Red VCSELs Research Articles

49‐2: Invited Paper: Blue and Green VCSEL for Full‐Color Display

VCSELs have recently received increasing attention from engineers and scientists. The progress of the research on GaN‐based VCSELs that allowed blue and green emissions are often one of the main topics discussed in this field. Combining these lasers with existing red VCSELs realized a full‐color light source with superior characteristics of VCSELs, such as small power consumption, circular beam profiles, and arraying ability. These features should be suitable for displays, for example, AR displays. In this report, a brief review of the recent progress regarding these VCSELs and their future applications is provided.

Advances in Red VCSEL Technology

Red VCSELs offer the benefits of improved performance and lower power consumption for medical and industrial sensing, faster printing and scanning, and lower cost, higher speed interconnects based upon plastic optical fiber (POF). However, materials challenges make it more difficult to achieve the desired performance than at the well-developed wavelength of 850 nm. This paper will describe the state of the art of red VCSEL performance and the results of development efforts to achieve improved output power and a broader temperature range of operation. It will also provide examples of the applications of red VCSELs and the benefits they offer. In addition, the packaging flexibility offered by VCSELs, and some examples of non-Hermetic package demonstrations will be discussed. Some of the red VCSEL performance demonstrations include output power of 14 mW CW at room temperature, a record maximum temperature of 115∘C for CW operation at an emission wavelength of 689 nm, time to 1% failure at room temperature of approximately 200,000 hours, lifetime in a 50∘C, 85% humidity environment in excess of 3500 hours, digital data rate of 3 Gbps, and peak pulsed array power of greater than 100 mW.

Optical in-situ process control yields optimized red VCSELS

Optical in-situ process control yields optimized red VCSELS

Low-threshold and high-temperature operation of InGaAlP-based proton-implanted red VCSELs

Low-threshold and high-temperature operation of InGaAlP-based proton-implanted red VCSELs

Low threshold current densities in red VCSELs

In this work, we have investigated the design and metalorganic vapor-phase epitaxial growth of red vertical cavity surface-emitting lasers (VCSEL, emission wavelength around 650–680 nm) with respect to low threshold current densities and a reduced temperature dependence. A VCSEL in the red regime implies a combination of AlGaInP (cavity) and AlGaAs/AlAs (distributed Bragg reflectors). In order to check the influence of the epitaxially critical P/As-interface on the laser performance, we have grown edge-emitting lasers where we varied the distance between this interface and the active quantum wells. We observed no increase of the threshold currents even for small distances as necessary in VCSEL structures when applying an optimized switching sequence at these interfaces. Consequently, red VCSELs could be grown which showed continuous wave operation at room temperature (670 nm, 0.15 mW at 20°C). In order to improve the temperature sensitivity of these VCSELs, we have studied a large number of devices with well-defined misalignment between gain and Bragg mirror reflectivity. For lasers where this misalignment resulted in somewhat worse room temperature properties (e.g. threshold current densities around 800 A/cm 2), we found a clearly enhanced temperature stability.

Fabrication of low-threshold red VCSELs

Red vertical cavity lasers (VCSELs) are ideally suited as optical sources for plastic optical fibre networks. These networks will form the communication backbone of future automobiles and aircraft replacing the current copper networks. However VCSELs at these wavelengths are difficult to realise due to the lower refractive index offsets and unsuitable band structure alignments. The Esprit BREDSELS project has addressed the design, growth and fabrication of low threshold red VCSELs. This paper reports the fabrication of record low threshold (200 μA at 20°C) VCSELs at a wavelength of 665 nm. This device performance has been achieved through the use of selective oxidation techniques. The devices operate CW to 50°C. The trade off between low threshold and high power will be discussed.

High-frequency modulation characteristics of red VCSELs

The authors have measured small- and large-signal modulation response characteristics of a red VCSEL (λ = 670 nm). A small-signal 3 dB bandwidth of 11 GHz was recorded at a bias current of 16 mA. The small-signal response for each bias current was fit to an analytic model to determine the resonance and damping factor. From these data the differential gain coefficient and K-factor were estimated. Large signal digital measurements were conducted showing suitability of this device for data communication applications. An open eye diagram at the receiver output is presented with no pre-bias current applied and the VCSEL modulated at 155 Mbit/s demonstrating the possibility of direct logic-level drive.

Large- and small-signal modulation properties of red (670 nm) VCSELs

The large- and small-signal properties of red GaInP-AlGaInP triple QW VCSELs (670 nm) were measured. For the fundamental mode the small signal bandwidth is 2 GHz. Large-signal modulation up to 1.5 Gb/s is achievable with a prebias. The turn-on delay of unbiased devices is found to saturate due to heating from the average of the data signal.