Stefan Mohrdiek

L-I characteristics of fiber Bragg grating stabilized 980-nm pump lasers

Light versus current (L-I) characteristics, of fiber Bragg grating stabilized 980-nm pump lasers, is experimentally studied and theoretically modeled. It is shown that a conventional design of such laser modules can result in sudden transitions between a coherence-collapse multimode emission, and a coherent single-mode state of operation.

Further development of high-power pump laser diodes

AlGaAs/InGaAs based high power pump laser diodes with wavelength of around 980 nm are key products within erbium doped fiber amplifiers (EDFA) for todays long haul and metro-communication networks, whereas InGaAsP/InP based laser diodes with 14xx nm emission wavelength are relevant for advanced, but not yet widely-used Raman amplifiers. Due to the changing industrial environment cost reduction becomes a crucial factor in the development of new, pump modules. Therefore, pump laser chips were aggressively optimized in terms of power conversion and thermal stability, which allows operation without active cooling at temperatures exceeding 70°C. In addition our submarine-reliable single mode technology was extended to high power multi-mode laser diodes. These light sources can be used in the field of optical amplifiers as well as for medical, printing and industrial applications. Improvements of pump laser diodes in terms of power conversion efficiency, fiber Bragg grating (FBG) locking performance of single mode devices, noise reduction and reliability will be presented.

980 nm single mode modules yielding 700 mW fiber coupled pump power

Fiber coupled light output power of highly reliable single mode laser diodes with an emission wavelength of around 980 nm has been increased by 40% as compared to former results. The devices reach in excess of 1.3 W ex-facet CW light output power with up to 60% power conversion efficiency and exhibit a vertical far-field of around 21/spl deg/. The maximum fiber coupled CW light output power amounts to more than 700 mW. The devices are designed to satisfy the stringent requirements of future cost efficient uncooled applications as well as the high power market of broadband multi channel networks.

External feedback optimization by means of polarization control in fiber Bragg grating stabilized 980-nm pump lasers

Effects of polarization change in the feedback provided by fiber Bragg gratings that stabilize 980-nm pump lasers are investigated. The effective feedback in the proper transverse-electric polarization is calculated from an easily measured parameter, describing the polarization at the fiber grating. This provides a useful experimental tool to investigate the effect of feedback loss due to polarization change that can occur in nonpolarization maintaining fibers. On the basis of our calculations, we give guidelines for optimum fiber layout to minimize polarization change.

Detuning characteristics of fiber Bragg grating stabilized 980 nm pump lasers

We investigate wavelength detuning effects between ridge waveguide 980 nm pump laser-fiber Bragg grating (FBG) pairs. A design point suppressing single-mode to multi-mode switching under coherence collapse is experimentally and theoretically developed.

Highly efficient 980 nm single mode modules with over 0.5 Watt pump power

We present narrow beam divergence InGaAs/AlGaAs 980 nm ridge waveguide laser diodes with over 1 W CW-rollover power. Together with superior power conversion efficiency a maximum fiber-coupled light output power of over 0.5 W has been reached.

Coolerless operation of 980 nm pump modules

Efficient fiber Bragg grating wavelength and power stabilization of 980 nm pump lasers at high fiber-coupled output power (150 mW at 75/spl deg/C and 95 mW at 100/spl deg/C) over a wide temperature range of 90/spl deg/C is demonstrated.

High-brightness broad-area lasers with high reliability for Yb-Er-fiber pumping applications

State-of-the-art pump lasers for fiber amplifiers in optical telecommunication systems can deliver up to 250 mW optical power in single mode emission. Power approaching 500 mW is seen as the upper limit for single mode lasers without sacrificing reliability. For yet higher power, broad area laser diodes coupled into the cladding of ytterbium-erbium doped fibers have a great potential to achieve more gain. Here, Diode lasers with a ridge width of 30 micrometer mounted junction-side-up using a hard-tin solder are presented as an alternative over EDFA pumping by single-mode lasers. Reliable broad area lasers are obtained by adopting standard narrow-stripe single-mode laser technology with proven 110 FIT at 150 mW and 25 degrees Celsius varying only the ridge width. Reliability and packaging problems commonly associated with p- side down mounting are avoided. Due to the high power conversion efficiency greater than 55% of the laser chip, a cw maximum output power as high as 1.1 W can be obtained. Submicron fiber alignment tolerances are no longer required, as compared to single mode lasers. Due to low heat dissipation these 30 micrometer stripe lasers can be operated in standard butterfly packages and high coupling efficiencies are achieved above 80% into standard 50 micrometer multimode fibers. YEDFAs with 23 dBm output power using these lasers have been demonstrated.

Optimization of fiber coupling in ultra-high power pump modules at λ = 980 nm

This work presents some aspects of development of ultra-high power single-mode pump modules at λ= 980 nm for erbium-doped fiber amplifiers. We report here on the results of numerical simulations and experimental data of modifications to the laser waveguide structure with a focus on improving the fiber coupling efficiency. The so-called integrated fiber wedge lens was used as a coupling element in the present investigation. Our simulations showed that between the two most widely used laser waveguide types: large optical cavity (LOC) and separate confinement (SCH or GRICC) heterostructures the difference in coupling efficiency can be as high as ten absolute percent We achieved an experimental coupling efficiency of 93 percent for LOC-like lasers structure. The SCH-based lasers showed maximum coupling efficiency of 83 percent. However, in spite of superior coupling efficiency, use of LOC-based lasers in pump modules does not bring any benefits because of subpar electro-optical performance. To improve the situation we had to find a reasonable compromise between LOC and SCH structures. Lasers resulting from this approach gave a coupling efficiency around 90 percent. The laser diodes based on the optimized structure achieve more than 3 W of output power and more than 2 W of kink-free power in CW regime at room temperature. They also demonstrate differential quantum efficiency above 85% and laser power conversion efficiency above 60 percent at use conditions. Thanks to the combination of all these factors pump modules built on these lasers produce 1W of wavelength-stabilized power at an operating current below 1.3 A. Maximum kink-free, wavelength-stabilized output from the pump module reached 1.8 W at room temperature.

A compact, narrow-band, and low-noise 800-mW laser source at 980 nm

We report on the development of a new cost-effective, small form-factor laser source at a wavelength of 980 nm. The laser module is based on proven technology commonly used for pump laser modules deployed in fiber amplifiers of telecommunication networks. The package uses a state-of-the-art 14-pin butterfly housing with a footprint of 30x15 mm2 with a Fabry-Perot AlGaAs-InGaAs pump laser diode mounted inside having an anti-reflection coating on its front facet. The light is coupled into a single-mode polarization-maintaining fiber with a mode-field diameter of 6.6 micrometer. The spectral properties of the source are defined by a fiber Bragg grating (FBG) that provides feedback in a narrow reflection band. The laser back facet and the FBG form a long resonant cavity of 1.7 m length in which laser light with a low coherence length of a few cm is generated. This configuration with the laser being operated in the coherence-collapse regime has the advantage of being robust against variations in the optical path, thus enabling stable and mode-hop free emission. The laser module has the following properties: a continuous-wave fiber output power exceeding 800 mW, a spectral bandwidth of less than 50 pm, a root-mean square power variation of less than 0.2 % from DC to 2 MHz over the entire power operating range, and a polarization extinction ratio of more than 20 dB. This is a compact, low noise, high power source for frequency conversion with nonlinear optical materials, such as blue light generation.