Applications Of Vertical-cavity Surface-emitting Lasers Research Articles

Application of VCSEL in Bio-Sensing Atomic Magnetometers.

Recent years have seen rapid development of chip-scale atomic devices due to their great potential in the field of biomedical imaging, namely chip-scale atomic magnetometers that enable high resolution magnetocardiography (MCG) and magnetoencephalography (MEG). For atomic devices of this kind, vertical cavity surface emitting lasers (VCSELs) have become the most crucial components as integrated pumping sources, which are attracting growing interest. In this paper, the application of VCSELs in chip-scale atomic devices are reviewed, where VCSELs are integrated in various atomic bio-sensing devices with different operating environments. Secondly, the mode and polarization control of VCSELs in the specific applications are reviewed with their pros and cons discussed. In addition, various packaging of VCSEL based on different atomic devices in pursuit of miniaturization and precision measurement are reviewed and discussed. Finally, the VCSEL-based chip-scale atomic magnetometers utilized for cardiac and brain magnetometry are reviewed in detail. Nowadays, biosensors with chip integration, low power consumption, and high sensitivity are undergoing rapid industrialization, due to the growing market of medical instrumentation and portable health monitoring. It is promising that VCSEL-integrated chip-scale atomic biosensors as featured applications of this kind may experience extensive development in the near future.

High Speed VCSEL Technology and Applications

Historically optical links up to 100–300m distances are served by light emitting devices in the 850 nm spectral range in combination with multimode glass fibers (MMF). As the silicon scaling continues, a single channel data rate is to double each 24 months. Light-emitting diodes had to be replaced by vertical cavity surface emitting lasers (VCSELs) and the data rate increased from 100 Mb/s to 10 Gb/s. At higher data rates problems with further scaling evolved. To avoid the collapse an anti-waveguiding VCSEL cavity design was invented, applied, and presently serves data links operating up to 50–100 Gb/s per channel. Another requirement in data communication is the bandwidth density scaling, with the number of channels per link increasing approximately 5-fold each 10 years, while keeping a similar space for connectors. A coarse short-wavelength division multiplexing allowing 850 nm, 880 nm, 910 nm, and 940 nm wavelengths in a single MMF is introduced. The bandwidth density increase is also possible by using multicore fiber (MCF) coupled to on-chip VCSEL arrays. The data rates up to 224 Gb/s are already reached by 850nm VCSELs. At such data rates significant transmission distance over MMF is only possible by applying ultra-narrow spectrum VCSELs minimizing the chromatic dispersion effects. On-chip mini-arrays of oxide-confined VCSELs allow a high coupling efficiency to MMFs, a narrow spectrum, a high power, a significant transmission distance at high data rates. Coherent lasing in such arrays allow photon-photon resonance engineering aimed at modulation bandwidths ∼50–100 GHz.

Vertical Cavity Surface Emitting Lasers as Sources for Optical Communication Systems: A Review

Next generation integrated photonic circuits will be dominated by small footprint devices with lower power consumption, low threshold currentsand high efficiencies. Vertical Cavity Surface Emitting Lasers (VCSELs) having those attractive qualities has shown results to meet the next generation demands for optical communication sources. VCSELs applications are sensors, data com, optical communication, spectroscopy, printers, optical storage, laser displays, atomic optical clocks, laser radar, optical signal processing to name a few. This review centres around on the basic operation of semiconductor lasers, structure analysis of the devices and parameter optimisation for optical communication systems. This paper will provide comparisons on growth techniques and material selection and intends to give the best material realisation for nano optical sources that are up to date as used in optical communication systems. It also provides summarised improvements by other research groups in realisation of VCSELs looking at speeds, efficiency, temperature dependence and the device physical dimensions. Different semiconductor device growth methods, light emitting materials and VCSELs state of art are reviewed. Discussions and a comparisons on different methods used for realising VCSELs are also looked into in this paper.

