Photorefractive Optical Limiters

1994 ◽  
Vol 374 ◽  
Author(s):  
Gregory J. Salamo ◽  
Galen C. Duree ◽  
Matthew Morin ◽  
Edward J. Sharp ◽  
Gary L. Wood ◽  
...  
Keyword(s):  
Electric Fields ◽  
Optical Density ◽  
Pulse Width ◽  
Optical Pulse ◽  
Laser Light ◽  
Photorefractive Crystal ◽  
Incident Laser ◽  
Optical Limiters ◽  
Optical Limiter

AbstractWe consider the application of photorefractive beam fanning as an optical limiter. Results indicate that by focusing the incident laser light into the photorefractive crystal and by applying electric fields that limiting is possible at the 10μJ range with an optical density or O. D. of 3. These results are independent of the incident optical pulse width.

scholarly journals Combined modulation of incident laser light by multiple surface scratches and their effects on the laser damage properties of KH2PO4 crystal

2020 ◽  
Vol 28 (6) ◽  
pp. 8764 ◽  
Author(s):  
Jian Cheng ◽  
Jinghe Wang ◽  
Enhong Peng ◽  
Hao Yang ◽  
Hao Chen ◽  
...  
Keyword(s):  
Laser Light ◽  
Laser Damage ◽  
Incident Laser

scholarly journals Quantitative characteristic of phase signal with changed pulse in the coherent PHI-OTDR system

2020 ◽  
Author(s):  
Zhen Zhong ◽  
Xuping Zhang
Keyword(s):  
Pulse Width ◽  
Peak Power ◽  
Optical Pulse ◽  
Quantitative Characteristic ◽  
Maximum Amplitude ◽  
Observation Point ◽  
Electrical Signal ◽  
Rayleigh Backscattering ◽  
Phase Signal ◽  
Measured Phase

In the coherent PHI-OTDR system, the phase signal is retrieved based on the reference point and the observation point which are off and closer to the two sides of step of the phase change. In the experiment, the optical pulse with the changed peak power, width or shape is injected into the fiber for interrogating the change of the quantitative characteristic of the measured phase signal. When the pulse width is fixed at 200 ns and its peak power is adjusted from 14 dBm to -23 dBm, the amplitude is slightly increased from 17.3575 rad to 17.4411 rad as long as the Rayleigh backscattering signal can be found in the electrical signal. Changing the pulse width from 260 ns to 80 ns when the peak power is fixed at 14 dBm, the maximum amplitude and the minimum amplitude of the measured phase signal are 17.4625 rad to 17.4509 rad, respectively. When the arbitrary shape of the optical pulse generated from the MZI structure with a changed delay fiber from 3 m to 6 m, the amplitude varies from 17.4558 rad to 17.4819 rad. For every measurement, the change of frequency is also small. And the small value of standard deviation supports the accuracy of the measurement. All the measurements show that the changed pulse nearly has no impact on the quantitative characteristic of the measured phase signal in the coherent PHI-OTDR system. Moreover, we also find that the phase signal of external event can be correctly extracted as long as the Rayleigh backscattering signal can be detected.<br>

Transient Two-Phase Flow Patterns by Application of a High Voltage Pulse Width Modulated Signal and the Effect on Condensation Heat Transfer

2010 ◽  
Author(s):  
K. Ng ◽  
C. Y. Ching ◽  
J. S. Cotton
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Electric Fields ◽  
High Voltage ◽  
Mass Flux ◽  
Pulse Width ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Pulse Width Modulated

The objectives of this study are (i) to determine the transient phase redistributions of a two-phase flow in a smooth horizontal annular channel by applying high voltage pulses to induce electric fields and (ii) to quantify the resultant changes in the condensation heat transfer. The experiments were performed using refrigerant R-134a flowing in a tube that was cooled on the outside by a counter-current flow of water. The electric fields are established by applying high voltage to a concentric rod electrode inside a grounded tube. The effect of the electrohydrodynamic (EHD) forces on the changes to the initial stratified/stratified wavy flow pattern was visualized using a high speed camera. The EHD effect results in the redistribution of the liquid-vapour phase within the channel and unique flow structures, such as twisted liquid cones and entrained droplets, are observed. These structures only appear during the initial application of EHD and are absent in the steady state flow pattern. Experiments were performed using a 8kV pulse width modulated (PWM) signal with duty cycles ranging from 0–100% to evaluate the heat transfer and pressure drop characteristics of the transient EHD flow patterns. The resultant heat transfer increased with the duty cycle to approximately 2.7-fold at a low mass flux (45–55kg/m2s) and 1.2-fold at a high mass flux (110kg/m2s). The enhancement was higher as the pulse width was increased.

Photorefractive Beam Fanning Optical Limiter

1997 ◽  
Vol 479 ◽  
Author(s):  
M. J. Miller ◽  
G. L. Wood ◽  
G. J. Salamo
Keyword(s):  
Response Time ◽  
Electric Fields ◽  
Optical Limiting ◽  
Major Obstacle ◽  
Speed Of Response ◽  
Optical Limiter

AbstractWe have investigated the potential for using photorefractive phenomena in optical limiting devices. The major obstacle preventing the photorefractive limiter from reaching this potential has been speed of response. In this paper we report on several techniques which are successful in enhancing the photorefractive beam fanning response time. In particular, we demonstrate and characterize the use of applied electric fields, gratings to seed the beam fan, and cylindrical focusing. We also report the first demonstration of a prototype beam fanning optical limiter encompassing many of the proposed improvements.

Optical Pulse Width Modulated Multilevel Transmission in CIS-Based VLC

2017 ◽  
Vol 29 (15) ◽  
pp. 1257-1260 ◽  
Author(s):  
Joon-Woo Lee ◽  
Se-Hoon Yang ◽  
Sang-Kook Han
Keyword(s):  
Pulse Width ◽  
Optical Pulse ◽  
Pulse Width Modulated ◽  
In Cis
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