Coherent power combination of two Master-oscillator-power-amplifier (MOPA) semiconductor lasers using optical phase lock loops

Abstract

Using heterodyne Optical Phase-Locked Loops (OPLLs), two 1W high power 1550 nm master-oscillator-power-amplifier (MOPA) semiconductor lasers operating as current controlled oscillators are phaselocked to a 1 mW reference laser. The signals of the two MOPAs are then coherently combined and their mutual coherence is studied. In each OPLL, the acquisition range is increased to +/-1.1GHz with the help of an aidedacquisition circuit. Control of the phase of a single slave MOPA is demonstrated using a RF phase shifter. The differential phase error between two MOPAs locked to the common reference laser is typically 22 degrees.

Phase-Controlled Apertures Using Heterodyne Optical Phase-Locked Loops

“…If is the power of each combining optical wave, the total combined power detected at the photodetector PD1 is (5) For maximum power combination efficiency, should be as close to zero as possible. From (4), the power combination efficiency can be tuned by varying , the free running frequency of the VCO.…”

“…In particular, the use of electronic phase control in coherent power combination systems enables efficient, low-cost, high-coherence, high-power sources. We have recently demonstrated the coherent power combination of commercial SCLs phase-locked to a common reference laser using heterodyne OPLLs [4], [5]. However, the combined power fluctuated "slowly" between its maximum value and zero due to thermal and mechanical variations in the (differential) optical path length traveled by each optical wave.…”

Coherent beam combining with multilevel optical phase-locked loops

“…We have recently performed the OPLL experiment on various SCLs [11,16]. The master laser used in this work is a 1064 nm NP Photonics fiber laser with a 3 dB linewidth of 2.5 kHz.…”

“…We further designed an active lag-lead filter can be used. The AAC compares the frequency of the beat signal with the frequency of the rf reference signal and generates a current ramp, which brings the frequency of the beat signal to be within the acquisition range of the OPLL [11]. The use of an AAC circuit in our OPLL improved the acquisition range from ±10 MHz to ± 1.1 GHz.…”

“…In this paper we propose and demonstrate a novel approach to control the frequency and phase of the beams using multiple optical phase locked loops (OPLLs) [9][10][11]. Figure 1 gives the schematic of a binary-tree filledaperture CBC system using OPLLs.…”