We gratefully acknowledge the financial support of Deutsche Telekom Innovation Laboratories.

1. Preparing the System (Figure 4)
<ol>
	<li>Insert the laser diodes LD1 and LD2 in the specific mount and connect it with the current (LDC) and temperature controllers (TEC). Turn the devices on and check the functionality of the laser diodes with the optical spectrum analyzer. Usually, a telecom wavelength around 1,550 nm is used.</li>
	<li>Connect the laser diode to the modulators (IM/PM and MZM1) according to the setup in Figure 4. The optical connectors need to be cleaned before use, to ensure the clean surface for coupling. Connect the power supply (not shown) and the signal from the waveform generator (AWG) with an additional electrical amplifier to the modulator. Ensure that the maximum optical and electrical input power at the modulator is not exceeded. Every Modulator is equipped with a polarization controller.</li>
</ol>
<img alt="Figure 4" fo:content-width="5in" fo:src="/files/ftp_upload/50468/50468fig4highres.jpg" src="/files/ftp_upload/50468/50468fig4.jpg" /> 
Figure 4. Experimental setup of the QLS whereby the storage of intensity and phase modulated signals is possible. The blue labeled section is only necessary for the detection of phase modulated signals. The QLS process takes place in the optical fiber. The yellow labeled section defines the heterodyne detection of the frequency comb. TEC: temperature controller, LDC: laser diode current source, LD: laser diode, IM: intensity modulator, PM: phase modulator, PC: polarization controller, AWG: arbitrary waveform generator, MZM: Mach-Zehnder modulator, EDFA: erbium doped fiber amplifier, C: circulator, Lo: local oscillator, Osci: oscilloscope, OSA: optical spectrum analyzer, PD: photodiode, ESA: electrical spectrum analyzer. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/50468/50468fig4highres.jpg" target="_blank">Click here to view larger image.</a>
<ol start="3">
	<li>Connect the fiber with the modulator for the data signal. For phase modulated signals it has to be a phase modulator (PM) and for intensity modulated signals an intensity modulator (IM). Usually, the data rate for the experiment is in the Gbps range. The other side of the fiber is connected with port 2 of the circulator (C). The used AllWave&#160;fiber in our experiments has the following specifications: L = 20 km, &#916;fSBS = 10.2 MHz, fSBS = 10.852 GHz, Pth &#8776; 9.1 dBm.</li>
	<li>Connect the amplitude modulator for the frequency comb generation (MZM1) with the optical amplifier (EDFA). The comb has to cover the bandwidth of the data signal. The output of the EDFA is connected with port 1 of the circulator.</li>
	<li>For the detection of phase modulated signals, a reference source is needed. Connect the local oscillator (LO) together with the output 3 of the circulator to a 50/50 coupler. For intensity modulated signals, this part is not required. As LO a fiber laser (Koheras) is used.</li>
	<li>For phase modulated signals: connect the third modulator (MZM2) for extracting the delayed copies with the output of the 50/50 coupler. For intensity modulated signals, connect MZM2 directly to port 3 of the circulator. Supply the modulator with a bias voltage (not shown) and a rectangular signal from the CH1 Mkr1 output port of the waveform generator for extracting. Therefore, the original data signals, as well as the rectangular signal for extracting are synchronized.</li>
	<li>For detection and analysis: connect a 90/10 coupler after MZM2. The oscilloscope is connected with the 90% port of the coupler and the 10% part is connected with the optical spectrum analyzer.</li>
	<li>Program the waveform generator with the required signals for the data packet, the frequency comb and the rectangular signal. The frequency comb is generated by a periodic sinc-function.</li>
</ol>
2. Measurement
<ol>
	<li>Turn on the output for the data signal at the waveform generator (AWG). Change the bias for the modulator (IM/PM) at the power supply and control the signal quality at the oscilloscope. After adjusting the best quality turn the output of the waveform generator off. The modulators should be set around the linear operating point. Exemplary values can be found in the results section.</li>
	<li>Adjust the quality of the frequency comb with heterodyne detection. An example for a relatively good quality frequency comb is shown in Figure 5. The frequency comb needs to be flat, e.g. all frequency components have the same intensity and are stable over time, as well as broad enough to cover the whole spectrum. Additionally, the edges of the comb should be steep, e.g. there are no apparent frequency components with a low intensity on the sides.</li>
	<li>Heterodyne comb detection I: Connect the output of MZM1 with a 50/50 coupler. The other port of the coupler is connected with a fiber laser (Koheras) as local oscillator.</li>
	<li>Heterodyne comb detection II: Due to the limited bandwidth of the photo-diode and the electrical spectrum analyzer, first the coupler output has to be connected to the optical spectrum analyzer in order to set the distance between the local oscillator and the signal to around 8 GHz by changing the temperature of the laser.</li>
	<li>Heterodyne comb detection III: After the adjustment remove the optical spectrum analyzer and connect the photodiode and the electrical spectrum analyzer to the output of the 50/50 coupler. Adjust the bias voltage of the comb modulator to achieve a flat frequency comb. After completion connect the output of the modulator again to the optical amplifier (EDFA).</li>
	<li>Adjust the distance between both laser diodes (IM/PM and MZM1) regarding the Brillouin shift with continuous wave signals. Thus, be sure that the output of the waveform generator is turned off.</li>
	<li>Turn on the optical amplifier. Have a look at the optical spectrum analyzer and set the output power of the EDFA to a value below the threshold of stimulated Brillouin scattering.</li>
	<li>Now shift the wavelength of the laser diode which generates the data signal (IM/PM) into the gain region of the pump (MZM1). The signal will be amplified if the wavelength is correct.</li>
	<li>For optimization change the polarization of the data signal and therefore the intensity to the maximum.</li>
	<li>Turn on both outputs (data signal and comb) of the waveform generator. Increase the output power of the EDFA. Now the frequency comb will extract equidistant components out of the spectrum. The oscilloscope should show the different copies generated by the QLS. For distortion reduction slightly shift the wavelength of the data signal and change the polarization.</li>
	<li>To extract one of the copies use one of the marker signals of the waveform generator or an external source that can produce a rectangular pulse. Set up a rectangular pulse with the length of the packet.</li>
	<li>Turn on the bias for MZM2 and change it to the operating point where the extracted signal is maximized and all other copies are suppressed. Now shift the rectangular pulse to the desired version of the stored pattern.</li>
	<li>The stored data pattern can be saved with the oscilloscope and evaluated with software, e.g. Origin.</li>
	<li>In order to switch between the measurement of intensity and phase modulated signals, the modulator for the data signal needs to be changed from IM for intensity modulated signals to PM for phase modulated signals. Additionally, for the phase modulated signals a local oscillator as a reference source needs to be added to the setup according to Figure 4.</li>
</ol>
<img alt="Figure 5" fo:content-width="5in" fo:src="/files/ftp_upload/50468/50468fig5highres.jpg" src="/files/ftp_upload/50468/50468fig5.jpg" /> 
Figure 5. Almost flat frequency comb with 13 branches. The comb was detected via heterodyne detection. For the detection a local oscillator was combined via a 3 dB coupler with the optical signal and detected with a photodiode. The frequency comb was measured and recorded with an electrical spectrum analyzer. The output power of the local oscillator was 6 dBm and the optical power of the comb 8 dBm. The distance between the local oscillator and the optical comb was 9.8 GHz. For a better overview the frequency axis is normalized to the center frequency of the comb which was around 193.5 THz (1,550 nm). <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/50468/50468fig5highres.jpg" target="_blank">Click here to view larger image.</a>

