Short Pass Filter (SP Filter for short) is an interferometric precision optical core component. Its core function is wavelength-selective separation, precisely allowing short-wavelength light to pass through while blocking long-wavelength light. It is widely used in high-end optical systems such as medical, laser, and industrial imaging.
I. Core Functions
The core function is to achieve high proportion transmission of short-wavelength light and efficient blocking of long-wavelength light, without affecting the intensity and propagation direction of the transmitted light. The core performance highlights "high transmission, high cut-off, and steep transition", with the transmittance in the transmission zone being ≥85% (reaching over 95% for high-end models), and the cut-off depth in the blocking zone being OD3 to OD6, which can precisely ensure the imaging quality and signal purity of the optical system.
II. Working Principle
Based on the interference effect of multi-layer optical films, it is different from the traditional color glass absorption filter. By depositing alternating high and low refractive index hard films on the optical substrate surface, the long-wavelength light undergoes destructive interference and is blocked, while the short-wavelength light undergoes constructive interference and passes through smoothly. It has the advantages of temperature stability, no energy loss, and long life. The cut-off wavelength can be flexibly customized in the full spectrum from ultraviolet to infrared.
III. Manufacturing Process
The process adopts a combination of precision optical coating and cold working techniques, adhering to optical-grade standards throughout. The core procedures are divided into four steps:
Substrate selection and pretreatment
K9 glass, fused quartz, sapphire and other substrates suitable for different scenarios are selected. After cleaning, polishing and drying, the substrates are ensured to be free of impurities and have a high degree of smoothness, laying a foundation for coating.
2. Core Coating Process
Two processes, namely ion beam sputtering (the top choice for high-end applications, featuring high precision and deep cut-off) and electron gun evaporation (a general-purpose mass production method, efficient and economical), are adopted to deposit multi-layer films in a vacuum environment. Real-time monitoring is carried out to ensure the accuracy of the film parameters.
3. Post-processing Optimization
The stress of the film layer is eliminated through annealing, followed by secondary cleaning and inspection. Then, precise edge grinding and chamfering are carried out to enhance the product's stability and assembly compatibility.
4. Finished Product Inspection and Screening
Core parameters such as transmittance, cut-off depth and surface shape accuracy are detected through precision equipment like spectrometers and interferometers. After ensuring that the products meet the standards, they are cleaned and packaged.
IV. Application Fields
Short-wave pass filters can precisely transmit short-wavelength light and effectively block long-wavelength light. They are widely used in the following core fields:
Laser system:
Filter infrared stray light and harmonics to ensure laser purity and equipment safety.
Medical imaging:
Separating excitation light from fluorescence signals to enhance the precision of microscopes and biochemical assays.
Industrial vision:
Eliminate long-wave interference and enhance the imaging contrast for the inspection of semiconductors, panels, etc.
Spectral instruments:
Selecting the short-wave range, used for material composition analysis and environmental monitoring.
Consumer electronics:
Optimize signal acquisition for mobile phone sensors, smart wearables, and security cameras.
Ultraviolet optics:
Through deep ultraviolet light, it supports high-end applications such as photolithography and ultraviolet detection.
Ultraopto’s Short Pass Filter is a high-performance edge pass optical filter engineered to transmit short-wavelength light while providing deep optical density rejection for long-wavelength radiation, serving as a core component in fluorescence imaging, Raman spectroscopy, laser systems and portable optical sensors. Crafted from premium optical-grade glass and ultra-thin PMMA/acrylic substrates, our Short Pass Filters deliver an average transmittance of over 80% in the target short-wavelength transmission band, with a sharp cut-off edge and strict cut-off wavelength tolerance of ±2% to ensure precise spectral separation and minimal light leakage. The rejection region features an optical density (OD) of ≥4 on average, and up to OD6 for high-performance models, efficiently blocking unwanted long-wavelength light and maximizing the signal-to-noise ratio in optical detection systems.
Manufactured with advanced high-vacuum ion beam sputtering coating technology and precision substrate processing, our Short Pass Filters achieve superior surface quality with a 60-40 scratch-dig rating and a clear aperture of over 90%, minimizing light scattering and reflection loss for optimal optical performance. We offer both standard thick glass and ultra-thin (≤0.3mm) flexible designs, with the ultra-thin version ideal for weight-sensitive and compact optical setups such as miniature medical diagnostics, autonomous vehicle sensors and portable spectroscopy equipment. The ultra-thin filters feature scratch-insensitive coatings and can be directly bonded to other optical components with acrylic-based adhesives, enabling seamless integration into miniaturized optical systems. Custom cut-off wavelengths are available across the UV, visible and near-infrared (NIR) spectral ranges (200nm-1200nm), with customizable filter sizes, shapes and mounting options to match specific application requirements.
As a leading manufacturer of precision optical filters, Ultraopto offers fully customized Short Pass Filter solutions to meet your unique spectral and application requirements. Our professional R&D and engineering team can tailor cut-off wavelengths, transmission/rejection performance, substrate materials (optical glass, PMMA/acrylic, fused silica) and filter dimensions, with ultra-strict tolerance control for high-precision optical systems. We also provide custom anti-reflection (AR) coatings on the back surface to eliminate ghost images and interference effects caused by back surface reflection, further enhancing optical performance.
All custom Short Pass Filter orders undergo multi-stage strict optical performance testing and quality inspection, including transmittance/absorbance measurement, cut-off wavelength verification and environmental stability testing, with a detailed quality inspection report provided to ensure the final product fully complies with your design specifications and application needs. Backed by advanced optical coating technology, precision substrate processing experience and a complete quality control system,
Ultraopto ensures stable batch supply capacity and consistent product quality, providing global customers with high-quality Short Pass Filter products and one-stop optical filter solutions. For more detailed technical parameters, product quotation information or custom design solutions for our Ultraopto Short Pass Filter, please contact our professional sales and technical team through the official website, and we will provide you with efficient, personalized and professional optical solutions to support the development and optimization of your high-precision optical systems.
