High-speed VCSEL Research Articles

Synergistic effect of proton irradiation and electrical stress on high-speed 850 nm vertical-cavity surface-emitting lasers

The synergistic effect significantly impact VCSEL's reliability for potential applications in spatial data communication. The synergistic effect of 3 MeV proton irradiation and electrical stress on 850 nm high-speed VCSELs is investigated. The degradation of VCSEL slow down under the influence of bias current. However, device degradation is more pronounced during irradiation under high bias current density. Low frequency noise (LFN) analysis results indicate that defects induced by proton irradiation are the primary cause of the optical-electrical parameter degradation in the device. The bias current density significantly influences the final defect yield, leading to variations in the degree of degradation after irradiation at different bias currents. At a bias current density of 6.03 × 105 A/m2, the degradation of the modulation bandwidth is reduced in comparison to the unbiased state. A mechanism investigation into the synergistic effect of proton irradiation and electrical stress on VCSELs lends support for accurately evaluating the radiation hardness of optical communication system composed of VCSELs in harsh radiation environments.

Word length dependent sensitivity penalty in high speed VCSEL based optical interconnects

Word length dependent sensitivity penalty in high speed VCSEL based optical interconnects

Progress in Short Wavelength Energy-Efficient High-Speed Vertical-Cavity Surface-Emitting Lasers for Data Communication

The current progress of energy-efficient high-speed VCSELs based on GaAs substrates is presented. Novel approaches for the design of VCSELs are presented, potentially leading to larger bandwidth bit rates and lower power consumption. The first approach is based on the optimization of the VCSEL photon lifetime. The second one introduces a novel design based on oxidizing the apertures from multiple etched holes of varying geometries. These designs are also essential for improving the energy efficiency of future modules by optimizing the match of the electronic driver and the photonic device.

50 Gbit/s PAM4 Data Transmission Over 500-m Single-Mode Fiber Using an 880-nm Single Mode VCSEL

Error-free 50 Gbit/s PAM4 data transmission over 500-m single mode fiber was successfully realized using our oxide-confined 880-nm single-mode high-speed VCSELs. This transmission was accomplished because of the flat frequency response of the VCSEL across a wide bias span. Static characteristics and high-speed modulation properties at room temperature and high operation temperature were studied in detail. Data transmission experiments for the 880-nm VCSEL with 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> oxide-aperture diameter was performed. A 50-Gbps PAM4 module was packaged for data transmission. Error-free 50 Gbit/s PAM4 data transmission over 500-m single mode fiber was successfully realized. The proposed VCSEL is fit for the 400G DR8 module because of its 500-m single-channel 50 Gbit/s error-free transmission. Compared with commonly used DML, VCSELs are evidently advantageous in cost and power consumption.

Numerical Investigation of Optical and Photoelectric Properties for 850 nm VCSELs with Arbitrary Crystal Orientation

High-speed VCSELs are widely used for high-capacity, short-range data communication links. Here, we numerically investigate the optical and electronic properties of a crystal orientation-dependent 1.06% compression InGaAs-AlGaAs laser emitting around 850 nm. The reduction of the density of states is observed in the largest energy range for the quantum well in the (110) orientation compared with the conventional (001) orientation. The calculated transparency carrier density decreases from 2.74 × 1018 cm−3 to 1.88 × 1018 cm−3 with the gain coefficient rising from 4969.4 cm−1 to 5427.2 cm−1 in (110) orientation. The 3 dB bandwidth of 31.25 GHz is realized in the (110) orientation, which can support 60 Gbps (NRZ) applications.

Directly Modulated VCSELs With Frequency Comb Injection for Parallel Communications

We propose a comb-locked multi-channel transmitter with high-speed VCSELs injection-locked by an optical frequency comb. VCSEL dynamics are analyzed with various injection parameters including number of comb tones, frequency detuning, and injection ratio. We evaluate the performance of filtering and amplification effect when multiple comb tones injection into single VCSEL and estimate the transmission performance considering the reflection from VCSEL. Compared to intrinsic parameters of VCSEL, a 2-fold increase in frequency response and a $2.6\times 10^4$ -fold reduction in linewidth have been verified experimentally when the bandwidth-limited VCSEL locked to an incident comb line. 14-Gb/s single-lane transmission is demonstrated through 20 km single-mode fiber based on a 3.4-GHz VCSEL without any dispersion compensation. The similar performance can be achieved for all generated 25 comb tones, verifying a potential high-capacity transmitter with distinct feature of two-dimensional VCSELs.

