transmission-multiple-signals-through-an-optical-fiber-using

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

The transmission of multiple independent optical signals through a multimode fiber is accomplished using wavefront shaping in order to compensate for the ...

TU Dresden

We introduce a method for depth-resolved photorefractive holographic imaging with potentially extremely short acquisition time for a complete three dimensional (3D) image. By combining the advantages of full-field frequency-domain optical coherence tomography with those of photorefractive holography our concept is capable of obtaining 3D information with only one single shot. We describe the operation principle of our concept and give a first experimental proof of principle.

Single-shot holography for depth resolved three dimensional imaging.

Utilizamos photorefractive dos-agita mezcla para amplificaci&oacute;n coherente de la viga del objeto en digital grabaci&oacute;n hologr&aacute;fica. Tanto la amplitud y la fase de reconstrucci&oacute;n se benefician de la amplificaci&oacute;n previa ya que tienen una mayor SNR. Experimentalmente, verificamos que el proceso de amplificaci&oacute;n no afecta a la fase de la wavefield. Esto permite el an&aacute;lisis de fase hologr&aacute;fica digital despu&eacute;s de la amplificaci&oacute;n. Como la formaci&oacute;n de la reja en photorefractive cristales s&oacute;lo es conducida por la luz coherente, el cristalino funciona como una puerta de coherencia. As&iacute; la combinaci&oacute;n propuesta permite aplicar holograf&iacute;a digital para la proyecci&oacute;n de imagen a trav&eacute;s de medios de difusi&oacute;n, despu&eacute;s de que la imagen de luz del cojinete es coherencia cerrada y filtrado de fondo dispersa. Mostramos resultados de principio de prueba experimental.

Photorefractive dos-agita la mezcla para la amplificaci&oacute;n de la imagen en holograf&iacute;a digital.

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We use photorefractive two-wave mixing for coherent amplification of the object beam in digital holographic recording. Both amplitude and phase reconstruction benefit from the prior amplification as they have an increased SNR. We experimentally verify that the amplification process does not affect the phase of the wavefield. This allows for digital holographic phase analysis after amplification. As the grating formation in photorefractive crystals is just driven by coherent light, the crystal works as a coherence gate. Thus the proposed combination allows for applying digital holography for imaging through scattering media, after the image bearing light is coherence gated and filtered out of scattered background. We show experimental proof-of principle results.

Photorefractive two-wave mixing for image amplification in digital holography.

Nous utilisons la k&eacute;ratectomie deux ondes de m&eacute;lange pour l&#39;amplification coh&eacute;rente de la poutre de l&#39;objet dans l&#39;enregistrement holographique num&eacute;rique. Amplitude et la phase de reconstruction b&eacute;n&eacute;ficient de l&#39;amplification pr&eacute;alable tel qu&#39;ils ont un SNR accrue. Nous avons v&eacute;rifier exp&eacute;rimentalement que le processus d&#39;amplification n&#39;affecte pas la phase de la wavefield. Ceci permet &agrave; l&#39;analyse des phases holographique num&eacute;rique apr&egrave;s amplification. Comme la formation de caillebotis dans des cristaux de k&eacute;ratectomie est juste dict&eacute;e par une lumi&egrave;re coh&eacute;rente, le cristal fonctionne comme une porte de coh&eacute;rence. La combinaison propos&eacute;e permet ainsi d&#39;application holographie num&eacute;rique pour l&#39;imagerie &agrave; travers les m&eacute;dias de diffusion, une fois l&#39;image portant la lumi&egrave;re coh&eacute;rence contr&ocirc;l&eacute; et filtr&eacute; hors contexte &eacute;pars. Nous montrons validation exp&eacute;rimentale de r&eacute;sultats de principe.

Photorefractive deux ondes m&eacute;lange amplification de l&#39;image en holographie num&eacute;rique.

Wir verwenden photorefraktive zwei-Wellen-Mischung f&uuml;r koh&auml;rente Verst&auml;rkung des Balkens Objekt in digitalen holographische Aufzeichnung. Amplitude und Phase Wiederaufbau profitieren die vorherige Verst&auml;rkung, da haben sie eine erh&ouml;hte SNR. Experimentell &uuml;berpr&uuml;fen wir, dass der Verst&auml;rkung-Prozess nicht die Phase der Wavefield auswirkt. Dies erm&ouml;glicht digitale holographische Phasenanalyse nach Verst&auml;rkung. Wie die Gitter-Formation photorefraktive Kristalle nur von koh&auml;rentes Licht angetrieben wird, arbeitet der Kristall als Koh&auml;renz Tor. So erm&ouml;glicht die vorgeschlagene Kombination f&uuml;r die Anwendung digitaler Holografie f&uuml;r Bildgebung durch Streuung Medien, nachdem das Bild mit Licht Koh&auml;renz Gating und aus verstreuten Hintergrund gefiltert ist. Wir zeigen experimentelle Nachweis der Grundsatz Ergebnisse.

