Md. Mottaleb Hossain received the Bachelor of Science (B. Sc.) degree in Electrical & Electronic Engineering (EEE) from Khulna University of Engineering & Technology (KUET), Bangladesh in 2009. He is involved in research on Laser applications, Optics, Nanophotonics, and Quantum Electronics. He has several publications in peer reviewed journals and conferences in the relevant fields. He is a Graduate Student Member of IEEE. He is also a member of IEEE EDS, IEEE Photonics Society, SPIE, IACSIT, and IEB. Recently he has been selected as a reviewer of IACSIT. He is now with the Department of EEE at Stamford University Bangladesh as a lecturer.
Verticalcavitysurfaceemittinglaser is one of the most improved optical transmitters for photonic integrated circuit . Its performance can be analyzed by tuning the structural parameters of the multiple quantumwell embedded in the active region, and also by tuning the various design parameters [2-3]. Resonant cavity or this structure is along the perpendicular plane of the active layer, and electromagnetic wave resonates between the mirrors to allow photons to emit within a very narrow passage of the active medium. It is now used in very low dispersion window (1470 -1610 nm) for optical fiber communication .
The light source for measuring the absorption spectra was a VCSEL diode (Vixar, V670S-002-0001) positioned on a diode mount (Thorlabs, TCLDM9). The temperature of the laserdiode was set at 4.01 ◦ C using a temperature controller (Profile, TED200). To scan the laser light fre- quency, we modulated the diode current by the voltage ap- plied to the external input of a current controller (Thorlabs, LDC202C) from a function generator (Agilent, 33220A) at a scan time of 100 ms.
Optically pumped vertical-external cavitysurface-emitting lasers (VECSEL)  combine the advantages of multiple quantumwell semiconductor lasers with optical pumping. Hence, they have the potential to generate high output powers with excellent beam quality. VECSEL technology is maturing rapidly and is finding applications in many diverse areas of science ranging from high-resolution spectroscopy through to medical imaging. The broad gain bandwidth associated with the multiple quantumwell system means that the VECSEL should be an ideal source for the production of ultrashort pulses. To date most research effort aimed at the generation of ultrashort pulses from VECSEL systems has concentrated on the passive mode-locking approach with a semiconductor saturable absorbing mirror (SESAM) acting as the mode-locking element . With this approach sub-picosecond pulses have been generated with repetition rates in the 10’s gigahertz regime . Such high repetition rates are ideal for communications applications, however the low peak power (~10W) associated with the generated pulses, which is a direct consequence of the high repetition rate, makes the passive mode-locking approaching using a SESAM unsuitable for many other applications such as two-photon fluorescence microscopy for biological imaging, or frequency conversion applications, where high peak powers are needed. Furthermore, low repetition rates in the hundred of MHz range are beneficial in the biological imaging applications due to the lifetimes of the typical dyes used.
ABSTRACT: There are a number of reasons why light can be used as an eﬃcient carrier of information. As a result, optical communication has gained much importance over the last few decades. The verticalcavitysurfaceemittinglaser (VCSEL) is a low cost light source with attractive performance characteristics such as low power consumption, high speed capabilities at low currents, and a circular output beam. These features have madeVCSEL an established component in digital communication networks as the optical source. In this paper, a 1550nm intra-cavity structure VerticalCavitySurfaceEmittingLaser (VCSEL) has been designed using quarter nary compound material of AlGaIn Asin both QW and barrier, but with different compositions, and InP as the substrate. Lattice matching has been obtained in the layers from the substrate upto the top contact layer except the quantumwell(QW) layers where small amount of compressive strain of 1.6% has been used. AlGaAsSb/AlAsSb has been used as the DBR material for achieving lattice matching with the substrate, and also for achieving higher refractive index contrast. The active material compositions have been chosen to obtain a peak gain at 1550 nm. The out come of this design is a top emitting VCSEL based on In P substrate using a different structure which is capable of producing 1550 nm light output and which can be constructed easily using widely used epitaxial techniques mixed with the MBE using digital alloy technique for the QW layers. The designed VCSEL is successfully simulated as an optical source, with an error free transmission of 70 km through a single mode optical fiber.The finalstructure of the VCSELis alsosuitablefor useinopticalICs.
