High Slope Efficiency and High Power 850nm Oxide-Confined Vertical Cavity Surface Emitting Lasers

High slope efficiency and high power selected oxide-confined 850nm VCSELs grown by MOCVD are reported.The slope efficiency and the threshold current respectively are 0 82mW/mA and 2 59mA with a 9μm diameter oxidation aperture at 25℃.The maximum power of 16mW is obtained at 23mA current bias.The minimum threshold current can be as low as 570μA with a 5μm diameter oxidation aperture at 25℃.The maximum saturated power is 5 5mW.

Lateral Oxidation in Vertical Cavity Surface Emitting Lasers

Lateral oxidation in vertical cavity surface emitting lasers （VCSELs） is described,and its characteristics are investigated.A linear growth law is found for stripe mesas. However, oxide growth （above 435℃ ） follows a nonlinear law for the two geometry mesa structures which we employ in VCSEL. Theoretical analysis indicates that mesa structure geometry influences oxide growth rate at higher temperatures.

Green Vertical‑Cavity Surface‑Emitting Lasers Based on InGaN Quantum Dots and Short Cavity

Room temperature low threshold lasing of green GaNbased vertical cavity surface emitting laser(VCSEL)was demonstrated under continuous wave(CW)operation.By using self-formed InGaN quantum dots(QDs)as the active region,the VCSEL emitting at 524.0 nm has a threshold current density of 51.97 A cm^(-2),the lowest ever reported.The QD epitaxial wafer featured with a high IQE of 69.94%and theδ-function-like density of states plays an important role in achieving low threshold current.Besides,a short cavity of the device(~4.0λ)is vital to enhance the spontaneous emission coupling factor to 0.094,increase the gain coefficient factor,and decrease the optical loss.To improve heat dissipation,AlN layer was used as the current confinement layer and electroplated copper plate was used to replace metal bonding.The results provide important guidance to achieving high performance GaN-based VCSELs.

An efficient approach to characterizing and calculating carrier loss due to heating and barrier height variation in vertical-cavity surface-emitting lasers

It is important to determine quantitatively the internal carrier loss arising from heating and barrier height variation in a vertical-cavity surface-emitting quantum well laser （VCSEL）. However, it is generally difficult to realize this goal using purely theoretical formulas due to difficulty h, deriving the parameters relat^i~g to the quantum well structure. In this paper, we describe an efl：icient approach to characterizing and calculating the carrier loss due to the heating and the barrier height change in the VCSEL. In the method, the thermal carrier loss mechanism is combined with gain measurement and calculation. The carrier loss is re-characterized in a calculable form by constructing the threshold current and gain detuning-related loss current using the measured gain data and then substituting them for the quantum well-related parameters in the formula. The result can be expressed as a product of an exponential weight factor linked to the barrier height change and the difference between the threshold current and gain detuning-related loss current. The gain variation at cavity frequency due to thermal carrier loss and gain detuning processes is measured by using an AllnGaAs-AIGaAs VCSEL structure. This work provides a useful approach to analysing threshold and loss properties of the VCSEL, particularly, gain offset design for high temperature operation of VCSELs.

Thermal Analysis of Implant-Defined Vertical Cavity Surface Emitting Laser Array

A three-dimensional electrical-thermal coupling model based on the finite element method is applied to study thermal properties of implant-defined vertical cavity surface emitting laser （VCSEL） arrays. Several parameters including inter-element spacing, scales, injected current density and substrate temperature are considered. The actual temperatures obtained through experiment are in excellent agreement with the calculated results, which proves the accuracy of the model. Due to the serious thermal problem, it is essential to design arrays of low self-heating. The analysis can provide a foundation for designing VCSEL arrays in the future.

Simulation of Far-Field Properties of Coherent Vertical Cavity Surface Emitting Laser Array

Far-field properties dependent on array scale, separation, element width and emitted wavelength are system atically analyzed theoretically and experimentally. An array model based on the finite-difference method is established to simulate the far-field profile of the coherent arrays. Some important conclusions are obtained. To achieve a higher quality beam, it is necessary to decrease separation between elements, or to increase the element width. Higher brightness can be achieved in the array with larger scale. Emitted wavelength also has an influence on the far-field profile. These analyses can be extended to the future design of coherent vertical cavity surface emitting laser arrays.

Vertical cavity surface emitting laser transverse mode and polarization control by elliptical hole photonic crystal

The polarization of traditional photonic crystal（PC） vertical cavity surface emitting laser（VCSEL） is uncontrollable,resulting in the bit error increasing easily.Elliptical hole photonic crystal can control the transverse mode and polarization of VCSEL efficiently.We analyze the far field divergence angle,and birefringence of elliptical hole PC VCSEL.When the ratio of minor axis to major axis b/a = 0.7,the PC VCSEL can obtain single mode and polarization.According to the simulation results,we fabricate the device successfully.The output power is 1.7 mW,the far field divergence angle is less than 10°,and the side mode suppression ratio is over 30 dB.The output power in the Y direction is 20 times that in the X direction.

