Ilya Golub

Polarization splitter/combiner in high index contrast Bragg reflector waveguides.

Novel designs of polarization devices based on Bragg reflector waveguides in a high index contrast silicon-on-insulator (SOI) platform have been proposed. Brewster angle condition is incorporated in the periodic structures. Numerical simulations with a 3D semivectorial beam propagation method demonstrate the device performance as TE mode polarizer with high TE to TM extinction ratio and TE/TM mode polarization splitter and combiner with high polarization splitting efficiency.

π-shifted Sagnac interferometer for characterization of femtosecond first- and second-order polarization mode dispersion

A novel configuration for measuring femtosecond polarization mode dispersion (PMD) with a π-shifted Sagnac interferometer is studied. The advantages of this configuration include a response that is independent of the orientation of the device under test. This independence allows characterization of the first- and second-order PMD by measurement of the wavelength dependence of the differential group delay and of the orientation of the device’s principal states of polarization. The method provides an extension of the dynamic range of the Sagnac interferometer technique to few-femtosecond PMD measurement.

Ring resonator in a Sagnac interferometer as a birefringence magnifier

A novel birefringence magnification technique that uses a ring resonator in a Sagnac interferometer is proposed and demonstrated. An enhancement factor of 38 was obtained experimentally. The scheme can be used to increase measurement sensitivity to small birefringence and polarization mode dispersion and to decrease the threshold for nonlinear switching and laser mode locking by a Sagnac interferometer.

Ring resonator in a Sagnac loop

A study of a ring resonator in a Sagnac loop is presented. The results of a theoretical analysis based on Jones calculus are confirmed by experiments. Comparison of a ring resonator in a Sagnac loop with a ring only is performed, and the advantages of our scheme are pointed out. The scheme can be used to increase the measurement sensitivity to small birefringence and associated polarization mode dispersion and to decrease the threshold for Sagnac-loop-based nonlinear switching and laser mode locking.

Low-current optical switching by carrier-injection-induced reconfigurable waveguiding

An improved compact 1x2 digital optical switch (DOS) in InGaAsP/InP is studied, and the experimental results are compared to numerical modeling. We present measurements of Mach-Zehnder and DOS devices fabricated with InGaAsP cores having bandgap energies corresponding to wavelengths of 1.2 um, 1.3 um, and 1.4 um. The results are compared with modeling evaluation of refractive index change versus carrier concentration in the different InGaAsP alloys. The effects of modifications in the wafer layer structure are presented as well. Switching current is significantly reduced from greater than 100 mA to about 20 mA, resulting in significant power savings, and in addition eliminating thermal overshoot in the switched optical pulse. The DOS has a measured switching contrast ratio of better than 12 dB with a switching rise time of less than 10 nsec.

InGaAsP digital optical wwitch on InP

We demonstrate Digital Optical Switches (DOS) on InP based on carrier-injection and on the quantum-confined Stark effect (QCSE). The active waveguide core is composed of either a double-heterostructure of InGaAsP for carrier-injection or a InGaAs-InGaAsP for reverse bias operation. O-Ion implantation was employed to isolate the branches of the DOS instead of the usual isolation by etching employed elsewhere.

Fast Bend Loss Attenuator Using Carrier Injection

A compact InGaAsP/InP waveguide bend loss attenuator with electrically modulated bend loss is demonstrated. The carrier injection device exhibits better than 15 dB modulation and <20 nanosecond response time.

Study of polarization splitter/combiner in high index contrast Bragg reflector waveguides

Novel designs of polarization devices based on Bragg reflector waveguides in a high index contrast silicon-on-insulator (SOI) platform have been proposed. Brewster angle condition is incorporated in the periodic structures. Numerical simulations with a 3D semivectorial beam propagation method demonstrate the device performance as TE mode polarizer with high TE to TM extinction ratio and TE/TM mode polarization splitter and combiner with high polarization splitting efficiency.

Digital optical switches with reconfigurable output waveguide branches in InP

A compact Y-junction waveguide switch with electrically reconfigurable output waveguide arms is demonstrated in InGaAsP/InP. Simulations indicate that the plasma effect or the thermo-optic effect can be used as the active switching mechanism, as corroborated by experimental tests. For the plasma effect the induced index change under the electrode, Δn, is negative. The Y-junction device has a measured switch contrast ratio ~ 20 dB, with a response time of ~ 5 ns. Using the thermo-optic effect Δn is positive and the observed contrast ratio is better than 10 dB. The highly localized nature of the thermal gradient in these devices yields thermo-optic switching into the hundred of nanoseconds range, several orders of magnitude faster than the overall thermal response time. This is the fastest thermo-optic switch reported to date. Fabrication of these switches, and in particular the use of O+-ion implantation to provide electrical isolation of the waveguide branches, is described.

Polarization properties of Bragg reflector waveguides

Polarization properties of Bragg reflector optical waveguides have been investigated. Grazing incidence and Brewster angle designs are compared. The proposed Brewster angle design works as a TE mode polarizer. Numerical simulations are presented.