We demonstrate InGaAs/GaAs quantum dot lasers with multimode lasing at room temperature immediately above threshold. The lasing modes are separated by about ten times the Fabry-Perot mode spacing, with several dark modes in between the lasing modes. Rate equation simulations indicate that this multimode behavior can be explained by a homogeneous broadening that is on the order of the mode spacing.
Vertical Cavity Surface Emitting Lasers (VCSEL) have made significant inroads into commercial realization especially in the area of data communications. Single VCSEL devices are key components in Gb Ethernet Transceivers. A multi-element VCSEL array is the key enabling technology for high-speed multi Gb/s parallel optical interconnect modules. In 1996, several companies introduced a new generation of fiber optic products based VCSEL technology such as multimode fiber transceivers for the ANSI Fiber Channel and Gigabit Ethernet IEEE 802.3 standards. VCSELs offer unique advantages over its edge-emitting counterparts in several areas. These include low-cost (LED-like) manufacturability, low current operation and array integrability. As data rates continue to increase, VCSELs offer the advantage of being able to provide the highest modulation bandwidth per milliamp of modulation current. Currently, most of the VCSEL-based products use short (780 - 980 nm) wavelength lasers. However, significant research efforts are taking place at universities and industrial research labs around the world to develop reliable, manufacturable and high-power long (1300 - 1550 nm) wavelength VCSELs. These lasers will allow longer (several km) transmission distances and will help alleviate some of the eye-safety issues. Perhaps, the most important advantage of VCSELs is the ability to form two-dimensional arrays much easier than in the case of edge-emitting lasers. These arrays (single and two-dimensional) will allow a whole new family of applications, specifically in very high-speed computer and switch interconnects.
VCSELs operating at 1.3 microns are the ideal laser source for meeting the exploding demand for bandwidth in local area and metro area networks. NCSELs will eventually replace the vast majority of 1.3 micron FP and DFB edge emitting lasers currently used in these applications, since they offer lower manufacturing cost, on wafer testability, extremely narrow linewidth, a circular output beam, high speed direct modulation, and the ability to be integrated into arrays. The primary challenge in 1.3 micron VCSELs has been to find an active region material that can be grown directly on high thermal conductivity and high reflectivity GaAs/AlGaAs distributed Bragg reflectors DBRs. In this work, we have developed MBE grown InGaAsN quantum wells that can be grown directly on GaAs substrates and integrated directly into high performance oxide VCSEL structures. We have demonstrated record room temperature CW single mode output powers in excess of 1 mW at an emission wavelength of 1287 nm. CW lasing has been observed as high as 125 degree(s)C, illustrating the excellent thermal performance of both the InGaAsN quantum wells and the GaAs/AlGaAs DBRs. Open eye diagrams were observed at 10 Gb/s, paving the way for OC-192 SONET and 10 Gb/s Ethernet applications.
We review the design, fabrication and characterization of 1.55micrometers , lattice-matched vertical-cavity surface-emitting lasers with AlAsSb/AlGaAsSb mirrors. The Sb-based mirrors provide both high reflectivity and an InP-lattice-matched structure. They lead to electrically pumped, pulsed operation of the lasers, but poor thermal conductivities of these ternary and quaternary materials and large voltage drop across them prevent the lasers from operating continuous-wave. A double-intracavity contacted structure along with thick, n-type InP cladding layers circumvents these drawbacks and finally leads to an excellent performance. For one embodiment, the threshold current is 800 (mu) A, the differential quantum efficiency is 23%, and the maximum output power is more than 1 mW at 20 degree(s)C and 110 (mu) W at 80 degree(s)C.
We will present the current state-of-the-art in widely tunable edge emitting lasers for WDM applications. Typical applications for a tunable laser will be discussed, and the different types of tunable lasers available today will be compared with respect to the requirements posed by these applications. We will focus on the DBR-type tunable lasers - DBR, SG-DBR and GCSR - which at present seem to be the only tunable lasers mature enough for real-life applications. Their main advantages are that they are all monolithic, with no moving parts, and can be switched from one frequency to the other very rapidly since the tuning is based on carrier injection and not on thermal or mechanical changes. We will briefly discuss the working principle of each of these devices, and present typical performance characteristics. From a manufacturing point of view, rapid characterization of the lasers is crucial; therefore an overview will be given of different characterization schemes that have recently been proposed. For the end user, reliability is the prime issue. We will show results of degradation studies on these lasers and outline how the control electronics that drive the laser can compensate for any frequency drift. Finally, we will also discuss the impact of the requirement for rapid frequency switching on the design of the control electronics.
