Kishio Yokouchi

Optical interconnect modules with fully integrated reflector mirrors

A robust and cost-effective technology for integration of 45/spl deg/ reflector mirrors and polymer waveguides (WGs) into optical interconnect (OI) substrates is developed. The planar WGs are formed from photopatternable polymers with propagation losses as low as 0.05 dB/cm. The mirrors with losses of 0.5-0.8 dB are fabricated by the microdicing technique allowing lateral and vertical positioning of the mirror plane within several microns. A prototype OI module with integrated channel WGs, mirrors, and assembled connectors is fabricated and successfully tested at 10-Gb/s transmission rate.

Integration technologies for pluggable backplane optical interconnect systems

Integration technologies for board-to-board optical interconnect systems are presented. In the module architecture, optical transmitters and receivers are placed on the line cards and the signals are routed to the optically passive backplane through optical jumpers. The backplane contains a light guiding layer with embedded polymer waveguides (WGs) and 45-deg reflector micromirrors. The WGs are fabricated by direct lithographic patterning and have propagation losses as low as 0.05 dB/cm. The wedge dicing technology is developed for fabrication of the 45-deg micromirrors with 0.5-dB excess losses. The pluggable optical connectors with microlens adaptors couple the light from the optical jumpers into the backplane WGs. Evaluation of the connector alignment tolerances demonstrates a very weak dependence of the coupling efficiency on the axial displacement and a more significant effect of the radial shifts. The presented results show that the displacement tolerances can be substantially improved with auxiliary lenses formed on the substrate. Prototype optical interconnect modules with integrated channel WGs, mirrors, and assembled connectors are fabricated with insertion losses of 5 to 6 dB. The modules successfully pass the high-speed transmission tests at data rates up to 11 Gbits/s.

Electrooptic planar deflector switches with thin-film PLZT active elements

First prototypes of electrooptic (EO) planar deflector switches (PDSs) are fabricated with hybrid integration on Si substrates. Planar optical modules, made in silica-on-silicon technology, consist of input and output (I/O) waveguide microlenses facing each other and slab waveguides in between. The modules interconnect the I/O fibers with laterally collimated light beams less than 400 /spl mu/m in width at distances up to 100 mm with losses lower than 3 dB. Thin lead lanthanum zirconium titanate (PLZT) films with prism-shaped electrodes grown on SrTiO/sub 3/ substrates form the deflector elements. The PLZT films are more than 10 /spl mu/m thick with EO coefficients about 40 pm/V. The deflector assembly technology provides chip vertical positioning accuracy better than 1 /spl mu/m. The deflector chips are attached to the optical substrates with thermo-compression flip-chip bonding. The optical power losses of the modules with test silica chips can be as low as 3.6 dB. However, the lowest module losses achieved with PLZT are about 10 dB. The channel-to-channel switching operations are demonstrated at about 40 V and switching times less than 500 ns.

Two-dimensional microlens arrays in silica-on-silicon planar lightwave circuit technology

Two-dimensional (2-D) microlens arrays have been fabricated with silica-on-silicon planar lightwave circuit (PLC) technology. Several experimental techniques and computer simulation methods are applied to characterize properties of single and double microlens arrays, with one and two refracting surfaces, respectively. Systematic comparison of the measured and simulated beam propagation profiles enables optimi- zation of the lens and module design resulting in higher input-output coupling efficiency. The insertion losses of the lens-slab-lens optical modules with 90-mm-long slab waveguides are measured to be 2.1 and 3.5 dB for the double and single lens modules, respectively. Comprehen- sive analysis reveals the major loss contributions. Excess losses of the modules caused by variations of the lens curvatures, material refractive indexes, light wavelength, etc., can be controlled within the acceptable limits. Further possibilities for the module loss reduction are discussed. Fairly weak wavelength dependence as well as overall stability of the module properties indicate that the microlens arrays are suitable for dense wavelength division multiplexing (DWDM) photonic networks.

