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.
The optimization of a 1300nm buried heterostructure(BH)InGaAsP/InP DFB laser for uncooled directly modulated 10Gbit/s operation is described. The development process as well as the key process parameters are discussed and results are presented on an optimized structure. Bandwidths in excess of 10GHz were measured at 90C chip base temperature. Clean open eye diagrams were recorded over the full temperature range, resulting in error free transmission over 40km. To our knowledge the results represent the current state of the art for uncooled BH DFB lasers operating at 1300nm.
A rate equation-based model of MQW semiconductor lasers, has been developed describing power and chirp dynamics. The equations are implemented using an equivalent circuit approach, exploiting the analogy between rate equations and a Kirchoff current balance equation at a capacitor node. Current and voltages across the circuit components are equivalent to the main elements of the rate equations.
This solution offers different advantages like the possibility to study the parasitic effects and the opportunity to integrate an high-speed laser model with an IC driver model in the same simulation environment. The model can be easily implemented in any circuit simulator (SPICE, Cadence, Agilent EESoft ADS). All parameters have been derived from measurements on real DFB devices. The model was used to improve static and dynamic performances of InGaAsP MQW-DFB laser 10Gb/s operations, as well as to study the problem of interfacing laser and IC driver. This optimization gave contributions to the realization of uncooled (up to 95°C chip temperature) DFB lasers directly modulated at 10 Gb/s for optical transceivers in 10Gb-Ethernet networks.