Calibration makes sensors intelligent
The market for optical sensors is growing as we tend to put them into more of our everyday necessities and gadgets. But for optical sensors to work properly, they need – like any other measurement instrument – to be calibrated.
Calibration and clever processing add value to an inexpensive sensor and transform it into, e.g. a power meter, a chemical sensor, an ambient light sensor etc. The calibration process adds value to the sensor by defining it relative to other sensors.
Almost any calibration process consists of submitting a sensor to well-defined and traceable stimuli and recording the response. In most cases, many different stimuli must be recorded to get the full picture.
Most light sources have limitations
Color sensitive optical sensors must be calibrated for a range of wavelengths. If a high spectral resolution or a high spatial resolution is needed, only few sources are suitable. And if both are needed, even fewer sources can be used.
Laser arrays and LED arrays offer relative high powers and especially lasers exhibit high brightness. But they lack spectral flexibility and continuous spectral coverage.
Incandescent lamps and most gas discharge lamps offer a broad and continuous spectral coverage but with poor brightness. The lack of brightness can be a challenge in applications where high spatial resolution is required for instance if there is a need to transmit the light far in free space with low loss to the device under test (e.g. inside a vacuum chamber). Furthermore, if filtering equipment requires a high spectral resolution, the high brightness is an advantage.
Why is that? Many narrowband tunable optical filters and monochromators require a relatively high brightness input to work efficiently. An example could be a monochromator where high spectral resolution requires a small input slit, which causes a significant power loss for low brightness sources.
Supercontinuum sources possess the broadness and brightness
Supercontinuum sources can alleviate a lot of the above challenges as they exhibit a high brightness as well as a broad continuous spectral coverage.
In conjunction with the appropriate filter technology, supercontinuum sources can be configured to freely generate tunable narrowband lines or fully adjustable broadband spectral synthesis, i.e. generate a user-specified spectrum such as a standard illuminant. With a SuperK supercontinuum source, you can cover any single color, any complex spectrum in any shape.
This allows calibration instrument builders to make rapidly tunable sources to map out the performance of the device under test as well as generate broadband standard illuminants for control purposes. These are features which make the supercontinuum source ideal for calibration of optical components.
Many years’ experience enables NKT Photonics to offer completely customized and full turnkey supercontinuum calibration solutions to our customers. All solutions include fully integrated sources, filters, software, and delivery optics and are based on a field-proven instrument architecture, industrial and scalable production, and backed by a worldwide support network.
- Spectrally resolved radiometric characterization and calibration using a supercontinuum laser in the NIR by L. Bünger, R.D. Taubert, and K. Anhalt for the AMA Conferences – Sensor 2015 and IRS2 2015, DOI 10.5162/irs2015/1.2