Characteristics Of Vertical-cavity Surface-emitting Lasers Research Articles

Vertical Cavity Surface Emitting Laser technology: A comprehensive review

Vertical Cavity Surface Emitting Laser (VCSEL) technology has become an indispensable element in optical communication systems and optoelectronics due to its many advantages, and the unique characteristics of VCSELs, including vertical emission, high-speed operation, and low power consumption, have attracted much interest from researchers and industry professionals. This paper provides a comprehensive overview of VCSELs, explaining their basic principles and two commonly used structures. It also delves into the field of optical communications, highlighting the challenges faced in the current development, from which it introduces the significant progress made by VCSELs over the past decade in various applications such as high-speed data transmission, multi-mode communications, and long-distance networks. In addition, this study provides valuable insights into the future trajectory and potential evolution of VCSEL technology to facilitate further research and innovation in the field of communications. By providing a holistic analysis, this study is a valuable resource for scientists and researchers to help them realize the full potential of VCSELs in advancing optical communication technologies to meet the ever-changing needs of modern communication networks.

Thermal characteristics of high-power vertical cavity surface emitting laser array

Due to the excellent characteristics such as good beam quality, dynamic single-longitudinal mode, low power consumption, and good wavelength stability, especially easy-to-integrate high-density 2D area arrays, vertical-cavity surface-emitting laser (VCSEL) is widely used in optical identification, optical interconnection systems, optical data storage and other fields. In recent years, with the improvement of materials and process technology, VCSEL has played an increasingly important role in the fields of smartphone face recognition, drone obstacle avoidance, virtual reality/augmented reality (VR/AR), sweeping robots, home cameras, etc., and with the rapid development and application of 5G communication, VCSEL will become an indispensable main component. However, due to the introduction of distributed Bragg mirrors, the thermal effect of VCSEL is very serious, especially when VCSEL is integrated into an array device, current-induced self-heating of each individual array cell and the thermal coupling among array cells have become the major factors contributing to thermal rollover and hence restraining the optical output performance of the VCSEL arrays. Therefor it is of great significance to study the thermal characteristics of VCSELs, in order to solve the problem of thermal crosstalk between single-tube devices, and increase the life of the device. This paper analyzes the influence of cell spacing and arrangement on the thermal crosstalk phenomenon and thermal diffusion performance of VCSEL array device based on the finite element model. The simulation results show that the maximum temperature of the device decays exponentially with the increase of cell spacing, the thermal crosstalk phenomenon and thermal diffusion performance of VCSEL array devices are significantly improved. When the cell spacing is 120 μm, the influence between the cells is small, the thermal crosstalk phenomenon is significantly improved, and the heat dissipation effect is better. On this basis, four non-square VCSEL arrays with 16 cells are designed, and it can be seen that compared with the square arrangement, the isosceles triangle, pentagonal and hexagonal configurations have improved the thermal crosstalk phenomenon and thermal diffusion performance, and the overall temperature rise of the VCSEL array is significantly reduced. The thermal crosstalk phenomenon of the pentagonal arrangement is significantly improved, and the device temperature is 37.32 ℃, which is the best effect among several arrangement methods. According to the results of theoretical simulation, the VCSEL array devices with different arrangements are prepared and characterized on the same epitaxial wafer by the same process. From the <i>P</i>-<i>I</i>-<i>V</i> characteristic curves, it can be seen that the threshold currents of isosceles triangles, pentagons and hexagons are lower than those of the square arrangement, and the maximum output power is higher than that of the square arrangement, especially the maximum output power value of the pentagonal is 150 mW. The results show that the new arrangement can effectively improve the thermal crosstalk phenomenon between the cells, increase the output power of the device, and make the VCSEL array device have good optoelectronic and thermal characteristics.

