Patent ID: 7555221

Claim:
An apparatus for polarization-independent RF spectrum analysis of an optical source under test, comprising: a coupler for coupling the light from the optical source under test with light from a continuous-wave (CW) laser to generate a combined signal, wherein the light from the optical source under test has an unspecified polarization state; a nonlinear apparatus coupled to the coupler for modulating the electric field of the light from the CW laser using the temporal intensity of the light from the optical source under test to generate a modulated signal substantially at the center frequency of the CW laser, wherein optical signals passing through the nonlinear apparatus undergo a nonlinear interaction selected from a group consisting of cross-phase modulation and cross-gain modulation, and wherein the nonlinear apparatus is adapted to mitigate or compensate for any phase difference between polarization components of the optical signals propagated through the nonlinear apparatus; a polarizer coupled to the nonlinear apparatus for generating a linearly polarized signal from the modulated signal; and an optical spectrum analyzer coupled to the polarizer for measuring the optical spectrum of the linearly polarized signal to determine the RF spectrum of the optical source under test, wherein the measured optical spectrum is defined by: I′″ (ω)=|α| 2 ·|∫ I (t)·exp[ i (ω-ω 0 ) t]dt| 2 , after omission of a Dirac function at the optical frequency ω 0 ; and the RF spectrum of the source under test, which is defined by: S (Ω)=|∫ I ( t )·exp( iΩt ) dt| 2 , and is given by the optical spectrum measured at the optical frequency ω=ω 0 +Ω.