Name: a silicon-tipped fiber-optic sensing platform with high resolution and fast response
Uploaded: 2019-01-07T14:00:00
Description: Watch this Scientific Journal Video about A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response at JoVE.com

This work was supported by U.S. Naval Research Laboratory (Nos. N0017315P0376, N0017315P3755); U.S. Office of Naval Research (Nos. N000141410139, N000141410456); U.S. Department of Energy (Nos. DE-SC0018273, DE-AC02-09CH11466, DE-AC05-00OR22725).

1. Fabrication of Low-Finesse Sensors
<ol>
	<li>Fabricate the silicon pillars. Pattern a piece of 200-&#181;m-thick double-side-polished (DSP) silicon wafer into standalone silicon pillars (Figure 2a), using standard micro-electro-mechanical system (MEMS) fabrication facilitates. 
	NOTE: The patterned wafer is bonded on another larger silicon wafer using a thin layer of photoresist. The bonding force of the photoresist is strong enough to hold the pillars upright, but also weak enough...

<ol>
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L., Han, M., Liu, G., Gv Eden, G., Evenblij, R., Haverdings, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+plasma+bolometers+using+fiber-optic+temperature+sensors.">Development of plasma bolometers using fiber-optic temperature sensors.</a> Review of Scientific Instruments. 87, 11E708 (2016).</li><li>Zhang, Y., 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=Fringe+visibility+enhanced+extrinsic+Fabry-Perot+interferometer+using+a+graded+index+fiber+collimator.">Fringe visibility enhanced extrinsic Fabry-Perot interferometer using a graded index fiber collimator.</a> IEEE Photonics Journal. 2, 469-481 (2010).</li><li>Hou, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ocean sensing and monitoring. , (2013).</li><li>Hou, W., Woods, S., Jarosz, E., Goode, W., Weidemann, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+turbulence+on+underwater+image+degration+in+natural+environments.">Optical turbulence on underwater image degration in natural environments.</a> Applied Optics. 51, 2678-2686 (2012).</li><li>Hou, W., Jarosz, E., Woods, S., Goode, W., Weidemann, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impacts+of+underwater+turbulence+on+acoustical+and+optical+signals+and+their+linkage.">Impacts of underwater turbulence on acoustical and optical signals and their linkage.</a> Optics Express. 21, 4367-4375 (2013).</li><li>Nootz, G., Jarosz, E., Dalgleish, F. R., Hou, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+optical+turbulence+in+the+ocean+and+its+effects+on+beam+propagation.">Quantification of optical turbulence in the ocean and its effects on beam propagation.</a> Applied Optics. 55, 8813-8820 (2016).</li><li>Nootz, G., Matt, S., Kanaev, A., Judd, K., Hou, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+and+numerical+study+of+underwater+beam+propagation+in+a+Rayleigh-B&#233;nard+turbulence+tank.">Experimental and numerical study of underwater beam propagation in a Rayleigh-B&#233;nard turbulence tank.</a> Applied Optics. 56, 6065-6072 (2017).</li><li>Matt, S., 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=A+controlled+laboratory+environment+to+study+EO+signal+degradation+due+to+underwater+turbulence.">A controlled laboratory environment to study EO signal degradation due to underwater turbulence.</a> Proceedings of SPIE. 9459, 94590H (2015).</li><li>Han, M., Liu, G., Hou, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiber-optic+temperature+and+flow+sensor+system+and+methods.">Fiber-optic temperature and flow sensor system and methods.</a> U.S. Patent. , (2018).</li><li>Kallenbach, A., 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=Impurity+seeding+for+tokamak+power+exhaust:+from+present+devices+via+ITER+to+DEMO.">Impurity seeding for tokamak power exhaust: from present devices via ITER to DEMO.</a> Plasma Physics and Controlled Fusion. 55, 124041 (2013).</li><li>. Alcator C-Mod Available from: <a target="_blank" href="https://commons.wikimedia.org/wiki/File:Alcator_C-Mod_Tokamak_Interior.jpg">https://commons.wikimedia.org/wiki/File:Alcator_C-Mod_Tokamak_Interior.jpg</a> (2018)</li><li>Meister, H., Willmeroth, M., Zhang, D., Gottwald, A., Krumrey, M., Scholze, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Broad-band+efficiency+calibration+of+ITER+bolometer+prototypes+using+Pt+absorbers+on+SiN+membranes.">Broad-band efficiency calibration of ITER bolometer prototypes using Pt absorbers on SiN membranes.</a> Review of Scientific Instruments. 84, 123501 (2013).</li><li>Peterson, B. 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The choice of the size (length and diameter) of the silicon FPI is made upon the tradeoff between requirements on the resolution and speed. In general, a smaller size provides a higher speed but also reduces the resolution2. A short length is advantageous for obtaining a higher speed, but it is not superior for obtaining a high resolution due to the expanded FWHM of the reflection notches. Using HR coatings to reduce the FWHM can help improve the resolution, but it will limit the dynamic range due...

