M. Küpfer

Optical waveguiding and nonlinear optics in high quality 2‐docosylamino‐5‐nitropyridine Langmuir–Blodgett films

The linear and nonlinear optical properties of well‐ordered Y‐type Langmuir–Blodgett (LB) multilayers of 2‐docosylamino‐5‐nitropyridine (DCANP) have been investigated. The nonlinear optical susceptibilities have been determined for the wavelengths λ=1064 nm [d33=(7.8±1) pm/V, d31=(2.0±0.5) pm/V] and λ=1318 nm [d33=(5.6±1) pm/V]. In first waveguiding experiments carried out TE0 and TM0 modes propagating over more than 20 mm could be excited. Coupling experiments allowed the determination of the dispersion of the refractive index n3 (n632.8 nm3 =1.598). Guided wave attenuation coefficients as low as 12 dB/cm (at the wavelength λ=632.8 nm) are reported.

Cerenkov-type phase-matched second-harmonic generation in DCANP Langmuir-Blodgett film waveguides

Abstract We report for the first time guided-wave second-harmonic generation in nonlinear optically active Langmuir-Blodgett (LB) films. Phase-matched frequency-doubling was observed in LB films of 2-docosylamino-5-nitropyridine (DCANP) by using the Cerenkov-type configuration. The charge transfer axis of the DCANP molecules essentially lies in a plane parallel to the dipping direction. Therefore the largest nonlinear optical coefficient d 33 could be used by exciting TE modes propagating in the film. Gratings were used to couple light at λ= 1064 nm into the LB film waveguide.

Phase-matched second harmonic blue light generation in ion implanted KNbO3 planar waveguides with 29% conversion efficiency

Abstract We report for the first time to our knowledge, noncritical phase-matched second harmonic generation in an ion-implanted KNbO 3 planar waveguide. The guided TM 0 mode of the fundamental wave (868 nm) is converted into the second harmonic TE 1 mode (434 nm). From 1.3 kW of internal fundamental peak power 385 W second harmonic blue light is generated giving a conversion efficiency of 29%. A comparison of the measured and the theoretical efficiencies implies that phase-matching is achieved over the full waveguide length. Based on these first experimental results we estimate that 100 mW of blue light can be generated from 400 mW of input power using an optimized KNbO 3 planar waveguide of 1 cm length.

Depth profile of the nonlinear optical susceptibility of ion‐implanted KNbO3 waveguides

We report on the depth profile of the nonlinear optical susceptibility in ion‐implanted potassium niobate (KNbO3) waveguides using reflected second harmonic generation from wedged samples. After irradiation the waveguide layer exhibits partial loss of its optical nonlinearity that can be recovered to better than 90% of its value of the virgin crystal by subsequent annealing and repoling. We propose microscopic depolarization due to ion implantation to be responsible for the observed decrease of the nonlinear optical susceptibility.

Investigation of chromophore orientation of 2-docosylamino-5-nitropyridine and derivatives by nonlinear optical techniques

Abstract 2-Docosylamino-5-nitropyridine (DCANP) is a strongly nonlinear optical molecule which forms high optical quality Langmuir-Blodgett (LB) films. DCANP shows higher nonlinearities as compared to its aliphatic chain derivatives (C18H37 to C26H53). To explain this we determined the orientation of the chromophores and the hyperpolarizabilities by means of nonlinear optical techniques.

Surface‐emitted green light generated in Langmuir–Blodgett film waveguides

We demonstrate second‐harmonic generation due to counterpropagating beams in planar waveguides of 2‐docosylamino‐5‐nitropyridine (DCANP). The DCANP molecules were deposited by Langmuir–Blodgett techniques and have a preferred alignment within the substrate plane. Four‐layer waveguide structures were used to optimize the trade‐off between propagation loss and efficient surface‐emitted green light.

Guided-wave frequency-doubling in Langmuir-Blodgett film waveguides

We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine. Using the Cerenkov-type configuration we can generate light down to a wavelength of 410 nm. Gratings as well as prisms were used to couple the fundamental beam into the waveguide.

Polymerized non-linear optical Langmuir-Blodgett films based on 2-(21-docosenyl)amino-5-nitropyridine

Abstract Using the Langmuir-Blodgett (LB) technique, multilayer films of 2-(21-docosenyl)amino-5-nitropyridine have been made by transferring stable monomolecular films from an air-water interface onto quartz substrates. Such multilayer films can be polymerized by X-ray irradiation. The films exhibit the same enhanced second harmonic generation efficiency before and after polymerization. No change in the morphology of the films has been observed after polymerization, probably because the vinyl group is at the terminal position of the hydrocarbon chain.

Optical second-harmonic generation from polymerized Langmuir-Blodgett films of 2-(21′-docosenyl)amino-5-nitropyridine

Abstract Thin films of 2-(21′-docosenyl)amino-5-nitropyridine (VECANP) have been prepared by the Langmuir-Blodgett (LB) method. Subsequently the films were polymerized by X-ray irradiation. UV/VIS-spectroscopy showed that the light transparency range extends from 450 nm to at least 2000 nm. The dispersion of the nonlinear optical susceptibilities d 33 and d 31 have been determined in the wavelength range between 840 nm and 1318 nm. The different solubilities of polymerized and non-polymerized VECANP in n-hexane offers the possibility to structure the films laterally (for example to fabricate strip waveguides); a necessary condition for application in integrated optics.

Phase-matched Frequency-doubling in Langmuir-Blodgett Film Waveguides Using the Cerenkov-type Configuration

ABSTRACT We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine (DCANP). The largest nonlinear optical coefficient d33 could be used by exciting TE modes propagating in the film. Using the Cerenkov-type configuration we can generate light in the absorption region of DCANP (at least down to λ = 410 nm where d33 = 27 pm/V, longest wavelength absorption maximum at λ = 380 nm). Conversion efficiencies of up to η meas conv = P2ω/Pω = 2·10−3 were measured (power Pω inside of the film) which is in agreement with the theory. Conditions for further optimization of the frequency-doubling efficiency are evaluated. Using a substrate material with optimized dispersion of the refractive index and a strip-waveguide geometry (width Wstrip = 2 µm) a conversion efficiency of η meas conv ∼ 10%W−1cm−1 could be obtained at a fundamental wavelength of λ = 795 nm.