Analysis of optical injection on red and blue laser diodes for high bit-rate visible light communication

In this work, self-injection and external-injection in ∼450 nm InGaN/GaN blue and ∼650 nm InGaP/AlGaInP red diode lasers are investigated. A distinct locking characteristic is observed in the self-injection case with small 19 cm cavity length, demonstrating enhanced ∼2.34 and ∼2.07 GHz 3-dB bandwidths, corresponding to a factor of ∼1.4 and ∼1.1 improvement, and reduced ∼60 and ∼80 pm spectral linewidths, for the blue and the red lasers, respectively. Moreover, this short external cavity self-injection locked system exhibited superior performance by a factor of 1.1–1.3 compared to the long cavity (26 cm) configuration. Conversely, the external optical injection exhibited weak locking signature with improved linewidths by a factor of ∼1.6–2.8 and reaching as small as ∼70 and ∼87 pm for the blue laser, respectively, while almost doubling in the peak powers. Later, on–off keying modulation technique based data transmission rates of up to 3.5 and 4.5 Gb/s are demonstrated on free-running blue and red laser diodes, respectively, employing an in-house laser diode mount based system. Moreover, owing to the bandwidth limitation of the optically injected systems, successful transmission of up to 2 Gb/s is demonstrated with better performance compared to the respective free-running cases, in particular, the external-optically injected system demonstrated more than double improvement in the bit-error-rate.