Technical Bulletin N°6

Experts in Next Generation Lightwave Test Equipment

Optical Complex Spectrum Analyzer for DPSK modulation measurements

AP2440A application note

The AP2440A is an optical complex spectrum analyzer; an optical spectrum analyzer able to measure intensity as well as phase of a modulated signal. Based on the patented "complex spectrum analysis" method, this instrument is ideal for evaluation of Differential Phase Shift Keying (DPSK) systems.

Complex Optical spectrum study of a DPSK modulation : In this example, we measured with the AP2440A the optical complex spectrum of a 10Gb/s DPSK modulation. After which the optical complex spectrum is converted into time domain by the AP2440A’s FFT software feature. The RED trace represents the phase variation and the BLUE trace represents the intensity variations both as a function of time. We can clearly observe the 180° phase change when the intensity is at a minimum.

Optical spectrum study of a DPSK demodulator output : Destructive port output Constructive port output The AP2440A can be utilized as an ultra high resolution optical spectrum analyzer (resolution = 20MHz (0.16pm)). In this example, 10GHz FSR of a DPSK demodulator was measured.

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