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The authors declare that they have no competing financial interests. The author, Thomas Schneider, is an employee of Deutsche Telekom AG. The author, Stefan Preu&#223;ler, received funding that was provided by Deutsche Telekom Innovation Laboratories.

The most critical step during the experiment is the adjustment of the frequency comb, i.e. the bandwidth, flatness and position in respect to the data signal in the frequency domain. According to the sampling theorem in frequency domain, signal distortions are avoided if the whole bandwidth of the optical packet is sampled with an ideally flat comb. Thus, the bandwidth of the optical packet defines the minimum bandwidth of the frequency comb and in this bandwidth the comb has to be as flat as possible. A nonidea...

The data transport in the telecommunications networks is optically, since only optical fibers offer the capacity required for today's data traffic transmitted around the world. However, in every node of the network the optical signal has to be transferred into the electrical domain in order to process it. After processing the signal is converted back to the optical domain for further transmission. This double-transfer between the domains is both time and power consuming. In order to use an all-optical processing of the data, the problem of the intermediate storage has to be solved. Thus, lots of methods for the storage or buffering of the optical signals have been suggested. The simplest way is to send the signals into a matrix of waveguides with different lengths2. However, these matrices are bulky and the storage time cannot be tuned since it is predefined by the waveguide length.
The "Slow-Light" method relies on a tunable change of the group refractive index of a medium to slow down the propagation speed of optical signal pulses2. Several physical effects and material systems can be used for this purpose3-6. However, with these methods the signal can be slowed down by just a few bit-lengths, which is by far not sufficient for optical network nodes7,8.
Another approach uses wavelength conversion and dispersion for the generation of tunable delays. Thereby, the center wavelength of the input signal is shifted via nonlinear optical conversion. Afterwards, the signal is fed into a highly dispersive fiber. The difference in the group velocity in the dispersive fiber leads to a delay that is proportional to the product of the wavelength shift and the group-velocity dispersion (GVD) in the fiber. With a second conversion the wavelength is shifted back to the original value. For the wavelength shift techniques like four-wave mixing or self phase modulation can be used. With the conversion and dispersion method storage times up to 243 nsec of tunable delay, which correspond to 2,400 bit, were reported10. However, wavelength conversion and dispersion methods in general need special components and setups for producing a large wavelength shift and/or large GVD. Additionally, they are among the most complex and power-hungry delay methods2.
Other methods store the optical signal into an excitation of a material system. A probe beam is then used to read out the information. Usually these systems cannot be used in the area of telecommunications since they require ultrahigh or -low temperatures11, will not work with telecommunications bandwidths, or require rather complicated setups and high power12-14.
Here we show how a basic property of signals (the time-frequency coherence) can be exploited for the storage of optical data packets. Since no excitation of a material system is used, we have called the method Quasi-light Storage (QLS)15-17. The QLS is independent of the modulation, data format and data rate of the packets and can store optical packets for several thousand bit lengths18.
The basic idea can be seen in Figure 1, here rectangular shaped pulses are shown. However, the method works for every pulse shape and for packets of pulses. The only restriction is that the signals have to be time-limited.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/50468/50468fig1highres.jpg" src="/files/ftp_upload/50468/50468fig1.jpg" /> 
Figure 1. Time-frequency coherence for an intensity modulated signal23. A single rectangular signal in the time domain (a) is represented by a sinc-function in the frequency-domain (b). Here the normalized intensity is shown, since it is not possible to measure the fields with optical equipment. The time domain representation for a sequence of rectangular signals is shown in (c). This sequence has still the same spectral shape. But, it consists of equidistant single frequencies under the sinc-envelope (d). The time axis are normalized to half the duration of a single signal and the frequency axis to the first zero crossings, respectively. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/50468/50468fig1highres.jpg" target="_blank">Click here to view larger image.</a>
