Polarized Fourier transform infrared FTIR spectroscopy has been used extensively to monitor orientation for polymer quality control and optimized the mechanical properties. In the manufacturing process, using an in-line portable spectrometer would be a great advantage providing near real-time feedback during polymer production processes including temperature, and drawing/stretching. The goal is to let the chains within a polymer disentangle and become more systematic/oriented with predictable properties. In this work, we present a measurement technique using microelectromechanical system (MEMS) based polarization controlled Fourier transform spectrometer in the extended near-infrared used to monitor the polymer quality. The spectrometer is operating in the wavelength range of 1300 nm to 2600 nm (about 3846 cm-1 to 7692 cm-1) with a spectral resolution of 66 cm-1. The polarized-FTIR data were collected for a commercial plastic CD sleeve with thickness of about 1 mm in transmission mode. An ultra-broadband wire grid linear polarizer is used, inserted in the light path and rotated 360º in steps 10º. The polarizer orientation is kept in the same position for both background and sample measurements. The dichroic ratios of different absorption bands have been determined with the polarizer oriented parallel and perpendicular to a reference direction. The orientation quality of the polymer can be detected from the dichroic ratio with dichroic ratio equals to one representing an isotropic material. Comparison with a benchtop device is conducted showing good agreement. The presented solution paves the way for a low-cost and portable device for on-line polymer quality control.
In this work, we present a novel architecture for Fourier transform spectrometers based on cascaded low-finesse FP interferometers. One of the interferometers has fixed path length while the second is a scanning one using a relatively large stroke electrostatic comb-drive actuator. The fixed interferometer results in a spectrum modulation and, hence, a shifted version of the interferogram away from the point of the zero spacing between the two mirrors. The shifted interferogram can then be used with the Fourier transform algorithm to obtain the spectrum of the measured light. This cascaded FP configuration results in a simple arrangement of mirrors on a line, which makes it much tolerant to misalignment errors. The proposed configuration is implemented using the MEMS DRIE technology on an SOI wafer with a simple MEMS process flow without metallization or dielectric coating of the vertical optical surface. The fabricated compact structure is measured with both a laser source with narrow spectrum at 1550 nm and a wide spectrum source composed of an SLED and the ASE of a semiconductor optical amplifier source. The obtained results validate the concept of the new configuration.
Fiber lasers are gaining wide attention nowadays due to their high stability, high reliability, low cost and compactness. Frequency modulation of the laser system has many applications such as wavelength tuning, active mode locking, generation of optical frequency combs and fiber sensors in general. In this work, we report frequency modulation of fiber ring laser system using transmission-type corner cube in-plane MEMS phase modulator fabricated by DRIE technology on an SOI substrate. The fiber-coupled MEMS-based phase modulator is inserted in a multilongitudinal mode fiber ring laser, which has a free spectral range of 345 kHz. By varying the applied voltage on the MEMS device, a wide range of the frequency modulation index can be achieved.
Notch filters based on fiber-coupled Fabry-Pérot cavity are formed by a reflector placed in close proximity to a
dielectric-coated end of an optical fiber. This kind of optical filters is easy to tailor for a given application because the
external mirror has less mechanical and optical constraints. In this paper we present a fiber-coupled Fabry-Pérot filter
based on dielectric-coated optical fiber inserted into a fiber groove facing a metallized micromirror, where the latter is
driven by a high-speed MEMS actuator. The microsystem is fabricated using Deep Reactive Ion Etching (DRIE)
technology on SOI wafer. The optical axis is in-plane and the components are self-aligned. The DRIE etching depth is
150 μm; chosen for improving the out-of-plane stiffness of the actuator and increasing the micromirror optical
throughput. The MEMS actuator type is closing-gap while its quality factor is improved by slotting the fixed plate. The
actuator, therefore, achieves a travel distance larger than 800 nm and has a resonance frequency of 90 kHz. The notch
filter exhibits a free spectral range up to 100 nm and a notch rejection ratio of 20 dB around a wavelength of 1300 nm.
The presented device provides low cost wafer level production of the filter.
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