Investigation of the Noise Characteristics of Vertical-Cavity Surface-Emitting Laser with a Rhomboidal Oxide Current Aperture for Use in a Cs-Based Compact Atomic Magnetometer

Investigation of the Noise Characteristics of Vertical-Cavity Surface-Emitting Laser with a Rhomboidal Oxide Current Aperture for Use in a Cs-Based Compact Atomic Magnetometer

Mode characteristics of VCSELs with different shape and size oxidation apertures

Vertical cavity surface emitting laser (VCSELs) as the ideal light source for rubidium (Rb) and cesium (Cs) atomic clocks is analyzed for its mode and polarization control. We fabricated three kinds of shapes: triangular, elliptic, and circular oxidation apertures which also have different sizes. We formed three different shape oxide apertures by wet-oxidation with 36 μm–39 μm circular mesa. Our results show that triangular oxidized-VCSEL has the advantages of mode and polarization selection over elliptic and circular oxide apertures. When triangular oxide-confined VCSELs emit in single mode, the measured side mode suppression ratio (SMSR) is larger than 20 dB and orthogonal polarization suppression ratio achieves 10 dB. Resonant blueshift of VCSELs with triangular and elliptic apertures is observed with the decrease of aperture size.

Investigation of the noise characteristics of vertical-cavity surface-emitting laser with a rhomboidal oxide current aperture for use in a Cs-based compact atomic magnetometer

The possibility of using vertical-emitting lasers with intracavity contacts (IC-VCSEL) and a rhomboidal oxide current aperture for creating a non-zero magnetic field optically pumped atomic magnetometers (OPM) with a 133Cs vapor cell for magnetoencephalographic (MEG) systems were demonstrated. Relative intensity noise (RIN) and polarization resolved RIN of the IC-VCSEL in the 895 nm range with different mirror losses (linewidth) in the frequency range from 1 Hz to 100 kHz were experimentally investigated. Lasers with low mirror loss (narrow linewidth) have polarization resolved RIN comparable to amplitude noise. For IC-VCSEL with an output optical power of 0.8 mW and a linewidth of 55 MHz, the noise level measured is 148 dB/Hz in 1 Hz bandwidth at 40 kHz frequency. The ultimate sensitivity of OPM based on two-beam MZ-scheme with studied VCSELs was estimated as ~ 11 fT/sqrt(Hz)sqrt. Keywords: vertical-cavity surface-emitting laser (VCSEL), magnetoencephalographic (MEG) systems, optically pumped atomic magnetometers (OPAM), relative intensity noise (RIN), polarization-resolved RIN.

Frequency Response Characteristics of Vertical-Cavity Surface-Emitting Lasers Based on Parasitic Network

Frequency Response Characteristics of Vertical-Cavity Surface-Emitting Lasers Based on Parasitic Network

Polarization control and mode optimization of 850\xa0nm multi-mode VCSELs using surface grating

To control the polarization of 850 nm multi-mode oxide-confined vertical-cavity surface-emitting lasers (VCSELs), monolithically integrated surface gratings are investigated. VCSELs with different grating parameters are simulated by the rigorous coupled-wave analysis (RCWA) method. Optical field intensity of two polarization orientations with different grating periods and duty cycles is obtained. The mode characteristics of VCSELs with different grating parameters are achieved by FDTD method. 850 nm surface grating VCSELs are fabricated and characterized, a maximum orthogonal polarization suppression ratio (OPSR) of 20.7 dB is observed. Meanwhile, VCSEL’s output mode characteristics are improved by integrating the surface grating. Application of integrated surface grating technique to achieve dynamically polarization-stable multi-mode VCSELs which enable polarization division multiplexed data transmission, the data throughput over a given link can be doubled.

Liquid crystal tunable vertical cavity surface emission laser with inner cavity sub-wavelength grating

With the rapid development of information technology, a wavelength-tunable vertical cavity surface emitting laser (VCSEL) is urgently needed as an optical signal source in dense wavelength division multiplexing (DWDM). Liquid crystal tunable VCSEL realized by utilizing the birefringence characteristics of liquid crystal has the advantages of stable polarization, high reliability, continuous wavelength tuning. In this paper, a liquid crystal tunable VCSEL structure based on intracavity sub wavelength grating is designed, and the influence of liquid crystal layer and sub wavelength grating on the wavelength tuning characteristics of VCSEL are analyzed and studied in depth. The results show that the thickness of the liquid crystal layer in the tunable VCSEL structure not only affects the wavelength tuning range, but also determines the mode hopping in the tuning process. In addition, an effective refractive index antireflection layer is formed by designing the subwavelength grating structure, and the refractive index difference between the liquid crystal layer and the semiconductor layer is optimized to further improve the wavelength tuning range and tuning efficiency. When the center wavelength is 980 nm, the tuning range is increased by 42%, reaching 41 nm, and the wavelength tuning efficiency is increased by 41%. It provides a new method of designing the VCSEL laser with high beam quality and continuous wavelength tuning.

