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://www.jove.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://www.jove.com/files/ftp_upload/50468/50468fig5highres.jpg" target="_blank">Click here to view larger image.</a>

<ol>
	<li>Spring, J., Tucker, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photonic+2+x+2+packet+switch+with+input+buffers.">Photonic 2 x 2 packet switch with input buffers.</a> Electron. Lett. 29 (3), 284-285 (1993).</li><li>Krauss, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+do+we+need+slow+light.">Why do we need slow light.</a> Nat. Photonics. 2, 448-450 (2008).</li><li>Hau, L. V., Harris, S. E., Dutton, Z., Behroozi, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light+speed+reduction+to+17+meters+per+second+in+an+ultracold+atomic+gas.">Light speed reduction to 17 meters per second in an ultracold atomic gas.</a> Nature. 397, 594-598 (1999).</li><li>Chang-Hasnian, C. J., Ku, P. C., Kim, J., Chuang, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Variable+optical+buffer+using+slow+light+in+semiconductor+nanostructures.">Variable optical buffer using slow light in semiconductor nanostructures.</a> Proc. IEEE. 91 (11), 1897-1810 (2003).</li><li>Gersen, H., Karle, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-space+observation+of+ultraslow+light+in+Photonic+Crystal+Waveguides.">Real-space observation of ultraslow light in Photonic Crystal Waveguides.</a> Phys. Rev. Lett. 94 (7), 073903-073907 (2005).</li><li>Th&#233;venaz, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Slow+and+fast+light+in+optical+fibres.">Slow and fast light in optical fibres.</a> Nature Photon. 2, 472-481 (2008).</li><li>Uskov, A. V., Sedgwick, F. G., Chang-Hasnian, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Delay+Limit+of+Slow+Light+in+Semiconductor+Optical+Amplifiers.">Delay Limit of Slow Light in Semiconductor Optical Amplifiers.</a> IEEE Photon. Technol. Lett. 18 (6), 731-733 (2006).</li><li>Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time+Delay+Limits+of+stimulated-Brillouin-scattering-based+slow+light+systems.">Time Delay Limits of stimulated-Brillouin-scattering-based slow light systems.</a> Opt. Lett. 33 (13), 1398-1400 (2008).</li><li>Sharping, J., Okawachi, Y., van Howe, J., Xu, C., Wang, Y., Willner, A., Gaeta, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All-optical,+wavelength+and+bandwidth+preserving,+pulse+delay+based+on+parametric+wavelength+conversion+and+dispersion.">All-optical, wavelength and bandwidth preserving, pulse delay based on parametric wavelength conversion and dispersion.</a> Opt. Express. 13 (20), 7872-7877 (2005).</li><li>Okawachi, Y., Foster, M., Chen, X., Turner-Foster, A., Salem, R., Lipson, M., Xu, C., Gaeta, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large+tunable+delays+using+parametric+mixing+and+phase+conjugation+in+Si+nanowaveguides.">Large tunable delays using parametric mixing and phase conjugation in Si nanowaveguides.</a> Opt. Express. 16 (14), 10349-10357 (2008).</li><li>Kash, M. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultraslow+group+velocity+and+enhanced+nonlinear+optical+effects+in+a+coherently+driven+hot+atomic+gas.">Ultraslow group velocity and enhanced nonlinear optical effects in a coherently driven hot atomic gas.</a> Phys. Rev. Lett. 82 (26), 5229-5232 (1999).</li><li>Turukhin, A. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+ultraslow+and+stored+light+pulses+in+a+solid.">Observation of ultraslow and stored light pulses in a solid.</a> Phys. Rev. Lett. 88 (2), 023602-023605 (2001).</li><li>Fleischhauer, M., Yelin, S. F., Lukin, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+trap+photons?+Storing+single-photon+quantum+states+in+collective+atomic+excitations.">How to trap photons? Storing single-photon quantum states in collective atomic excitations.</a> Opt. Commun. 179 (1-6), 395-410 (2000).</li><li>Zhu, Z., Gauthier, D. J., Boyd, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stored+Light+in+an+Optical+Fiber+via+Stimulated+Brillouin+Scattering.">Stored Light in an Optical Fiber via Stimulated Brillouin Scattering.</a> Science. 318 (5857), 1748-1750 (2007).</li><li>Preu&#223;ler, S., Jamshidi, K., Wiatrek, A., Henker, R., Bunge, C. A., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quasi-Light-Storage+based+on+time-frequency+coherence.">Quasi-Light-Storage based on time-frequency coherence.</a> Opt. Express. 17 (18), 15790-15798 (2009).</li><li>Jamshidi, K., Preu&#223;ler, S., Wiatrek, A., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+to+the+all+optical+Quasi+Light+Storage.">A review to the all optical Quasi Light Storage.</a> IEEE J. Sel. Top. Quantum Electron. Special Issue: Nonlinear Optical Signal Processing. 18 (2), 884-890 (2012).</li><li>Preu&#223;ler, S., Jamshidi, K., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quasi-Light-Storage+Enhancement+by+Reducing+the+Brillouin+Gain+Bandwidth.">Quasi-Light-Storage Enhancement by Reducing the Brillouin Gain Bandwidth.</a> Appl. Opt. 50 (22), 4252-4256 (2011).</li><li>Schneider, T., Jamshidi, K., Preu&#223;ler, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quasi-Light+Storage:+A+Method+for+the+Tunable+Storage+of+Optical+Packets+With+a+Potential+Delay-Bandwidth+Product+of+Several+Thousand.">Quasi-Light Storage: A Method for the Tunable Storage of Optical Packets With a Potential Delay-Bandwidth Product of Several Thousand.</a> Bits, J. Lightwave Technol. 28 (17), 2586-2592 (2010).</li><li>Boyd, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nonlinear Optics. , (2003).</li><li>Yeniay, A., Delavaux, J., Toulouse, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+and+Stimulated+Brillouin+Scattering+Gain+Spectra+in+Optical+Fibers.">Spontaneous and Stimulated Brillouin Scattering Gain Spectra in Optical Fibers.</a> J. Lightwave Technol. 20 (8), 1425-1432 (2002).</li><li>Preu&#223;ler, S., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=All+optical+storage+of+phase-shift-keyed+data+packets.">All optical storage of phase-shift-keyed data packets.</a> Opt. Express. 20 (16), 18224-18229 (2012).</li><li>Preu&#223;ler, S., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bandwidth+reduction+in+a+multistage+Brillouin+system.">Bandwidth reduction in a multistage Brillouin system.</a> Opt. Lett. 37 (19), 4122-4124 (2012).</li><li>Preu&#223;ler, S., Jamshidi, K., Wiatrek, A., Schneider, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Einfache+variable,+optische+Datenspeicherung+bis+zu+800+ns.">Einfache variable, optische Datenspeicherung bis zu 800 ns.</a> Proceedings Photonische Netze. (ITG-FB 228), P8. , (2011).</li></ol>

