Coherent fiber combining by digital holography

Bellanger, Cindy; Brignon, A.; Colineau, Joseph; Huignard, J.-P.

doi:10.1117/12.807428

Cited by 13 publications

(10 citation statements)

References 19 publications

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“…To address these limitations in the context of biophotonics applications, an optoelectronic digital OPC system (DOPC) was developed [23,24]. Such a system consists of two parts: a CCD or CMOS camera for wavefront recording and a spatial-light modulator (SLM) for wavefront playback.…”

Section: Introductionmentioning

confidence: 99%

Method for auto-alignment of digital optical phase conjugation systems based on digital propagation

et al. 2014

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Optical phase conjugation (OPC) has enabled many optical applications such as aberration correction and image transmission through fiber. In recent years, implementation of digital optical phase conjugation (DOPC) has opened up the possibility of its use in biomedical optics (e.g. deep-tissue optical focusing) due to its ability to provide greater-than-unity OPC reflectivity (the power ratio of the phase conjugated beam and input beam to the OPC system) and its flexibility to accommodate additional wavefront manipulations. However, the requirement for precise (pixel-topixel matching) alignment of the wavefront sensor and the spatial light modulator (SLM) limits the practical usability of DOPC systems. Here, we report a method for auto-alignment of a DOPC system by which the misalignment between the sensor and the SLM is auto-corrected through digital light propagation. With this method, we were able to accomplish OPC playback with a DOPC system with gross sensor-SLM misalignment by an axial displacement of up to~1.5cm , rotation and tip/tilt of ~5  , and in-plane displacement of ~5mm (dependent on the physical size of the sensor and the SLM). Our auto-alignment method robustly achieved a DOPC playback peak-to-background ratio (PBR) corresponding to more than ~30% of the theoretical maximum. As an additional advantage, the auto-alignment procedure can be easily performed at will and, as such, allows us to correct for small mechanical drifts within the DOPC systems, thus overcoming a previously major DOPC system vulnerability. We believe that this reported method for implementing robust DOPC systems will broaden the practical utility of DOPC systems.

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Section: Introductionmentioning

confidence: 99%

Method for auto-alignment of digital optical phase conjugation systems based on digital propagation

et al. 2014

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“…A previous demonstration was already done using digital holography [18]. However, the probe beams used to measure the phase errors between the fibers and the phase-locked signal beams were counter-propagating.…”

Section: Digital Holography For Coherent Beam Combiningmentioning

confidence: 99%

Interferometric phase measurement techniques for coherent beam combining

et al. 2015

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Coherent beam combining of fiber amplifiers provides an attractive mean of reaching high power laser. In an interferometric phase measurement the beams issued for each fiber combined are imaged onto a sensor and interfere with a reference plane wave. This registration of interference patterns on a camera allows the measurement of the exact phase error of each fiber beam in a single shot. Therefore, this method is a promising candidate toward very large number of combined fibers. Based on this technique, several architectures can be proposed to coherently combine a high number of fibers. The first one based on digital holography transfers directly the image of the camera to spatial light modulator (SLM). The generated hologram is used to compensate the phase errors induced by the amplifiers. This architecture has therefore a collective phase measurement and correction. Unlike previous digital holography technique, the probe beams measuring the phase errors between the fibers are co-propagating with the phase-locked signal beams. This architecture is compatible with the use of multi-stage isolated amplifying fibers. In that case, only 20 pixels per fiber on the SLM are needed to obtain a residual phase shift error below λ/10rms. The second proposed architecture calculates the correction applied to each fiber channel by tracking the relative position of the interference finges. In this case, a phase modulator is placed on each channel. In that configuration, only 8 pixels per fiber on the camera is required for a stable close loop operation with a residual phase error of λ/20rms, which demonstrates the scalability of this concept.

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“…[1][2][3] Moreover, optical phase conjugation with photorefractive crystals has been recently suggested as a technique to image through scattering layers of biological tissue. 4 Digital phase conjugation 5 implements the same physical principle as conventional optical phase conjugation by substituting the photorefractive crystal with the ensemble of two digital devices, a Spatial Light Modulator (SLM) and a CCD image sensor. In the field of free space scattering media, Digital Phase Conjugation has already been exploited as a technique to focus light behind such scattering media either in the fundamental 6 or in the double wavelength through Second Harmonic Generation.…”

Section: Introductionmentioning

confidence: 99%

Focused light delivery and all optical scanning from a multimode optical fiber using digital phase conjugation

2013

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We demonstrate a digital phase conjugation technique for generating a sharp focus point at the end of a multimode optical fiber. A sharp focus is experimentally obtained at the distal end of a 200µm core multimode fiber. By recording the digital holograms for different excitation conditions, the sharp focus can be digitally scanned over a 175µm diameter regular grid. The demonstrated technique is used for high resolution scanning lensless imaging based on multimode fibers, of stained biological samples that can enable diagnosis from the investigation of cellular phenotype.

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Coherent fiber combining by digital holography

Cited by 13 publications

References 19 publications

Method for auto-alignment of digital optical phase conjugation systems based on digital propagation

Method for auto-alignment of digital optical phase conjugation systems based on digital propagation

Interferometric phase measurement techniques for coherent beam combining

Focused light delivery and all optical scanning from a multimode optical fiber using digital phase conjugation

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