Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2606.21542

Phase Stable Integrated Delay Line Asymmetric Mach Zehnder Interferometers Enabled by High Efficiency 3 dB Couplers for Chip Scale QKD

Mahsa. Ghezelbash, Abdollah Eslami Majd

physics.opticsquant-phSubmitted Jun 19, 2026• Announced Jun 22, 2026• 0 citations
arXivHTMLPDF

Abstract

Precise temporal delay generation is a key requirement for asymmetric Mach-Zehnder interferometers (aMZIs) used in high-speed quantum key distribution (QKD) receivers. In this work, a compact integrated aMZI architecture based on a silicon nitride on silicon dioxide (Si3N4/SiO2) photonic platform is presented. A 3-dB directional coupler enabling accurate 50:50 power splitting at the 1550 nm telecommunication wavelength is designed and optimized. The coupling length is initially estimated from the effective index difference between the even and odd supermodes and subsequently refined using three-dimensional eigenmode expansion (EME) simulations. The optimized structure employs single-mode Si3N4 waveguides with a cross section of 1 um x 0.4 um, providing a group index close to 2 and enabling accurate delay engineering. Spectral analysis demonstrates stable 3-dB power splitting across the C-band with insertion loss below 0.5 dB and negligible power imbalance, indicating high transmission efficiency and structural symmetry. An integrated Si3N4 aMZI delay line providing a 500 ps optical delay, corresponding to a 2 GHz free spectral range (FSR), is further demonstrated. Simulations show nearly constant group delay across the 190-200 THz frequency range with sub-10 ps variation and a smooth, near-linear phase response. These characteristics enable interference visibility above 0.99, corresponding to an estimated quantum bit error rate (QBER) below 0.5 percent for gigahertz-rate time-bin QKD systems. The wideband linear phase behavior also indicates compatibility with wavelength division multiplexed (WDM) QKD architectures. The results confirm that the proposed Si3N4 integrated aMZI provides a low-loss, dispersion-controlled, and spectrally stable delay solution suitable for scalable chip-scale quantum photonic receivers.

Related papers

Temperature characterizations of silica asymmetric Mach-Zehnder interferometer chip for quantum key distribution

Dan Wu, Xiao Li, Liangliang Wang +9 more

Quantum key distribution (QKD) system based on passive silica planar lightwave circuit (PLC) asymmetric Mach–Zehnder interferometers (AMZI) is characterized with thermal stability, low loss and sufficient integration scalability. However, waveguide stresses, both intrinsic and temperature-induced stresses, have significant impacts on the stable operation of the system. We have designed silica AMZI chips of 400 ps delay, with bend waveguides length equalized for both long and short arms to balance the stresses thereof. The temperature characteristics of the silica PLC AMZI chip are studied. The interference visibility at the single photon level is kept higher than 95% over a wide temperature range of 12 °C. The delay time change is 0.321 ps within a temperature change of 40 °C. The spectral shift is 0.0011~nm/0.1 °C. Temperature-induced delay time and peak wavelength variations do not affect the interference visibility. The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.

Chinese Physics B•Sep 15, 2022•2 citations

Generation of balanced pulse pairs based on a dual-chip coupling structure

Jin You, Pan Pan, Pengwei Cui +3 more

An asymmetric Mach-Zehnder interferometer (AMZI) is an essential device to generate pulse pairs in quantum key distribution systems. An AMZI based on a dual-chip coupling structure in a silica-on-silicon planar light wave circuit platform is proposed, which includes a variable optical splitter (VOS), a delay line (DL), and a directional coupler (DC). The AMZI chip is divided into a VOS-DL part and a DC part, and the two parts are independently manufactured and then coupled. Since the DC part occupies the smallest area of the AMZI chip and is most sensitive to manufacturing errors, separate production can reduce the process difficulty and fabrication errors. In the experiment, balanced pulse pairs with a delay time of 402 ps are obtained in the condition of single photon transmission, and the excess loss is 0.8 dB. This dual-chip coupling structure can improve the yield and reduce the manufacturing cost when producing large chips.

Applied Optics•Jul 31, 2023•1 citation

Silicon nitride Mach-Zehnder interferometer for on-chip quantum random number generation

A. I. Prokhodtsov, Vadim V. Kovalyuk, Pavel P. An +6 more

Abstract In this work, we experimentally studied silicon nitride Mach-Zehnder interferometer (MZI) with two directional couplers and 400 ps optical delay line for telecom wavelength 1550 nm. We achieved the extinction ratio in a range of 0.76-13.86 dB and system coupling losses of 28-44 dB, depending on the parameters of directional couplers. The developed interferometer is promising for the use in a compact random number generator for the needs of a fully integrated quantum cryptography system, where compact design, as well as high generation speed, are needed.

