Modal Behavior of Buried Heterostructure Vertical Cavity Semiconductor Lasers

Random source is important for the security of key distribution. In this paper, a novel secure key distribution scheme based on unidirectional injection of vertical cavity surface emitting laser (VCSEL) system is proposed. In the proposed scheme, a chaotic signal without time delay signature is generated by a VCSEL subject to unidirectional optical injection, which is regarded as a master laser. The chaotic signal generated by the master VCSEL is further injected into two slave VCSELs to obtain synchronized bandwidth-enhanced chaotic signals. After that, by sampling, quantizing and XOR operation on the two synchronized chaotic signals, two key streams can be obtained. Based on the well-known spin-flip model, the time delay signature of chaotic signals generated by master VCSEL and the synchronization performance between the master VCSELs and two slave VCSELs are numerically investigated in detail. It is shown that by the unidirectional injection, the chaotic outputs can be achieved in the master VCSEL in a wide range of frequency detuning and coupling strength. More importantly, no time delay signature can be observed in the auto correlation function of the chaotic intensity time series generated by the master VCSEL. Besides, we find that high quality synchronization is achieved between the bandwidth-enhanced chaotic signals generated by two slave VCSELs under the common driving of master VCSEL. The synchronization coefficient between two slave VCSELs increases up to 0.99, and the synchronization coefficient between master VCSEL and salve VCSEL is only 0.74. Note that such a high quality synchronization between two slave VCSELs while relatively low quality synchronization between the master and slave VCSEL is conducible to ensuring the security of key distribution. In addition, the effects of tunable parameters on key bit error rate are considered, and two quantization methods are employed for comparison. Numerical simulation results show that the key bit error rate between two legitimate users is as low as 1%, and the key bit error rate between legitimate user and eavesdropper is higher than 10% in the single-threshold case; the bit error rate can even be as low as 10-6 in the double-threshold case. The influence of parameter mismatch on key bit error rate is also discussed, and it is suggested that two salve VCSELs should be finely matched to ensure low bit error rate. Finally, NIST randomness test is performed for the generated key streams. Hence, the proposed scheme enhances the security of key distribution, which is valuable for further developing the chaos communication systems.

Remarkable progress made in performance characteristics and reliability of high-speed (> 10 GHz) 850-nm multi-mode (MM) oxide-confined vertical cavity surface emitting lasers (VCSELs) during the last decade has led them to find applications in space satellite systems. The main advantage of deploying high-speed VCSELs in space satellites over directly modulated 850-nm edge emitting lasers is the absence of COMD (catastrophic optical mirror damage). In recent years, leading VCSEL manufacturers introduced higher speed (~ 20 GHz or 25 Gbps) VCSELs with encouraging characteristics. However, little has been reported on reliability and failure modes of these state-of-the-art VCSELs although it is crucial to understand failure modes and degradation mechanisms in these VCSELs through physics of failure investigation and subsequently develop VCSELs that exceed lifetime requirements for space satellite systems. For the present study, we performed short-term and long-term accelerated life-tests on 25 Gbps oxide-confined MM VCSELs to study reliability of these devices. Our goal is to extract credible reliability model parameters (thermal activation energy and current exponent factor) from these life-tests to determine suitability of these lasers for future space satellite systems. We also performed failure mode analysis on VCSELs at different stages of degradation using various techniques. We employed nondestructive techniques including optical beam induced current (OBIC) and electron beam induced current (EBIC) techniques as well as destructive techniques including focused ion beam (FIB) and high-resolution TEM techniques. Our detailed reliability and failure mode analysis results are reported along with our understanding on the physical origin of degradation in high-speed VCSELs with strained InGaAs quantum wells.

