Parallel Confocal Microscope using Vertical-Cavity Surface Emitting Laser Array

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.

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.

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 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.

An optical levitation and translation method for a microscopic particle by use of the resultant force induced by multiple light beams is studied. We show dependence of the radiation pressure force on the illuminating distribution by numerical calculation, and we find that the strongest axial force is obtained by a specific spacing period of illuminating beams. Extending the optical manipulation technique by means of vertical-cavity surface-emitting laser (VCSEL) array sources [Appl. Opt. 40, 5430 (2001)], we are the first, to our knowledge, to demonstrate levitation of a particle and its translation while levitated by using a VCSEL array. The vertical position of the target particle can be controlled in a range of a few tens of micrometers with an accuracy of 2 microm or less. The analytical and experimental results suggest that use of multiple beams is an effective method to levitate a particle with low total illumination power. Some issues on the manipulation method that uses multiple beams are discussed.

Cavity interactions due to lateral fringe field overlap or stray reflections from optical elements in a vertical-cavity surface-emitting laser (VCSEL) array based interconnects are studied. Interacting cavity pairs act as coupled oscillators. Depending on the bit sequence the cavity that switches on first acts as a master oscillator that affects the switch on jitter for the other. Earlier analytic formalism for the bit error rate (BER) is extended to include the influence of the cavity coupling strength on the switch on jitter. Analytic results, including pre-biasing, demonstrate the potential for a large degradation in BER at small coupling strengths, if anti-phasing develops during bit coupling. Numerical results show that extreme cases result into complete pulse suppression (bit skipping). On the other hand, achieving in-phase coupling among bits improves BER.

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.

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.

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.

Vertical-cavity surface-emitting laser (VCSEL) arrays are a key light source for high-speed data transmission in Co-Packaged Optics (CPO). In VCSEL array packaging, Au–Au bump bonding is commonly used to connect the VCSEL array to the substrate. However, the force applied to flatten Au bumps during the flattening process, along with the layout of the cold-work die steel bonding head in the Au-Au bonding process, affects both the mechanical and optical performance of the VCSEL array. In this work, the effects of Au bump flattening force and bonding head design on VCSEL array packaging are systematically investigated through a combination of experiments and Finite Element Analysis (FEA). Flattening forces of 500 gF, 1000 gF, and 2000 gF were evaluated to study Au bump mechanical before bonding the Au-Au bump. Results show that increasing flattening force improves bump flatness but significantly increases equivalent stress and induces corner cracking. A flattening force of 500 gF provides an optimal balance between flatness and mechanical integrity. Furthermore, two bonding head layouts were compared during Au–Au bonding process at 310°C. The type 1 bonding head applies uniform force over the entire VCSEL surface, resulting in lower equivalent stress but causing surface damage and reduced luminance due to direct contact with the emitting area. In contrast, the type 2 bonding head avoids direct contact with the emission region, achieving higher overall luminance. However, it introduces a non-uniform force distribution and higher Au bump equivalent stress. These results provide critical insights for optimizing Au bump processing and bonding head geometry, enabling more reliable and high-performance VCSEL array packaging for next-generation CPO applications.

Two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays are defined using an etched photonic crystal pattern and ion implantation. The 2×2 laser arrays are shown to operate in a single in-phase mode from threshold to maximum output power. The in-phase interference between the multiple lasers constituting the array form an angularly narrow, on-axis peak in the far field. These coherently-coupled laser arrays are of interest owing to their ease of fabrication and potential for creating low-diffraction beams with increased output power.

A high-density multi-point LAPS set-up using a VCSEL array and FPGA control

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.

In this paper, we report high performance 850 nm bottom-emitting arrays of vertical-cavity surface-emitting lasers (VCSELs) wafer-bonded on sapphire substrates.