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser.

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280–320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320–400 nm) to UVC (<280 nm).

Gaussian-like transverse-mode profile characteristics of high-power large-area red-emitting VCSELs.

We demonstrate a large-area red-emitting vertical-cavity surface-emitting laser (VCSEL) structure with significant improvement in the uniformity of charge carrier distribution by adopting a Si-doped $ {{\rm Al}_{0.20}}{\rm GaInP} $Al0.20GaInP current spreading layer and a bottom disk contact. The new structure emitting at 670 nm with a bottom disk contact diameter of 20 µm was compared with the conventional oxide-confined top-emitting structure with a similar aperture size. The maximum output peak power increased from 8.8 mW to 22.5 mW under pulsed-mode operation at room temperature. The far field improved from a strong multiple-mode pattern to a Gaussian-like profile. The corresponding divergence angle of the far-field pattern at $ 2{\rm {I}}_{\rm{th}} $2Ith injection current reduced from 16.2° to 10.9°.

Вертикально-излучающий лазер спектрального диапазона 1.55 &amp;mu;m с туннельным переходом на основе слоев n-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InAlGaAs

The design of the n++-InGaAs/р++-InGaAs/р++-InAlGaAs tunnel junction (TJ) for 1.55 μm range vertical-cavity surface-emitting lasers (VCSELs), developed by wafer fusion technique of InAlGaAsP/InP optical cavity with AlGaAs/GaAs distributed Bragg reflectors is proposed and realized. The presence of oxidation-resistant InGaAs layers allows the use of molecular-beam epitaxy at all stages of the heterostructure fabrication, including for regrowth of the TJ surface relief. In the case of using the n++-InGaAs/р++-InGaAs/р++-InAlGaAs TJ, a noticeable increase in the internal optical losses compared to the n++/р++-InAlGaAs TJ design was not obtained. The increase in internal optical loss in lasers can be avoided due to Burshtein-Moss effect in n++-InGaAs layers and thickness minimization of р++-InGaAs layer. As a result, the characteristics of fabricated lasers are comparable with characteristics of VCSELs with n++/p++-InAlGaAs TJ with a similar level of mirror losses.

Effect of VCSEL Characteristics on Ultra-High Speed Sigma-Delta-Over-Fiber Communication Links

State-of-the-art high-speed multi-mode vertical-cavity surface-emitting-lasers (VCSELs) have a 3-dB analog bandwidth of $\sim$ 25 GHz and can operate up to 55 Gbps error-free, without need of equalization electronics. This makes them strong candidates as optical sources for ultra-high speed sigma-delta-over-fiber (SDoF) communication links. This paper examines the effects of VCSEL characteristics on a 32-Gbps SDoF communication link with a 50 m, OM4, multimode optical fiber. Three high-speed, 850-nm-wavelength VCSELs with oxide aperture sizes of 8.3, 6.6, and 4.6 $\mu$ m were tested. The effects of different modulation voltage amplitudes and bias currents were also investigated. The link performance and VCSEL power consumption were used as figures-of-merits. By avoiding sub-laser threshold modulation for the VCSEL, each of three VCSELs could provide similar link performance. We show that, compared to conventional datacom links, eased bit-error-rate requirements enabled by bi-level nature of sigma-delta modulation makes it possible to use significantly lower VCSEL bias currents. This in turn enables a reduced VCSEL power consumption (50% lower heat-to-bit ratio) and a potential longer VCSEL lifespan. For a SDoF modulated, 160-Mbaud, QAM64 signal centered at 12 GHz an error vector magnitude of $-$ 28 dB was achieved with the VCSEL having oxide aperture size of 4.6 $\mu$ m operating at only 2 mA bias current and 0.25 V modulation amplitude. This results in a heat-to-bit ratio of only 0.1 mW/Gb/s (or equivalently 0.1 pJ/b), and a current density in the VCSEL that is less than 10 kA/cm $^2$ .

