Roland Germann

A very short planar silica spot-size converter using a nonperiodic segmented waveguide

To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter for a wavelength of 1.55 /spl mu/m is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a three-dimensional (3-D) finite difference beam propagation method (FD-BPM) program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (/spl sim/140 /spl mu/m) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures.

SiON high-refractive-index waveguide and planar lightwave circuits

The rapidly growing optical communication market requires photonic components with ever-increasing functionality and complexity that can be fabricated reliably at low cost. Of the various approaches used to fabricate photonic components, those based on planar waveguides have achieved high performance and represent a promising path toward compact integration of optical functions. We present an overview of an approach used to produce an optical single-mode waveguide. Through its strong mode confinement, the approach makes it possible to integrate optical filter functions with higher functionality, as required for high-data-rate communication networks. The waveguide is based on the use of a silicon oxynitride (SiON) core and silicon oxide cladding layers, and can be fabricated using conventional chip fabrication techniques. Using the new approach, conventional passive optical components such as arrayed waveguide gratings for wavelength-division-multiplexed transmission systems can be fabricated in a more compact way than using standard silica-on-silicon waveguide methods. Moreover, the realization of more enhanced, adaptive optical functions such as finite- impulse-response as well as infinite-impulse-response filters is possible. Reconfiguration is achieved through the thermo-optic effect. A reconfigurable gain-flattening filter and an adaptive dispersion compensator are presented as examples.

Apodized surface-corrugated gratings with varying duty cycles

We present the first realization of a Bragg grating apodization based on a concatenation of different duty cycles. The gratings were fabricated in SiON planar waveguides. The reflected signal exhibits a sidelobe suppression better than -20 dB outside a bandwidth of 1.36 nm. At the same time the reflection is stronger than 99.9%, i.e., the resonant light is suppressed better than -30 dB in transmission over 0.22 nm. The gratings are perfectly suited to serve as the wavelength-selective element of a Mach-Zehnder add/drop filter.

Wavelength tunable optical add-after-drop filter with flat passband for WDM networks

A tunable optical add-after-drop filter is presented with add and drop functions optimized individually. The add function exhibits a conventional passband, whereas the drop passband is flattened (less than 0.1 dB ripple over more than 0.5 nm). The design is based on the resonant coupler principle. The free spectral range is 6.4 nm and the channel spacing 1.6 nm. The device is realized in a newly developed, high-refractive-index-contrast SiON technology that permits small bending radii of 1.5 mm. Thermo-optic heaters are used to tailor and tune the filter characteristic. The on-chip losses are about 3.5 dB, the wavelength channel isolation is better than 27 dB, and the TE-TM polarization shift is smaller than 0.1 nm.

Wavelength division multiplexed add/drop ring technology in corporate backbone networks

The Corporate Optical Backbone Network (COBNET) project is a joint research project within the ACTS program of the European Commission. The COBNET consortium is considering the use of advanced optical networking technologies for the backbones of future corporate networks. In particular, multichannel add/drop ring networks based on wavelength division multiplexing (WDM) as well as on optical space-division multiplexing (SDM) technologies are being pursued. An overview is given of the system concept, the device technology, and the demonstration network that was developed within COBNET. The WDM ring option and specifically the related add/drop devices are focused on in more detail. These devices are fabricated in a newly developed highrefractive- index contrast planar silica-on-silicon technology by using silicon-oxynitride (SiON) as the core waveguide material. Compact add/ drop components based on the resonant coupler concept are realized. The filter characteristic can be tailored and tuned by thermo-optic heaters, which enables the selection of any given wavelength out of a series of wavelengths from the WDM ring using the same device.

Add–drop filter based on apodized surface-corrugated gratings

We report on the fabrication of a grating-based add–drop filter in SiON planar waveguide technology. We achieved apodization of the Bragg grating by concatenating subgratings with various duty cycles. We present the theoretical and experimental dependence of the coupling coefficient on the duty cycle, which leads to a minimum coupling coefficient of 30%. With a breeder genetic algorithm we were able to find optimal apodization profiles within this limited coupling coefficient range. The final device is compatible with a 100-GHz channel spacing and has a bandwidth utilization factor of 36%.

Compact tunable FIR dispersion compensator in SiON technology

We present a tunable dispersion compensator, based on a sixth-order finite impulse response lattice filter. The filter has a free spectral range of 100 GHz and can be tuned for linear group delay slopes between -100 and 100 ps/nm with less than 1-ps ripple over a usable bandwidth of more than 60 GHz. Within this usable bandwidth, the average polarization-mode dispersion is low, reaching 2.4 ps only for extreme group delay slopes. The filter can also generate higher order group delay curves, for example for dispersion slope compensation.

Low-threshold strained GaInP quantum-well ridge lasers with AlGaAs cladding layers

Visible lasers with two strained GaInP quantum wells and AlGaAs cladding layers have been fabricated using metalorganic vapor phase epitaxy. A dry-etched surface ridge has been chosen as a device structure, which results in a small astigmatism and a low threshold current. Owing to an electroplated heat spreader on top of the ridge, the devices can be operated continuous-wave (CW) junction-side-up at temperatures up to 100 degrees C. Lasers mounted junction-side-down with coated mirror facets operating at 30 mW output power show single-mode behavior and good reliability, as proven by a lifetime test of over 3000 h. >

Integrated optic tunable add-drop filters for WDM ring networks

This paper deals with two types of thermo-optically tunable add-drop filters realized by means of different technologies: fiber-matched low-pressure chemical vapor deposited (LPCVD)-grown SiO/sub 2/ waveguides and plasma-enhanced chemical vapor deposition (PECVD)-grown high-refractive-index-contrast SiON waveguides. Design and technology aspects are outlined. The device characterizations, drawn from laboratory and field trial measurements, are reported. The description focuses on the device applications in a system context. In particular, the usefulness of the components as the basic elements of an optical add-drop multiplexer node, suitable for a ring network, is shown. The key component aspects are presented as strictly related to system requirements and issues.

Tunable optical add/drop components in silicon-oxynitride waveguide structures

Ultra-compact tunable add/drop components, based on the resonant coupler concept, are realized in high index-contrast silicon-oxynitride waveguides. Thermo-optic heaters are used to tailor and tune the filter characteristic.