In this work, we present a compact size and highly efficient nanosecond pulsed 1550nm single mode fiber laser that can operate from -40C to +95C. The laser generates 2 to 10 ns pulses at a repetition rate of hundreds kHz to a few MHz with hundreds to kilowatt peak power. The design of this laser is optimized to achieve over 10% wall-plug efficiency at room temperature with an ultra-low ASE noise less than 1%. The performance is also well maintained with less than 30% EO (electrical-optical) efficiency degradation at extreme temperatures and demonstrates high reliability consistent with deployment into harsh environments.The robust performance makes the laser an ideal source for lidar and sensing applications, along with other medical, scientific, and industrial applications.
High brightness semiconductor diode lasers can provide tremendous system-level advantages for many applications. Recent advancements in InP-based edge-emitting diode lasers operating in the 1500 – 1600 nm wavelength band could enable compact, direct diode solutions with performance metrics that previously could only be met by fiber-based lasers or solid-state laser systems. We report on high power, high beam quality diode lasers at 1550 nm based on a tapered chip architecture. We have demonstrated ⪆5 W of continuous wave output power at room temperature, with a slow axis beam propagation factor M2 of 1.1, corresponding to a slow axis linear brightness of 9.2 W mm-1 mrad-1. We have also demonstrated a fully packaged watt-class single mode fiber-coupled Semiconductor Optical Amplifier (SOA) based on this technology. This package delivers ⪆30 dBm (1.2 W) ex-fiber saturation output power, ten times higher saturation power than the prior state-of-the-art. This result is achieved with an input seed power of 30 mW (approximately 15 dBm), corresponding to an overall gain of approximately 16 dB. To demonstrate the functionality of the SOA, we have carried out linewidth measurements and data transmission measurements. These tapered lasers and amplifiers offer great potential benefit for many pumping and direct use applications.
The performance of advanced laser systems for defense and aerospace applications rely heavily on the capabilities of the system building blocks. Due to the sensitive nature of the end applications, such components also often require domestic US sources to ensure supply chain security and facilitate engagement in the product development cycle.
Coherent maintains a full range of domestic critical component manufacturing capabilities to support the defense and aerospace laser industry, including optical fiber, semiconductor diode lasers, crystals, optical isolators, coatings and freeform optics, all from US-based manufacturing locations.
Coherent has also expanded the internal manufacturing capabilities, enabling the manufacture of complete laser component assemblies and subsystems, allowing contract partners to leverage our internal laser manufacturing expertise. We will review our latest component capabilities and discuss how these components map to critical defense applications.
High Power multi-kW class fiber lasers have become a leading technology in Directed Energy applications. With Direct Energy weapons and countermeasures moving closer to a deployable technology, industry players are now looking to ensure the components within their systems can withstand the harsh environments in which they will be used. With limited power available in the field, efficiency is a key criterion for these systems and there is a careful balance for diode laser pumps as a piece of the overall system. Increasing the cooling capacity delivered to the diode pumps will increase their Electrical-to-Optical efficiency, but requires more energy be consumed in the cooling loop through lowering the coolant temperature or increasing the pump speed to increase flow rate. In this paper, Coherent|DILAS aims to map these uncharted waters for its Low SWaP diode lasers by exploring trade space for the parameters that are critical to the overall system efficiency. By changing coolant types from water to glycol mixes, coolant freezing can be eliminated while the effects of coolant viscosity are explored. Additionally, direct changes to the coolant temperature and flow rates further explore cooling/efficiency trade space. Experiments are then repeated with an external grating to lock the center wavelength at the 976nm absorption band. The range at which locking is maintained and the efficiency change will be explored for various coolant, flow, and temperature configurations. With a large web of interacting processes being explored, Coherent|DILAS aims to enable further overall system optimization within Directed Energy community.
