Fast coherence switching of an injection-locked vertical-cavity laser array

Abstract

Summary form only given.In a first step the stationary autostable injection locking of 5/spl times/5 array of vertical-cavity lasers (VCSEL) is demonstrated. One of the 25 emitters serves as master laser. All beams are collimated by a microlens array. The master laser beam is expanded and redirected onto the microlens array. In that way a very small part of the master laser radiation is injected frontally into each of the N=24 slave lasers. If the frequencies of the free-running slaves are close to the master frequency, i.e., inside the locking range, the slaves are running phase locked at the master frequency. The master laser radiation and the slave laser radiation are separated by an optical isolator. All VCSELs are driven by the same DC voltage source with small individual series resistors to tune their free-running frequencies to the master frequency. Small deviations of the slave frequency from the master frequency within the locking range in addition allow to shift the relative phase of the two lasers. Adjusting the relative phases of the slave lasers allows to get a strong diffraction-limited central peak in the common far-field power-density distribution of the slave lasers with an enhancement of the peak power density by nearly a factor of N compared to the incoherent operation. The coherent operation is autostable for hours, i.e., no phase, voltage or temperature control is needed. The optical output power is scalable with the number of slave lasers since there is no slave-slave interaction. The number of slave lasers can be one thousand or more.