Numerical analysis of injected current effects on thermal characteristics of vertical-cavity surface-emitting laser

The present study aims to numerically investigate thermal characteristics of the Vertical-cavity surface-emitting lasers (VCSELs) considering current flows, non-radiative recombination, spontaneous emission transfer, and heat generation. The finite-volume method is used for discretizing the governing equations, and the comparison between prediction and measurement is made to evaluate the simulation code developed in this study. From literature, the numerical models are established for resistive heating inside Bragg reflector and contacts, non-radiative recombination between electrons and holes in the active region, and absorptive heating of created photons, and spontaneous emission. It is found that the numerical prediction shows good agreement with experimental data of temperature rise, and local heating exists mainly near the active layer of VCSEL during operation. Near the active region, thermal sources and temperature increase with injected current, whereas the electrical potential is mainly distributed in the active and p-mirror regions. Also, the maximum temperature rise appears in the active region owing to non-radiative recombination and reabsorption of spontaneous light emission. Even though the heat source significantly increases at the edge of the active region and high resistive regions, the temperature does not change much because of the small size of the active region. Moreover, the resistive and active heating, and total heating dissipation increase with injected currents. The resistive heating dissipation is larger than the active heat dissipation because of high resistivity materials.

Temperature dependence of characteristic parameters of 1550 nm vertical-cavity surface-emitting laser

Compared with conventional edge-emitting semiconductor lasers, vertical-cavity surface-emitting lasers (VCSELs) exhibit many advantages such as low power consumption, low threshold current, single longitudinal-mode operation, circular output beam with narrow divergence, on-wafer testing capability, high bandwidth modulation, low cost and easy large-scale integration into two-dimensional arrays, etc. VCSELs have been widely adopted in various applications such as optical communication, optical storage, parallel optical links, etc. At the same time, the rich dynamic characteristics of VCSELs have always been one of the frontier topics in the field of laser research, and many theoretically and experimentally investigated results have been reported. For theoretically investigating the dynamical characteristics of VCSELs, the spin-flip model (SFM) is one of most commonly and effectively used methods. In order to accurately predict the nonlinear dynamical performance of a 1550 nm-VCSEL, six characteristic parameters included in the rate equations of the SFM need to be given accurately. The six characteristic parameters are the decay rate of field k, the decay rate of total carrier population N, the linear anisotropies representing dichroism a, the linear anisotropies representing birefringence p, the spin-flip rate s, and the linewidth enhancement factor . In this work, through experimentally analyzing the output performances of a 1550 nm-VCSEL under free-running and parallel polarized optical injection, such six characteristic parameters included in the SFM are extracted first in the case that the temperature of the VCSEL is set to be 20.00℃. Furthermore, through gradually increasing the temperature of the 1550 nm-VCSEL from 10.00℃ to 30.00℃, the dependence of the six characteristic parameters on the temperature of the 1550 nm-VCSEL is investigated emphatically. The results show that with the increase of temperature of the 1550 nm-VCSEL, the linear anisotropy representing birefringence p behaves as an increasing trend, and the linewidth enhancement factor shows a decreasing trend. However, the other four characteristic parameters present complex varying trends with the increase of the temperature of the 1550 nm-VCSEL. The research in this paper is helpful in accurately understanding and controlling the dynamical characteristics of the VCSEL, and we hope that it can give a guidance for practical applications.

A comparative study of thermal characteristics of GaN-based VCSELs with three different typical structures

Thermal characteristics of GaN-based vertical cavity surface emitting lasers (VCSELs) with three typical structures were investigated both theoretically and experimentally. The simulation results based on a steady state quasi three-dimensional cylindrical model show that the thermal resistance (Rth) is affected by cavity length, mesa size, as well as the bottom distributed Bragg reflector (DBR) size, and the detail further depends on different structures. Among different devices, GaN VCSEL with a hybrid cavity formed by one nitride bottom DBR and another dielectric top DBR is featured with lower Rth, which is meanwhile affected strongly by the materials of the epitaxial bottom DBR. The main issues affecting the thermal dissipation in VCSELs with double dielectric DBRs are the bottom dielectric DBR and the dielectric current-confinement layer. To validate the simulation results, GaN-based VCSEL bonded on a copper plate was fabricated. Rth of this device was measured and the results agreed well with the simulation. This work provides a better understanding of the thermal characteristics of GaN-based VCSELs and is useful in optimizing the structure design and improving the device performance.

