Single-mode 780 nm vertical-cavity surface-emitting lasers with multi-leaf holey tructure

A single-mode oxide-confined vertical-cavity surface-emitting laser (VCSEL) with multi-leaf holey structure for fiber-optic applications is demonstrated. The optical confinement was done by a multi-leaf holey structure. The deep etched leaf holes were used to provide better mode confinement and suppression of higher order modes. Single fundamental mode continuous-wave output power of over 1.1 mW has been achieved in the 780 nm range, with a threshold current of approximately 0.9 mA. Side-mode suppression ratio (SMSR) larger than 24 dB has been measured.     

Mid-infrared vertical-cavity surface-emitting lasers for chemical sensing

The first (to our knowledge) III-V mid-IR vertical-cavity surface-emitting lasers (lambda = 2.9 mum) are demonstrated and show promising characteristics for chemical detection applications. The cw optical-pumping threshold is low (4 mW at 80 K) and efficiency is high (5.6% W/W). Pulsed operation is obtained up to 280 K and cw up to 160 K. Lateral-mode confinement will lead to spectrally pure, single-mode output for chemical identification.     

Narrow-linewidth vertical-cavity surface-emitting lasers for oxygen detection

The use of vertical-cavity surface-emitting lasers (VCSEL's) for optical detection of atmospheric oxygen is described. The VCSEL's were custom designed for single-mode emission in the 763-nm wavelength range, with low noise and narrow optical linewidth. Using standard wavelength modulation spectroscopy and a second-harmonic detection scheme with a 1-m air path, we determined an oxygen concentration resolution of 0.2%. Because of its small size, low power dissipation, and good tunability characteristics, the VCSEL promises to be an attractive light source for use in compact, low-cost optical sensor microsystems for trace gas detection.     

Low current density, inverted polarity, high-speed, top-emitting 850 nm vertical-cavity surface-emitting lasers

High-speed, oxide-confined, inverted polarity (n-up), polyimide-planarised 850 nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated and characterised. The lasers exhibit a -3 dB frequency modulation bandwidth (f_3dB) up to 15.2 GHz with a 10 mum oxide aperture diameter, at the lowest current density (/bias) ever reported of 6.4 kA/cm². The ratio f_3dB ²/J_bias = 36.1 (GHz²/kA/cm²) represents a 21% increase when compared with the highest previously reported ratio. The threshold voltage and current were as low as 1.45 V and 0.9 mA, respectively, with a series resistance of 65 Omega. A rate-equation-based thermal VCSEL model was used to predict the device performance at different temperatures. Good agreements between measured and simulated DC characteristics were obtained.     

Three-dimensional analysis of mode discrimination in vertical-cavity surface-emitting lasers

Optical mode discrimination in vertical-cavity surface-emitting lasers that contain distributed Bragg reflectors (DBRs) and a spatially limited gain medium is analyzed numerically. It is assumed that the output field is linearly polarized owing to gain selectivity. The analysis employs a three-dimensional model and an angular spectrum of plane-wave decomposition with the proper polarizations. Two types of round aperture are considered, namely, a Gaussian aperture and a ring-peak aperture that represents gain saturation. Coupled with the DBRs, the former aperture yields nearly Laguerre-Gaussian modes, whereas the latter aperture significantly distorts the mode shapes. In both cases, narrowband DBRs provide the best mode discrimination.     

940nm高功率列阵半导体激光器

利用分子束外延生长方法生长出ＩｎＧａＡｓ／ＧａＡｓ应变量子阱材料。利用该材料制作出的应变量子阱列阵半导体激光器准连续（５００μｓ,１００Ｈｚ）输出功率达到２７Ｗ（室温）,峰值波长为９３９￣９４１ｎｍ,并分析了影响列阵半导体激光器输出功率的因素。     

Ultrafast beam self-switching by using coupled vertical-cavity surface-emitting lasers

