Km Of Optical Fiber Research Articles

Low-power optical feeder for VDSL over twisted pair for last mile access networks

In this paper, we describe an ultra-low-power optoelectronic very-high-data-rate digital subscriber line (VDSL) system, enabling broadband access to the home over 10 km of optical fiber and 1 km of twisted pair. The cabinet/distribution point interface has a footprint of just 3 /spl times/ 3 /spl times/ 1 cm, and consumes only 165 mW. A quadrature-amplitude-modulation (QAM) scheme was used for system tests with 10 Mb/s full duplex achieved, and up to 40-dB up/downstream channel isolation is obtained using hybrid transformers.

Long-distance distribution of time-bin entanglement generated in a cooled fiber

This paper reports the first demonstration of the generation and distribution of time-bin entangled photon pairs in the 1.5-microm band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences.

100 km differential phase shift quantum key distribution experiment with low jitter up-conversion detectors

We present a quantum key distribution experiment in which keys that were secure against all individual eavesdropping attacks allowed by quantum mechanics were distributed over 100 km of optical fiber. We implemented the differential phase shift quantum key distribution protocol and used low timing jitter 1.55 microm single-photon detectors based on frequency up-conversion in periodically poled lithium niobate waveguides and silicon avalanche photodiodes. Based on the security analysis of the protocol against general individual attacks, we generated secure keys at a practical rate of 166 bit/s over 100 km of fiber. The use of the low jitter detectors also increased the sifted key generation rate to 2 Mbit/s over 10 km of fiber.

Chaos-based communications at high bit rates using commercial fibre-optic links

Chaotic signals have been proposed as broadband information carriers with the potential of providing a high level of robustness and privacy in data transmission. Laboratory demonstrations of chaos-based optical communications have already shown the potential of this technology, but a field experiment using commercial optical networks has not been undertaken so far. Here we demonstrate high-speed long-distance communication based on chaos synchronization over a commercial fibre-optic channel. An optical carrier wave generated by a chaotic laser is used to encode a message for transmission over 120 km of optical fibre in the metropolitan area network of Athens, Greece. The message is decoded using an appropriate second laser which, by synchronizing with the chaotic carrier, allows for the separation of the carrier and the message. Transmission rates in the gigabit per second range are achieved, with corresponding bit-error rates below 10(-7). The system uses matched pairs of semiconductor lasers as chaotic emitters and receivers, and off-the-shelf fibre-optic telecommunication components. Our results show that information can be transmitted at high bit rates using deterministic chaos in a manner that is robust to perturbations and channel disturbances unavoidable under real-world conditions.

Long-distance entanglement swapping with photons from separated sources

We report the first experimental realization of entanglement swapping over large distances in optical fibers. Two photons separated by more than two km of optical fibers are entangled, although they never directly interacted. We use two pairs of time-bin entangled qubits created in spatially separated sources and carried by photons at telecommunication wavelengths. A partial Bell state measurement is performed with one photon from each pair which projects the two remaining photons, formerly independent onto an entangled state. A visibility high enough to violate a Bell inequality is reported, after both photons have each travelled through 1.1 km of optical fiber.

Laser frequency noise suppression by arm-locking in LISA: progress towards a bench-top demonstration

Overcoming laser frequency noise is a significant technical challenge for achieving the design sensitivity of the Laser Interferometer Space Antenna (LISA) gravitational wave detector. Arm-locking is a recently proposed technique for suppressing frequency noise in LISA and can be used in addition to the established techniques of pre-stabilization and time-delay interferometry. Incorporation of arm-locking into LISA could provide many benefits, however experimental verification and testing is needed. We present the progress of an experimental test of arm-locking which uses 10 km of optical fibre to generate a large propagation time delay, analogous to the propagation delay in LISA.

Distribution of Time-Bin Entangled Qubits over 50 km of Optical Fiber

We report experimental distribution of time-bin entangled qubits over 50 km of optical fibers. Using actively stabilized preparation and measurement devices we demonstrate violation of the Clauser-Horne-Shimony-Holt Bell inequality by more than 15 standard deviations without removing the detector noise. In addition we report a proof-of principle experiment of quantum key distribution over 50 km of optical fibers using entangled photon.