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://www.jove.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://www.jove.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://www.jove.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 ...

quasi-light-storage-for-optical-data-packets

Research

Education

JoVE Core

JoVE Journal

Electrical Engineering

Engineering

Unit 1

Linear Time- Invariant Systems

SCIENTISTS IN ACTION

10.7K vues.  Hochschule für Telekommunikation, Leipzig.  L'article décrit une procédure pour stocker les paquets de données optiques avec une modulation arbitraire, longueur d'onde, et le taux de données. Ces paquets sont à la base des télécommunications modernes. 

Vidéo: Quasi-light Storage for Optical Data Packets

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Gradient Echo Quantum Memory in Warm Atomic Vapor

Gradient echo memory (GEM) is a protocol for storing optical quantum states of light in atomic ensembles. The primary motivation for such a technology is that quantum key distribution (QKD), which uses Heisenberg uncertainty to guarantee security of cryptographic keys, is limited in transmission distance. The development of a quantum repeater is a possible path to extend QKD range, but a repeater will need a quantum memory. In our experiments we use a gas of rubidium 87 vapor that is contained in a warm gas cell. This makes the scheme particularly simple. It is also a highly versatile scheme that enables in-memory refinement of the stored state, such as frequency shifting and bandwidth manipulation. The basis of the GEM protocol is to absorb the light into an ensemble of atoms that has been prepared in a magnetic field gradient. The reversal of this gradient leads to rephasing of the atomic polarization and thus recall of the stored optical state. We will outline how we prepare the atoms and this gradient and also describe some of the pitfalls that need to be avoided, in particular four-wave mixing, which can give rise to optical gain.

