The financial support by DFG (German research foundation, project CZ 55/30-1) for parts of this work is gratefully acknowledged.

1. Assembling the Experimental Setup
<ol>
	<li>Preparing the proximal side
	<ol>
		<li>Place and fix the laser providing a collimated light beam &#8211; or use a fiber-coupled laser with collimation optics at the exit facet of the fiber.</li>
		<li>Put the polarizing beam splitter (PBS) to split the laser beam into reference and object beam. Turn the orientation of the half wave plates (HWP) by rotating the HWP in its rotation mount until the power of reference beam and object beam (at the distal side)...

<ol>
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Photonics. 5 (6), 372-377 (2011).</li></ol>

The assembling of the experimental setup (step 1 in the protocol) requires a thorough alignment of the optical components with respect to each other. The most important aspect is the rectangular incidence of the reference beams onto the SLM in order to ensure a high PBR.
In order to enhance the setup to more than two transmitted signals, additional beam splitters could be used. As an alternative, a fiber-based implementation would be more compact and robust allowing the system to be portable f...

The transmission of multiple light signals through a multimode fiber (MMF) is evident in communications engineering1 and biophotonics2. In communications engineering, space-division multiplexing (SDM) is believed to be a viable solution in order to enhance the transmission capacity of optical fibers for future data transfer applications benefiting from a higher utilization of the limited space, compared to multiple single-mode fibers3. In biophotonics, biological samples are manipulated by light transmitting through an MMF endoscope4. For example, the independent optical control of individual neurons using MMF endoscopes is of interest for optogenetics in order to study neuronal networks in the brain5. However, the light projected onto the MMF input facet is subject to distortion due to mode mixing and dispersion during propagation to the output facet of the MMF. As a result, the light propagation is altered, which makes signal transmission challenging.
Wavefront shaping methods6,7 are applied in scattering media using spatial light modulators (SLM) and enable the compensation for the distortion due to scattering during light propagation8. There are iterative approaches that optimize the output using an optical feedback9. These approaches are rather time consuming because of the necessity for numerous iterations and the high degree of freedom, corresponding to a large number of modulator elements. Another approach is to completely determine the distortion within the MMF described by its transmission matrix10. If the number of modes to be transmitted is large, this will be time consuming as well. In contrast, digital optical phase conjugation (DOPC) is considered to be fast and advantageous here, since only few focal spots have to be generated at the output facet of the MMF. Phase conjugation approaches have also been demonstrated for focusing or imaging through biological tissue12,13,14.
So far, DOPC was employed for a single time signal only15,16, and was applied for the transmission of light through an MMF17. A DOPC approach for multiple independent signals has not been accomplished. We have developed an enhanced DOPC method providing the independent transmission of multiple light signals using individual wavefront shaping for each signal employing a single phase-only SLM18. To this aim, the SLM is segmented into regions, one for each signal to be transmitted. The proposed experimental setup is depicted in Figure 1, where a calibration is performed in a) before the actual transmission happens in b).
<img alt="Figure 1" src="/files/ftp_upload/55407/55407fig1.jpg" /> 
Figure 1: Experimental setup. BS = beam splitter, CCD = charge-coupled device, OM = optical modulator, CMOS = complementary metal-oxide semiconductor, HWP = half wave plate, L = lens, LP = linear polarizer, MMF = multimode fiber, OBJ = microscope objective, PBS = polarizing beam splitter, SLM = spatial light modulator (phase only) &#8212; only relevant beams for&#160;(a) the calibration and&#160;(b) the transmission are depicted <a href="http://cloudflare.jove.com/files/ftp_upload/55407/55407fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>spatial light modulator</td>
			<td>Holoeye</td>
			<td>PLUTO&#8208;VIS&#8208;016</td>
			<td></td>
		</tr>
		<tr>
			<td>CMOS camera</td>
			<td>Mikrotron</td>
			<td>MC4082</td>
			<td></td>
		</tr>
		<tr>
			<td>diode&#8208;pumped solid state laser</td>
			<td>Laser Quantum</td>
			<td>torus 532</td>
			<td></td>
		</tr>
		<tr>
			<td>CCD camera</td>
			<td>IDS</td>
			<td>U3&#8208;3482LE&#8208;M</td>
			<td>CMOS camera; suitable as well</td>
		</tr>
		<tr>
			<td>lens 1</td>
			<td>Qioptiq</td>
			<td>G063204000</td>
			<td></td>
		</tr>
		<tr>
			<td>lens 2</td>
			<td>Qioptiq</td>
			<td>G063203000</td>
			<td></td>
		</tr>
		<tr>
			<td>lens 3</td>
			<td>Thorlabs</td>
			<td>AC508&#8208;180&#8208;A&#8208;ML</td>
			<td></td>
		</tr>
		<tr>
			<td>multimode fiber</td>
			<td>Thorlabs</td>
			<td>M14L02</td>
			<td></td>
		</tr>
		<tr>
			<td>beam splitters</td>
			<td>Thorlabs</td>
			<td>BS013</td>
			<td>9x</td>
		</tr>
		<tr>
			<td>polarizing beam splitters</td>
			<td>Thorlabs</td>
			<td>PBS251</td>
			<td></td>
		</tr>
		<tr>
			<td>mirrors</td>
			<td>Thorlabs</td>
			<td>PF10&#8208;03&#8208;P01</td>
			<td>5x</td>
		</tr>
		<tr>
			<td>microscope objectives</td>
			<td>Thorlabs</td>
			<td>RMS20X</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>half wave plates</td>
			<td>Thorlabs</td>
			<td>WPH10M&#8208;532</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>linear polarizer</td>
			<td>Thorlabs</td>
			<td>LPVISB050&#8208;MP2</td>
			<td></td>
		</tr>
		<tr>
			<td>optical modulators</td>
			<td>Thorlabs</td>
			<td>MC2000B&#8208;EC</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>linear and rotation stage for CMOS camera</td>
			<td>Thorlabs</td>
			<td>XYR1/M</td>
			<td></td>
		</tr>
		<tr>
			<td>fiber connector</td>
			<td>Thorlabs</td>
			<td>S120&#8208;SMA</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>reducing ring for microscope objectives</td>
			<td>Qioptiq</td>
			<td>G061621000</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>xy adjustment for objective adapters</td>
			<td>Qioptiq</td>
			<td>G061025000</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>z translation mount for fiber adapter</td>
			<td>Thorlabs</td>
			<td>SM1Z</td>
			<td>2x</td>
		</tr>
		<tr>
			<td>rods for fiber alignment to objectives</td>
			<td>Qioptiq</td>
			<td>G061210000</td>
			<td>8x</td>
		</tr>
		<tr>
			<td>mounts for lenses 1 and 2 plus two phantom mounts</td>
			<td>Qioptiq</td>
			<td>G061047000</td>
			<td>4x</td>
		</tr>
		<tr>
			<td>rail carriers for objective and lens mounts</td>
			<td>Qioptiq</td>
			<td>G061372000</td>
			<td>6x</td>
		</tr>
		<tr>
			<td>rail for rail carriers</td>
			<td>Qioptiq</td>
			<td>G061359000</td>
			<td>2x</td>
		</tr>
		<tr>
			<td colspan="2">adapter for CCD camera to 1 post</td>
			<td></td>
			<td>in-house</td>
		</tr>
		<tr>
			<td>adapter for laser to 4 posts</td>
			<td></td>
			<td></td>
			<td>in-house</td>
		</tr>
		<tr>
			<td>mount for lens 3</td>
			<td>Thorlabs</td>
			<td>LMR2/M</td>
			<td></td>
		</tr>
		<tr>
			<td>mounts for half wave plates</td>
			<td>Thorlabs</td>
			<td>RSP1D/M</td>
			<td>2</td>
		</tr>
		<tr>
			<td>mounts for mirrors</td>
			<td>Thorlabs</td>
			<td>KM100</td>
			<td>5x</td>
		</tr>
		<tr>
			<td>mount for linear polarizer</td>
			<td>Thorlabs</td>
			<td>RSP05/M</td>
			<td></td>
		</tr>
		<tr>
			<td>mounts for beam splitters and SLM</td>
			<td>Thorlabs</td>
			<td>KM100PM/M</td>
			<td>11x</td>
		</tr>
		<tr>
			<td>clamping arms for beam splitters and SLM</td>
			<td>Thorlabs</td>
			<td>PM4/M</td>
			<td>11x</td>
		</tr>
		<tr>
			<td>posts for mounts, rail carriers and adapters</td>
			<td>Thorlabs</td>
			<td>TR75/M</td>
			<td>29x</td>
		</tr>
		<tr>
			<td>holders for posts</td>
			<td>Thorlabs</td>
			<td>PH50/M</td>
			<td>29x</td>
		</tr>
		<tr>
			<td>pedestals for holders</td>
			<td>Thorlabs</td>
			<td>BE1/M</td>
			<td>29x</td>
		</tr>
		<tr>
			<td>clamping forks for pedestals</td>
			<td>Thorlabs</td>
			<td>CF125</td>
			<td>29x</td>
		</tr>
	</tbody>
</table>

