Ming-Chuan Yang

Subwavelength imaging with a multilayer silver film structure

A Ag/SiO2 multilayer imaging structure is shown to have subwavelength performance. Loss is the major limitation, and selection of low-loss materials and suitable operating wavelengths has a significant impact on performance. The influence of the variables is presented, and vortices are shown to exist.

Poynting vector analysis of a superlens

A power analysis of the lossy negative refractive index or left-handed slab lens is described. The presence of vortices in the image plane is revealed with small loss or gain, and these are attributed to the influence of field growth in the evanescent spectrum.

Quantum steering of electron wave function in an InAs Y-branch switch

We report experimental results on gated Y-branch switches made from InAs ballistic electron waveguides. We demonstrate that gating modifies the electron wave functions as well as their interference pattern, resulting in anticorrelated oscillatory transconductances. Our data provide evidence of steering the electron wave function in a multichannel transistor structure.

Functional waveguide mode transformers

Field transformers having irregular scattering elements in a rectangular waveguide are introduced as a means to achieve frequency-dependent mode conversion, mode-selective reflection, multiple mode conversion, and phase shifting. A stepwise wall profile provides for a large number of degrees of freedom and also induces large evanescent field content. A multiresolution optimization strategy allows good convergence during synthesis. The resulting structures are compact, with dimension of a few wavelengths, and can have functionality not achievable through periodic means. In some cases, more than one solution can be found that have different spectral characteristics, a result of the large number of degrees of freedom and the constraint set. This structure class may prove useful in microwave sources where multiple or higher order modes are excited, in waveguide transitions, in frequency-dependent switching, and as phase-shifting elements.

Demonstration of mode conversion in an irregular waveguide

Communications wavelength waveguide mode conversion is demonstrated in an irregular metal-walled structure that was designed by using multiresolution optimization. Strong scatter and a large number of degrees of freedom allowed high-efficiency conversion in a device having a length of just a few wavelengths. The fabrication approach draws on standard semiconductor processing. Mode-selective reflectors, splitters, phase shifters, and other elements can be achieved by using this principle.

Functional field transformation with irregular waveguide structures

We demonstrate functional field transformation in irregular waveguide structures having strong scatter from a stepped conducting wall geometry. The resulting degrees of freedom and significant evanescent field content make it possible to accomplish virtually perfect transformation in a distance of several wavelengths. A microwave experiment verifies frequency-dependent transformation, suggesting that wavelength division multiplexing based on this principle is possible. A mode-selective transformation, which exhibits disparate reflectivities for different modes at the same frequency, may find application in multimode laser cavities.

Demonstration of terahertz frequency-dependent field transformation in an irregular waveguide structure with direct measurement of the internal electric fields.

We demonstrate irregular scattering structure frequency-dependent field control at terahertz frequencies by means of a TM(10) to TM(30) mode converter designed for operation near 300 GHz and fabricated out of lithium niobate. Imaging of the electric fields in the sample, with a Fourier analysis of the time domain signal, yielded the performance as a function of frequency.

Demonstration of near-field waveguide mode conversion with an irregular waveguide

A 1.55 mum scanning microscope experiment shows that wavelength-dependent mode conversion in micrometer-scale metallic waveguide structures is feasible, thereby paving the way for compact signal processing elements. The design, fabrication and optical measurement are described.

Resolution Limits of a Negative Refractive Index Lens

The influence of loss in a negative refractive index slab is described using a plane wave expansion. Sensitivity of the decaying fields to small loss has an adverse impact on resolution

Irregular Field Transformation Structures

Irregular waveguides and diffractive elements with strong scatter provide degrees of freedom which allow new functionalities and compact devices necessary for solid state processing. Simulations and also experiments illustrate their efficacy.