The gradient echo memory is a protocol for storing optical quantum states of light in atomic ensembles. Quantum memory is a key element of a quantum repeater, which can extend the range of quantum key distribution. We outline the operation of the scheme when implemented in a 3-level atomic ensemble.

Gradient  echo memory (GEM) is a protocol for storing optical quantum states of light in  atomic ensembles. The primary motivation for such a technology ...

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

Laser-induced Forward Transfer for Flip-chip Packaging of Single Dies

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics industry. In this technique the chip and/or the substrate is bumped and the two are bonded via these conductive bumps. Many bumping techniques have been developed and intensively investigated since the introduction of the FC technology in 19601 such as stencil printing, stud bumping, evaporation and electroless/electroplating2. Despite the progress that these methods have made they all suffer from one or more than one drawbacks that need to be addressed such as cost, complex processing steps, high processing temperatures, manufacturing time and most importantly the lack of flexibility. In this paper, we demonstrate a simple and cost-effective laser-based bump forming technique known as Laser-induced Forward Transfer (LIFT)3. Using the LIFT technique a wide range of bump materials can be printed in a single-step with great flexibility, high speed and accuracy at RT. In addition, LIFT enables the bumping and bonding down to chip-scale, which is critical for fabricating ultra-miniature circuitry.

We demonstrate the use of the Laser-induced Forward Transfer (LIFT) technique for flip-chip assembly of optoelectronic components. This approach provides a simple, cost-effective, low-temperature, fast and flexible solution for fine-pitch bumping and bonding on chip-scale for achieving high-density circuits for optoelectronic applications.

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics ...

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential.

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs ...

A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This FOSP relies on a silicon Fabry-Perot interferometer (FPI) attached to the fiber end, referred to as Si-FOSP in this work. The Si-FOSP generates an interferogram determined by the optical path length (OPL) of the silicon cavity. Measurand alters the OPL and thus shifts the interferogram. Due to the unique optical and thermal properties of the silicon material, this Si-FOSP exhibits an advantageous performance in terms of sensitivity and speed. Furthermore, the mature silicon fabrication industry endows the Si-FOSP with excellent reproducibility and low cost toward practical applications. Depending on the specific applications, either a low-finesse or high-finesse version will be utilized, and two different data demodulation methods will be adopted accordingly. Detailed protocols for fabricating both versions of the Si-FOSP will be provided. Three representative applications and their according results will be shown. The first one is a prototype underwater thermometer for profiling the ocean thermoclines, the second one is a flow meter to measure flow speed in the ocean, and the last one is a bolometer used for monitoring exhaust radiation from magnetically confined high-temperature plasma.

This work reports an innovative silicon-tipped fiber-optic sensing platform (Si-FOSP) for high-resolution and fast-response measurement of a variety of physical parameters, such as temperature, flow, and radiation. Applications of this Si-FOSP span from oceanographic research, mechanical industry, to fusion energy research.

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This ...

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference

We present a high-performance source of unconditional polarization-entangled photons that have a high-emission rate, a broadband distribution, are degenerated and postselection free. The property of the source is based on the multiple quantum interference effect with a round-trip configuration of a Sagnac interferometer. The quantum interference effects make it possible to use the high generation efficiency of the polarization-entangled photons to process parametric down-conversion, and separate degenerated photon pairs into different optical modes without a postselection requirement. The principle of the optical system was described and experimentally used to measure the fidelity and Bell parameters, and also to characterize the generated polarization-entangled photons from a minimum of six combinations of polarization correlated data. The experimentally obtained fidelity and Bell parameters exceeded the classical local correlation limit and are clear evidence of the generation of unconditional polarization-entangled photons.

We describe an optical system for the generation of unconditional polarization-entangled photons based on multiple quantum interference effects with a detection scheme to estimate the experimental fidelity of generated entangled photons.