Electro-Optical Co-Design of Power-Efficient 100-Gbps/λ VCSEL Transmitter

In this paper, we propose a comprehensive electro-optical co-design framework for power-efficient high-speed VCSEL transmitter targeting at 50 Gbaud. The framework integrates a rate-equation based VCSEL chip model and driver circuit models. Subject to the transmitter specifications defined by IEEE 400G standard, the driver circuit design of NRZ and PAM-4 modulations, together with the energy efficiency of transmitter, is analyzed and compared for two types of 20-GHz class VCSELs with different damping factors while keeping the same parasitic parameters. For NRZ modulation, analysis results indicate that both types of VCSEL transmitters show similar achievable data rate and energy efficiency. Both types of VCSEL transmitters are beneficial with small driver resistance in order to achieve high-speed signaling integrity. The best energy efficiency for both types of VCSEL transmitters is 520.8 fJ/bit under NRZ modulation. For PAM-4 modulation, higher achievable data rate can be reached by the over-damped VCSEL transmitter compared with the under-damped one, for which trade-offs of choosing the appropriate driver parameters are required for high-speed operation. The optimized over-damped VCSEL transmitter can have 16.13% higher achievable data rate and around 4.12% of energy efficiency improvement compared with the under-damped counterpart, but the signal quality is more sensitive to driver parameters. The best energy efficiencies are 365.1 fJ/bit and 380.8 fJ/bit for the over- and under-damped VCSEL transmitter under PAM-4 modulation. This co-design framework can provide a guidance in the VCSEL enabled co-packaging design.

Application-Oriented Investigation of Parasitic Limitation on Multilevel Modulation of High-Speed VCSELs

In this paper, we present an application-oriented investigation of parasitic limitation on the large signal performance of VCSELs when multilevel modulation is applied. VCSELs with different damping are taken into consideration. The parasitic parameters are extracted by fitting the measured $S_{11}$ data toward a frequency of 40 GHz. In the large signal analysis, four-level pulse amplitude modulation (PAM-4) signaling is embedded into the tool of VCSEL integrated spatio-temporal advanced simulator (VISTAS) and analyzed with extracted parameters. The transmitter and dispersion eye closure quaternary (TDECQ) of the 50-Gb/s PAM-4 signals from VCSEL model is evaluated to understand the relationship between parasitic parameters and signal quality. It is found that the over-damped VCSEL would benefit from larger parasitic bandwidth for PAM-4 modulation while the under-damped VCSEL with moderate parasitic bandwidth would present the best large signal response for PAM-4 modulation. The results indicate that for multilevel modulation, the parasitic parameters need to be carefully designed according to the VCSEL intrinsic parameters to achieve better large signal performance. By co-optimizing the key parasitic parameters, the parasitic circuit design criteria for each type of VCSEL are provided to obtain the best large signal performance under multilevel modulation. The results could provide a designing guidance for VCSELs aiming at multilevel modulation applications.

Growth and fabrication of 850 nm AlGaAs/GaAs vertical cavity surface emitting laser structure

In this work, we demonstrate the NIP’s all in-house development of a vertical cavity surface emitting laser structure. The VCSEL structure grown via MBE consists of an AlAs/AlGaAs distributed Bragg reflector and an AlGaAs/GaAs quantum well designed to issue at the 850 nm region. Reflectance spectroscopy showed that the stop band is centered around the designed wavelength. The electroluminescence spectra displayed that the maximum light emission corresponded to its design. This is a crucial step in the NIP’s development of semiconductor lasers, leading towards future high-speed and highly-tunable VCSEL devices.

Impact of damping on high speed 850 nm VCSEL performance * * Project supported by the National Natural Science Foundation of China (Nos. 61335004, 61675046, 61505003), the Open Fund of IPOC2017B011 (BUPT).