shallow surface etching of the top mirror reflectivity can also improve the direct modu- lation (Westbergh et al 2010, 2011). The second, fundamentally different, approach to increasing the modulation speed is by using the modulation of the photon lifetime in the cavity as an alternative to current modulation; see e.g. (Avrutin et al. 1993; Germann TD 2012; Panajotov et al. 2010; Paraskevopoulos et al. 2006; Shchukin et al. 2014; Stanley et al. 1994). Advanced semiconductor lasers involving direct modulation of the photon lifetime promise better dynamic properties than lasers with current modulation because their operating speed is less strongly limited by the electron-photon resonance. Several laser designs to implement this principle have been proposed, and initial measurements are all promising. For example, Germann and co-authors have experimentally demonstrated a modulation bandwidth of 30 Gbit/s with 100 mV and 27 dB electrooptic (EO) modulation changes in the voltage and the optical amplitude for small signal modulation, respectively (Germann TD 2012). Large-signal Non-return-to-zero (NRZ) modulation at 40 ? GBit/s has been confidently and repeatedly demonstrated in (Shchukin et al. 2014). By using a non-absorbing EO modulator in the first known compound VCSEL (Paraskevopoulos et al. 2006), the electrical bandwidth up to 60 GHz and optical bandwidth more than 35 GHz, restricted by the photodetector response, have been achieved. Strain-compensated multiple quantum wells were used in the active gain region in the VCSEL cavity with 960 nm reference frequency and 3–4 nm blue shift in the modulator region. A more recent experimental achievement for photon lifetime modulation was conducted by utilizing the influence of the aperture size on the performance of 850 nm InGaAlAs oxide-confined VCSELs (Bobrov et al. 2015). When the aperture size is decreased to an optimum value of 4–6 lm and the photon lifetime is reduced from 4 to 1 ps, there is a saturation in the the maximum 3 dB modulation bandwidth at 21 GHz.
mental setup is schematically shown in Fig. 1. The VCSEL is submitted to optical injection from an external cavitydiodelaser in Littrow configuration (Sacher Lasertechnik TEC100-960-60), isolated from the rest of the setup by an optical isolator. The direction of linear polarization of injected light is modified using a half-wave plate, before being purified with a Glan-Thompson prism. Optical injection power is then tuned by changing the orientation of the half wave plate. A 10/90% beam splitter is set between the polarizer and the VCSEL to allow a measurement of the optical injection power and to direct the light coming from the VCSEL towards the analysis branch. The analysis branch is made of an optical spectrum analyser (ANDO AQ6317-B), a photodiode, and a CCD camera, on which an image of the near field profile of the VCSEL is formed.
In order to have lasing action there are three basic requirements: gain, optical feedback, and external stimulation. This was first achieved in a semiconductor p-n junction in 1962 16 . In these first devices there was electron hole recombination in the p-n junction depletion layer for gain. The lasercavity was formed by cleaved or polished semiconductor surfaces providing the optical feedback, and the p-n junction was forward biased for external stimulation. In 1969 the double heterostructure was introduced, and the edge emitting stripe geometry laser 16 become the standard semiconductor laser configuration. The output of this laser was parallel to the substrate and was not a circle but an ellipse. Many researchers found that a surfaceemitting structure would better accomplish tasks such as coupling light into optical fiber and making multi-dimensional laserarrays. Before the invention of the VCSEL, many tricks were played with mirrors incorporated in edge emitting lasers to transform them into surfaceemitting lasers. Then as stated above, the first VerticalCavitylaser was created. The lasercavity is
Abstract. In order to simulate the light-current (LI) characteristics of the VerticalCavitySurfaceEmittingLaser (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.
