Ultra-Precision Optical Machining Processes Compared: The Complete Guide to CCOS, IBF, MRF, MJP, and FJP

When you need to finish an optical surface to nanometer-level precision, the choice of machining process is the single most important decision you’ll make. The wrong process wastes time, damages subsurface integrity, and leaves you with a part that can’t meet spec. The right one delivers sub-nanometer accuracy with predictable throughput.

Five technologies dominate modern ultra-precision optical manufacturing: CCOS (Computer Controlled Optical Surfacing), IBF (Ion Beam Figuring), MRF (Magnetorheological Finishing), MJP (Magnetorheological Jet Polishing), and FJP (Fluid Jet Polishing). Each operates on a different physical principle, excels in a different regime, and occupies a specific position in the manufacturing chain.

This guide compares all five so you can build the optimal process chain for your optics — whether you’re producing telescope mirrors, semiconductor lithography lenses, or laser-grade aspheres.

Quick Comparison: All Five Processes

1. CCOS — Computer Controlled Optical Surfacing

CCOS is the foundation of modern deterministic optical manufacturing. It uses a computer-controlled polishing machine that moves a small pitch or polyurethane tool across the surface along a calculated tool path. The dwell time at each position is computed from a measured surface error map, allowing the machine to remove material where it’s needed most.

How it works

1. Measure the surface with an interferometer or profilometer
2. Compute a dwell-time map based on the removal function and error distribution
3. Execute the tool path — the tool dwells longer on high spots, less on low spots
4. Iterate measure-polish-measure until the target accuracy is reached

Key characteristics

• Bulk material removal — removes significant material per cycle, ideal for grinding-to-polishing transition
• Flexible tooling — pitch, polyurethane, or bonded abrasive tools depending on the stage
• Scalable to large apertures — used on telescope mirrors up to several meters
• Mature and well-understood — decades of process knowledge and tool design

Limitations

• Contact pressure can cause subsurface damage and edge roll-off
• Tool wear introduces uncertainty in the removal function over time
• Typically requires multiple iterations to reach sub-nanometer accuracy
• Not ideal for thin or stress-sensitive substrates

Where it fits: CCOS is the workhorse for initial figure correction after grinding. It takes a ground surface from several microns of error down to a few hundred nanometers, setting the stage for finer technologies like IBF or MRF.

2. IBF — Ion Beam Figuring

Ion beam figuring is a non-contact, deterministic finishing technology. It directs a focused beam of accelerated ions at the optical surface, removing material atom by atom through physical sputtering. Because there is no tool contact, there is no mechanical load, no edge roll-off, and no subsurface damage.

Key characteristics

• Non-contact — no tool wear, no clamping stress
• Atomic-level removal — nanometer-scale form correction
• Deterministic — removal rate can be precisely modeled and controlled
• Ideal for final figure correction — fixes residual form errors after pre-polishing
• Vacuum chamber required — adds equipment complexity and cycle time

IBF excels at correcting low-frequency surface form errors to sub-nanometer RMS. It is the go-to final step for precision aspheres and freeform optics where absolute form accuracy is non-negotiable.

Deep dive: For a detailed explanation of IBF principles, advantages, and applications, see our companion article: What Is Ion Beam Figuring? How IBF Achieves Sub-Nanometer Optics

3. MRF — Magnetorheological Finishing

Magnetorheological finishing is a sub-aperture polishing technique that uses a magnetically stiffened fluid. When a magnetic field is applied, the fluid’s viscosity increases dramatically, forming a precise polishing ribbon that conforms to the surface. This ribbon removes material with exceptional control and produces a smooth, damage-free finish.

Key characteristics

• Conformal polishing tool — the fluid ribbon adapts to the surface shape
• Superior surface quality — minimal subsurface damage, low roughness
• Deterministic — stable removal function enables accurate figure control
• Ideal for final polishing — achieves both figure and finish in one step
• Atmospheric operation — no vacuum chamber needed, better throughput

MRF is prized for its ability to produce smooth surfaces with minimal subsurface damage — critical for optics used in high-energy laser and short-wavelength applications.

Deep dive: For a detailed explanation of MRF principles, advantages, and applications, see our companion article: What Is Magnetorheological Finishing? How MRF Polishing Works

4. MJP — Magnetorheological Jet Polishing

Magnetorheological jet polishing is a newer addition to the ultra-precision toolkit, designed to solve problems that conventional sub-aperture tools cannot. It projects a jet of magnetorheological fluid through a nozzle. As the jet exits the magnetic field region, the fluid stiffens momentarily, creating a highly localized, non-contact removal spot.

How it works

1. Magnetorheological fluid is pumped through a nozzle positioned above the surface
2. An electromagnetic field at the nozzle exit stiffens the fluid jet
3. The stiffened jet impacts the surface in a small, well-defined spot
4. Material is removed by fluid shear and abrasive action
5. The spent fluid flows away, carrying debris with it

Key characteristics

• Non-contact jet — no tool pressure on the surface
• Small, well-defined removal spot — suitable for steep surfaces and tight curves
• Access to complex geometries — can reach inner cavities, steep slopes, and freeform features
• Gentle removal — low normal force, minimal subsurface damage
• Medium throughput — faster than IBF, slower than MRF for large areas

Best applications

• Freeform and steep-surface optics where MRF’s ribbon can’t conform
• Inner cavities and concave features that contact tools can’t reach
• Lightweight mirrors with ribbed back structures
• Correction of local errors on large surfaces without disturbing surrounding areas

Limitations

• Removal rate is lower than MRF for large flat or gentle-curve surfaces
• Requires careful nozzle design and fluid management
• Surface roughness is slightly higher than MRF (0.5-1.5 nm vs 0.3-0.8 nm)

Where it fits: MJP fills the gap between MRF’s conformal ribbon and IBF’s broad beam — it brings deterministic non-contact polishing to complex geometries that neither MRF nor IBF can handle effectively.

