A Guide to Transmission Diffraction Gratings

As the dispersive optic that separates light by wavelength, a grating shapes the performance of a whole system, so getting it right matters. Here’s everything you need to know before specifying one.

The first decision is whether your application requires a reflective or transmission type. While both disperse light, they differ in direction: reflective components bounce it back, and transmission diffraction gratings let it pass through.

Because transmission types keep optical paths in line rather than folding back, they’re popular for more compact, lighter-weight devices. As such, these gratings are typically used in aerospace and defence applications, such as earth observation (EO) spectrometers and airborne hyperspectral imaging systems, where size, weight and power (SWaP) are at a premium.

In every instance, how the grating is specified determines how well it performs.

 

Stock & Custom Capabilities

Held in stock or supplied as custom-made optics, our transmission diffraction gratings are less sensitive to alignment errors, thereby simplifying assembly and integration. As surface-relief gratings, they’re etched in our dedicated lithography department, where each is patterned with periodic grooves that diffract light. Spectral coverage ranges from ultraviolet (UV) to visible (VIS) and infrared (IR) bands, with wavelength-specific substrate options – including UV fused silica and silicon – to match the system’s operating band.

Engineered for high diffraction efficiency, each optic is tested in our in-house metrology laboratory and QA-inspected before dispatch, ensuring groove and wavefront quality, as well as efficiency consistency, across every grating.

Transmission Diffraction Gratings Suited to Your Application

Each grating must be matched to its system, and that depends on several choices, starting with groove density. This determines how widely the light is dispersed: a higher density offers finer spectral resolution but a narrower range, whereas a lower density covers a wider span at coarser resolution. The application dictates where this balance lies; for example, resolving closely spaced features, such as distinguishing camouflage from foliage in defence settings, calls for finer grooves, while surveying a broad spectral range favours coarser ones.

In addition to transmitting the operating wavelengths, substrates must withstand environmental conditions. Aerospace and drone optics, in particular, face challenges such as thermal swings, vibration and radiation exposure, so materials need to remain dimensionally stable.

Optical coatings are another factor. An anti-reflective (AR) coating tuned to the operating band lifts throughput where it’s strongest, improving signal-to-noise ratio (SNR).

Some applications also call for additional configurations, and transmission diffraction gratings are sometimes combined with prisms to create what’s known as a ‘grism’. This is particularly useful for ground-based astronomical instruments, where the assembly can be inserted and removed to switch between standard imaging and spectroscopy.

Why Specification Matters

Transmission diffraction gratings determine how light is dispersed, so correct specification drives the resolution and signal quality of an entire instrument. This means it’s as critical to get right as any optic in the chain.

To discuss requirements for your next project, get in touch with a member of our technical sales team today.