Single F-theta Lens for MEMS Laser Scanning Linearity
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Solution Overview
Problem
Traditional laser scanning units using rotating polygon mirrors face challenges such as high manufacturing costs, noise, complex assembly, and non-linear scanning due to the sinusoidal movement of MEMS reflecting mirrors, which affect scanning linearity and image quality.
Innovation Solution
A single fθ lens with a meniscus shape and aspherical surfaces is designed to correct the non-linear scanning of MEMS reflecting mirrors, ensuring constant speed scanning and uniform spot size across the image surface, thereby enhancing image quality and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional rotating polygon mirror is used for laser beam scanning, then scanning functionality is achieved, but manufacturing cost increases and device complexity increases
Solution Approach 1:
The patent replaces the traditional mechanical rotating polygon mirror system with a MEMS (Micro-Electro-Mechanical Systems) mirror system. The MEMS mirror uses electrostatic actuation to achieve scanning motion, eliminating the need for high-speed mechanical rotation and complex polygon mirror assemblies. This substitution significantly reduces manufacturing cost and device complexity while maintaining scanning functionality.
Solution Approach 2:
The patent changes the operating parameters from high-speed mechanical rotation (40,000 rpm) to resonant frequency oscillation of MEMS mirrors. By operating at the resonant frequency of the MEMS structure, the system achieves efficient scanning with much lower mechanical stress and complexity. This parameter change enables simpler manufacturing and reduces the overall device complexity.
2Speed
If a high-speed rotating polygon mirror is used, then scanning speed is improved, but noise level increases and warming-up time increases
Solution Approach 1:
The patent substitutes high-speed mechanical rotation with resonant frequency oscillation of MEMS mirrors. The MEMS mirrors operate at their resonant frequency, which allows for efficient energy transfer and reduced mechanical noise. This substitution eliminates the high noise levels and warming-up time associated with accelerating and decelerating high-speed mechanical polygon mirrors.
3Manufacturing precision
If a cylindrical lens is added to focus the laser beam, then scanning linearity is improved, but device complexity and assembly difficulty increase
Solution Approach 1:
The patent combines the functions of multiple optical components into a single integrated fθ lens. This lens incorporates the focusing and scanning linearity correction functions that were previously achieved by separate cylindrical lenses and polygon mirror arrangements. The merged design reduces the number of components and simplifies assembly while maintaining scanning linearity.
4Ease of manufacture
If the laser beam central axis is not precisely aligned with the polygon mirror central rotating axis, then manufacturing tolerance is relaxed, but fθ lens design and manufacturing difficulty increase
Solution Approach 1:
The patent modifies the optical parameters of the fθ lens to compensate for potential misalignment between the laser beam central axis and the MEMS mirror central axis. By designing the lens with specific optical characteristics that are tolerant to small misalignments, the system maintains scanning linearity without requiring precision alignment during assembly. This parameter optimization allows for easier manufacturing while preserving manufacturing precision.
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 fθ lens corrects the non-uniform speed scanning and distortion in both main and sub-scanning directions, resulting in a consistent spot size and improved image quality, addressing the limitations of traditional laser scanning units.
Implementation Method 1
a single fθ lens used for a micro-electro mechanical system (MEMS) laser scanning unit... focusing a laser beam reflected by the reflecting mirror
Implementation Method 2
the reflecting layer is oscillated for reflecting the light and further for the scanning... θ(t)=θs·sin(2π·f·t)
Data Source
AI summary
A single f-θ lens used for a micro-electro mechanical system (MEMS) laser scanning unit is in a meniscus shape formed by the lens in which a concave surface faces towards the side of a MEMS reflecting mirror. The single f-θ lens has a first optical surface and a second optical surface, at least one optical surface is aspherical surface in both main scanning direction and sub scanning direction, and satisfies specifical optical conditions. The single f-θ lens converts the nonlinear relationship between scanned angle and the time into the linear relationship between the imaged spot distances and the time. Meanwhile, the single f-θ lens focuses the scan light to the target in the main scanning and sub scanning directions, such that the purpose of the scanning linearity effect and the high resolution scanning can be achieved.