Single-mode Rib Waveguides Research Articles

Guided-wave Si 1− xGe x/Si wavelength demultiplexer based on multimode interference

A novel multi-mode interference wavelength demultiplexer design in Si 1− x Ge x /Si for 1.3 and 1.55 μm operation is investigated. From the theory of large single-mode rib waveguides, the width of the rib waveguides, height and etched depth were derived for a Ge content x=0.04. Using the modal-propagation analysis method, the coupler length of the device is evaluated and the transmission characteristics are investigated. The results indicate that at the optimum coupler length of 1850 μm and the optimum coupler width of 10 μm, the contrasts achieved by this device are 40.6 dB and 39.9 dB at 1.3 and 1.55 μm, respectively. Insertion loss is less than 0.1 dB at both wavelengths.

Silicon-on-silicon rib waveguides with a high-confining ion-implanted lower cladding

The realization of single-mode rib waveguides in standard epitaxial silicon layer on lightly doped silicon substrate, using ion implantation to form the lower cladding, is reported. The implanted buffer layer enhances' the vertical confinement and improves the propagation characteristics. Respect to similar standard all-silicon waveguides a propagation loss reduction of about 7 dB/cm, in the single-mode regime, has been measured. A numerical analysis has been performed to evaluate the theoretical attenuation and the transverse optical field profiles. As a result of the presence of the ion implanted buffer layer, an increase of the fundamental mode confinement factor from 0.3 to 0.85 has been calculated. This results in a great enhancement of the coupling efficiency with standard single-mode optical fibers. Moreover, the proposed technique is low cost, fully compatible with standard VLSI processes, and allows a great flexibility in the integration of guided-wave devices and electronic circuits. Finally, the very high thermal conductivity characterizing these waveguides makes them attractive host-structures for electrically and thermally controlled active optical devices.

Electrooptic polymer modulators operating in both TE and TM modes incorporating a vertically tapered cladding

We propose a modified electrooptic (EO) PMMA polymer waveguide structure supporting both TE and TM modes in spite of the large birefringence induced by the poling. A vertically tapered structure is employed to connect a single-mode rib waveguide and a confinement-enhanced rectangular buried waveguide. This waveguide structure can be easily fabricated by a two-step reactive ion etching (RIE) process with a shadow mask. To demonstrate TE/TM confinement and single-mode operation, Mach-Zehnder intensity modulators are fabricated by incorporating the proposed waveguide structure. The extinction ratio is better than -15 dB, which proves the single-mode operation. Half-wave voltages for TM and TE modes are 6 and 24 V, respectively.

Silicon-on-insulator asymmetric optical switch based on total internal reflection

Based on the large cross-section single-mode rib waveguide condition, total internal reflection (TIR) and the plasma dispersion effect, a silicon-on-insulator (SOI) asymmetric optical waveguide switch with transverse injection structure has been proposed and fabricated, in which the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. The device performance is measured at a wavelength of 1.3 μm. It shows that the extinction ratio and insertion loss are less than -18.1 and 6.3 dB, respectively, at an injection current of 60 mA. Response time is 110 ns.

Silicon-on-Insulator 2 × 2 Symmetric Optical Switch Based on Total Internal Reflection

Based on the large cross-section single-mode rib waveguide condition, the total internal reflection and the free-carrier plasma dispersion effect, a silicon-on-insulator (SOI) 2 × 2 symmetric optical waveguide switch with a transverse injection structure has been proposed and fabricated, in which the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. The device performance is measured at the wavelength of 1.3 μm. It shows that the crosstalk and insertion loss are less than - 18.1 and 4.8 dB, respectively, at an injection current of 60 mA, and response time is 110 ns.

