Injection locking of VCSELs

Injection locking has been actively researched for its possibility to improve laser performance for both digital and analog applications. When a modulated follower laser (also termed "slave" laser) is locked to the master laser, its nonlinear distortion and frequency chirp may be reduced. As well, the resonance frequency can increase to several times higher than its free running case. We show that the frequency response (S21) of an injection-locked laser is similar to a parasitic-limited laser with a high resonance frequency. The S21 was studied experimentally and the condition to achieve a flat, enhanced frequency response was identified. For analog applications, a record 112 dB-Hz²3/, single-tone third harmonic spur-free dynamic range of a 1.55-μm vertical cavity surface emitting lasers (VCSEL) was demonstrated. An improvement was attained for a wide-injection parameter space. In a 50-km 2.5-Gb/s digital link, a 2-dB power penalty reduction at 10/sup -9/ bit error rate was also demonstrated. As a novel application, an injection-locked uncooled tunable VCSEL was shown to have a reasonable modulation performance in a wide abient temperature range. The VCSEL was locked to a designated wavelength and the injection compensated the temperature-induced performance degradation. This concept can be extremely attractive for low-cost dense wavelength division muliplexed transmitters.

I. Introduction

Injection locking of semiconductor lasers is a research topic that has attracted much interest since the early 1980s. Its applications include receiver end design in optical coherent communication [1], laser spectral narrowing [2], suppression of laser noise [3], the reduction of frequency chirp under modulation [4], and improving the laser intrinsic frequency response [5].