Lidu Huang

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.

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.

Planar waveguide microlenses for nonblocking photonic switches and optical interconnects

Different types of planar waveguide microlenses are fabricated with PLC technologies from a variety of optical materials such as silica, photo-definable epoxy resins, and a number of other optical polymers. Hybrid microlenses are also fabricated in which the base of the lens, with a double concave gap, is formed from silica and the gap is filled with an optical polymer. The optimized lens structures provide the maximum coupling efficiencies between the input and output channels at distances up to 100 mm with a minimum channel pitch of 0.5-0.7 mm. Experimental and theoretical studies provide results on collimation and focusing properties of single and double microlenses made of silica, polymer, and silica/polymer. The evaluation of the temperature and wavelength effects on the collimation characteristics of the lenses demonstrate that the single lenses are more stable and, thus, more suitable for operations under varying conditions. Examples of the planar waveguide microlens applications are presented. In one application the microlens arrays are integrated in fast electrooptic photonic switching modules. In the other application the microlenses are embedded in the backplanes with nonblocking optical interconnects.