Phase-matched Waveguide Research Articles

Direct Measurement of Higher-Order Nonlinear Polarization Squeezing.

We report on nonlinear squeezing effects of polarization states of light by harnessing the intrinsic correlations from a polarization-entangled light source and click-counting measurements. Nonlinear Stokes operators are obtained from harnessing the click-counting theory in combination with angular-momentum-type algebras. To quantify quantum effects, theoretical bounds are derived for second- and higher-order moments of nonlinear Stokes operators. The experimental validation of our concept is rendered possible by developing an efficient source, using a spectrally decorrelated type-II phase-matched waveguide inside a Sagnac interferometer. Correlated click statistics and moments are directly obtained from an eight-time-bin quasi-photon-number-resolving detection system. Macroscopic Bell states that are readily available with our source show the distinct nature of nonlinear polarization squeezing in up to eighth-order correlations, matching our theoretical predictions. Furthermore, our data certify nonclassical correlations with high statistical significance, without the need to correct for experimental imperfections and limitations. Also, our nonlinear squeezing can identify nonclassicality of noisy quantum states which is undetectable with the known linear polarization-squeezing criterion.

Ultraviolet to mid-infrared supercontinuum generation in single-crystalline aluminum nitride waveguides.

We demonstrate ultrabroadband supercontinuum generation from ultraviolet to mid-infrared wavelengths in single-crystalline aluminum nitride waveguides. Tunable dispersive waves are observed at the mid-infrared regime by precisely controlling the waveguide widths. In addition, ultraviolet light is generated through cascaded second-harmonic generation in the modal phase-matched waveguides. Numerical simulation indicates a high degree of coherence of the generated spectrum at around the telecom pump and two dispersive waves. Our results establish a reliable path for multiple octave supercontinuum comb generation in single-crystalline aluminum nitride to enable applications including precision frequency metrology and spectroscopy.

RF and Electronics Design of the Compact Ocean Wind Vector Radiometer

The Compact Ocean Wind Vector Radiometer (COWVR) was developed at the Jet Propulsion Laboratory as a proof of concept technology demonstration mission for the Air Force. COWVR is a fully polarimetric imaging radiometer system operating at 18.7, 23.8, and 33.9 GHz . Its receiver subsystem is based on the Jason-3 advanced microwave radiometer, which was launched in early 2016 and is currently in operation. Its enabling components are presented in this article, including the phase-matched waveguide components, noise injection, receivers, and polarimetric backend units.

Monolithic fabrication of quasi phase-matched waveguides by femtosecond laser structuring the χ(2) nonlinearity

We demonstrate second harmonic generation in quasi phase-matched waveguide structures fabricated by direct laser writing. Circular waveguides are inscribed in z-cut lithium niobate that provide well confined guiding of the fundamental and second harmonic wave. In contrast to classic schemes that employ periodically poled crystals, quasi phase-matching is realized by a laser-induced modulation of the nonlinearity inside the waveguide core. The proposed design allows monolithic integration of buried frequency conversion devices with tailored nonlinear response and excellent compatibility to on-chip optical elements. Second harmonic generation of 1064 nm radiation is demonstrated for different grating periods and associated matching temperatures. A maximum conversion efficiency of 5.72% is obtained for a 6 mm long, laser-induced quasi phase-matching grating.

Highly-efficient fully resonant vertical couplers for InP active-passive monolithic integration using vertically phase matched waveguides

A new active-passive monolithic integration approach for photonic components based on vertical evanescent coupling is presented. Two vertically stacked waveguides are used in order to provide full resonant power transfer between them and avoiding the need of tapered structures. Light confinement in each waveguide is achieved combining strong lateral asymmetric structures and bent waveguides, both defined during lithography. Low propagation losses for the active waveguide and coupling efficiencies to the passive section as high as 97% have been obtained.

Dual transmission band Bragg grating assisted asymmetric directional couplers

The use of artificial dispersion by material structuring is investigated for the design of highly wavelength selective directional couplers. Systems of two highly asymmetric coupled waveguides are considered with the artificial dispersion created by distributed Bragg gratings (BGs) operated near photonic band gap. It is shown that even in the case of an asymmetrical directional coupler with initially phase matched waveguides, the achievement of high wavelength selectivity requires the fulfillment of a threshold condition on the BG coupling coefficient. The presence of BG(s) leads in turn to the appearance of two transmission bands instead of one. The wavelength selectivity associated to one of these bands is much higher than that obtained in the absence of BG(s). It is also shown that under particular circumstances, dual band operation can be achieved without threshold condition. The directional coupler then exhibits two transmission bands with approximately the same width and a very low level of insertion losses. Such a dual band transmission coupler is expected to offer new functionalities for wavelength demultiplexing applications.

