We have demonstrated WSi-based superconducting nanowire single-photon detectors coupled to SiN_x waveguides with integrated ring resonators. This photonics platform enables the implementation of robust and efficient photon-counting detectors with fine spectral resolution near 1550 nm

Beyer, Andrew D.

Briggs, Ryan M.

Cohen, Justin D.

Marsili, Francesco

Meenehan, Sean M.

Painter, Oskar J.

Shaw, Matthew D.

Andrew D. Beyer

Ryan M. Briggs

Francesco Marsili

Justin D. Cohen

Sean M. Meenehan

Oskar J. Painter

Matthew D. Shaw

Crossref

Waveguide-Coupled Superconducting Nanowire Single-Photon Detectors

Caltech Authors - Main

STh1I.2.pdf CLEO:2015 © OSA 2015
Waveguide-Coupled Superconducting Nanowire Single-
Photon Detectors 
Andrew D. Beyer,1,* Ryan M. Briggs,1 Francesco Marsili,1 Justin D. Cohen,2 Sean M. Meenehan,2 Oskar J. 
Painter,2 and Matthew D. Shaw1 
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA 
2Thomas J. Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, California 91125, USA 
*andrew.d.beyer@jpl.nasa.gov 
Abstract: We have demonstrated WSi-based superconducting nanowire single-photon detectors 
coupled to SiNx waveguides with integrated ring resonators. This photonics platform enables the 
implementation of robust and efficient photon-counting detectors with fine spectral resolution near 
1550 nm. 
OCIS codes: (040.3780) Low light level detectors; (130.3120) Integrated optics devices; (250.0250) Optoelectronics. 
© Copyright 2014 California Institute of Technology
Superconducting nanowire single-photon detectors (SNSPDs) based on amorphous WSi are excellent single-
photon detectors at near-infrared wavelengths, with demonstrated system detection efficiency up to 93% at 1550 nm, 
jitter as low as 150 ps, dark count rates of ~1 cps, and reset times of ~40 ns [1]. Fiber-coupled SNSPDs have 
become widely used in quantum optics and in free space optical communication demonstrations [2,3]. Here, we 
report our efforts to integrate SNSPDs with low-stress silicon nitride (SiNx) waveguides and ring resonators in order 
to develop a platform combining on-chip spectral filtering with photon counting capability.  Waveguide-coupled 
SNSPDs can ultimately enable wavelength-division multiplexing for optical communication in photon-starved 
applications, and can also be used for near-infrared on-chip spectrometers and repeaters for optical quantum 
communication [4,5]. 
A schematic of our device architecture is shown in Fig. 1.  Light is coupled into an input waveguide and filtered 
through a ring resonator. On the resonator drop port, light is evanescently coupled to a WSi-based SNSPD in a 
hairpin geometry. Simulations indicate lengths on the order of tens of micrometers are necessary for efficient 
coupling to the SNSPD. We implemented 40-µm-long hairpins, and an additional inductor section in series with the 
SNSPD absorber prevents latching [6].  Fiber couplers, consisting of self-aligned inverse-taper couplers suspended 
above etched v-grooves, allow light to be coupled on and off the chip at cryogenic temperatures, as previously 
demonstrated in Ref. 7. Separate through- and drop-port fiber couplers were fabricated for each SNSPD to allow 
independent characterization of the resonator and detector.   
Fig. 1. (a) Optical micrograph of the SiNx waveguide architecture, showing a ring resonator with through- and drop-port waveguides. (b) Higher-
magnification view of a waveguide-coupled WSi-based SNSPD. (c) Scanning electron micrograph of an inverse-taper coupler suspended above 
an etched v-groove.  The depth of the v-groove allows the fiber to be self-aligned to the taper. 
Devices were fabricated on Si wafers with 400 nm of low-stress SiNx deposited by low-pressure chemical vapor 
deposition on top of 3.5 µm of thermally grown SiO2.  The SiNx thickness was chosen for optimal confinement of 
light near 1.5 µm, and low-stress SiNx was used to avoid cracking.  Typical losses in single-mode waveguides were 
measured to be 5 dB/cm. Amorphous WSi-based SNSPDs and contacts were patterned and protected by sputtered 
SiO2, and ridge waveguides were etched into the SiNx using an SF6/C4F8 plasma etching process.  After protecting 
978-1-55752-968-8/15/$31.00 ©2015 Optical Society of America
STh1I.2.pdf CLEO:2015 © OSA 2015
the SNSPDs with an alkaline-resistant polymer coating, the suspended waveguide tapers were undercut with 
buffered HF and v-grooves were etched into the Si substrate using KOH. 
Waveguide-coupled detectors were tested in a closed-cycle He-3 cryostat at 0.5 K. A single-mode laser with a 
tuning range of 1510 to 1620 nm was used to measure system detection efficiency (SDE) and spectral response. 
Figures 2(a) and (b) show the SDE and background count rate (BCR) observed for a fixed input wavelength of 
1615.5 nm.  SDE of ~2.5 % was observed with a detector bias current greater than 1.5 µA, where the saturated 
internal efficiency indicates that nearly all the evanescently coupled light was collected by the SNSPD.  The BCR is 
nearly indistinguishable with the input fiber either blanked or connected to fiber outside of the cryostat, implying 
negligible dark counts from the fiber. Figure 2(c) shows the spectral response of a SNSPD coupled to the drop-port 
of a ring-resonator filter with a diameter of 50 µm. The resonance shown in Fig. 2(d) indicates a typical linewidth of 
~100 pm, corresponding to an intrinsic resonator quality factor of approximately 30,000. 
Fig. 2.  (a) System detection efficiency versus bias current measured for a waveguide-coupled SNSPD at a fixed input wavelength of 1615.5 nm. 
(b) Background count rate measured for the same device with the input fiber connected and blanked. (c) Detector count rate versus wavelength 
for a SNSPD coupled to the drop-port of an integrated ring resonator, and (d) the detector spectral response measured near 1600 nm. 
[1] F. Marsili, et al., “Detecting single infrared photons with 93% system efficiency,” Nature Photonics 7, 210-214 (2013). 
[2] M.  Shaw, et al., “A Receiver for the Lunar Laser Communication Demonstration Using the Optical Communications Telescope Laboratory,” 
CLEO: Science and Innovations, SM4J.2 (2014). 
[3] D. M. Boroson, et al., “Overview and Results of the Lunar Laser Communication Demonstration,” Proc. SPIE 8971, 89710S (2014). 
[4] W. H. P. Pernice, et al., “High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits,” Nature 
Communications 3, 1325 (2012). 
[5] F. Najafi, et al., “Membrane-integrated superconducting nanowire single photon detectors,”  CLEO: QELS Fundamental Science, QF1A.6  
(2013). 
[6] A. J. Kerman, et al., “Kinetic-inductance-limited reset time of superconducting nanowire photon counters,” Applied Physics Letters 88, 111116 
(2006). 
[7] J. Cohen, et al., “Optical coupling to nanoscale optomechanical cavities for near quantum-limited motion transduction”, Optics Express 21, 
11227-11236 (2013).


We have demonstrated WSi-based superconducting nanowire single-photon detectors coupled to SiNx waveguides with integrated ring resonators. This photonics platform enables the implementation of robust and efficient photon-counting detectors with fine spectral resolution near 1550 nm

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Waveguide-Coupled Superconducting Nanowire Single-Photon Detectors

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