High speed VCSELs are important optical devices in short-reach optical communication links and interconnects because of their low cost and high modulation speeds. In this paper, the impact of damping on the their static and dynamic characteristics is analyzed and demonstrated. Through the shallow corrosion of the top layer DBR, the VCSELs with different damping is designed and fabricated. With the increase of the surface etch depth from 0 to ~55 nm for 9 μm oxide-aperture VCSEL, the K factor related with the damping is reduced from 0.31 to 0.23 ns−1. When the etch depth of the VCSEL with 9 μm oxide-aperture is decreased to ~25 nm, output power is increased from 4.03 to 4.70 mW and small signal modulation bandwidth is also increased from 15.46 to 16.37 GHz. It shows that there is a tradeoff between damping and differential gain for improving modulation speed.

An integrated OADM based on Bragg trans-reflectance in 1550 nm VCSEL optical fibre access networks

We experimentally demonstrate an all passive OADM using a single BGF, a pair of optical circulators and the low cost and energy efficient VCSELs. In this study, double reflection due to Bragg effect on a single fibre grating has been used to create drop and add multiplexers at 1549.9 nm wavelength with 31.4 dB wavelength isolation ratio. In performance evaluation at the 10−9 BER threshold level, a 0.3 dB add and drop receiver penalty for a 8.5 Gb/s data signal is incurred while a 0.8 dB transmission penalty is incurred for ∼25.5 km fibre distance. Using optical trans-reflectance, this paper, provides a less costly and less power consuming channel management using OADMs for high speed VCSEL transmission.

Comparative study on stained InGaAs quantum wells for high-speed optical-interconnect VCSELs

The gain-carrier characteristics of InGaAs quantum well for 980 nm high-speed, energy-efficient vertical-cavity surface-emitting lasers are investigated. We specially studied the potentially InGaAs quantum well designs can be used for the active region of energy-efficient, temperature-stable 980-nm VCSEL, which introduced a quantum well gain peak wavelength-to-cavity resonance wavelength offset to improve the dynamic performance at high operation temperature. Several candidate quantum wells are being compared in theory and measurement. We found that ∼5 nm InGaAs QW with ∼6 nm barrier thickness is suitable for the active region of high-speed optical interconnect 980 nm VCSELs, and no significant improvement in the 20% range of In content of InGaAs QWs. The results are useful for next generation green photonic device design.

LDQ10: a compact ultra low-power radiation-hard 4 × 10 Gb/s driver array

A High-speed and low-power VCSEL driver is an important component of the Versatile Link for the high-luminosity LHC (HL-LHC) experiments. A compact low-power radiation-hard 4 × 10 Gb/s VCSEL driver array (LDQ10) has been developed in 65 nm CMOS technology. Each channel in LDQ10 can provide a modulation current up to 8 mA and bias current up to 12 mA. Edge pre-emphasis is employed to compensate for the bandwidth limitations due to parasitic and the turn-on delay of VCSEL devices. LDQ10 occupies a chip area of 1900 μm × 1700 μm and consumes 130 mW power for typical current settings. The modulation amplitude degrades less than 5% after 300 Mrad total ionizing dose. LDQ10 can be directly wire-bonded to the VCSEL array and it is a suitable candidate for the Versatile Link.

850-nm VCSELs With p-Type $\mathrm {{\delta }}$ -Doping in the Active Layers for Improved High-Speed and High-Temperature Performance

In this paper, we study the influence of p-type modulation doping on the dynamic/static performance of high-speed 850-nm VCSELs with highly strained multiple quantum wells. The studied device structure has a 3/ $2~\lambda $ asymmetric cavity design, which can let the internal transit time of injected carriers be as short as that of 1/ $2~\lambda $ cavity design and further improve its performance in terms of speed and output power for high single-mode operation. Our proposed VCSEL structure with p-type doping shows superior modulation speed with an output power comparable with that of the un-doped reference device under room temperature operation. Furthermore, when the operating temperature reaches 85 °C, there is a significant improvement in both the modulation speed and maximum power of the p-doped structures. According to our simulation, this can be attributed to the change in the quasi-Fermi levels of the injected carriers after the addition of p-doping in the active layers, which minimizes the electron leakage under high-temperature operation.