Photorefraktive zwei-Wellen-Mischung f&uuml;r Bild Verst&auml;rkung in Digitale Holografie.

Usiamo photorefractive due-onda di miscelazione per l&#39;amplificazione coerente del fascio oggetto in digitale registrazione olografica. Ampiezza e la fase di ricostruzione beneficio dalla previa amplificazione come hanno un&#39;aumentata SNR. Verifichiamo sperimentalmente che il processo di amplificazione non pregiudica la fase della wavefield. Questo permette analisi di fase digitale olografico dopo amplificazione. Come la formazione del reticolo in cristalli fotorifrattivi &egrave; appena cacciata dalla luce coerente, il cristallo funziona come un cancello di coerenza. Cos&igrave; la combinazione proposta consente di applicare olografia digitale per l&#39;imaging attraverso mezzi di diffusione, dopo l&#39;immagine tenendo la luce &egrave; coerenza gated e filtrata da sfondo sparso. Mostriamo sperimentali prova-dei risultati di principio.

Photorefractive due-onda di miscelazione per l&#39;amplificazione di immagine in olografia digitale.

&#x30D5;&#x30A9;&#x30C8;&#x30EA;&#x30D5;&#x30E9;&#x30AF;&#x30C6;&#x30A3;&#x30D6; 2 &#x6CE2;&#x6DF7;&#x5408;&#x306E;&#x30C7;&#x30A3;&#x30B8;&#x30BF;&#x30EB;&#x30DB;&#x30ED;&#x30B0;&#x30E9;&#x30D5;&#x30A3;&#x8A18;&#x9332;&#x306B;&#x304A;&#x3051;&#x308B;&#x30AA;&#x30D6;&#x30B8;&#x30A7;&#x30AF;&#x30C8; &#x30D3;&#x30FC;&#x30E0;&#x306E;&#x30B3;&#x30D2;&#x30FC;&#x30EC;&#x30F3;&#x30C8;&#x5897;&#x5E45;&#x3092;&#x4F7F;&#x7528;&#x3057;&#x307E;&#x3059;&#x3002;&#x632F;&#x5E45;&#x3068;&#x4F4D;&#x76F8;&#x306E;&#x5FA9;&#x8208;&#x5F7C;&#x3089;&#x306F;&#x5897;&#x52A0;&#x306E; SNR &#x304C;&#x4E8B;&#x524D;&#x306E;&#x5897;&#x5E45;&#x304B;&#x3089;&#x3054;&#x5229;&#x7528;&#x304F;&#x3060;&#x3055;&#x3044;&#x3002;&#x5B9F;&#x9A13;&#x7684;&#x5897;&#x5E45;&#x904E;&#x7A0B;&#x306F;&#x3001;&#x5F3E;&#x6027;&#x6CE2;&#x52D5;&#x306E;&#x4F4D;&#x76F8;&#x306B;&#x306F;&#x5F71;&#x97FF;&#x3057;&#x307E;&#x305B;&#x3093;&#x3092;&#x78BA;&#x8A8D;&#x3057;&#x3066;&#x304F;&#x3060;&#x3055;&#x3044;&#x3002;&#x3053;&#x308C;&#x306F;&#x3001;&#x5897;&#x5E45;&#x5F8C;&#x30C7;&#x30B8;&#x30BF;&#x30EB; &#x30DB;&#x30ED;&#x30B0;&#x30E9;&#x30D5;&#x30A3;&#x30FC;&#x4F4D;&#x76F8;&#x89E3;&#x6790;&#x3067;&#x304D;&#x307E;&#x3059;&#x3002;&#x30D5;&#x30A9;&#x30C8;&#x30EA;&#x30D5;&#x30E9;&#x30AF;&#x30C6;&#x30A3;&#x30D6;&#x7D50;&#x6676;&#x4E2D;&#x306E;&#x683C;&#x5B50;&#x5F62;&#x6210;&#x306F;&#x3061;&#x3087;&#x3046;&#x3069;&#x30B3;&#x30D2;&#x30FC;&#x30EC;&#x30F3;&#x30C8;&#x5149;&#x306B;&#x3088;&#x308B;&#x99C6;&#x52D5;&#x3055;&#x308C;&#x3001;&#x7D50;&#x6676;&#x30B3;&#x30D2;&#x30FC;&#x30EC;&#x30F3;&#x30B9; &#x30B2;&#x30FC;&#x30C8;&#x3068;&#x3057;&#x3066;&#x52D5;&#x4F5C;&#x3057;&#x307E;&#x3059;&#x3002;&#x3057;&#x305F;&#x304C;&#x3063;&#x3066;&#x3001;&#x63D0;&#x6848;&#x306E;&#x7D44;&#x307F;&#x5408;&#x308F;&#x305B;&#x8EF8;&#x53D7;&#x5149;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x304C;&#x30B2;&#x30FC;&#x30C8;&#x3057;&#x3001;&#x6563;&#x4E71;&#x306E;&#x80CC;&#x666F;&#x304B;&#x3089;&#x30D5;&#x30A3;&#x30EB;&#x30BF;&#x30FC;&#x51E6;&#x7406;&#x30B3;&#x30D2;&#x30FC;&#x30EC;&#x30F3;&#x30B9;&#x306E;&#x5F8C;&#x6563;&#x4E71;&#x30E1;&#x30C7;&#x30A3;&#x30A2;&#x3092;&#x901A;&#x3058;&#x3066;&#x30A4;&#x30E1;&#x30FC;&#x30B8;&#x30F3;&#x30B0;&#x306E;&#x30C7;&#x30B8;&#x30BF;&#x30EB; &#x30DB;&#x30ED;&#x30B0;&#x30E9;&#x30D5;&#x30A3;&#x30FC;&#x3092;&#x9069;&#x7528;&#x3059;&#x308B;&#x305F;&#x3081;&#x4F7F;&#x7528;&#x3067;&#x304D;&#x307E;&#x3059;&#x3002;&#x79C1;&#x9054;&#x306E;&#x5B9F;&#x9A13;&#x7684;&#x8A3C;&#x62E0;&#x539F;&#x5247;&#x7D50;&#x679C;&#x3092;&#x793A;&#x3057;&#x307E;&#x3059;&#x3002;

