Thermal management optimization in high-power 3D sensing VCSELs

A 780 nm-range 40 channels vertical-cavity surface-emitting laser (VCSEL) array was developed as a writing light source for printers. A 15° off missoriented GaAs substrate, an aluminum-free GaInAsP/GaInP compressively-strained multiple quantum well and an anisotropic-shape transverse-mode filter were employed to control polarization characteristics. The anisotropic-shape transverse-mode filter also suppressed higher transverse-mode and enabled high-power single-mode operation. Thus, orthogonal-polarization suppression-ratio (OPSR) of over 22 dB and side-mode suppression-ratio (SMSR) of 30 dB were obtained at operation power of 3mW at same time for wide oxide-aperture range below 50 μm2. Moreover, a thermal resistance was reduced for 38% by increasing a thickness of high thermal conductivity layer (3λ/4-AlAs layer) near a cavity. By this structure, a peak-power increased to 1.3 times. Moreover, a power-fall caused by self-heating at pulse-rise was decreased to 10% and the one caused by a thermal-crosstalk between channels was decreased to 46%. The VCSEL array was mounted in a ceramic package with a tilted seal glass to prevent optical-crosstalk caused by other channels. Thus, we achieved stable-output and high-quality beam characteristics for long-duration pulse drive.

Here we show a confocal microscope system where a vertical-cavity surface-emitting laser (VCSEL) array is introduced for the parallel probing beams.A VCSEL array is a semiconductor laser device that emits circular beams vertically to the surface of the chip, which can directly be used as confocal laser microscope applications. The VCSEL device itself can be the parallel beam source of the confocal laser system, whereas in conventional Nipkow disc-based system, several lenses are required to form probing beams. Figure 1 shows the basic structure of VCSEL-based confocal microscope systems. Since there is typically no correlation between individual channels of VCSEL, there are no interferences among dense parallel beam arrays. Additionally, in the case of Nipkow disc system, the signal to noise ratio of the detected light is another problem: some of the light from the source laser reflects at the surface of the disc, which eventually could be detected by the sensor as noise. in the proposed system no such problem occurs as shown in Fig. 2(a). in addition, “all” optical beam from VCSEL is used as probing beam whereas most of the power is lost at the disc as compared in Fig. 2(b). in addition, pixel parallel illumination control is also achievable by controlling each channel of the VCSEL so that the dynamic range of the detected signal is maximized.

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.

High performance GaAs- and InGaAs-based selectively oxidized vertical-cavity surface-emitting laser (VCSEL) arrays emitting in the 780 to 980 nm wavelength regime are investigated as light sources for high bit rate optical interconnects. Solid source molecular beam epitaxy (MBE) with carbon as p-type dopant is used for crystal growth. Single-mode devices show record-high output powers up to 4.8 mW with a butt-coupling efficiency of more than 80% into single-mode fiber. Linear 1/spl times/8 and 1/spl times/16 as well as two-dimensional 4/spl times/8 VCSEL arrays have been employed as transmitters in optical fiber links. Non-return-to-zero (NRZ) pseudo-random bit sequence (PRBS) signals with 2/sup 31/-1 wordlength at total data rates up to 24 Gb/s (8/spl times/3 Gb/s) have been transmitted over 500 m of multimode fiber. Bias-free data transmission of 2.5 Gb/s over 500 m of multimode fiber is demonstrated. Polymer optical fiber (POF) was used for short distance data transmission. A visible, red emitting VCSEL (/spl lambda/=780 nm) is employed to transmit 2.5 Gb/s over 1 m of small core diameter (120 /spl mu/m) POF. For all data transmission experiments bit-error rates (BERs) of better than 10/sup -11/ were observed for back-to-back testing as well as for fiber transmission.

In recent years, optical manipulation has gained increasing interest, especially in combination with microfluidics. This combination offers promising tools for a fast and cost-effective sample analysis and manipulation. The contamination-free handling of micrometer-sized particles without any mechanical contact is an attractive tool for biology and medicine. VCSELs (vertical-cavity surface-emitting lasers) are an excellent choice for the trapping lasers, offering the opportunity of parallel particle manipulation by using two-dimensional VCSEL arrays, and of miniaturization by means of integration. In this paper, we present two novel concepts for the realization of the so-called integrated optical trap, resembling a strongly miniaturized version of the typically bulky setup of an optical trap. For this purpose, AlGaAs-GaAs-based VCSEL arrays with a very small device pitch were fabricated. We show the realization of integration-ready particle manipulation devices, both with top-emitting and with bottom-emitting densely packed VCSEL arrays. The smallest pitch of 18 μm is achieved with bottom-emitting VCSEL arrays, having mesa diameters of only 16 μm.