Here we report the experimental observation of different forms of (PS) and (PB) induced by circularly polarized optical injection into a 1300nm dilute nitride spin-VCSEL operating at room temperature. The dilute nitride (GaInNAs/GaAs) spin-VCSEL sample used in this work was grown by a solid source molecular beam epitaxy (MBE). The 3-λ cavity of the device consisted of five stacks of three quantum wells (QWs) placed approximately at the antinodes of the standing wave pattern of the optical field. Each 7nm Ga 0.67 In 0.33 N 0.016 As 0.984 QW was located between 2 nm
The Garnache design was implemented in an MBE-grown InGaAs/GaAs VECSEL, which exhibited the power output characteristics shown in figure 3. Unlike the Kuznetsov device, this laser used no post-growth processing of any kind to reduce thermal impedance: the back surface of the intact substrate of the gain structure was made to contact a Peltier cooler using thermally conductive paste. The VECSEL was pumped with up to 1.5 W of 830-nm radiation from a fibre-coupled diode, imaged onto a 90-µm-diameter spot on the surface of the gain structure. Figure 3 shows the output power of this laser as a function of incident pump power for two temperature settings of the Peltier cooler. With the device running above ambient temperature, at a Peltier setting of 60˚C, the output power rolls over slowly and smoothly, passing through a maximum of >190 mW. The broad rollover characteristic indicates a device limited only by the intrinsic temperature dependence of the quantumwell gain and not by thermal tuning of the longitudinal confinement factor. The laser was almost completely turned off for an incident pump power of 1.3 W, at which point the temperature of the active region reached an estimated 130˚C. With the Peltier cooler set to 0˚C, the laser reached a maximum output power of >400 mW, corresponding to an overall power conversion efficiency of ∼30%, enhanced by careful design of the DBR to back-reflect the unabsorbed pump light through the wells. The VECSEL operated in a TEM 00 mode up to the
Figure 1: Scheme of the setup that was used for the experiments on the polarization dynamics of VCSELs. The abbreviations in the figure denote the different elements of the setup as follows: CL, collimation lens; λ/4, quarter-wave plate; λ/2, half-wave plate; WP, Wollaston prism; L, lenses; APD, avalanche photo-diode (1.8 GHz bandwidth); D, low-bandwidth detector; ISO, optical isolator; FPD, fast photo detectors of different types (10 GHz and 26 GHz bandwidth, respectively); FPI, scanning Fabry-Perot interferometer; NDF, neutral density filters; CCD, charge-coupled device camera. Mirrors are denoted by thick solid lines. The beam path is indicated by a dashed line. Further explanations are given in the text. of the fractional polarization and appear as sidebands in the optical spectrum. Within the framework of the above model, characteristic spectra or similar phenomena are not predicted for type I PS. One therefore has to look for other manifestations of the switching to a mode with lower net gain. We will find it in the fact that a switching event to the gain disfavored mode is accompanied by a decrease of the output power of the laser at the point of PS. The paper is organized as follows: In the next section we will discuss the experimental setup. Then, we will present experimental results on polarization dynamics and polarization switching of type 1 as well as of type 2. In Sect. 4, we will compare these findings with theoretical predictions by the SFM. The focus will be on our own results but we will try to put them in context with the findings of other groups. Finally, a brief outlook is given.
We used commercial blue-emitting InGaN LED wafers grown by metal organic chemical vapor deposition on (0001) sapphire substrates. The LED epitaxial structure consists of a typical p-i-n structure with an n-GaN layer, InGaN/GaN multiple quantum wells (MQWs) and a p-GaN layer. We started from large-area mesas of 1 mm×1 mm down to sapphire substrates defined by photolithography and dry etch processes. Indium-tin-oxide (ITO) and Ti/Ag/Ti/Au layers were deposited in sequence on the mesas to form p-type ohmic contacts and reflective mirrors, respectively. To allow metal-to-metal bonding, Pd/Ti/Au layers were deposited on a Si wafer to make a transfer substrate. By controlling the heating and cooling down processes, the LED wafer was bonded onto the Si transfer substrate by a 50-μm-thick flexible AuSn (80:20 wt.%) layer within a vacuum furnace. Then, a frequency-tripled, nanosecond-pulse Nd:YAG laser with an energy density of about 600 mJ/cm 2 was used to irradiate from the
Subplots (b–d) present the corresponding plasma tem- perature, carrier density and N Eq for the first conduc- tion band. In analogy to the wavelength considerations of Fig. 20, the characteristics of the temperature, density and N Eq follow the laser emission. To separate the nonequi- librium effects on the carrier density causing higher thresh- old losses from the modified pump absorption, we plot in subplots (e–h) the same quantities as in (a–d) as functions of the absorbed pump intensity. Here, the observed sub- linearity of the power characteristics is suppressed and the different slope efficiencies virtually vanishes. From this, we conclude, that the primary effect of the elevated carrier temperatures and the nonequilibrium carrier distributions is a reduction of the pump-absorption. Nevertheless, both, temperature increase and nonequilibrium, leads to a den- sity increase which is followed by an increase of the car- rier losses and thus results in the remaining sublinearity in Fig. 21 (e). This is supported by the carrier density in sub- plot (g) being less sublinear than the temperature increase in (f).
