RF crosstalk in multiple-wavelength vertical-cavity surface-emitting laser arrays

We present the crosstalk measured in multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays under RF modulation. The array consists of eight bottom-emitting VCSEL's arranged with a "pie"-like configuration within a 60-μm-diameter circle with a 3-μm spacing for coupling into a multimode fiber. The crosstalk is investigated by measuring a cross-modulation response of two VCSEL's in the array using a monochromator in an optical spectrum analyzer as a receiver. Excess crosstalk is minimized by flip-chip mounting the array and introducing a proper bias condition. The crosstalk observed In the adjacent VCSEL's is less than -40 dB at the modulation frequency below 700 MHz and it Increases at 20 dB/decade above this frequency when both VCSEL's are biased at 5.0 mA.