Manfred Rode

Wide passband grating multiplexer for multimode fibers

A grating multiplexer in Littrow-configuration is presented, whose passband width-normalized to channel spacing-is comparable with grating demultiplexers. As shown by calculation, a wide passband is attainable by very small input fiber spacing. Using a standard-(50/125 \mum)-GI-fiber as transmission fiber, a 1-dB pass-band of 30 nm with a channel spacing of 46 nm is achieved in an 8- channel device. The insertion losses for each channel are in the range 1.4-2.5 dB for 8- or 10-channel devices.

Self-aligned positioning of microoptical components by precision prismatic grooves impressed into metals

Grooves embossed into metallic substrates are proposed for self-aligned positioning of microoptical components like microlenses, optical fibers, glass rods with mirrors or filters, etc. As substrates, both ductile metals such as aluminum or copper, and hard alloys like CrNi steel can be used, which allows adaptation to requirements concerning thermal expansion coefficient, thermal conductance, hardness, mechanical strength, solderability, weldability, etc. Compared to other methods such as anisotropic etching in silicon substrates and LIGA, this technique offers more design flexibility and much lower investment cost and is well suited for medium production numbers. By the embossing process, the shape and surface quality of the embossing die are virtually transferred into the groove. The residual deviation between die and groove is in the order of 5-10 /spl mu/m. The reproducibility is better than 5 /spl mu/m, thus allowing self-aligned positioning with multimode fiber applications. Without reconditioning, several thousand embossing cycles can be made with the same die. The manufacturing of embossing dies is based on precision tooling techniques. The paper concludes with two application examples of optical communication components.

Polymer waveguides for 100-cm (40) optical backplanes

Optical backplanes are attractive components for systems with high data rates between subsystems and a large number of interconnects. An optical backplane which uses multimode polymer waveguides was originally developed for avionic applications but can be used in telecom switching systems as well. For transmission distances in the range of 100cm and data rates up to 10Gbps, the modal dispersion can be negelected. The waveguides are fabricated on large substrates (aluminum, FR4 and others) by a direct writing technique. Splitters and couplers can be fabricated with the same technique. The waveguides have a low loss (0.04dB/cm) and high temperature stability (up to 250°C) and are used with 840nm vertical cavity lasers. The waveguide cross section can be chosen between approx. 250μm x 250μm and 50μm x 50μm. We have successfully transmitted up to 10Gbit/s over multimode polymer waveguides with lengths of 100cm. A free space, expanded beam coupling is used for the board-backplane transition, resulting in high alignment tolerances. The overall insertion loss for a backplane connection is typically between 2 and 8 dB, depending on waveguide length, radius of curvature, number of waveguide crossings etc. A typical transceiver power budget of 15-20dB allows the integration of star couplers with up to 16 ports. Several test systems with different interconnection schemes have been realized and tested. Tests include mechanical stability (vibration), thermal stability (cycles, shocks and accelerated aging) and gamma irradiation as well as optical power levels, signal integrity and bit error rates.

Single-mode fiber WDM unit for duplex subscriber link using a substrate with embossed alignment grooves

A wavelength division multiplexing (WDM) unit for single-mode fiber (SMF) duplex transmission, with light source, photodiode (PD), and WDM coupler arranged on a common substrate, is described. Using a tolerant optical design, the optical elements, e.g. lenses and fibers, are positioned in embossed high-precision V grooves without active adjustments. Only the light source, a laser diode (LD) or an edge-emitting LED (ELED), must be aligned for optimum coupling and fixed by laser welding. Typical values of LD-to-fiber and fiber-to-PD coupling loss and crosstalk are 5 dB, 1.2 dB, and -44 dB, respectively. Hence, in spite of the potentially low-cost design, the optical performance of the device is virtually competitive with separated transmitter and receiver units. >

Optical backplane in planar technology

Optical interconnects are expected to overcome the limitations imposed by electrical interconnects. For board- to-board and board-to-multiboard communication we have developed an optical backplane for applications in mobile systems. Compared to existing realizations it is compact, rugged and has the potential to be fabricated at low cost. The main features of the optical backplane in planar technology are free space expanded beam transmission between boards and backplane and guided wave transmission within the backplane. No optical connectors are required. Due to the expanded beams and highly multimode waveguides large coupling tolerances of several 100 micrometers are achieved. Low loss polymer backplane waveguides allow transmission length of more than 19 inches. Demonstrators for board-to-board interconnections and for ring and star networks have been realized. Transmission experiments at 1GBit/s have been successfully performed. First environmental test with respect to dust, moisture, temperature and vibrations showed the feasibility of the concept.