Single Vertical-cavity Surface-emitting Laser Research Articles

910 nm vertical-cavity surface-emitting laser arrays with 100 W output power level and low driving current

In this paper, we present monolithic 910 nm high-power vertical-cavity surface-emitting laser (VCSEL) arrays with addressable sectors suitable for long-distance light detection and ranging (LIDAR). The peak output power of a single VCSEL array (163 devices) reaches 25.5 W under 30-ns-pulse operation. The peak power of the larger sectored 2×2 VCSEL array reaches 100 W at an operating current of 55 A. To the best of our knowledge, this is the first report on achieving a 100 W output power level with a 910 nm VCSEL array at such a low driving current. Our VCSEL array shows stable impulse response characteristics and uniform far-field spot morphology.

1.6 MHz scanning rate direct absorption temperature measurements using a single vertical-cavity surface-emitting laser diode.

This paper presents 1.6MHz scan rate, non-intrusive, time-resolved temperature measurements of a normal shock reflection from a plane end wall within a shock tube. A vertical-cavity surface-emitting laser (VCSEL) was used to conduct tunable diode laser absorption spectroscopy with water vapor as the probe species. The results are compared with analytical predictions. Temperatures measured with this technique agree within a single-scan standard deviation of ±33 K with calculated temperatures at a VCSEL modulation frequency of 800kHz, which is sufficiently rapid enough to be used to investigate highly transient shock wave interaction processes.

Bidirectional Visible Light Communication System Using a Single VCSEL With Predistortion to Enhance the Upstream Remodulation

The demand of higher data rates has made it attractive to consider a low-cost laser diode (LD), such as vertical-cavity-surface-emitting laser (VCSEL) for use in visible light communication (VLC) transmitters (Tx) due to their higher electrical-to-optical modulation bandwidth, beam convergence, and energy efficiency. Many reported LD-based VLC systems only had a solitary downstream transmission. We demonstrate a 3-m bidirectional signal remodulated VCSEL-based VLC system using visible-light modulator to produce the upstream signal. The visible-light external modulator usually has limited modulation bandwidth. By using the predistortion, the upstream remodulated data rate is enhanced by ∼2.8 times. Hence, the VCSEL-based VLC system with 10.64-Gb/s downstream signal and 5-Mb/s upstream remodulated signal can be achieved. We also analyze via numerical simulations how the predistorted signal can enhance the transmission data rate by mitigating the intersymbol interference introduced by the bandwidth limitation of the upstream modulator.

Simultaneous concealment of time delay signature in chaotic nanolaser with hybrid feedback

Simultaneous suppression of time delay (TD) signature in all observables of optical chaos emission, i.e. in both intensity and phase, has been achieved using two or more semiconductor laser (SL) sources or using two independent polarization components of single vertical cavity surface-emitting laser (VCSEL). In this paper, we examine for the first time the simultaneous TD feature suppression using a single nanolaser of single polarization state. The influence of hybrid optical/electrooptic feedback schemes employing either conventional, phase-conjugate, or grating mirror is evaluated. The concealment of TD signature is then investigated by means of the autocorrelation function. The results reveal the operational regions in each case with well eliminated TD signature in all observables. A secure communications system utilizing chaotic nanolaser is presented. Security analysis for a message transmitted in the form of a colored image is carried out which verifies the immunity of the system against possible statistical, brute force and differential attacks.

Vertical-Cavity Surface-Emitting Lasers With Two Emission-Controllable Transverse Modes

We propose a vertical-cavity surface-emitting laser (VCSEL) with two transverse modes independently controlled by two contacts. By directly etching a trench in the p-doped distributed Bragg reflector, we form an air gap and two sub-mesas as waveguides above the oxide layer. Contacts are deposited on each sub-mesa. Emission control on two different spatial modes in a single VCSEL is achieved by changing the driving condition of one-contact or two-contact injection. Owing to this feature, the proposed VCSEL has a potential as a cost-effective source for optical communications using spatial-division multiplexing.