Generation of polarization-entangled photon pairs and violation of Bell’s inequality using spontaneous four-wave mixing in a fiber loop

We report the generation of polarization entangled photon pairs in the 1550-nm wavelength band using spontaneous four-wave mixing in a dispersion-shifted fiber loop. The use of the fiber-loop configuration made it possible to generate polarization entangled states very stably. With accidental coincidences subtracted, we obtained coincidence fringes with $>90%$ visibilities, and observed a violation of Bell's inequality by seven standard deviations. We also confirmed the preservation of the quantum correlation between the photons even after they had been separated by 20 km of optical fiber.

Long distance quantum teleportation in a quantum relay configuration.

A long distance quantum teleportation experiment with a fiber-delayed Bell state measurement (BSM) is reported. The source creating the qubits to be teleported and the source creating the necessary entangled state are connected to the beam splitter realizing the BSM by two 2 km long optical fibers. In addition, the teleported qubits are analyzed after 2.2 km of optical fiber, in another laboratory separated by 55 m. Time-bin qubits carried by photons at 1310 nm are teleported onto photons at 1550 nm. The fidelity is of 77%, above the maximal value obtainable without entanglement. This is the first realization of an elementary quantum relay over significant distances, which will allow an increase in the range of quantum communication and quantum key distribution.

Practical quantum key distribution with polarization entangled photons

We present an entangled-state quantum cryptography system that operated for the first time in a real-world application scenario. The full key generation protocol was performed in real-time between two distributed embedded hardware devices, which were connected by 1.45 km of optical fiber, installed for this experiment in the Vienna sewage system. The generated quantum key was immediately handed over and used by a secure communication application.

Remote microwave wavelength spectrometry using an infrared fibre optic telecommunication network

Reported is the first experimental demonstration of remote microwave spectroscopy of an absorbing gas over a fibre optic link [J.F. Alder, J.G. Baker, Quantitive Millimetre Wavelength Spectrometry, Royal Society of Chemistry, Cambridge, 2002]. Using a high speed telecommunication network and a 12 GHz YIG source, a microwave modulated infrared carrier has been transmitted down 1 km of optical fibre. Absorption lines as weak as 2.83×10 −5 m −1 have been observed by coupling the recovered microwave signal through a 2 m Stark modulated absorption cell.

Perfectly synchronized bit-parallel WDM data transmission over a single optical fiber

We demonstrate a bit-level synchronization technique by conducting a bit-parallel wavelength-division-multiplexed (WDM) data transmission over 27.5 km of optical fiber. Multiple WDM channels, which may represent individual bits in a byte or a word in parallel computer input-output, are transmitted in the optical fiber in non-return-to-zero format. These bits experience time skew due to group velocity dispersion. By sampling with an all-optical switch in the range where all these bits overlap, we obtained perfectly synchronized WDM signals. The synchronized WDM channels are demultiplexed with an array waveguide grating. Bit error rates below 10/sup -10/ are measured for each channel. The spectral range of the experimental demonstration covers about 24 nm with the smallest wavelength separation of 1.4 mm, enough to pack 16 bits into the span. More bits are available if smaller channel-separation and wider spectral span are employed.

1.24 Gbit/s optical code division multiplexing transmission over 40 km dispersion-shifted fibre by bipolar coding using broadband incoherent light source

Error-free 1.24 Gbit/s OCDM transmission over 40 km of optical fibre based on the bipolar coding of spectrum sliced broadband incoherent light has been experimentally demonstrated for the first time.

Multifunctional fiber-optic microwave links based on remote heterodyne detection

The multifunctionality of microwave links based on remote heterodyne detection (RHD) of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection (DD) in conjunction with optical intensity modulation is used to implement fiber-optic microwave links. The resulting links are inherently transparent. As opposed to DD links, RHD links can perform radio-system functionalities such as modulation and frequency conversion in addition to transparency. All of these three functionalities are presented and experimentally demonstrated with an RHD link based on a dual-frequency laser transmitter with two offset phase-locked semiconductor lasers. In the modulating link, a 1-Gb/s baseband signal is QPSK modulated onto a 9-GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100-Mb/s PSK signal from a 2-GHz carrier to a 9-GHz carrier with penalty-free transmission over 25 km of optical fiber. Finally, the transparent link transmits a standard FM video 7.6-GHz radio-link signal over 25 km of optical fiber without measurable distortion.

