Tsutomu Yanagawa

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.

Reducing photorefractive effect in periodically poled ZnO- and MgO-doped LiNbO3 wavelength converters

The photorefractive effect in annealed proton-exchanged waveguides in periodically poled nondoped, MgO- and ZnO-doped LiNbO3 was evaluated by monitoring the quasiphase matching (QPM) wavelength shift induced by a 0.784-μm-irradiating light. The QPM wavelength shift was reduced at room temperature by a factor of 3–6 in ZnO- and MgO-doped samples compared with the nondoped samples within a 104–105-W/cm2-irradiation intensity range. The doped samples exhibited no significant wavelength shifts when the temperature was raised to slightly above room temperature (50–60 °C).

All-optical switching based on cascading of second-order nonlinearities in a periodically poled titanium-diffused lithium niobate waveguide

We report efficient all-optical switching by using a periodically poled titanium-diffused lithium niobate (Ti:PPLN) waveguide. The periodically domain inversion of the Ti:PPLN waveguide is achieved by electric field poling. The switching is driven by the second-order nonlinear effect of the cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes. It is found that about 12% of the signal is switched by a 20-W gate power.

Widely tunable 3.4 μm band difference frequency generation using apodized χ (2) grating

We achieved apodization in a quasi-phase-matched wavelength converter. The new design yields a large bandwidth and a flat phase-matching response with a high conversion efficiency. Using the method, we demonstrate widely tunable 3.4 μm band difference frequency generation in a LiNbO3 ridge waveguide.

Broadband difference frequency generation around phase-match singularity

It is shown that a wide tunability range of greater than 500 nm can be obtained in the 2μm band in an 18 mm long periodically poled lithium niobate chip with a single quasiphase-matching grating period at a constant temperature. This letter demonstrates the difference frequency generation bandwidth. A tunable bandwidth of over 130 nm is experimentally confirmed in the 2μm region. This broad bandwidth can be realized by means of the phase-match curve distortion caused by the phase-match singularity. The wavelength conversion temperature dependence is also shown for several quasiphase-matching grating periods.

CH4 monitoring in ambient air by communication band laser diode based difference frequency generation in a quasi-phase-matched LiNbO3 waveguide

Methane in ambient air is detected by difference frequency generation in a direct-bonded quasi-phase-matched LiNbO3 ridge waveguide using near infrared communication band laser diodes as pump and signal sources. Absorption lines for the Q branch in the 3.3μm ν3 band are measured by using a Hanst configuration multipass cell with a 107m path length. The authors detect 35ppb CH4 in 2kPa ambient air with a single wavelength scan of a signal external cavity laser diode by suppressing various spectroscopic fringes and stabilizing the pump laser diode oscillation mode with a fiber Bragg grating.

Unequally spaced multiple mid-infrared wavelength generation using an engineered quasi-phase-matching device.

We propose a novel quasi-phase-matched (QPM) device that can generate unequally spaced multiple wavelengths. Unequally spaced multiple QPM peaks can be obtained by employing the optimized phase modulation of a periodic domain structure. We fabricated a LiNbO3 waveguide device for 3.2-3.4 microm band difference frequency generation based on the design. Using the multiple mid-infrared outputs, we demonstrate the detection of multiple hydrocarbon gases, namely, methane, ethylene, and ethane.

Simultaneous observation of CO isotopomer absorption by broadband difference-frequency generation using a direct-bonded quasi-phase-matched LiNbO 3 waveguide

Rovibration absorption lines both of 12CO and 13CO are observed simultaneously with the output of a 2 microm broadband difference frequency generated in a direct-bonded quasi-phase-matched LiNbO3 waveguide, which is a 50 mm device with a single quasi-phase-matching period that is operated at a constant temperature. The wavelength conversion efficiency and the difference-frequency generation bandwidth reach 100%/W and 100 nm, respectively. The idler output bandwidth in the 2 microm region is obtained by group-velocity matching or phase-mismatch minimization when a 0.94 microm pump laser diode and a 1.55 microm tunable signal source are used.

Widely Tunable and Highly Efficient 2.3-μm-Band Difference Frequency Generation in Direct-Bonded Quasi-Phase-Matched LiNbO3 Ridge Waveguide

We fabricate a direct-bonded quasi-phase-matched LiNbO3 ridge waveguide for 2.3-µm-band difference frequency generation. The waveguide exhibits a 100 nm bandwidth for a 0.937-µm pump and a 1.55-µm-band signal. A 100%/W conversion efficiency and 0.4 mW output are obtained. We also discuss the temperature dependence of the quasi-phase-matched wavelength.

Widely tunable 2.3 μm-band difference frequency generation in quasiphase-matched LiNbO3 ridge waveguide using index dispersion control

We describe widely tunable 2.3 μm difference frequency generation in direct-bonded quasiphase-matched (QPM)-LiNbO3 (LN) ridge waveguides by controlling the refractive index dispersion. We calculate the phase matching characteristics of waveguides with various core areas for a fixed pump wavelength of 0.934 μm and show that a larger core area results in a wider signal tuning range in the 1.55 μm band. Based on the calculation, we fabricate QPM-LN ridge waveguides with two different waveguide core sizes. A wide tuning range of over 173 nm with a conversion efficiency of 56%/W is demonstrated in the 2.3 μm range using the waveguide with the larger core size. We also carry out CO gas measurements using a signal wavelength in the telecommunication band and detect 44 lines of the CO absorption owing to the wide tuning range and efficient conversion efficiency of the waveguide.