Beam Steering Analysis in Optically Phased Vertical Cavity Surface Emitting Laser Array

Beam steering in implant defined coherently coupled vertical cavity surface emitting laser （VCSEL） arrays is simulated using the FDTD solution software. Angular deflection dependent on relative phase differences among elements, inter-element spacing, element size and emitted wavelength is analyzed detailedly and systematically. We design and fabricate 1×2 implant defined VCSEL arrays for optimum beam steering performance. Electroni- cally controlled beam steering with a maximum deflection angle of 1.6° is successfully achieved in the 1 × 2 VCSEL arrays. The percentage of the power in the central lobe is above 39% when steering. The results show that the steering is controllable. Compared with other beam steering methods, the fabrication process is simple and of low cost.

Simplified modeling of frequency behavior in photonic crystal vertical cavity surface emitting laser with tunnel injection quantum dot in active region

In this work, the characteristics of the photonic crystal tunneling injection quantum dot vertical cavity surface emitting lasers（Ph C-TIQD-VCSEL） are studied through analyzing a modified modulation transfer function. The function is based on the rate equations describing the carrier dynamics at different energy levels of dot and injector well. Although the frequency modulation response component associated with carrier dynamics in wetting layer（WL） and at excited state（ES） levels of dots limits the total bandwidth in conventional QD-VCSEL, our study shows that it can be compensated for by electron tunneling from the injector well into the dot in TIQD structure. Carrier back tunneling time is one of the most important parameters, and by increment of that, the bias current dependence of the total bandwidth will be insignificant. It is proved that at high bias current, the limitation of the WL-ES level plays an important role in reducing the total bandwidth and results in rollovers on 3-d B bandwidth-I curves. In such a way, for smaller air hole diameter of photonic crystal, the effect of this reduction is stronger.

Improvement of InGaAs/GaAs vertical-cavity surface-emitting lasers by post-oxidation annealing

InGaAs/GaAs vertical-cavity surface-emitting lasers （VCSELs） are fabricated by a thermal selective wet- oxidation confinement technique. Post-oxidation annealing in a nitrogen environment at high temperatures is then conducted to improve the performance of the oxide-confined InGaAs/GaAs VCSELs. The optimum post-oxidation annealing conditions are determined by changing the furnace temperature and annealing time. Compared with a unannealed laser device, the light output power increases by about 12%. An aging test is carried out to examine the reliability of the annealed oxide-confined VCSEL device. The temperature dependence of the lasing wavelength of the annealed oxide-confined VCSELs is also investigated.

Reconfigurable dynamic all-optical chaotic logic operations in an optically injected VCSEL

In a chaotic system of vertical cavity surface emitting laser （VCSEL） with external optical-injection, we propose a novel implementation scheme for reconfigurable dynamic all-optical chaotic logic operations （AOCLOs）. Under different key parameters, such as the bias current, the injection strength and the frequency detuning of the injected light field and the VCSEL, we also explore the evolutions of the polarization-bistability with the amplitude of the injected light field when the output of VCSEL is chaotic wave. According to the dynamic evolutions, we find out the optimal value of the frequency detuning that is considered as a control logic signal, and further implement different AOCLOs, such as AND, NAND, OR, NOR, XOR, and XNOR, by controlling the logic operation of the control logic signal between two logic inputs. Moreover, the ability to reconstruct these logic operations is demonstrated under relatively low noise strength of the spontaneous emission.

Single fundamental mode photonic crystal VCSEL with high power and low threshold current optimized by modal loss analysis

The characteristics of the photonic crystal vertical cavity surface emitting lasers（PhC-VCSELs） were investigated by using the full vector finite-difference time-domain（FDTD） method through the transverse mode loss analysis. PhC-VCSELs with different photonic crystal structures were analyzed theoretically and experimentally. Through combining the dual mode confinement of oxide aperture and seven-point-defect photonic crystal structure, the PhC-VCSELs with low threshold current of 0.9 mA and maximum output power of 3.1 mW operating in single fundamental mode were demonstrated. Mode loss analysis method was proven as a reliable and useful way to analyze and optimize the PhC-VCSELs.

High power vertical-external-cavity surface-emitting laser

A high power optically-pumped vertical-external-cavity surface-emitting laser with a diamond heatspreader is demonstrated.Owing to the good thermal conductivity,diamond can accelerate the dissipation of heat in the active region and increase the output power significantly.The effects of the curvature radius,the transmission of output coupler,the spot size of the pump,and the temperature of the heat sink on the output power are investigated.A maximum output power of 880 mW is obtained under the conditions of 10℃temperature,15-mm curvature radius,3%transmission of the output coupler,and 8500-mW pump power.The slope efficiency and the optical-to-optical conversion efficiency of the laser are about 17%and 15%,respectively.

