Comparing ultrastable lasers at 7 × 10−17 fractional frequency instability through a 2220 km optical fibre network

Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented measurement precision that impacts on fields such as atomic timekeeping, tests of fundamental physics, and geodesy. To characterise an ultrastable laser it needs to be compared with a laser of similar performance, but a suitable system may not be available locally. Here, we report a comparison of two geographically separated lasers, over the longest ever reported metrological optical fibre link network, measuring 2220 km in length, at a state-of-the-art fractional-frequency instability of 7 × 10−17 for averaging times between 30 s and 200 s. The measurements also allow the short-term instability of the complete optical fibre link network to be directly observed without using a loop-back fibre. Based on the characterisation of the noise in the lasers and optical fibre link network over different timescales, we investigate the potential for disseminating ultrastable light to improve the performance of remote optical clocks.

Endoscopic Imaging Using a Multimode Optical Fibre Calibrated with Multiple Internal References

The interferometric acquisition of the transmission matrix (TM) of a multimode optical fibre (MMF), which is at the heart of multimode fibre-based endoscopic imaging methods, requires using a reference beam. Attempts to use an internal reference, that is to provide the reference in a common pathway geometry through the MMF itself, lead to a speckled reference intensity and consequential occurrence of “blind spots”—locations where insufficient optical power in the reference wave inflicts strong measurement errors. Here we show that combining a relatively small number of TMs, which are measured using different internal references, facilitates a complete elimination of blind spots, and thereby a significant enhancement of the imaging quality.

Nonlinear Mixing of Two Laser Beams and THz Plasmons Generation in Graphene Coated Optical Fibre

Graphene is a most suitable material for Terahertz (THz) radiation generation. An efficient mechanism of THz surface plasmons (THz SPs) generation in graphene coated optical fibre by nonlinear mixing of two laser beams is proposed. The graphene coated fiber supports THz SPs with plasmon resonance in the THz regime and controllable by thickness of graphene and radius of optical fibre. The laser beams exert a difference frequency ponderomotive force on the electrons of the graphene. This ponderomotive force induces a nonlinear current in graphene which driving the difference frequency THz SPs. The normalized amplitude of THz SPs decreases with frequency as the nonlinear coupling gets weaker. The efficiency of the device is around 0.01% at a laser intensity of 3x1014 W/cm2. This scheme will be useful making the compact THz radiation source and THz plasmon sensor.

Design of Radio Over Plastic Optical Fibre for Broadband Indoor Access Network

Indoor wireless traffic increases exponentially. Radio over fibre technology has been used to provide broadband services in the access network. Plastic Optical Fibre (POF) has been considered as a promising waveguide to be used as backhaul link for indoor access network. The RoF system uses an improved POF cable as a backhaul. A photonic antenna is developed by integrating a microstrip patch antenna with an opto-electronic converter. A standard inset fed microstrip patch antenna used for the wireless transmission and reception is designed using CST software tool. A RoF communication system based on the developed POF is designed and simulated using Optisystem software tool. The Bit Error Rate (BER) performance of the system in terms of Quality factor is evaluated. A maximum achievable POF cable length of 117 m for an On-Off Keying (OOK) transmission data rate of 1 Gbps with an acceptable Quality factor of 7.0 is obtained. When the developed RoF system was used to transmit 10 Gbps and 50 Gbps data, the achievable cable lengths reduced to 80 m and 63 m, respectively. Keywords— Plastic Optical Fibre, RoF, photonic antenna, and modal dispersion