Self-Referenced Locking of Optical Coherence by Single Detector Electronic Frequency Tagging(LOCSET)

The present invention is a unique coherent beam combining system for a laser amplifier array. In one embodiment, the output power of the signal from a single master oscillator is split by a 1 by N splitter and directed simultaneously into an array of the N optical modulators where each of the N signals is modulated by a unique electronic frequency. One of these modulated signals is selected as the reference signal. The modulation frequencies must be selected so that beat notes between the reference and other M element optical signals (N -1 = M) can be uniquely isolated. The M modulated signals are fed to M phase adjusters and then optically amplified. The reference signal proceeds directly to an amplifier. A small portion of the array output is split off and imaged onto a photodetector. The photodetector output is fed to a signal processor that produces phase error signals that drive the M phase adjustors. The final output is thus a high-powered optically-coherent signal. Thus, a complex and difficult to implement spatial isolation of the phase error signals of previous systems is replaced with an easy to implement electronic isolation of the phase error signals between the reference signal and each of the M modulated optical signals. A single detector is used, and there is no separate reference beam. Furthermore, the method can easily be scaled to large numbers of array elements because the scaling is done in the electronic instead of the spatial domain. The present invention relates generally to multiple element optical amplifier arrays used to achieve a high power beam and in particular, to a coherent beam combining system to facilitate such laser amplifier arrays. Benefits: The current invention eliminates the need for an optical reference beam on each amplified optical output beam to achieve optical phase locking and coherent beam combining. Previous methods for phase locking required multiple photodetectors and were cumbersome to align and maintain. The simplicity of using a single photodetector leads to a robust and deployable architecture for many applications.