MEMS — the key to low-cost components
The latest roadmap report published by the European Nexus consortium regards MST/MEMS as the future basis of low-cost, mass-produced components for optical telecommunications.
Micro-machining methods, combined with IC-based processing techniques, enable the bulk fabrication of complex optoelectronic integrated circuits and micro-electro-mechanical alignment devices. Initial cost reductions can be achieved by means of multi-function integration, advanced packaging and diversification. Operational costs can be reduced by component compactness and tunability.
MST/MEMS-based components will play a major role in enabling performance enhancements such as multi-channel operation, broadband switching and fibre-optic interconnects in tomorrow's transmission systems.
The following MST/MEMS-based components will feature strongly: mux/demultiplexers; wavelength and tunable filters; micro-aligners and fibre positioning components; stabilised optical sources; optical polarisation controllers; and integrated optical pumps and optical amplifiers. In addition to the above examples, systems will continue to require precision fibre-optic connectors, splices and supporting microstructures.
These technologies offer a number of opportunities to reduce the cost of optical systems. Component integration and hybrid integration (chip-to-chip) are steps towards future monolithic integration of devices onto a single chip.
Integrated fibre-attachment concepts are being implemented to eliminate the need for fibre strain relief and optical alignment to be coincident.
Component designs that replace hand assembly with precision robotics (Fig.1) are being pursued for all production, but full-scale automation at this time is proving too costly until production volumes reach millions of modules.
Design requirements for low-cost robotic component assembly are:
- Fibre-optic attachment with passive V-groove alignment and advanced MST/MEMS silicon optical benches (SiOB) to replace active-optical alignment;
- Stable and reliable soldering and laser welding for mechanical
- strain relief to replace glues; and
- Low-cost alternatives that meet Telcordia specifications to replace expensive Kovar 'butterfly' packages.
Aggregating demand for telecom and non-telecom applications increases production volumes more rapidly to allow lower cost over all markets. Designing optical components in a building-block manner allows functionality in products that are outside classical telecom applications. Optical MST/MEMS building blocks can then be assembled in innovative ways to address new areas like micro-displays and micro-sensors for environmental and medical applications.
Analysis of the cost of provisioning, space and power requirements and inventory shows that there is a dramatic reduction in price with tunability. Tunable devices will be key building blocks in creating the flexibility to enable dynamic provisioning and restoration.
MST/MEMS-based VOAs are adjustable elements that can interrupt a light beam, thereby tuning the light power level. They can be integrated with a DWDM unit for gain equalisation of individual wavelengths. The VOA should be protocol- and wavelength-independent, making it more suitable for dynamic channel balancing for DWDM systems, power management, and gain tilt in multi-stage optical amplifiers and as a building block for multi-function integration in OADMs and OXCs.
Figure 2 shows a MST/MEMS-based VOA with fibre-fixation structures. On this "top down" view, one can see the etched V-groove and the fibre stops that create a gap between the fibres and the cantilever-shaped microshutter.
A linear microactuator moves the microshutter into the beam to lower the light power level. This VOA can be coupled with drive electronics to provide active feedback.
This technology has been developed in cooperation between Colibrys and MST/MEMS design innovator Coventor. With this design, automated attachment of fibre ribbons can be achieved to significantly reduce manufacturing cost.
There is little doubt that soon the telecommunications arena will resume expansion at a staggering rate on a worldwide scale. MST/MEMS will play a crucial role in enabling this expansion.
The current downturn opens opportunities for innovative technology providers to re-assess the options of microtechnologies and gain market share once the systems providers need to invest again.
Cooperation between traditional telecoms component/system companies and MST/MEMS providers will be another clear trend to lower cost in optical systems. "Open foundries" undertake custom designs directly for customers, depending on the application and need to protect intellectual property — or to provide total solutions. An open foundry can work closely with external MST/MEMS design houses that provide local regional support to end-users worldwide.
Design houses have special understanding of the breadth of a foundry's process and technology platform. A flexible MST/MEMS foundry, such as Colibrys, can adapt to requests from the systems level quickly and can achieve the desired cost savings with its large portfolio of underlying MST/MEMS technologies.
A typical product creation procedure consists of five phases from basic business evaluation through to development, industrialisation, pre-production, and finally release for regular volume production.
Current full-custom products include a silicon-based array of electro-magnets for high-speed magneto-graphic printing machines, an optical variable-entrance-slit unit for spectrometers for analytical instrumentation, high-speed optical shutter arrays, a sensing element for microphones for portable telecom applications, and optical switching and variable attenuator chips for optical telecom applications.
GalayOr Silicon PhotonICs, an Israel-based innovator in telecom components, has recently demonstrated its new Moving Waveguides technology.
This can produce highly integrated optical circuits on a chip using standard silicon material and processes and low-cost VLSI packaging solutions.
Colibrys, which has been chosen as the foundry to fabricate GalayOr's waveguide-based DVOA, is using a hybrid combination of MEMS silicon-on-insulator (SOI) technology and integrated electronic circuits.
Through the use of the standard semiconductor SOI material, low-cost manufacturing, high yield, and high reliability can be achieved.
Since the pre-developed library components differ from each other only by their mask design, single chips with more functionality such as switching and power monitoring can also be manufactured with the same Colibrys/GalayOr process technology.
Optical mother boards (OMB) are in a development stage in which moving waveguides are used as flexible interconnects between the different components that are placed on the board. The OMB is a perfect example of a system on a chip that integrates several micro-actuators with waveguides.