We present a high-performance source of unconditional polarization-entangled photons that have a high-emission rate, a broadband distribution, are ...

Fixed Target Serial Data Collection at Diamond Light Source

Serial data collection is a relatively new technique for synchrotron users. A user manual for fixed target data collection at I24, Diamond Light Source is presented with detailed step-by-step instructions, figures, and videos for smooth data collection.

We present a comprehensive guide to fixed target sample preparation, data collection, and data processing for serial synchrotron crystallography at Diamond beamline I24.

Serial data collection is a relatively new technique for synchrotron users. A user manual for fixed target data collection at I24, Diamond Light Source is ...

Biochemistry

Optical Recording of Electrical Activity in Guinea-pig Enteric Networks using Voltage-sensitive Dyes

The enteric nervous system (ENS) is a self-contained network with identified functions, capable of performing complex behaviors in isolation. Its neurons (10 to 25 &mu;m in diameter) are arranged in plexuses that are confined to distinct planes of the gut wall 1; the myenteric plexus can be found between the longitudinal and circular muscle layers, and the submucous plexus between the circular muscle layer and the mucosa. Since the effector systems for these plexuses (transporting epithelium, endocrine cells, immune elements, blood vessels and smooth muscle) are also contained within the gut wall, semi-intact preparations can be dissected that preserve individual components of different reflex pathways. The behavior of the effector systems is controlled by the submucous and myenteric plexuses acting in concert. Therefore, detailed knowledge of synaptic interactions within and between ganglia, and of communication between the plexuses, is essential for understanding normal gastrointestinal function. The ENS, as an intact nervous system, is a unique experimental model in which one can correlate molecular and cellular events with the electrical behavior of the neuronal network and its physiological outputs. Because of the quasi-two-dimensional organization of its plexuses, the ENS is particularly well suited for the study of neural networks using multiple site optical recording techniques that employ voltage-sensitive dyes 2,7,8,9. We will illustrate here the use of a relatively new naphthylstyryl-pyridinium dye (di-4-ANEPPDHQ) 3 that offers multiple advantages over its predecessors, including very low phototoxicity, slow rate of internalization, and remarkable chemical stability. When used in conjunction with a camera that permits sub-millisecond time resolution, this dye allows us to monitor the electrical activity of all the neurons in the field of view with a maximal spatial resolution of ~ 2.5 &mu;m at 100X magnification. At lower magnification (10X or 20X), the sacrifice of single-cell resolution is compensated by a gain in perspective, revealing the intricacies of the inter-ganglionic circuitry.

This protocol illustrates how voltage-sensitive dyes enable optical recording of electrical activity from intact neural networks such as the plexuses of the guinea-pig enteric nervous system, with an adjustable resolution that ranges from single-cells to multi-ganglionic circuitry.

The enteric nervous system (ENS) is a self-contained network with identified functions, capable of performing complex behaviors in isolation. Its neurons ...

Biology

Optimizing Brillouin Optical Time-Domain Analyzers Based on Gain Spectrum Engineering

Demonstrated is a unique method for sensing performance enhancement in Brillouin optical time-domain analyzers (BOTDA). A Brillouin gain spectrum (BGS) is superimposed with two symmetric Brillouin loss spectra (BLS). This leads to a complex engineered spectrum shape that is more resistant to the sensing system noise. Instead of only one pump and probe interaction as in the conventional BOTDA setup, three optical probe waves are exploited, with one probe located in the BGS and the other two symmetrically in the BLS. Due to the resistance and insensitivity of the engineered spectrum shape to the noise, the sensing performance is enhanced by 60% and the measurand resolution is doubled.

A protocol for Brillouin optical time-domain analyzers based on gain spectrum engineering is presented. Enhancements in the sensing performance, including sensing range and measurand resolution are achieved and the excess Brillouin intensity noise is studied. The protocol introduces a new way to enhance distributed Brillouin sensing performance.

Demonstrated is a unique method for sensing performance enhancement in Brillouin optical time-domain analyzers (BOTDA). A Brillouin gain spectrum (BGS) is ...