Midinfrared broadband achromatic astronomical beam combiner for nulling interferometry.

Integrated optic beam combiners offer many advantages over conventional bulk optic implementations for astronomical imaging. To our knowledge, integrated optic beam combiners have only been demonstrated at operating wavelengths below 4 µm. Operation in the midinfrared wavelength region, however, is highly desirable. In this paper, a theoretical design technique based on three coupled waveguides is developed to achieve fully achromatic, broadband, polarization-insensitive, lossless beam combining. This design may make it possible to achieve the very deep broadband nulls needed for exoplanet searching.

Quasi-phase matched second-harmonic generation through thermal poling in femtosecond laser-written glass waveguides.

Quasi-phase matched second-harmonic generation at 532 nm is demonstrated in a channel waveguide that is written in bulk fused silica using a femtosecond laser. The second-order nonlinear grating is fabricated using uniform thermal poling followed by periodic erasure inside an e-beam deposition system caused, by what we believe to be, x-rays. A SHG conversion efficiency of 2 x10(-5) %/W-cm(2) was obtained for a 1 cm long device, corresponding to an effective nonlinear coefficient of 0.0075 pm/V.

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange.

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling.

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.

Design and fabrication of a glass waveguide optical add-drop multiplexer by use of an amorphous-silicon overlay distributed Bragg reflector.

We report the fabrication of a distributed Bragg reflector (DBR) on a silver ion-exchanged glass waveguide with a patterned overlay of sputter-deposited amorphous silicon (a-Si). Using this high-refractive-index overlay DBR technology, we demonstrate a fully functional glass-integrated optic add-drop multiplexer (OADM). The OADM consists of a Mach-Zehnder interferometer (MZI) containing overlay DBR gratings in both arms. The design, fabrication, and characterization procedures of the sputter-deposited a-Si overlay DBR and the ion-exchanged glass waveguide MZI are discussed in detail. The completed 3-cm-long OADM exhibited a 24-dB transmission dip with a 3-dB bandwidth of 0.5 nm. The 1-cm-long a-Si overlay DBR induced an additional attenuation of 1.2 dB. A simplified method for overlay DBR fabrication that utilizes a lift-off technique is also proposed and demonstrated.