Fiber-optic sensors (FOSs) have been the focus for many researchers due to its unique properties, such as its small size, its low cost, its light weight, and its immunity to electromagnetic interference (EMI)1. These FOSs have found wide applications in many areas such as environmental monitoring, ocean surveillance, oil exploration, and industrial process among others. When it comes to the temperature-related sensing, the traditional FOSs are not superior in terms of resolution and speed for the cases where measurement of minute and fast temperature variations is desirable. These limitations stem from the optical and thermal properties of the fused silica material on which many traditional FOSs are based. On one hand, the thermo-optic coefficient (TOC) and thermal expansion coefficient (TEC) of silica are 1.28x10-5 RIU/&#176;C and 5.5x10-7 m/(m&#183;&#176;C), respectively; these values lead to a temperature sensitivity of only about 13 pm/&#176;C around the wavelength of 1550 nm. On the other hand, the thermal diffusivity, which is a measure of the speed of temperature change in response to thermal energy exchange, is only 1.4x10-6 m2/s for silica; this value is not superior for improving the speed of silica-based FOSs.
The fiber-optic sensing platform (FOSP) reported in this article breaks the above limitations of fused silica-based FOSs. The new FOSP utilizes crystalline silicon as the key sensing material, which forms a high-quality Fabry-Perot interferometer (FPI) on the end of the fiber, here referred to as silicon-tipped FOSP (Si-FOSP). Figure 1 shows the schematic and operational principle of the sensor head, which is the core of the Si-FOSP. The sensor head essentially consists of a silicon FPI, whose reflection spectrum features a series of periodic fringes. Destructive interference occurs when the OPL satisfies 2nL=N&#955;, where n and L are the refractive index and length of the silicon FP cavity, respectively, and N is an integer that is the order of the fringe notch. Therefore, positions of the interference fringes are responsive to the OPL of the silicon cavity. Depending on the specific applications, the silicon FPI can be made into two types: low-finesse FPI and high-finesse FPI. The low-finesse FPI has a low reflectivity for both ends of the silicon cavity, while the high-finesse FPI has a high reflectivity for both ends of the silicon cavity. The reflectivities of silicon-air and silicon-fiber interfaces are roughly 30% and 18%, thus the sole silicon FPI shown in Figure 1a is essentially a low-finesse FPI. By coating a thin high-reflectivity (HR) layer on both ends, a high-finesse silicon FPI is formed (Figure 1b). Reflectivity of the HR coating (either dielectric or gold) can be as high as 98%. For both types of Si-FOSP, both n and L increase when temperature increases. Thus, by monitoring the fringe shift, the temperature variation can be deduced. Note that for the same amount of wavelength shift, the high-finesse FPI gives a better discrimination due to the much narrower fringe notch (Figure 1c). While the high-finesse Si-FOSP has better resolution, the low-finesse Si-FOSP has a larger dynamic range. Therefore, the choice between these two versions depends on the requirements of a specific application. Furthermore, due to the large difference in full width at half maximum (FWHM) of the low-finesse and high-finesse silicon FPIs, their signal demodulation methods are different. For example, the theoretical FWHM of 1.5 nm is reduced by about 50 times to only 30 pm when both ends of the sole silicon FPI are coated with a 98% HR layer. Therefore, for the low-finesse Si-FOSP, a high-speed spectrometer would suffice for the data collection and processing, while a scanning laser should be used to demodulate the high-finesse Si-FOSP due to the much narrower FWHM that cannot be resolved well by the spectrometer. The two demodulation methods will be explained in the protocol.
The silicon material chosen here is superior for temperature sensing in terms of resolution. As a comparison, the TOC and TEC of silicon are 1.5x10-4 RIU/&#176;C and 2.55x10-6 m/(m&#8729;&#176;C), respectively, leading to a temperature sensitivity of around 84.6 pm/&#176;C which is about 6.5 times higher than that of all silica-based FOSs2. &#160;In addition to this much higher sensitivity, we have demonstrated an average wavelength tracking method to reduce the noise level and thus improve the resolution for a low-finesse sensor, leading to a temperature resolution of 6x10-4 &#176;C 2, in comparison to the resolution of 0.2 &#176;C for an all silica-based FOS3. The resolution is further improved to be 1.2x10-4 &#176;C for a high-finesse version4. &#160;The silicon material is also superior for sensing in terms of speed. As a comparison, the thermal diffusivity of silicon is 8.8x10-5 m2/s, which is more than 60 times higher than that of silica2. &#160;Combined with a small footprint (e.g., 80 &#181;m diameter, 200 &#181;m thickness), the response time of 0.51 ms for a silicon FOS has been demonstrated2, &#160;in comparison to the 16 ms of a micro-silica-fiber coupler tip temperature sensor5. &#160;Although some research work related to temperature measurement using very thin silicon film as the sensing material has been reported by other groups6,7,8,9, &#160;none of them possesses the performance of our sensors in terms of either resolution or speed. For example, the sensor with a resolution of only 0.12 &#176;C and a long response time of 1 s was reported.7 A better temperature resolution of 0.064 &#176;C has been reported10; &#160;however, the speed is limited by the relatively bulky sensor head. What makes the Si-FOSP unique lies in the new fabrication method and data processing algorithm.
Besides the above advantages for temperature sensing, the Si-FOSP can also be developed into a variety of temperature-related sensors aiming at measuring different parameters, such as gas pressure11, air or water flow12,13,14 , and radiation4,15. &#160;This article presents a detailed description of the sensor fabrication and signal demodulation protocols along with three representative applications and their results.

