Hou Lan-Tian

Fabrication of glass photonic crystal fibers with a die-cast process

We demonstrate a novel method for the fabrication of glass photonic crystal fibers (PCFs) with a die-cast process. SF6 glass is used as the material for PCFs, and the die is made of heat-resisting alloy steel, whose inner structure matches the PCFs structure. The die is put vertically in the vessel with SF6 glass, and the vacuum hose is attached to the top of the die. The die and glass are put in the furnace to heat at 870 K. The die is slowly filled with the softening glass under vacuum conduction until it is full. It is kept in the furnace to anneal at a rate of 20 K/h to remove the thermal stress that could lead to cracks. The outer tube of the die is taken apart when its temperature is close to room temperature, and the fused glass bundle is etched in an acidic solution to remove the heat-resisting alloy steel rods. Thus, the etched bundle is ready to use as a PCF preform. The PCF is observed in the generation of a supercontinuum, with the flat plateau in the spectrum of the output emission stretching from 400 to 1400 nm by experimental measurement. The transmission loss is 0.2-0.3 dB/m at wavelengths of 420-900 nm.

Tailoring nonlinearity and dispersion of photonic crystal fibers using hybrid cladding

We present a hybrid cladding photonic crystal fiber for shaping high nonlinear and flattened dispersion in a wide range of wavelengths. The new structure adopts hybrid cladding with different pitches, air-holes diameters and air-holes arrayed fashions. The full-vector finite element method with perfectly matched layer is used to investigate the characteristics of the hybrid cladding photonic crystal fiber such as nonlinearity and dispersion properties. The influence of the cladding structure parameters on the nonlinear coefficient and geometric dispersion is analyzed. High nonlinear coefficient and the dispersion properties of fibers are tailored by adjusting the cladding structure parameters. A novel hybrid cladding photonic crystal fiber with high nonlinear coefficient and dispersion flattened which is suited for supercontinuum generation is designed.

Perfect punctured binary sequence pairs

This paper presents the definition of perfect punctured binary sequence pair and the combinatorial admissible conditions for searching the perfect punctured binary sequence pairs and proves that all of the pseudo-random binary sequences satisfy these conditions. Computer calculation verifies that the pseudo-random binary sequences with length up to N=127 can be easily turned into perfect punctured binary sequence pairs.

Design of Nearly Zero Dispersion Flattened Photonic Crystal Fiber with Double Cladding

A novel design of nearly zero dispersion Battened photonic crystal fiber (PCF) with double cladding is proposed. To employ traditional stack and draw technology, the cladding is composed of a traditional triangular lattice of air-holes and silica. The dispersion of the fiber is mainly engineered by the small air holes in the inner cladding, which are easily preserved in the fiber drawing procedure. The large air-holes in the outer cladding are mainly for light confinement. Thus, the dispersion property of the PCF is insensitive to the deformation of the air holes in the outer cladding. Using 8 layers of air-hole ring, the loss of the fundamental mode for the PCF is as low as 0.13 dB/km at 1.55 μm. The dispersion of the PCF fluctuates from −0.023 to 0.021 pskm−1 nm−1 in the range 1.45–1.625 μm.

Design of Double Cladding Nearly Zero Dispersion Flattened Nonlinear Photonic Crystal Fiber

We present a design of double cladding nearly zero dispersion flattened nonlinear photonic crystal fiber (PCF) with the core consisting of seven missing holes. The dispersion of the designed PCF fluctuates from -0.28 to 0.29 ps·km−1·nm−1 in the range of 1.35-1.795μm and the dispersion slope is −0.0038 ps·km−1·nm−2 at 1.55 μm. Due to its small air-hole to air-hole pitch in the inner cladding, the effective mode area is 6.48μm2 and the effective nonlinearity γ is as high as 13.78 W−1 km−1 at 1.55 μm. Two layers of air-hole rings in the outer cladding ensures the loss of the fundamental mode to be 2.9dB/km at 1.55 μm and two more air-hole rings can further reduce the fundamental modes loss to the level of 4.2 × 10−3 dB/km.

Flat Supercontinuum Generation within the Telecommunication Wave Bands in a Photonic Crystal Fiber with Central Holes

Flat supercontinuum in the telecommunication wave bands of E+S+C is generated by coupling a train of femtosecond pulses generated by a mode-locked Ti:sapphire laser into the fundamental mode of a photonic crystal fiber with central holes fabricated in our lab. The pulse experiences the anomalous dispersion regime, and the soliton dynamic effect plays an important role in supercontinuum generation. The output spectrum in the wavelength range of 1360–1565 nm does not include significant ripples due to higher pump peak power, and the normalized intensity shows less fluctuation.

Design of a High-Nonlinearity Single-Mode Holey Fiber with Flattened Dispersion around 800 nm

We numerically demonstrate a high-nonlinearity single-mode holey fiber with flattened dispersion around the Ti-Za laser band at 800 nm. The dispersion profile of the fiber has the shape of a quadratic curve, which reaches its maximum 5.96 ps.km−1 .nm−1 at 800 nm and its minimum –0.897 ps.km−1 .nm−1 at both 750 and 850 nm. The nonlinear coefficient is 170 W−1 km−1 at 800 nm and no higher order modes exit. A six-layer air-hole cladding ensures a loss less than 0.067 db/m in the 750 to 850 nm range. Two more air-hole rings will reduce the loss to below 0.1 db/km.

Anti-Stokes Line in an Index-Guiding Photonic Crystal Fibre with Two Zero-Dispersion Wavelengths

An index-guiding photonic crystal fibre with a small hole in the core is fabricated. The simulated results show that the first higher order mode possesses two zero-dispersion wavelengths, and the phase-matching is possible in the anomalous dispersion regime between the two zero-dispersion wavelengths. Using 200 fs Ti: sapphire laser of 820, 830 and 840 nm, the anti-Stokes line around 530 nm can be generated efficiently. The maximum ratio of the anti-Stokes signal energy to the pump component in the output spectrum is estimated to be 1.03 and the conversion efficiency is above 50%.

Small-Pitch Kagome Hollow-Core Photonic Crystal Fibre

A hollow-core photonic crystal fibre (HC-PCF) based on small-pitch kagome lattice cladding is designed and fabricated. The pitch of the fibre is only 2.45μm and it corresponds to a region of low normalized frequency which has never been investigated before. Both experiments and calculations show that this kagome HC-PCF has a broad optical transmission band from 400 nm to 900 nm, covering the whole visible and near infrared region of the spectrum. Additionally, the loss curve of the fibre is flat in the visible region and the minimum of the loss achieves 0.16dB/m, which is lower than the loss of the kagome HC-PCFs reported before. Furthermore, this fibre can well confine the modes in the air core. No surface modes can be detected in the surrounding silica of the hollow core.

Adaptive split-step Fourier method for simulating ultrashort laser pulse propagation in photonic crystal fibres

In this paper, the generalized nonlinear Schrodinger equation (GNLSE) is solved by an adaptive split-step Fourier method (ASSFM). It is found that ASSFM must be used to solve GNLSE to ensure precision when the soliton self-frequency shift is remarkable and the photonic crystal fibre (PCF) parameters vary with the frequency considerably. The precision of numerical simulation by using ASSFM is higher than that by using split-step Fourier method in the process of laser pulse propagation in PCFs due to the fact that the variation of fibre parameters with the peak frequency in the pulse spectrum can be taken into account fully.