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Cell sheet engineering allows investigators/clinicians to prepare cell-dense three-dimensional (3-D) tissues, and various clinical trials with these fabricated tissues have already been performed for regenerating damaged tissues. Cell sheets are easily manipulated and 3-D tissues can be rapidly fabricated by layering the cell sheets. This study used optical coherence tomography (OCT) to noninvasively analyze the following processes: (1) adhesions between layered cell sheets, and (2) the beating and functional interaction of cardiac cell sheet-tissues for fabricating functional thicker 3-D tissues. The tight adhesions and functional couplings between layered cell sheets could be observed cross-sectionally and in real time. Importantly, the noninvasive and cross-sectional analyses of OCT make possible to fabricate 3-D tissues by confirming the adherence and functional couplings between layered cell sheets. OCT technology would contribute to cell sheet engineering and regenerative medicine., Highlights • Development of an OCT system to noninvasively analyze three-dimensional cell sheet-tissues. • Noninvasive and cross-sectional observation of the adhesions between layered cell sheets in detail. • Noninvasive and cross-sectional observation of beating three-dimensional cardiac tissues.

We propose a novel method for controlling the shape of a short period domain-inverted structure utilizing a multi-pulse poling method. Using this technique, periodically domain-inverted structures with periods of 1.4-2.4 μm were fabricated for over 10 mm interaction length in 2 mm thick Z-cut MgO: LiNbO3 crystal. We have demonstrated highly efficient ultraviolet light generation (340-390 nm) using bulk QPM-SHG devices with these structures. Continuous wave 72 mW at wavelength of 372 nm was generated with conversion efficiency of 17 %.

Quasi-phase matched (QPM) second-harmonic generation (SHG) device offers various application for blue and ultra-violet (UV) radiations. Advanced poling technology made it possible to realize micron and sub-micron poling geometry in efficient nonlinear materials. Using these techniques, first-order nonlinear gratings have been realized for high power blue and UV SHG. Based on these devices, high power short wavelength laser sources were demonstrated for practical use. Recent progress in this area is reviewed with emphasis on research work of the author's group using bulk and waveguide QPM devices.

We demonstrate highly efficient frequency doubling of a 160 mW-AlGaAs three-section tunable distributed Bragg reflector (DBR) laser diode with real refractive-index-guided structure in a quasi-phase-matched second harmonic generation (QPM-SHG) ridge-type waveguide device. We realized high coupling efficiency of the DBR laser diode and the QPM-SHG waveguide device using a planar-type butt-coupling configuration. High-power SHG blue violet laser was fabricated, whose volume is 0.3 cc. This SHG blue-violet laser satisfied the several specifications for optical disk systems, and the pulsed blue-violet light (410 nm) power of 62 mW was generated.

We present a method for controlling the shape of the domain-inverted structure in an off-cut MgO: LiNbO3 crystal utilizing two-dimensional high-voltage application. Using this technique, a periodically domain-inverted structure with a period of 3.2 Jim and thickness of 2.0 μm was fabricated over a 10-mminteraction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated a cw blue-violet second-harmonic generation of 17.3 mW at the wavelength of 426 nm with a single pass of 55 mW of cw AlGaAs laser diode input, which corresponded to a 31 % power conversion efficiency.

The resistance to photorefractive damage is investigated for several nonlinear crystals. A quasi-phase-matched (QPM) second harmonic generation (SHG) waveguide device is fabricated in 5 mol% Mg-doped LiNbO3 which has high resistance to optical damage. The SHG blue laser of the QPM-SHG waveguide device and a tunable distributed Bragg reflector (DBR) laser diode is demonstrated, wherein output stability of continuous blue light is measured. The SHG blue laser, using the QPM-SHG waveguide device with broadened flat matching response, shows good modulation characteristics. The pulsed peak power of 23 mW with rectangular modulated waveform is generated. The SHG blue laser is installed to an optical head, and good recording and readout characteristics are demonstrated. Moreover, butt-coupled SHG blue laser is examined to gain a miniature module with volume of 0·8 cc.

A compact, high power SHG green light source with wide operation temperature range over 30 degrees Celsius has been developed by using a wavelength-locked laser diode and a 0.5mm-long periodically poled Mg:LiNbO3(PPMgLN). A continuous green light of 1.7W was generated by intracavity frequency doubling of a Nd:YVO4 laser with the PPMgLN. The wall-plug efficiency was as high as 18.9%. The volume of the green light source was 2cc.

A high power SHG blue laser with direct modulation capability at high frequency has been demonstrated usinga tunable distributed Bragg reflector (DBR) laser diode and a waveguide-type quasi-phase-matched secondharmonic generation (QPM-SHG) device in x-cut Mg doped LiNbO3. Continuous blue light power of 12 mWand pulsed peak power of 26 mW were generated. The SHG blue laser was installed to an optical head, andreadout of ROM disk and recording on phase change optical disk were performed. A butt-coupling-type 0.8cc SHG blue laser was also fabricated. It was indicated that SHG blue laser is applicable to high-density opticaldisk system.

A half-wave thin film was formed on the facet of a proton-exchanged waveguide by the oblique deposition of Ta2O5. Planar-type butt coupling of the waveguide on the z-cut LiTaO3 substrate to the AlGaAs laser diode in transverse electric mode oscillation was realized with coupling efficiency as high as 53%.

We report wavelength stabilization of a laser diode using a highly efficient distributed Bragg reflector (DBR) grating formed on a LiTaO3 quasi-phase-matched second harmonic generation (QPM-SHG) device. Fabricating the second-order DBR on the LiTaO3 waveguide, the reflectivity of 90% and FWHM wavelength bandwidth of 0.2 nm were obtained. By stabilizing the oscillation wavelength of the laser diode, 3.1 mW of blue light was generated in the QPM-SHG device with the monolithic grating.

The fabrication of a periodic domain inversion in LiTaO3 and LiNbO3 using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si2+ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO3. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W.

Direct frequency doubling of a wavelength locked laser diode with an optical bandpass filter in a confocal optical configuration is demonstrated. The wavelength of the laser diode was locked in single longitudinal mode oscillation and tuned to phase-matching wavelength of a quasi-phase-matched second harmonic generation device based on a LiTaO3 Waveguide. Stable blue light of 4.2 mW was obtained for incident power of 48 mW.