Integrated waveguide micro-optic elements for 3D routing in board-level optical interconnects

Planar waveguides and embedded microelements such as 45o vertical mirrors, lateral mirrors, bends, and microlenses comprise main building blocks of the waveguide-based optical printed circuit boards (PCB) for board-level optical interconnects (OI). These microelements enable a variety of three dimensional (3D) routing architectures which are required to support high density interconnects in optical boards. Optical polymers have proved to be the materials of choice for large-scale OI modules with propagation dimensions exceeding 100 mm. In order to meet the loss budget available for the integrated OI modules, the polymers are expected to have optical losses less than 0.05 dB/cm. Both channel and slab waveguides can be used to transmit the signals between the input and output ports. In the case of channel waveguides, the critical issues are the waveguide core shaping, propagation losses and ability to form various passive elements such as bends, crossings and reflective mirrors. In the case of slab waveguides, two dimensional waveguide microlenses have to be designed to collimate the light beams for propagation at longer distances with the controllable beam divergences. The 45o micromirrors can be used to couple the light signal in and out of the waveguiding layer and enable 3D routing of the optical signal in the waveguiding layers. In this work, we present the experimental and computational results on the development of different waveguide devices and microelements for the board level OI.

Planar hybrid polymer-silica microlenses with tunable beamwidth and focal length

Thermally tunable planar microlenses have been fabricated with a hybrid process utilizing silica-on-silicon and polymer planar lightwave circuit technologies. The silica microlens has a double concave gap filled with an optical polymer. The lens collimates the light beam with a beamwidth of less than 450 /spl mu/m at distances up to 100 mm. The experiments presented demonstrate that by varying the lens temperature in a range of 60/spl deg/C the beamwidth can be tuned by /spl plusmn/40% at different distances from the lens. The beam-propagation-method simulations show that adjusting the lens curvature can control the beamwidth tunability range and thermal sensitivity. That allows optimization of the lens designs for different applications.

10+ Gb/s board-level optical interconnects: fabrication, assembly, and testing

Fabrication and assembly technologies for high-speed board-to-board optical interconnect (B2OI) systems are presented. In the system architecture, the transmitters and receivers are placed on the linecards and the optical signals are routed to the optically passive backplane through the optical jumpers with MTP connectors. The backplane contains an optical layer with embedded polymer waveguides and 45° reflector micromirrors. The waveguides are fabricated by direct lithographic patterning and have propagation losses as low as 0.05 dB/cm at 850 nm. Hot-embossing is also evaluated for the waveguide fabrication demonstrating the waveguide propagation losses in the range of 0.06-0.1 dB/cm but rather poor channel-to-channel uniformity. The wedge dicing technology is developed for fabrication of the 45° reflector micromirrors with 0.5 dB losses. The pluggable optical connectors with microlens adaptors are used to couple the light from the optical jumpers into the backplane waveguides. The fabricated prototype optical interconnect modules with integrated channel waveguides, mirrors, and assembled connectors demonstrate insertion losses of 5-6 dB. The modules successfully pass high-speed transmission tests at data rates up to 11 Gb/s.

Backplane photonic interconnect modules with optical jumpers

Prototypes of optical interconnect (OI) modules for backplane applications are presented. The transceivers attached to the linecards E/O convert the signals that are passed to and from the backplane by optical jumpers terminated with MTP-type connectors. The connectors plug into adaptors attached to the backplane and the microlens arrays mounted in the adaptors couple the light between the fibers and waveguides. Planar polymer channel waveguides with 30-50 μm cross-sections route the optical signals across the board with propagation losses as low as 0.05 dB/cm @ 850 nm. The 45º-tapered integrated micromirrors reflect the light in and out of the waveguide plane with the loss of 0.8 dB per mirror. The connector displacement measurements indicate that the adaptor lateral assembly accuracy can be at least ±10 μm for the excess loss not exceeding 1 dB. Insertion losses of the test modules with integrated waveguides, 45º mirrors, and pluggable optical jumper connectors are about 5 dB. Eye diagrams at 10.7 Gb/s have typical width and height of 70 ps and 400 mV, respectively, and jitter of about 20 ps.

A novel method to measure refractive index of liquid and curable liquid substances

A novel method to measure refractive index (RI) of liquid and curable liquid substances is presented. Planar microlenses with two refracting interfaces facing each other are fabricated with a planar lightwave circuit technology. A liquid, whose RI is to be determined, is filled between the two refracting surfaces and the width of the beam passing through the lens is measured. By comparing the measured beam width with the analytical results, the RI of the liquid can be determined accurately. This method is applicable for measurements of RI absolute values of almost any liquid or curable liquid substances, and can routinely achieve a precision of 1/spl times/10/sup -4/ by using a simple setup with a standard beam profiler. The method easily enables measurements of RI dependences on temperature, wavelength, polarization, etc.

Optical interconnect modules for high-speed backplane applications

Prototype optical interconnect modules with integrated polymer waveguides, out-of-plane reflector mirrors, and pluggable optical jumper connectors are fabricated. The modules have 5 dB insertion losses and can support 10+ Gb/s transmission at 850 nm.