Journal of Physics Conference Series•Dec 1, 2020•12 citations

Optimization of the classical interference visibility of an asymmetric Mach–Zehnder interferometer based on planar lightwave circuit technology

Meizhen Ren, Xiao Li, Jiashun Zhang +7 more

Silicon-based devices offer great potential for quantum key distribution (QKD) with the benefits of miniaturization, scalability, complexity, and improved performance. Based on the planar lightwave circuit technology, a 200 ps delay-time asymmetric Mach-Zehnder interferometer (AMZI) decoding chip was designed and fabricated that can adjust the power ratio of the two arms by introducing a variable beam splitter. The measured delay time is approximately 200 ps, and the two output pulses' peaks can be balanced by loading an appropriate voltage on the variable beam splitter. The classical interference visibility of the AMZI versus temperature was studied, and it is highly temperature dependent. The interference visibility can reach as high as 99.72% under appropriate temperature control. This AMZI can act as a passive decoder in fiber-based QKD systems.

Applied Optics•Sep 25, 2019•5 citations

Quantum decoding integrated chip for quantum key distribution based on silica planar lightwave circuit technology

Jin You, Yue Wang, Dan Wu +1 more

Silica-based planar lightwave circuit (PLC) devices can offer great potential for quantum key distribution (QKD) with the benefits of low-loss, low-cost, large-scale integration, miniaturization, stability and mass production. A quantum decoding integrated chip for QKD based on silica PLC technology was demonstrated, which consists of a variable optical splitter (VOS), an asymmetric Mach–Zehnder interferometer (AMZI) with a thermo-optic phase modulator (TOPM) and a delay line (DL) whose delay time is 400ps, and a variable directional coupler (VDC). The balanced pulsepairs of double channels with measured delay times of 396ps and 398ps respectively were obtained in the conditions of both classical optics and single-photon transmissions. The chip has advantageous to achieve high interference visibilities of double channels simultaneously for BB84 phase and time-bin protocols.

International Conference on Optoelectronic and Microelectronic Technology and Application•Dec 4, 2020•0 citations

Integrated transceiver chip for metropolitan WDM quantum key distributions

Yu Zhou, Yan‐Yang Zhou, Heng Zhang +8 more

The realization of large-scale, practical quantum key distribution (QKD) networks relies on the development of scalable architectures and integrated hardware. We demonstrate a metropolitan wavelength-division multiplexing (WDM) QKD network based on hybrid-integrated quantum node transceiver chips that integrate both transmitter and receiver functionalities, including high-speed pulse modulation, decoy-state modulation, tunable attenuation, time-bin encoding, and decoding. The packaged module offers a wavelength tuning range exceeding 85 nm, with its silicon photonic Mach–Zehnder modulator (MZM) achieving a single-photon equivalent dynamic extinction ratio (SP-EDER) of over 20 dB across the entire tuning range at a 1.25 GHz pulse repetition rate. In combination with a simple 1.25 GHz clocked integrated time-bin QKD system, we generate secret keys at a rate of 865.4 kbps over a channel with 9.08 dB of fixed attenuation and at a rate of 168.2 kbps over a distance of 80 km at 1550.12 nm. Our work demonstrates an integrated WDM QKD network capable of supporting scalable and cost-effective metropolitan quantum-secure communications.