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.

We have developed high power vertical cavity surface emitting lasers (VCSELS) for multimode or single mode operation. We have characterized new cavity designs for individual lasers and 2-dimensional VCSEL arrays to maximize output power. Using broad area high power VCSELS under pulsed excitation, we have demonstrated the triggering of a photoconductive semiconductor switch (PCSS) with a VCSEL. We also have developed designs for high output power in a single mode. The first approach is to engineer the oxide aperture profile to influence the optical confinement and thus modal properties. A second approach focuses on "leaky-mode" concepts using lateral modification of the cavity resonance to provide the lateral refractive index difference. To this end, we have developed a regrowth process to fabricate single-mode VCSELS. The overall objective of this work was to develop high-power single-mode or multimode sources appropriate for many applications leveraging the many inherent advantages of VCSELS.

This study investigates the thermal design of 2-D vertical-cavity surface-emitting laser (VCSEL) arrays for optical output power improvement. Considering the temperature dependencies of bias current, internal quantum efficiency, internal optical loss, and thermal resistance of each array cell, a compact electro-opto-thermal model of 2-D VCSEL arrays with linear power dissipation and quadratic power dissipation in each array cell is established to study the effects of array cell spacing and layout on the device performance. At the same time, the power dissipation mechanisms contributing to thermal rollover are also studied. It is found that the array cell spacing has a strong influence on the linear power dissipation, and the layout (such as hexagonal design) influences quadratic power dissipation obviously. With the careful design of array cell spacing and layout, both the temperature profile and the thermal resistance matrix of VCSEL arrays are improved, which is helpful to delay the onset of thermal rollover and hence enhance the optical output power. The simulation results are consistent with experimental results.

In this paper we present a device concept for long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the InGaAlAs/InP material system incorporating a buried tunnel junction (BTJ). A major issue of long-wavelength VCSELs is the dissipation of heat because of the low thermal conductivity of ternary and quaternary alloys. With the BTJ-VCSEL, a significant reduction of the thermal resistance is achieved by the use of a hybrid backside mirror made of a stack of amorphous dielectrics with Au-coating and the monolithic integration of a heat sink. These provide improved heat sinking capability compared to a conventional epitaxial semiconductor DBR. In addition, the tunnel junction facilitates a substitution of most of the p-doped layers by n-doped material, reducing heat generation due to ohmic losses. These features significantly improve the VCSEL characteristics. At 1.55 μm wavelength, we demonstrated single-mode cw-output powers of 1.7mW at room temperature [1], multi-mode cw-output powers of 7mW [2], laser operation up to heat sink temperatures of 110 °C [2], and optical data transmission with 10 Gbit/s and low bit error rates [3]. These are record values to the best knowledge of the authors. Using strained quantum wells, the emission wavelength can be tailored to any value in the range between 1.3 μm and 2.0 μm [4], sample results are presented for the telecommunication wavelengths 1.3 μm and 1.55 μm, 1.8 μm, and the currently upper limit of 2.0 μm. The slight wavelength tuning with driving current is brought about by the tiny volume of the devices and makes VCSELs ideal components for tunable diode laser absorption spectroscopy (TDLAS) [5, 6]. The maximum detuning typically reaches 4 nm (≙500 GHz). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Vertical-cavity surface-emitting laser (VCSEL) arrays that can emit orthogonally polarized light have shown broad application potential and market demand in the fields of optical communication, optical sensors, and biomedicine. Two kinds of polarization-switching VCSEL arrays based on anti-parallel (AP) oriented liquid crystal (LC) external cavities and twisted nematic (TN) oriented LC external cavities are proposed in this paper. The light is independently guided by the LC electrically, achieving uniform lasing of linearly polarized light with mutually orthogonal polarization modes and equal power. The uniformity and polarization tunable ability of the lasing orthogonally polarized light power is guaranteed by the integration of the LC external cavity and the VCSEL array.