Short-wavelength infrared second harmonic generation in quantum cascade lasers

We propose an electrically pumped intersubband laser capable of operating at short infrared wavelengths ∼1.5–2.5 μm. Short-wavelength operation is achieved via resonant intracavity second harmonic generation in quantum cascade (QC) lasers based on high band offset heterostructures. This approach overcomes the fundamental problem of intervalley scattering that prohibits direct lasing in QC lasers in this spectral range. The proposed devices can be modulated at a rate exceeding 100 GHz, which may be interesting for a variety of applications. We present detailed calculations of bandstructure design, phase-matched waveguide, and current-output power dependence for the devices based on GaInAs/AlAsSb/InP heterostructures. Accurate position of highly excited subbands is determined by calculating the conduction band (CB) dispersion with the energy-dependent 14-band effective mass, in which matrix elements are adjusted to fit the CB structure obtained with a 30-band k⋅p method. We also discuss the controversial location of lateral valleys, which imposes the limitation on the fundamental laser transition energy.

Waveguides in lithium niobate fabricated by focused ultrashort laser pulses

We report on investigations of the bulk microstructuring of lithium niobate crystals with intense femtosecond laser pulses. In different crystal cuts, optical waveguides were produced whose properties depend strongly on the processing parameters. To explore the origin of the refractive index changes, we subjected the crystals to different conditions (like temperature, illumination, etc.) while monitoring the waveguide output. This way several mechanisms for the change in refractive index could be singled out. These include the photorefractive effect, inhomogeneous ion concentrations and stress in the crystalline lattice. As an application, we demonstrate frequency doubling of 1064 nm laser radiation in a microstructured phase-matched waveguide.

Phase-matched waveguide four-wave mixing scaled to higher peak powers with large-core-area hollow photonic-crystal fibers

Hollow photonic-crystal fibers with large core diameters are shown to allow waveguide nonlinear-optical interactions to be scaled to higher pulse peak powers. Phase-matched four-wave mixing is predicted theoretically and demonstrated experimentally for millijoule nanosecond pulses propagating in a hollow photonic-crystal fiber with a core diameter of about 50 microm , suggesting the way to substantially enhance the efficiency of nonlinear-optical spectral transformations and wave mixing of high-power laser pulses in the gas phase.

特集 超薄膜の構造と機能 有機高分子非線形光学材料：最近のトピックス

The present review is mainly concerned with the macromolecular organic nonlinear optical materials for frequency doubling. Organic polymer materials are expected to apply the optical devices for the transparent, easy processability and so on. Recently some studies were carring out about the polymer, chromophore and device structures. These topics are introduced in this review. One of the major problems for poled polymer systems is the lack of thermal stability after aligningchromophore units. In order to prevent the decay, some ferroelectric or crosslinkable polymers carrying chromophore moiety were prepared. They showed large d coefficients and stability. Previously, the chromophores having shorter absorption wavelength band than the harmonic wavelength have been used. However, it has made possible to apply the longer absorption wavelength chromophores by using Cherenkov type phase matching. Besides, it has reported that the novel two-directional charge transfer molecules possessed large off-diagonal, β components has shown a small decay of d 33 even when the order parameter has relaxed. In optical waveguide structure, quasi phase matching accomplished by periodically poled or bleached waveguide structure was effective method to obtain harmonic light. As the practical and adroid method to achieve phase matching in waveguide, a attempt was made to adjust and suppress the phase matching condition by continuing to apply external dc voltage during frequency doubling. The guide-layer made of low Tg polymer was effective for quick response of chromophore alignment and change of refractive index against external electric field.

Phase-Matched Waveguide Using the Artificial Anisotropic Structure and its Application to a Mode Converter (Short Papers)

Phase matching by the artificial anisotropic structure and its application to a mode converter are proposed for millimeter-wave dielectric circuitry. A phase-matched dielectric planar waveguide is designed and mode conversion characteristics are studied. An experimental result of the nonreciprocal mode converter are presented to show the usefulness of the structure.