A rectangular pulse in the time domain (Figure 1a) has a "sinus cardinalis" or sinc function sin(px) / px shaped spectrum (Figure 1b), where all frequencies under the envelope are present. A train of rectangular pulses in the time domain (Figure 1c) has still a sinc function shaped spectrum (Figure 1d) with the bandwidth &#916;f. But due to the periodicity, not all frequencies are present anymore. Instead, the spectrum consists of equidistant frequencies and the inverse of the frequency spacing defines the time separation between the pulses &#916;T = 1/&#916;v.
The basic idea of the QLS is now simply to extract equidistant frequencies out of the spectrum of the input packet. Due to time-frequency coherence this results in a copying of the packet in the time domain. The copy with the desired delay can be extracted by a time domain switch.
The principle of our experiment is shown in Figure 2. A time-limited input signal is multiplied with a frequency comb in the frequency-domain. For the multiplication the nonlinear effect of stimulated Brillouin scattering (SBS) is used. The results are equidistant copies of the input signal in the time-domain. One of the signals is extracted with a switch driven by a rectangular function. Thus, at the output of the memory in principle a distortion-free copy of the input pulse can be expected.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/50468/50468fig2highres.jpg" src="/files/ftp_upload/50468/50468fig2.jpg" /> 
Figure 2. Basic idea of the Quasi-light Storage15. A time limited input signal (a) is multiplied with a frequency comb (b) in the frequency-domain, which is denoted with a X. This leads to various copies of the signal in the time domain (c). From the generated pulse train one of the copies (d) is extracted with a time-domain switch by a rectangular read signal (e). The switch can be a modulator. The result is a storage of the optical signal. The storage time is defined by the frequency spacing between the comb lines and the read signal. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/50468/50468fig2highres.jpg" target="_blank">Click here to view larger image.</a>
SBS itself is a nonlinear effect that can occur in standard single mode fibers (SSMF) at low powers. Thereby, the signal interacts with an optical density change which is generated by a counter propagating pump wave. If the signal wave is downshifted in frequency, a gain region is formed in which the signal will be amplified. If it is up-shifted the signal will be attenuated in the corresponding loss region. The frequency shift between pump and signal is defined by the acoustic wave, which depends on the material properties. The biggest advantage of SBS for the presented application is the narrow bandwidth &#916;fSBS of the gain region. Thus, practically SBS forms a narrow linewidth optical filter. The narrow bandwidth of the gain region depends on the effective length and area of the fiber as well as on the used pump power19. The natural full-width at half-maximum (FWHM) bandwidth of the SBS gain in a SSMF is around 30 MHz. In special waveguides, such as AllWave fibers, and with high pump powers, the bandwidth can be reduced down to 10 MHz20. Due to the filter bandwidth the different copies are covered with an envelope. Therefore, the maximum storage time of the QLS inversely depends on the SBS bandwidth. A bandwidth of 10 MHz would result in a maximum storage time of 100 nsec. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/50468/50468fig3highres.jpg" target="_blank">Click here to view larger image.</a>
For very high bit-rate transmission the information has to be encoded into the phase of the carrier instead of its amplitude, since this offers a lot of advantages. Thus, contrary to pulses, the signals in these optical networks have constant amplitude. Figure 3 shows such a phase modulated signal in the time (left) and frequency domain (right). This spectrum can be sampled in the same way as that of the amplitude modulated signal21. In fact the spectrum of the rectangular function for intensity- and phase-modulated signals is filtered due to the transmission, which limits the spectrum.
<img alt="Figure 3" fo:content-width="5in" fo:src="/files/ftp_upload/50468/50468fig3highres.jpg" src="/files/ftp_upload/50468/50468fig3.jpg" /> 
Figure 3. Time-frequency coherence for a phase modulation21. In a phase modulated signal the phase of the carrier is changed by the signal which has to be transmitted. If each symbol consists of 1 bit, the phase is changed between 0 and &#960;, for instance. The left side of the figure shows the resulting time-domain representation for such a binary phase shift keyed (BPSK) signal. The resulting frequency-domain signal is shown on the right side. By comparison with Figure 1 it can be seen that the spectrum of the phase modulated signal is qualitatively the same as that of the intensity modulated signal. Thus, the QLS can be applied in the same way.

