Optical Injection Locking on VCSELs
Direct modulated lasers, as optical transmitters in fiber-optic communication system, are cost-effective and compact. However, its inherent photon-carrier interactive nonlinear process makes it relatively noisy and slow compared with external modulation. Thus high performance of direct modulated semiconductor laser is highly desirable in both analog and digital links. One method that can drastically improve the performance of a direct modulated laser is optical injection-locking, which uses a second laser (master laser) to inject photons at a similar wavelength into the transmitter laser (follower laser). The transmitter laser is thus locked (in wavelength and phase) to the master due to the coherent non-linear interaction.
Fortunately, optical injection locking has been shown to be an effective technique to improve the performance of VCSELs significantly. By employing optical injection locking on 1.55µm VCSELs, we have demonstrated a high-speed record of 50 GHz frequency response resonance frequency, >10 dB RF gain enhancement and >10 dB distortion reduction for analog communication, spurious-free dynamic range (SFDR) improvement by over 20 dB, and laser RIN noise reduction by 10dB. A cost-effective, low distortion, high speed direct modulated laser transmitter will be ideal for RF and wireless communication.