Daniel Creeden, Mitchell Underwood, Tiffanie D'Alberto, Tony Tero, David Hosmer, Ronald Basque, Joshua Galipeau, Jill Sears, David Paquette, Chris Ebert
KEYWORDS: Optical amplifiers, Fiber amplifiers, Amplifiers, Diodes, Packaging, High power fiber amplifiers, Electronics, Signal to noise ratio, Head, Optics manufacturing
Coherent | Nufern has a long history of high power Yb-doped fiber amplifier and component development. This ranges from amplifiers in the >1.5kW regime up to demonstrations of >3kW output power. In this paper, we discuss our latest advancements in the performance of high power, narrow linewidth, kW-class, monolithic Yb-doped fiber amplifiers, as well as the packaging of our two newest amplifier systems. Our lightest amplifier offers 1.6kW output power at <4.5kg/kW. This is an OEM version which requires external power, but offers a significant (nearly 1.5x) decrease in overall mass compared to our previous generation of amplifiers. Our 2.1kW amplifier is our smallest and highest power amplifier. It contains integrated electronics to offer a complete stand-alone amplifier, requiring only DC voltage input, external cooling, and software control. This has nearly a 2x reduction in volume compared to our previous generation. We discuss the performance and specifications of these two amplifier packages. This includes power scaling with narrow linewidth, as well as a significant and simultaneous reduction in volume and mass compared to our previous generations. We discuss the packaging challenges with these architectures, as well as the diode technologies which have enabled such a reduction in our packaging volume and mass. We also discuss experimental results in the power scaling of these fiber amplifiers.
KEYWORDS: Diodes, Fiber lasers, Cooling systems, High power lasers, Defense and security, Energy efficiency, Directed energy weapons, Laser development, High power fiber lasers, Semiconductor lasers
Recent developments in fiber lasers show the field has reached a high level of maturity, and several demonstration programs have shown successful scaling of output power into the 30-50kW regime while maintaining good beam quality. Despite these successes, much work remains before fibers lasers are ready for the range of field applications currently envisioned. Constraints set by small system size, limited power availability, and harsh environmental conditions demand that novel modes of operation be considered. The variety of use conditions for which high power fiber lasers are being considered poses additional challenges to the system architect, and the full trade-space is not yet clear.
In advance of full system definition, Coherent|DILAS has continued to develop technologies that will extend the trade-space available to the system designer and facilitate transition to the field. We will report on a variety of efforts to extend the use range of existing, SWaP optimized fiber pump modules into territory appropriate for the more demanding of these applications.
Of particular concern are the system cooling architectures needed to support diode pump modules, which in the case of large systems, comprise a significant size and power demand. While efforts to improve SWaP of cooling systems generally have negative effects on diode performance, here we show that negative effects resulting from coolant system design can be mitigated. Operational results that pair existing lightweight, high power modules with non-standard cooling architectures, pulse schemes, and wavelength stabilization will be discussed.
KEYWORDS: Diodes, Fiber couplers, Fiber coupled lasers, Computer aided design, Calibration, Fiber lasers, High power lasers, Semiconductor lasers, Thulium, Ytterbium, Defense and security, Control systems
DILAS offers a variety of high power pump diode lasers, optimized for different gain media. Systems optimized for DPAL pumping at 766nm will be discussed, including results demonstrating precise wavelength and spectral width control necessary to optimal overlap with atomic lines. In addition, pump modules optimized at 793 nm for Tm fiber laser pumping have been demonstrated, including a low SWaP module targeted for airborne applications. Lastly, DILAS’ line of high-efficiency/low-SWaP pump at 976nm for Yb fiber laser will be presented. Starting with the 330W IS46 module, DILAS has demonstrated >53% efficiency, and has now increased brightness up to 625W from a 225 um/ 0.22 NA fiber. Developments towards a module with >900W output power will also be shown.
