SBIR-STTR Award

Q-Peak proposes a high power Thulium (Tm) doped fiber amplifier design operating at 2 m wavelength utilizing a novel lateral fiber fusion side-pumping method and a nanoparticle doping technique to generate significant signal power and performance. The proposed fusion side-pumping method will distribute the pump power along the length of the active fiber, allowing the high power amplifier to yield a relatively uniform gain distribution and a distributed thermal load. The fusion side-pumping method, consisting of fusing a coreless passive fiber to a Tm-doped double clad fiber, will provide significant cross-coupling between the input pump power and the cladding of the active fiber. This high power amplifier model will avoid thermal loading issues seen experimentally in end-pumping high power Thulium fiber lasers. Q-Peaks high power amplifier design will utilize a fusion region between the two fibers long enough to be able to efficiently pump bi-directionally without damaging any pump diode lasers. Additionally, the proposed nanoparticle doping method, developed by NRL, will intentionally cluster Tm ions into intimate contact in order exploit the two-for-one cross-relaxation phenomena observed in Thulium ions in close proximity. The location of the Tm ions will be effectively controlled, causing the cross-relaxation process to require less ions. Therefore, there is less absorption and less thermal load on the active fiber. Utilizing these two methods will allow for a novel amplifier prototype capable of signal power in excess of 1 kW without having significant thermal load issues in the active fiber.

Benefit:
With the development of reliable high power side-pumped Thulium fiber laser/amplifier models, Q-Peak would establish itself as an expert in the generation of high power 2 m light sources, operating in the eye-safe range (i.e. wavelength longer than 1.4 m). Q-Peak will immediately pursue economic opportunities in the fields of laser urology and plastic bottle manufacturing. The high power Thulium fiber amplifier model described in this work would provide significant and long lasting financial opportunities with companies from these fields.

Keywords:
Thulium, Thulium, fiber amplifier, Lasers, side-pumping, nanoparticle, high power, fiber laser, fusion

In this SBIR program, Q-Peak will develop a continuous manufacturing process to facilitate deterministic cross coupling between optical fibers. The process will allow managing mode coupling in two-fiber sensor architectures, coupling of power from pump fibers to gain fibers for fiber lasers in a distributed length methodology and formation of unique signal add/drop functionality for optical networks. Q-Peak will focus on the process development of a side-pumping architecture for fiber lasers as this allows managing the amount of energy coupled per unit length between pump fibers and the gain fiber. The primary advantage for fiber lasers is that length management of pump coupling is, to first order, equivalent to managing thermal rise in the gain fiber avoiding thermal runaway and destructive effects of over pumping based on specific dopant ions and dopant density in the active fiber. We will address the manufacturability, electrical-to-optical and optical-to-optical efficiency, and a risk assessment of other parameters important to the energy transfer process. While side-pumping has been demonstrated for Ytterbium-doped fiber lasers, the diversity of ions used in fiber lasers (Yb, Nd, Yb-Er, Er, Tm, and Pr) requires a flexible and adaptable coupling process where the energy transfer can be tailored to the specific fiber construction, mode space, materials, and the specific dopant ion density.