Application of VCSELs in next-generation telescope array networks such as the Square Kilometre array

The distribution of precise and accurate optical clock signals across fibre links has a significant impact in various fields. Many applications require the transfer of stable and precise timing signals from a single central location to multiple remote users via a fibre network. One such application is the big data instrument, the Square Kilometre Array (SKA). An increase in demand for more bandwidth by broadband providers has prompted the expansion and development of attractive and intelligent, modern communication networks. Vertical cavity surface-emitting lasers (VCSELs) are an attractive solution and a potential candidate for realizing low cost and high bandwidth data transmission. In this paper a novel and unique, all-optical technique for measuring the one-way transmission time delay of the propagating signal along an optical fibre is presented. This has been successfully achieved by optically injecting a pulse-per-second (PPS) signal into the secondary mode of a 1550 nm VCSEL located at the client end. A round-trip latency time of 113.2 μs was experimentally measured over a 22 km G.652 single mode fibre (SMF). A novel VCSEL capacity upgrade technique is further demonstrate. This was experimentally achieved by simultaneously modulating a single 1310 nm VCSEL with a 10 Gbps 27 − 1 pseudorandom binary sequence (PRBS) and a polarization based PPS clock signal. An error free transmission over 11 km of G.652 SMF was reported, with a measured transmission penalty of 0.52 dB when the VCSEL was simultaneously modulated with the 27 − 1 PRBS and the polarization based PPS signal.

Single-material Bragg reflectors and their applications in VCSELs

We present single-material distributed Bragg reflectors (DBRs) fabricated by oblique-angle deposition of amorphous silicon (a-Si). The high and low refractive indices of a-Si films were obtained at two incident vapour flux angles (θα) of 0° and 80° by determining the quarter-wavelength thicknesses of 67 nm at 0° and 128 nm at 80°. The fabricated single-material Bragg reflectors with only five pairs provide high reflectivity values of over 95%. The proposed DBRs were applied to intra-cavity contacted vertical-cavity surface-emitting lasers (VCSELs) to reduce fabrication costs and step. For the fabricated five pair a-Si/a-Si DBRs on VCSELs, the normalized stop bandwidth of 31.63% was measured while high reflectivity values over 95% were maintained over a wide wavelength range of 710 - 1020 nm. The fabricated VCSELs with Da = 7 μm obtained output power and threshold current, which are reasonable measured results.

6-mW Single-Mode High-Speed 1550-nm Wafer-Fused VCSELs for DWDM Application

This paper presents data on wafer-fused 1550-nm vertical-cavity surface-emitting lasers (VCSELs) based on the active region and distributed Bragg reflectors (DBRs) grown by molecular beam epitaxy. VCSELs with a tunnel junction aperture diameter of 8 μm show lasing at a threshold current density j th <; 3 kA/cm 2 , an output optical power of ~4 mW, and a -3 dB bandwidth of approximately 7 GHz at a 10-mA bias current. The devices demonstrate single-mode continuous wave operation with the transverse side-mode suppression ratio (SMSR) varying in the range of 40-45 dB up to roll-over currents. The increase in mirror losses due to the etching of the top DBR makes the output optical power increase to 6 mW and causes the wallplug efficiency value to reach 20%, but SMSR remains in the range of 40-45 dB. This also makes it possible to reduce both the photon lifetime and, as a result, the effect of damping and increase the modulation bandwidth to 9 GHz. The observed open and clear eye diagrams indicate that non-return-to-zero operation is possible at bit rates of up to 30 Gbps without equalization or forward error correction. The high-output optical power and modulation performance pave the way for the dense wavelength division multiplexing application of wafer-fused 1550-nm VCSELs.

Single-mode temperature and polarisation-stable high-speed 850nm vertical cavity surface emitting lasers