<table border="0" cellpadding="0" cellspacing="0" width="603">
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Laser diode</td>
			<td style="width:147px;">3S Photonics</td>
			<td style="width:185px;">A1905LMI</td>
			<td style="width:160px;">2x</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Laser Mount</td>
			<td style="width:147px;">Tektronix</td>
			<td style="width:185px;">LDH BFY-B2</td>
			<td style="width:160px;">2x</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Temperature Controller</td>
			<td style="width:147px;">LightWave</td>
			<td style="width:185px;">LDT-5948</td>
			<td style="width:160px;">2x</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Current Controller</td>
			<td style="width:147px;">LightWave</td>
			<td style="width:185px;">LDX-3220</td>
			<td style="width:160px;">2x</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Optical amplifier</td>
			<td style="width:147px;">High-Wave</td>
			<td style="width:185px;">HWT-EDFA-B-30-1-FC/PC</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Circulator</td>
			<td style="width:147px;">OFR</td>
			<td style="width:185px;">OCT-3-IR2</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Waveform Generator</td>
			<td style="width:147px;">Tektronix</td>
			<td style="width:185px;">AWG7102</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Fiber 20km</td>
			<td style="width:147px;">OFS</td>
			<td style="width:185px;">AllWave-ZWP G652C-D</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Polarization Controller</td>
			<td style="width:147px;">Thorlabs</td>
			<td style="width:185px;">Fiber Pol. Contr. IPC030</td>
			<td style="width:160px;">2x</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Modulator</td>
			<td style="width:147px;">Avanex</td>
			<td style="width:185px;">IM-10-P</td>
			<td style="width:160px;">Phase</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Modulator</td>
			<td style="width:147px;">Avanex</td>
			<td style="width:185px;">SD20</td>
			<td style="width:160px;">Amplitude, extract</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Modulator</td>
			<td style="width:147px;">Avanex</td>
			<td style="width:185px;">PowerBit F-10</td>
			<td style="width:160px;">Amplitude, data</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Modulator</td>
			<td style="width:147px;">Covega</td>
			<td style="width:185px;">Mach10</td>
			<td style="width:160px;">Amplitude, comb</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:111px;">Optical Spectrum Analyzer</td>
			<td style="width:147px;">Yokogawa</td>
			<td style="width:185px;">AQ6370C</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Oscilloscope</td>
			<td style="width:147px;">Agilent</td>
			<td style="width:185px;">DCA-J 86100C</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Measurement Modul</td>
			<td style="width:147px;">Agilent</td>
			<td style="width:185px;">86106B</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Fiber Laser</td>
			<td style="width:147px;">Koheras</td>
			<td style="width:185px;">Adjustik</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Coupler</td>
			<td style="width:147px;">Newport</td>
			<td style="width:185px;">F-CPL-L22151-P</td>
			<td style="width:160px;">Ratio: 90/10</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Coupler</td>
			<td style="width:147px;">Newport</td>
			<td style="width:185px;">F-CPL-L12155-P</td>
			<td style="width:160px;">Ratio: 50/50</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Power supply</td>
			<td style="width:147px;">Zentro-elektrik</td>
			<td style="width:185px;">LD 2x15/1 GB</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Electrical amplifier</td>
			<td style="width:147px;">SHF</td>
			<td style="width:185px;">826H</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Supply port</td>
			<td style="width:147px;">SHF</td>
			<td style="width:185px;">B826</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:111px;">Electrical amplifier</td>
			<td style="width:147px;">Amplifier Research</td>
			<td style="width:185px;">10W1000</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:111px;">Photo diode</td>
			<td style="width:147px;">Newport</td>
			<td style="width:185px;">D-8ir</td>
			<td style="width:160px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:111px;">Electrical spectrum analyzer</td>
			<td style="width:147px;">HP</td>
			<td style="width:185px;">8563E</td>
			<td style="width:160px;"></td>
		</tr>
	</tbody>
</table>