KEYWORDS: Laser applications, Current controlled current source, Thulium, Fiber lasers, Semiconductor lasers, Manufacturing, Defense technologies, High power lasers
DILAS has leveraged its industry-leading work in manufacturing low SWaP fiber-coupled modules extending the wavelength range to 793nm for Tm fiber laser pumping. Ideal for medical, industrial and military applications, modules spanning from single emitter-based 9W to TBar-based 200W of 793nm pump power will be discussed. The highlight is a lightweight module capable of <200W of 793nm pump power out of a package weighing < 400 grams. In addition, other modules spanning from single emitter-based 9W to TBar-based 200W of 793nm pump power will be presented. In addition, advances in DPAL modules, emitting at the technologically important wavelengths near 766nm and 780nm, will be detailed. Highlights include a fully microprocessor controlled fiber-coupled module that produces greater than 400W from a 600 micron core fiber and a line width of only 56.3pm. The micro-processor permits the automated center wavelength and line width tuning of the output over a range of output powers while retaining excellent line center and line width stability over time.
DILAS Diode Laser, Inc. continues to improve and optimize high-brightness fiber-laser pump modules. Highlights include a 330W module weighing in at 300 grams, achieving greater than 55% electrical-to-optical efficiency at the operating power from a 225micron/0.22NA fiber and a power-scaled version capable of >600 W, >50% efficiency and weighing in at less than 400 grams. The macro-channel coolers enabling these modules eliminate the need for microchannels and deionized water and reduce pressure drop across the system. A road map to modules with >900W of output power will also be presented.
Targeted at the 793nm absorption band, DILAS Diode Laser, Inc. offers a range of products specifically designed for Thulium fiber laser pumping, spanning from 12 W to <300W of pump power and coupled into fiber sizes starting at 105um and upwards. A variety of different diode architectures are utilized, ranging from single-emitters, conduction-cooled bars, and DILAS's T-bar structure extended to the 793nm range, resulting in a wide variety of power levels and packaging options to support different applications. As IRCM for airborne platforms is a major application for Tm fiber lasers, packages optimized for low SWaP will be presented, which utilize a combination of the T-bar structure and macrochannel coolers specifically designed for compact, lightweight applications. Examples and results of Tm fiber lasers pumped using DILAS diodes will also be presented and discussed.
Specifically optimized for both high efficiency and low SWaP, DILAS Diode Laser, Inc. continues to improve and optimize high-brightness fiber-laser pump modules. Starting with a <53% electrical-optical efficient 330W module in full production, power-scaled versions capable of 625 W and 900 W will also be covered. Utilizing a 225um/0.22 NA fiber output, these pumps enable single-mode kW-class fiber amplifiers ranging from 1 kW to 3kW. Designed for low SWaP, these modules are produced using mounted diode laser bars from a standard manufacturing line and commercial, off-theshelf optics. Cooling is accomplished through macro channel coolers that eliminate the need for micro-channels and the associated coolant issues. This innovative macro channel cooler is specifically designed to reduce both weight and thermal resistance, and also provides an ideal substrate for power-scaling the diode module while maintaining efficiency. Utilizing AuSn hard solder on CTE matched substrates eliminates the problems associated with Indium-based diode solder joints and permits hard pulsing of the laser diodes with any pulse width/duty cycle parameter set. Optional VBG stabilization is available on all versions for applications requiring wavelength stability over a wide temperature range.
Diode laser modules based on arrays of single emitters offer a number of advantages over bar-based solutions including
enhanced reliability, higher brightness, and lower cost per bright watt. This approach has enabled a rapid proliferation of
commercially available high-brightness fiber-coupled diode laser modules. Incorporating ever-greater numbers of
emitters within a single module offers a direct path for power scaling while simultaneously maintaining high brightness
and minimizing overall cost. While reports of long lifetimes for single emitter diode laser technology are widespread, the
complex relationship between the standalone chip reliability and package-induced failure modes, as well as the impact of
built-in redundancy offered by multiple emitters, are not often discussed. In this work, we present our approach to the
modeling of fiber-coupled laser systems based on single-emitter laser diodes.
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