical beams are limited by diffractive spreading, making it difficult to achieve both a narrow waist and long propagation distance, and are often costly and complex to manufacture, especially in compact fiber devices.
Innovation Solution
A simple and low-cost method involving the splicing of a single-mode optical fiber to a multimode optical fiber, where the single-mode fiber outputs a substantially single-mode beam that is converted to multiple modes by the multimode fiber, reducing diffractive spreading and allowing for a narrower and brighter central spot with easier manipulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional Gaussian beams are used, then the beam can be easily generated and propagated, but the beam suffers from diffractive spreading that limits the non-diffracting propagation distance
Solution Approach 1:
The invention segments the optical field into multiple transverse modes (LP0n modes) that are excited in the multimode fiber. These modes interfere constructively along the propagation axis to form a Bessel-like beam pattern with reduced diffractive spreading, thereby extending the non-diffracting propagation distance while maintaining ease of generation through standard fiber coupling.
Solution Approach 2:
The invention changes the modal parameter distribution by exciting specific LP0n modes in the multimode fiber. By controlling which modes are excited and their relative amplitudes, the system transforms the conventional Gaussian beam profile into a Bessel-like intensity distribution that exhibits reduced diffractive spreading over extended propagation distances.
2Length of moving object
If axicons are used to generate Bessel beams, then non-diffracting beams can be obtained, but the device becomes bulky and requires careful alignment
Solution Approach 1:
The invention replaces the mechanical axicon element with an all-optical fiber-based solution. The multimode fiber inherently performs the beam transformation function through its waveguide modes, eliminating the need for external axicons and their associated alignment requirements. The fiber acts as an integrated beam shaper that is immune to alignment issues.
Solution Approach 2:
The invention nests the beam transformation function within the fiber structure itself. The Bessel-like beam generation capability is embedded in the multimode fiber's modal properties, creating a compact integrated device where the function is contained within the fiber rather than requiring external optical elements.
3Volume of moving object
If microaxicons are fabricated on fiber ends, then compact fiber devices can be created, but the manufacturing process becomes costly and complicated
Solution Approach 1:
The invention extracts the beam transformation function from complex manufacturing processes and implements it through the inherent modal properties of standard multimode fibers. By using off-the-shelf multimode fibers without any end-face modifications, the system achieves compactness while avoiding costly and complicated fabrication processes such as chemical etching, focused ion beam machining, or mechanical polishing.
Solution Approach 2:
The invention uses standard, inexpensive multimode fibers that can be readily obtained from conventional sources. These fibers serve as disposable or replaceable components that provide the beam transformation function without requiring expensive custom fabrication, making the system cost-effective and easy to manufacture.
4Length of moving object
If long-period fiber Bragg gratings are inscribed to generate Bessel beams, then diffraction-free beams can be obtained, but special equipment is needed and the beam shape is strongly wavelength-dependent
Solution Approach 1:
The invention makes the fiber device universal by using standard multimode fibers that work across different wavelengths without requiring wavelength-specific gratings. The modal interference mechanism that generates Bessel-like beams is inherent to the fiber structure and operates broadly across the spectral range, providing wavelength-insensitive beam generation.
Solution Approach 2:
The invention replaces the grating-based beam transformation mechanism with a modal interference mechanism in multimode fibers. This substitution eliminates the need for special grating inscription equipment and wavelength-dependent designs, as the modal properties of the fiber provide the beam transformation function in a wavelength-agnostic manner.
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 method generates non-diffractive beams with reduced diffractive spreading compared to Gaussian beams, offering a compact, flexible, and cost-effective solution for generating beams with a narrower and brighter central spot, capable of long non-diffracting propagation.
Implementation Method 1
The multimode second optical fiber converts light in the single mode optical beam from the first optical fiber to light of multiple modes
Data Source
AI summary
A first optical fiber (12) having a first end and a second end is connected to a multimode second optical fiber (14) at the second end. The first optical fiber (12) outputs a substantially single mode optical beam at its second end. The multimode second optical fiber (14) converts light in the optical beam of single mode from the first optical fiber to light of multiple modes, and provides an output beam that has less diffractive spreading than that of a Gaussian beam.