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We examined characteristics of Au-Au thin films bonding after annealing for getter activation. From SAM observation, almost whole area was well bonded except defects due to particles. The bonding strength was so high that the bonded specimen was fractured not from the bonding interface but from bulk substrate in tensile test. Even after annealing, Ti/Pt/Au film layers were not diffused into each other. On the other hand, Au crystal grains were recrystallized and continuously connected across Au-Au bonding interface.

We propose a model to reduce the influence that the light-shift induced frequency drift has on the long-term stability of coherent population trapping (CPT)-based low-power atomic clocks. We experimentally validated the proposed model using the chip-scale atomic clock architecture. The model considers both the drift of the dc-bias current to compensate for the wavelength aging of the vertical-cavity surface-emitting laser (VCSEL) and the variation in the modulation index of the light field generated by the VCSEL. We investigated the dc-bias-current-dependency of the frequency drift in an atomic clock module both theoretically and experimentally, confirming that the frequency drift can change as a function of the VCSEL basic parameters. When the atomic clock module was operated over a period of five months at the dc-bias current affording a zero-crossing of the clock frequency drift, the Allan standard deviation and clock frequency drift for long-term stability were 8.0 × 10 − 12 for averaging times of 4 × 10 6 s and 2.4 × 10 − 13/day, respectively. Our approach is promising to improve the long-term stability of CPT-based low-power atomic clocks.

Spatial resolutions of diffracted beams by photorefractive polymers are investigated in detail for applying the polymers to diffractive optical elements. The coupled wave equations for the four-wave mixing in photorefractive polymers and their solutions by applying the two-beam coupling approximation are derived taking the orientational enhancement effect into consideration. Characteristics of the diffraction efficiency of the polymers for the applied electric field, the incident angles of beams, the incident radiation intensity and the polarization are clarified. Furthermore, resolutions of diffracted images with the polymers are discussed by a numerical analysis from the viewpoint of the Bragg diffraction in a spatial frequency domain. An experiment with the TPD (tetra-phenyl-diphenyldiamine) acrylate based photorefractive polymers and the USAF test target is also performed to measure the spatial resolution of two-dimensional images diffracted by the polymer and to verify the calculated results. It is r...

We propose an image cross-connector using an organic photorefractive polymer. With this device, it is possible to perform a reconfigurable connection between multiple input–output image ports by setting the incident angle of individual control beams to minute levels. The use of a polymer can reduce the thickness of the index grating to be induced inside the medium, which can also reduce the distortion of the output image and bring about high precise image connection without an additional optical system. We conduct an experiment with a hole-transport polymer PATPD to verify the operations of an image cross-connector, in which different images from a vertical array of input images would be connected separately to two output ports by two control beams that were injected at different angles.

A 780 nm-range 40 channels vertical-cavity surface-emitting laser (VCSEL) array was developed as a writing light source for printers. A 15° off missoriented GaAs substrate, an aluminum-free GaInAsP/GaInP compressively-strained multiple quantum well and an anisotropic-shape transverse-mode filter were employed to control polarization characteristics. The anisotropic-shape transverse-mode filter also suppressed higher transverse-mode and enabled high-power single-mode operation. Thus, orthogonal-polarization suppression-ratio (OPSR) of over 22 dB and side-mode suppression-ratio (SMSR) of 30 dB were obtained at operation power of 3mW at same time for wide oxide-aperture range below 50 μm2. Moreover, a thermal resistance was reduced for 38% by increasing a thickness of high thermal conductivity layer (3λ/4-AlAs layer) near a cavity. By this structure, a peak-power increased to 1.3 times. Moreover, a power-fall caused by self-heating at pulse-rise was decreased to 10% and the one caused by a thermal-crosstalk between channels was decreased to 46%. The VCSEL array was mounted in a ceramic package with a tilted seal glass to prevent optical-crosstalk caused by other channels. Thus, we achieved stable-output and high-quality beam characteristics for long-duration pulse drive.

We propose an all-optical switching device, photorefractive connection module (PRCM), with an organic photorefractive polymer PATPD. Spatially multiplexed time-series signals propagating in optical bus line can be branched by illuminating matrix patterned control beams.

We propose an optically controllable device Photorefractive Connection Module (PRCM) for free-space optical interconnection between boards. The optical signal composed of a large number of spatially divided channels passes through the photorefractive material which is core of PRCM. In the photorefractive material, diffraction gratings are induced only where the control beam and the pump beam are illuminated. The signal beams in desired spatial channels can be diffracted by setting an appropriate pattern of the control beam and extracted by separating from the control beam with a beam splitter. In this study, we use organic photorefractive polymer PATPD as the photorefractive material. Diffraction efficiency of PATPD is comparable with thick inorganic crystals although the thickness of PATPD is less than 1/10 of these crystals. Thin gratings have a large advantage for PRCM because the thickness of the gratings causes large crosstalk between spatial channels. In addition, the constraint of phase matching is reduced because the phase mismatch is proportional to the thickness of the material. The decrease of the phase mismatch provides large allowance for misalignment of incident angle of beams; therefore it becomes easy to adjust incident angles. We reveal the relation of diffraction efficiency to angular difference of PATPD by analysis and experiment. Diffraction efficiency decreases by half at the difference of 0.5°, which is about ten times larger than that of thick crystals. We demonstrate that it is possible to extract the signal beams in desired channels and reconfigure the extraction pattern according to optical control by using PATPD.