Patent ID: 8953647
Filing Date: 2015-02-10
Classification: G01B,G01S,H01S,H04B

Abstract:
1. A method comprising: providing a fiber gain medium, wherein the fiber gain medium is arranged as a ring laser; optically pumping the fiber gain medium; forcing a majority of a signal beam to travel in a first direction around the ring laser; forming a free-space version of the signal beam in the ring laser; filtering the signal beam to limit a linewidth of the signal beam in the ring laser; at a timing independently controlled by an electrical signal for each of a plurality of pulses, amplitude-modulating the signal beam to form the plurality of pulses; polarizing the signal beam to a linear polarization; extracting the signal beam as an intermediate optical signal output beam having a first wavelength between 1800 nm and 2000 nm from the free-space version of the signal beam using a polarizing beam splitter; rotating a direction of polarization on both of two sides of the polarizing beam splitter, wherein the forcing of the majority of the signal beam is done between the two rotatings of the direction of polarization; frequency quadrupling the intermediate optical signal output beam to form a frequency-quadrupled optical signal at a wavelength different from the first wavelength of the intermediate optical signal output beam; transmitting the frequency-quadrupled optical signal through water; providing an optical parametric oscillator; optically coupling the frequency-quadrupled optical signal into the optical parametric oscillator; outputting, from the optical parametric oscillator, an idler wavelength and a signal wavelength; and frequency doubling the idler wavelength and the signal wavelength to form a frequency-doubled idler wavelength and a frequency-doubled signal wavelength, wherein the transmitting of the frequency-quadrupled optical signal includes transmitting at least one of the frequency-doubled idler wavelength and the frequency-doubled signal wavelength through the water.