A Practical Guide to Endoscopy Imaging Filters: Selecting Long-Pass, IR-Cut, and UV-Cut Optics

A Practical Guide to Endoscopy Imaging Filters: Selecting Long-Pass, IR-Cut, and UV-Cut Optics

In medical imaging, success is measured in clarity, stability, and repeatability. The powerful light sources used in endoscopy are essential, but they produce more than just the light we see. Unmanaged ultraviolet (UV) and infrared (IR) light can reduce contrast, cause colors to drift, and create image artifacts.

At KUPO Optics, we help engineers enhance endoscopy imaging by mastering the light with three workhorse filters:

• Long-Pass Filters for deeper, clearer tissue visualization.
• IR-Cut Filters for distortion-free, true-to-life color.
• UV-Cut Filters to protect equipment and ensure long-term precision.

This guide explains how each filter solves common imaging challenges and what to consider when integrating them into your endoscopy systems.

Achieve True-to-Life Color with IR-Cut Filters

Role: An IR-cut filter is essential for maintaining color fidelity. It blocks invisible near-infrared (NIR) light, typically from 700 nm to 1100 nm, that medical sensors can detect. This "NIR noise" can wash out images and confuse a device's automatic white balance, leading to inaccurate color representation.

Key Considerations:

• Clean Visible Signal: By passing only visible light (e.g., 400 nm−650 nm), these filters ensure your camera captures what the human eye would see. This leads to stable, consistent color calibration across all your devices.
• Source Compatibility: Whether you use white LEDs or xenon light sources, they all have different levels of NIR leakage. An IR-cut filter standardizes the output, ensuring a clean signal.
• Durable Coatings: We use hard-coat, multi-cavity designs that offer excellent durability and performance, even when light enters at an angle—a common reality in compact optical systems.

See Deeper into Tissue with Long-Pass Filters

Role: A long-pass filter is designed to improve contrast for specific diagnostic tasks. It works by transmitting light only above a certain wavelength, effectively highlighting features like mucosal boundaries and vasculature by leveraging the way hemoglobin absorbs light.

Key Considerations:

• Targeted Visualization: These filters are tuned for your application. A common design transmits light above 650 nm to make fine details stand out, but this can be customized based on your needs, including dye-assisted or narrow-band imaging modes.
• High Transmission: A well-designed long-pass filter allows over 90-95% of the desired light to pass through, ensuring a bright, clear image for the targeted band.
• Stray Light Control: To achieve high signal-to-noise, the filter must powerfully block light below its cut-on wavelength. Pairing it with anti-reflection (AR) coatings is also crucial to prevent ghosting and internal reflections.

Protect Your Equipment and Preserve Precision with UV-Cut Filters

Role: A UV-cut filter is the bodyguard for your optical system. Just like sunlight can degrade materials, the high-energy UV radiation from an endoscope's light source can cause adhesives and coatings to fail and optical glass to "yellow" over time, reducing performance.

Key Considerations:

• System Longevity: By blocking harmful UV radiation below 390 nm−400 nm, this filter protects the entire optical train, preserving image quality for the lifetime of the device.
• Preventing Noise: It also suppresses unwanted fluorescence from materials in the optical path, which could otherwise show up as noise in the final image.
• Durability & Fit: Our UV-cut filters are designed to withstand common cleaning and disinfection protocols. We also work with you on precise mechanical dimensions to ensure a perfect fit and seal within your device.

A Typical Filter Specification Example

While every project is unique, a reference specification for a filter set could look like this:

• IR-Cut Filter: Passes over 90% of light between 400 nm and 650 nm while strongly blocking light from 700 nm to 1100 nm.
• Long-Pass Filter: Transmits over 92% of light from 660 nm to 900 nm while strongly blocking wavelengths from 350 nm to 600 nm.
• UV-Cut Filter: Blocks nearly all UV light below 390 nm while passing over 92% of the entire visible spectrum (400 nm−700 nm).

These filters are commonly produced on optical glass substrates like B270 with a thickness of 0.7 mm to 2.0 mm and a surface quality of 60-40, suitable for most high-performance imaging.

Frequently Asked Questions (FAQ)

1) What’s the difference between an IR-cut and a long-pass filter? An IR-cut filter passes the visible spectrum and blocks the infrared. A long-pass filter does the opposite for its portion of the spectrum—it blocks shorter wavelengths and passes longer ones. They can be used together, but careful design is needed to manage reflections between them.

2) Will a filter with a very steep cut-off edge cause image artifacts? A steep edge provides sharp spectral separation but can be more sensitive to the angle of light. We recommend testing during prototyping to ensure uniform performance across the entire field of view, especially if your sensor uses microlenses.

3) How do I match a filter to my LED or xenon light source? Start with your source's spectral data. White LEDs typically require strong blocking (OD≥3) in the NIR range. We align the filter’s blocking bands with your source's unwanted peaks to maximize image quality.

4) Can your filters withstand high-temperature steam sterilization? This depends on the coating and substrate. For demanding protocols like steam sterilization above 121∘C, we strongly recommend in-system validation. We can work with you to find the most robust solution.

5) What sizes do you offer? We commonly produce circular filters from Ø5 mm to Ø25 mm and custom squares. We support non-standard shapes and rapid prototyping to help you validate your design before committing to production volumes.

Your Next Steps to Better Imaging

• For maximum color accuracy and stable white balance, start with a high-quality IR-Cut filter.
• To reveal sharper mucosal and vascular details, select a Long-Pass filter with a cut-on wavelength tailored to your target.
• To ensure long-term reliability and performance, integrate a protective UV-Cut filter.

By choosing the right filters, you can significantly lower image noise, lock in true-to-life color, and protect your optics—all while achieving dependable clinical performance.

Ready to enhance your endoscopy imaging? Contact KUPO Optics to discuss your requirements or request a custom sample.