Regional Pulsewidth and Delay Nonuniformity of Modulated 940 nm Vertical‐Cavity Surface‐Emitting Laser Array

Abstract

Under pulsed modulation, the emission uniformity in terms of pulsewidth and delay of a 940 nm multimode vertical‐cavity surface‐emitting laser (MM‐VCSEL) array is characterized by analyzing the position‐dependent pulsating and chirping dynamics among localized 600 VCSEL elements. In addition, the MM‐VCSEL array biased nearly threshold current (Ith) of 350 mA with a low resistance of 0.72 Ω reveals serious impedance mismatching with a high reflection coefficient (Γ) of −0.97. The MM‐VCSEL array biased below threshold (at Idc: ≈0.9 Ith) reveals low‐impedance and high‐capacitance behavior to result in large modulation reflection with allowable −3 dB bandwidth of 0.8 GHz. The nonuniform optical intensity and delay distribution among all MM‐VCSEL elements corroborate that the gradually enlarged inductance attenuates the modulation current away from bond wires. By modulating the 0.9Ith‐biased MM‐VCSEL array with an 127 ps‐wide electrical pulse with a peak amplitude of 15.3 V, a multimode fiber probe collects the single MM‐VCSEL output with average power, peak voltage, and pulsewidth of 0.08 mW, 25.1 mV, and 602 ps. The delay time as large as 273.4 ps between the nearest and farthest parts of local MM‐VCSEL elements in the array determines its impulse response and uniformity for applications.

Keywords

• delay time
• multimode vertical-cavity surface-emitting laser arrays
• optical pulses
• pulsed modulation
• reflection of modulations