850 nm Vertical-Cavity Surface-Emitting Laser Arrays With Enhanced High-Speed Transmission Performance Over a Standard Multimode Fiber

The functionality of novel parallel and series high-speed vertical-cavity surface-emitting laser (VCSEL) arrays, which can greatly relax the tradeoff between output power and modulation speed, is demonstrated. Both types of array structure allow improvement in the output power with no degradation in their maximum modulation speed as compared to a single reference unit. The observed invariant electrical–optical bandwidth shown for these array structures is mainly due to the effective reduction of the differential resistance and parasitic capacitance, arising from the Zn-diffusion and oxide-relief apertures fabricated in the VCSEL unit. This in turn minimizes the degradation in the RC -limited bandwidth with the VCSEL arrays. Furthermore, the dense packing of single VCSELs, with Zn-diffusion apertures for optical mode control, minimizes the coupling loss between the output from the array into a standard multimode fiber (MMF). Compared with the single VCSEL unit, the parallel VCSEL array shows a significant enhancement in transmission performance over a standard OM4 MMF, which includes a larger eye margin, a higher signal-to-noise ratio, as well as a higher error-free data rate (48 versus 44 Gbit/sec). The device modeling technique is used to perform device analysis. From the results we can conclude that the improvement with the parallel array is because the value of the internal impedance is closer to the 50-Ω signal source, which minimizes the microwave reflection induced timing jitter in the eye-patterns.

Capacity upgrade in short-reach optical fibre networks: simultaneous 4-PAM 20 Gbps data and polarization-modulated PPS clock signal using a single VCSEL carrier

In this work, a four-level pulse amplitude modulation (4-PAM) format with a polarization-modulated pulse per second (PPS) clock signal using a single vertical cavity surface emitting laser (VCSEL) carrier is for the first time experimentally demonstrated. We propose uncomplex alternative technique for increasing capacity and flexibility in short-reach optical communication links through multi-signal modulation onto a single VCSEL carrier. A 20 Gbps 4-PAM data signal is directly modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm, therefore, doubling the network bit rate. Carrier spectral efficiency is further maximized by exploiting the inherent orthogonal polarization switching of the VCSEL carrier with changing bias in transmission of a PPS clock signal. We, therefore, simultaneously transmit a 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal using a single VCSEL carrier. It is the first time a signal VCSEL carrier is reported to simultaneously transmit a directly modulated 20 Gbps 4-PAM data signal and a polarization-based PPS clock signal. We further demonstrate on the design of a software-defined digital signal processing (DSP)-assisted receiver as an alternative to costly receiver hardware. Experimental results show that a 3.21 km fibre transmission with simultaneous 20 Gbps 4-PAM data signal and polarization-based PPS clock signal introduced a penalty of 3.76 dB. The contribution of polarization-based PPS clock signal to this penalty was found out to be 0.41 dB. Simultaneous distribution of data and timing clock signals over shared network infrastructure significantly increases the aggregated data rate at different optical network units (ONUs), without costly investment.

Nonpolar III-nitride vertical-cavity surface-emitting laser with a photoelectrochemically etched air-gap aperture

We demonstrate a III-nitride nonpolar vertical-cavity surface-emitting laser (VCSEL) with a photoelectrochemically (PEC) etched aperture. The PEC lateral undercut etch is used to selectively remove the multi-quantum well (MQW) region outside the aperture area, defined by an opaque metal mask. This PEC aperture (PECA) creates an air-gap in the passive area of the device, allowing one to achieve efficient electrical confinement within the aperture, while simultaneously achieving a large index contrast between core of the device (the MQW within the aperture) and the lateral cladding of the device (the air-gap formed by the PEC etch), leading to strong lateral confinement. Scanning electron microscopy and focused ion-beam analysis is used to investigate the precision of the PEC etch technique in defining the aperture. The fabricated single mode PECA VCSEL shows a threshold current density of ∼22 kA/cm2 (25 mA), with a peak output power of ∼180 μW, at an emission wavelength of 417 nm. The near-field emission profile shows a clearly defined single linearly polarized (LP) mode profile (LP12,1), which is in contrast to the filamentary lasing that is often observed in III-nitride VCSELs. 2D mode profile simulations, carried out using COMSOL, give insight into the different mode profiles that one would expect to be displayed in such a device. The experimentally observed single mode operation is proposed to be predominantly a result of poor current spreading in the device. This non-uniform current spreading results in a higher injected current at the periphery of the aperture, which favors LP modes with high intensities near the edge of the aperture.

Flat Broadband Chaos in Mutually Coupled Vertical-Cavity Surface-Emitting Lasers

The flatness of chaos generated by mutually coupled vertical-cavity surface-emitting lasers (VCSELs) has been investigated experimentally in two configurations. Power variation between dc and the bandwidth frequency and flat bandwidth are used to quantitatively study the flatness of chaos. The power spectrum of chaos from a single VCSEL in both configurations is not flat due to a peak at relaxation oscillation frequency. This uneven nature will affect the application of chaos in random number generation. The experimental results show that the power spectra of chaos can easily be flattened by combining two uneven chaos. Flat bandwidth of the combined output can be 15 times higher than that of chaos from a single VCSEL at the optimum frequency detuning. The mechanism for this flattening is attributed to the frequency beating.