Research on Photoelectric Characteristics of VCSEL

In order to simulate the light-current (LI) characteristics of the Vertical Cavity Surface Emitting Laser (VCSEL), we adopted the simplex method to determine the optimal solution of the model parameters on the basis of experimental data. Besides, improvement was made to fit the current-voltage (IV) data using the relationship which accounted for a resistance in series with a diode, and it was more appropriate to fit LI curves according to the model evaluation index. Furthermore, the improved model can be applied to fit the LI curves at different ambient temperatures, and it illustrates that maximum value of the output power decreases as the ambient temperature increases.

Amplitude/phase modulation and spectrum of the vertical-cavity surface-emitting laser output

A new approach has been proposed for analysing the dynamics of the laser field amplitude on the basis of Maxwell’s equations. This approach has been used to develop a theory for calculating modulation characteristics of vertical-cavity surface-emitting lasers in the small modulation limit. The present analysis allows one to sequentially examine the dynamics of the amplitude and phase of the electromagnetic field of light in the framework of a single physical model, proceeding from fundamental principles. The proposed approach offers a natural and unique procedure for finding all laser cavity parameters necessary for calculation. An analytical calculation in the ‘small’-signal approximation has ensured good agreement with experimental data.

VCSEL-Based Interconnects for Current and Future Data Centers

The vast majority of optical links within the data center are based on vertical cavity surface emitting lasers (VCSELs) operating at 850 nm over multimode optical fiber. Deployable links have evolved in speed from 1 Gb/s in 1996 to 28 Gb/s in 2014. Serial data links at 40 and 56 Gb/s are now under development and place even more demand on the VCSEL and photodiodes. In this paper, we present the characteristics of VCSELs and photodiodes used in current generation 28 Gb/s links and present several methods to extend link distances using more advanced data encoding schemes. Finally, we will present results on wavelength division multiplexing on multimode optical fiber that demonstrate 40 Gb/s Ethernet connections up to 300 m on duplex OM3 optical fiber, and present results on fiber optimized for modal bandwidth in the 850 to 980 nm range.

Nonpolar III-nitride vertical-cavity surface emitting lasers with a polarization ratio of 100% fabricated using photoelectrochemical etching

Photoelectrochemical (PEC) band gap selective undercut etching is discussed as an alternative technique to chemical-mechanical polishing and laser-lift off for substrate removal for III-nitride vertical-cavity surface-emitting lasers (VCSELs). A top-down PEC etch is also described, which offers the ability to epitaxially define an etch-stop layer, thereby achieving a high degree of cavity length control. The temperature-dependent lasing characteristics of m-plane VCSELs fabricated using PEC etching techniques are analyzed. Measurements of multiple VCSELs from the same wafer yielded lasing emission polarized along the a-direction with a polarization ratio of 100%, indicating that the entire array was uniformly polarized.

Vertical-Cavity Surface-Emitting Laser With Cholesteric Liquid Crystal Overlay

We study theoretically the spectral and polarization threshold characteristics of vertical-cavity surface-emitting lasers with an overlay of cholesteric liquid crystal (CLC-VCSELs). Due to the existence of CLC band gap for circularly polarized (CP) light the polarization state of the resonant modes in the compound system evolves from linear (LP) inside the VCSEL to elliptical and circular (CP) inside the CLC. As a result, the output mirror reflectivity is increased and CLC-VCSEL threshold gain is decreased. We elucidate the transition from LP to CP state of the generated light by studying the role of the CLC thickness and the top distributed Bragg reflector reflectivity. This transition takes place for 5-6 μm thick CLC and is not gradual but happens in an oscillatory fashion. When the CLC thickness is fixed and the VCSEL top mirror reflectivity is decreased a profound gradual red shift of the resonant mode wavelength and increase of threshold gain are observed.