Vertical cavity surface emitting lasers (VCSELs) with ultralow threshold and high efficiency have been fabricated using oxide apertures formed by selective oxidation of AlAs. Recent studies by Cheng et al. (1996) have shown that the expected reduction in threshold with aperture size is not achieved due to current spreading and lateral carrier diffusion even for rather large apertures (>5 /spl mu/m). To minimize these losses, we are exploring the use of a buried active region in VCSELs. To achieve the desired confinement in a buried heterostructure (BH) VCSEL, it is necessary to use selective area growth or regrowth of active region. Selective area epitaxy (SAE) also allows one to vary the cavity design locally by varying the masking pattern to achieve WDM arrays. SAE or regrowth must be done with tight regrowth process control to achieve very small thickness changes during the process and a low electrical and optical loss after regrowth. In this paper, we describe the impact of multiple step regrowth of device structures with Al containing layers on the luminescence and lasing characteristics of the resultant devices.

Vertical-cavity surface-emitting lasers (VCSELs) are low-cost high-performance light sources for high-speed data communication systems, optical interconnects and different sensors [1]. New VCSEL applications (spectroscopy, compact atomic clock) require single-mode operation with stable linear polarization combined with high temperature stability. While conventional GaAs-based VCSELs with small selectively-oxidized current apertures demonstrate stable fundamental transverse mode operation they have unstable polarization due to cylindrical symmetry and isotropic gain. Currently the most popular method for VCSEL polarization control is based on precise etching of sub-wavelength grating in output distributed Bragg reflector [2]. Drawbacks of this approach are relatively complicated fabrication technology and limited output power. In this work we discuss alternative approach for single-mode polarization-stable VCSELs based on rhomboidal selectively-oxidized current aperture combined with intracavity contacts.

Vertical cavity surface emitting laser (VCSEL) is an important laser source for their evident plentiful applications in optical communication. The present investigation reports a comparison of the modeling and optimization of long wavelengths 1310 nm and 1550 nm high speed short cavity VCSEL for continuous wave operation at various temperature (283-3230K) for various diameters. The continuous wave lasing is demonstrated for the device diameter from 2 to 5 μm with threshold current of 1.07-1.33 mA with threshold power consumption of 1.86-2.57 mW for 1310 nm and threshold current of 0.94-1.24 mA and threshold power consumption 1.67-2.1 mW for 1550 nm VCSEL. The results demonstrate that the threshold current, peak emitted power and power consumption increases with the increase in device diameter. The results confirm that VCSELs with 2 μm diameter is most suitable to achieve energy-efficient operation. Although rollover current increases with the diameter, but, due to the advantage of lower threshold current and power consumption, VCSEL having smaller diameter is best suited. The power conversion efficiency for proposed long wavelength VCSELs is approximately 50% which is extremely useful for low power applications. The proposed VCSELs are suitable for very short reach (<2 m) optical interconnects such as chip-to-chip and board-to-board communication in high performance computers.

ABSTRACTAn electrically pumped 1.24um GaxIn1-xAsyP1-y Vertical Cavity Surface Emitting Laser (VCSEL) has been designed and simulated. Threshold gain of 153cm-1 and threshold current of 1.00mA was obtained. The external efficiency predicted is 0.31. Also the optimized design of VCSEL structure is presented in this article. GaInAsP and AlInAs constitute the Distributed Bragg Reflectors (DBRs) multilayer stack. Reflectivity of the top DBRs is 0.97 and reflectivity of the bottom DBRs is 0.9978 and is shown to provide a good resonant cavity and sufficient lasing intensity. Compared with other reported structures, the present VCSEL has a lower threshold current and higher threshold gain.