Simultaneous Suppression of Time-Delay Signature in Intensity and Phase of Dual-Channel Chaos Communication

In this paper, we propose a novel dual-channel optical chaos system with a time-delay (TD) feature simultaneously suppressed in all observables, i.e., in both intensity and phase. A hybrid optical and electro-optic feedback for a single vertical-cavity surface-emitting laser (VCSEL) is verified to induce simultaneous TD suppression for the polarization-resolved components of the chaotic output. A comprehensive mathematical model is developed to incorporate the optical and electro-optic time delays into the rate equations of the VCSEL. The suppression of TD signature is then examined by means of autocorrelation function and delayed mutual information. The results show that the output chaotic signal has the TD feature well eliminated in both the intensity and phase over certain regions of parameter space identified using the peak signal to mean ratio technique. The independent evolution of the two orthogonal VCSEL modes renders the polarization-resolved output modes appropriate for the enhanced dual-channel chaos applications. To the best of our knowledge, this is the first time that a dual-channel chaos communication system is reported with simultaneous suppression of the TD feature in all the transmitted observables.

Flip-chip bonding of vertical-cavity surface-emitting lasers using laser-induced forward transfer

This letter reports the use of the Laser-Induced Forward Transfer (LIFT) technique for the fabrication of indium micro-bumps for the flip-chip (FC) bonding of single vertical-cavity surface-emitting laser chips. The FC bonded chips were electrically and optically characterized, and the successful functioning of the devices post-bonding is demonstrated. The die shear and life-time tests carried out on the bonded chips confirmed the mechanical reliability of the LIFT-assisted FC bonded assemblies.

大功率VCSEL器件的空间相干性的研究

The spatial coherence properties of high power vertical cavity surface emitting lasers (VCSELs) are studied based on the theorem of partially coherent light proposed by Van Cittert-Zernike. The interference stripe patterns are gauged using the Young's double-slit experiment for the devices of 980 nm wavelength VCSEL single emitters. Then interference patterns are switched to grayscale by intensity distribution patterns for data collection. In this paper, the integral average value method is proposed to calculate the degree of spatial coherence. The proposed integral average value method and traditional average method are used respectively to calculate the light intensity of the pattern. The results are compared with those calculated by the theoretical value of Van Cittert-Zernike theorem. The VCSEL optical apertures' influence on coherent characteristics are also discussed. The experimental results show that, a relative error within 2.5%~9.4% is reached by our integral average value method. On the contrary, a relative error of 7.5%~67.4% are got from the traditional average method. Apparently, traditional average value method causes the error generally 1.5~27 times worse than our integral average value method. Moreover, for single emitter VCSELs with optical aperture from 200 m to 500 m, the smaller the optical aperture are, the larger the coherent degrees (between 0.731~0.426) are. The conclusion can be wildly used on theoretical and experimental design for VCSEL coherent arrays.

Power-stabilized tunable narrow-band source using a VCSEL and an EDFA for FBG sensor interrogation

Wavelength tuning with a current of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) was studied for application to wavelength readout of fiber Bragg grating (FBG) sensors. 1.5 µm single-longitudinal-mode VCSELs with a spectral line width of 30 MHz were used. To decrease the variation in the output power with the current, saturated amplification of the VCSEL output by an erbium-doped fiber amplifier (EDFA) was proposed. In the experiment, the wavelength readout of an FBG by variation in the VCSEL current was studied first, and then amplification characteristics using a commercially available EDFA module were measured. Two VCSELs with different wavelengths and tuning ranges were used as input and compared. For a VCSEL with a wavelength tuning range of 2.5 nm, there was a threefold change in the VCSEL output power. However, the variation in the amplified output power was within ±14%. For another VCSEL with a wavelength tuning range of 3.9 nm, the variation in the amplified output power was within ±18% for variation in the VCSEL output power by 2.2 times. The power slope with respect to the wavelength was also decreased by the stabilization. Computer simulation was performed to study the wavelength shift in the measured Bragg wavelength induced by the power slope. The simulation showed that the wavelength shift can be reduced to 1/2.5–1/5 by the stabilization compared with that using a single VCSEL. Application to long-period grating sensors was also discussed.

