Vertical-cavity Surface-emitting Laser Diodes Research Articles

Self-consistent model of 650 nm GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers

A comprehensive fully self-consistent model of oxide-confined GaAs-based vertical-cavity surface-emitting diode lasers (VCSELs) with GaInP/AlGaInP quantum-well active regions to simulate their room-temperature (RT) continuous-wave (CW) operation is presented. The model takes into consideration all observed or expected special features of GaInP/AlGaInP VCSELs. A complete set of model parameters is given. The model enables a deeper understanding of a VCSEL operation with full complexity of many inter-related physical phenomena taking place within its volume. It may also be used to design and optimize the above VCSEL structures for their numerous applications, in particular as sources of the 650 nm carrier wave in communication systems using plastic optical fibres. With the aid of this model, anticipated VCSEL RT CW performance characteristics may be determined.

Comparison of Exactness of Scalar and Vectorial Optical Methods Used to Model a VCSEL Operation

In the paper, a comparison between results of the optical scalar and vectorial optical methods, using the scalar effective frequency method and the vectorial method of lines, respectively, as their typical examples, applied for simulating an operation of vertical-cavity surface-emitting diode lasers (VCSELs) is presented. Both optical approaches has been applied to simulate an operation of the standard 1.3-mum GaAs-based oxide-confined GaInAsN double quantum-well VCSEL, but comparison conclusions seem to be more general and concerns all VCSELs. Validity limits of the simplified scalar approach have been determined by comparing its approximate results with more exact ones obtained with the aid of the accurate vectorial model. The scalar model has been found to be quite exact in the case of a determination of the wavelength of emitted radiation, whereas its exactness in the lasing threshold analysis is much worse, especially in the case of higher order modes, smaller aperture diameters and/or weak radial optical guidance. Our analysis leads also to more general designing conclusions concerning the optimal position and the thickness of the oxide layer assuring, respectively, the stable single mode operation and the lowest threshold gain

Bidirectional Hybrid DWDM-PON for HDTV/Gigabit Ethernet/CATV Applications

A new scheme for bi-directional HDTV/Gigabit Ethernet/CATV transmission over a hybrid densewavelength-division-multiplexing passive optical network (DWDM-PON) is proposed and demonstrated. It is based on injection-locked vertical-cavity surface-emitting lasers and distributed-feedback laser diodes as transmitters. Services with 129 HDTV channels, a 1.25 Gbps Gigabit Ethernet connection, and 77 CATV channels are successfully demonstrated over 40 km single-mode fiber links. Good performance of bit error rate, carrier-to-noise ratio, composite second order, and composite triple beat is achieved in our proposed bidirectional DWDM-PON.

GaInNAsSb/GaNAs quantum-well VCSELs: Modeling and physical analysis in the 1.50−1.55 μm wavelength range

Physical analysis of the long-wavelength room-temperature (RT) continuous-wave (cw) emission within the 1.50−1.55 μm range from the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) is carried out. To this end, a comprehensive three-dimensional optical-electrical-thermal-gain self-consistent simulation of physical processes taking place inside a laser volume is applied. While the 1.50-μm emission has been found to be reached practically without trouble, the 1.55-μm emission needs additional optimizations. For the optimal QW structure, the 1.55-μm emission in highly detuned VCSELs requires RT cw threshold currents more than 18 times higher than those of the 1.50-μm one. Some threshold reduction may be achieved by adding the second quantum well. The 3λ-cavity design has been proved to be optimized for the 1.50-μm emission ensuring stable fundamental-mode operation even at elevated temperatures whereas the 1.5λ-cavity is optimal for the 1.55-μm emission for which threshold reduction is more important. For the 1.50-μm emission, some structure optimizations have been proposed. The GaInNAsSb/GaNAs structure offers promising prospects to manufacture VCSELs emitting 1.55-μm radiation, but some technology and construction improvements are still necessary.

Modal behavior of photonic-crystal vertical-cavity surface-emitting diode laser analyzed with Plane Wave Admittance Method

A three-dimensional, full vectorial model has been applied for investigation the modal characteristics of a phosphide photonic-crystal vertical-cavity surface-emitting diode laser. The photonic crystal has been defined as a regular, hexagonal net of holes, etched in the upper, p-type Distributed Bragg Reflector of the laser. The electromagnetic field has been confined to the active region by a single defect of the photonic crystal providing overlapping with carriers funneled by a tunnel junction. We have determined the range of design parameters, which provide single mode operation.

Single mode condition and modes discrimination in photonic-crystal 1.3 μm AlInGaAs/InP VCSEL

We determine the single mode condition and analyze the modes discrimination of 1.3 mum InP based photonic-crystal vertical-cavity surfaceemitting diode laser. To this aim we apply the fully vectorial, three dimensional Plane Wave Admittance Method and analyze a broad range of photonic-crystal parameters such as hole etching depth, distance between the holes and their diameters.

