R. Baets

Fabrication of Photonic Wire and Crystal Circuits in Silicon-on-Insulator Using 193-nm Optical Lithography

High-index contrast silicon-on-insulator technology enables wavelength-scale compact photonic circuits. We report fabrication of photonic circuits in silicon-on-insulator using complementary metal-oxide-semiconductor processing technology. By switching from advanced optical lithography at 248 to 193 nm, combined with improved dry etching, a substantial improvement in process window, linearity, and proximity effect is achieved. With the developed fabrication process, propagation and bending loss of photonic wires were characterized. Measurements indicate a propagation loss of 2.7 dB/cm for 500-nm photonic wire and an excess bending loss of 0.013 dB/90deg bend of 5-mum radius. Through this paper, we demonstrate the suitability of high resolution optical lithography and dry etch processes for mass production of photonic integrated circuits.

Subnanometer Linewidth Uniformity in Silicon Nanophotonic Waveguide Devices Using CMOS Fabrication Technology

We report subnanometer linewidth uniformity in silicon nanophotonics devices fabricated using high-volume CMOS fabrication tools. We use wavelength-selective devices such as ring resonators, Mach-Zehnder interferometers, and arrayed waveguide gratings to assess the device nonuniformity within and between chips. The devices were fabricated using 193 or 248 nm optical lithography and dry etching in silicon-on-insulator wafer technology. Using 193 nm optical lithography, we have achieved a linewidth uniformity of 2 nm (after lithography) and 2.6 nm (after dry etch) over 200 mm wafer. Furthermore, with the developed fabrication process, using wavelength-selective devices, we have demonstrated a linewidth control better than 0.6 nm within chip and better than 2 nm chip-to-chip. The necessity for high-resolution optical lithography is demonstrated by comparing device nonuniformity between the 248 and 193 nm optical lithography processes.

Efficient silicon-on-insulator fiber coupler fabricated using 248-nm-deep UV lithography

We present a silicon-on-insulator (SOI) waveguide to fiber coupler fabricated using 248-nm-deep ultraviolet lithography. The loss of the taper structure is around 1 dB while the coupling loss from a lensed fiber into a 590-nm-wide SOI waveguide was measured to be 1.9 dB.

Growth behavior during nonplanar metalorganic vapor phase epitaxy

The growth behavior during nonplanar metalorganic vapor phase epitaxy on patterned GaAs substrates was investigated by using a periodic structure of GaAs/AlGaAs layers. At the channel edges, nongrowing and slow growing low‐index planes were observed, indicating local kinetic limitation of growth. A number of different channel orientations were studied and a theoretical model was used to explain the resulting growth planes. The kinetic limitation is further demonstrated by the temperature dependence of the growth behavior and by the use of different profiles. The influence of misoriented substrates is discussed. A reduction of the growth velocity was observed in the channels as compared with the surrounding area.

Guided wave modulators and switches fabricated in electro-optic polymers

In this paper the fabrication of directional couplers (2×2 switches) and Mach–Zehnder interferometers (intensity modulators) using electro‐optic polymeric multilayer structures, is described. Results show attractively low switching voltages (<10 V for 1.4 cm long devices) and very good on‐off ratios (17 dB) for the directional couplers. In the case of the Mach–Zehnder interferometers, Vπ‐values of 4.5 V have been obtained, also for 1.4 cm long devices.

Recent Developtents In Optically Nonlinear Polymers And Related Electro-Optic Devices

Side chain polymers, containing hyperpolarizable moieties as pendant groups, have been applied as optically nonlinear materials. Electro-optic properties have been induced via electric field poling of nultilayer structures incorporating the nonlinear polymers. For a poling field strength of 156 Wpm, the obtained i r33 coefficient was equal to 28 pn/V at the wavelength of 1.3 pm, which is close to r33 = 32 of the inorganic single crystal lithium niobate. Low loss mcnomode charnel waveguides (< 1 dB/cm @ 1.3 μm wavelength) have been realized in the optically nonlinear polymer nultilayers. Tunable Fabry-Perot etalons, monamode phase and intensity modulators and monomode Mach-Zehnder interferameters, have been made and tested; their performances will be discussed. Owing to their considerable electro-optic coefficients and attractive processing properties, polymers are becoming serious alternatives for the currently often applied lithium niobate.

Reflectionless grating couplers for Silicon-on-Insulator photonic integrated circuits

We propose a novel grating coupler design which is inherently reflectionless by focusing the reflected light away from the entrance waveguide. The design rules for this reflectionless grating coupler are explained and the grating coupler design is investigated by means of 3D FDTD simulations for the case of a Silicon-on-Insulator based platform.

Design of index-coupled DEB lasers with reduced longitudinal spatial hole burning

Methods for reducing or eliminating longitudinal spatial hole burning in antireflection-coated, index-coupled distributed feedback (DFB) lasers are discussed. It is shown that elimination of spatial hole burning in DFB lasers can be achieved by the introduction of well-chosen variations of coupling strength and/or internal absorption in the longitudinal direction. It is shown that a theoretical laser structure with uniform power can always be obtained by choosing two arbitrary functions. The authors describe some of the more basic solutions with uniform power. Practical approximations of these structures, their numerical modeling, and some methods to fabricate them are presented. >

Coupling schemes for heterogeneous integration of III-V membrane devices and silicon-on-insulator waveguides

We present and numerically analyze two schemes for efficient, large-bandwidth, and fabrication-tolerant optical coupling of bonded III-V membrane active components to an underlying nanophotonic waveguide circuit in silicon-on-insulator (SOI). Coupling of active membrane components to passive waveguides enables the integration of ultracompact passive waveguide circuits and active optoelectronic devices.

Monolithic integration of diffractive lenses with LED-arrays for board-to-board free space optical interconnect

Since optical interconnections can severely reduce problems associated with electrical interconnect technology (including bandwidth limitations, electromagnetic cross talk, signal delay and EMI aspects), the development of suitable electrooptic components is of crucial importance for implementation of optical interconnects in future computer systems. This paper addresses the design, modeling, fabrication as well as experimental assessment of LED-arrays, with diffractive lenses etched into the rear side of the LED-substrate. The suitability of such optical sources for board-to-board optical interconnections will be demonstrated. >