&#x30D5;&#x30A9;&#x30C8;&#x30EA;&#x30D5;&#x30E9;&#x30AF;&#x30C6;&#x30A3;&#x30D6; 2 &#x6CE2;&#x6DF7;&#x5408;&#x306E;&#x753B;&#x50CF;&#x5897;&#x5E45;&#x30C7;&#x30B8;&#x30BF;&#x30EB; &#x30DB;&#x30ED;&#x30B0;&#x30E9;&#x30D5;&#x30A3;&#x30FC;&#x3067;&#x3002;

Photorefractive 2 &#xD30C; &#xB514;&#xC9C0;&#xD138; &#xD640;&#xB85C;&#xADF8;&#xB7A8; &#xB179;&#xD654;&#xC5D0;&#xC11C; &#xAC1C;&#xCCB4; &#xAD11;&#xC18D;&#xC758; &#xC77C;&#xAD00; &#xB41C; &#xC99D;&#xD3ED;&#xC5D0; &#xB300; &#xD55C; &#xD63C;&#xD569; &#xC0AC;&#xC6A9; &#xD569;&#xB2C8;&#xB2E4;. &#xC9C4;&#xD3ED;&#xACFC; &#xC704;&#xC0C1; &#xC7AC;&#xAD6C;&#xC131; &#xB4E4;&#xC740; &#xC99D;&#xAC00; SNR &#xC774;&#xC804; &#xC99D;&#xD3ED;&#xC5D0;&#xC11C; &#xD61C;&#xD0DD;. &#xC6B0;&#xB9AC;&#xB294; &#xC2E4;&#xD5D8;&#xC801;&#xC73C;&#xB85C; &#xC99D;&#xD3ED; &#xACFC;&#xC815;&#xC740; wavefield&#xC758; &#xB2E8;&#xACC4;&#xC5D0; &#xC601;&#xD5A5;&#xC744; &#xC8FC;&#xC9C0; &#xC54A;&#xC2B5;&#xB2C8;&#xB2E4; &#xD655;&#xC778; &#xD569;&#xB2C8;&#xB2E4;. &#xB530;&#xB77C;&#xC11C; &#xB514;&#xC9C0;&#xD138; &#xD640;&#xB85C;&#xADF8;&#xB7A8; &#xC704;&#xC0C1; &#xBD84;&#xC11D; &#xD655;&#xB300; &#xD6C4; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. Photorefractive &#xACB0;&#xC815;&#xC5D0;&#xC11C; &#xACA9;&#xC790; &#xD615;&#xC131;&#xC740; &#xB2E8;&#xC9C0; &#xC77C;&#xAD00; &#xB41C; &#xBE5B;&#xC5D0; &#xC758;&#xD574; &#xAD6C;&#xB3D9; &#xB429;&#xB2C8;&#xB2E4;, &#xD06C;&#xB9AC;&#xC2A4;&#xD0C8; &#xC77C;&#xAD00;&#xC131; &#xAC8C;&#xC774;&#xD2B8;&#xB85C; &#xC791;&#xB3D9; &#xD569;&#xB2C8;&#xB2E4;. &#xB530;&#xB77C;&#xC11C; &#xC81C;&#xC548; &#xB41C; &#xC870;&#xD569; &#xBCA0;&#xC5B4;&#xB9C1; &#xBE5B; &#xC774;&#xBBF8;&#xC9C0;&#xB294; &#xC77C;&#xAD00;&#xC131; &#xBB38;&#xC774; &#xACE0; &#xD769;&#xC5B4;&#xC838; &#xBC30;&#xACBD;&#xC5D0;&#xC11C; &#xD544;&#xD130;&#xB9C1; &#xD55C; &#xD6C4; &#xC0B0;&#xB780; &#xC5B8;&#xB860;&#xC744; &#xD1B5;&#xD574; &#xC774;&#xBBF8;&#xC9D5; &#xB514;&#xC9C0;&#xD138; &#xD640;&#xB85C; &#xADF8;&#xB798;&#xD53C;&#xB97C; &#xC801;&#xC6A9;&#xD560; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC; &#xC2E4;&#xD5D8;&#xC801;&#xC778; &#xC99D;&#xAC70;&#xC758; &#xC6D0;&#xB9AC; &#xACB0;&#xACFC; &#xBCF4;&#xC5EC;&#xC90D;&#xB2C8;&#xB2E4;.

Photorefractive 2 &#xD30C; &#xB514;&#xC9C0;&#xD138; &#xD640;&#xB85C; &#xADF8;&#xB798;&#xD53C;&#xC5D0;&#xC11C; &#xC774;&#xBBF8;&#xC9C0; &#xD655;&#xB300;&#xB97C; &#xC704;&#xD55C; &#xD63C;&#xD569;.

