F. Kenneth Hopkins

Processing techniques for deoxyribonucleic acid: Biopolymer for photonics applications

Marine-based deoxyribonucleic acid (DNA), purified from waste products of the Japanese fishing industry, has recently become a material of interest in photonics applications. Using highly purified DNA, unique processing techniques developed specifically to transform the purified DNA into a biopolymer suitable for optical device fabrication are reported.

Performance of an electro-optic waveguide modulator fabricated using a deoxyribonucleic-acid-based biopolymer

An electro-optic (EO) planar waveguide modulator using a deoxyribonucleic acid (DNA)-based biopolymer for both the waveguide core and cladding layers has been fabricated and its performance evaluated. A cross-linked DNA-surfactant biopolymer was used for the top and bottom cladding layers and the core layer was a cross-linked DNA-surfactant biopolymer with 3wt% Disperse Red 1. The EO coefficient r33 was induced through contact poling. The fabricated device was found to exhibit EO modulating behavior. Using an estimated value of r33=0.5pm∕V, a sine-squared fit to the modulating data was obtained with Vπ=263V±10%.

DNA Photonics [Deoxyribonucleic Acid]

ABSTRACT Purified deoxyribonucleic acid (DNA) derived from salmon and scallop sperm has demonstrated excellent passive and active optical properties. Characterization of the optical and electromagnetic properties of DNA suggests suitability for photonic applications. One of interesting features of DNA we discovered was an intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules. We found that various optical dyes inserted into the double helix of DNA molecules rendered active optical waveguide materials with excellent nonlinear optical properties. Our research included the investigation of DNA for use as an optical waveguide material as well as intercalation of fluorescent dyes, photochromic dyes, nonlinear optic chromophores, two photon dyes and rare earth compounds into DNA for use as a nonlinear optical material.

Enhanced electro-optic poling in guest–host systems using conductive polymer-based cladding layers

We report on the development of conductive polymer-based cladding layers for use in multilayered electro-optic (EO) device structures. The waveguide claddings used in these studies were based on blends formed from the conductive polymer poly (ethylene dioxythiophene) with poly (vinylalcohol). Thin films of the blended materials were spun to form cladding layers having tunable conductivity and optical absorption. We tested these materials using a well-known guest–host core layer to determine their effect on the polar alignment of second order nonlinear optical chromophores. The claddings tested were shown to provide a large effective poling field across the active layer, and thus produced larger EO coefficients than systems having comparable, but more highly resistive, claddings.

New Nonlinear Optical Crystal for Mid-IR OPOs: CdSiP 2

CdSiP2is a new negative uniaxial NLO crystal for 1-μm- or 1.5-μm-pumped mid-IR OPOs with much higher nonlinearity and thermal conductivity than existing materials such as AgGaS2, AgGaSe2, and PPLN.

MILITARY LASER APPLICATIONS: PROVIDING FOCUS TO NONLINEAR OPTICS R&D

Hopkins shares his view from the nonlinear optics R&D arena, looking at the military laser applications that drive and focus efforts in nonlinear optics.

Calculation of giant third‐order nonlinear susceptibilities due to excitonic processes in rectangular GaAs quantum well wires

Exciton and biexciton biding energies and wave functions are calculated variationally for rectangular GaAs quantum well wires in an effective mass approximation. Coulomb interaction terms are treated exactly in their full three‐dimensional form throughout the calculation, a more physically realistic procedure than employed in previous calculations that used effective one‐dimensional potentials. Our treatment is unique in the use of a two‐dimensional Fourier expansion of the Coulomb potential, that removes the difficulty of dealing with the 1/r singularity and considerably reduces the computational effort. Using the results of exciton and biexciton calculations and following the approach of T. Ishihara [Phys. Status Solidi 159, 371 (1990)] in order to eliminate the dimensional dependence of the third‐order nonlinear optical susceptibility χ(3), we estimate its magnitude for near‐resonant excitonic absorption. We obtain χ(3)’s on the order of 10−1–1 esu for various wire sizes.

Noncollinear optical parametric oscillator design for walk-off reduction in GaSe crystals

We grow and fabricate GaSe crystals for nonlinear optical applications. One possible application for this material is an optical parametric oscillator (OPO), which could be pumped with a Nd:YAG laser, but due to the large walk-off, is generally impractical. We present a noncollinear OPO design that significantly reduces the effect of walk-off, which could make an OPO possible with GaSe. The pump, signal, and idler propagation directions are arranged to form nearly collinear rays of power flow. The design minimizes the overlap angle between the rays, and as much as an order of magnitude improvement is obtained compared to the walk-off angle of a collinear OPO. With a 1.06-μm pump, an overlap angle as small as 0.35 deg can be achieved, which is half that of a conventional OPO using ZnGeP 2 .

Status of CdSiP2 development for scaling mid-infrared laser power

Laser sources operating near a wavelength of four microns are important for a broad range of applications that require power scaling beyond the state-of-the-art. The highest power demonstrated in the spectral region from a solid-state laser source is based upon nonlinear optical (NLO) conversion using the NLO crystal ZnGeP2 (ZGP). High-power operation in ZGP is known to be limited by thermal lensing. By comparing the figure of merit for thermal lensing in ZGP with other NLO crystal candidates, CdSiP2 (CSP) particularly offers significant advantages. However as was the case with ZGP during its early development, the physics of observed crystal defects, and their relevance to power scaling, was not at first sufficiently understood to improve the crystal’s characteristics as a NLO wavelength conversion element. During the past decade, significant progress has been made (1) with the first reported growth of a large CSP crystals, (2) in understanding the crystal’s characteristics and its native defects, (3) in improving growth and processing techniques for producing large, low-loss crystals, and (4) in demonstrating CSP’s potential for generating high-power mid-infrared laser light. The paper will summarize this progress.