quasi-light storage for optical data packets

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

For the measurement a 10110101 intensity modulated data pattern with a data rate of 1 Gbps was used. The black line in Figure&#160;6 represents the original signal and the colored lines represent the different storage times achieved with the QLS.&#160; The reference is measured without the QLS and the deactivated switch at the output. Under ideal conditions storage times up to 100&#8239;nsec are achievable. The results for the stored 11001101 data pattern of a phase modulated signal, again with a data ra...

Watch this Scientific Journal Video about Quasi-light Storage for Optical Data Packets at JoVE.com

Quasi-light Storage for Optical Data Packets

The article describes a procedure to store optical data packets with an arbitrary modulation, wavelength, and data rate. These packets are the basis of modern telecommunications.

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing ...

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10.7K Views.  Hochschule für Telekommunikation, Leipzig. The article describes a procedure to store optical data packets with an arbitrary modulation, wavelength, and data rate. These packets are the basis of modern telecommunications.

Video: Quasi-light Storage for Optical Data Packets

Construction and Testing of Coin Cells of Lithium Ion Batteries

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime. Lithium ion batteries have also been considered to be used in electric and hybrid vehicles1 or even electrical grid stabilization systems2. All these applications simulate a dramatic increase in the research and development of battery materials3-7, including new materials3,8, doping9, nanostructuring10-13, coatings or surface modifications14-17 and novel binders18. Consequently, an increasing number of physicists, chemists and materials scientists have recently ventured into this area. Coin cells are widely used in research laboratories to test new battery materials; even for the research and development that target large-scale and high-power applications, small coin cells are often used to test the capacities and rate capabilities of new materials in the initial stage. 
 In 2010, we started a National Science Foundation (NSF) sponsored research project to investigate the surface adsorption and disordering in battery materials (grant no. DMR-1006515). In the initial stage of this project, we have struggled to learn the techniques of assembling and testing coin cells, which cannot be achieved without numerous help of other researchers in other universities (through frequent calls, email exchanges and two site visits). Thus, we feel that it is beneficial to document, by both text and video, a protocol of assembling and testing a coin cell, which will help other new researchers in this field. This effort represents the "Broader Impact" activities of our NSF project, and it will also help to educate and inspire students.
In this video article, we document a protocol to assemble a CR2032 coin cell with a LiCoO2 working electrode, a Li counter electrode, and (the mostly commonly used) polyvinylidene fluoride (PVDF) binder. To ensure new learners to readily repeat the protocol, we keep the protocol as specific and explicit as we can. However, it is important to note that in specific research and development work, many parameters adopted here can be varied. First, one can make coin cells of different sizes and test the working electrode against a counter electrode other than Li. Second, the amounts of C black and binder added into the working electrodes are often varied to suit the particular purpose of research; for example, large amounts of C black or even inert powder were added to the working electrode to test the "intrinsic" performance of cathode materials14. Third, better binders (other than PVDF) have also developed and used18. Finally, other types of electrolytes (instead of LiPF6) can also be used; in fact, certain high-voltage electrode materials will require the uses of special electrolytes7.