Multi-functional fibre-optic microwave links

The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition to signal transmission. All three functionalities are presented and experimentally demonstrated with a remote heterodyne detection link based on a dual-frequency laser transmitter with two offset phase locked semiconductor lasers. In the modulating link a 1Gbit/s baseband signal is QPSK modulated onto a 9GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100Mbit/s PSK signal from a 2GHz carrier to a 9GHz carrier with penalty-free transmission over 25km of optical fibre. Finally, the transparent signal recovering link transmits a standard FM video 7.6GHz radio-link signal over 25km of optical fibre without measurable distortion.

Vertical cavity lasers for telecom applications

The authors review the development of long-wavelength vertical cavity lasers (VCLs) for telecommunications applications. Long-wavelength VCLs provide an attractive choice for inexpensive fiber optic communication. The different designs of such lasers are presented, along with the advantages and disadvantages of each. System requirements and experiments are also presented at 2.5 Gb/s over 200 km of optical fiber.

A mobile broad-band communication system based on mode-locked lasers

A concept is proposed for a pico-cellular network for broad-band mobile communication on a millimeter-wave basis. How microwave optical-signal-processing techniques based on mode-locked lasers (MLLs), optical modulators, and high-speed photo diodes (PD's) can advantageously be applied in the optical feeder lines of a pico-cellular network at 60 GHz is investigated. The external cavity MLL (at 81.25 GHz) used for the experiments showed a single-sideband (SSB) phase noise of -59 dBc/Hz at 100-Hz offset, when actively locked at 6.25 GHz. With the PD, and limited by the V-band mixer equipment, spectral harmonics up to 100 GHz could be detected. For the downlink configuration, a 400-MHz subcarrier is modulated with a 155-Mb/s data signal and upconverted to 62.9 GHz using an MLL and a fast PD. The upconverted sideband at 62.9 GHz was received with an optical power of -14.3-dBm at a bit-error-rate (BER) equal to 10/sup -9/ without any additional penalty due to transmitting the signal over 3 km of optical fiber. BER measurements at 155 Mb/s down to 10/sup -11/ were made. For the uplink, the digitally encoded RF signal is downconverted also by optical microwave signal processing. A 155-Mb/s data encoded 19.21-GHz signal is downconverted to 460 MHz using a mode-locked laser, an optical modulator, and a 600-MHz optical receiver front end. A receiver sensitivity of -24.5 dBm (BER equal to 10/sup -9/) is demonstrated with the microwave signal being transmitted over a 1-m radio link and 3 km of optical fiber.

Transmission of millimeter-wave signals using uncoated telecommunications-grade distributed feedback lasers

Transmission of 2-Mb/s data at a subcarrier frequency of 35 GHz over 2.2 km of optical fiber by resonant modulation of an uncoated monolithic single-contact distributed feedback (DFB) laser is demonstrated. Modulation response, carrier-to-noise ratio and bit-error-rate results are reported. The tolerance of the resonant round-trip frequency to the DFB facet cleaving process and the device length uncertainty due to cleaving is also addressed in detail by computer simulation.

Transmission of 60-GHz signals over 100 km of optical fiber using a dual-mode semiconductor laser source

High-purity 60-GHz signals, generated using a dual-mode DFB semiconductor laser, have been transmitted over 100 km of standard optical fiber with no observable degradation in purity. This device is shown to be a simple and compact optical source of high-purity 60-GHz signals for long-reach fiber-fed millimeter-wave radio systems.

120 Mbit/s QPSK radio-fibre transmission over 100 km of standard fibre at 60 GHz using a master/slave injection-locked DFB laser source

A 120 Mbit/s QPSK radio signal has been transported over 100 km of optical fibre and then transmitted on a 60 GHz carrier in free-space. This was achieved using an injection-locked master/slave DFB arrangement to generate the carrier centrally and a remote modulation architecture for mixing the carrier with data signals.