The Absolute Radiometric Calibration Facility (ARCF) at TNO operates a unique optical scatter measurement set-up for the characterization of optical components for space applications and has been recently refurbish to extend the working wavelength domain from UV/VIS/NIR to SWIR, making accurate measurements possible in the entire 240-2400 nm range. A second extension currently being performed is the addition of an optical parametric oscillator (OPO) laser light source, tunable over the same wavelength range. The increased light levels made possible by this new source will improve the signal-to-noise-ratio (SNR), significantly reducing measurement time and potentially further increasing the measurement accuracy. In this article we will present the challenges encountered in expanding such a setup to the SWIR and their solutions, show the new capabilities of the setup and explain the possibilities of using tunable pulsed OPO lasers in calibration applications.
Composite constructions are indispensable in current and future society. Fiber Bragg Gratings (FBGs) embedded in composite need to be carefully aligned with the material fibers to reduce inhomogeneous lateral load exerted onto the FBG which occurs due to the inhomogeneous nature of composite materials. Inhomogeneous load causes distortion of the reflection spectrum. We proposed to solve the FBG spectral distortion by incorporating a dedicated design structure inside the optical fiber. This allows the FBG to sense the strain in the axial direction accurately regardless of the optical fiber alignment with respect to the composite matrix. In this paper, the basic design will be discussed and the results of the first prototype of this structured fiber will be presented. Prototype FBGs are embedded in different composite samples of various thicknesses and materials (glass or carbon fiber based). The spectrum before and after curing is measured and direct comparisons are performed with embedded standard commercial FBG to verify the improvement. Effects of depth of the embedding and FBG direction with respect to the composite material fiber are investigated. Bending and tension tests are performed to ensure the special FBG in the structured fiber has the directional sensitivity to the strain applied. During all experiments, the special FBG is found to have a better or comparable spectrum than the standard FBGs. The improvement varies for the different tests. This can be caused by the unknown orientation of the structure inside the fiber. According to the first FEM analysis, this affects the effectiveness depending on the detail design of the structure. Information of the FEM analysis will be used to further optimize the design and for the development of a prototype.
A freeform optical surface is typically defined as any surface that does not have an axis of rotational symmetry. These surfaces provide additional degrees of freedom that can lead to improved performance compared to systems that make use solely of conventional optics.
Aerosols affect Earth’s energy level by scattering and absorbing radiation and by changing the properties of clouds. Such effects influence the precipitation patterns and lead to modifications of the global circulation systems that constitute Earth’s climate. The aerosol effects on our climate cannot be at full scale estimated due to the insufficient knowledge of their properties at a global scale. Achieving global measurement coverage requires an instrument with a large instantaneous field of view that can perform polarization measurements with high accuracy, typically better than 0.1%. Developing such an instrument can be considered as the most important challenge in polarimetric aerosol remote sensing.
Using a novel technique to measure polarization, we have designed an instrument for a low-Earth orbit, e.g. International Space Station, that can simultaneously characterize the intensity and state of linear polarization of scattered sunlight, from 400 to 800 nm and 1200 to 1600 nm, for 30 viewing directions, each with a 30° viewing angle. In this article we present the instrument’s optical design concept.
The presented interferometer concept enables high-accuracy target displacement measurement in difficult accessible locations and the development of small fiber optic sensor to measure other physical parameters e.g. pressure, vibration, gravity force, etc.. Furthermore, this configuration is basically insensitive to disturbances to the lead fiber between the passive sensor head and the measurement system including the electro-optical parts and the detection interferometer. Two test setups are built and tested to demonstrate the feasibility of high-speed measurement up to 50 kHz, low system drift of ~0.5 nm over 500 s and a low displacement noise level down to 2.8 pm/√ Hz.