Measuring with light
PhotonFirst is expert in measuring the world with light. We use fiber optics sensors in combination with the most advanced and in-house developed interrogator systems based on Photonics Integrated Circuits using spectrometry and interferometry principles for improved resolution, minitiaturization, reduced energy consumption and cost.
Over the last years, fibre optic strain sensors based on Fibre Bragg Grating (FBG) technique, have been developed. The basic principle is: light is sent through a fibre optic cable and partially reflected by FBGs. Strain on, or a temperature change of the fibre causes a shift in wavelength of the reflected light, which can be measured very precisely and translated into strain or temperature values.
Most current sensor detection devices (interrogators) are based on free-space spectrometer configurations. This approach implies fundamental limits with regard to device dimensions, measurement resolution and accuracy, power consumption, etc. The increasing demand for applications using this technology tends to sharpen these requirements. As the technology matures, device dimensions, power consumption and costs need to be optimized to serve these increasing application requirements. Based on the current state of technology and its industrialization capabilities, Photonics Integrated Circuits (PIC) is considered to be the most promising technology for the next generation of interrogation devices for fibre optic sensing.
As current PhotonFirst detection systems are based on spectrometry, capable of detecting wavelength shifts of 15 femtometer that corresponds to about 20 nanostrain, improved resolutions can be achieved by using interferometry. A fibre optics based Mach-Zehnder Interferometer was developed for high resolution wavelength analysis. This interferometer makes the reflected light of the FBG interfere with itself resulting in a phase change which is proportional to a wavelength change. For improving resolution this appears to be a very promising approach. However, the system as a free-space design still has limited practical use for integration in demanding environments due to its high sensitivity and associated erratic behavior.
An Application Specific Photonic Integrated Circuit (ASPIC) is an optical chip designed for a dedicated purpose. Similar to electronics, ASPICs allows a variety of solutions, all based on a small set of components.
Application Specific Photonic Integrated Circuits
Unlike integrated electronics where silicon is the dominant material, ASPICs have been fabricated on different material platforms having each of them providing advantages and limitations depending on the functions to be integrated. For instance, Silica has desirable properties for passive components like Arrayed Waveguide Gratings (AWGs) while GaAs or InP allow direct integration of active components, i.e. lights sources, detectors and others. Although the fabrication process is similar to integrated electronics, there is no dominant device like the transistor. The range of photonic functions include low loss interconnect waveguides, power splitters, optical amplifiers, optical modulators, filters, lasers, detectors, etc.
The versatile ability to replace traditional assemblies of multiple discrete optical or micro-optical components by a single small sized chip, make ASPICs highly favorable for next generation optical systems for benefits in cost reduction, functionality aggregation and standardization of specifications and processes. Certainly this broad applicable versatility requires the need for standardization to preserve compatibility between the development platforms allowing to integrate the best of worlds to provide the best possible solution available. In that respect valuable lessons in platform material selection for ASPICs are repeatedly discussed which ultimately will determine the success of the ASPICs industry. For instance, several successes have been achieved in both InP, SOI and TriPleX based systems. As cost and performance may currently prove silicon-based devices preferable, it is certainly the capability of having both passive and active functions combined that proves InP more worthwhile depending on the required system functionality. Moreover, the integration of both electronic circuits with photonics circuits, i.e. hybrid systems, will most likely lead to more applicable development platforms yet to be invented.
Fibre Optic Sensing
The increasing demand for applications using this technology sharpens the requirements. As the technology matures, device dimensions, power consumption and costs need to be optimized to serve these increasing application requirements. Based on the technology perspective and its industrialization capabilities, Application Specific Photonic Integrated Circuits is considered to be the most promising technology for the next generation of interrogation devices for fibre optic sensing.
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