Yasuki Sakurai

Demonstrated fossil-fuel-free energy cycle using magnesium and laser

The authors propose an energy cycle based on a renewable fuel. Magnesium is chosen as an energy carrier and is combusted with water to retrieve energy using many power devices. MgO, the combustion residue, is reduced back to Mg by laser radiation generated from solar and other renewable energy sources. They have achieved an energy recovery efficiency of 42.5% for converting MgO to magnesium, using a laser. Combined with a demonstrated 38% efficiency for converting an artificial sunlight source (metal halide lamp) into laser output energy indicates that the proposed energy cycle is already in a feasible range for practical use.

Control of Group Delay and Chromatic Dispersion in Tunable Hollow Waveguide with Highly Reflective Mirrors

We propose the control of group delay and chromatic dispersion in a hollow waveguide with a variable air core and highly reflective mirrors. Both group delay and chromatic dispersion in a hollow optical waveguide increase markedly with decreasing air core. A wide tunability of group velocity and chromatic dispersion is predicted by reducing the air core to nearly half of wavelength. We discuss the potential applications of the proposed hollow waveguide for compact photonic integrated circuits including tunable optical delay lines, interferometers, chromatic dispersion compensators and dispersion slope compensators.

Tunable hollow waveguide distributed Bragg reflectors with variable air core

We demonstrate a tunable hollow waveguide distributed Bragg reflector consisting of a grating loaded slab hollow waveguide with a variable air-core. The modeling shows that a change in an air-core thickness enables a large shift of several tens of nanometers in Bragg wavelength due to a change of several percents in a propagation constant. We fabricated a slab hollow waveguide Bragg reflector with 620 mum long and, 190 nm deep 1st-order circular grating composed of SiO2, exhibiting strong Bragg reflection at 1558 nm with an air-core thickness of 10 mum for TM mode. The peak reflectivity is 65% including fiber coupling losses, the 3-dB bandwidth is 2.8 nm and the grating-induced loss is less than 0.5 dB. We demonstrate a 3 nm wavelength tuning of the fabricated hollow waveguide Bragg reflector by changing an air-core thickness from 10 mum to 7.9 mum.

Tunable stop-band hollow waveguide Bragg reflectors with tapered air core for adaptive dispersion-compensation

We propose a tunable stop-band hollow waveguide Bragg reflector with a variable tapered air-core. We demonstrate the tunable operation of both bandwidth and center-wavelength by changing a tapered air-core thickness. Wavelength tuning of over 1.0% and stop-band expansion up to 5 nm are realized

Tunable hollow waveguide Bragg grating with low-temperature dependence

We demonstrate a tunable hollow waveguide Bragg grating with low-temperature dependence. We fabricated a distributed Bragg reflector consisting of a grating loaded slab semiconductor hollow waveguide with a variable air-core. A change in an air-core thickness enables us to achieve a tunable propagation constant of several percents resulting in a large shift of several tens of nanometers in Bragg wavelength. We demonstrate 10nm continuous wavelength tuning of a peak reflectivity. This value corresponds to a propagation constant change of 0.64%, which is larger than that of thermo-optic effects or electro-optic effects. The measured temperature sensitivity of the peak wavelength is as low as 0.016nm∕K, which is seven times smaller than that of conventional semiconductor waveguide devices.

Proposal of tunable hollow waveguide distributed Bragg reflectors

We propose a novel tunable distributed Bragg reflector (DBR) consisting of a grating loaded slab hollow waveguide with a variable air core. A change in an air core thickness of the tunable hollow waveguide gives us a large shift of over 100 nm in Bragg wavelength due to a change of several percents in a propagation constant. In order to obtain the high reflectivity and wide tunability of the tunable hollow waveguide DBR, the optimisation of the grating depth and grating length is carried out with minimizing radiation loss and distortion of reflection spectra induced by the corrugation. The modelling result shows a possibility of wide tunability of several tens nm with maintaining a high reflectivity of more than 90% without noticeable radiation loss and distortion of reflection spectra. We expect various device applications of the proposed tunable hollow waveguide DBR, which may include tunable band-pass filters, gain equalizers and dispersion compensators.

Air core thickness dependence of propagation loss of slab hollow waveguide

We present the core thickness dependence of the propagation loss and the polarization dependence loss (PDL) of hollow waveguides of various air core thicknesses. The addition of phase-control layers to GaAs/AlAs multilayer mirrors enables us to reduce the PDL by one order of magnitude. The propagation loss and the PDL of a 5 µm air core hollow waveguide are 2.8 dB/cm and 1.7 dB/cm, respectively, which are currently limited by the reflectivity (0.998) of the GaAs/AlAs multilayer mirrors.

Giant Bragg Wavelength Tuning of Tunable Hollow Waveguide Bragg Reflector

We demonstrate a giant Bragg wavelength tuning with a grating loaded hollow waveguide Bragg reflector. An air-core thickness change of a hollow waveguide enables us to achieve a large propagation constant change over few tens percent, which would be useful for various tunable optical devices. Our observed Bragg-wavelength tuning range is over 160 nm at an air-core thickness change from 10.7 to 1.8 µm, which corresponds to a propagation constant change of over 10%. This is the record large tuning value ever reported in conventional tuning schemes such as thermo-optic or electro-optic effects.

Temperature insensitive operation of widely tunable hollow waveguide grating

We demonstrate the widely tunable operation and low temperature dependence of a hollow waveguide grating for the first time. The obtained tuning range and temperature sensitivity of the grating filter wavelength is 10 nm and less than 0.016 nm/K, respectively.

Experimental Study of Magnesium Production with Laser for Clean Energy Cycle

A new scheme of generating power called magnesium injection cycle [MAGIC] engine was developed. Magnesium [Mg] and water are put into the chamber and ignited at 500 degree Celsius. Mg reaction with water produces hydrogen [H2] gas. The hydrogen blows out and reacts with oxygen [O2] gas to generate H2O and energy at the exit nozzle. These reactions occur simultaneously and generate thrust. In order to reproduce Mg, the residual MgO is irradiated by focused cw CO2 laser (1000 W) at 20 Pa. Then, high temperature (over 4000 degree Celsius) is exerted in tiny spot thus MgO reduction in equilibrium is achievable. Spectroscopic analysis was conducted on the Mg/MgO vapor under atmospheric condition. The Mg line at 518 nm, MgO line at 500 nm and O+ line were confirmed. This proves that the MgO is dissociated by laser irradiation These experiments confirm that the scheme can be used for magnesium energy cycle system with practical efficiency and large throughput.