Name: transmission of multiple signals through an optical fiber using wavefront shaping
Uploaded: 2017-03-20T15:00:00
Description: Watch this Scientific Journal Video about Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping at JoVE.com

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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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 ...

The overall goal of this procedure is to transmit multiple individual spatially separated light signals through a single multi-mode fiber, while compensating for the light distortion by mode conversion inside the fiber. This novel technique can help to answer key questions in biomedicine and communication engineering via multiple biological cells or data signal channels have to be egressed individually. The main advantage of this technique which enables spacial temporal light modulation is that only a single spatial light modulator is needed to both calibrate and transmit multiple independent signals.The implications of this technique extends towards noninvasive studies and prospective therapies or neurological dysfunctions like Parkinson's disease. While monitoring and control of neurons is a combination to using spatial temporal light signals. Generally individuals new to this method will struggle because of the high effort for alignment of the optical pass, which is inevitable for high-quality transmission.The experiment takes place on an optical bench. The optical elements have already been arranged. Some elements are only used for calibration.This spatial light modulator is among the elements used for data signal transmission on the proximal side of the setup. This CCD camera is the data signal receiver on the distal side. The data signal travels through this multi-mode optical fiber connecting the two sides.This schematic provides an overview of the apparatus and identifies the proximal and distal elements. A laser provides a collimated coherent light beam which is split by a polarizing beam splitter. Use the half wave plates to keep the two beams at approximately equal power.The object beam goes to the distal side. For now focus on the reference beam which goes to the proximal side. Split the reference beam in two whith each resulting beam going through an optical modulator.Then have the two beams follow the same path with the spatial separation. During calibration the beams will be superposed by light from the distal side that is passed through the multi-mode fiber, a microscope objective, and linear polarizer, and eventually interfere. A final beam splitter directs the two beams perpendicularly on to the special light modulator.In preparing the experiment, be sure to orient the polarizing beam splitter so that polarization of the reference beam aligns with the polarization sensitive spatial light modulator. For calibration purposes the two beams also pass through lenses focused on a CMOS camera. Please note that nothing is displayed on the special light modulator for now.Therefore the modulator acts like a mirror during the calibration. Work with the two lenses on the bench. Adjust their position and the distance between them.The goal is to get a sharp image of the special light modulator plane in the CMOS camera. Now focus on the distal side of the setup for calibration. The object beam is transformed by beam splitters and mirrors into two spatially separated beams.Another beam splitter directs the beams into a microscope objective and from there to a lens focused on a CCD camera. At the bench focus the microscope objective on the distal end of the multi-mode fiber. Check the focus using the lens and CCD camera to observe the back reflection of the light from the multi-mode fiber.Work with the objective lens on the proximal side as well. Use it to collimate the light exiting the multi-mode fiber. Now view the interference pattern at the CMOS camera and work to change the interference fringe spacing.This is done by adjusting the mirrors and beam splitters in the reference and object beams. This changes the angle at which the object and reference beams intersect at the spatial light modulator, which should be at less than one degree. Stop when the interference fringe spacing is roughly the size of two pixels.Finally work with the linear polarizer, adjust its orientation to match the polarization of the object and reference beams. This will produce the maximum contrast in the CMOS camera image which will show distinct fringes. The first calibration sequence involves finding the pixel relation between the spatial light modulator and the CMOS camera.Begin with the object beam just after the polarizing beam splitter. Block the object beam between the half wave plate and the next beam splitter. Next, work with one of the two reference beams immediately after they have passed through the optical modulators.Block only one of them so the spatial light modulator is illuminated by the other. Capture an image of the spatial light modulator with the CMOS camera. Use graphic software to identify the coordinates of the upper left corner of the modulator, which will serve as the point of origin for the spatial light modulator.When done, remove both of the beam blocks to complete finding the pixel relation between the spatial light modulator and the CMOS camera. The next calibration sequence is for the signal paths. At this point these are the beam paths.The first step is to block object beam two just after two beam splitters in its path. And to block reference beam two after the light modulator. Then, use the CMOS camera to capture an image of the hologram.From this, calculate the inverted phase in region one of the beam. Continue by removing the blocks from the beams. Next, block object beam one and reference beam one.Calculate the inverted phase in region two of the beam from the hologram captured by the camera. Be sure to remove all beam blocks before proceeding. The setup for the transmission experiments is simpler.Signal transmission does not require the CMOS camera and the object beam is blocked. Now the two reference beams are reflected from two regions of the spatial light modulator. From there, the reflected beams pass through the multi-mode fiber to the CCD camera.At the computer, prepare the image for the spatial light modulator. For the image arrange the region one and two inverted phase images in their corresponding positions. Then, stitch these images together for display on the spatial light modulator using its computer graphics port.At the bench make the final preparations for the experiment. The reference beams pass through light intensity modulators. Activate these on both reference beams to proceed.At the computer observe and record the output signals from the CCD camera. These are typical results recorded by the camera on the distal side after the signal has traversed a two-meter long fiber. The images correspond to only signal one being on.Only signal two being on. And both signals being on. In addition to the desired peaks in each image, there is speckle due to limitations of digital optical phase conjugation.The peak to background ratio can be increased by using fibers that support a larger number of modes. There is cross talk between the two periodic output signals. The frequency spectrum of signal one shows the expected peak at frequency f1 and a smaller one at frequency f2.Similarly the frequency spectrum of signal two has the expected peak at f2 and a smaller one at f1. While attempting this procedure it's important to mesh the spatial light modulator and the CMOS camera carefully for the digital optical phase conjugation to work. In order to enhance this procedure model-based calibration techniques can be applied to perform the transmission without access to the distal end of the fiber.After watching this video you should have a good understanding of how to apply individual wave shaping for the transmission of independent signals through a multi-mode fiber. After its development, this novel technique will pave the way for researchers in optogenetics to explore neurodegenerative diseases in model organisms as well as in human induced pluripotent stem cell-derived neurons or cardiomyocytes.

