Krishnan R. Parameswaran

All-optical diode in a periodically poled lithium niobate waveguide

We have demonstrated a guided-wave all-optical diode based on engineered quasiphase Matching in a LiNbO3 channel waveguide. For input peak powers beyond 1.5 W at 1.55 μm, the device exhibited a spatially nonreciprocal response, leading to optical isolation with contrasts as high as 90% at 3.1 W, in agreement with theoretical predictions.

Highly efficient second-harmonic generation in buried waveguides formed by annealed and reverse proton exchange in periodically poled lithium niobate

Efficient three-wave mixing devices have numerous applications, including wavelength conversion, dispersion compensation, and all-optical switching. Second-harmonic generation (SHG) is a useful diagnostic for near-degenerate operation of these devices. With buried waveguides formed in periodically poled lithium niobate by annealed and reverse proton exchange, we demonstrate what is believed to be the highest normalized conversion efficiency (150%/W cm(2)) for SHG in the 1550-nm communications band reported to date.

Multiple-channel wavelength conversion by use of engineered quasi-phase-matching structures in LiNbO3 waveguides

We report difference frequency generation-based wavelength converters with multiple phase-matching wavelengths that use engineered quasi-phase-matching structures in LiNbO(3) waveguides. Multiple-channel wavelength conversion is demonstrated within the 1.5-mum band and between the 1.3- and 1.5-mum bands. With simultaneous use of M pump wavelengths, these devices can also be used to perform wavelength broadcasting, in which each of N input signals is converted into M output wavelengths.

Observation of 99% pump depletion in single-pass second-harmonic generation in a periodically poled lithium niobate waveguide

We report 99% pump depletion in single-pass second-harmonic generation. Quasi-cw pulses at 1550 nm were frequency doubled in an annealed proton-exchanged waveguide formed in periodically poled lithium niobate. Measurements of pump depletion and second-harmonic generation agree with results from numerical integration of the coupled-mode equations that describe the process.

Difference frequency generation of 8-µm radiation in orientation-patterned GaAs

First-order quasi-phase-matched difference frequency generation of narrowband tunable mid-infrared light is demonstrated in orientation-patterned GaAs. The all-epitaxial orientation-patterned crystal is fabricated by a combination of molecular beam epitaxy and hydride vapor phase epitaxy. Lasers at 1.3 and 1.55 microm were mixed to give an idler output at 8 microm, with power and wavelength tuning consistent with theoretical estimates, indicating excellent material uniformity over the 19-mm-long and 500-microm-thick device.

Vapor-transport equilibrated near-stoichiometric lithium tantalate for frequency-conversion applications.

Near-stoichiometric lithium tantalate (SLT) crystals were produced from congruent lithium tantalate by a vapor-transport equilibration process. Because of the resultant increase in photoconductivity and reduction in photogalvanism, the crystals showed no observable photorefractive damage at 514.5 nm up to the highest intensity used, 2 MW/cm2. The crystals also exhibited low green-induced infrared absorption, a Curie temperature of 693 degrees C, and a coercive field of 80 V/mm. The SLT samples were periodically poled with an 8-microm-period grating, permitting first-order quasi-phase-matched second-harmonic generation of 532-nm radiation at 43 degrees C. A 17-mm-long sample generated 1.6 W of continuous-wave output power at 532 nm for 50 h. With 150-ns pulses at a 100-kHz repetition rate in the same sample, 5-W average-power, 532-nm radiation was generated for 1000 h. No damage to the crystal and no aging effects were observed during these experiments.

Efficient wide-band and tunable midspan spectral inverter using cascaded nonlinearities in LiNbO 3 waveguides

We report on efficient (-7-dB fiber-to-fiber), wide-band (over 70 nm), tunable, and excess-noise-free mid-span spectral inverters based on cascaded second-order nonlinearities in periodically poled LiNbO/sub 3/ waveguides. We demonstrate their performance in a 4/spl times/10 Gb/s transmission over 150 km of standard single-mode fiber.

Periodic poling of magnesium-oxide-doped lithium niobate

In this article, poling characteristics and periodic poling of magnesium-oxide-doped lithium niobate (MgLN) are described. Periodic poling was done by the electric field method, with which uniform gratings were produced. The domain wall velocity as a function of poling field was measured and used to determine conditions for self-terminating periodic poling. A computational model for the self-termination method is also discussed here. In the experiment, it was found that thermal history prior to poling has a significant influence on the poling quality.

Femtosecond second-harmonic generation in periodically poled lithium niobate waveguides with simultaneous strong pump depletion and group-velocity walk-off

We report studies of second-harmonic generation (SHG) of femtosecond pulses in long periodically poled lithium niobate waveguides under large conversion conditions. Strong saturation of the SHG efficiency was observed, accompanied by spectral and temporal distortion of the pump pulse. Our simulation studies suggest that the pulse distortions may be caused by the interaction of the phase-matched SHG process and an additional cascaded χ(2) process or processes, leading to a large nonlinear phase modulation. Such additional cascaded χ(2) processes could be caused by the existence of multiple transverse modes in the nonlinear waveguide. These phenomena, which to our knowledge have not been reported previously, may have a significant effect on studies of high-power short-pulse parametric process in waveguide devices and on the design of novel nonlinear optical waveguide devices for such applications.

Low-power all-optical gate based on sum frequency mixing in APE waveguides in PPLN

We present an all-optical gate implemented in periodically poled lithium niobate (PPLN) (LiNbO/sub 3/). Efficient mixing is achieved by using a phase-matched guided-wave interaction. A control wave at 1.537 /spl mu/m is used to gate a signal at 1.552 /spl mu/m, where a control power of 185 mW is sufficient to achieve 96% depletion of a low-power signal. A simple switch configuration is described whereby high-contrast low-power all-optical switching can be performed.