Optimal radii of photonic crystal holes within DBR mirrors in long wavelength VCSEL

The modal characteristics of a Photonic-Crystal Vertical-Cavity Surface-Emitting diode Laser (PC-VCSEL) have been investigated. Photonic crystal structure, realized by a regular net of air holes within the layers, has been etched in the upper DBR mirror. An advanced three-dimensional, vectorial electromagnetic model has been applied to a phosphide - based device design featuring InGaAlAs active region, AlGaAs/GaAs mirrors and a tunnel junction to confine the current flow. For the structure under consideration a single mode operation has been found for the hole diameter over photonic crystal lattice constant ratio between 0.1 - 0.3.

Optimization of oxide-confined vertical-cavity surface-emitting diode lasers

The performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSELs) is distinctly different than that of earlier VCSEL designs. As a result, hitherto known optimal VCSEL designs cannot be considered as the best ones any longer; they need new analysis to determine their optimal OC designs for their various applications. Therefore, in this paper, a comparative analysis of the room-temperature (RT) continuous-wave (CW) threshold operation of various designs of OC VCSELs is carried out using the 1.3 µm OC intra-cavity-contacted GaAs-based quantum-well (GaIn)(NAs)/GaAs VCSEL as a typical example. The analysis has been made with the aid of a comprehensive fully self-consistent three-dimensional optical-electrical-thermal-gain model. Depending on an application, different OC VCSEL designs have been found to be optimal. The lowest RT CW lasing threshold has been found to be achieved in the 1.5λ-cavity design with only one oxide aperture (for smaller active regions) or in the 3λ-cavity design with two oxide apertures (for larger active regions). On the other hand, to reach the single-fundamental-mode operation and/or longer lasing wavelengths, the 3λ-cavity OC VCSEL with one oxide aperture happened to be the best lasing design, especially for relatively large active regions.

Separate-confinement-oxidation vertical-cavity surface-emitting laser structure

In the present paper, a comprehensive self-consistent three-dimensional model is used to analyze physical aspects of the operation of oxide-confined vertical-cavity surface-emitting diode lasers (VCSELs) and to optimize their structures. The impact of the built-in radial confining mechanisms created by oxide apertures, i.e., the influence of their diameters and localizations on radial confinements of both the current injection into VCSEL active regions and electromagnetic fields of successive cavity modes, has been investigated. Basically, there are two extreme cases: the index-guided (IG) VCSELs with the aperture localized at the antinode position of the optical standing wave, characterized by a very low lasing threshold but exhibiting rather poor mode selectivity, and the gain-guided (GG) VCSELs with the aperture shifted to the node position, ensuring usually the single-fundamental-mode operation, but at the expense of much higher lasing threshold. In the present paper, the separate-confinement-oxidation VCSEL structure has been proposed exhibiting simultaneously advantages of both the IG VCSELs (the low lasing threshold) and the GG ones (the single-fundamental-mode operation).

Multichip Shared Memory Module with Optical Interconnection for Parallel-Processor System

A new multichip shared memory module with optical interconnection for a parallel-processor system was introduced. The new shared memory module mainly consists of shared memory units optically connected to one another through polyimide waveguides and electrically connected to processor elements. We designed and fabricated a static random access memory (SRAM) test chip which has an optical/electrical (O/E) receiver circuit and electrical/optical (E/O) transmitter circuit for optical data transfer. A vertical-cavity surface-emitting laser diode (VCSEL) was integrated onto an LSI chip by the beam-lead bonding technique. Optical data transfer was achieved using polyimide optical waveguides with Al micromirrors formed on a Si substrate called an optical plate, and the optical writing and electrical reading operation in the SRAM test chip was successfully demonstrated.

Structure Optimisation of a Possible 1.5-μm GaAs-based Vertical-cavity Surface-emitting Laser Diode with the GaInNAsSb/GaNAs Quantum-well Active Region

Structure optimisation of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) has been carried out using the comprehensive three-dimensional self-consistent physical model of their room-temperature (RT) continuous-wave (CW) threshold operation. The model has been applied to investigate a possibility to use these devices as carrier-wave lasing sources in the third-generation optical-fibre communication. In this simulation, all physical (optical, electrical, thermal and gain) phenomena crucial for a laser operation including all important interactions between them are taken into consideration. As expected, the 1.5λ-cavity VCSEL has been found to demonstrate the lowest RT CW threshold. However, for many VCSEL applications, the analogous VCSEL equipped with a longer 3λ-cavity should be recommended because it exhibits only slightly higher threshold but manifest much better mode selectivity – the desired single-fundamental-mode operation has been preserved in these devices up to at least 380 K. The Auger recombination has been found to be decidedly the main reason of the threshold current increase at higher temperatures. A proper initial red detuning of the resonator wavelength with respect to the gain spectrum may drastically decrease CW lasing thresholds, especially at higher temperatures.