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			<td style="width:201px;">3822-2</td>
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		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Optical Microscope and Monitor</td>
			<td style="width:213px;">Ikegami Tsushinki Company</td>
			<td style="width:201px;">PM-127</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Optical Spectrum Analyzer</td>
			<td style="width:213px;">Yokogawa</td>
			<td style="width:201px;">AQ6370C</td>
			<td>wavelength range: 600-1700 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Polish Machine</td>
			<td style="width:213px;">ULTRA TEC</td>
			<td style="width:201px;">41076</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Post-mountable Irises</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:201px;"></td>
			<td>Quantity: 2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Pump Laser</td>
			<td style="width:213px;">Gooch and Housego</td>
			<td style="width:201px;">0400-0974-SM</td>
			<td>Wavelength: 980 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Si Amplified Photodetector</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:201px;">PDA36A</td>
			<td>Wavelength: 350-1100 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Silicon wafer</td>
			<td style="width:213px;">University Wafer</td>
			<td style="width:201px;"></td>
			<td>thickness: 10 &#181;m, 200 &#181;m, 75 &#181;m, 40 &#181;m</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Single mode fiber&#160;</td>
			<td style="width:213px;">Corning</td>
			<td style="width:201px;">SMF-28</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:251px;">Single Mode Fused&#160; Fiber Coupler</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:201px;"></td>
			<td>Wavelength: 1550 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">SM 125 interogrator</td>
			<td style="width:213px;">Micron Optics</td>
			<td style="width:201px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Submersible Aquarium Pump</td>
			<td style="width:213px;">Songlong</td>
			<td style="width:201px;">SL-403</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Superluminscent LED</td>
			<td style="width:213px;">Denselight Semiconductors</td>
			<td style="width:201px;">DL-BP1-1501A</td>
			<td>wavelength range:1510-1590 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Syringe Pump</td>
			<td style="width:213px;">Cole Parmer</td>
			<td style="width:201px;">74905-02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">Travel Translation Stage</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:201px;">LT1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">UV curable glue</td>
			<td style="width:213px;">Epoxy Technology</td>
			<td style="width:201px;">PB109077</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:251px;">UVGL-15 Compact UV Lmap</td>
			<td style="width:213px;">UVP</td>
			<td style="width:201px;">P/N:95-0017-09</td>
			<td>254/365 nm</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:251px;">Variable Optical Attenuators</td>
			<td style="width:213px;">Tholabs</td>
			<td style="width:201px;">M-VA/00016951 P/N: VOA50-APC</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Si-FOSP as an underwater thermometer for profiling ocean thermoclines 
Recent oceanographic research has demonstrated that the blurring of underwater imaging stems not only from turbidity in contaminated waters but also from temperature microstructures in clean ocean17,18. The latter effect has been the focus of many oceanographers, aiming to find an effective way to rectify the blurred images<sup class="xref...

Watch this Scientific Journal Video about A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response at JoVE.com

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

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 ...

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