Abstract

Many optical communication systems, such as those based on free-space propagation, require significantly higher diffraction-limited transmitter power than is available from single-stripe laser diodes. An attractive solution is to use a high-power coupled stripe laser-diode array or broad stripe laser that is externally injection locked to achieve a diffraction-limited far-field emission.¹ To encode the transmitted information, we could use direct array current modulation, but this requires large drive currents and is limited by relatively low modulation bandwidth of the array. One alternative is to frequency modulate the master laser for FSK transmission.² Recent advances in optical damage-resistant waveguides³ permit the use of another approach, described here and shown in Fig. 1, where the information is first encoded as phase modulation on the master laser signal by using a LiTaO₃ proton-exchanged waveguide phase modulator. Modulated output is then used to injection lock a coupled stripe array. When the phase-modulation spectral sidebands in the injected signal are within the locking bandwidth, the phase-modulated signal is amplified and transmitted by the injection-locked laser without suppression of the modulation index.⁴

© 1990 Optical Society of America