A.N. Lepore

Direct measurement of nanoscale sidewall roughness of optical waveguides using an atomic force microscope

An atomic force microscope (AFM) with an ultrasharp tip was used to directly measure the sidewall profile of InP/InGaAsP waveguide structures etched using an inductively coupled plasma reactive ion etching (ICP-RIE) in Cl2-based plasma. A special staircase pattern was devised to allow AFM tip to access the etched sidewall of the waveguides in the normal direction. Statistical information such as correlation length and rms roughness of the sidewall profile obtained through three-dimensional imaging by AFM has been presented. rms roughness as low as 3.45 nm was measured on the sidewall of 4-μm-deep etched InP/InGaAsP heterostructures.

Effect of H2 on the etch profile of InP/InGaAsP alloys in Cl2/Ar/H2 inductively coupled plasma reactive ion etching chemistries for photonic device fabrication

This study demonstrates etch profile engineering of InP, In1−xGaxAs1−yPy, and In0.53Ga0.47As heterostructures results from adding H2 to standard Cl2/Ar inductively coupled plasma-reactive ion etching chemistries. Etch rate curves of bulk InP, In1−xGaxAs1−yPy, and In0.53Ga0.47As show a general parabolic trend as a function of the H2 component of the Cl2/Ar/H2 ratio. Three distinct etching profiles of InP/InGaAsP layers were realized by varying the Cl2/Ar/H2 ratio. Highly anisotropic profiles result for Cl2/Ar/H2 ratios between 2/3/1 and 2/3/2. Waveguiding structures fabricated using this technology are presented with a loss as low as 2 dB/cm. An InP racetrack resonator with a quality factor (Q)>8000 is also presented.

Characterization of sidewall roughness of InP/InGaAsP etched using inductively coupled plasma for low loss optical waveguide applications

The effects of etch depth on the sidewall roughness (SWR) of InGaAsP/InP waveguides fabricated utilizing two types of masks, NiCr/SiO2 and SiO2/NiCr/SiO2, were investigated with an atomic force microscopy. All the waveguides were etched in an inductively coupled plasma–reactive ion etching to depths ranging from 4 to 8 μm. The root-mean-square (rms) sidewall roughness values of the waveguides etched to depths of 4, 6, and 8 μm with SiO2 remasking layer were measured to be 2.97, 3.45, and 3.64 nm, respectively. Also the rms SWR values of the waveguides etched without the remasking layer were 3.2, 3.65, and 3.89 nm, respectively. The SiO2 thin remasking layer deposited on NiCr/SiO2 mask structure reduced the SWR of the waveguides. Measurements indicated that SWR increased with etch time, which is ascribed to an increase in mask erosion during etching.

Study of the evolution of nanoscale roughness from the line edge of exposed resist to the sidewall of deep-etched InP∕InGaAsP heterostructures

The evolution of line edge roughness and sidewall roughness was monitored during the fabrication of deep-etched optical waveguides in InP∕InGaAsP heterostructures. Scanning electron microscopy was used to extract line edge profiles of the electron beam exposed resist and the lifted-off NiCr metal mask. Atomic force microscopy with an ultrasharp tip was utilized to extract the sidewall profiles of InP∕InGaAsP mesa waveguides that were etched using inductively coupled plasma reactive ion etching. The processing step that critically influences the roughness of the etched waveguides was determined by studying the evolution of the roughness.

Indium-Phosphide-Based Mutation-Designed Optical Waveguides for Application

Altering morphology at scales insensible to optical waves by nanofabrication mutates optical properties of semiconductors. Low-optical-overlap modes (LOOMs) are capable of ultra-low propagation loss, nonlinearity and dispersion in high power and signal processing applications.

Indium-phosphide-based microresonator modulators and wavelength multiplexers

In this paper, we report on the combination of nanofabrication techniques, laterally coupled micro-ring-resonator modulator design, angled multimode interference couplers, and highly efficient InP-based modulator materials, to demonstrate wavelength selective modulators arrays. Wavelength selective modulator permits the modulation of a single optical carrier without the wavelength multiplexing.