As a key part of vertical cavity surface emitting laser (VCSEL), active region will seriously affect the threshold and efficiency of the device. To obtain the appropriate laser wavelength and material gain, the design of In&lt;sub&gt;0.18&lt;/sub&gt;Ga&lt;sub&gt;0.82&lt;/sub&gt;As strain compensated quantum well is optimized. The relationship between the lasing wavelength of multiple quantum wells (MQWs) and the thickness is calculated. Considering the influence between the active region temperature and the lasing wavelength, the thickness of the quantum well is chosen as 6 nm, and the quantum barrier thickness is chosen as 8 nm, corresponding to the lasing wavelength of 929 nm. The material gain characteristics of the MQWs at different temperatures are simulated by Rsoft. The material gain exceeds 3300/cm at 300 K, and the temperature drift coefficient of the peak wavelength is 0.3 nm/K. In this work, Al&lt;sub&gt;0.09&lt;/sub&gt;Ga&lt;sub&gt;0.91&lt;/sub&gt;As and A&lt;sub&gt;l0.89&lt;/sub&gt;Ga&lt;sub&gt;0.11&lt;/sub&gt;As are chosen as the high- and the low-refractive index material of distributed Bragg reflector (DBR), and 20 nm graded layer is inserted between two types of materials. The influence of the graded layer thickness of DBR on the valence band barrier and reflection spectrum are calculated and analyzed. The increase of graded layer thickness can lead the band barrier peak and the reflection spectrum bandwidth to decrease. The reflection spectrum and phase spectrum of P-DBR and N-DBR are calculated by the transmission matrix mode (TMM): the reflectance of DBR is over 99% and the phase shift is zero at 940 nm. The optical field distribution of the whole VCSEL structure is simulated, in which the standing wave peak overlaps with the active region, and the maximum gain can be obtained. Using the finite element method (FEM), the effect of oxidation confined layer on the injection current is simulated. The current in the active region is effectively limited to the position corresponding to the oxidation confined hole, and its current density is stronger and more uniform. The optical field distributions in different modes of photonic crystal-vertical cavity surface emitting laser (PC-VCSEL) are simulated, and different modes have different resonant wavelengths. The values of quality factor Q in different modes of VCSEL and PC-VCSEL are calculated, Q of the fundamental mode is higher than that of higher transverse mode. It is demonstrated that the photonic crystal air hole structure can realize the output of basic transverse mode by increasing the loss of high order transverse mode. The VCSEL and PC-VCSEL with oxidation hole size of 22 μm are successfully fabricated, in which the photonic crystal period is 5 μm, the air pore diameter is 2.5 μm, and the etching depth is 2 μm. Under continuous current test, the maximum slope efficiency of VCSEL is 0.66 mW/mA, the output power is 9.3 mW at 22 mA, and the lasing wavelength is 948.64 nm at 20 mA injection current. Multiple wavelengths and large spectrum width are observed in the spectrum of VSCEL, which is an obvious multi-transverse mode. The maximum fundamental transverse mode output of PC-VCSEL reaches 2.55 mW, the side mode suppression ratio (SMSR) is more than 25 dB, and the spectrum width is less than 0.2 nm, indicating that the photonic crystal air hole has a strong control effect on the transverse mode, and the laser wavelength is 946.4 nm at 17 mA.

A high-power single-mode vertical cavity surface emitting laser (VCSEL) based on a slow light mode (SLM) concept is demonstrated. Shallow surface gratings were implemented to select a single slow light mode in mm long oxide aperture VCSELs. The vertical structure and well-established fabrication processes are unchanged from those of conventional 850 nm VCSELs. An electron-beam lithography is used to form a 1st-order shallow grating on the surface. Thanks to the low effective index and the intensity penetration of the SLM to the surface, the grating fabrication process is much easier than conventional guided mode distributed feedback lasers. A stable single mode with a high side suppression ration of more than 30 dB is obtained for the entire current range under CW operations. A narrow divergence of 0.038° in far field patterns is achieved for a 6 mm long device. A record single-mode power of more than 5 W is realized before saturation under 50 ns pulse operations. Unlike long cavity in-plane edge emitting lasers, a SLM-based VCSEL can provide higher output powers without limitation of catastrophic optical mirror damage. The high power, superior mode stability, and good beam quality of our unique design paves a way for VCSELs to be used for wide ranges of high-power applications.