Dynamic beam switching of vertical-cavity surface-emitting lasers (VCSELs) has important applications for switching and routeing in optical interconnect networks. VCSEL arrays of various kinds have been quite extensively researched for tailoring and engineering near- and far-field patterns. In this paper, a new method of directional beam switching is proposed that uses two coupled VCSELs. When two VCSELs are coupled by a small separation and biased at the same steady current near threshold, then the resulting light output is dynamic at an extremely high frequency. The model equations are based on an approximation to the semiconductor Maxwell-Bloch equations. The simulations are for coupled VCSELs operating at 980 nm with circular current apertures of 5.6 μm diameter. Figures of the results will show far-field beam intensity patterns during a cycle of oscillation. The simulation results show directional switching at a speed of about 40 μm GHz and between directions about 8° apart. Results of addition simulations are also presented. Simulations that use two square VCSELs show that the frequency of oscillation increases to 50 GHz and that the far-field pattern remains similar. Finally, for four round VCSELs in a square pattern, two far-field circularly shaped beams moved left and right at a frequency of 50 GHz.     

Long-wavelength vertical-cavity surface-emitting lasers for high-speed applications and gas sensing

Long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (LW-VCSELs) covering the wavelength range from 1.3 to 2.3 mum are presented. Furthermore, these lasers can be fabricated in a novel high-speed design-reducing parasitics to enable bandwidths in excess of 11 GHz at 1.55 mum. To the best of the authors' knowledge, this is the fastest 1.55 mum VCSEL ever presented. As a proof-of-concept one- and two-dimensional arrays have been fabricated with high yield. All devices use a buried tunnel junction for current confinement and a dielectric backside reflector with integrated electroplated gold-heatsink. This concept enables CW operation at room temperature with typical single-mode output powers above 1 mW. Both, wavelength range and modulation performance, together with VCSEL features such as operation voltage around IV and power consumption as low as 10-20 mW enable applications in tunable diode laser spectroscopy (TDLS) and optical data transmission. Error-free data transmission at 10 Gbit/s over 22 km which can be readily applied in uncooled coarse wavelength division multiplex passive optical networks is presented. A laser hygrometer using a 1.84 mum VCSEL demonstrates the functionality of TDLS systems with VCSELs.     

Transverse-mode control in vertical-cavity surface-emitting lasers via a patterned phase aperture

Transverse-mode discrimination in vertical-cavity surface-emitting lasers that contain a patterned phase aperture is analyzed numerically. The two lowest-order modes are calculated for different aperture shapes and sizes. They are then expanded in Laguerre-Gaussian modes to study the power distribution as well as their beam propagation factor. The mode selection depends on the aperture's size and degree of symmetry. The maximum value for the mode discrimination in the case of a specific phase aperture is determined, and an enhancement by a factor of 3, compared to the case without a phase aperture, is found.     

All-optical crossbar switch using wavelength division multiplexing and vertical-cavity surface-emitting lasers

A design for an all-optical crossbar network utilizing wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) technology and a combination of free-space optics and compact optical waveguides is presented. Polymer waveguides route the optical signals from a spatially distributed array of processors to a central free-space optical crossbar, producing a passive, all-optical, fully connected crossbar network directly from processor to processor. The analyzed network could, relatively inexpensively, connect local clusters of tightly integrated processors. In addition, it is also believed that such a network could be extended, with wavelength reuse, to connect much larger numbers of processors in a multicluster network.     

Parallel self-mixing imaging system based on an array of vertical-cavity surface-emitting lasers

In this paper we investigate the feasibility of a massively parallel self-mixing imaging system based on an array of vertical-cavity surface-emitting lasers (VCSELs) to measure surface profiles of displacement, distance, velocity, and liquid flow rate. The concept of the system is demonstrated using a prototype to measure the velocity at different radial points on a rotating disk, and the velocity profile of diluted milk in a custom built diverging-converging planar flow channel. It is envisaged that a scaled up version of the parallel self-mixing imaging system will enable real-time surface profiling, vibrometry, and flowmetry.     

