Delta Optical Thin Film A/S — Revolutionizing Optical Filtering with Continuously Variable Filters

At Spectronet, we are proud to have Delta Optical Thin Film (DOTF) as one of our long-standing cluster partners. With more than 50 years of experience and a legacy of pioneering thin-film coating techniques, DOTF continues to push the boundaries of what is possible in optical filtering — most notably through their development and production of advanced Continuously Variable Filters (CVFs).

What are Continuously Variable Filters — and Why They Matter

Traditionally, spectrometers and imaging systems have relied on fixed-wavelength interference filters: each filter has a uniform coating across its aperture and a fixed center or edge wavelength. This approach often meant that multiple filters or complex filter wheels were required to cover a broad spectral range, increasing mechanical complexity, cost, and footprint.

By contrast, a CVF is a wedged thin-film filter whose spectral properties — such as center wavelength, edge wavelength, and bandwidth — vary continuously along one dimension of the substrate. In practice, this means that by simply sliding (or rotating) a CVF within an optical system, the user can smoothly tune the transmission characteristics over a large wavelength range — effectively replacing many fixed filters or even a monochromator.

Delta Optical Thin Film has refined this concept, raising CVF performance to levels suitable for demanding applications in spectroscopy, fluorescence, hyperspectral imaging, and other high-precision optical instrumentation.

What Sets DOTF’s CVFs Apart

What makes DOTF’s continuously variable filters stand out? Several factors highlight their technological leadership:

• Ultra-hard surface coatings on single fused-silica substrates: The filters are produced with advanced hard-coating processes, yielding high durability, minimal auto-fluorescence, and a high laser damage threshold.

• Excellent spectral performance — steep edges, high transmission, and strong blocking: Modern CVFs from DOTF offer edge steepness and out-of-band blocking comparable or superior to traditional fixed filters, making them suitable even for demanding fluorescence measurements.

• Wide tunability: By combining different types of CVFs — such as Continuously Variable Long-Wave-Pass (CVLWP), Short-Wave-Pass (CVSWP), or even dichroic variants — users can build tunable bandpass filters that cover a broad spectral range (e.g., 320 nm to 850 nm), with adjustable center wavelength and bandwidth.

• Reduced system complexity: A single CVF can replace multiple fixed filters or a grating-based monochromator. This reduces the number of optical components and mechanical parts required in a system, saving cost, space, and increasing reliability.

• Customisable production for OEM and volume applications: Harnessing in-house developed design and deposition-control software, DOTF is capable of customizing filters precisely to customer specifications — from tiny filters for point-of-care devices to larger optics for scientific instrumentation — all in scalable volume production.

  
  

Why This Matters for Spectronet Members

For companies within our Spectronet network — especially those involved in spectroscopy, imaging, biomedical diagnostics, quality control, materials inspection, or any domain requiring flexible spectral filtering — DOTF’s CVFs offer substantial advantages:

• Greater flexibility and adaptability: One filter can cover a wide spectral range, and be tuned as needed — ideal for R&D labs or production lines where spectral requirements may change.

• Higher performance with fewer compromises: Steep edges, low fluorescence, strong blocking, and high durability mean that CVFs from DOTF meet the rigorous demands of high-end spectrometers, fluorescence microscopes, hyperspectral imagers, and other precision instruments.

• Reduced hardware and maintenance overhead: Replacing filter wheels or monochromators with CVFs simplifies instrument design and reduces mechanical complexity, which can lower costs and increase long-term reliability.

• Custom integration for OEMs and high-volume production: Whether for medical diagnostics devices, industrial sensors, or research equipment, DOTF’s ability to deliver custom filters at scale makes them an excellent partner for companies seeking tailored optical solutions.

  
  

Delta Optical: Decades of Expertise, Built for the Future

Delta Optical Thin Film’s strength lies not only in their advanced manufacturing capabilities, but also in their deep heritage: with roots going back to the 1960s, the company pioneered optical monitoring techniques for thin-film deposition and has since accumulated decades of know-how in filter design and production.

Their unique design and deposition-control software, combined with state-of-the-art coating equipment, allow rapid prototyping as well as scalable volume production — making DOTF a reliable partner for both innovative R&D and industrial-scale OEM manufacturing.

Moreover, DOTF’s compliance with environmental and material-sourcing standards (e.g., REACH, RoHS) and their commitment to sustainable production practices further underline their suitability for modern, responsible supply chains.

Looking Ahead

As optical and photonic technologies evolve — from hyperspectral imaging and advanced biomedical diagnostics to compact point-of-care devices and industrial sensors — the demand for adaptable, high-performance, tunable filters will only grow. With its CVF technology, Delta Optical Thin Film is exceptionally well positioned to meet this demand.

At Spectronet, we are excited to continue our collaboration with DOTF and to support joint efforts in delivering state-of-the-art optical solutions to our network. We believe their continuously variable filters are not just an incremental improvement, but a paradigm shift — enabling more flexible, efficient, and future-proof optical systems across a wide range of applications.

For more information visit our Clusterpartner website.