880nm Bandpass Filter

Context: This patent describes a multi-wavelength "Aethalometer" (air pollution sensor) designed to quantify different types of carbon particles in the air, specifically distinguishing between Black Carbon (soot from diesel/fossil fuels) and Brown Carbon (from biomass burning).

Usage of Filter: The 880nm bandpass filter is used in the optical detection path to isolate the 880nm wavelength from a light source (often an LED) before it reaches the detector.

Function: Its function is to ensure that only light interacting with Black Carbon is measured. Black Carbon absorbs light strongly at 880nm, whereas organic compounds (Brown Carbon) absorb primarily at UV/blue wavelengths (like 370nm) and are transparent at 880nm.

Result: The system achieves a precise, real-time calculation of Black Carbon concentrations (soot), effectively ignoring interference from other organic aerosols (tobacco smoke, wood smoke) that would otherwise skew the data.

Context: This patent details a medical device used for visualizing diseased tissue (such as tumors in the lung or bladder) and performing targeted ablation (removal) using laser energy. It relies on the spectral differences between healthy and diseased tissue.

Usage of Filter: The bandpass filter (likely in the Near-Infrared or NIR range for deeper tissue penetration) is placed in front of the imaging sensor (camera).

Function: The filter functions as a blocking element for the excitation light. It blocks the high-intensity light used to illuminate the tissue and selectively transmits only the weaker fluorescence emission (which can occur in the 800nm-900nm window for certain contrast agents or autofluorescence) to the camera.

Result: It achieves a high-contrast image where the target tissue "glows" against a dark background, allowing the surgeon (or automated system) to precisely direct the ablation laser only at the diseased cells, sparing healthy tissue.

Context:
This patent describes the fabrication of advanced thin-film optical filters, specifically using hydrogenated silicon layers to create filters with high transmission in the Near-Infrared (NIR) spectrum (800nm–1100nm) while blocking visible light.

Usage of Filter:
The 880nm bandpass filter (or a filter covering this specific band) is used as a Signal-to-Noise enhancer in optical sensors, such as 3D gesture recognition sensors or proximity detectors found in consumer electronics.

Function:
The filter passes the 880nm active sensing signal (emitted by an IR emitter) with high efficiency (>90%) while blocking sunlight and ambient visible light (noise) that would otherwise saturate the detector.

Result:
The result is a sensor that is highly sensitive even in bright outdoor environments, with a physically thinner and more durable coating than traditional interference filters.