Although automatic fire detection is used in road tunnels since the late sixties, the subject has been of growing importance since the big tunnel fires in 1999 / 2001. Besides introduction of new detection technologies, safety and reliability of these systems is an important issue. On one side early detection versus fault alarm rate has to be considered. On the other hand automatic detection versus control room decision is a subject. And another question is how much redundancy can be put into the budget? This paper gives an overview on actual tunnel fire detection systems including their safety and reliability features. TUNNEL FIRE DETECTION SYSTEMS Whereas line type heat detectors have been used as the most important technology for a long time, today new technologies as smoke detection, video and others have been coming up or are under investigation [1]. In addition, many countries started to implement these new technologies for early fire warning in the directives for tunnel safety equipment [2,3]. Actual systems are: • Semiconductor temperature sensor cable (multipoint heat detector) • Fiber optic sensor cable • Pneumatic line type heat detector (copper tube system) • Non resettable line type heat detectors • Visibility monitors • Video analysis • Flame detectors

A modified LIGA process is well suited to fabricate hybrid mounted low-cost microoptical benches for fibre and free-space applications. The benches enable optical components to be assembled with lithographic precision in the LIGA plane without any active alignment. Due to the different sizes of the optical components, stepped substrates for X-ray lithography are required in order to guarantee a vertical alignment on the optical axis. Silicon and high-precision mechanical micromachining have been combined with the LIGA process to fabricate these benches. In addition, two alignment strategies were tested.

Article Polymere Komponenten für die Mikrooptik und Integrierte Optik / Polymer components for microoptics and integrated optics was published on September 1, 1993 in the journal tm - Technisches Messen (volume 60, issue 9).

The LIGA process is a new technology for the fabrication of precisely shaped polymer or metal structures. Using x-ray lithography, electroforming and micromolding as basic technologies, an accuracy in the submicron range can be achieved. For applications in fiber to fiber or fiber to chip coupling technology, mechanical structures with an accuracy of down to 0.3 micrometers have been realized and investigated using different techniques and materials. Additionally, passive waveguide components for optical fiber networks have been fabricated by molding techniques in polymer materials. These components show a low insertion loss, a well defined power splitting ratio and a compact device geometry.

A low-cost mass fabrication of optical precision components and waveguide structures with optimized properties is possible using improved moulding techniques and new micromoulding processes. Applications are in optical data transmission and sensor analysis. The potential of these techniques is demonstrated by passive single- and multi-mode waveguide components and refractive and diffractive microoptical structures.

The LIGA process, which is based on deep-etch X-ray lithography, electroplating, and moulding allows the commercial fabrication of three-dimensional microstructures. The actual state of the art of the LIGA process is summarized. This contains new process developments, like the possibility of realizing movable, stepped or inclined microstructures as well as the availability of new materials like nickel-cobalt alloys or ceramics. In the second part, applications of LIGA structures demonstrating the characteristic LIGA properties are presented. Examples are given for the fields of sensors, actuators and communication technologies.

Moveable and flexible microstructures can be fabricated by a combination of the LIGA process and sacrificial layer techniques. A promising application of such flexible structures can be seen in the field of integrated optics, where the problem of precisely coupling fibers to integrated optical chips still demands a satisfactory solution. In the LIGA structure the fibers are guided by precisely positioned stop faces and then precisely located and prefixed by integrated spring elements. The fabrication of these spring-element arrays by the LIGA process has several advantages: the thermal expansion coefficient of the substrate can be matched to the optical chip material; the use of spring elements for prefixing simplifies the handling; and adhesives and related problems can be avoided. Additionally, a small center spacing of the fibers can be reached with a curved parabolic profile of the spring elements using the LIGA advantage of unrestricted design in the cross-sectional shape. First measurements of load deformation on the spring elements show that the values for the modulus of elasticity and for tensile strength found in literature for bulk nickel can be used for electrodeposited nickel too.

The LIGA process which is based on deep-etch lithography in combination with high-precision electroforming and moulding processes is a particularly promising method for the fabrication of three-dimensional microstructures. Some interesting applications can be seen in the field of integrated optics. Passive waveguide structures can be fabricated by deep-etch synchrotron radiation lithography of multilayer resist systems. Using this technique, multimode strip waveguides with a PMMA core and a P (TFPMA/MMA) cladding as well as a planar grating spectrograph have been realized. The attenuation of 0.18 dB/cm measured at a wavelength of 850 nm can be reduced, especially in the near IR-region, by the use of deuterated PMMA as a core material. For plastic fiber LAN applications, moulding processes for the replication of passive multimode waveguide components like Y-couplers or star couplers are under investigation. The advantages of the LIGA process--unrestricted design in the cross-sectional shape and a small surface roughness in the range of 10 - 20 nm--are of special interest for these developments. For coupling fibers to integrated-optical chips, structures of a coupling array have been fabricated. The fibers are guided by exactly positioned stop faces and then precisely located and prefixed by integrated spring elements. The main advantages are as follows: the thermal expansion coefficient of the array can be matched to the optical chip material, the use of spring elements for prefixing simplifies the handling, and adhesives and the connected problems can be avoided.