How are polarizing beam splitters made?

Manufacturing process of Polarizing Prism (PBS) (Technical Description)

UltraOpto polarizing beam splitting prisms (PBS) are made using highly uniform optical substrates and ultra-precision coating processes, with the core function of splitting S-polarized light with high reflection and p-polarized light with high transmission, and are widely used in laser systems, imaging equipment, optical measurement and other fields. The following is the standardized manufacturing process and quality control system to precisely ensure the stability of the optical performance of the product.

1. Core Manufacturing Processes (8 Key processes)

Substrate selection and pre-treatment

Material selection: 

Choose optical glass such as BK7 Grade A (visible light), fused silica  (infrared/high power laser), or calcium fluoride (deep ultraviolet) based on the application band and power requirements to ensure low dispersion,  high transmittance and excellent thermal stability.

Raw material inspection: 

Internal uniformity and stress of the glass are inspected by laser interferometer, full-band transmittance is verified by spectrophotometer,  and defects such as bubbles, streaks, and stones are removed to ensure the  quality of the base material.

Blank cutting: 

Use a diamond  re saw to cut the glass blocks into rectangular blanks close to the size of the finished product, with the size allowance controlled at 0.5-1.0mm  to reduce subsequent processing losses.

Precise positioning of the upper plate (clamping core)

Fix the blank using the glue-free contact method (van der Waals force bonding) or the low-temperature firevarnish mounting methodto avoid the impact of adhesive layer stress on Angle accuracy. Strictly control the flatness and parallelism of the reference plane during clamping, with clamping deviation ≤0.001mm/m to provide a high-precision reference for subsequent processing.

Contour rough grinding and fine grinding (forming base)

Rough grinding: 

Use a diamond  grinding wheel to roughly grind the four right-angle surfaces to the designed size, remove most of the allowance, and form a regular cuboid  shape with surface roughness controlled below Ra 1.6μm.

Fine grinding: 

With the reference plane as the positioning, the incident surface, exit surface and bonding surface are finely ground with resin-bonded grinding wheels, with  the core control that the 90° right Angle tolerance between each surface is ≤±3 ", and  the surface shape accuracy is λ/[email protected], laying the foundation for polishing and coating.

Ultra-precision polishing (core of the surface shape)

Polishing is carried out in a clean environment with constant temperature (20±0.5 ° C) and constant humidity using a polyurethane polishing mold in combination with cerium oxide or silica polishing liquid. The incident/exit surface should reach a surface quality of 20-10 (scratches/pitting), surface shape accuracy λ/[email protected] (λ/20 for high-precision custom parts), and ensure no light scattering or distortion.

Polarizing film system deposition (Functional core)

This is the most critical step in PBS manufacturing and directly determines the spectral performance.

Film system  design: 

Based on the target band (such as 400-700nm visible light), design a multilayer dielectric film system composed of alternating stacking of high refractive index (such as TiO₂, Ta₂O₅) and low  refractive index (such as SiO₂) materials, with the thickness precise to the nanometer level.

Vacuum coating: 

In an ultra-high vacuum environment, the film system is deposited over the 45° inclined plane    of one of the prisms by ion beam-assisted deposition (IAD) or magnetron  sputtering technology. The film system can achieve a reflectance of  S-polarized light > 99% and a transmittance of p-polarized light >  95%.

Film layer inspection:

The thickness, refractive index and spectral performance of the film layer  were inspected using a spectrophotometer and an ellipsometer to ensure  compliance with design requirements.

Optical bonding and curing

Bond a prism coated with a beam splitter to another uncoated prism using an optical epoxy adhesive. With the assistance of a high-precision fixture, ensure that the 45° bevels of the two prisms are precisely aligned, that the adhesive layer is uniform (usually < 5μm), and that there are no bubbles or impurities. Slow curing in a temperature-controlled box after bonding to release stress and ensure bonding strength and optical stability.

Secondary processing and edge strengthening

Precision cutting: 

Cut the glued cuboid blank into the final prism shape to the designed size.

Chamfering: 

Use diamond chamfering wheels to chamfer all sharp edges by 0.2-0.5mm to prevent  chipping and chipping, and to enhance the impact resistance of the product.

Anti-reflection coating:

Apply a broadband anti-reflection coating (AR) on both the incident and exit surfaces to further reduce Fresnel reflection and enhance overall  transmission efficiency.

Final inspection and packaging for outbound

Full-dimensional inspection of finished products in a Class 100 cleanroom:

Use a spectrophotometer to measure the spectral ratio and extinction ratio (P/S).

Use a laser interferometer to measure surface shape accuracy and wavefront distortion.

Check the Angle tolerance using an autocollimator.

After passing the inspection, pack independently in anti-static, scratch-resistant packaging material along with a detailed inspection report to ensure no damage during transportation.

 2. Key quality control nodes and UltraOpto precision standards

3. Process characteristics and application Fit

Excellent spectral performance: 

With a precision multilayer dielectric film system, the spectral ratio is stable, the extinction ratio is high, and polarized light is effectively separated.

Precision is controllable: 

From rough grinding to final inspection, the entire process is managed in a closed loop with metrology-grade equipment to ensure Angle and surface shape accuracy.

High stability:

Glue-free clamping and vacuum coating process effectively avoid stress deformation  and environmental erosion, ensuring stable performance of prisms for long-term use.

Strong customization: 

The substrate, size, working band, splitting ratio and coating scheme can be customized according to customer requirements to adapt to different scenarios.

UltraOpto polarizing prism, with itsstrict process control and customization capabilities, provides highly reliable optical core components for lidar, machine vision, medical imaging and other fields, helping customers' systems achieve precise polarizing beam splitting control.