Validity of Scalar Approaches to Radiation Modes of the GaAs-Based 1.3-μm Diode Lasers Designed for the Optical–Fibre Communication

The work presents a comparison between results of optical simulations based on the scalar and vectorial models applied to both stripe – geometry Fabry-Perot (FPL) as well as vertical-cavity surface-emitting (VCSEL) diode lasers designed for the 1.3-μm optical–fibre communication. As compared to vectorial optical approaches, scalar ones are known to be less exact but simultaneously they need as many as approximately 100 times shorter computation time, which favours those models in many applications. Therefore, vectorial models should be applied only in cases of confirmed faulty performance of scalar ones. While the Effective Index Method and the Effective Frequency Method have been chosen as scalar approaches to FPLs and VCSELs, respectively, simulations, the Method of Lines has been used in both cases as a vectorial one. Scalar models have been found to be quite exact in the case of a determination of the effective refractive index and wavelength of emitted radiation, whereas their exactness in the lasing threshold analysis is much worse, especially in the case of higher-order modes. Our analysis is concluded with the determination of the regions where both models give satisfactorily close results.

Usability limits of the scalar effective frequency method used to determine modes distributions in oxide-confined vertical-cavity surface-emitting diode lasers

The accuracy of the commercially used, simplified scalar optical effective frequency method (EFM) is verified by comparing its results with those obtained using more accurate vectorial models represented by the method of lines (MoL). Both EFM and MoL methods are applied to the modern telecommunication oriented GaAs-based oxide-confined vertical-cavity surface-emitting diode laser (VCSEL) emitting 1.3 µm radiation from the InGaAsN/GaAs double quantum well active region. Although both methods are applied to the specific laser structure, the conclusion remains valid for a broad range of different VCSEL designs. The scalar EFM approach has been found to remain surprisingly often quite exact; nevertheless, it fails for structures violating its fundamental assumption of plane wave propagation within the laser cavity. Therefore, a noteworthy discrepancy between modes calculated with the aid of scalar and vectorial approaches occurs for weaker guidance, i.e. for higher-order modes, smaller aperture diameters, thinner oxidation layers and/or apertures shifted from the antinode position. These cases need an exclusive use of the more exact but also more time-consuming vectorial algorithms.

Designing strategy to enhance mode selectivity of higher-output oxide-confined vertical-cavity surface-emitting lasers

Performance of modern oxide-confined (OC) vertical-cavity surface-emitting diode lasers (VCSEL s) is more sensitive to the construction details than in the case of other VCSEL s. In particular, a stable single-fundamental-mode operation is difficult to be achieved in these VCSEL s especially in higher-output large-size continuous-wave (cw) operating devices at higher temperatures. In the present paper, an operation of OC VCSEL s has been investigated with the aid of the comprehensive fully self-consistent model using the (GaIn)(NAs)/GaAs quantum-well VCSEL with two oxide apertures as a typical example. A new approach is proposed to enhance cw RT single-fundamental-mode low-threshold operation in higher-output OC VCSEL s. One of their oxide apertures should be shifted to the node position of the resonator standing wave where it is working as the electrical aperture only. Then diameters of both apertures may be changed independently giving an additional degree of freedom for VCSEL designing, which enables their optimisation. While the larger-diameter optical aperture placed in the anti-node position creates an efficient radial waveguiding effect, the smaller-diameter electrical aperture enhances a more uniform current injection into the VCSEL active region. Due to combining influence of both the apertures, the single-fundamental-mode operation is predicted in a large device with the 10-μm-diameter active region even for 80 K active-region temperature increase over RT of the ambient. An impact of intentional detuning at room-temperature (RT) of VCSEL active-region gain spectrum towards shorter wavelengths with respect to the resonator mode improves mode selectivity is also analysed.

Comprehensive characterization of MOVPE-grown AlGaAs/AlAs distributed Bragg reflector structures by optical reflectance, X-ray diffraction and atomic force microscopy

Abstract This paper reports on a comprehensive characterization of MOVPE-grown AlxGa1−xAs/AlAs distributed Bragg reflector (DBR) structures via optical reflectance, X-ray diffraction (XRD) and atomic force microscopy (AFM). These analytical techniques are used to investigate the influence of parameters like substrate misorientation, aluminum content and number of mirror pairs on the characteristics of high-reflectivity AlxGa1−xAs/AlAs-based Bragg mirrors. We find a strong correlation between the optical reflectivity of the DBR mirrors and the quality of X-ray rocking curves as well as the surface/interface roughness as measured by AFM. The data provided by these analytical techniques are used to optimize the DBR performance for its application in visible-wavelength vertical-cavity surface-emitting laser (VCSEL) diodes.