High-Speed VCSELs With Strong Confinement of Optical Fields and Carriers

We present the design, fabrication, and performance of our latest generation high-speed oxide-confined 850-nm vertical-cavity surface-emitting lasers. Excellent high-speed properties are obtained by strong confinement of optical fields and carriers. High-speed modulation is facilitated by using the shortest possible cavity length of one half wavelength and placing oxide apertures close to the active region to efficiently confine charge carriers. The resulting strong current confinement boosts internal quantum efficiency, leading to low threshold currents, high wall-plug efficiency, and state-of-the-art high-speed properties at low bias currents. The temperature dependent static and dynamic performance is analyzed by current-power-voltage and small-signal modulation measurements.

An optimized design based on coaxial packaging of the high speed VCSEL

An optimized design based on coaxial packaging of the high speed VCSEL

Active inductor shunt peaking in high-speed VCSEL driver design

An all-transistor active-inductor shunt-peaking structure has been used in a prototype of 8 Gbps high-speed VCSEL driver which is designed for the optical link in ATLAS liquid Argon calorimeter upgrade. The VCSEL driver is fabricated in a commercial 0.25 μm Silicon-on-Sapphire (SoS) CMOS process for radiation tolerant purpose. The all-transistor active-inductor shunt-peaking is used to overcome the bandwidth limitation from the CMOS process. The peaking structure has the same peaking effect as the passive one, but takes a small area, does not need linear resistors and can overcome the process variation by adjust the peaking strength via an external control. The design has been taped out, and the prototype has been proven by the preliminary electrical test results and bit error ratio test results. The driver achieves 8 Gbps data rate as simulated with the peaking. We present the all-transistor active-inductor shunt-peaking structure, simulation and test results in this paper.

0.18㎛ CMOS 3.1Gb/s VCSEL Driver 코아 칩 설계

We propose a novel driver circuit design using CMOS process technology that drives a 1550 nm high-speed VCSEL used in optical transceiver. We report a distinct improvement in bandwidth, voltage gain and eye diagram at 3.1Gb/s data rate in comparison with existing topology. In this paper, the design and layout of a 3.1Gb/s VCSEL driver for optical transceiver having arrayed multi-channel of integrating module is confirmed.

AlGaInAsPSb-based high-speed short-cavity VCSEL with single-mode emission at 1.3 μm grown by MOVPE on InP substrate

In this paper we present the first InP-based short-cavity Vertical-Cavity Surface-Emitting Laser with an AlGaInAsP/GaInAsP active region and a re-grown and structured GaAs0.51Sb:C/Ga0.47InAs:Si buried tunnel junction (BTJ), which serves as current aperture, grown by LP-MOVPE. We achieved over 1mW single-mode continuous-wave (cw) emission at around 1.3μm wavelength and room-temperature. The small-signal modulation bandwidth exceeds 7.5GHz, which is appropriate for 10Gb/s data transmission, and the series resistance is as low as 24Ω. The latter value indicates around three times lower dissipated power consumption than comparable MOVPE grown InP-based VCSELs.

Active Region Design for High-Speed 850-nm VCSELs

Higher speed short-wavelength (850 nm) VCSELs are required for future high-capacity, short-reach data communication links. The modulation bandwidth of such devices is intrinsically limited by the differential gain of the quantum wells (QWs) used in the active region. We present gain calculations using an 8-band k·p Hamiltonian which show that the incorporation of 10% In in an InGaAs/AlGaAs QW structure can approximately double the differential gain compared to a GaAs/AlGaAs QW structure, with little additional improvement achieved by further increasing the In composition in the QW. This improvement is confirmed by extracting the differential gain value from measurements of the modulation response of VCSELs with optimized InGaAs/AlGaAs QW and conventional GaAs/AlGaAs QW active regions. Excellent agreement is obtained between the theoretically and experimentally determined values of the differential gain, confirming the benefits of strained InGaAs QW structures for high-speed 850-nm VCSEL applications.