Spatial Light Modulator for Multimode Fiber Mode Selectivity
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Solution Overview
Problem
Current methods for characterizing mode propagation time differences in optical multimode fibers, such as the DMD measurement, are limited by low selectivity in exciting higher mode groups, leading to inaccurate transmission quality assessments, especially at higher bit rates like 10 Gbit/s and beyond, as they primarily excite lowest modes and fail to account for disturbances in the outer core regions.
Innovation Solution
Employing a spatially resolved light modulator to selectively excite individual modes or mode groups by controlling the intensity and phase of the light beam at specific cross-sectional areas, allowing for precise field distribution matching the mode to be excited, thereby enabling direct measurement of propagation times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-mode fiber with lateral offset is used to excite modes in DMD measurement, then the measurement setup is simple and easy to implement, but the selectivity in exciting higher mode groups is poor and measurement accuracy is limited
Solution Approach 1:
The patent introduces a spatial light modulator as an intermediary device between the light source and the fiber under test. This SLM selectively modulates the amplitude and phase of different spatial regions of the input beam, enabling precise control over which modes are excited in the fiber. This mediator allows high-selectivity mode excitation without requiring complex mechanical alignment or multiple fibers.
Solution Approach 2:
The patent applies local quality by independently controlling the amplitude and phase of different spatial regions of the input beam through the spatial light modulator. Each local region of the beam can be tailored to match the field distribution of specific fiber modes, enabling selective excitation of individual modes or mode groups while leaving other regions unchanged. This local control achieves high measurement precision while maintaining system simplicity.
2Stability of the object's composition
If standardized coupling conditions are used for bandwidth measurement, then the measurement procedure is standardized and reproducible, but the accuracy is poor because real power distributions vary significantly from standardized distributions
Solution Approach 1:
The patent employs dynamic control of the excitation conditions through the spatial light modulator, which can be programmed to generate any desired amplitude and phase distribution. This allows the measurement system to adapt to the specific characteristics of each fiber under test, exciting exactly the modes needed for accurate transmission quality assessment. The dynamic reconfigurability maintains reproducibility through digital control while achieving accuracy by matching real-world operating conditions.
Solution Approach 2:
The patent changes the excitation parameters (amplitude distribution, phase distribution, spatial profile) using the spatial light modulator to precisely match the field distribution of target fiber modes. By dynamically adjusting these parameters, the system achieves accurate mode selection and excitation, enabling precise measurement of mode propagation times and transmission quality without being constrained by fixed standardized distributions.
3Adaptability or versatility
If overfilled launch excitation is used to excite all modes evenly, then information about overall fiber behavior is obtained, but power is excessively coupled into highest modes where profile errors occur, creating a critical measurement condition
Solution Approach 1:
The patent applies partial action by using the spatial light modulator to excite only the specific modes or mode groups that need to be characterized, rather than exciting all modes simultaneously as in overfilled launch. This selective partial excitation avoids coupling excessive power into problematic higher modes while still providing comprehensive fiber characterization through systematic measurement of individual modes. The approach obtains overall fiber behavior information through aggregated mode data without suffering from the harmful effects of over-excitation.
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 significantly improves the characterization of mode propagation times by exciting a broader range of modes, providing more accurate transmission quality assessments independent of specific excitation conditions, and allows for the determination of individual mode propagation times, enhancing the understanding of fiber performance at higher data rates.
Implementation Method 1
modulating the phase of an input light beam with a spatially resolved light modulator (3)
Implementation Method 2
modulating the amplitude of an input light beam with a spatially resolved light modulator (3)
Implementation Method 3
coherent light is generated with a laser (1)
Implementation Method 4
expanded and collimated by means of a lens (2)
Implementation Method 5
projected onto an end surface of a multimode fiber (5) to be examined by means of imaging optics (4)
Implementation Method 6
The output light beam emerging from the multimode fiber is recorded with a photodiode
Data Source
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AI summary
The method involves generating an input light beam (11) or a collimated light by a light generating unit (1) such as laser. A spatial resolution light modulator (3) is applied with the input light beam to generate a locally modulated light beam. The locally modulated light beam that is to be examined is directed by a multimode fiber (5). A light beam output from the multimode fiber is examined. The output light beam is received by a light sensor (6), where the output light beam is analyzed after being received by the sensor. An independent claim is also included for an arrangement for examining optical multimode fibers.