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For the first time the optical connectivity method was applied in a real size DI injector where the light was coupled in through one of the nozzle holes. After further optimizations the optical connectivity method might be a promising tool for investigating the length of the intact core. It is found that the fuel can be analyzed without the need of seeding with a dye as a tracer. High speed imaging was done with up to 25 kHz. The length of the intact core can be analyzed automatically from the high temporal resolution image series. First measurements show that the initial phase of the intact core length is strongly time dependent. Although the temporal behavior seems to be qualitatively similar to theoretical expectations during the initiation of the spray process with increasing Reynolds number (passing through various regimes), we have indication that here another mechanism is relevant, where the onset of cavitation influences the dense core length. With further enhancements we expect that the optical connectivity method can provide valuable information in addition to established measurement techniques like Mie scattering, being needed for the physical and numerical model development of the near nozzle spray processes. Therefore consecutive or even simultaneous measurement of the optical connectivity method and standard spray imaging methods will be considered. Furthermore, the effect of a centered coupling of the optical fiber to through an additional hole in the center of the nozzle tip will be studied. A more even illumination pattern is expected in this case. Combined with a stronger cw-light source, a better SNR(Signal to Noise Ratio) at all times of the injection should make this novel technique more stable, universal and useful. Finally, to intensify these studies, a comparison to the hydraulic injector fingerprints would connect standard measurement techniques with advanced optical techniques and thus might lead to new scientific insight.