R. Scarmozzino

Realization of a compact and single-mode optical passive polarization converter

A single-section, compact, passive polarization converter has been designed and fabricated on GaAs-AlGaAs. The device uses an optimized waveguide structure with angled-facets to obtain 90/spl deg/-polarization rotation in a single section; this waveguide structure eliminates the need for longitudinal variation and hence avoids any section-to-section coupling losses. A transverse electric (TE) to transverse magnetic (TM) polarization conversion of 96% is achieved for a conversion length of /spl ap/720 /spl mu/m.

Carbon nanotube tipped atomic force microscopy for measurement of <100 nm etch morphology on semiconductors

The use of carbon nanotubes as tips in atomic force microscopy for a systematic study of dry etching pattern transfer in GaAs is described. The GaAs samples are patterned via electron beam lithography and then etched using magnetron reactive ion or chemically assisted ion beam processing. The technique allows diagnosis, in air, of etched features with scale sizes of <100 nm.

The Laser‐Controlled Micrometer‐Scale Photoelectrochemical Etching of III–V Semiconductors

Laser-controlled photoelectrochemical etching of III-V semiconductors using micrometer-sized illumination regions has been investigated for varying laser parameters (power, spot size, wavelength) and etching solutions. The etching has been applied to a wide variety of semiconductor doping types. The micrometer spot size of the laser can induce higher etch rates for a given intensity when compared to broad illumination. In addition, the process has micrometer-scale resolution and highly directional etch anisotropy. In this electroless process the laser etching rate is influenced by light-induced voltage shifts in the surface potential. Finally, the dependence of the process resolution on carrier diffusion and etch depth is discussed

A new design approach to large input/output number multimode interference couplers and its application to low-crosstalk WDM routers

A new design approach for N/spl times/N multimode interference (MMI) couplers with large N is described which yields a device design with extremely low imbalance and insertion loss. Analytical expressions for the phase errors in MMI devices are derived from basic principles; these expressions enable significant phase-error reduction to be obtained by optimizing the index-contrast. This optimization in conjunction with the proper placement of the access waveguides allows significant improvement in the device performance. An application of the design approach is illustrated through the design of an 8/spl times/8 MMI-based, phased-array demultiplexer with low crosstalk.

Laser direct writing of aluminum conductors

We report, for the first time, the laser direct writing of high‐conductivity aluminum interconnects from dimethylaluminum hydride (DMAlH). These lines were deposited from this metalorganic gas using a focused deep‐ultraviolet laser beam, and the deposition process was studied as a function of several process parameters. Electrical measurements and Auger electron spectroscopy were used to characterize the quality of the laser‐deposited films.

An improved ADI-FDTD method and its application to photonic simulations

When the alternating direction implicit-finite difference time domain method (ADI-FDTD) is applied to simulating photonic devices, full efficiency can not be achieved if reasonable accuracy is to be kept, due to numerical errors such as numerical dispersion. A simple modification to ADI-FDTD is proposed by calculating the envelope rather than the fast-varying field, so that errors are minimized. A factor of two-five in speed can usually be gained while retaining the same level of accuracy compared with conventional FDTD. The efficiency and the accuracy of this improved approach is demonstrated on several problems, from simple waveguide structures to complex photonic crystal structures.

A new design for ultracompact multimode interference-based 2 x 2 couplers

We introduce here a new multimode interference-based 3-dB coupler that has a substantially smaller device geometry than conventional multimode interference structures. This new structure is based on a special multimode region shape and an appropriate launching technique which aids in circumventing the proximity limitations. Simulations show this structure can provide a decrease of a factor of three or more in the device size of the smallest 3-dB MMI coupler made to date.

Length reduction of tapered N x N MMI devices

The length of N/spl times/N multimode interference-based (MMI) devices scales as the square of the MMI region width, and as a result, the use of these structures for large-N applications can require large chip areas. We discuss the N/spl times/N applications of a recently proposed MMI structure that has smaller device dimensions than conventional multimode interference structures. Numerical simulations of such structures and design rules are presented. Limitations on device performance are discussed.

Adiabatic couplers: design rules and optimization

Explicit analytic design rules are derived for both 3 dB and full adiabatic couplers. The design rules are in excellent agreement with numerical calculations using the beam propagation method (BPM). It is shown that the length scaling for 3 dB couplers compared to full couplers makes the former more difficult to design. The design for each case is optimized to obtain the upper limit of performance and a comparison is carried out between two different design geometries for both 3 dB and full adiabatic couplers.

A low-loss and compact waveguide Y-branch using refractive-index tapering

A new approach to an integrated Y-branch power splitter, useful for strongly guiding waveguide circuits, is proposed, fabricated and tested. The device uses adiabatic mode evolution by effective-refractive-index tapering to achieve a compact, low-loss geometry. Device performance is examined numerically by twoand three-dimensional beam propagation simulations. Y-branches with an overall length of /spl sim/330 /spl mu/m and losses of <0.2 dB are then fabricated in GaAs-AlGaAs. A compact and low-loss 1/spl times/4 power splitter incorporating this Y-branch is also described and demonstrated.