Ultra-Narrow Linewidth and Highly Stable Laser for Radio over Fiber Distributed Antenna Systems

Active distributed antenna systems and fiber-optic cellular repeaters, feeding wireless LAN and cellular networks that support smart applications, require ultra-narrow linewidth laser diodes with precision wavelength control and high stability. A 2.2-kHz linewidth single-mode hybrid laser is presented. A high side-mode suppression ratio of 45 dB is reported. An excellent long-term wavelength stability is measured under free running conditions to be within ±0.2 pm for unpackaged device. This stability has been estimated to be locked to within ±11 Hz if the device is in a hermetically sealed package. Precise wavelength tuning with a wavelength- current coefficient of 0.017 pm/mA (~2.18 MHz/mA) is reported for the first time.