An optical dome is a transparent, protective enclosure designed to house and protect optical instruments or sensors while allowing light or electromagnetic radiation to pass through with minimal optical distortion. Optical domes are widely used in:
- Underwater cameras and ROV systems
- Surveillance and security cameras
- Environmental monitoring instruments
- Aerospace and satellite imaging systems
Unlike flat windows, optical domes—most commonly hemispherical or near-hemispherical—are engineered to reduce optical aberrations while providing strong mechanical protection against water, pressure, dust, impact, and harsh environments.
Why Dome Geometry Matters
The shape of the dome plays a critical role in optical performance. Compared to flat windows, dome optics offer:
- Reduced defocus and spherical aberration in underwater imaging
- Lower chromatic aberration at the edge of the field of view
- Improved off-axis performance in wide-angle systems
A well-designed dome can approach optical “invisibility,” meaning it introduces minimal additional aberration to the system.
While true invisibility is impossible—due to refractive index differences between the dome material and surrounding media (air or water)—optical effects can be minimized through careful design.
Key Parameters That Control Dome Optical Performance
1. Thickness
- Thinner domes reduce optical path length differences
- Excess thickness increases aberrations and absorption
- Thickness must balance optical performance vs mechanical strength
2. Refractive Index
- Each application has an optimal refractive index
- Index mismatch between dome and surrounding medium affects refraction
- Common materials are selected to minimize ray bending and aberration
3. Concentricity (Centration)
- Inner and outer surfaces must be highly concentric
- Non-concentric domes act like unwanted lenses
- Thickness variation introduces power and distortion
4. Pupil Position
- For best performance, the entrance pupil of the optical system should be placed at the center of curvature of the dome
- Incorrect pupil placement leads to residual aberrations
- Dome and lens must be designed as one optical system
Material Selection for Optical Domes
Material choice directly impacts optical, mechanical, and environmental performance.
Key Material Criteria
- Optical Clarity: High transmission in the required wavelength range
- Mechanical Strength: Resistance to pressure, impact, and fatigue
- Environmental Resistance: UV stability, chemical resistance, saltwater compatibility
- Thermal Expansion: CTE matching with housing to prevent stress and cracking
Common Dome Materials
- Optical glass (e.g. BK7, K5, specialty glass)
- Acrylic (PMMA)
- Other engineered transparent polymers
Optical Coatings
To further enhance performance, optical domes often use:
- Anti-Reflection (AR) Coatings: Reduce surface reflections and increase transmission
- Hydrophobic Coatings: Improve water shedding for underwater or outdoor use
- Scratch-Resistant Coatings: Protect against abrasion and handling damage
Mechanical Integration and Environmental Design
Mechanical Considerations
- Secure mounting and sealing against water ingress
- Stress management under pressure and temperature cycling
- Compatibility with housing materials
Environmental Factors
- Temperature extremes and thermal shock
- External pressure (underwater or aerospace)
- Long-term exposure to UV and chemicals
Finite Element Analysis (FEA) is commonly used to validate dome strength and deformation under operating conditions.
Manufacturing and Quality Control
Optical dome performance depends heavily on manufacturing quality.
Key factors include:
- Precision molding or machining
- Surface polish quality
- Avoidance of inclusions, bubbles, and internal stress
- Accurate control of radius and thickness
Testing and Validation
Before deployment, optical domes undergo:
- Optical Testing: Transmission, distortion, wavefront error
- Environmental Testing: Pressure, temperature cycling, durability
- Coating Verification: Adhesion, durability, spectral performance
Optical Glass Dome Specifications
- Substrate: Visible-band optical glass (Schott N-BK7, N-BK10, WG295, N-K5, etc.)
- Diameter Range: 10 mm – 350 mm
- Thickness: 1 mm – 10 mm
- Surface Quality: 60/40, 40/20, 20/10
- Surface Fringe: 10(5) – 3(0.5)
- Coating: Anti-Reflection (AR)
- Strengthening: Heat-treated / tempered
Note: Custom radii, thicknesses, coatings, and materials are available for volume or specialized applications.