Low power penalty tunable slow light using vertical-cavity surface-emitting laser amplifier

A tunable slow light of 2.5-Gb/s pseudo-random binary sequence signal using a 1550-nm vertical-cavity surface-emitting laser （VCSEL） is experimentally demonstrated. The influences of the bias current and the gain saturation on the slow light are investigated. With bias current increasing, tunable optical group delay up to 98 ps is obtained at room temperature. Demonstration of the time delay between 16 and 24 ps by signal intensity change is reported. Under an appropriate bias current, by tuning the input signal to track the peak gain wavelength of the VCSEL, slow light of a power penalty as low as 1 dB is achieved. With such a low power penalty, the VCSEL has a great potential application as a compact optical buffer.

From MEMS to NEMS： Smart Chips with Senses and Muscles

The last half-century was transformed by the electronic revolution that essentially reproduced the human brain and its computing capacity on a chip. But over time, scientists have realized that something was missing to give life, so to speak, to the small chip with a brain： One needed to awaken its senses and develop its muscles! This challenge was solved through MEMS （micro electro mechanical systems）. Indeed, MEMS today are equipped with the sense of sight, smell, hearing, taste and touch through microsensors. They are also capable of physical exertion through small muscles called microactuators. These new capabilities open wide fields of imagination and important specific applications.

Wet Oxidation of Al_x Ga_(1-x)As/GaAs Distributed Bragg Reflectors

The wet oxidation of AlGaAs with high Al content in a distributed Bragg reflectors （DBR） is studied by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Some voids distribute along the oxide/GaAs interfaces due to the stress induced by the wet oxidation of the AlGaAs layers. These voids decrease the shrinkage of the Al2O3 layers to 8% instead of the theoretical 20% when compared to the unoxidized AlGaAs layers. With the extension of oxidation time, the reactants are more completely transported to the front interface and the products are more completely transported out along the porous interfaces. As a result,the oxide quality is better.

Stable single-mode operation of 894.6 nm VCSEL at high temperatures for Cs atomic sensing

In this paper, stable single-mode operation at high temperatures is produced by the surface-relief-integrated vertical cavity surface emitting laser（VCSEL）. The gain-cavity mode detuning technique is employed to realize high operating temperatures for the VCSEL. The surface relief is etched in the centre of the top side as a mode discriminator for the fundamental mode output, and the threshold current minimum is 1.94 mA at high temperatures by the gain-cavity mode detuning technique. Maximum single-fundamental-mode output power of 0.45 mW at 80℃ is obtained, and the side mode suppression ratios（SMSRs） are more than 30 dB with increasing temperature and current, respectively.

850/940-nm VCSEL for optical communication and 3D sensing

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/AlGaAsmultiple quantum well （MQW） was used to increase the differential gain and photon density in VCSEL. The multiple oxidelayers 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.

A novel lateral cavity surface emitting laser with top sub-wavelength grating

We report a novel lateral cavity surface emitting laser based on sub-wavelength high-index-contrast grating with in-plane resonance and surface-normal emission. The device is fabricated on a simple commercial wafer without the distributed Bragg reflector and it needs no wafer bonding. It exhibits a side mode suppression ratio of 23.0 d B and a high output power of 5.32 m W at 1552.44 nm. The specific single mode lasing agrees well with the band edge mode calculation of the grating. In 3D simulation, we observe obvious light output from the grating.

Configuration of an optical waveguide interconnect mesh network based on EOPCB

An optical waveguide interconnect mesh network scheme for parallel multiprocessor systems based on an electro-optical printed circuit board （EOPCB） with multimode polymer waveguide is proposed. The system consists of 2×2 processor element chips interconnected in a mesh network configuration. An additional layer with optical waveguide structure is embedded in a conventional printed circuit board to construct the EOPCB. Vertical cavity surface emitting laser （VCSEL）/positive intrinsic-negative （PIN） arrays are ap- plied as the optical transmitters/receivers. Three 1 ~ 12 VCSEL/PIN parallel optical transmitting/receiving modules are used to provide 32 input/output optical channels required by the 2~2 chip-to-chip optical mesh interconnect system. The data rate in each optical channel is 3.125 Gbps and thus 10 Gbps parallel optical interconnect link for each direction of a chip is obtained. The optical signals from a processor element chip can be transmitted to another chip through optical waveguide interconnect embedded in the board. Thus the optical interconnect mesh network for parallel multiprocessor system can be implemented.