Noise performance of high-speed radio over fiber links employing vertical-cavity surface-emitting lasers

This study investigates the intensity noise in high-speed vertical-cavity surface-emitting lasers (VCSELs) and its contribution to the noise performance of radio over fiber (RoF) links. We evaluate the sinusoidal modulation of VCSELs in terms of the second-order harmonic distortion (2HD) and third-order intermodulation distortion (IMD3) in additions to the relative intensity noise (RIN). The spurious-free dynamic range of the proposed VCSEL is estimated. The noise performance of the RoF link is assessed by the noise figure. The modulation characteristics of the VCSEL and the gain and noise factor (NF) of the fiber link are compared under conventional and high-speed modulations of VCSELs. Also, we present comparison of the NF between short (300 m) and relatively long (2 km) fibers.     

Multichip free-space global optical interconnection demonstration with integrated arrays of vertical-cavity surface-emitting lasers and photodetectors

The experimental optical interconnection module of the Free-Space Accelerator for Switching Terabit Networks (FAST-Net) project is described and characterized. Four two-dimensional (2-D) arrays of monolithically integrated vertical-cavity surface-emitting lasers (VCSEL's) and photodetectors (PD's) were designed, fabricated, and incorporated into a folded optical system that links a 10 cm x 10 cm multichip smart pixel plane to itself in a global point-to-point pattern. The optical system effects a fully connected network in which each chip is connected to all others with a multichannel bidirectional data path. VCSEL's and detectors are arranged in clusters on the chips with an interelement spacing of 140 mum. Calculations based on measurements of resolution and registration tolerances showed that the square 50-mum detector in a typical interchip link captures approximately 85% of incident light from its associated VCSEL. The measured optical transmission efficiency was 38%, with the losses primarily due to reflections at the surfaces of the multielement lenses, which were not antireflection coated for the VCSEL wavelength. The overall efficiency for this demonstration is therefore 32%. With the measured optical confinement, an optical system that is optimized for transmission at the VCSEL wavelength will achieve an overall efficiency of greater than 80%. These results suggest that, as high-density VCSEL-based smart pixel technology matures, the FAST-Net optical interconnection concept will provide a low-loss, compact, global interconnection approach for high bisection-bandwidth multiprocessor applications in switching, signal processing, and image processing.     

Effect of multiple transverse modes in self-mixing sensors based on vertical-cavity surface-emitting lasers

We investigate the effect of coexisting transverse modes on the operation of self-mixing sensors based on vertical-cavity surface-emitting lasers (VCSELs). The effect of multiple transverse modes on the measurement of displacement and distance were examined by simulation and in laboratory experiment. The simulation model shows that the periodic change in the shape and magnitude of the self-mixing signal with modulation current can be properly explained by the different frequency-modulation coefficients of the respective transverse modes in VCSELs. The simulation results are in excellent agreement with measurements performed on single-mode and multimode VCSELs and on self-mixing sensors based on these VCSELs.     

Performance optimisation of epitaxially regrown 1.3-μm vertical-cavity surface-emitting lasers

A number of GaAs-based long-wavelength, vertical-cavity, surface-emitting laser structures with optical and electrical confinement based on selective area epitaxy have been fabricated and evaluated. The influence on output power, threshold current, thermal stability and modal properties from design parameters such as bottomdistributed Bragg reflector (DBR) doping, cavity doping, dielectric top DBR design and carrier confinement barriers is evaluated. More than 7 mW of output power is emitted from multimode devices with a square active region size of 10 μm. Single-mode power from smaller devices is restricted to 1.5 mW because of a non-optimal cavity shape.     