A new intracavity-contacted design to realize temperature and polarization-stable high-speed single-mode 850 nm vertical cavity surface emitting lasers (VCSELs) grown by molecular-beam epitaxy is proposed. Temperature dependences of static and dynamic characteristics of the 4.5 pm oxide aperture InGaAlAs VCSEL were investigated in detail. Due to optimal gain-cavity detuning and enhanced carrier localization in the active region the threshold current remains below 0.75 mA for the temperature range within 20-90°C, while the output power exceeds 1 mW up to 90°C. Single-mode operation with side-mode suppression ratio higher than 30 dB and orthogonal polarization suppression ratio more than 18 dB was obtained in the whole current and temperature operation range. Device demonstrates serial resistance less than 250 Ohm, which is rather low for any type of single-mode short- wavelength VCSELs. VCSEL demonstrates temperature robust high-speed operation with modulation bandwidth higher than 13 GHz in the entire temperature range of 20-90°C. Despite high resonance frequency the high-speed performance of developed VCSELs was limited by the cut-off frequency of the parasitic low pass filter created by device resistances and capacitances. The proposed design is promising for single-mode high-speed VCSEL applications in a wide spectral range.

Two dimensional analysis of finite size high-contrast gratings for applications in VCSELs.

2-dimensional simulations of high-contrast gratings (HCGs) of finite size are carried out, targeting at their applications in vertical-cavity surface-emitting lasers (VCSELs). Finite HCGs show a very different behavior from infinite grating ones. The reflectivity of a finite HCG strongly depends on the HCG size and the source size. Our simulation results predict finite reflectivity and transmission values, well consistent with reported experimental results. The band of high reflectivity (>99.5%) of finite HCGs is less broad as compared to the infinite case. Losses into a guided mode excited in the HCG plane are identified as being at the root. This guided mode is excited due to the nonzero angular components in the finite source size, and greatly enhances the transmission and the light leakage from the slab. In addition, the simulation results show that the details of the finite HCG can shape the output beam, whilst a Gaussian-like reflected wave is typically achieved. Our simulations can explain the current discrepancies between numerical predictions of reflectivities approaching 100% and working HCG-VCSELs showing finite reflectivities and nearly Gaussian-like output. Consequently, our analysis of finite HCGs is indispensable for HCG-VCSEL design.

III–V Oxidation: Discoveries and Applications in Vertical-Cavity Surface-Emitting Lasers

Since the discovery of III-V oxidation by Dallesasse and Holonyak in 1989, significant progress has been made, both technically and commercially, on the use of oxides in compound semiconductor devices. The process-induced modification of refractive index and conductivity allows control of the two carriers of information in optoelectronic systems, the photon and the electron, enabling wide-ranging device applications. Of great technical and commercial importance has been the use of oxidation for the fabrication of high-speed vertical-cavity surface-emitting lasers (VCSELs), first implemented by Deppe's group at The University of Texas at Austin (Austin, TX, USA). Here, the low refractive index III-V oxide's interaction with the optical modes inside the VCSEL creates an optimal overlap of gain and field, enabling lasers with ultralow threshold currents and desirable optical beam properties. The discovery of III-V oxidation, key technical milestones in the fabrication of photonic and electronic devices that use oxidation, and the application to VCSELs are reviewed.

A method for improved VCSEL packaging using MEMS and ink-jet technologies

Vertical-cavity surface-emitting lasers (VCSELs) have been recognized as low-cost low-power light sources for applications, such as, optoelectronic (OE) interconnects for high-speed optical data communication. However, many VCSEL applications have not been fully realized due to the lack of solutions to technical issues such as optical coupling, alignment, interconnects, and RF compatibility. In this paper, the authors propose microelectromechanical systems (MEMS) and MEMS-enabled ink-jet printing technologies to provide improved solutions to these technically challenging problems in OE-device packaging. Wafer-level microoptical elements consisting of transparent polymeric pedestals and microlenses were designed and fabricated directly on top of the VCSEL-emitting facets to improve the optical-coupling efficiency between the VCSEL and the optical fiber. Self-aligning MEMS clampers and micromold structures were designed and fabricated for precise packaging and reliable electrical connection of diced VCSEL arrays. This novel packaging process is substrate independent and relatively simple. This technique will provide a reliable assembly of OE devices in miniature optical systems on various substrates

High-performance single-mode VCSELs in the 1310-nm waveband

High-performance vertical-cavity surface-emitting lasers (VCSELs) emitting in the 1310-nm waveband are fabricated by bonding AlGaAs-GaAs distributed Bragg reflectors on both sides of a InP-based cavity. A 2-in wafer bonding process is optimized to produce very good on-wafer device parameter uniformity. Carrier injection is implemented via double intracavity contact layers and a tunnel junction. A 1.2-mW single-mode output power is obtained in the temperature range of 20/spl deg/C-80/spl deg/C. Modulation capability at 3.2 Gb/s is demonstrated up to 70/spl deg/C. Overall VCSEL performance complies with the requirements of the 10 GBASE-LX4 IEEE.802.3ae standard, which opens the way for novel applications of VCSELs emitting in the 1310-nm band.