A novel two-dimensional near-field optical system has been studied to realize more effective and simple optical disk of the high memory capacity and fast data transfer rate. This parallel optical memoryis based on a multi-beam recording/reading head and a small spot size using the vertical cavity surface emitting laser (VCSEL) microprobe array as an evanescent light source. In this research, we have simulated the optical efficiency and spot size of near-field optical heads using the FDTD method and understood the best structuraldesign of pyramidal microprobes having an asymmetric metal coating. The microprobe array head has been also realized using the micro-fabrication processes of Si and GaP wafer with a newly developed apertureformation technique. The research will continue to complete the parallel near-field optical disk of 1000Gbit/in2 data capacity and 10 Gbps transfer rate with the integration of the VCSEL array and microprobe array having high optical efficiency.

A simple formalism is reported for studying the modes of an infinite two-dimensional (2-D) phase-locked array of vertical-cavity surface-emitting diode lasers. In this approach, the Helmholtz equation is approximately separated into products of solutions of the associated one-dimensional (linear) arrays. This formalism allows the knowledge gained from years of research into the modal properties of linear diode arrays to be applied directly to 2-D arrays. As a result, it is expected that both 2-D gain-guided and index-guided arrays (except those with excess gain in the low-index channels) will lase in the high-order mode characterized by emission into four distinct off-axis far-field lobes. In contrast, it is expected that properly constructed 2-D leaky-mode arrays would lase preferentially in the fundamental mode well above threshold.

We achieve 13.5 mW optical output power, 48% power conversion efficiency, 1.17 W/A slope efficiency and 17 kW/cm2 laser power density with top-surface-emitting 940 nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The physical mechanism of minimum threshold current generation in oxide-confined VCSEL has been thoroughly studied theoretically and experimentally. Further, we also succeeded in 90.8 mW optical output power, 40% power conversion efficiency with 2 × 4 VCSEL arrays. We find an increase in output power and PCE of 2 × 2 VCSEL arrays as we increase the array spacing which we attribute primarily to increased heat dissipation and reduced thermal crosstalk between the emitters. Thermal properties in oxide-confined 2 × 2 VCSEL arrays were analyzed numerically and experimentally. The simulated results are in good agreement with the measurement. It is proved that theoretical simulation is very useful for the future device optimization.

Construction of optoelectronic memory arrays with signals optical input-output is the actual problem, because it allows removing from the record-storage- reading process ineffective optical-electronic and electronic-optical conversion. This increases the speed of the memory arrays. Construction of 2-D memory elements, based on optically controlled electroabsorption modulators with a large number of quantum wells using the quantum Stark effect, and vertical cavity surface emitting lasers (VCSEL) arrays is considered. The technology combining optically controlled electroabsorption modulators and VCSEL arrays for production cascades of connected 2-D arrays of memory based on developed optoelectronic asynchronous RS-trigger¹ and optoelectronic synchronous RS-trigger, which allows to create asynchronous and synchronous arrays of optoelectronic memory is suggested. Possibility of 2-D arrays aggregation is done by means of their serial connection due to appropriate organization of interconnections and by increasing the dimensionality via connection of similar 2-D arrays of both vertically and horizontally. Optoelectronic circuit memory cells based on optically controlled electroabsorption modulators and VCSEL arrays with the appropriate organization of interconnections. They can be built on the base of asynchronous RS-trigger and optoelectronic synchronous RS-trigger. The use of VCSEL with coupled cavities as input and output 2-D arrays for optoelectronic memory cascades is considered.

Vertical cavity surface-emitting laser (VCSELs) have large mode spacing due to the very short cavity and are particularly suitable for continuous wavelength tuning. In addition, the low threshold currents, low beam divergence angles, and their ability to form two-dimensional arrays make them attractive for free-space optical interconnect applications. In this paper, we demonstrate a continuously tunable, individually addressable 8/spl times/6 VCSEL array using integrated heaters. VCSELs with a mesa size of 12 /spl mu/m/spl times/12 /spl mu/m exhibit a threshold current of 4.2 mA, output power of 1.2 mW (cw, room temperature), and continuous tuning range of 10 nm are obtained.