Active Silicon Integrated Optical Circuits

AbstractActive Silicon integrated Optical Circuits (ASOC™) is a technology based on single-mode rib waveguides formed on silicon-on-insulator that is being used to manufacture commercial integrated optics components. Silicon waveguides have excellent properties for many applications in the 1.3 and 1.55 micron telecommunications bands including relatively low loss. An important aspect of ASOC™ technology is the development of a set of waveguide-based elements that can be assembled into practical integrated optics devices. The fundamental waveguide elements include bends, couplers and fiber-waveguide interfaces, and additional elements include doped structures and waveguide gratings. Discrete lasers and photodetectors are also incorporated into ASOC™ technology to form hybrid devices. The technology is being used to manufacture devices for applications in telecomunications and optical sensing, the first major product being a two-wavelength single-fiber bi-directional optical transceiver.

Zero-gap directional coupler switch integrated into a silicon-on insulator for 13-μm operation

A silicon-on insulator (SOI) zero-gap directional coupler switch is studied based on the large-cross-section singlemode rib waveguide condition, the dual-mode interference principle, and the free-carrier plasma dispersion effect, in which the SOI technique uses silicon and silicon dioxide thermal bonding and backpolishing. The SOI is fabricated by potassium hydroxide anisotropic etching. Its insertion loss and cross talk are measured to be less than 4.81 dB and 218.6 dB, respectively, at a wavelength of 1.3 microm and a switching voltage of 0.91 V. Response time is ~210 ns.

Silicon-on-insulator optical intensity modulator based on waveguide-vanishing effect

A silicon-on-insulator (SOI) optical intensity modulator has been proposed and fabricated, and is based on the large cross-section singlemode rib waveguide condition, the waveguide-vanishing effect and the free-carrier plasma dispersion effect. In the modulator the SOI technique uses silicon and silicon dioxide thermal bonding and back-polishing. The insertion loss of the device is measured to be 3.65 dB at a wavelength of 1.3 µm. The modulation depth is 96% at an injection current of 45 mA. Response time is ~160 ns.

Silicon on insulator Mach–Zehnder waveguide interferometers operating at 1.3 μm

Mach–Zehnder (MZ) waveguide interferometers integrated on SOI (silicon on insulator) for 1.3 μm operation are studied on the basis of the large cross-section single-mode rib waveguide condition and the free-carrier plasma dispersion effect in Si wafer direct bonding SOI by back-polishing. And the MZ interferometers are fabricated by using KOH anisotropic etching. Their insertion losses and modulation depths are measured to be 4.81 dB and 98%, respectively, at the wavelength of 1.3 μm when a forward bias voltage applied to a p+n junction is 0.95 V and the active zone length of the MZ interferometers is 816.0 μm.

Si1-xGex/Si Single-Mode Rib Waveguides with 0.5 dB/cm by Molecular Beam Epitaxy

Si1-xGex/Si single-mode rib waveguides with 0.5 dB/cm losses have been fabricated, in which the SiGe layers are grown by molecular beam epitaxy. The single-mode waveguide dimensions determined experimentally are consistent with the single-mode theory of SiGe waveguides.

Integration of waveguides and photodetectors in SiGe for 1.3 /spl mu/m operation

The integration of single-mode rib waveguides and photodetectors in silicon using MBE-grown SiGe-layers is reported. Short photodetectors exhibit dark currents below 200 nA at 7 V reverse bias. For the fiber-waveguide-detector coupling an overall quantum efficiency of 11% has been achieved at 7 V reverse bias for /spl lambda/=1.3 /spl mu/m. The maximum bandwidth is 2 GHz. >

Deeply-etched singlemode GeSi rib waveguides for silicon-based optoelectronic integration

The fabrication and characterisation of deeply-etched single-mode GeSi rib waveguides, grown on an intrinsic silicon substrate, for monolithic optoelectronic integration are reported. The waveguides exhibit strong singlemode guiding and good confinement with a propagation loss of ∼2.5±1dB/cm at 1.3μm.

Low loss singlemode optical waveguides with large cross-section in silicon-on-insulator

The realisation of singlemode rib waveguides in silicon-on-insulator (SOI) having a width and height of several micro-metres is reported. Measurements at a wavelength of 1.3 and 1.55 μm yield waveguide losses below 0.5 dB/cm and an excellent agreement of the near field intensity distribution with the one predicted by a BPM simulation.