Photonics Research•Jul 1, 2026•0 citations
Precise temporal delay generation is a key requirement for asymmetric Mach-Zehnder interferometers (aMZIs) used in high-speed quantum key distribution (QKD) receivers. In this work, a compact integrated aMZI architecture based on a silicon nitride on silicon dioxide (Si3N4/SiO2) photonic platform is presented. A 3-dB directional coupler enabling accurate 50:50 power splitting at the 1550 nm telecommunication wavelength is designed and optimized. The coupling length is initially estimated from the effective index difference between the even and odd supermodes and subsequently refined using three-dimensional eigenmode expansion (EME) simulations.
The optimized structure employs single-mode Si3N4 waveguides with a cross section of 1 um x 0.4 um, providing a group index close to 2 and enabling accurate delay engineering. Spectral analysis demonstrates stable 3-dB power splitting across the C-band with insertion loss below 0.5 dB and negligible power imbalance, indicating high transmission efficiency and structural symmetry. An integrated Si3N4 aMZI delay line providing a 500 ps optical delay, corresponding to a 2 GHz free spectral range (FSR), is further demonstrated.
Simulations show nearly constant group delay across the 190-200 THz frequency range with sub-10 ps variation and a smooth, near-linear phase response. These characteristics enable interference visibility above 0.99, corresponding to an estimated quantum bit error rate (QBER) below 0.5 percent for gigahertz-rate time-bin QKD systems. The wideband linear phase behavior also indicates compatibility with wavelength division multiplexed (WDM) QKD architectures. The results confirm that the proposed Si3N4 integrated aMZI provides a low-loss, dispersion-controlled, and spectrally stable delay solution suitable for scalable chip-scale quantum photonic receivers.
Quantum key distribution (QKD) system based on passive silica planar lightwave circuit (PLC) asymmetric Mach–Zehnder interferometers (AMZI) is characterized with thermal stability, low loss and sufficient integration scalability. However, waveguide stresses, both intrinsic and temperature-induced stresses, have significant impacts on the stable operation of the system. We have designed silica AMZI chips of 400 ps delay, with bend waveguides length equalized for both long and short arms to balance the stresses thereof. The temperature characteristics of the silica PLC AMZI chip are studied. The interference visibility at the single photon level is kept higher than 95% over a wide temperature range of 12 °C. The delay time change is 0.321 ps within a temperature change of 40 °C. The spectral shift is 0.0011~nm/0.1 °C. Temperature-induced delay time and peak wavelength variations do not affect the interference visibility. The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.
An asymmetric Mach-Zehnder interferometer (AMZI) is an essential device to generate pulse pairs in quantum key distribution systems. An AMZI based on a dual-chip coupling structure in a silica-on-silicon planar light wave circuit platform is proposed, which includes a variable optical splitter (VOS), a delay line (DL), and a directional coupler (DC). The AMZI chip is divided into a VOS-DL part and a DC part, and the two parts are independently manufactured and then coupled. Since the DC part occupies the smallest area of the AMZI chip and is most sensitive to manufacturing errors, separate production can reduce the process difficulty and fabrication errors. In the experiment, balanced pulse pairs with a delay time of 402 ps are obtained in the condition of single photon transmission, and the excess loss is 0.8 dB. This dual-chip coupling structure can improve the yield and reduce the manufacturing cost when producing large chips.
Abstract In this work, we experimentally studied silicon nitride Mach-Zehnder interferometer (MZI) with two directional couplers and 400 ps optical delay line for telecom wavelength 1550 nm. We achieved the extinction ratio in a range of 0.76-13.86 dB and system coupling losses of 28-44 dB, depending on the parameters of directional couplers. The developed interferometer is promising for the use in a compact random number generator for the needs of a fully integrated quantum cryptography system, where compact design, as well as high generation speed, are needed.
Silicon-based devices offer great potential for quantum key distribution (QKD) with the benefits of miniaturization, scalability, complexity, and improved performance. Based on the planar lightwave circuit technology, a 200 ps delay-time asymmetric Mach-Zehnder interferometer (AMZI) decoding chip was designed and fabricated that can adjust the power ratio of the two arms by introducing a variable beam splitter. The measured delay time is approximately 200 ps, and the two output pulses' peaks can be balanced by loading an appropriate voltage on the variable beam splitter. The classical interference visibility of the AMZI versus temperature was studied, and it is highly temperature dependent. The interference visibility can reach as high as 99.72% under appropriate temperature control. This AMZI can act as a passive decoder in fiber-based QKD systems.
Silica-based planar lightwave circuit (PLC) devices can offer great potential for quantum key distribution (QKD) with the benefits of low-loss, low-cost, large-scale integration, miniaturization, stability and mass production. A quantum decoding integrated chip for QKD based on silica PLC technology was demonstrated, which consists of a variable optical splitter (VOS), an asymmetric Mach–Zehnder interferometer (AMZI) with a thermo-optic phase modulator (TOPM) and a delay line (DL) whose delay time is 400ps, and a variable directional coupler (VDC). The balanced pulsepairs of double channels with measured delay times of 396ps and 398ps respectively were obtained in the conditions of both classical optics and single-photon transmissions. The chip has advantageous to achieve high interference visibilities of double channels simultaneously for BB84 phase and time-bin protocols.
The realization of large-scale, practical quantum key distribution (QKD) networks relies on the development of scalable architectures and integrated hardware. We demonstrate a metropolitan wavelength-division multiplexing (WDM) QKD network based on hybrid-integrated quantum node transceiver chips that integrate both transmitter and receiver functionalities, including high-speed pulse modulation, decoy-state modulation, tunable attenuation, time-bin encoding, and decoding. The packaged module offers a wavelength tuning range exceeding 85 nm, with its silicon photonic Mach–Zehnder modulator (MZM) achieving a single-photon equivalent dynamic extinction ratio (SP-EDER) of over 20 dB across the entire tuning range at a 1.25 GHz pulse repetition rate. In combination with a simple 1.25 GHz clocked integrated time-bin QKD system, we generate secret keys at a rate of 865.4 kbps over a channel with 9.08 dB of fixed attenuation and at a rate of 168.2 kbps over a distance of 80 km at 1550.12 nm. Our work demonstrates an integrated WDM QKD network capable of supporting scalable and cost-effective metropolitan quantum-secure communications.