Masaki Asobe

Applications of highly nonlinear chalcogenide glass fibers in ultrafast all-optical switches

Applications of chalcogenide glass fibers in ultrafast all-optical switches have been investigated. Ultrafast all-optical switching has been accomplished in an optical Kerr shutter configuration using As/sub 2/S/sub 3/-based glass fiber. The nonlinear refractive index of the As/sub 2/S/sub 3/-based glass is estimated to be n/sub 2/=4.0*10/sup -14/ (cm/sup 2//W), which is higher by two orders of magnitude than that of silica glass fiber. Nonlinear absorption due to two-photon absorption has been revealed to be negligible, and up to a 2 pi -phase shift has been obtained. Switching speed and switching power were investigated experimentally and through calculations. A switching time of 12 ps and a switching power of 5 W can be achieved using a 10-ps gate pulse and only a 1-m chalcogenide glass fiber. However, signal transformation due to cross-phase modulation and group velocity dispersion is not negligible for shorter gate pulses. Lower switching power is possible by reducing the transmission loss and the core area and by optimizing the driving conditions. >

Ultrafast all-optical switching using highly nonlinear chalcogenide glass fiber

Ultrafast all-optical switching with a switching power of 14 W was demonstrated in a Kerr shutter configuration using a single-mode As/sub 2/S/sub 3/-based glass fiber only 48 cm long. The nonlinear refractive index of the fiber was evaluated from the switching characteristics to be n/sub 2/=4.2*10/sup -14/ (cm/sup 2//W), which is higher by two orders of magnitude than silica glass fiber.<<ETX>>

Laser-diode-driven ultrafast all-optical switching by using highly nonlinear chalcogenide glass fiber

Laser-diode-driven all-optical switching is demonstrated with an As2S3-based glass fiber only 2 m long and assistance from an erbium-doped fiber amplifier. The laser-diode operation makes it easy to control ultrafast pulse trains with low timing jitter. Ultrafast switching at as much as 80-GHz repetition rates is successfully demonstrated. The nonlinear refractive index of the fiber is estimated to be 9.3 × 10−15 (cm2/W) at a 1.55-μm wavelength.

Multiple quasi-phase-matched LiNbO3 wavelength converter with a continuously phase-modulated domain structure.

We have devised a novel device structure for a multiple quasi-phase-matched wavelength converter. Optimized continuous phase modulation of a periodic domain structure makes possible multichannel pumping with minimum loss of efficiency. Using the device, we demonstrate variable and simultaneous wavelength conversion of wavelength-division multiplexed signals.

Efficient 3-μm difference frequency generation using direct-bonded quasi-phase-matched LiNbO3 ridge waveguides

We fabricate 50-mm-long direct-bonded quasi-phase-matched LiNbO3 ridge waveguides for difference frequency generation in the 3-μm wavelength range. Conversion efficiency of 40%/W is achieved using a 1-μm-band pump and a 1.55-μm-band signal, and a 0.26-mW output is obtained. We also use the device to demonstrate methane gas detection at around 3.3μm.

Nonlinear refractive index measurement in chalcogenide‐glass fibers by self‐phase modulation

Nonlinear refractive index (n2) of chalcogenide‐glass (As2S3) fibers has been evaluated for the first time from spectral broadening due to self‐phase modulation. The obtained value of n2 was 1.7×10−14 (cm2/W) which is two orders of magnitude higher than the value with silica‐glass fiber. This large n2 value is useful in reducing switching power and size when fiber is used for all‐optical switches.

Efficient 494 mW sum-frequency generation of sodium resonance radiation at 589 nm by using a periodically poled Zn:LiNbO3 ridge waveguide

A solid-state-laser based single-frequency 589 nm light source that can be easily used in the laboratory is needed for sodium spectroscopy studies and cold sodium atom experiments. This paper shows that by using a periodically poled Zn-doped LiNbO(3) ridge waveguide for sum-frequency generation, we can obtain a high conversion efficiency to 589 nm light from two sub-watt 1064 and 1319 nm Nd:YAG lasers via a simple single pass wavelength conversion process without employing an enhancement cavity. A 494 mW light at 589 nm is generated and achieves overall conversion efficiency from the laser power of 41%. Excellent long-term stability of output power is obtained and its standard deviation is characterized to be 0.09%.

Efficient entanglement distribution over 200 kilometers.

Here we report the first demonstration of entanglement distribution over a record distance of 200 km which is of sufficient fidelity to realize secure communication. In contrast to previous entanglement distribution schemes, we use detection elements based on practical avalanche photodiodes (APDs) operating in a self-differencing mode. These APDs are low-cost, compact and easy to operate requiring only electrical cooling to achieve high single photon detection efficiency. The self-differencing APDs in combination with a reliable parametric down-conversion source demonstrate that entanglement distribution over ultra-long distances has become both possible and practical. Consequently the outlook is extremely promising for real world entanglement-based communication between distantly separated parties.

Generation of pulsed polarization-entangled photon pairs in a 1.55-µm band with a periodically poled lithium niobate waveguide and an orthogonal polarization delay circuit

We report a scheme for generating pulsed polarization-entangled photon pairs based on conversion from time-bin entanglement to polarization entanglement by use of an orthogonal polarization delay circuit and post-selection. We have experimentally demonstrated the scheme, using a periodically poled lithium niobate waveguide, and successfully obtained polarization entanglement in the 1.55-microm telecom wavelength band.

Highly Efficient Wavelength Converter Using Direct-Bonded PPZnLN Ridge Waveguide

We fabricated a periodically poled and ZnO-doped LiNbO3 ridge waveguide by employing direct bonding and dry etching techniques. We obtained a second-harmonic generation (SHG) conversion efficiency of 2400%/W, and converted 92% of the pump light into SH light at a pump power of 160 mW. We developed a fiber-coupled module using the fabricated ridge waveguide. The high conversion efficiency and high damage resistance of the ridge waveguide result in the parametric amplification of the signal and converted signal lights. The low insertion loss of the module (-4 dB) and sufficient parametric conversion gain (+8 dB) enable us to achieve a wavelength converter with + 4 dB fiber-to-fiber gain, which means the wavelength converter operates without loss.