Low Loss Rib-Waveguides in SOI

ABSTRACTThe realization of single-mode rib-waveguides with dimensions of several micrometers in Silicon-On-Insulator (SOI) is reported. The predicted monomode behaviour is confirmed by comparison of a simulated and a measured nearfield intensity distribution. Waveguide losses below 0.5dB/cm were obtained at wavelengths of 1.3μm and 1.55μm, respectively, independent of the polarization state.

Efficient beam propagation techniques

It is shown that suitable modifications of the free-space-propagation operator in the standard fast-Fourier-transform beam propagation procedure yield a far more rapid code in the context of semiconductor rib waveguide calculations. The procedure curtails the diffraction experienced by the high-order Fourier components of the electric field and mirrors the structure of the recently introduced finite-difference beam propagation algorithm. It is used to investigate the propagation losses of a Y-junction composed of single-mode rib waveguides and illuminated by its normalized guided mode.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaAs/GaAlAs asymmetric Mach-Zehnder demultiplexer with reduced polarization dependence

A two-channel GaAs/AlGaAs asymmetric Mach-Zehnder wavelength demultiplexer with reduced polarization dependence was demonstrated. The device was fabricated on a single heterostructure comprising a 1.45- mu m-thick layer of GaAs on a 6.0- mu m-thick Ga/sub 0.85/Al/sub 0.15/As buffer layer. The epitaxial layers were grown by MOCVD (metalorganic chemical vapor deposition) on an n/sup +/ GaAs substrate. The single-mode rib waveguides, 3 mu m wide and 0.29 mu m high, were fabricated using standard photolithographic techniques followed by chemical etch and removal of the resist mask. Extinction ratios of 24.1 dB for transverse electric (TE) and 22.5 dB for transverse magnetic (TM) polarized light were measured on a device with an anti-reflection coating on its input and output facets. The active length of the device is approximately 6.5 mm and total loss of 1.1 dB was obtained in a 16-mm-long chip. >

Fresnel equation studies of longitudinally varying semiconductor rib waveguides: reference wavevector dependence

We demonstrate that the accuracy of paraxial loss calculations for longitudinally varying semiconductor rib waveguides is significantly affected by the value assumed for the reference refractive index, n0. We then perform a full threedimensional simulation of a weakly guiding single-mode rib waveguide Y-junction, and compare our results to those of the effective index method, obtaining excellent agreement when n0 nearly coincides with the refractive index of the guided mode.

Fabrication of tapered couplers in GaAs/GaAlAs rib waveguides

Tapered couplers have been fabricated in GaAs/GaAlAs single-mode rib waveguides. A new etching technique has been used to fabricate transitions of 1μm over lengths of approximately 160 to 300 μm. Losses for the TE and TM fundamental modes have been measured at a wavelength of 1.3μm.

Scattering in low-loss GaAs/AlGaAs rib waveguides

Single-mode rib waveguides with low propagation loss (0.2 dB/cm) were fabricated on GaAs/AlGaAs single heterostructures by dry etching. The attenuation of these guides was measured to study the effect of rib structure on propagation loss at 1.52 μm. An increase in loss with increased rib height and decreased rib width was associated with scattering due to a rib surface roughness of approximately 50 nm for ion milled waveguides. Fabrication with reactive ion etching reduced the rib roughness and its associated scattering loss by a factor of 3 or more in waveguides with strong optical confinement (effective index difference of 0.012) of the fundamental guided mode.

Optical properties of (Al,Ga)As/GaAs multiple quantum well planar waveguides and the fabrication of single-mode rib waveguides and directional couplers by reactive ion etching

An anisotropic absorption edge was observed in an (Al,Ga)As/GaAs multiple quantum well double-heterostructure (MQW-DH) single-mode planar optical waveguide. Single-mode rib waveguides and directional couplers were fabricated by SiCl(4) reactive ion etching. The results were found to be consistent with the assumption that the refractive index of the MQW structure for TE propagation is given by the weighted rms average value of the refractive indices of the constituent layers.