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4-Pixel NbN Hot-Electron Bolometer Integrated in a Si$_3$N$_4$ Planar Optical Waveguide with On-Chip Fiber-Alignment Trench

N. A. Vovk, G. A. Matveev, M. A. Mumlyakov, M. V. Shibalov, I. A. Filippov, I. D. Burkov, S. D. Perov, N. V. Porohov, N. N. Osipov, M. A. Tarkhov

Abstract

In this work, we design and characterize a 4-pixel superconducting hot-electron bolometer (HEB) based on niobium nitride (NbN), integrated with individual planar silicon nitride (Si$_3$N$_4$) waveguides. The implemented architecture enables simultaneous detection of an optical signal in four independent channels. To efficiently couple optical radiation under cryogenic conditions, we employ an edge (end-fire) coupling approach using dedicated U-shaped grooves that provide accurate and stable positioning of an optical fiber with respect to the on-chip waveguide facet. The device responsivity is measured as a function of the HEB operating point. The measured voltage responsivity reaches $3800~\mathrm{V/W}$ at a modulation frequency of $3~\mathrm{GHz}$. We demonstrate detection of optically modulated signals in the gigahertz range. The developed fabrication route is promising for compact integrated receiver systems and low-noise cryogenic microwave transducers, including superconducting nanowire single-photon detectors (SNSPDs).

4-Pixel NbN Hot-Electron Bolometer Integrated in a Si$_3$N$_4$ Planar Optical Waveguide with On-Chip Fiber-Alignment Trench

Abstract

In this work, we design and characterize a 4-pixel superconducting hot-electron bolometer (HEB) based on niobium nitride (NbN), integrated with individual planar silicon nitride (SiN) waveguides. The implemented architecture enables simultaneous detection of an optical signal in four independent channels. To efficiently couple optical radiation under cryogenic conditions, we employ an edge (end-fire) coupling approach using dedicated U-shaped grooves that provide accurate and stable positioning of an optical fiber with respect to the on-chip waveguide facet. The device responsivity is measured as a function of the HEB operating point. The measured voltage responsivity reaches at a modulation frequency of . We demonstrate detection of optically modulated signals in the gigahertz range. The developed fabrication route is promising for compact integrated receiver systems and low-noise cryogenic microwave transducers, including superconducting nanowire single-photon detectors (SNSPDs).
Paper Structure (5 sections, 5 equations, 3 figures, 1 table)

This paper contains 5 sections, 5 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. HEB Fabrication
  3. Methodology for Measuring the HEB Responsivity
  4. Results
  5. Conclusions

Figures (3)

  • Figure 1: (a) Schematic of HEB structures integrated with planar Si$_3$N$_4$ optical waveguides. (b) Schematic of the chip endface with the HEB in the waveguide region is outlined in red (a). (c) Optical micrograph of the fabricated chip with U-shaped grooves for end-fire coupling. (d) SMF-to-planar-waveguide coupling through an on-chip groove. (e) Optical micrograph of a waveguide array with cross-shaped optical scatterers.
  • Figure 2: Schematic of the electrical and optical interconnects to the sample inside the cryostat.
  • Figure 3: (a) Family of $I$--$V$ characteristics at different temperatures, color-coded according to $R_{\mathrm{resp}}$ for $P_{\mathrm{optic}} = 4.6~\mu\mathrm{W}$, $f = 3~\mathrm{GHz}$, and $U_{\mathrm{bias}}$. The black curve ($T = 7.47~\mathrm{K}$) corresponds to the maximum responsivity; the pink ($T = 7.28~\mathrm{K}$) and green ($T = 8.28~\mathrm{K}$) curves represent boundary regimes. The inset shows $R_{\mathrm{HEB}}(T)$ with $T_c = 7.5~\mathrm{K}$. (b) Family of $R_{\mathrm{resp}}(U_{\mathrm{bias}})$ curves measured at different temperatures $T$, illustrating how the responsivity maximum shifts with temperature. The black line highlights the $I$--$V$ characteristic at $T = 7.47~\mathrm{K}$ corresponding to the maximum-responsivity regime.