December 30, 2022

Optics for Metrology and Testing

Metrology greatly impacts many sectors, including energy, environmental, health, industry, manufacturing, and economics. Optics for metrology and testing must be precise and reliable to ensure the consistency and traceability of the measurements and the precision of the optical components themselves.

What Are Metrology and Testing?

Metrology is the science of measurement, as defined by the International Bureau of Weights and Measures.^[1] It uses both experimental and theoretical determinations at any level of uncertainty in any field of science and technology.

Metrology may be divided into:

The definition of units of measurement
The realization of these units of measurement in practice
Traceability, or the linking of measurements in practice to established standards

There are several subfields of metrology, including:

Scientific or fundamental metrology that establishes the units of measurement
Applied, technical, or industrial metrology, which applies measurement to manufacturing and other processes
Legal metrology, which covers regulation and statutory requirements for measurement instruments and measurements

What Is Optical Metrology and How Is It Used?

Optical metrology is the science and technology concerning measurements with light. Such measurements can target properties of light and light sources or properties of objects such as dimensions, distances, and temperatures.

These fields often overlap because one may use measured properties of light not just to characterize the source but for other purposes.

Some examples of metrology include:

Optical Distance Measurements

Distance measurements include lasers and may be based on interferometers or measurements of the time-of-flight of light pulses in dimensional metrology.

Optical Time-Domain Reflectometers

These are used for inspecting fiber-optic links and thin-film optical devices.

Spectral Optical Properties

This may be measured with devices like spectrometers, wavemeters, and self-heterodyne setups.

Optical Frequency Metrology

This measures optical frequencies with high precision, such as ultraprecise optical clocks.

Optical Temperature Sensors

The optical temperature sensors are based on the analysis of the thermal emission of hot bodies.

Optical Power Measurement

This can be measured with photodiodes, thermal power meters, or other equipment. Illumination measurements can identify pure physical quantities like optical intensity or perceived brightness.

Optical Profilometers

Optical profilometers are used for measuring surface topographies, such as with semiconductor chip production, or for quality control in optical fabrication.^[2]

How Are Optics Involved in Metrology and Testing Equipment?

Almost as important as standardized units, metrology is concerned with the suitability of measurement instruments, calibration, and quality control. Producing precise, accurate measurements impacts the value and quality of the end product and its production costs.

Optics engineering teams have multidisciplinary expertise and experience in the design and setup of metrology and testing equipment. The optical performance of individual optics, complex lens assemblies, and metrology stations is necessary for a quality final product.

Metrology and testing are key parts of the production process. We have a dedicated team for assembling and testing optical components, assemblies, and subsystems operating in visible and near-infrared wavelength ranges.

Some examples of optics in metrology equipment include:

Stereo endoscopes
Camera modules and endoscopes
Camera response
Optical elements and lens assemblies
Illumination modules

In all of these products, it’s vital to understand critical performance metrics like surface roughness and surface accuracy to determine test parameters.

What Is the Process of Designing Optics for Metrology?

Metrological traceability is the property of a measurement result whereby the result can be related to a reference through a documented chain of calibrations, each contributing to measurement uncertainty. This allows for the comparison of measurements and evaluation of different results.

The chain of traceability allows any measurement to be referenced to high levels of measurement back to the original definition of the unit. This is most commonly obtained by calibration, which establishes the relationship between an indication of metrology equipment and the value of a standard.

The calibration process determines the measurement value and the uncertainty of the device being calibrated with a traceability link to the measurement standard. Calibration informs traceability, ensures that the equipment consists of other measurements, and determines reliability and accuracy.

Because traceability and calibration are such important parts of metrology, it’s vital that the optical components within the metrology and testing equipment are precise. Otherwise, the entire instrument and the testing process could be unreliable and essentially useless.

At Apollo Optical Systems, we rely on metrology equipment to confirm the quality of optical components and their precise specifications. We also understand the importance of precision when designing optical components for metrology equipment and traceability.

Designing optics for metrology and testing equipment has a similar design process as other optical components. We can work with your standard metrology tools to design custom optical components that ensure success at all stages of product development.