Polarization Imperfections of Light in Interferometry

Disertační práce pojednává o polarizačních nedokonalostech optických komponentů, které jsou využívány ke kontrole a k transformaci polarizačního stavu světla. Získané teoretické výsledky jsou pak využity ve vybraných aplikacích, jež ke své činnosti využívají právě polarizace světla. Konkrétně se jedná o zařízení měřící vibrace oscilujících objektů, dále o interferenční měření dvojlomu v transparentních materiálech a konečně, o vybraná témata z optické kvantové komunikace.The emphasis of the dissertation is put on the investigating of polarization imperfections of optical components which are used to control and transform polarization of light. The theoretical results of this investigation are then applied to different applications which exploit light polarization, namely to the arrangements for high-resolution measurement of vibrating targets, to interferometric measurements for the determination of stress-induced birefringence in transparent materials and to the selected topics in quantum optical communication.

Interferometry-based Free Space Communication And Information Processing

This dissertation studies, analyzes, and experimentally demonstrates the innovative use of interference phenomenon in the field of opto-electronic information processing and optical communications. A number of optical systems using interferometric techniques both in the optical and the electronic domains has been demonstrated in the filed of signal transmission and processing, optical metrology, defense, and physical sensors. Specifically it has been shown that the interference of waves in the form of holography can be exploited to realize a novel optical scanner called Code Multiplexed Optical Scanner (C-MOS). The C-MOS features large aperture, wide scan angles, 3-D beam control, no moving parts, and high beam scanning resolution. A C-MOS based free space optical transceiver for bi-directional communication has also been experimentally demonstrated. For high speed, large bandwidth, and high frequency operation, an optically implemented reconfigurable RF transversal filter design is presented that implements wide range of filtering algorithms. A number of techniques using heterodyne interferometry via acousto-optic device for optical path length measurements have been described. Finally, a whole new class of interferometric sensors for optical metrology and sensing applications is presented. A non-traditional interferometric output signal processing scheme has been developed. Applications include, for example, temperature sensors for harsh environments for a wide temperature range from room temperature to 1000 degree C

Displacement laser interferometry with sub-nanometer uncertainty

Development in industry is asking for improved resolution and higher accuracy in mechanical measurement. Together with miniaturization the demand for sub nanometer uncertainty on dimensional metrology is increasing rapidly. Displacement laser interferometers are used widely as precision displacement measuring systems. This thesis describes the error sources which should be considered when measuring with these systems with (sub-)nanometer uncertainty, along with possible methods to overcome these errors. Whenconsidering interferometricdisplacementmeasurementswithnanometer uncertainty over small distances (below 1 mm) the measurements are influenced by periodic deviations originating frompolarizationmixing. Inmeasurements with nanometer uncertainty over larger distances this errormay become negligible compared to errors introduced by the refractive index changes of the medium in which the measurement takes place. In order to investigate the effect of periodic deviations, models were developed and tested. A model based on Jones matrices enables the prediction of periodic deviations originating from errors in optical alignment and polarization errors of the components of the interferometer. In order to enable the incorporation of polarization properties of components used in interferometers, different measurement setups are discussed. Novel measurement setups are introduced to measure the polarization properties of a heterodyne laser head used in the interferometer system. Based on ellipsometry a setup is realized to measure the polarization properties of the optical components of the laser interferometer. With use of measurements carried out with these setups and the model it can be concluded that periodic deviations originating from different error sources can not be superimposed, as interaction exists whichmay cause partial compensation. To examine the correctness of the predicted periodic deviations an entire interferometer system was placed on a traceable calibration setup based on a Fabry-P´erot interferometer. This system enables a calibration with an uncertainty of 0,94 nm over a range of 300 µm. Prior to this measurement the polarization properties of the separate components were measured to enable a good prediction of periodic deviations with the model. The measurements compared to the model revealed a standard deviation of 0,14 nm for small periodic deviations and a standard deviation of 0,3 nm for periodic deviations viii 0. ABSTRACT with amplitudes of several nanometers. As a result the Jones model combined with the setups for measurement of the polarization properties form a practical tool for designers of interferometer systems and optical components. This tool enables the designer to choose the right components and alignment tolerances for a practical setup with (sub-)nanometer uncertainty specifications. A second traceable calibration setup based on a Fabry-P´erot cavity was developed and built. Compared to the existing setup it has a higher sensitivity, smaller range and improved uncertainty of 0,24 nm over a range of 1 µm, and 0,40 nm over a range of 6 µm. To improve the uncertainty of existing laser interferometer systems a new compensation method for heterodyne laser interferometerswas proposed. It is based on phase quadraturemeasurement in combination with a compensation algorithm based on Heydemann’s compensation which is used frequently in homodyne interferometry. The system enables a compensation of periodic deviations with an amplitude of 8 nm down to an uncertainty of 0,2 nm. From measurements it appears that ghost reflections occurring in the optical system of the interferometer cannot be compensated by this method. Regarding the refractive index of air three measurement methods were compared. The three empirical equations which can be found in literature, an absolute refractometer based on a commercial interferometer and a newly developed tracker system based on a Fabry-P´erot cavity. The tracker was tested to investigate the feasibility of the method for absolute refractometry with improved uncertainty. The developed tracker had a relative uncertainty of 8 ·10-10. The comparison revealed some temperature effectswhich cannot be explained yet. However the results of the comparison indicate that an absolute refractometer based on a Fabry-P´erot cavity will improve the uncertainty of refractive index measurement compared to existing methods

