How are Dove prisms manufactured?

The manufacturing process of Dove Prism

Dove Prism is a key component used in optical systems to achieve image rotation, flipping, or optical path deflection, and is widely used in laser pointing, imaging systems, and spectroscopic instruments. It has extremely high requirements for angular accuracy, surface shape quality and material uniformity. Here is the complete manufacturing process for industrial-grade and high-precision applications:

1. Material selection and pre-treatment

Selection of base materials

Visible light/near-infrared applications: 

BK7 optical glass (refractive index uniformity ≤ 5×10⁻⁶, visible light transmittance ≥ 92%) is preferred.

Ultraviolet/deep ultraviolet applications: 

Use fused silica (JGS1/JGS2), suitable for the 193nm to 2.5μm band, with low dispersion and high resistance to laser damage.

Infrared application: 

Usecalcium fluoride (CaF₂) or germanium (Ge)crystals, suitable for the 2μm to 15μm infrared band.

Raw material inspection and annealing

Ultrasonic scanning and laser interferometer inspection are used to remove internal bubbles, impurities, streaks and other defects to ensure stress-free birefringence.

High-temperature annealing treatment: BK7 glass is held at 450 to 500 ° C for 12 to 18 hours, fused silica is held at 600 to 700 ° C for 24 hours, and then cooled slowly at a rate of 0.5 to 1 ° C per hour to eliminate internal stress and ensure stable optical properties.

2. Roughing and forming of blanks

Precision cutting

Use a diamond wire cutter to cut the annealed glass blank into a prism blank close to the size of the finished product, with dimensional tolerance controlled within ±0.2mm, and the top and bottom corners initially controlled within ±30 "of the design value to avoid excessive machining allowance resulting in out-of-control precision.

Rough grinding and forming

Use a 200-400 mesh diamond grinding wheel to roughly grind the incident surface, exit surface, and bevel surface of the prism to remove the cut damage layer.

Surface roughness Ra ≤ 0.8μm and Angle error ≤ 10 "after rough grinding lay the foundation for fine grinding.

The entire process is carried out in a constant-temperature (20±0.5℃) workshop to avoid processing errors caused by temperature changes.

3. Ultra-precision grinding and polishing

Fine grinding optimization

Replace the 800-1500 mesh fine-grained diamond grinding paste and grind the critical surfaces (bevel, incident/exit surfaces) in stages.

After fine grinding, the Angle accuracy is controlled within ±5 ", the surface shape accuracy reaches λ/5 (λ=632.8nm), and the surface roughness Ra is ≤ 0.1μm.

Use a CNC fine grinding machine in conjunction with a vacuum suction cup fixture to avoid prism deformation caused by clamping force.

Ultra-precision polishing of bevels

Core process: Chemical mechanical polishing (CMP) + ion beam polishing (IBF) combined process, completed in a Class 100 cleanroom.

After polishing, the surface roughness of the inclined plane is Ra ≤ 0.05nm, the surface shape accuracy is λ/20, and the Angle tolerance is ≤ ±1 "(high precision grade) /±3" (industrial grade).

Focus on controlling edge sharpness (chamfer ≤ 0.05mm) to avoid image distortion caused by edge chipping.

Polish the auxiliary surface

The incident and emergent surfaces were polished with nano-scale cerium oxide polishing solution, with surface roughness Ra ≤ 0.1nm, and the surface quality before the anti-reflection film adaptation met ISO 10110-7 standard (scratches ≤ 20/10, pitting ≤ 0.05mm).

4. Key Processes: Angle calibration and inspection

Use a high-precision goniometer (accuracy ±0.5 ") to measure the top and bottom angles. If there is a deviation, perform nanoscale calibration through ion beam grinding.

Wavefront distortion was detected using a laser interferometer to ensure ≤ λ/20, meeting the requirements for high-definition imaging.

Verify the imaging quality with a star point detector to ensure no ghosting or distortion caused by Angle errors.

5. Coating Process (Optional)

Anti-reflection coating (AR coating) on the incident/exit surfaces for the target band, with a single surface reflectance of no more than 0.2% in the visible light band and no more than 0.5% in the infrared band.

High-reflection films (dielectric films/metal films) can be applied to the inclined surfaces, with a reflectance of ≥ 99.5% to enhance the reflection efficiency of the optical path.

After coating, high-temperature baking (150-200 ° C for 2 hours) + salt spray test is conducted to ensure that the adhesion of the coating meets the MIL-C-675C standard.

6. Final Inspection and cleaning Packaging

Full-dimensional final inspection

Cleaning and packaging

Ultrasonic cleaning: Clean in sequence with deionized water, anhydrous ethanol, and acetone to remove surface polishing powder and oil stains.

After blowing dry with nitrogen, vacuum-packed in a class 100 clean environment with built-in desiccants to prevent moisture and dust during transportation/storage.

The finished product comes with a test report containing key indicators such as Angle, surface shape accuracy, and imaging quality.

Application scenario fit

Laser pointing system: 

Use fused silica high-precision prisms to adapt to extreme temperature and humidity environments.

Imaging telescope: 

Use BK7 material industrial-grade prism to balance cost and imaging effect.

Infrared spectrometer: 

Use CaF₂/Ge crystal prisms to ensure high transmittance in the infrared band.

UltraOpto can customize Dawei prisms based on the optical system parameters of customers (band, resolution, installation space). From material selection to polishing process, the entire process is controllable to ensure that the performance of the prism is perfectly matched with the equipment.