Haojie Zhang

Enhanced all-optical modulation in a graphene-coated fibre with low insertion loss

Graphene is a highly versatile two-dimensional material platform that offers exceptional optical and electrical properties. Of these, its dynamic conductivity and low effective carrier mass are of particular interest for optoelectronic applications as they underpin the material’s broadband nonlinear optical absorption and ultra-fast carrier mobility, respectively. In this paper, we utilize these phenomena to demonstrate a high-speed, in-fibre optical modulator developed on a side-polished optical fibre platform. An especially low insertion loss (<1 dB) was achieved by polishing the fibre to a near atomically smooth surface (<1 nm RMS), which minimized scattering and ensured excellent contact between the graphene film and the fibre. In order to enhance the light-matter interaction, the graphene film is coated with a high index polyvinyl butyral layer, which has the added advantage of acting as a barrier to the surrounding environment. Using this innovative approach, we have fabricated a robust and stable all-fibre device with an extinction ratio as high as 9 dB and operation bandwidth of 0.5 THz. These results represent a key step towards the integration of low-dimensional materials within standard telecoms networks.

Graphene-Based Fiber Polarizer With PVB-Enhanced Light Interaction

Graphene is a two-dimensional material which, as a result of its excellent photonic properties, has been investigated for a wide range of optical applications. In this paper, we propose and fabricate a commercial grade broadband graphene-based fiber polarizer using a low loss side-polished optical fiber platform. A high index polyvinyl butyral layer is used to enhance the light-graphene interaction of the evanescent field of the core guided mode to simultaneously obtain a high extinction ratio ~37.5 dB with a low device loss ~1 dB. Characterization of the optical properties reveals that the polarizer retains low transmission losses and high extinction ratios across an extended telecoms band. The results demonstrate that side-polished fibers are a useful platform for leveraging the unique properties of low-dimensional materials in a robust and compact device geometry.

Optical-resonance-enhanced nonlinearities in a MoS 2 -coated single-mode fiber

Few-layer molybdenum disulfide (MoS2) has an electronic band structure that is dependent on the number of layers and, therefore, is a very promising material for an array of optoelectronic, photonic, and lasing applications. In this Letter, we make use of a side-polished optical fiber platform to gain access to the nonlinear optical properties of the MoS2 material. We show that the nonlinear response can be significantly enhanced via resonant coupling to the thin film material, allowing for the observation of optical modulation and spectral broadening in the telecom band. This route to access the nonlinear properties of two-dimensional materials promises to yield new insights into their photonic properties.

Data set for Optical-Resonance-Enhanced Nonlinearities in a MoS2-Coated Single-Mode Fiber

Data for the paper Healy, N et al (2018) Optical-resonance-enhanced nonlinearities in a MoS2-coated single-mode fiber Optical Letters.The file contains the data for plotting:Fig. 2. (a) Experimental absorption spectrum of the MoS2 - coated fiber device (∼ ± 5% uncertainty for each measurement). (b) Simulated absorption spectrumFig. 3. Nonlinear saturable absorption measurements (∼ ± 5% uncertainty for each measurement). Transmittance of MoS2 - coated fiber device as a function of average input powerFig. 4. Output spectral evolution at different input peak powers to illustrate spectral broadeningFig. 6. Normalised intensity of the probe light as a function of the pump-probe time delay.Fig. 6 Inset exponential fit of the falling edgeDetails of the methods used for the generation of the data can be found in the paper.

MoS 2 coated side polished fibers for nonlinear optics

Owing to their wide range of exceptional properties, two-dimensional (2D) materials have emerged as exciting media for the development of highly functional optoelectronic devices. Of these materials, the transition-metal dichalcogenides (TMDCs) are of particular interest as, unlike graphene, they are often semiconductors, and their optoelectronic properties can be tuned quite dramatically by controlling the material thickness. For example, in some materials it is possible to tune the electronic bandgap from indirect in a few layers, to direct in a single layer, of significant interest for the development of lasers. Here we focus our investigations on few-layer molybdenum disulfide (MoS2) materials for use in nonlinear optical applications. In this material, as well as controlling the bandgap, the layer thickness can be used to control the size of the nonlinear coefficients, with the second order nonlinearity turning on when the layer number is odd [1].

A Tuneable Multi-Core to Single Mode Fiber Coupler

We demonstrate a low loss, wideband multi-core to single-mode fiber coupler using a modified side-polishing technique. The coupler was designed to access light from a single core of the multi-core fiber without disrupting the signal propagation in the remaining cores. The coupling ratio between the two fibers can be continuously tuned over the entire spectral band via a simple mechanical displacement method. We expect that such couplers will be of use for monitoring, splitting, and multiplexing applications in future multi-core communication and sensing systems.

Functionalized optical fibers for non-linear optics

The state of the art of functionalized optical fibers will be reviewed. The discussion will include, but not be limited to, semiconductor optical fibers and fibers that have been integrated with low-dimensional materials.