Nanoscale tilt measurement using a cyclic interferometer with phase stepping and multiple reflections

High accuracy tilt or roll angle measurement is required for a variety of engineering and scientific applications. Optical interferometry is normally used because it is non-contact and can measure tilt with a very high degree of accuracy. In this thesis, a cyclic interferometer has been developed with four mirrors to measure tilt angles as small as a few nanoradians. To measure the phase, a novel and simple method of phase shift by polarization was developed to enhance measurement sensitivity and accuracy. Since the cyclic interferometer is insensitive to external vibrations and turbulences, polarization phase step was accomplished with relative ease. To introduce the phase shift, a quarter wave plate and a half wave plate were used with a polarized laser beam. Multiple reflections were also introduced in the cyclic interferometer to enhance tilt measurement capability. A new method was developed to evaluate phase and eventually measure the tilt even in the case of changing fringe visibility. The results of these studies show that the multiple reflection cyclic interferometer can be used to measure object tilts in the order of 0.2 nanoradians or 10-5 arc second

Investigation of noise sources in the LTP interferometer S2-AEI-TN-3028

All breadboards for the LTP interferometer showed an extra noise term that was, until recently, not fully understood. In this report that noise term is investigated in detail. It turns out that it is caused by sidebands on the light. In our lab, these sidebands were caused by nonlinear mixing processes in the power amplifiers that drive the AOM, if electromagnetic interference at a frequency near the operating frequency (ca. 80 MHz) is picked up by the power amplifier. The disturbing nearby frequency is the frequency of the other AOM, with a difference of exactly f_het, causing multiple sidebands at integer multiples of f_het from the carrier. They appear as pairs with a phase relationship that corresponds to phase-modulation (PM). Experiments with a very different electrical setup (in Glasgow) also showed sidebands which demonstrates that they are not caused by peculiarities of the Hannover setup. While the effect of a pair of first-order PM sidebands cancels and causes no harm, only one of the second-order sidebands produces noise which cannot be cancelled by its second-order mirror image. Hence the second-order sidebands are the dominant noise source. Various strategies of mitigation are also investigated. The two most important ones, both of which are already implemented as baseline for the LTP interferometer, are (1) to reduce the sidebands by careful EMC design and dedicated testing, and (2) to stabilize the optical pathlength difference (OPD) between the two fibers with a Piezo device. The combination of these two measures will reduce this error term to insignificance. We have also investigated other noise sources such as laser amplitude noise and beam jitter noise. Laser amplitude noise does have an influence on the total performance of the interferometer. Using a laser amplitude stabilization (part of the baseline), its influence can also be sufficiently reduced. Contrary to earlier worries, we did not find a significant noise contribution from beam jitter noise in conjunction with quadrant photodiodes. As part of this investigation we have also developed a mathematical model for the sideband coupling that fully describes their effect and has been experimentally verified. Furthermore we have developed various numerical procedures to find correlations between auxiliary data streams (such as alignment signals) and the main interferometer output. They are useful for diagnostic purposes, but in general too complex to implement on LTP. Using only those procedures that are the baseline for the FM, the noise performance of the LTP EM interferometer in the lab is now well below its specifications at all frequencies, with remaining noise sources mainly driven by ground-based disturbances, such that we are confident that the LTP interferometer will perform well on orbit and will enable the detailed study of the behaviour and noise performance of the inertial sensor and DFACS systems, which indeed is the primary job of the interferometer. Comment of the Author: Version 1.2 2008/07/0

Solid-state lasers for coherent communication and remote sensing

Semiconductor-diode laser-pumped solid-state lasers have properties that are superior to other lasers for the applications of coherent communication and remote sensing. These properties include efficiency, reliability, stability, and capability to be scaled to higher powers. We have demonstrated that an optical phase-locked loop can be used to lock the frequency of two diode-pumped 1.06 micron Nd:YAG lasers to levels required for coherent communication. Monolithic nonplanar ring oscillators constructed from solid pieces of the laser material provide better than 10 kHz frequency stability over 0.1 sec intervals. We have used active feedback stabilization of the cavity length of these lasers to demonstrate 0.3 Hz frequency stabilization relative to a reference cavity. We have performed experiments and analysis to show that optical parametric oscillators (OPO's) reproduce the frequency stability of the pump laser in outputs that can be tuned to arbitrary wavelengths. Another measurement performed in this program has demonstrated the sub-shot-noise character of correlations of the fluctuations in the twin output of OPO's. Measurements of nonlinear optical coefficients by phase-matched second harmonic generation are helping to resolve inconsistency in these important parameters