High-Performance Short-Wave Pass Filter with Strong Blocking in the NIR Region

In this edition, we present a cutting-edge short-wave pass filter designed for superior blocking in the near-infrared (NIR) range. Featuring a highly transparent visible passband and ultra-steep edges, this filter enhances contrast and sensitivity for applications like biomedical imaging, laser-induced fluorescence, and precision spectroscopy.

Where the quality of the data obtained is at stake, signal purity is an absolute priority.

That said, fields like biomedical imaging, laser-induced breakdown spectroscopy, and precision spectrometry place some of the most stringent demands on the equipment. And the main challenge here is managing background radiation effectively – specifically, stray visible and near-infrared light.

It was for tackling this very problem that our new short-wavepass filter was originally developed.

Its party trick is an ultra-narrow passband in the visible range paired with spectral edges. To put things simpler, it lets through the light you want and nothing more. That very precision delivers an amazing level of contrast and sensitivity (even in some complex setups), which minimizes noise and seriously ups the image and measurement quality.

Here’s a breakdown of what exactly it offers:

• High target transmittance. It delivers a bright, clear signal with an average transmittance >90% within the 520-690 nm band.

• Deep blocking out-of-band. It offers >6 optical density from 690-940 nm, and >4 all the way out to 1070 nm.

• Exceptional cut-off steepness. It features a sharp transition near the 690 nm edge, with a slope of just 0.02%.

• Proven accuracy. The filter isn‘t just theory as the actual spectrophotometer measurements align almost perfectly with our models, – you know exactly what you‘re getting.

What is a Short-Wave Pass Filter, Anyways?

A short-wave pass filter is a component that allows smaller wavelengths of light to pass through, whilst reflecting or absorbing bigger wavelengths. The performance of this or that filter is defined by its cut-on edge – the wavelength at which transmission rises from nearly 0% to over 80% or 90%. 

The Technology Behind the Performance

It all comes down to building up an incredibly thin layers of material. That said, the main way this‘s done is through thin-film deposition, with two methods being:

1. Ion beam sputtering.

2. Plasma-assisted deposition.

Here’s the idea: inside a vacuum chamber, specific materials (usually oxides like Ta2O5, SiO2, or Nb2O5) are vaporized. They then condense and stick to an optical substrate (like a piece of glass) in precise, nanoscale layers.

The filters, in their turn, work on by controlling the index of dozens (sometimes even hundreds) of these very layers. So to speak, this’s a single field. And I-Photonics has the digestible solution here: a filter that was designed in-house at OTF Studio and manufactured on a Meridian1100 coating system, which uses the proprietary PARMS (Plasma Activated Reactive Magnetron Sputtering) technology.

And here’s what makes it special:

• Complex structure. The coating is built from 130 alternating layers of Ta2O5 and SiO2.

• Precision foundation. The layers, with a total thickness of 12 um, are applied to a substrate of pure-fused quartz.

• Superior performance. It‘s the ion beam sputtering technology that lets us create complex and stable coatings, way beyond what traditional methods can achieve.

Key Applications

These filters are indispensable in a bunch of high-tech fields:

• Advanced imaging systems. Everything from machine vision cameras on a production line to biomedical imagers, earth observation satellites, and movie cameras use these filters – in order to get color fidelity and an accurate picture.

• Fluorescence microscopy & biodsensing. They’re also a core part of the filter cubes used in microscopes, acting as emission filters to isolate a dim fluorescent signal from the very bright laser light used to excite it.

• Consumer electronics. One may find them in phones, webcams, and DSLRs. They correct for the sensor’s natural sensitivity to near-infrared (NIR) light, which is key for getting true-to-life color in the photos.

• Industrial sorting & machine vision. They are deployed in automated systems to enhance contrast based on color or spectral signature, which’s vital for sorting materials, inspecting products, or guiding robotic arms.
  
  

  Why Strong NIR Blocking Is That Important 

  While a basic filter might get the job done for some simpler tasks, the ‘high-performance‘ label is rearned by delivering exceptional and deep blocking in the NIR region (typically 700 – 2500 nm). But why is this so critical? Let’s break it down:

  • Silicon sensor sensitivity. The sensors (CCD or CMOS) in pretty much every digital camera are silicon-based. And while our eyes can’t see light beyond ~700 nm, silicon sensors are a sensitive way out into the NIR region. That said, without a proper filter, the invisible light creates a haze, messes up colors, kills contrast, and just makes the image look flat. A strong NIR-blocking SWP filter makes the camera ‘see‘ only the visible light, so it captures colors the way we perceive them.

  • Killing thermal noise. In super sensitive applications (astronomy, microscopy), even a tiny bit of unwanted light can overwhelm the whole detector. So, the deep NIR blocking is key to stopping thermal background radiation from muddying the signal, which results in cleaner data and way more accurate measurements.

   

  I-Photonics isn‘t just another vendor. Instead, we‘re a team of experts in thin film physics and ion beam technologies. Our deep R&D experience means we can deliver not only standard products, yet also comprehensive, turnkey solutions for the unique challenges.

  Our expertise covers the entire process:

  • The direct creation of optical coatings.

  • The development and modernization of the very equipment used to make them.

  The full-cycle control over both the tech and the tools allows us to offer the highly effective and competitive solutions for a wide band of applications.

High-Performance Short-Wave Pass Filter | I-Photonics Blog