Michele A. Milbrodt

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. >

A low-voltage 8*8 Ti:LiNbO/sub 3/ switch with a dilated-Benes architecture

An 8*8 switch array with a dilated-Benes architecture that greatly relaxes the crosspoint extinction ratio requirements needed to achieve low overall switch array crosstalk is discussed. This, combined with the low uniform switching voltages (9.2+0.2 V) of the 48 directional coupler crosspoints, facilitates high-speed low-crosstalk operation. The crosspoints can be switched in about 1 ns. The switch array is fully packaged with permanently attached single-mode fiber pigtails. The high data transfer rate inherent in lithium niobate switches in general, combined with the low crosstalk and high switching speed of this switch array, is a good match to the requirements of time-multiplexing switching. >

Polarization-independent silica-on-silicon Mach-Zehnder interferometers

The birefringence induced by compressive strain in silica waveguides on silicon substrates is compensated with a silicon nitride patch placed below the core. We demonstrate Mach-Zehnder interferometers with polarization-independent spectral response, including a compensated Mach-Zehnder interferometer suitable for stabilization of multiple laser sources in a dense wavelength division multiplexed fiber optic communication network. Furthermore, we show how silicon nitride can also be used to compensate polarization dependent losses. Polarization independence achieved with a silicon nitride patch is applicable to a wide variety of other devices such as arrayed waveguide grating multiplexers and Bragg reflectors. >

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. >

Planar waveguide Mach-Zender bandpass filter fabricated with single exposure UV-induced gratings

Summary form only given. Future optical fiber communication systems employing wavelength-division multiplexing will require narrow bandwidth multiplexing and demultiplexing components with good isolation and cross talk performance and minimal insertion loss. Mach-Zehnder interferometers containing UV-induced Bragg gratings have previously been demonstrated for use as a wavelength-multiplexing /demultiplexing device in planar waveguides. Bandpass filters are presented here which exhibit good performance without requiring any interferometer balancing after writing the gratings.

Calculated wavelength sensitivity of lithium niobate switches

A method is presented for calculating the wavelength sensitivity for electrooptic guided-wave stitches that work by mode interference, including directional-coupler and balanced-bridge switches. The method relies on a coupled-mode theory, using measured wavelength sensitivity of the coupling. Crosstalk is taken as the bandwidth-limiting property and is calculated by expanding in bandwidth. It is found that the wavelength sensitivity depends on the coupler gap, the amount of coupling, and the electrode configuration. Numerical examples show that switches with proper design can exhibit better than 25 dB of crosstalk with a 100- mu m bandwidth. Modulators have a still wider bandwidth. >

Polarization independent Silica-on-Silicon waveguide devices

Silica-on-silicon (SiO2/Si) waveguide devices show great promise for practical integrated optical circuits. One of the challenges of this technology is to overcome the intrinsic strain birefringence which causes polarization dependent response. A number of methods have been suggested and demonstrated to achieve polarization independent response[1-4]. We present a novel method for achieving polarization independence in SiO2/Si waveguide devices by placing a thin patch of silicon nitride (Si3N4) under the waveguide core to achieve polarization independence in Mach-Zehnder interferometers (MZIs) and for compensation of polarization dependent loss (PDL). Our method requires an additional photolithography step but does not but does not require active tuning and is applicable to a wide variety of SiC2/Si waveguide devices.