Hybrid device of hexagonal boron nitride nanoflakes with defect centres and a nano-fibre Bragg cavity

Solid-state quantum emitters coupled with a single mode fibre are of interest for photonic and quantum applications. In this context, nanofibre Bragg cavities (NFBCs), which are microcavities fabricated in an optical nanofibre, are promising devices because they can efficiently couple photons emitted from the quantum emitters to the single mode fibre. Recently, we have realized a hybrid device of an NFBC and a single colloidal CdSe/ZnS quantum dot. However, colloidal quantum dots exhibit inherent photo-bleaching. Thus, it is desired to couple an NFBC with hexagonal boron nitride (hBN) as stable quantum emitters. In this work, we realize a hybrid system of an NFBC and ensemble defect centres in hBN nanoflakes. In this experiment, we fabricate NFBCs with a quality factor of 807 and a resonant wavelength at around 573 nm, which matches well with the fluorescent wavelength of the hBN, using helium-focused ion beam (FIB) system. We also develop a manipulation system to place hBN nanoflakes on a cavity region of the NFBCs and realize a hybrid device with an NFBC. By exciting the nanoflakes via an objective lens and collecting the fluorescence through the NFBC, we observe a sharp emission peak at the resonant wavelength of the NFBC.

Effect of anisotropy of a single-mode fibre on lightning-induced rotation of polarisation of a light signal in an optical ground wire

A numerical model is constructed for calculating lightning-induced rapid changes in the polarisation state of a light signal at the output of a fibre-optic communication line with an optical ground wire. It is shown that taking into account anisotropy of real optical fibres has a noticeable effect on the shape of the polarisation rotation speed time profile. It is found that the maximum rate of change in the polarisation state and its temporal profile depend on the location of the lightning strike in the fibre span, the magnitude of fibre anisotropy and the direction of propagation of a light wave.

SDM transmission of orbital angular momentum mode channels over a multi-ring-core fibre

Spatial division multiplexed optical transmission over a multi-ring-core orbital angular momentum (OAM) fibre is reported for the first time. The seven cores in the fibre each supports OAM modes belonging to mode groups (MGs) of topological charge |l| = 0–4. The MGs of |l| = 1–4 each contains four near-degenerate OAM modes that carry the combinations of opposite orbital and spin angular momenta. The weak coupling between these higher-order MGs as well as between the cores enables the simultaneous transmission of 56 OAM mode channels (two MGs per core of the topological charges |l| = 2 and 3) over the 60-km span, while only requiring modular 4 × 4 multi-input multi-output (MIMO) signal processing to equalize the mixing among the four mode channels in each MG that are strongly coupled – a feature that also minimizes the number of filter taps. The mode channels are launched using seven-core single-mode fibre fan-in devices, with the light in all seven cores converted into OAM modes via specially designed plates that carry seven off-axis-compensated phase masks matching the hexagonal configuration of the multi-core fibres. Each mode channel carries 10 WDM wavelengths, equivalently aggregating to a capacity of 31.4 Tbit/s (net 25.1 Tb/s) and a spectral efficiency (SE) of 62.7 bit/s/Hz (net 50.2 bit/s/Hz) with 28-GBaud QPSK modulation per data channel.

Raman Amplification Optimization in Short-Reach High Data Rate Coherent Transmission Systems

We compared the transmission performances of 600 Gbit/s PM-64QAM WDM signals over 75.6 km of single-mode fibre (SMF) using EDFA, discrete Raman, hybrid Raman/EDFA, and first-order or second-order (dual-order) distributed Raman amplifiers. Our numerical simulations and experimental results showed that the simple first-order distributed Raman scheme with backward pumping delivered the best transmission performance among all the schemes, notably better than the expected second-order Raman scheme, which gave a flatter signal power variation along the fibre. Using the first-order backward Raman pumping scheme demonstrated a better balance between the ASE noise and fibre nonlinearity and gave an optimal transmission performance over a relatively short distance of 75 km SMF.

Hybrid Device of Hexagonal Boron Nitride Nanoflakes with Defect Centres and a Nano-Fibre Bragg Cavity

Solid-state quantum emitters coupled with a single mode fibre are of interest for photonic and quantum applications. In this context, nanofibre Bragg cavities (NFBCs), which are microcavities fabricated in an optical nanofibre, are promising devices because they can efficiently couple photons emitted from the quantum emitters to the single mode fibre. Recently, we have realized a hybrid device of an NFBC and a single colloidal CdSe/ZnS quantum dot. However, colloidal quantum dots exhibit inherent photo-bleaching. Thus, it is desired to couple an NFBC with defect centres in hexagonal boron nitride (hBN) as stable quantum emitters. In this work, we realize a hybrid system of an NFBC and defect centres in hBN nanoflakes. In this experiment, we fabricate NFBCs with a quality factor of 807 and a resonant wavelength at around 573 nm, which matches well with the fluorescent wavelength of the defect centres in hBN, using a helium focused ion beam (FIB) system. We also develop a manipulation system to place hBN nanoflakes on a cavity region of the NFBCs and realize a hybrid device with an NFBC. By exciting the nanoflakes via an objective lens and collecting the fluorescence through the NFBC, we observe a sharp emission peak at the resonant wavelength of the NFBC.

Fabrication and Qualitative Analysis of an Optical Fibre EFPI-Based Temperature Sensor

The following presents a comparison of an extrinsic Fabry–Perot interferometer (EFPI)-based temperature sensor, constructed using a novel diaphragm manufacturing technique, with a reference all-glass EFPI temperature sensor. The novel diaphragm was manufactured using polyvinyl alcohol (PVA). The novel sensor fabrication involved fusing a single-mode fibre (SMF) to a length of fused quartz capillary, which has an inner diameter of 132 μm and a 220 μm outer diameter. The capillary was subsequently polished until the distal face of the capillary extended approximately 60 μm beyond that of the single mode fibre. Upon completion of polishing, the assembly is immersed in a solution of PVA. Controlled extraction resulted in creation of a thin diaphragm while simultaneously applying a protective coating to the fusion point of the SMF and capillary. The EFPI sensor is subsequently sealed in a second fluid-filled capillary, thereby creating a novel temperature sensor structure. Both temperature sensors were placed in a thermogravimetric analyser and heated from an indicated 30 °C to 100 °C to qualitatively compare sensitivities. Initial results indicated that the novel manufacturing technique both expedited production and produces a more sensitive sensor when compared to an all-glass construction.

Optically Powered Gas Monitoring System Using Single-Mode Fibre for Underground Coal Mines

We present an optically powered, intrinsically safe gas monitoring system to measure four essential environmental gases (CH4, CO2, CO and O2), together with ambient temperature and pressure, for underground mines. The system is based on three key technologies developed at UNSW: (1) power-over-fibre (PoF) at 1,550 nm using a single industry-standard, low-cost single-mode fibre (SMF) for both power delivery and information transmission, (2) liquid-crystal-based optical transducers for optical telemetry, and (3) ultra-low power consumption design of all electronics. Together, this approach allows each gas monitoring station to operate with less than 150 mW of optical power, meeting the intrinsic safety requirements specified by the IEC60079-28 standard. A 2-month field trial at BMA’s Broadmeadow underground mine proved the cabling compatibility to the mine’s existing optical network and the stability of the system performance. Compared with conventional electrically powered gas sensors, this technology bypasses the usual roadblocks of underground gas monitoring where electrical power is either unsafe or unavailable. Furthermore, using one fibre for both power delivery and communication enables longer distance coverage, reduces optical cabling and increases multiplexing possibilities and data throughput for better awareness of underground environment.