The schematic structure of the VECSEL gain element and the lasercavity are shown in Fig. 1. The VECSEL wafer used in this work was grown by MOCVD. It was originally designed for conventional barrier pumping. A semiconductor Bragg mirror was first deposited on top of a GaAs wafer. This high-reflectivity (HR) mirror has its central wavelength at 850 nm for normal incidence and a bandwidth of 85 nm FWHM. Above the mirror is a 17 QW strain compensated gain structure with a peak emission at 850 nm. The 10 nm wide wells are separated by approximately half a wavelength of AlGaAs. A further layer of AlGaAs is added on top of the gain structure to increase the total length of the micro-cavity to 2.55 µm. This corresponds to an anti-resonant structure at 850 nm. Compared with a resonant gain structure [17, 18], the anti-resonant design minimizes spectral filtering and thus provides a larger gain bandwidth beneficial for wavelength tuning and generation of ultra-short pulses through mode-locking. Finally, a 20 nm layer of GaAsP was added to prevent oxidation. A detailed discussion and characterization of the material is reported by McGinily et al. . The band- gap of the AlGaAs barriers is 1.748 eV corresponding to a wavelength of 710 nm so wavelengths longer than this are only absorbed by the quantum wells. Due to the correspondingly smaller volume of absorbing material the absorption is significantly reduced. It is therefore desirable to choose an in-well pumping wavelength that is sufficiently long to be reflected by the Bragg mirror and sent through the MQW region a second time (or potentially recycled several times with a more sophisticated pumping scheme).
VCSELs have small size, are low cost, have high‐speed operation, have low power consumption, and can be fabricated into arrays [1,2]. These advantages cause VCSELs to attract much attention for use in photonics, e.g. fiber communications, radio‐over fiber networks, optical data centers. Because the modern versions of these applications require dense traffic and high‐ speed transmission, the development of high speed VCSELs is a key issue. Various approaches have been reported to increase the speed of VCSELs. Subjecting the semiconductor laser to external OFB is an efficient technique to enhance modulation bandwidth. OFB has been used for increasing the bandwidth frequency of VCSELs [3,4], linewidth narrowing [5,6], decreasing the frequency chirp , and the stability of mode operation . 60% improvement in modulation bandwidth was expected by Dalir and Koyama using TCC feedback [9,10]. Ahmed et al.  analyzed the modulation characteristics of TCC VCSELs and explained the bandwidth improvement as a type of photon‐photon resonance.
By analogy with the quasi-scalar case [28–32, 39, 40] one might anticipate also the possibility of stabilization of vector vortices in the flow-equilibrium of driven dissi- pative systems like cavities. VCSELs are attractive for this kind of studies as they allow a huge variety of spatial [41–45] as well as polarization [41, 44, 46–50] states due to their high Fresnel number and nominal circular sym- metry. Theoretically, vector vortex beams were predicted for VCSEL modes in , but never experimentally ob- served. We are not aware of any experimental or theo- retical work on vector vortex solitons, but indications for non-trivial polarization states were found for fundamen- tal solitons . The present letter first focuses on the generation of anti-vortex solitons that present a charac- teristic hyperbolic polarization pattern. The generation of spiral and radially-polarized vortex solitons will be dis- cussed afterwards.
cal stability analysis  to provide insight into the nature and evolution of the dynamics, together with numerical simulations targeted on specific regions of interest informed by experimen- tal observations. The stability analysis indicates that a Hopf bifurcation leads to these stable polarization oscillations and the agreement between numerical simulations and experimental findings is excellent. Moreover, the work reveals both routes for controlling these oscillations as well as prospects for very high frequency operation limited only by the birefringence rate. Since this can be made very high, up to hundreds of GHz , this offers in turn great prospects for novel, simple and inexpen- sive ultrafast laser sources with ample expected impact in data communications and spectroscopy applications.
Light emitting diodes are emerging as compact, rugged, bright and efficient light sources making them a compelling substitute for general lighting applications. Recent breakthroughs in GaN-based blue light emittingdiode device growth techniques have not only led to a substantial progress in their internal quantum efficiency but also to the improvement of their light extraction efficiency. Previous experimental data reported an enhancement of almost 3 times in the light output intensity of an InGaN/GaN multiple quantumwell light emittingdiode overgrown by the embedded voids approach on sapphire substrate using the metal organic chemical vapor deposition technique.