Pump combiner loss as a function of input numerical aperture power distribution

Abstract

High-power combiner designs (such as kilowatt-class combiners and beyond) are increasingly aggressive on brightness conservation in order to reduce the brightness loss of the pumps as much as possible in both direct diode combining and pump and signal coupling, especially with the advent of next-generation high-power pumps. Since most of the pump loss is due to brightness loss across the combiner, tighter designs (close to the brightness limit) are considerably more sensitive to variations in the input power distribution as a function of numerical aperture ; for instance, next-generation, high-power multi-emitter pumps are likely to have larger numerical apertures than conventional single-emitter diodes. As a consequence, pump insertion loss for a given combiner design sitting close to the brightness limit should be dependant on the input power distribution. Aside from presenting a manufacturing challenge, high brightness combiners also imply more sophisticated testing to allow a deeper understanding of the loss with respect to the far-field distribution of the pump inputs and thus enable the extrapolation of loss for an arbitrary, cylindrically symmetric radiant intensity distribution. In this paper, we present a novel test method to measure loss as a function of numerical aperture (NA) fill factor using a variable NA source with square-shaped far field distributions. Results are presented for a range of combiners, such as 7x1 and 19x1 pump combiners, with different brightness ratio and fiber inputs. Combiners violating the brightness conservation equation are also characterized in order to estimate the loss as a function of input power vs. NA distribution and fill factor.

High-power pump combiners for Tm-doped fibre lasers

“…36 where very high transmission efficiency was observed. Pump combiner losses can be easily estimated by the brightness ratio, which is defined as [37] sented in Ref. 36 the BR parameter is > 5, thus, we have a high transmission level (97-99%).…”

Research on fiber coupling technology of kilowatt laser diode by single emitters

“…For diode laser, because of its complex beam, it is difficult to accurately solve the mode-field distribution, so the geometric optical coupling theory is generally adopted. According to the theory of geometrical coupling, two conditions are needed to be satisfied when the beam is coupled into the fiber: the incident diameter of the beam must be smaller than the core diameter of the fiber; the beam must meet the total reflection condition during transmission [4][5][6]. In figure 1, the laser beam coupling condition can be expressed as equation (1) and (2): …”

40 W All-Fiber Er/Yb MOPA System Using Self-Fabricated High-Power Passive Fiber Components

“…A splice between non-matched fibers can cause leaking of high power radiation, leading to point overheating and even damaging the fiber and the setup. It is often a problem to match commercial components to the fibers used in the experimental setup, which is still under investigation by many research teams [20][21][22][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. It is important to achieve a low transmission loss of the pump radiation, but most of all, it is essential to achieve a very low transmission loss of the signal radiation, which is more expensive than pump radiation (according to price per W).…”

“…Construction with bulk optics [7] LMA The most important components of all-fiber construction techniques of high-power sources are mode field adaptors (MFAs) and fiber power combiners [20][21][22][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. MFAs enable signal transmission between two fibers with different mode-field diameters.…”