We introduce depth-filtered digital holography (DFDH) as a method for quantitative tomographic phase imaging of buried layers in multilayer samples. The procedure is based on the acquisition of multiple holograms for different wavelengths. Analyzing the intensity over wavelength pixel wise and using an inverse Fourier transform leads to a depth-profile of the multilayered sample. Applying a windowed Fourier transform with a narrow window, we choose a depth-of interest (DOI) which is used to synthesize filtered interference patterns that just contain information of this limited depth. We use the angular spectrum method to introduce an additional spatial filtering and to reconstruct the corresponding holograms. After a short theoretical framework we show experimental proof-of-principle results for the method.

Depth-filtered digital holography.

In this paper we analyze the capability of adaptive lenses to replace mechanical axial scanning in confocal microscopy. The adaptive approach promises to achieve high scan rates in a rather simple implementation. This may open up new applications in biomedical imaging or surface analysis in micro- and nanoelectronics, where currently the axial scan rates and the flexibility at the scan process are the limiting factors. The results show that fast and adaptive axial scanning is possible using electrically tunable lenses but the performance degrades during the scan. This is due to defocus and spherical aberrations introduced to the system by tuning of the adaptive lens. These detune the observation plane away from the best focus which strongly deteriorates the axial resolution by a factor of ~2.4. Introducing balancing aberrations allows addressing these influences. The presented approach is based on the employment of a second adaptive lens, located in the detection path. It enables shifting the observation plane back to the best focus position and thus creating axial scans with homogeneous axial resolution. We present simulated and experimental proof-of-principle results.

Axial scanning in confocal microscopy employing adaptive lenses (CAL).

In this Letter, we present a new approach to processing data from a standard spectral domain optical coherence tomography (OCT) system using depth filtered digital holography (DFDH). Intensity-based OCT processing has an axial resolution of the order of a few micrometers. When the phase information is used to obtain optical path length differences, subwavelength accuracy can be achieved, but this limits the resolvable step heights to half of the wavelength of the system. Thus there is a metrology gap between phase- and intensity-based methods. Our concept addresses this metrology gap by combining DFHD with multiwavelength phase unwrapping. Additionally, the measurements are corrected for aberrations. Here, we present proof of concept measurements of a structured semiconductor sample.

