Current research / employment

Short abstract about IMPRS PhD project:

The transverse microstructure of air-silica photonic crystal fibers (PCFs) provides great flexibility in terms of dispersion and mode profile, as well as offering opportunities for the fabrication of a wide range of different in-fiber devices. In a unique procedure called selective hole closure technique, individual hollow channels in silica-air photonic crystal fibers are filled with pure Germanium by pumping in molten germanium at high pressure. The smallest channels filled so far are 600 nm in diameter, which is 10× smaller than in previous work. Electrical conductivity and micro-Raman measurements indicate that the resulting cm-long wires have a high degree of crystallinity.

Optical transmission spectra are measured in a sample with a single wire (diameter 1.7 micron, length 0.8mm) placed adjacent to the core of an endlessly single-mode photonic crystal fiber Fig.1 (a). This renders the fiber birefringent, as well as causing strong polarization-dependent transmission losses, with extinction ratios as high as 30 dB in the visible wavelength. In the IR, anti-crossings happens between the glass-core mode and resonances on the high index Ge wire which create a series of clear peaks in the loss spectrum of the fiber (related to the dips in the transmission spectrum) Fig. 1(b). The measurements agree closely with the results of finite-element simulations (using JCMWave) in which the wavelength dependence of the dielectric constants is taken fully into account. A toy model based on a multilayer structure is used to help interpret the results.

The temperature dependence of the anti-crossing wavelengths is measured, the preliminary results suggests that the structure might form the basis of a compact optical thermometer. Since Ge provides electrical conductance together with low-loss guidance in the mid-IR, Ge-filled PCF seems likely to lead to new kinds of in-fiber detector and sensor, as well as having potential uses in ultra-low-threshold nonlinear optical devices.

Figure 1: (a) Scanning electron Micrograph (SEM) of an ESM-PCF with a single Ge-wire adjacent to its glass core (hole spacing 2.90 μm, hole diameter 1.7 μm). (b) Loss of a PCF with a single Ge wire (length 0.8 mm) adjacent to the core for Y-polarization. (red: FEM simulation, black: experiments)

Publications H. K. Tyagi, H. W. Lee, P. Uebel, M. A. Schmidt, N. Y. Joly, M. Scharrer, P. St.J. Russell, Plasmon resonances on gold nanowires directly drawn in a step-index fibre, Opt. Lett., 35(15), 2573-2575, (2010)

H. W. Lee, M. A. Schmidt, H. K. Tyagi, L. N. Prill Sempere, P. St.J. Russell, Polarization-dependent coupling to plasmon modes on submicron gold wire in photonic crystal fiber, Appl. Phys. Lett., 93, 111102, (2008)

M. A. Schmidt, L. N. Prill Sempere, H. K. Tyagi, C. G. Poulton, P. St.J. Russell, Waveguiding and plasmon resonances in two-dimensional photonic lattices of gold and silver nanowires, Phys. Rev. B, 77, 033417, (2008)

H. K. Tyagi, M. A. Schmidt, L. N. Prill Sempere, P. St.J. Russell, Optical properties of photonic crystal fiber with integral micron-sized Ge wire, Opt. Express, 16, 17227-17236, (2008)