Tsuyoshi Aoki

High bandwidth optical interconnection for densely integrated server

We developed optical interconnect technologies, i.e., an optical mid-plane, high-density connector, and a compact transceiver for future servers that enable high-bandwidth and dense integration. Using these technologies, 1500 optical connections and 37.5 Tb/s of bandwidth were built in a blade-server form factor.

Optical interconnect architecture for servers using high bandwidth optical mid-plane

We describe an interconnect architecture that utilizes high bandwidth optical mid-plane. Enabling technologies for high density optical mid-plane are discussed. We developed a prototype to determine the feasibility. The results showed proposed architecture is practical.

Piezoelectric Properties of PZT Film Prepared by Chemical Solution Deposition Method

The influence of the stress and orientation of a lead zirconate titanate (PZT) film on its piezoelectric properties was investigated. Preferentially (111) oriented PZT films were prepared on various substrates with different thermal expansion coefficient, such as stainless steel, alumina, magnesia, and silicon by the CSD method. Preferentially (100) oriented PZT films were also prepared on stainless steel. The displacements of cantilevers of the PZT films with the substrates were measured by the laser Doppler vibration method, and the d31 piezoelectric coefficient was calculated from the displacement. Compressive stress degraded the d31 piezoelectric coefficient of (111) oriented PZT film. In the PZT film with compressive stress, the change of orientation to the (100) direction effectively improved the d31 coefficient. An excellent piezoelectric coefficient (d31 = 55 pm/V) of PZT film was obtained on the stainless steel substrate.

No-polish elastic optical multifiber connector for optical interconnection

An elastic optical multifiber connector compatible with a standard mechanically transferrable connector was realized. The elastic connector has N-shape folded frame parts which are elastically deformable of 100 μm. Physical contact connections between no-polish fibers and a film-waveguide were confirmed. The average insertion loss of the cables terminated at one side with an elastic connector shows 0.16 dB which is almost same as those terminated at both ends with mechanical transferrable connectors. The durability for 250 times mating/demating tests in a mid-plane connector housing were also confirmed. Furthermore, the laser-cleaved fiber facets have smooth surfaces and convex shapes like those of polished connectors. Using the connector and the process, physical contact connections between no-polish fibers were achieved.

Development of low-cost polish-less optical multifiber backplane connector

We developed a novel low-cost polish-less elastically deformable optical multifiber backplane connector. The ferrule deformation and fibers buckling were enabled to cancel the variation in the lengths of unpolished cut fibers. We confirmed the physical contact connection between unpolished cut fibers in the ferrule and a polymer waveguide in a connector for polymer-waveguides connected with mechanical transfer connector (PMT) ferrule. The connection loss is almost the same as that between a conventional polished mechanical transfer (MT) ferrule and the PMT ferrule. We prepared a connector housing to mount the ferrules on a backplane/midplane. The insertion loss and return loss results in the housing show no degradations during 200 mating/demating tests, and there were no fiber breakages or damage to the waveguide core.

Development of low-cost elastic optical multifiber connector for optical interconnection

We propose and demonstrate a novel low-cost elastic optical multifiber connector to realize optical interconnections. The ferrule deformation and fibers buckling are enable to cancel the variation in lengths of unpolished cut fibers. We confirmed a physical contact connection between the ferrule and a PMT ferrule. The connection loss was almost the same as that between a conventional polished MT and the PMT. Also, we prepare A connector housing for mounting the ferrules on a MP is prepared. The insertion loss and return loss measurements in the housing shows no degradations during 250 mating/demating tests.

Measurement of d15 Shear-Mode Piezoelectric Response in PZT Thin Film

Piezoelectric films using d15 shear-mode can be applied to many useful MEMS devices. The small displacement derived from the d15 shear-mode was directly observed by a SPM measurement. An isolated PZT(52/48) active part having a pair of driving Cu electrodes was processed in a 5 m-thick sputtering film. The displacement measurement of the active part and its FEM analysis suggested that the estimated d15 piezoelectric constant of the film was 590 pm/V. And, the d31 value of the film was -120 pm/V measured by a conventional cantilever method. The obtained piezoelectric constants of the PZT film are near those of bulk.

Crystallinity of Microscopically Patterned (Pb,La)(Zr,Ti)O3 Films on (001)Nb-Doped SrTiO3 Substrates Prepared by Chemical Solution Deposition Process with Resist Molds

Arrays of lead lanthanum zirconate titanate (PLZT) precursor square pillars on (001) niobium-doped strontium titanate substrates were prepared by a chemical solution deposition process with resist molds. After firing the precursor pillars, arrays of PLZT ceramic square pillars with various widths ranging from 0.4 to 1.3 µm and heights of 0.5 and 0.7 µm were obtained. The relationship between the crystallinity and width of ceramic pillars was investigated by X-ray diffraction measurements. The crystallinity of PLZT pillars, evaluated on the basis of the peak intensity of the (002) reflection, showed an interesting pattern of behavior in a plot against the width, which is characterized by a sharp peak at a width of 0.7 µm and a sharp decrease in crystallinity at lower this width. Experimental results are interpreted in terms of the stress between the PLZT pillars and substrates for pillars with a width of >0.7 µm and the evaporation of the lead component for pillars with a width of <0.7 µm during the sintering process.

Low-loss connections between no-polish optical fibers in elastically deformable connectors

Low-loss connections between no-polish optical fibers were realized by using a combination of elastically deformable connectors and a laser cleaving process. The elastic connectors have an elastically deformable mechanism, which enables one to cancel out variations both in the fiber length in a fiber ribbon and in the fixed positions of the fiber ribbons in the connectors. A laser cleaving process was employed to cleave no-polish fiber facets. The fiber facets show slightly protruded convex shapes, which were almost the same as those of the polished facets. We confirmed that physical contact connections between the laser-cleaved no-polish fibers in the elastic connectors were realized. The average insertion loss and return loss of cables including connection between the no-polish fibers in elastic connectors were 0.19 dB and 23.4 dB, respectively. The values were almost the same as those of cables including connection between polished fibers in mechanically transferable connectors. Furthermore, the durability of the connections between the elastic connectors over 250 repeated mating/dematings in a high-density mid-plane connector housing was also confirmed.

Optical interconnect technologies enabling high-performance servers

High-speed and compact optical interconnect is indispensable to realize high-performance servers. We developed compact optical transceiver and optical mid-plane with high-density connectors and wiring. Using them, 1500-optical-connections and 37.5 Tb/s-bandwidth in a server were achieved.