Jing Hou

Mutual Injection-Locking and Coherent Combining of Two Individual Fiber Lasers

In this paper, mutual injection-locking and coherent combining are demonstrated with two individual erbium-doped fiber lasers that were coupled by two fiber splitters. Mutual injection-locking theory of two lasers is analyzed. In the free-running state, the far-field beam profile is a simple intensity superposition, as expected of two incoherent beams. Under mutual injection-locking, interference fringes with high contrast ratio are obtained, and the two fiber lasers lase at the same wavelength with a stable output power. We have found that the two fiber lasers are always in out-of-phase mode, which is consistent with theoretical analysis. Coherent beam combining by mutual injection-locking is realized without the need for length or amplitude control. This method can be easily scaled to combine more beams.

Synchronization and coherent combining of two pulsed fiber lasers

We demonstrate a scalable architecture for coherent combining of pulsed fiber lasers. A new method for generating synchronous pulsed fiber lasers by direct phase modulation is proposed and investigated. It is shown that phase modulated mutually coupled laser array can be a steady synchronous pulsed fiber laser source. The synchronous pulsed fiber lasers are coherently combined with an invariable phase difference of pa in adjacent lasers. Neither active phase control nor polarization control is taken in our experiment.

Theoretical Study on Phase Locking of Arrays of Mutually-Injected Fiber Lasers

Phase locking of arrays of mutually-injected fiber lasers is investigated theoretically. The phase-locked states of this array are analytically discussed. It is revealed that phase locking of this array is affected by the transfer characteristic of the coupler used for mutual injection. Arrays fabricated with two kinds of couplers (i.e., 1 × 3 coupler and the compound coupler built with two 1 × 2 couplers) are studied. It is found that the compound coupler is more suitable for phase locking of the array. The relationship between the phase-locked states and the number of elementary lasers of the array is also studied.

Modeling self-organized coherent fiber laser array

Self-organized coherent laser array seems to be a promising method for coherent combining fiber lasers. Phase locking is realized by mutual energy injection, without any active phase stabilization, requirement of the fiber length or the output power for individual lasers. In this paper, rate equations describing time evolution of the complex, slow varying electric field and gain of an array of single transverse and longitudinal mode lasers proposed in former literature was referred to for modeling the self-organized fiber laser array. The process for phase-locking evolution of each individual laser in a fiber laser array was modeled and analyzed theoretically and numerically. For the case of an array containing 2 or more than 4 lasers, the array will be in an out-of-phase mode, with a phase difference of π between adjacent laser output modes. For an array containing 3 lasers, phase difference between adjacent lasers would be ±2π/3. We will cite experiments to validate our verdict. We can also obtain by investigating on the model that more powers can be extracted than the summation individual free running lasers. Those phenomenons have been reported but not explained. At the end of this paper, we perform system level analysis on the fiber laser array numerically. We find that with the number of lasers increasing, the array will have a more critical condition on detuning frequency for phase locking.

Optimum design of the phase control system of coherent beam combining of fiber amplifiers

Combining fiber laser beams are of current interest for scaling lasers to high average output power. The Master Oscillator Power Amplifier (MOPA) configuration is important in fiber laser beam combination. The efficiency of coherent beam combining is depended on the phase control precision of the system mostly, which is equivalent to the closed loop output phase noise. In this paper, a simplified negative feedback model of the phase control system is constructed to study the optimum design of the system. The effects of the transfer function of the system on the phase noise of the optical fiber amplifier, the measured noise and the stability of the system are analyzed. The relationship between the closed loop output noise and the system parameters is analyzed and calculated. The results show that there is a set of system parameters to minimize the closed loop output noise for different phase noise of the optical fiber amplifier, and for a fixed set of system parameters, the closed loop output noise of the system almost changes linearly with the change of the input noise. The effective means to achieve optimal system parameters for higher degree of control precision are obtained.