Robert W. Sadowski

Analysis of nonlinear optical switching in an erbium-doped fiber

A mathematical model of the strong, resonantly enhanced nonlinear phase shift recently reported in Er-doped fibers which relates the phase shift and signal loss to the fiber parameters and the pump and signal wavelengths, is presented. Predictions are in fair agreement with the phase shift and loss measured in an experimental Er-doped fiber switch based on this effect. A strong, nearly wavelength independent contribution to the nonlinear phase shift is observed in the switch. The model suggests that this effect is due to the same nonlinear effect arising from one or more vacuum ultraviolet (VUV) transitions in Er/sup 3+/. >

Laser-diode-pumped nonlinear switch in erbium-doped fiber

We describe a two-mode fiber switch made of a short length of erbium-doped fiber in which switching is accomplished by a nonlinearity that is resonantly enhanced by the dopant. In a 0.95-m fiber pumped with a 1.48-μm laser diode, a 906-nm signal is switched with only 8 mW of absorbed power at a signal absorption loss of 0.25 dB.

Microsecond optical-optical switching in a neodymium-doped two-mode fiber

We report on optically induced optical switching of a 632.8-nm signal in a Nd3+-doped, two-mode fiber based on a nonlinearity resonantly enhanced by the dopant. A fast, 0.38-μs component was observed in the switched signal, which we believe is due to cross relaxation between clustered ions. We demonstrated a 600-kHz switch in a 1.14-m elliptical-core fiber with 0.31 μJ of launched 807-nm pump energy. Information about cluster size and speed of the cross-relaxation process is inferred from the switch dynamics.

Experimental evidence for strong UV transition contribution in the resonant nonlinearity of doped fibers

We report a new theoretical interpretation of the strong resonantly-enhanced third-order nonlinearity observed in fibers doped with Nd/sup 3+/, Er/sup 3+/, or Yb/sup 3+/. For each fiber, the absolute contributions of the near resonance (IR-visible) and far from resonance (UV) transitions to the nonlinearity are calculated and compared to experimental values. We show that in all cases, a large fraction of the measured nonlinearity is due to strong UV transitions. The consequences of this observation on the bandwidth, switching power and response time of switches based on this effect are discussed.

All-optical switching using color centers in an irradiated phosphorus-doped fiber

We report on all-optical switching of a 900-nm signal in a two-mode silica fiber based upon a resonant nonlinearity introduced by phosphorus color centers in a 22-cm irradiated P/sub 2/O/sub 5/-SiO/sub 2/ fiber. Full switching was observed with only 1 /spl mu/J of absorbed 532-nm pump energy, with a projected response time under 10 ns. This switch required a peak power two orders of magnitude lower than for a fiber Kerr effect device operated under identical conditions.

Resonantly enhanced nonlinear optical switching in rare-earth-doped fibers

We report low loss, low pump power, optical-optical switches in rare-earth-doped fibers based on the third-order optical nonlinearity resonantly enhanced by the dopant. In a 0.95-m Er- doped two-mode fiber switch pumped with a 1.48-micrometers diode laser, the absorbed pump power required for switching a 906-nm signal was 8 mW, for a signal loss of only 0.25 dB. This is an enhancement by a factor of 6200 in power-length product over undoped silica. The phase shift was found to be due in part to a non-resonant contribution, thought to arise from a strong UV-VUV transition, and in part to a resonant term from the 980-nm transition. In a 0.98-m Nd-doped, elliptical-core, two-mode fiber switch, switching of a 632.8-nm signal was achieved with only 6.6 mW of absorbed power at 900 nm. The dynamic response of the switch was found to have two components, a slow component equal to the metastable level lifetime (approximately equals 380 microsecond(s) ) and a fast component (approximately equals 2 microsecond(s) ). The latter is believed to arise from rapid cross-relaxation between paired ions, a mechanism which shows promises for low- power, microsecond switching in fibers.

Submicrosecond all-optical switching in neodymium-doped fiber

We report on optically induced, sub-microsecond optical switching in an elliptical core neodymium doped, two-mode fiber. The improved response time of this switch, which is three orders of magnitude faster than the 400 microsecond(s) metastable lifetime of Nd3+, was provided by rapid cross relaxation within neodymium clusters.

Surface optomechanics: Calculation of love surface acoustic waves on microresonators

We calculate optomechanically excited Love waves on the surface of a silica whispering-gallery microresonator surrounded by air and pollutants. We show a method for sensing and distinguishing type or concentration of pollutant via frequency shift.

GPU assisted processing of point cloud data sets for ground segmentation in autonomous vehicles

In autonomous ground systems, developing a clear model of the surroundings is crucial for operating in any environment. Three-dimensional light detection and ranging (LIDAR) sensors, such as the Velodyne HDL-64E S2, are powerful tools for robotic perception. However, these sensors generate large data sets exceeding one million points per second that can be difficult to use on space, power, and processing constrained platforms. We report on GPU assisted processing within a Robotic Operating System (ROS) environment capable of achieving greater than an order of magnitude reduction in point cloud ground segmentation processing time using a gradient field algorithm with only a small increase in power consumption.

Error Diffusion Network Implementation for Real-Time Halftoning Applications

We report a hardware approach to implement an error-diffusion neural network for image halftoning. We present simulation and experimental results using modified current-starved comparator based quantizers with forty-fold reduction in pixel current over previous designs.