Optical noise index calculation method, optical noise index calculation apparatus, and optical sampling oscilloscope

A method for calculating an optical noise index of a signal light extraction apparatus that extracts signal light in a polarization plane by inputting signal light and a sampling pulse, different from the signal light in polarization plane by a given angle, to a nonlinear optical medium, and by passing light output from the nonlinear optical medium through an orthogonal polarizer having a polarization plane orthogonal to that of the signal light, the method comprising:

• measuring a power of light output from the nonlinear optical medium as a first optical power, a power of light obtained by passing the light output from the nonlinear optical medium through an identical polarizer having a same polarization plane as that of the signal light as a second optical power, and a power of light having passed through the orthogonal polarizer as a third optical power;
• calculating a parametric gain of the nonlinear optical medium using the second optical power;
• calculating a quantum noise power of the light having passed through the orthogonal polarizer using the first optical power and the third optical power, and the parametric gain;
• and
• calculating an output optical noise of the signal light extraction apparatus using the quantum noise power and the parametric gain, and using the calculated output optical noise to calculate an optical noise index.

An optical sampling oscilloscope that measures signal light by inputting the signal light and a sampling pulse, different from the signal light by a given angle, to a nonlinear optical medium, and by passing light output from the nonlinear optical medium through an orthogonal polarizer having a polarization plane orthogonal to that of the signal light, the optical sampling oscilloscope comprising:

• an optical power measuring unit that measures a power of light output from the nonlinear optical medium as a first optical power, a power of light obtained by passing the light output from the nonlinear optical medium through an identical polarizer having a same polarization plane as that of the signal light as a second optical power, and a power of light having passed through the orthogonal polarizer as a third optical power;
• a gain calculating unit that calculates a parametric gain of the nonlinear optical medium using the second optical power measured by the optical power measuring unit;
• a quantum noise calculating unit that calculates a quantum noise power of the light having passed through the orthogonal polarizer using the first optical power and the third optical power measured by the optical power measuring unit, and the parametric gain calculated by the gain calculating unit;
• and
• an index calculating unit that calculates an output optical noise using the quantum noise power calculated by the quantum noise calculating unit and the parametric gain calculated by the gain calculating unit, and uses the calculated output optical noise to calculate an optical noise index.