Search

We report the development of a fiber-coupled diode laser module with high spatial and spectral brightness. Four arrays of diode laser bars are multiplexed using polarization and narrow-band wavelength combination. The module achieves 500 W of output power from a 200 μm, 0.2 NA fiber. The output spectrum, composed of contributions from more than 150 emitters, is narrowed using VBGs and has nearly 100% content within +/- 1.5 nm of 975 nm at full power.

Fiber lasers have made significant progress in terms of power output, beam quality and operational robustness over the past few years. Key to this progress has been advances in two technologies - fiber technology and 9xx nm diode laser pump technology based on single emitters. We present the operational characteristics of our new high brightness 9xx nm fiber laser pump sources based on diode laser bars and diode laser bar arrays and discuss the design trade offs involved for realization of devices focused on this application. These trade offs include achieving the lowest slow axis divergence while maintaining high wall plug efficiency and minimizing facet power density to maximize reliability.

We present the latest development of high brightness, diode laser systems at Coherent Direct Diode Systems. Experimental results on diode laser modules with greater than 100 W with beam quality better than 10 mm•mrad will be presented. Through a combination of diode laser emitter improvements and narrow-band (< 10 nm) wavelength combination, we improve the spatial beam quality of diode laser systems significantly. The presentation will show a path that scales these diode laser systems to a kW-class output power from a 100 μm fiber with a single wavelength.

Using wavelength beam combination, we report greater than 100 W out of a 100 μm core, 0.2 numerical aperture fiber. We emphasize that this is reliable CW power from an optical system that does not suffer from distortion due to heating in gold-coated, polymer-based diffraction gratings. We show that using high-brightness bars with single-mode emitters, the wavelength beam combination technique is capable of achieving high power out of a 50 μm core, 0.2 numerical aperture fiber with good coupling efficiency.

In this work, we present the development of a suite of high brightness, fiber-coupled diode lasers at Coherent Direct Diode Systems. Experimental results of high coupling efficiency into 50-200 μm, 0.2 numerical aperture (NA) fibers will be presented. In addition to the high-brightness laser diode bar with single mode emitters, various configurations of diode laser bars with multimode, broad area emitters will be utilized to achieve similar level of brightness. The enabling technology in these products is supported by key developments in micro and macro optics, diode laser packaging, and system architecture.

Fiber-coupled systems based on broad-area multimode emitters require complicated optical trains in order to transform their poor quality output beam into a usable form. Recently, Nuvonyx has reported implementations of a single spatial mode, high-brightness laser diode bar with significantly improved beam quality. These laser bars represent a broad technology platform at the core of many Nuvonyx systems. The low output divergence of these devices enables efficient coupling into a 400 mm core, 0.22 numerical aperture fiber with a single focusing lens. Larger systems using stacks of high-brightness diode laser bars can achieve greater than 1.7 kW output from this same fiber size, corresponding to a power density level exceeding 1.4 MW/cm 2 . The high-brightness bars reported here are compatible with techniques for achieving high spatial or spectral brightness. Using external feedback elements such as a volume Bragg grating, the output spectrum can be narrowed to less than 0.25 nm and is stabilized to dλ/dI = 4 pm/A and dλ/dT = 2 pm/°C. Using spectral beam combination, a single high brightness bar can be coupled into a 100 mm core, 0.22 NA fiber with approximately 90% efficiency.

There are many advantages of delivering optical power from high power laser diode arrays through an optical fiber. However, most high power diode lasers require complicated optical trains in order to couple their light into a fiber because of the poor beam quality. Recently, Nuvonyx has reported implementations of a single spatial mode, high brightness laser diode bar technology that exhibits much improved beam quality. Optical power from the high brightness laser diode arrays is coupled into a 400 mm core fiber with a 0.22 numerical aperture (NA) at power density levels exceeding 1.4 MW/cm 2 . These systems are suitable as standalone industrial direct diode laser systems or as multikilowatt fiber laser pump sources. In addition, Nuvonyx presents experimental results of further development in its fiber coupled diode laser systems program including techniques for wavelength stabilization and spectral beam combination.

In order to meet the ever increasing demands of many high power laser diode customers, Nuvonyx has worked to improve a number of key metrics of the diode laser package. The most often challenged specifications are power per bar, efficiency, and reliability in both hard pulse and constant current mode. In response to these requests, Nuvonyx has worked to offer commercial component devices in excess of 100 and 150 watts per bar package in multiple wavelengths. The packages are routinely combined to form single stacks that generate greater than 3.5 kilowatts each and two-dimensional arrays which produce light in excess of 10 kilowatts. These parts all demonstrate predicted lifetimes in excess of 10,000 hours. The micro-channel cooled heat sink has also been improved by closer matching the coefficient of thermal expansion of the cooler to the laser diode bar, which allows for harder solders such as gold-tin to be employed. All of this work has helped to meet the specifications of the most demanding laser diode customers.