Temperature and wavelength dependence of gain and threshold current detuning with cavity resonance in vertical-cavity surface-emitting lasers

Heating-induced threshold current detuning with different cavity resonances of AlInGaAs-AlGaAs vertical-cavity surface-emitting lasers (VCSELs) was studied based on gain spectrum analysis and threshold current construction as functions of cavity resonance wavelength and temperature. The quantitative correlations between gain peak, cavity resonance and the minimal threshold current were established. The results showed that the minimal threshold current was in agreement with the gain peak in wavelength only at the temperatures of 300-320 K. Higher temperatures led to a detuning difference between the gain peak and the minimal threshold current relative to the cavity resonance due to band-like nature of the states. In addition, this theoretical analysis about thermal tuning of the cavity resonance pointed out that the wavelength of cavity resonance shifted in an exponential function of temperature. The linear approximation was consistent with the experimental results in the temperature range 300-400 K. A new approach for the gain offsetting is provided so that the minimum in threshold currents can be aligned with the cavity resonance, instead of doing it with the gain peak to achieve the lowest threshold current of the VCSEL at a given temperature.     

Impact of relative intensity noise of vertical-cavity surface-emitting lasers on optics-based micromachined audio and seismic sensors

The relative intensity noise of vertical-cavity surface-emitting lasers (VCSELs) in the 100 mHz to 50 kHz frequency range is experimentally investigated using two representative single-mode VCSELs. Measurements in this frequency range are relevant to recently developed optical-based micromachined acoustic and accelerometer sensing structures that utilize VCSELs as the light source to form nearly monolithic 1 mm3 packages. Although this frequency regime is far lower than the gigahertz range relevant to optical communication applications for which VCSELs are primarily designed, the intensity noise is found to be low and well within the range of cancellation using basic reference detection principles.     

Wavelength modulation detection of water vapor with a vertical cavity surface-emitting laser

A vertical cavity surface-emitting laser was studied for gas-sensing applications. Properties of the 962-nm laser that were measured include side-mode suppression, wavelength tuning with temperature and current, power versus injection current, and the amplitude noise spectrum. With wavelength modulation spectroscopy, a rms noise level of 2 x 10(-4) absorbance units was achieved. The large current tuning range (25 cm(-1)) and smaller amplitude modulation (11%/cm(-1)) of the vertical cavity laser compare favorably with Fabry-Perot and distributed feedback diode lasers for spectroscopic gas sensing, especially at atmospheric pressure.     

Precise etch-depth control of microlens-integrated intracavity contacted vertical-cavity surface-emitting lasers by in-situ laser reflectometry and reflectivity modeling

We studied the etch-depth control of 980 nm intracavity contacted vertical-cavity surface-emitting laser (VCSEL) structures with GaAs/AlGaAs distributed Bragg reflectors by in-situ laser reflectometry and reflectivity modeling in SiCl₄/Ar inductively coupled plasmas. Highly accurate etch-depth control can be achieved by counting the number of oscillation peaks in the experimental reflectance signal through the fitting of the reflectivity data calculated theoretically using a transfer matrix method. The fits provide a very good agreement, allowing us to distinguish individual layers precisely and stop the etching at a desired depth. After confirmation of the validity of in-situ dry etch monitoring, this technique was employed in the fabrication of microlens-integrated intracavity contacted VCSELs including composition-graded digital alloy AlGaAs for high precision control of the etch depth in intracavity region. The etch-depth difference between calculated and experimental results was kept below 20 nm, indicating a good etch performance. The spatial uniformity of ~ 5% was obtained over 1 × 1 cm² sample size.     

Decreasing parasitic capacitance in vertical-cavity surface-emitting laser with selectively oxidized aperture

Results of a comparative study of the structural parameters and the static and dynamic characteristics of vertical-cavity surface-emitting lasers (VCSELs) with microresonators based on Al_0.15Ga_0.85As and Al_0.8Ga_0.2As are presented. It is established that the vertical oxidation of layers in the Al_0.8Ga_0.2As microresonator during formation of the current aperture leads to a significant increase in the oxide thickness. This leads to a considerable decrease in parasitic capacitance of the device and a 1.7- to 2-fold growth in the cut-off frequency of a low-frequency filter formed by parasitic elements of the equivalent electric scheme of the device.