Renen Adar

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. >

Less than 1 dB per meter propagation loss of silica waveguides measured using a ring resonator

Phosphorus doped silica on silicon waveguide propagation loss, bend loss and their polarization dependence have been measured using a set of different radii ring resonators. For a 30 mm ring radius a finesse of 132 was measured and the inferred propagation loss was 0.85 dB/m, the lowest value yet reported. To characterize the finesse of the high Q resonator we proposed and used for the first time a stable Er/sup +3/ fiber grating laser source which was thermally tuned. This configuration provides improved and accurate measurements capability for finesse values in the range well beyond 100. >

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. >

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.

Phase coherence of optical waveguides

The effective refractive index of real waveguides is not constant, but fluctuates as a result of variations in composition and waveguide dimensions. Consequently, the accumulated phase during propagation has a component that undergoes a random walk and whose mean square increases with length =2L/L/sub coh/. These phase fluctuations result in wavelength fluctuations in Mach-Zehnder interferometers, especially in interferometers of low order. By measuring these fluctuations for Mach-Zehnder interferometers of different order, we have verified the above relation and determined that L/sub coh//spl ap/27 m for our phosphorus-doped core silica on silicon waveguides. >

Wide‐band Bragg reflectors made with silica on silicon waveguides

We report the fabrication of strong Bragg reflectors embedded into fiber matched silica on silicon waveguides. First order gratings are dry etched into the waveguide core and are covered with a thin Si3N4 layer prior to cladding deposition. Reflection bands 225 A wide for TE and 193 A wide for TM polarizations are obtained with 200 A Si3N4 cover layers. The TE and TM spectra are overlapping, resulting in nearly polarization independent Bragg reflectors.