Investigation of the influence of optical nonlinearity on combining efficiency in ultrashort pulsed fiber laser coherent combining system

In this paper, the influence of optical nonlinearity on combining efficiency in ultrashort pulsed fiber laser coherent combining system is investigated theoretically and experimentally. In the theoretical work, a new theoretical algorithm for the coherent combining efficiency, which can be used to quantify the spectral coherence decay induced by optical nonlineary imbalance between the sub-beams, is presented. The spectral information of the sub-beam is obtained by numerically solving the nonlinear Schrödinger equation (NLSE) in this algorithm to ensure an accurate prediction. In the experimental work, the coherent combining of two all-fiber picosecond lasers is achieved, and the influence of imbalanced optical nonlinearity on the combining efficiency is studied, which agrees with the theoretical prediction. This paper reveals the physical mechanism for the influence of optical nonlinearity on the combining efficiency, which is valuable for the coherent combining of ultrashort pulsed fiber laser beams.

Low-insertion-loss Gysel power combiner with high power density and high isolation

A suspended-stripline Gysel low-insertion-loss power combiner is presented in this paper. The multi-layer cavity structure reduces the circuit size and increases power density, composed of suspended strip lines and coaxial lines. The transmission-line theory is used to analyze this proposed power combiner, and the equivalent circuit model is developed to investigate the characteristics and design of the power combiner. The measured input return loss is greater than 20 dB from 7.15 to 9.35 GHz. The measured insertion loss is less than 0.36 dB, and the power-combining efficiency is greater than 92% from 7.39 to 9.19 GHz. The maximum power-combining efficiency is 98.8% at 8.1 GHz. Besides, the measured isolation is greater than 20 dB from 7 to 10 GHz. The power capacity is analyzed, and the cross-sectional power density is greater than 3.57 kW/cm2. The measured and simulated results show reasonable agreement with each other.

Spectral beam combining of discrete quantum cascade lasers

In this paper, we report a spectral beam combining technique based on discrete quantum cascade lasers at l~ 4.8 mm. Good beam qualities of M 2 < 1.3 for both fast and slow axes are obtained. The entire spectrum span is approximately 29.1 cm -1 , which is consistent with the theoretical results of grating equation. Maximum beam combining efficiency of 58.9% with output power exceeding 1 W is demonstrated under continuous wave operation at room temperature. The limit of beam combining efficiency is theoretically investigated. The independent temperature control for the discrete lasers circumvented the issue of thermal crosstalk between the lasers on an array and pave the way to high power and high efficiency laser spectral beam combining.

Analysis and Design of Coherent Combining of two Q-Switched Fiber Laser in Mach-Zehnder Type Cavity

In this work, we have developed an analytical model of an actively Q-switched Ytterbium-doped fiber laser by using two coupled cavities with amplifying fibers in Mach–Zehnder interferometer configuration. This oscillator system provides high peak power and high energy nanosecond pulse. The pulse energy is almost twice the energy of an individual fiber laser with a combining efficiency goes up 99%. This concept brings some novel perspectives for scaling the high energy and high peak power of nanosecond pulse fiber laser.