R. C. Kistler

Optical doping of waveguide materials by MeV Er implantation

Implantation of MeV erbium ions into micron‐thick silica and phosphosilicate glass films and 1200‐A‐thick Si3N4 films is studied with the aim of incorporating the rare‐earth dopant on an optically active site in the network. Implantation energies and fluences range from 500 keV to 3.5 MeV and 3.8×1015 to 9.0×1016 ions/cm2. After proper thermal annealing, all implanted films show an intense and sharply peaked photoluminescence spectrum centered around λ = 1.54 μm. The fluorescence lifetime ranges from 6 to 15 ms for the silica‐based glasses, depending on annealing treatment and Er concentration. Silicon nitride films show lower lifetimes, in the range <0.2–7 ms. Annealing characteristics of all materials are interpreted in terms of annealing of ion‐induced network defects. These defects are identified using photoluminescence spectroscopy at 4.2 K. Concentration quenching, diffusion and precipitation behavior of Er is also studied.

Efficient coupling of a semiconductor laser to an optical fiber by means of a tapered waveguide on silicon

A Si3N4 core waveguide, matched to a laser mode, is adiabatically tapered into a SiO2:P core waveguide, matched to a fiber mode. When used to couple the light from a semiconductor laser into an optical fiber, a loss of 3.1 dB is obtained, compared to a loss of 4.5 dB obtained with a lensed fiber.

Broad-band array multiplexers made with silica waveguides on silicon

A waveguide array multiplexer design that is particularly suitable for making broadband low-order devices is presented. Two-channel multiplexers at 1.0-1.55 mu m, 1.31-1.53 mu m, and 1.47-1.55 mu m are demonstrated. Compared to conventional waveguide multiplexers, these devices have wide spectral ranges of low crosstalk. The devices are polarization independent. The crosstalk and fiber-to-fiber insertion loss for the 1.31-1.53 mu m multiplexer were about -35 and -2 dB, respectively. >

Four-channel wavelength division multiplexers and bandpass filters based on elliptical Bragg reflectors

Four-channel multiplexers and four-wavelength bandpass filters based on elliptical Bragg reflectors (EBRs) are discussed. The channel spacing is 50 AA near 1.56 mu m. The EBRs are narrowband elliptical mirrors that can refocus light from an input waveguide to any one of a number of output waveguides. Spectrally, they perform similarly to Bragg reflectors. The devices were fabricated on silicon using silica-based waveguide technology. The elliptical gratings with 0.53- mu m periods were patterned using deep UV spatial frequency doubling photolithography. Multiplexers with single filtering and double filtering were demonstrated. With single filtering, the fiber-to-fiber insertion loss was 3.0+or-0.5 dB, and the crosstalk was -20 dB; with double filtering, the insertion loss was 4.0+or-0.5 dB, and the crosstalk was -30 dB. About 2 dB of this loss was due to coupling between the fibers and the waveguide. The additive loss associated with the EBR, including propagation, Bragg reflection, and coupling between input and output waveguides, was about 1 dB. >

Integrated optic adiabatic devices on silicon

A study of integrated optic devices based on adiabatic principles is reported. The components are a 3-dB coupler, a full coupler, a polarization splitter, a wavelength multiplexer, and two mode shape transformers. All components were fabricated from doped silica and silicon nitride films on silicon substrates. Results are given for an adiabatic full coupler and an adiabatic 3-dB coupler, an asymmetric Y-coupler for a 1.3-1.55- mu m-wavelength multiplexer, and a tapered waveguide for mode shape transformation. >

Integrated optic adiabatic polarization splitter on silicon

An adiabatic polarization splitter, fabricated with silica and silicon nitride films on a silicon substrate, is demonstrated. A rejection of the unwanted polarization (cross talk) of −20 to −34 dB was achieved with single filtering and −35 to −45 dB with double filtering. The device had a 1.5 dB insertion loss and a very small wavelength dependence.

Measurement of very low-loss silica on silicon waveguides with a ring resonator

The loss in phosphorus‐doped silica on silicon waveguides was accurately measured using a 6‐cm‐diam ring resonator, by recording the transmission of a narrow linewidth external‐cavity laser through the resonator as a function of temperature. A finesse of 45 and resonance width of 24.2 MHz were obtained, indicating guide loss of 2.6 dB per meter, which is the best result thus far measured for these waveguides. The shift in the modes with temperature was measured in the temperature range 30–120 °C and found to be close to 1/8 A/deg.

Adiabatic 3-dB couplers, filters, and multiplexers made with silica waveguides on silicon

The performance of adiabatic 3-dB couplers and V-branches is reported. These devices are broadband and divide power equally. They have no observable polarization dependence. Typical excess losses relative to a straight waveguide is 0.1-0.2 dB for the 3-dB couplers and about 0.4 dB for the V-branches. Fiber to fiber insertion loss of 0.31 dB was measured for a 2.5-cm straight waveguide. The devices were used to fabricate transmission filters peaked at 1.55 mu m and power combiners having two channels at 1.48 and 1.55 mu m. The device fabrication was improved by use of a flowable top cladding layer containing boron and phosphorous which easily filled-in between closely spaced waveguides. >

1.54 μm room‐temperature luminescence of MeV erbium‐implanted silica glass

MeV erbium implantation doping of 10‐μm‐thick silica glass films on a Si substrate is studied with the aim of incorporating the rare‐earth dopant on an optically active site in the silica network. As‐implanted samples (3.5 MeV, 5×1015 Er ions/cm2) show a strong luminescent transition at a wavelength of 1.54 μm, even at room temperature, corresponding to an intra‐4f transition of Er3+. Thermal annealing at temperatures up to 900 °C increases the luminescence intensity by a factor of 2 to 3. For temperatures above 1000 °C the intensity decreases drastically as a result of Er precipitation. The lifetime of the excited state is in the order of 10 ms. Photoluminescence studies at 4.2 K are used to identify implantation‐induced damage.

Polarization independent narrow band Bragg reflection gratings made with silica‐on‐silicon waveguides

We report polarization independent Bragg reflectors, centered at 1.55 μm and made with silica‐on‐silicon waveguides. Gratings are etched into the upper core surface and glass doped with boron and phosphorus is used to fill in the grating corrugation and for the top cladding. The Bragg coupling length in these gratings is independent of polarization. Post‐processing anneals at temperatures above 780 °C weaken the gratings and can be used to tailor the reflection stop band in the range 15–1.5 A. By etching trenches along the sides of the waveguides, the strain induced birefringence in practically eliminated and the TE and TM reflection peaks overlap to within 0.4 A.