Progress and prospects of long=wavelength VCSELs

The story of long-wavelength vertical cavity surface emitting lasers (VCSELs) reminds us of an age-old proverb - with a small modification: where there is a will <and money="" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">, there is a way. Although the realization of long-wavelength VCSELs was once considered nearly impossible, the progress of the field during the last three to four years has been tremendous, in part due to the abundance in funding. Although at the present time it is difficult to forecast the market, we believe the technical ground for potential applications of long-wavelength VCSELs is sound. The authors provide an overview of the exciting progress and discuss application requirements for these emerging optoelectronic sources.</and>

Quantum dots for VCSEL applications at [formula omitted

GaAs-based vertical cavity surface-emitting lasers (VCSELs) using self-organized quantum dots (QDs) emitting at 1.3 μm demonstrate device-acceptable parameters. Threshold currents below 2 mA , operation voltage below 2 V and differential efficiency in excess of 60% are demonstrated. Maximum CW output power of 0.8 mW is realized for 8 μm oxide-confined aperture device. Using fully oxidized top and bottom distributed Bragg reflectors allows reducing the total thickness of the structure to only 5– 6 μm . Lifetime and temperature cycling tests confirm high reliability of the device. Confinement of nonequilibrium carriers in the QDs facilitates applications in VCSEL arrays with ultrasmall apertures and microcavities. Low homogeneous line width in single QDs makes potentially possible realization of single QD VCSELs.

VCSEL Applications to Optical Information Processing Systems.

The technical issues involved in applying vertical-cavity surface-emitting lasers (VCSELs) to optical interconnections and optoelectronic processing systems are discussed from the viewpoint of system applications. We review the parallel optical links and switching smart pixel chips as application examples and discuss the VCSEL requirements on system applications.

ANALYSIS OF THE NOISE IN VCSEL USING RATE EQUATION

The noise characteristics of vertical cavity surface emitting laser (VCSEL) are analysed by using rate equations with a reasonable noise simulating method,and the effect of device parameters (such as spontaneous emission factor,output power,injection current and threshold current) on relative intensity noise,frequency noise and spectral linewidth is calculated under single-mode condition.The results are in agreement with experiments.These results may be helpful for optimising the structure design and determing the factors in the application of VCSEL.

Vertical-Cavity Surface-Emitting Lasers for Optical Data Storage

The application of vertical-cavity surface-emitting laser (VCSEL) diodes for optical data storage has been investigated. VCSELs suitable for compact disc optical heads have been designed and fabricated. A photo diode for optical power monitoring is integrated in a VCSEL chip, and a holographic optical head using VCSEL is also manufactured. Single transverse mode operation up to 1.5 mW shows good performance.

Temperature characteristics of a vertical-cavity surface-emitting laser with a broad-gain bandwidth

Temperature-insensitive characteristics are of great importance in implementing the actual applications of vertical-cavity surface-emitting lasers (VCSEL's) because of the temperature change in the surroundings. To extend the operational temperature range of such lasers, we fabricated a VCSEL with a broad gain bandwidth. The active layers in VCSEL's consist of multiple quantum wells (MQW's) with different bandgap energies. From the change in the threshold current, with temperature as a parameter, we found that the operational temperature range of a VCSEL with a broad gain bandwidth is more than 20/spl deg/C wider than that of conventional VCSEL's, whose active layers consist of a single type of MQW. We demonstrate that the extended-gain bandwidth gives better temperature characteristics. In addition, we simulated the structure of the active layers, and the optimized structure resulted in a 1-mW light output power at less than 5 mA in a single transverse mode oscillation from 20-70/spl deg/C.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>