Which material should I choose for a subsea optical dome — sapphire, BK7 or fused silica?

Which material should I choose for a subsea optical dome — sapphire, BK7 or fused silica?

Which material should I choose for a subsea optical dome — sapphire, BK7 or fused silica?

4. Sapphire vs BK7 vs fused silica — how do I choose?

There is no single "best" material. Pick against your optical band, mechanical needs and environment:

Material Best optical range Strengths Typical use
Sapphire Visible to near-IR Extremely scratch-resistant, high hardness, strong in marine service Demanding ROV/AUV ports, foul-prone or abrasion-exposed systems
BK7 optical glass Visible Good imaging, cost-efficient, easy to coat Wide-angle / fisheye camera ports, visible-light underwater imaging
Fused silica UV through visible / near-IR High UV transmission, very low thermal expansion UV fluorescence, scientific sensing, thermally sensitive systems

Tell us your optical band and environment, and we'll confirm a grade. If you need sapphire, specify the crystal grade and any orientation requirement where relevant. Browse the full underwater optical dome product family.


5. Does the material alone set the depth rating?

No — and this is the line we won't blur.

A sapphire dome is not automatically a "deeper" dome than a BK7 one. Actual pressure performance depends on wall thickness, curvature, thickness uniformity, mounting support, surface defects, seal condition, and pressure-cycle history — not on the material name on the drawing.

That's why you won't see a fixed "3000 m" or "7000 m" tag on our domes. A depth rating is something you and we define and validate together for your specific dome + mount + seal arrangement.


6. How should I specify coatings (AR / BBAR / DLC) for quoting and acceptance?

Coatings are where quotes drift and acceptance disputes start, because "anti-reflection" by itself means nothing. In your inquiry, specify:

  • Working wavelength band (e.g. 400–700 nm, or the IR band you image in).
  • Angle of incidence the dome actually sees.
  • Performance target — residual reflectance or transmission range you'll accept.
  • Whether you need DLC — for IR transmission or extra abrasion resistance.

Not every imaging dome needs a coating. Specify the real requirement and we'll quote the right one — and we'll agree the inspection record up front, so there's no argument about whether the coating passed.

REQUEST A CUSTOM QUOTE

Related: browse the underwater optical dome product family, read the subsea optical dome engineering hub, or explore the subsea dome FAQ library.