Inside the IR Mirror: How It Works in Automotive LiDAR

Every Automotive LiDAR system eventually meets the same question: where does the light go, and how much of it survives the turn? A well-specified IR Mirror answers both,…

Every Automotive LiDAR system eventually meets the same question: where does the light go, and how much of it survives the turn? A well-specified IR Mirror answers both, which is why it earns a place on the bill of materials long before the enclosure is drawn.

At its core, the IR Mirror is a silicon, germanium or ZnSe element carrying a gold or dielectric for the infrared. That stack is engineered to return incident light efficiently over 700 nm – 10.6 µm, giving designers a predictable, low-loss way to steer a beam where they need it.

When light meets the IR Mirror, almost all of it bounces from the front coating. The substrate merely holds the coating in place; it does not need to be traversed by the useful beam, so transmission losses and secondary reflections stay minimal — a real advantage in sensitive Automotive LiDAR setups.

Coating a IR Mirror means laying down a gold or dielectric for the infrared whose optical thickness is controlled to a fraction of a wavelength. Done well, the part holds > 98% over 700 nm – 10.6 µm; done carelessly, it drifts and the system loses light it cannot afford to lose.

Substrate choice for a IR Mirror is a trade between optical grade and budget. silicon, germanium or ZnSe is a common pick because it can be cut and polished to λ/4 flatness and a 40-20 surface, which is plenty for the reflection quality most Automotive LiDAR systems require.

A practical IR Mirror datasheet reads: silicon, germanium or ZnSe substrate, λ/4 flatness, 40-20 quality, 1–6 mm thick, > 98% over 700 nm – 10.6 µm. Those five lines settle most design reviews for Automotive LiDAR. See the standard size list for what we stock and what we cut to order.

Where measuring distance by timing reflected light pulses, a IR Mirror earns its place by doing one job reliably: turning the beam without adding noise. In Automotive LiDAR that reliability is the difference between a prototype and a shippable product. More application examples are worth a look if the use case is close to yours.

Behind the performance

What reads on a datasheet as "> 98% over 700 nm – 10.6 µm" is really the outcome of interference. The gold or dielectric for the infrared on a silicon, germanium or ZnSe base is built layer by layer so reflected waves reinforce. Flatness λ/4 then keeps that wavefront from bending. The physics is old; the discipline to repeat it is the hard part.

A short checklist covers most Automotive LiDAR cases: what band (700 nm – 10.6 µm)? at what angle? how much loss is allowed (> 98%)? then pick gold or dielectric for the infrared on silicon, germanium or ZnSe at 1–6 mm. Getting these four right avoids the most common rework — the application notes show how each sector resolves them.

A IR Mirror is tougher than it looks but softer than you think. Fingerprints on the gold or dielectric for the infrared are the usual cause of field failures, so edge-handling and capped storage pay off. A little discipline keeps > 98% where it belongs.

Because we control cutting, coating and finishing in one place, a IR Mirror can move from your drawing to a finished part without hand-offs. The silicon, germanium or ZnSe is cut to ±0.01 mm, the gold or dielectric for the infrared is vacuum-deposited for > 98% over 700 nm – 10.6 µm, and the result is inspected to λ/4 flatness and 40-20 quality.

Selecting a IR Mirror for Automotive LiDAR starts with the wavelength and angle of incidence, then the acceptable loss. Match the gold or dielectric for the infrared to 700 nm – 10.6 µm, confirm > 98%, and make sure the silicon, germanium or ZnSe and 1–6 mm fit the mount you already have. The spec and size tables make that comparison quick.

Our production of a IR Mirror follows a simple, repeatable route: laser-cut the silicon, germanium or ZnSe to ±0.01 mm, smooth the edges, deposit the gold or dielectric for the infrared, and inspect to λ/4 / 40-20. Thickness options span 1–6 mm, and the same Hangzhou line that builds first-surface mirrors also runs windows, substrates and custom coatings.

Mounting notes

A IR Mirror is only as good as its mount. Use edge contact rather than clamping the face, avoid over-tightening that bends the silicon, germanium or ZnSe and degrades λ/4, and keep the coated side clear of adhesive. In Automotive LiDAR a kinematically supported mirror stays aligned through thermal cycles and shipping.

The IR Mirror is not exclusive to Automotive LiDAR. Universities, service centers and R&D groups use it wherever a beam must turn, which makes a flexible, customizable part a quiet workhorse across the optics world.

Because we control cutting, coating and finishing in one place, a IR Mirror can move from your drawing to a finished part without hand-offs. The silicon, germanium or ZnSe is cut to ±0.01 mm, the gold or dielectric for the infrared is vacuum-deposited for > 98% over 700 nm – 10.6 µm, and the result is inspected to λ/4 flatness and 40-20 quality.

At JYOPTO we make IR Mirror parts by cutting silicon, germanium or ZnSe with laser accuracy of ±0.01 mm, then applying the gold or dielectric for the infrared under vacuum. Standard blanks run 1–6 mm thick, edges are smoothed for safe handling, and every shipped mirror meets λ/4 flatness with a 40-20 surface — the same disciplines we apply across our optical glass, vacuum-coating and precision cold-processing lines since 2020.

One term worth knowing

"Reflectivity" on a IR Mirror is the fraction of incident light returned by the gold or dielectric for the infrared. Quoting > 98% without the band (700 nm – 10.6 µm) is meaningless, because the same coating can be excellent at one wavelength and poor at another — always pair the number with the range.

Environment matters. A IR Mirror headed for Automotive LiDAR may see condensation, vibration and frequent handling. Specifying a sealed-edge, protected coating and a stable silicon, germanium or ZnSe substrate means the mirror keeps its figure (λ/4) and its reflectance through warranty periods and beyond.

In real service a IR Mirror meets more than the optical table. Humidity, temperature swings and routine cleaning all test the gold or dielectric for the infrared. A good protective layer keeps the metal from oxidizing, so the part holds > 98% across 700 nm – 10.6 µm for years rather than months — exactly what Automotive LiDAR equipment that ships to varied climates needs.

Environment matters. A IR Mirror headed for Automotive LiDAR may see condensation, vibration and frequent handling. Specifying a sealed-edge, protected coating and a stable silicon, germanium or ZnSe substrate means the mirror keeps its figure (λ/4) and its reflectance through warranty periods and beyond.

In short

For Automotive LiDAR, the IR Mirror is less a commodity than a tuned component. Specify the band (700 nm – 10.6 µm), the reflectivity (> 98%) and the figure (λ/4), and you will spend less time debugging light you cannot see. That is the whole game. Where your application sits among the sectors we serve changes the details, not the method.