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 light distortion during the propagation within the fiber. Our methodology is based on digital optical phase conjugation employing only a single spatial light modulator, where the optical wavefront is individually modulated at different regions of the modulator, one region per light signal. Digital optical phase conjugation approaches are considered to be faster than other wavefront shaping approaches, where (for example) a complete determination of the wave propagation behavior of the fiber is performed. In contrast, the presented approach is time-efficient since it only requires one calibration per light signal. The proposed method is potentially appropriate for spatial division multiplexing in communications engineering. Further application fields are endoscopic light delivery in biophotonics, especially in optogenetics, where single cells in biological tissue have to be selectively illuminated with high spatial and temporal resolution.

Typical output signals at the distal side of the 2 m long fiber are depicted in Figure 2. Note that the desired focal spot (peak) is accompanied by an undesired speckle pattern (background), which is due to imperfection of the DOPC as a matter of principle. The corresponding peak-to-background ratio (PBR) amounts to 53 (solely signal 1 is &#39;on&#39;), 36 (solely signal 2 is &#39;on&#39;) and 20 (both signals 1 and 2 are &#39;on&#39;) here, respectively. The PBR can be i...

Watch this Scientific Journal Video about Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping at JoVE.com

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping

We demonstrate the transmission of multiple independent signals through a multimode fiber using wavefront shaping employing a single spatial light modulator. By modulating the wavefront for each signal individually, spatially separated foci are transmitted. Potential applications are multiplexed data transfer in communications engineering and endoscopic light delivery in biophotonics.

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

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9.7K Views.  TU Dresden. We demonstrate the transmission of multiple independent signals through a multimode fiber using wavefront shaping employing a single spatial light modulator. By modulating the wavefront for each signal individually, spatially separated foci are transmitted. Potential applications are multiplexed data transfer in communications engineering and endoscopic light delivery in biophotonics.