WHITE PAPER
New High Power Single-Emitter Diodes for Ytterbium Fiber Laser Systems
Overview
The FACTOR 976 nm series support higher pumping of Ytterbium fiber lasers in a very compact and lightweight package, and are capable of powers up to 400 W with a mere 21 A of operating current with no additional cooling. These new diodes are suitable for high power industrial, medical or defense applications, and provide VBG locking to further reduce thermal influence on wavelength performance.
While many fiber-coupled modules have traditionally been based on high power diode laser bars, recent improvements in facet passivation provides a higher COMD threshold, and therefore enables higher power per single emitter. Emitters are arranged in a into a stair-step structure that increases the distance between emitters, which enhances cooling. This arrangement also facilitates spatial multiplexing of multiple emitters, and polarization multiplexing can be used in some FACTOR diode packages.
The new FACTOR 976 nm diodes are offered in two configurations:
| Verdi | Factor - 22 | Factor - 16 |
| Output Power (W) | 400 | 150 |
| Operating Current (A) | 21 | 12 |
| Electro-Optical Efficiency | >45 (typ. 50) | >48 (typ. 51) |
| Fiber Core / Cladding Diameter (µm) | 200 / 240 | 106.5 / 125 |
| 90% Power Content | NA 0.16 (typ. 93%) | NA 0.15 (typ. 93%) |
| VBG | VBG | VBG |
| FIber Output | Pigtail | Pigtail |
| Dimensions (nm) | 97 x 76 x 12 | 96 x 50 x 12 |
| Weight (g) | 500 | 230 |
The FACTOR-16 is capable of pumping up to 150 W in a 106.5/125 µm fiber, and is based on a 16-single emitter array. The unit has been designed with alternate side mounting holes to stagger the diodes in a very dense array. Cooling is done by conduction through the bottom side of the module. This model does not contain a modestrip fiber, and the attached fiber pigtail is compact.
The FACTOR-22 is capable of pumping up to 400 W in a 200/240 µm fiber, and is based on a 22-single emitter array. The unit includes a fiber modestrip, which introduces some heat into the area. The heat is removed by the conduction cooling applied to the bottom side of the module, and customers can install a cooling plate if needed. Two holes are available for the mounting of a temperature sensor.
Both models have been robustly designed to virtually eliminate potential bending of the module during the mounting process, which will ensure proper heat dissipation with or without an installed cooling plate.
VGB Locking
Coherent design goals for VGB locking were to achieve 90% power content in less than 1nm. For the FACTOR 22, the line width was 0.7 nm with an efficiency of 52.6% and for the FACTOR 16, it was 0.9 nm with an efficiency of 51.2%.
The chart below shows the wavelength locking at 976nm over temperature range.
"Coherent is a leader in providing VGB locked products with various power levels and wavelengths."
Coherent is a leader in providing VGB locked products with various power levels and wavelengths. With in-house VGB capabilities, these FACTOR diodes benefit from improvements in locking performance. Perfect locking (that is, 99% power in-band for the locked spectrum) was achieved at power ranges from 4 A to 24 A and across a temperature range that varied from 20° C to 50°, indicating that no active temperature control was required to achieve these results. The locking range presented is ±6 nm, meaning that locking works for an unlocked center wavelength between 970 nm and 982 nm, which is among the widest locking range on the market.
Ex-Fiber Numerical Apertures
The Numerical Aperture (NA) of the FACTOR 976 nm series is an important factor in designing the fiber combiner. Here, the far profile beam is measured using a simple CCD Camera with high resolution and no oversaturation. The aperture of NA 0.16 is shown as the white ring below.
The results show the cross section in both the horizontal and vertical plane is a typical Gauss-like distribution without any unexpected side peaks. The bottom left shows the NA for each power requirement. Each module built is put through this test to ensure quality assurance across the complete diode family.
"Excessive environmental testing has been done to validate the robust design and performance under a wide range of conditions…"
Additional Models
FACTOR Diodes are also available in other wavelengths, including 793 nm for Thulium fiber pumping from 10 to 40 W from 106.5 µm fiber, and 88X for Nd3+ based DPSS lasers from 150 W from 200 µm and 400 µm fiber cores for a more efficient and less complicated pumping scheme for designing highly sophisticated lasers. Additional models are offered in 808 nm for Nd end-pumping, medical and materials processing applications, and in 1060 nm for medical applications if required.