Vertical-cavity electrically driven lasers with three GaInAs
quantum wells and diameters of several μm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength.

Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers

By doping an organic compound functioning as an electron donor (hereinafter referred to as donor molecules) into an organic compound layer contacting a cathode, donor levels can be formed between respective LUMO (lowest unoccupied molecular orbital) levels between the cathode and the organic compound layer, and therefore electrons can be injected from the cathode, and transmission of the injected electrons can be performed with good efficiency. Further, there are no problems such as excessive energy loss, deterioration of the organic compound layer itself, and the like accompanying electron movement, and therefore an increase in the electron injecting characteristics and a decrease in the driver voltage can both be achieved without depending on the work function of the cathode material.

Light Emitting Device

The vertical-cavity surface-emitting laser (VCSEL) has become a light source of great importance for industrial and consumer applications. This includes communication and sensing in particular, where dynamics and optical mode behavior are key performance characteristics. This tutorial treats relevant VCSEL basics, performance requirements and recent progress toward higher speed, higher single-mode power, and polarization control.

Advances in VCSELs for Communication and Sensing

The vast majority of optical links within the data center are based on vertical cavity surface emitting lasers (VCSELs) operating at 850 nm over multimode optical fiber. Deployable links have evolved in speed from 1 Gb/s in 1996 to 28 Gb/s in 2014. Serial data links at 40 and 56 Gb/s are now under development and place even more demand on the VCSEL and photodiodes. In this paper, we present the characteristics of VCSELs and photodiodes used in current generation 28 Gb/s links and present several methods to extend link distances using more advanced data encoding schemes. Finally, we will present results on wavelength division multiplexing on multimode optical fiber that demonstrate 40 Gb/s Ethernet connections up to 300 m on duplex OM3 optical fiber, and present results on fiber optimized for modal bandwidth in the 850 to 980 nm range.

VCSEL-Based Interconnects for Current and Future Data Centers

A method and structure for stabilizing an array of micro devices is disclosed. The array of micro devices is formed on an array of stabilization posts formed from a thermoset material. Each micro device includes a bottom surface that is wider than a corresponding stabilization post directly underneath the bottom surface.

Micro device stabilization post

Vertical-cavity surface-emitting lasers (VCSELs) are the ideal optical sources for data communication and sensing. In data communication, large data rates combined with excellent energy efficiency and temperature stability have been achieved based on advanced device design and modulation formats. VCSELs are also promising sources for photonic integrated circuits due to their small footprint and low power consumption. Also, VCSELs are commonly used for a wide variety of applications in the consumer electronics market. These applications range from laser mice to three-dimensional (3D) sensing and imaging, including various 3D movement detections, such as gesture recognition or face recognition. Novel VCSEL types will include metastructures, exhibiting additional unique properties, of largest importance for next-generation data communication, sensing, and photonic integrated circuits.

https://depositonce.tu-berlin.de/bitstream/11303/13913/1/Liu_etal_2021.pdf

Vertical-cavity surface-emitting lasers for data communication and sensing

The design, fabrication, and performance of the presently most energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. We employ a novel current spreading layer to reduce differential resistance. Compared to our previous designs, a higher indium content is used in the InGaAs quantum wells to increase the differential gain at low injected current densities. The influence of the oxide aperture diameter on the energy efficiency is determined by comparing the key performance parameters for a batch of VCSELs produced on the same epitaxial wafer, but with varying aperture diameters from 2.5 to 9.0 μm. The static light output power-current-voltage characteristics, small-signal modulation response, and large signal performance of our VCSELs are investigated in detail. The parameters important for energy-efficient operation are analyzed including threshold current, differential quantum efficiency, and differential resistance. We observe that our single-mode VCSELs are more energy efficient than our multimode VCSELs, although our multimode VCSELs typically exhibit a larger maximum static wallplug efficiency. Error-free (defined as a bit error ratio <;1 × 10 -12) data transmission at 25 Gb/s with a record-low dissipated heat energy of only 56 fJ/bit is achieved using a single-mode VCSEL with an oxide aperture diameter of 3.5 μm.

Energy Efficiency of Directly Modulated Oxide-Confined High Bit Rate 850-nm VCSELs for Optical Interconnects

New oxide-confined 980-nm vertical-cavity surface-emitting lasers (VCSELs) with record temperature-stable small-signal bandwidths of 25.6 to 23.0 GHz at 25 to 85 °C are designed, fabricated, and characterized. Technology-based device parameters essential for system-level models of VCSEL-based short-reach and ultrashort-reach optical interconnects are extracted. These parameters include key intrinsic figures-of-merit, including the −3-dB modulation bandwidth, the bandwidth-to-electrical power ratio, and device input impedance, all as functions of temperature, oxide-aperture diameter, and desired range of bias current or current density. Further, the M-factor, relating the intrinsic VCSEL bandwidth to the error-free bit rate for a given external systems configuration and application, is introduced. Our present 980-nm VCSEL technology is capable of 40 Gb/s operation at 85 °C at a simultaneously low current density of 10 kA/cm2 with an energy of only 100 fJ per bit.

Impact of the Oxide-Aperture Diameter on the Energy Efficiency, Bandwidth, and Temperature Stability of 980-nm VCSELs

We present extremely energy-efficient oxide-confined 850-nm single-mode vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects. Error-free transmission at 17 Gb/s across 1 km of multimode optical fiber is achieved with an ultra-low energy-to-data ratio of 99 fJ/bit, corresponding to a record-low energy-to-data-distance ratio of 99 fJ/(bit ·km). This performance is achieved without changing any of the driving parameters up to 55 °C. To date our VCSELs are the most energy-efficient directly modulated light-sources for data transmission across all distances up to 1 km of multimode optical fiber.

99 fJ/(bit $\cdot$ km) Energy to Data-Distance Ratio at 17 Gb/s Across 1 km of Multimode Optical Fiber With 850-nm Single-Mode VCSELs

With the separation of optical and current apertures, photonic crystal vertical-cavity surface-emitting lasers can reach a 3-dB small-signal modulation bandwidth of > 18 GHz while lasing in the fundamental mode. Because of reduced chromatic dispersion, such devices enable error-free transmission over 1-km OM4 multimode fiber at a data rate of 25 Gb/s and operating at a current density of 5.4 kA/cm2. This can potentially lead to a laser source that is useful for rack-to-rack transmissions in large data centers and potentially long device lifetime.

James A. Lott

Papers

Vertical-cavity surface-emitting lasers for data communication and sensing

Energy Efficiency of Directly Modulated Oxide-Confined High Bit Rate 850-nm VCSELs for Optical Interconnects

Impact of the Oxide-Aperture Diameter on the Energy Efficiency, Bandwidth, and Temperature Stability of 980-nm VCSELs

99 fJ/(bit $\cdot$ km) Energy to Data-Distance Ratio at 17 Gb/s Across 1 km of Multimode Optical Fiber With 850-nm Single-Mode VCSELs

Error-Free Transmission Over 1-km OM4 Multimode Fiber at 25 Gb/s Using a Single Mode Photonic Crystal Vertical-Cavity Surface-Emitting Laser