Stable-beam operation to high coherent powers from large aperture devices can only be obtained from active-photonic- lattice (APL) structures of large built-in index step. Resonant phase-locked arrays of antiguides, so called ROW array, have provided 1.6W CW coherent power from 200micrometers - wide apertures. Two-dimensional surface-emitting APLs combining ROW arrays and DFB-DBR structures with central (pi) phase-shift are capable of providing coherent powers in the multi-watt range. ARROW-type devices, simpler APL structures, hold the potential for emitting 1W single-mode CW power reliability in stable beam patterns.
The demand for ever-increasing system performance- channel count, bit rate and span length- is driving the development of higher-performance erbium doped fiber amplifiers (EDFAs) and the deployment of distributed Raman amplification. This in turn has driven requirements for increasing output power from the highly reliable 1420nm to 1510nm laser diodes used in the power amplifier stage(s) of EDFAs and as the basis for C- and L-band Raman amplification. Wavelength division multiplexing (WDM) of pump lasers for higher-power EDFAs and control of the gain spectrum in Raman amplification have also driven the increased need for wavelength stabilization of these devices. At the same time, tight system space constraints have driven the need for improved efficiency and thermal management as the operating currents of these devices have increased. This paper reports progress at Agere Systems in the development and manufacture of extremely high-reliability, high-power laser diode pump sources, including >300mW Fiber Bragg Grating (FBG) -stabilized and Distributed FeedBack (DFB) -based wavelength stabilized modules, for current and future-generation telecommunications systems.
High power buried heterostructure 1.55micrometers tunable DBR lasers have been designed, fabricated and characterized. The laser consists of a gain section, a distributed Bragg reflector, a semiconductor optical amplifier and front photodetector for automated power control. The heterostructures were grown by MOCVD with the help of selective area growth techniques and dual waveguide heterostructure. Several advantages stem from this integration scheme which include simplicity of design and fabrication, increased reliability and low cost. The laser exhibits output power of 13dBm in the fiber and is tunable over 30(50GHz) ITU channels. The laser exhibits excellent performance and long-term control and reliability. The laser/transmitter also demonstrates significant increase of its functionality while its size remains small.
Laser performance degradation at elevated temperature often requires the use of costly cooling devices. Much effort has been devoted to understand and overcome the high-temperature failure of laser diodes used in telecommunication applications (wavelength 1.3-1.6micrometers ). Various physical mechanisms have been proposed to explain high-temperature effects, including Auger recombination, carrier leakage, intervalence-band absorption, gain reduction and others. The discussion of the dominating effects is still controversial. One reason for this controversy is the use of simplified theoretical models that emphasize selected mechanisms. One-sided models lead to one-sided interpretations of measurements. In this paper, high- temperature measurements on InP laser diodes are analyzed using a comprehensive laser model that includes all relevant physical mechanisms self-consistently. The software combines two-dimensional carrier transport, heat flux, strained quantum well gain computation, and optical wave guiding with a longitudinal mode solver. Careful adjustment of material parameters leads to an excellent agreement between simulation and measurements at all temperatures. At lower temperatures, Auger recombination controls the threshold current. At high temperatures, vertical electron leakage from the separate confinement layer is the main cause of performance degradation. The increase of internal absorption is less important. However, all these carrier and photon loss enhancements with higher temperature are mainly triggered by the reduction of the optical gain due to Fermi spreading of carriers.
In this paper we analyze the frequency response of 1.3+m highly strained InAsP/InGaAsP MQW lasers under small signal conditions. We show that in these lasers, electrical parasitics limit the high frequency response. These parasitics which are inherent to the laser structure, show an inductance-like behavior as determined from impedance measurements. We further show that the effect of the parasitic inductance in the laser modulation response can be significantly reduced by modifying the laser driving circuit.