Lily Y. Pang

Analysis of grating-assisted directional couplers using the Floquet-Bloch theory

The Floquet-Bloch theory is used to develop a theory for grating-assisted directional couplers which predicts the coupled power and coupling lengths and is applicable to lossy waveguides. This theory views grating-assisted directional couplers as conceptually similar to conventional synchronous (nongrating) couplers. In the Floquet-Bloch analysis of the directional coupler, it is necessary to include both proper and improper space harmonics. The determination of which space harmonics are improper is critical to the understanding of the coupler performance. The choice of the improper space harmonics used for the analysis of the coupler is different from that used in contemporary papers.

Grating-assisted coupling of light between semiconductor and glass waveguides

Floquet-Bloch theory is used to calculate the electromagnetic fields in a leaky-mode grating-assisted directional coupler (LM-GADC) fabricated with semiconductor and glass materials. One waveguide is made from semiconductor materials (refractive index /spl ap/3.2) while the second is made from glass (refractive index /spl ap/1.45). The coupling of light between the two waveguides is assisted by a grating fabricated at the interface of the glass and semiconductor materials. Unlike typical GADC structures where power is exchanged between two waveguides using bound modes, this semiconductor/glass combination couples power between two waveguides using a bound mode (confined to the semiconductor) and a leaky mode (associated with the glass). The characteristics of the LM-GADC are discussed. Such LM-GADC couplers are expected to have numerous applications in areas such as laser-fiber coupling, photonic integrated circuits, and on-chip optical clock distribution. Analyses indicate that simple LM-GADCs can couple over 40% of the optical power from one waveguide to another in distances less than 1.25 mm.

Integrated optic switches for phased-array applications based on electrostatic actuation of metallic membranes

Photonic ON/OFF and routing switches can be made using alterations of the modal effective index caused by changing the cladding on a dielectric waveguide. Drumhead-like aluminum membranes are formed electrostatically pulled into contact with the waveguides, with operating times of tens to hundreds of microseconds. An ON/OFF switch (or digital modulator) with an extinction ratio of 19 dB has been demonstrated using the change in the imaginary part of the effective index of a silicon nitride rib waveguide. Routing switches based on directional couplers are under development, and their feasibility has been demonstrated with a deposited (fixed) aluminum film. The switches are fabricated on silicon using VLSI-compatible processes, and can be used to select optical time delays for phased-array signal processing.

AlGaInAs/InP ridge-guide lasers operating at 1.55 μm

The InGaAsP/InP material system has a large conduction band offset ((Delta) Ec equals 0.72 (Delta) Eg which provides strong electron confinement and prevents carrier overflow under high temperature operation. Therefore, AlGaInAs/InP lasers have better performance at high temperature operation.

Silica-based optical delay lines and switches for phased-array radar control

We report our progress on integrated phosphorus-doped SiO2 optical waveguide delay lines and membrane optical routing switches for phased-array radar control. We have completed the design and layout of the delay lines for the two shortest bits. We have demonstrated the concept of a microelectromechanical membrane optical routing switch with a Mach-Zehnder interferometer and a fixed aluminum thin film. Channel crosstalk values as low as -12.4 dB and -20.3 dB were measured with and without a 3 mm aluminum film, respectively. We have designed the membrane structure for the switch to have better yield, improved reliability, and lower excitation voltage.

Integrated silica-based optical switch for radar phase control

The development of low-loss, low-cost integrated optical switches is critical for radar phase control applications. We report recent progress in integrated phosphorous-doped SiO2 on Si (PSG) waveguide optical routing switches based on electro-static actuation of an aluminum membrane. We have demonstrated the membrane switching concept and its implementation feasibility with a Mach-Zehnder interferometer and a deposited aluminum thin film. Without the metal film, 95% of the output light was measured in the cross channel, with a channel crosstalk of -13.37 dB. With a 3 mm long aluminum film being deposited on one of the interferometer arms as a phase shifter, 94% of the output light was measured in bar channel. The switch structure is currently being optimized for better performance, and a deformable aluminum membrane switch is being developed.

How many probes is enough? A low cost method for probe card depopulation with low risk

The number of bumps that are touched during probe is a key factor in the cost of a probe card. DFT techniques have been commonly used to reduce the number of signal bumps that need to be probed, but the vast majority of bumps in a typical SoC are allocated to core power and ground. In this paper we describe a technique using power supply noise simulations to develop special bump masks that reduce multi-site probe card costs by eliminating a significant percentage of power and ground bumps. With these new techniques we have shown savings of between

Lateral mode confinement in bent waveguide structures

30K and

Micromechanical microwave switching

50K per production probe card while maintaining overall speed on critical paths and without a noticeable reduction in yield.

Integrated laser and coupled waveguide

Bent waveguides have been used for many years to provide lateral guiding in semiconductor lasers. Since the simple effective index method applied to the bent waveguide structure is at best an estimation, we have applied the beam propagation method and the finite difference method to this problem. Our preliminary findings qualitatively agree with the effective index predictions: for a uniform index central layer, guiding on the mesa is obtained if the thickness of the sidewall layer is sufficiently thin; otherwise, guiding on the sloped regions may occur, as reported recently for visible semiconductor lasers.