Quantum mechanics has played a big role in the development of our understanding of the smallest things in the universe. It has provided descriptions for phenomena like single electrons or single photons, which are single particles of light. One of the most mysterious properties of quantum systems is the ability to behave as a particle or a wave. In 1978, J. A. Wheeler devised an experiment to investigate if a quantum system knows in advance if it should propagate as a wave or as a particle through an experiment, by changing the experiment after the quantum system has entered the experimental set-up.  Here an optical all-in fiber platform for a Wheeler's delayed choice experiment is modeled, constructed and tested using commercially available fiber optic components. This is in contrast to previous delayed choice experiments, which have used free-space components in some parts of their experimental set-up. The optical set-up was modeled and simulated using a quantum formalism, with future work in mind if the platform is used to perform a quantum delayed-choice experiment. The platform used a Sagnac interferometer as the second beamsplitter in a Mach-Zehnder interferometer, to perform the choice of measuring either particle or wave properties. Using a fiber platform, the length of the platform can easily be extended with more fiber to accommodate a large separation between the beamsplitter in the beginning of the set-up, and the Sagnac interferometer at the end of the set-up. The result was a stable platform to measure particle behavior of light with good performance, and the ability to switch between these measurements on the fly. The system was tested with classical light, but the light source can be changed from a laser, to for example an attenuated laser, to enter the quantum domain for performing a quantum delayed-choice experiment using the platform. / Kvantmekaniken har inneburit stora genombrott i vår förståelse av de allra minsta tingen i universum. Kvantmekaniken har gett oss beskrivningar av fenomen som enstaka elektroners beteende eller enstaka ljuspartiklar, så kallade fotoner. En av de märkligaste egenskaperna som finns hos subatomära partiklar är förmågan att upptärda som en våg eller som en partikel, beroende på sammanhanget. År 1978 beskrev J. A. Wheeler ett experiment för att undersöka om en kvantmekanisk partikel, till exempel en foton, vet i förväg om den skall färdas som en partikel eller som en våg genom en experimentuppställning. Undersökningen av detta görs genom att ändra experimentuppställningen samtidigt som den kvantmekaniska partikeln färdas genom uppställningen.  En fiberoptisk plattform för Wheelers experiment med sent val modelleras, byggs med kommersiella fiberoptiska komponenter och testas i denna uppsats. Detta skiljer sig från tidigare experiment som har använt frirymds optik i någon del av experimentuppställningen. Den optiska kretsen modelleras med kvantmekanikens formalism, detta för att underlätta för framtida experiment som använder plattformen för att genomföra den kvantmekaniska varianten av Wheelers experiment med sent val.  Plattformen består av en Sagnac interferometer som ersätter den andra stråldelaren i en Mach-Zehnder interferometer, och därmed ger funktionen att kunna byta mellan mätning av partikelegenskaper och mätning av vågegenskaper. Den fiberoptiska plattformen är enkel att förlänga för att skapa ett långt avstånd mellan den första stråldelaren och Sagnac interferometern. Resultatet var en stabil plattform med god förmåga att mäta partikelegenskaper respektive vågegenskaper hos ljus och byta mellan dessa mätlägen under experimentets gång. Systemet testades med klassikt laserljus men denna ljuskälla kan enkelt bytas ut mot en dämpad laser för att komma ned på ljusnivåer med enstaka fotoner, och därmed kunna genomföra den kvantmekaniska varianten av Wheelers experiment med sent val.

This master’s thesis explores a space-division-multiplexing (SDM) platform fora delayed-choice experiment. SDM is a multiplexing technique for optical datatransmission that employs spatial modes in a multi- or few-mode fiber to increasethe transmission capacity. The spatial modes can thus be used as separate channels. SDM have shown great potential for quantum information systems, making it intriguing to investigate its broad applications by examining its use in adelayed-choice experiment. The delayed-choice experiment was proposed by J.A.Wheeler in 1978 explored the particle- and wave-like behavior of quantum particles and observe if the particle knows in advance if it should propagate as a waveor a particle through the experimental platform. Hence, it was suggested thatthe experiment should be changed after the particle entered the experimentalplatform. The experiment has afterward been realized in many different constellations but previous wave-particle delayed-choice experiments have not beendemonstrated with SDM nor with an all in fiber platform. The research involved modeling and constructing a SDM fiber-optic platform,only utilizing commercially available fiber optical telecommunication components. The platform was constructed with photonic lanterns, used as spatial division multiplexer and demultiplexer, and a two-input fiber Sagnac Interferometer,as a removable beam splitter. The system was tested with classical light but without difficulties, the platform could move to the quantum domain for performingthe delayed-choice experiment with single photons on the platform. The thesis resulted in a SDM platform with good performance for future measurement of bothparticle- and wave-like behavior of photons in a delayed-choice experiment.