Research

JoVE Journal

Bioengineering

Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

Attaching Biological Probes to Silica Optical Biosensors Using Silane Coupling Agents

In order to interface with biological environments, biosensor platforms, such as the popular Biacore system (based on the Surface Plasmon Resonance (SPR) ...

Induction of Adhesion-dependent Signals Using Low-intensity Ultrasound

In multicellular organisms, cell behavior is dictated by interactions with the extracellular matrix. Consequences of matrix-engagement range from ...

In vitro Synthesis of Native, Fibrous Long Spacing and Segmental Long Spacing Collagen

In vitro Synthesis of Native, Fibrous Long Spacing and Segmental Long Spacing Collagen

Collagen fibrils are present in the  extracellular matrix of animal tissue to provide structural scaffolding and  mechanical strength. These native ...

Quantitative Optical Microscopy: Measurement of Cellular Biophysical Features with a Standard Optical Microscope

We describe the use of a standard optical microscope to perform quantitative measurements of mass, volume, and density on cellular specimens through a ...

Label-free Single Molecule Detection Using Microtoroid Optical Resonators

Detecting small concentrations of molecules down to the single molecule limit has impact on areas such as early detection of disease, and fundamental ...

Multicolor Fluorescence Detection for Droplet Microfluidics Using Optical Fibers

Fluorescence assays are the most common readouts used in droplet microfluidics due to their bright signals and fast time response. Applications such as ...

Determination of Zeta Potential via Nanoparticle Translocation Velocities through a Tunable Nanopore: Using DNA-modified Particles as an Example

Nanopore technologies, known collectively as Resistive Pulse Sensors (RPS), are being used to detect, quantify and characterize proteins, molecules and ...

Using Extraordinary Optical Transmission to Quantify Cardiac Biomarkers in Human Serum

For a biosensing platform to have clinical relevance in point-of-care (POC) settings, assay sensitivity, reproducibility, and ability to reliably monitor ...

A Protocol for Multiple Gene Knockout in Mouse Small Intestinal Organoids Using a CRISPR-concatemer

CRISPR/Cas9 technology has greatly improved the feasibility and speed of loss-of-function studies that are essential in understanding gene function. In ...