A protocol to construct and test coin cells of lithium ion batteries is described. The specific procedures of making a working electrode, preparing a counter electrode, assembling a cell inside a glovebox and testing the cell are presented.

Rechargeable lithium ion batteries have wide applications in electronics, where customers always demand more capacity and longer lifetime.  Lithium ion ...

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Bringing the Visible Universe into Focus with Robo-AO

The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, &lambda;, divided by the size of its primary mirror's aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best.
Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images.
The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled1. Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a 'laser guide star'. The Robo-AO laser adaptive optics system2,3 employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.

Light from astronomical objects must travel through the earth's turbulent atmosphere before it can be imaged by ground-based telescopes. To enable direct imaging at maximum theoretical angular resolution, advanced techniques such as those employed by the Robo-AO adaptive-optics system must be used.

The angular  resolution of ground-based optical telescopes is limited by the degrading  effects of the turbulent atmosphere. In the absence of an ...

The Generation of Higher-order Laguerre-Gauss Optical Beams for High-precision Interferometry

Thermal noise in high-reflectivity mirrors is a major impediment for several types of high-precision interferometric experiments that aim to reach the standard quantum limit or to cool mechanical systems to their quantum ground state. This is for example the case of future gravitational wave observatories, whose sensitivity to gravitational wave signals is expected to be limited in the most sensitive frequency band, by atomic vibration of their mirror masses. One promising approach being pursued to overcome this limitation is to employ higher-order Laguerre-Gauss (LG) optical beams in place of the conventionally used fundamental mode. Owing to their more homogeneous light intensity distribution these beams average more effectively over the thermally driven fluctuations of the mirror surface, which in turn reduces the uncertainty in the mirror position sensed by the laser light.
We demonstrate a promising method to generate higher-order LG beams by shaping a fundamental Gaussian beam with the help of diffractive optical elements. We show that with conventional sensing and control techniques that are known for stabilizing fundamental laser beams, higher-order LG modes can be purified and stabilized just as well at a comparably high level. A set of diagnostic tools allows us to control and tailor the properties of generated LG beams. This enabled us to produce an LG beam with the highest purity reported to date. The demonstrated compatibility of higher-order LG modes with standard interferometry techniques and with the use of standard spherical optics makes them an ideal candidate for application in a future generation of high-precision interferometry.

Large laser-interferometers are being constructed to create a new type of astronomy based on gravitational waves. Their sensitivities, as for many other high-precision experiments, are approaching fundamental noise limits such as the atomic vibration of their components. We are pioneering technologies to overcome these limits using novel laser beam shapes.

Thermal noise in high-reflectivity mirrors is a major impediment for several  types of high-precision interferometric experiments that aim to reach the  ...

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Data Acquisition Protocol for Determining Embedded Sensitivity Functions

The effectiveness of many structural health monitoring techniques depends on the placement of sensors and the location of input forces. Algorithms for determining optimal sensor and forcing locations typically require data, either simulated or measured, from the damaged structure. Embedded sensitivity functions provide an approach for determining the best available sensor location to detect damage with only data from the healthy structure. In this video and manuscript, the data acquisition procedure and best practices for determining the embedded sensitivity functions of a structure is presented. The frequency response functions used in the calculation of the embedded sensitivity functions are acquired using modal impact testing. Data is acquired and representative results are shown for a residential scale wind turbine blade. Strategies for evaluating the quality of the data being acquired are provided during the demonstration of the data acquisition process.

The data acquisition procedure for determining embedded sensitivity functions is described. Data is acquired and representative results are shown for a residential scale wind turbine blade.

The effectiveness of many structural health monitoring techniques depends on the placement of sensors and the location of input forces. Algorithms for ...

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.