Xin Gai

Producing air-stable monolayers of phosphorene and their defect engineering

It has been a long-standing challenge to produce air-stable few- or monolayer samples of phosphorene because thin phosphorene films degrade rapidly in ambient conditions. Here we demonstrate a new highly controllable method for fabricating high quality, air-stable phosphorene films with a designated number of layers ranging from a few down to monolayer. Our approach involves the use of oxygen plasma dry etching to thin down thick-exfoliated phosphorene flakes, layer by layer with atomic precision. Moreover, in a stabilized phosphorene monolayer, we were able to precisely engineer defects for the first time, which led to efficient emission of photons at new frequencies in the near infrared at room temperature. In addition, we demonstrate the use of an electrostatic gate to tune the photon emission from the defects in a monolayer phosphorene. This could lead to new electronic and optoelectronic devices, such as electrically tunable, broadband near infrared lighting devices operating at room temperature.

Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber

A low-loss suspended core As(38)Se(62) fiber with core diameter of 4.5 μm and a zero-dispersion wavelength of 3.5 μm was used for mid-infrared supercontinuum generation. The dispersion of the fiber was measured from 2.9 to 4.2 μm and was in good correspondence with the calculated dispersion. An optical parametric amplifier delivering 320 fs pulses with a peak power of 14.8 kW at a repetition rate of 21 MHz was used to pump 18 cm of suspended core fiber at different wavelengths from 3.3 to 4.7 μm. By pumping at 4.4 μm with a peak power of 5.2 kW coupled to the fiber a supercontinuum spanning from 1.7 to 7.5 μm with an average output power of 15.6 mW and an average power >5.0 μm of 4.7 mW was obtained.

Mid-infrared supercontinuum generation in chalcogenides

Yi Yu acknowledges the financial support from the China Scholarship Council for her PhD Scholarship No. 201206110048. This research was conducted by the Australian Research Council Centre of Excellence for Ultrahigh Bandwidth Devices for Optical Systems (project number CE110001018). Dr Zhiyong Yang is supported by ARC DECRA project DE120101036 and Dr Duk-Yong Choi by ARC Future Fellowship FT110100853.

Progress in optical waveguides fabricated from chalcogenide glasses

We review the fabrication processes and properties of waveguides that have been made from chalcogenide glasses including highly nonlinear waveguides developed for all-optical processing.

Low-loss chalcogenide waveguides for chemical sensing in the mid-infrared.

We report the characteristics of low-loss chalcogenide waveguides for sensing in the mid-infrared (MIR). The waveguides consisted of a Ge₁₁.₅As₂₄Se₆₄.₅ rib waveguide core with a 10nm fluoropolymer coating on a Ge₁₁.₅As₂₄S₆₄.₅ bottom cladding and were fabricated by thermal evaporation, photolithography and ICP plasma etching. Over most of the functional group band from 1500 to 4000 cm⁻¹ the losses were < 1 dB/cm with a minimum of 0.3 dB/cm at 2000 cm⁻¹. The basic capabilities of these waveguides for spectroscopy were demonstrated by measuring the absorption spectrum of soluble Prussian blue in Dimethyl Sulphoxide.

Net-gain from a parametric amplifier on a chalcogenide optical chip

We report first observation of net-gain from an optical parametric amplifier in a planar waveguide. This was achieved in a low-loss As(2)S(3) planar waveguide, with a strong nonlinearity (gamma approximately 10 /W/m) and tailored anomalous dispersion yielding efficient Raman-assisted four-wave mixing at telecom wavelengths. The experiments were in good agreement with theory, and indicate a peak net-gain greater than +16 dB for the signal and idler (+30 dB neglecting coupling losses) and a broad bandwidth spanning 180 nm.

Systematic z-scan measurements of the third order nonlinearity of chalcogenide glasses

We report measurements of the third order optical nonlinearity of 51 chalcogenide glasses in the near infrared. Substituting more polarizable elements (Se for S, Sb for As) into the glasses increased their nonlinearity but also reduced the optical bandgap increasing two-photon absorption. Overall the measured values are an extremely good fit to the semi-empirical Miller’s rule whilst the normalized real and imaginary parts are in satisfactory agreement with the scaling for indirect gap semiconductors reported by Dinu. At 1550nm we find that there is an upper limit to the nonlinearity of ≈10−13cm2/W above which two-photon absorption becomes significant.

Supercontinuum generation in the mid-infrared from a dispersion-engineered As2S3 glass rib waveguide.

We report the generation of a mid-infrared supercontinuum created by ≈7.5 ps duration pulses at 3260 nm passing through a dispersion engineered As(2)S(3) rib waveguide. The threshold for a 6.6 cm long waveguide was around 800 W and at 1700 W the spectrum extended from ≈2.9-4.2 μm and was limited on the long wavelength side by absorption in the cladding of this particular waveguide.

Dispersion engineered Ge₁₁.₅As₂₄Se₆₄.₅ nanowires with a nonlinear parameter of 136W⁻¹m⁻¹ at 1550nm

We have fabricated 630 × 500 nm nanowires from Ge(11.5)As(24)Se(64.5) chalcogenide glass by electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. The loss of the nanowire was measured to be 2.6 dB/cm for the fundamental TM mode. The nonlinear coefficient (γ) was determined to be ≈136 ± 7 W(-1)m(-1) at 1550 nm by both CW four-wave-mixing (FWM) and modeling. Supercontinuum (SC) was produced in an 18 mm long nanowire pumped by 1 ps pulses with peak power of 25 W.

Photowritten high-Q cavities in two-dimensional chalcogenide glass photonic crystals

We demonstrate a high-Q(approximately 125,000) photonic crystal (PhC) cavity formed using a postprocessing optical exposure technique where the refractive index of a photosensitive chalcogenide PhC is modified locally. The evolution of the cavity resonances was monitored in situ during writing using a tapered fiber evanescent coupling system, and the Q of 125,000 represents 1 order of magnitude increase over previously reported cavities in two-dimensional chalcogenide glass PhC.