Abstract:The secure distribution of a secret key is the weakest point of shared-key encryption protocols. While quantum key distribution schemes could theoretically provide unconditional security, their practical implementation remains technologically challenging. Here we provide an extended analysis and present an experimental support of a concept for a classical key generation system, based on establishing laser oscillation between two parties, which is realized using standard fiber-optic components. In our Ultra-long Fiber Laser (UFL) system, each user places a randomly chosen, spectrally selective mirror at his/her end of a fiber laser, with the two-mirror choice representing a key bit. We demonstrate the ability of each user to extract the mirror choice of the other using a simple analysis of the UFL signal, while an adversary can only reconstruct a small fraction of the key. The simplicity of this system renders it a promising alternative for practical key distribution in the optical domain. References and links1. S. Singh, The Code Book: The science of secrecy from ancient Egypt to quantum cryptography (Fourth Estate, 1999). 2. G. Vernam, "Cipher printing telegraph systems for secret wire and radio telegraphic communications," J.Am. Inst. Electr. Eng. 45, 109-116 (1926). 3. C. H. Bennett, and G. Brassard, "Quantum public key distribution system," IBM Tech. Discl. Bull. 28, 3153-3163 (1985). 4. A. K. Ekert, "Quantum cryptography based on Bell's theorem," Phys. Rev. Lett. 67, 661-663 (1991). 5. N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, "Quantum cryptography," Rev. Mod. Phys. 74, 145-195 (2002). 6. P. W. Shor, and J. Preskill, "Simple proof of security of the BB84 quantum key distribution protocol," Phys.Rev. Lett. 85, 441-444 (2000). distribution over a 40-dB channel loss using superconducting single photon detectors," Nat. Photon. 1, 343-348 (2007). 21. L. Tancevski, I. Andonovich, and J. Budin, "Secure optical network architecture utilizing wavelength hopping / time spreading codes," IEEE Photon.

We propose an on-chip integrated differential optical microring refractive index sensing platform which leverages laminar flow conditions. Close spacing between a sensing and a reference resonator, and sharing the same microfluidic channel allows the two resonators to experience similar environmental disturbances, such as temperature fluctuations and fluidic-induced transients, achieving reliable and sensitive sensing performance. We obtain a noise floor of 80.0 MHz (0.3 pm) and a bulk refractive index sensitivity of 17.0 THz per refractive index unit (RIU) (64.2 nm/RIU), achieving a limit of detection of 1.4×10(-5) RIU in a 30 min and an 8°C window.

Abstract-A simple and reconfigurable scheme for photonic generation of ultra-wideband (UWB) waveforms is proposed, simulated, and demonstrated. The technique relies on pulse compression in a highly nonlinear fiber and subsequent differential detection. A center frequency of 25 GHz and a fractional bandwidth of 120% are obtained. The generated waveform is also adjusted to closely approximate the spectral mask for unlicensed UWB indoor wireless communications.

Abstract-The generation of ultra-wideband (UWB), high-frequency waveforms based on nonlinear propagation of pulses in optical fibers is reported. Self-phase modulation and subsequent optical filtering are used to implement all-optical edge detectors, which generate two temporally-narrowed replicas of each input pulse. The shapes of the narrowed pulses are subtracted from that of the original one in a balanced differential detector, providing a UWB waveform. The use of multiple replicas and nonlinear propagation allows for the generation of higher-order pulse shapes, beyond those of a Gaussian monocycle or doublet. The output pulse shape is reconfigurable through adjusting the input power and detuning the optical filters. The central radio-frequency of the generated waveforms is as high as 34 GHz, with a fractional bandwidth of 70%.

The output of a mode-locked erbium-doped ring fiber laser incorporating a section of a polarization-maintaining (PM) fiber is investigated in both numerical simulations and experiments. With proper inline polarization control, the laser can be set to emit a train of pulses, separated by the differential group delay of the PM section. Repetition rates as high as 500 GHz are experimentally observed. The results provide an added insight into the role of birefringence in mode-locked lasers based on nonlinear polarization rotation.