Determination of gas temperature and thermometric species in inductively coupled plasmas by emission and diode laser absorption

A vertical cavity surface-emitting laser diode (VCSEL) was used as a spectrally tunable emission source for measurements of the radial-integrated gas temperature inside an inductively coupled plasma reactor. The data were obtained by profiling the Doppler-broadened absorption of metastable Ar atoms at 763.51 nm in argon and argon/nitrogen plasmas (3%, 45%, and 90% N2 in Ar) at pressures of 0.5–70 Pa and inductive powers of 100 and 300 W. The results were compared to the rotational temperature derived from the N2 emission at the (0,0) vibrational transition of the C 3Πu–B 3Π g system. The differences in integrated rotational and Doppler temperatures were attributed to non-uniform spatial distributions of both temperature and thermometric species (Ar* and ) that varied depending on the conditions. A two-dimensional, three-temperature fluid plasma simulation was employed to explain these differences. This work should facilitate further development of a miniature sensor for non-intrusive acquisition of data (temperature and densities of multiple plasma species) during micro- and nano-fabrication plasma processing, thus enabling diagnostic-assisted continuous optimization and advanced control over the processes. Such sensors would also enable us to track the origins and pathways of damaging contaminants, thereby providing real-time feedback for adjustment of processes. Our work serves as an example of how two line-of-sight integrated temperatures derived from different thermometric species make it possible to characterize the radial non-uniformity of the plasma.

Optimisation of GaAs-based (GaIn)(NAs)//GaAs vertical-cavity surface-emitting diode lasers for high-temperature operation in 1.3-μm optical-fibre communication systems

Performance of GaAs-based (GaIn)(NAs)/GaAs vertical-cavity surface-emitting diode lasers (VCSELs) at higher temperatures for second-generation optical-fibre communication systems is examined with the aid of the comprehensive threshold fully self-consistent optical-electrical-thermal-gain model. As expected, in standard double-oxide-confined VCSELs, an increase in the active-region diameter is followed by an increase in the lowest-threshold transverse mode order, especially at higher temperatures. It has been found that reduction of a diameter of the bottom aperture may ensure fundamental LP 0 1 mode operation even at higher temperatures.

Modeling of the threshold operation of 1.3-/spl mu/m GaAs-based oxide-confined (InGa)As-GaAs quantum-dot vertical-cavity surface-emitting lasers

In the paper, the self-consistent optical-electrical-thermal-gain threshold model of the oxide-confined (OC) quantum-dot (QD) (InGa)As-GaAs vertical-cavity surface-emitting diode laser (VCSEL) is demonstrated. The model has been developed to enable better understanding of physics of an operation of GaAs-based OC QD VCSELs in a full complexity of many interactions in its volume between individual physical phenomena. In addition, the model has been applied to design and optimize the low-threshold long-wavelength 1.3-/spl mu/m GaAs-based OC QD VCSELs for the second-generation optical-fiber communication systems and to examine their anticipated room-temperature (RT) performance. An influence of many construction parameters on device RT lasing thresholds and mode selectivity has been investigated. Some essential design guidelines have been proposed to support efforts of technological centers in producing low-threshold single-mode RT devices.

Operation of a Passively Mode-Locked Extended-Cavity Surface-Emitting Diode Laser in Multi-GHz Regime

We report on passive mode-locking of vertical cavity surface-emitting diode lasers at 980-nm wavelength, applied to different extended resonator configurations. Stable mode-locking producing pulses of approximately 50 ps in duration at up to 6-GHz repetition rate has been achieved. The use of external feedback results in pronounced harmonic pulse generation, extending the operational range of these new devices.

Comprehensive self-consistent three-dimensional simulation of an operation of the GaAs-based oxide-confined 1.3-μm quantum-dot (InGa)As/GaAs vertical-cavity surface-emitting lasers

In the paper, a comprehensive fully self-consistent three-dimensional simulation of an operation of the GaAs-based oxide-confined long-wavelength 1.3-μm quantum-dot (QD)(InGa)As/GaAs vertical-cavity surface-emitting diode lasers is demonstrated. The model has been intentionally prepared for the PC-class microcomputers to enable its easy application in designing optimal structures of the above devices with desired performance characteristics. An impact of some structure parameters on QD VCSEL room-temperature (RT) continuous-wave (CW) lasing thresholds is discussed. A stable RT CW operation on a single fundamental mode has been found to be possible in modern QD VCSELs with active regions containing more uniform and more dense QDs in stacks of QD layers. The desired single fundamental-transverse-mode operation is possible for smaller active regions of diameters not exceeding 8 μm. In the case of larger active regions, on the other hand, higher-order transverse modes of an increasing order are excited first because of increasingly more non-uniform optical-gain distributions.