5. FJP — Fluid Jet Polishing

Fluid jet polishing is the simplest non-contact finishing technique in this comparison. It pumps an abrasive slurry through a nozzle at low pressure, directing the jet onto the optical surface. Material is removed by the impact of abrasive particles in the fluid stream.

How it works

1. An abrasive slurry (water + polishing abrasive) is pumped through a nozzle
2. The jet impinges on the surface at a controlled angle and distance
3. Abrasive particles in the jet remove material by micro-machining
4. The spent slurry is collected and recirculated
5. Dwell time and path are computer-controlled for deterministic correction

Key characteristics

• Simple setup — nozzle, pump, and slurry are the main components
• Non-contact — no tool pressure, no tool wear
• Adjustable spot size — nozzle diameter controls the removal area
• Wide abrasive compatibility — alumina, ceria, diamond, depending on the material
• Low normal force — suitable for thin and stress-sensitive substrates

Best applications

• Pre-finishing before MRF or IBF — brings surface from grinding roughness to polish
• Large surfaces where a simple, low-cost process is preferred
• Materials that are difficult to polish conventionally — hard ceramics, glasses
• Quick correction of mid-spatial-frequency errors

Limitations

• Lower accuracy than IBF or MRF (30-80 nm RMS vs sub-nanometer)
• Surface roughness is typically higher (0.5-2 nm Ra)
• Removal function can be sensitive to standoff distance and jet angle
• Not suitable for final figure correction on precision optics

Where it fits: FJP is the preparation step — it transitions a ground or roughly polished surface to a state where MRF or IBF can efficiently perform the final correction. It’s the bridge between grinding and precision finishing.

Detailed Comparison: Choosing the Right Process

Material Removal and Accuracy

Operating Environment and Cost

Surface Geometry Capability

When to Choose Each Process

Choose CCOS when

• You need bulk material removal from a ground surface
• You’re working with large-aperture optics (>500 mm)
• Cost is a primary concern and sub-nanometer accuracy isn’t required yet
• You need a mature, well-understood process with decades of data

Choose IBF when

• You need sub-nanometer form accuracy on aspheric or freeform surfaces
• You’re correcting residual errors after grinding or pre-polishing
• You’re working with thin, fragile, or easily deformed optics (non-contact is essential)
• Edge quality and minimal edge roll-off are critical
• No subsurface damage is acceptable

Choose MRF when

• You need superior surface finish with minimal subsurface damage
• You’re processing optics for high-energy laser or UV applications
• You want figure and finish correction in a single deterministic step
• Throughput and process stability matter for production
• You’re working with gentle aspheres or flat-to-moderate curvature surfaces

Choose MJP when

• You’re finishing freeform or steep-surface optics that MRF can’t conform to
• You need to polish inner cavities or concave features
• You’re working with lightweight mirrors with complex ribbed structures
• You need localized correction on specific areas without disturbing the surroundings

Choose FJP when

• You need a cost-effective pre-finishing step before MRF or IBF
• You’re working with large surfaces and need a simple, reliable process
• You’re polishing hard or unusual materials that need abrasive flexibility
• You need to correct mid-spatial-frequency errors quickly

Building the Optimal Process Chain

No single process can take a raw blank to final precision efficiently. The key to cost-effective ultra-precision manufacturing is building the right process chain — combining technologies so each operates in its sweet spot.

Chain 1: Precision Asphere (Medium Volume)

1. CNC grinding — generate the aspheric profile to ~5 μm error
2. CCOS — coarse figure correction to ~1 μm
3. MRF — fine figure correction + smooth finish to ~15 nm RMS
4. IBF — final figure correction to < 0.5 nm RMS

Chain 2: Freeform Optic (Complex Geometry)

1. CNC grinding — generate the freeform profile
2. FJP — pre-finishing to remove grinding damage and reduce roughness
3. MJP — deterministic figure correction on steep and complex curves
4. IBF — final correction on accessible areas to sub-nanometer

Chain 3: Large Telescope Mirror (>1m)

1. CNC grinding — bulk material removal
2. CCOS — iterative figure correction over multiple cycles
3. CCOS with stress-lap — handle aspheric departure
4. IBF — final figure correction (for smaller segments) or large-aperture IBF

Chain 4: High-Energy Laser Optic

1. CNC grinding — profile generation
2. CCOS — figure correction
3. MRF — figure + finish, critical for low subsurface damage
4. IBF — final figure if sub-nanometer accuracy is required

Why AFiSy Technologies

With 20 years of ultra-precision optical processing experience and a proven track record — 176 equipment sets delivered, including 115 ion beam figuring machines — AFiSy Technologies is a trusted partner for mid-to-high-end optical manufacturing.

Our product lines cover the full spectrum of ultra-precision finishing:

• IBF series — ion beam figuring machines for sub-nanometer final correction
• MRF series — magnetorheological finishing machines for deterministic polishing
• CCOS series — computer-controlled optical surfacing systems for bulk correction
• Custom solutions — integrated process chains combining multiple technologies

By developing all core technologies in-house, we help customers build complete, deterministic finishing lines that achieve results no single technology could deliver alone. Whether you need one machine or a full process chain, we provide the equipment, process knowledge, and support to get your optics to spec.

Related articles:

• What Is Ion Beam Figuring? How IBF Achieves Sub-Nanometer Optics
• What Is Magnetorheological Finishing? How MRF Polishing Works
• Ion Beam Figuring vs Magnetorheological Finishing: Which Do You Need?
• The Future of Ultra-Precision Optics: An In-Depth Analysis of IBF Techniques