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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

20-Gb/s QPSK transmission over 4km-long holey fiber using a wavelength tunable quantum dot light laser in T-band

Akihiro Murano, Shoko Yamada, Atsushi Kanno, Naokatsu Yamamoto, Hideyuki Sotobayashi

Published Feb 13, 2016• 0 citations
Publisher

Abstract

We successfully demonstrate 10-Gbbaud quadrature phase-shift keying signal transmission over a 4-km-long endlessly single-mode holey fiber using a wavelength-tunable semiconductor quantum dot (QD) laser. The transmission is carried out in the waveband of 1040.72–1070.02 nm with a bandwidth of 7.89 THz, which is broader than conventional wavebands such as the C and L bands. In the study, a QD laser notable for its wavelength stability and tunability is employed for its broad bandwidth availability on the transmission. Observed bit error rates are within a forward error correction limit of 2×10–3 under homodyne coherent detection configuration with offline digital signal processing. The abundant frequency resources in this T band (1000–1260 nm) help increase the capacity of a transmission link using a large number of wavelength channels by the QD laser.

DOI
10.1117/12.2211697

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We successfully demonstrate 10-Gbbaud quadrature phase-shift keying signal transmission over a 4-km-long endlessly single-mode holey fiber using a wavelength-tunable semiconductor quantum dot (QD) laser. The transmission is carried out in the waveband of 1040.72–1070.02 nm with a bandwidth of 7.89 THz, which is broader than conventional wavebands such as the C and L bands. In the study, a QD laser notable for its wavelength stability and tunability is employed for its broad bandwidth availability on the transmission. Observed bit error rates are within a forward error correction limit of 2×10–3 under homodyne coherent detection configuration with offline digital signal processing. The abundant frequency resources in this T band (1000–1260 nm) help increase the capacity of a transmission link using a large number of wavelength channels by the QD laser.
We successfully demonstrate 20-Gb/s quadrature phase-shift keying (QPSK) signal transmission. The transmission was carried out over endlessly single-mode holey fiber in the waveband of 1276.02–1304.26 nm, whose bandwidth of 5.09- THz is broader than the traditional C-band. A wavelength-tunable quantum dot (QD) laser with broad wavelength tunability helps realize bandwidth availability. A single InAs/InGaAs QD optical gainchip was grown using a sandwiched sub-nanometer separator technique in the wavelength of 1.3-μm band. Using this gain chip, the QD light source has good wavelength stability, compactness and wavelength tunablility. The measured transmission results show bit error rates within a forward error correction limit of 2×10–3 using intradyne coherent detection with offline digital signal processing. In this study, it is expected that abundant frequency resources such as the O-band are coherently enhanced by the use of a large number of wavelength channels by effectively using the QD- laser.
Quantum-dot single-photon sources are promising for quantum communication. Yet, the most advanced devices operate near 900 nm, where standard single-mode fibers experience significant losses. We address this by employing a hollow-core fiber engineered for low-loss transmission at quantum-dot wavelengths, with measured loss of 0.65 dB/km and potentially as low as 0.13 dB/km near 934 nm. The same fiber also supports strong classical signals at 1550 nm without introducing detectable Raman noise. Using this platform, we transmit all four BB84 polarization states from an InAs quantum dot over 340 m with a quantum bit error rate of 0.1% while preserving single-photon purity and indistinguishability even in the presence of a strong classical signal. These results establish an integrated transmission platform that combines a custom-engineered anti-resonant hollow-core fiber with co-existence of classical and quantum channels, enabling practical quantum-dot-based quantum key distribution beyond the conventional telecom bands.
Future quantum networks will rely on the ability to coherently transfer optically encoded quantum information between different wavelength bands. Bragg-scattering four-wave mixing in optical fiber is a promising route to achieving this, but requires fibers with precise dispersion control and broadband transmission at signal, target, and pump wavelengths. Here, we introduce a photonic crystal fiber with a germanium-doped core featuring group velocity matching at 1550 nm, the telecoms C-band, and 920 nm, within the emission range of efficient single photon sources based on InAs quantum dots. With low chromatic walk-off and good optical guidance even at long wavelengths, large lengths of this fiber are used to achieve nanometer-scale frequency shifts between wavelengths around 920 nm with up to 79.4% internal conversion efficiency, allowing dissimilar InAs dots to be interfaced. We also show how cascading this frequency conversion can be used to generate a frequency comb away from telecoms wavelengths. Finally, we use the fiber to demonstrate tunable frequency conversion of weak classical signals around 918 nm to the telecoms C-band.
Quantum dot single-photon sources are promising for quantum communication. Yet, the most advanced devices operate near 900 nm, where standard single-mode fibers experience significant losses. We address this by employing a hollow-core fiber engineered for low-loss transmission at quantum dot wavelengths, with measured loss of 0.65 dB/km and potentially as low as 0.12 dB/km near 934 nm. The fiber also supports strong classical signals at 1550 nm without adding Raman noise. Using this platform, we transmit all four BB84 polarization states from an InAs quantum dot over 340 m with 0.1% QBER, preserving single-photon purity and indistinguishability even in the presence of a strong classical signal. These results highlight how tailored transmission media enable quantum networks beyond the limits of standard telecom fibers.
A quantum key distribution (QKD) system has been developed, using a standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz. The QKD system implements a polarization encoded version of the B92 protocol. The system employs vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, and silicon single photon avalanche diodes as the single photon detectors. A distributed feedback laser of emission wavelength 1.3 /spl mu/m, and a linear gain germanium avalanche photodiode was used to optically synchronize individual photons over the standard telecommunications fiber. The QKD system exhibited a quantum bit error rate (QBER) of 1.4%, and an estimated net bit rate (NBR) greater than 100 000 bits/sup -1/ for a 4.2-km transmission range. For a 10-km fiber range, a QBER of 2.1%, and an estimated NBR of greater than 7000 bits/sup -1/ was achieved.