Multiwavelength phase unwrapping and aberration correction using depth filtered digital holography.

The minimum achievable systematic uncertainty of interferometric measurements is fundamentally limited due to speckle noise. Numerical and physical experiments, regarding the achievable measurement uncertainty of Mach-Zehnder based velocity and position sensors, are presented at the example of the laser Doppler distance sensor with phase evaluation. The results show that the measurement uncertainty depends on the number of speckles on the photo detectors. However, while the systematic uncertainty due to the speckle effect decreases, the random uncertainty due to noise from the photo detector increases with increasing speckle number. This results in a minimal total measurement uncertainty for an optimal speckle number on the photo detector, which is achieved by adjusting the aperture of the detection optics.

On the speckle number of interferometric velocity and distance measurements of moving rough surfaces.

Due to their high stiffness-to-weight ratio, glass fiber-reinforced polymers are an attractive material for rotors, e.g., in the aerospace industry. A fundamental understanding of the material behavior requires non-contact, in-situ dynamic deformation measurements. The high surface speeds and particularly the translucence of the material limit the usability of conventional optical measurement techniques. We demonstrate that the laser Doppler distance sensor provides a powerful and reliable tool for monitoring radial expansion at fast rotating translucent materials. We find that backscattering in material volume does not lead to secondary signals as surface scattering results in degradation of the measurement volume inside the translucent medium. This ensures that the acquired signal contains information of the rotor surface only, as long as the sample surface is rough enough. Dynamic deformation measurements of fast-rotating fiber-reinforced polymer composite rotors with surface speeds of more than 300 m/s underline the potential of the laser Doppler sensor.

Optical dynamic deformation measurements at translucent materials.

Electrically tunable lenses exhibit strong potential for fast motion-free axial scanning in a variety of microscopes. However, they also lead to a degradation of the achievable resolution because of aberrations and misalignment between illumination and detection optics that are induced by the scan itself. Additionally, the typically nonlinear relation between actuation voltage and axial displacement leads to over- or under-sampled frame acquisition in most microscopic techniques because of their static depth-of-field. To overcome these limitations, we present an Adaptive-Lens-High-and-Low-frequency (AL-HiLo) microscope that enables volumetric measurements employing an electrically tunable lens. By using speckle-patterned illumination, we ensure stability against aberrations of the electrically tunable lens. Its depth-of-field can be adjusted a-posteriori and hence enables to create flexible scans, which compensates for irregular axial measurement positions. The adaptive HiLo microscope provides an axial scanning range of 1 mm with an axial resolution of about 4 μm and sub-micron lateral resolution over the full scanning range. Proof of concept measurements at home-built specimens as well as zebrafish embryos with reporter gene-driven fluorescence in the thyroid gland are shown.

Volumetric HiLo microscopy employing an electrically tunable lens.

Multimode fibers are attractive for a variety of applications such as communication engineering and biophotonics. However, a major hurdle for the optical transmission through multimode fibers is the inherent mode mixing. Although an image transmission was successfully accomplished using wavefront shaping, the image information was not transmitted individually for each of the independent pixels. We demonstrate a transmission of independent signals using individually shaped wavefronts employing a single segmented spatial light modulator for optical phase conjugation regarding each light signal. Our findings pave the way towards transferring independent signals through strongly scattering media.

Transmission of independent signals through a multimode fiber using digital optical phase conjugation.

Imaging-based flow measurement techniques, like particle image velocimetry (PIV), are vulnerable to time-varying distortions like refractive index inhomogeneities or fluctuating phase boundaries. Such distortions strongly increase the velocity error, as the position assignment of the tracer particles and the decrease of image contrast exhibit significant uncertainties. We demonstrate that wavefront shaping based on spatially distributed guide stars has the potential to significantly reduce the measurement uncertainty. Proof of concept experiments show an improvement by more than one order of magnitude. Possible applications for the wavefront shaping PIV range from measurements in jets and film flows to biomedical applications.

Wavefront shaping for imaging-based flow velocity measurements through distortions using a Fresnel guide star.

A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.

Nektarios Koukourakis

Faculty of Electrical and Computer Engineering

TU Dresden

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

Nektarios Koukourakis

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Faculty of Electrical and Computer Engineering

TU Dresden

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

Faculty of Electrical and Computer Engineering