Study on effect of quantum well number on performance characteristics of GaN-based vertical cavity surface emitting laser

The effect of number of quantum wells and quantum well thickness on the optical performance of InGaN vertical cavity surface emitting laser (VCSEL) was numerically investigated using Integrated System Engineering Technical Computer Aided Design (ISE TCAD) simulation program. The simulation results indicated that the output power and differential quantum efficiency of the double quantum well (DQW) laser were increased and threshold current decreased as compared to the single and triplet quantum wells VCSEL. Threshold current enhancement in the single quantum well (SQW) is attributed to the electron carrier leakage increasing from active layers because of the lower optical confinement factor. Simulation results show that in the double quantum well, the optical material gain and electron and hole carrier densities are approximately uniform with respect to the SQW and TQW. Also these results indicated that the electron current density in the DQW is the lowest. In the active region, electrical field decreased for the double quantum well because of the built-in electrical field reduction inside the quantum well. Finally the effect of quantum well thickness in DQW GaN-based VCSEL was investigated and it was observed that DQW VCSEL with 3nm quantum wells thickness had the optimum threshold current.

High-Speed 1550 nm VCSEL Data Transmission Link Employing 25 GBd 4-PAM Modulation and Hard Decision Forward Error Correction

Current short-range optical interconnects capacity is moving from 100 to 400 Gb/s and beyond. Direct modulation of several laser sources is used to minimize bandwidth limitations of current optical and electrical components. This total capacity is provided either by wavelength division multiplexing or parallel optics; it is important to investigate on the ultimate transmission capabilities of each laser source to facilitate current capacity standards and allow for future demands. High-speed four-level pulse amplitude modulation at 25 GBd of a 1.5 μ m vertical-cavity surface-emitting laser (VCSEL) is presented in this paper. The 20 GHz 3 dB-bandwidth laser is, at the time of submission, the largest bandwidth of a 1.5 μ m VCSEL ever reported. Forward error correction (FEC) is implemented to achieve transmission over 100 m virtually error free after FEC decoding. Line rate of 100 Gb/s is achieved by emulation polarization multiplexing using 50 Gb/s signal obtained from a single VCSEL.

Ultra Small Integrated Optical Fiber Sensing System

This paper introduces a revolutionary way to interrogate optical fiber sensors based on fiber Bragg gratings (FBGs) and to integrate the necessary driving optoelectronic components with the sensor elements. Low-cost optoelectronic chips are used to interrogate the optical fibers, creating a portable dynamic sensing system as an alternative for the traditionally bulky and expensive fiber sensor interrogation units. The possibility to embed these laser and detector chips is demonstrated resulting in an ultra thin flexible optoelectronic package of only 40 μm, provided with an integrated planar fiber pigtail. The result is a fully embedded flexible sensing system with a thickness of only 1 mm, based on a single Vertical-Cavity Surface-Emitting Laser (VCSEL), fiber sensor and photodetector chip. Temperature, strain and electrodynamic shaking tests have been performed on our system, not limited to static read-out measurements but dynamically reconstructing full spectral information datasets.

Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems

We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks.

Polarization and Time-Resolved Dynamics of a 1550-nm VCSEL Subject to Orthogonally Polarized Optical Injection

We report a first experimental study of the simultaneous temporal and polarization-resolved dynamics of a 1550-nm vertical-cavity surface-emitting laser (VCSEL) subject to orthogonally polarized optical injection. A novel technique is used to reveal the behavior of both polarizations at the VCSEL's output. In general, the same type of dynamics can be seen in both polarizations of the fundamental transverse mode but with unequal intensity/modulation depth. We show that both polarizations exhibit period one and chaotic dynamics and reveal antiphase dynamics. These results offer promise for the development of dual-channel, anticorrelated periodic and chaotic-signal generators with a single VCSEL for use as oscillators or chaotic sources in present and future optical networks.

Reconfigurable Multifunctional Operation Using Optical Injection-Locked Vertical-Cavity Surface-Emitting Lasers

In this paper, we extend the system application of optical injection-locked (OIL) vertical-cavity surface-emitting lasers (VCSELs) to future optical networks by realizing multifunctional operation using a filter-assisted OIL-VCSEL scheme that can be reconfigured. By using a single chirp-adjustable injection-locked VCSEL (either single mode or multimode) followed by a tunable delay line interferometer, we experimentally demonstrate three functions, showing ultra-wide band (UWB) monocycle generation, nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion, and NRZ-data clock recovery at 10 Gb/s.

Simple VCSEL Base-Station Configuration for Hybrid Fiber-Wireless Access Networks

A simple and compact base-station (BS) configuration that exploits the optical properties of a vertical-cavity surface-emitting laser (VCSEL) for use in hybrid fiber-wireless access networks is proposed and experimentally demonstrated. Compared to existing configurations in the literature, the proposed configuration eliminates the need for external and custom-designed optical elements. Experiments demonstrate that radio-frequency-over-fiber channels can be successfully reflected, added, and rewritten at the BS with low penalty, thereby highlighting the potential of a single VCSEL as an integrated reflector for ldquothrurdquo channels and a transmitter to ldquoaddrdquo and ldquorewriterdquo channels.