Multimode VCSEL(Vertical Cavity Surface Emitting Laser) coupling into MMF (Multimode Optical Fiber) and its influence on MMF link has been numerically studied. Considering the transverse misalignment between VCSEL and MMF, coupling efficiency between VCSEL higher-order modes and modes of MMF is calculated and the Mode Power Distribution in the MMF is obtained. Simulation of MMF link with multimode VCSEL indicates that the higher-order VCSEL modes lead to decreasing of the eye opening of received signal. The transverse misalignment of VCSEL between MMF greatly deteriorates the eye opening. With 300m OM3-MMF link , the EOP (eye-opening-penalty) is greater than 14dB when the misalignment between VCSEL and MMF is lager than 5&mu;m.

Improved carrier confinement and stimulated recombination rate in GaN-based vertical-cavity surface-emitting lasers with buried p-AlGaN inversion layer

This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.

We demonstrate 1.55-/spl mu/m buried-heterostructure (BH) vertical-cavity surface-emitting lasers (VCSELs) on a GaAs substrate. Thin-film wafer-fusion technology enables InP-based BH VCSELs to be fabricated on GaAs/AlAs distributed Bragg reflectors. Detailed investigations of the device resistance are also described. As a result of introducing BH and obtaining low device resistance, the threshold current density under CW operation shows the independence of mesa size due to a strong index guide and small noneffective current. A 5-/spl mu/m VCSEL exhibits a record threshold current of 380 /spl mu/A at 20/spl deg/C. This VCSEL also operates with single transverse mode up to the maximum optical output power.

High-performance 808 nm double and triple-junction vertical cavity surface emitting lasers (VCSELs) are designed and investigated. The light-current-voltage (L-I-V) characteristics of 808-nm single, double, and triple-junction VCSELs are compared. In the paper, the double-junction VCSELs with two oxide apertures exhibit a very high slope efficiency (SE) of 2.32 W/A at 25 °C, and the peak SE of 2.51 W/A is achieved at 10 °C. The power conversion efficiency (PCE) of 53.14% is achieved for double-junction individual VCSEL emitter. The peak SE of the triple-junction VCSELs reach 3.40 W/A with the PCE of 53.02% for individual VCSEL emitter. Under narrow pulse test conditions (400 Hz, 60 ns pulse width), the peak output powers of the designed double-junction and triple-junction VCSEL arrays reach 216.11 W and 325.77 W under the injection current of 80 A, respectively. Such high-performance multi-junction 808-nm VCSELs are very important for pumping solid state lasers and medical aesthetics.

The aim of this work is to fabricate high-power, single mode vertical cavity surface emitting lasers (VCSELs). Multiple junction VCSELs provide a pathway towards scaling optical output power. However, especially in the case of oxide confinement, these lasers have a greater tendency to exhibit multimode behavior when compared to their single junction counterparts. To achieve high-power, single mode multi-junction VCSELs, more advanced single mode strategies must be employed. A two-dimensional complex refractive index model was applied to model the transverse modes of photonic crystal VCSELs in order to determine the most suitable designs. Oxide confined VCSELs were fabricated using 850 nm single and double junction wafers, as well as 940 nm double and triple junction wafers. We report a maximum single mode power of 8.0 mW from the 850 nm double junction VCSELs and 10.7 mW from the 940 nm triple junction VCSELs. Double junction implant/oxide VCSELs were also fabricated and produced a peak single mode power of 8.1 mW.

High electro-optical conversion efficiency is one of the most distinctive features of semiconductor lasers as compared to other types of lasers. Its further increase remains a significant objective. Further enhancing the efficiency of edge-emitting lasers (EEL), which represent the highest efficiency among semiconductor lasers at present, is challenging. The efficiency of vertical cavity surface emitting lasers (VCSELs) has always been relatively low compared to EEL. This paper, combining modeling with experiments, demonstrates the potential of multi-junction cascaded VCSELs to achieve high efficiency beyond that of EELs, our simulations show, that a 20-junction VCSEL can achieve an efficiency of more than 88% at room temperature. We fabricated VCSEL devices with different numbers of junctions and compared their energy efficiency. 15-junction VCSELs achieved a maximum efficiency of 74% at room temperature under nanosecond driving current, the corresponding differential quantum efficiency exceeds 1100%, being the largest electro-optical conversion efficiency and differential quantum efficiency reported until now for VCSELs.