Single-Mode 940 nm VCSELs With Narrow Divergence Angles and High-Power Performances for Fiber and Free-Space Optical Communications

Using the Zn-diffusion and oxide-relief techniques with the optimized aperture sizes, we demonstrate a novel single-mode 940 nm vertical-cavity surface-emitting laser (VCSEL) with high brightness performance. The highly single-mode (SM) output optical spectra (SMSR>50 dB) can be sustained under a full range of bias currents and from room temperature (RT) to 85°C operation. Under RT operation, the maximum SM power can be as high as 7.1 mW with a moderate threshold current (<inline-formula> <tex-math notation="LaTeX">$\text{I}_{\mathrm {th}}$ </tex-math></inline-formula>: 1.1mA) and narrow divergence angles in the far-field pattern (FWHM: 5°, 1/e²: 7-8°). Furthermore, the maximum 3-dB E-O modulation bandwidth of this high-power SM VCSEL can reach 15 GHz without the low-frequency roll-off induced by spatial hole burning effect. By using this novel device as the transmitter, we can achieve 25 Gbit/sec error-free (bit-error-ratio (BER) <inline-formula> <tex-math notation="LaTeX">$ < 1\times 10^{-12}$ </tex-math></inline-formula>) transmission over a 400 meter OM5 fiber without using any signal processing technique. This novel high-speed and high-brightness SM 940 nm VCSEL can serve as a light source in single-mode fiber for medium-reach (>0.3 km) data communications as well as in free-space optical communication.