Light Sources For Optical Interconnects Research Articles

Impact of cavity design on the modulation properties of a GaAs-based VCSEL

GaAs-based vertical-cavity surface-emitting lasers (VCSELs) are commonly used as light sources for optical interconnects in short-range systems. Here, we analyse the impact of the cavity Q factor and the number of quantum wells in the active region on the small-signal modulation response of a GaAs-based VCSEL. By tuning the reflectivity of the mirror it is possible to obtain flat response curves with a high −3 dB bandwidth. It is also beneficial to increase the number of quantum wells in the active region.

Thermal analysis of high-bandwidth and energy-efficient 980 nm VCSELs with optimized quantum well gain peak-to-cavity resonance wavelength offset

The static and dynamic performance of vertical-cavity surface-emitting lasers (VCSELs) used as light-sources for optical interconnects is highly influenced by temperature. We study the effect of temperature on the performance of high-speed energy-efficient 980 nm VCSELs with a peak wavelength of the quantum well offset to the wavelength of the fundamental longitudinal device cavity mode so that they are aligned at around 60 °C. A simple method to obtain the thermal resistance of the VCSELs as a function of ambient temperature is described, allowing us to extract the active region temperature and the temperature dependence of the dynamic and static parameters. At low bias currents, we can see an increase of the −3 dB modulation bandwidth f−3dB with increasing active region temperature, which is different from the classically known situation. From the detailed analysis of f−3dB versus the active region temperature, we obtain a better understanding of the thermal limitations of VCSELs, giving a basis for next generation device designs with improved temperature stability.

Spectral Efficiency and Energy Efficiency of Pulse-Amplitude Modulation Using 1.3 μm Wafer-Fusion VCSELs for Optical Interconnects

We compare the modulation efficiency of on–off keying (OOK) and four-level pulse-amplitude modulation (PAM4) using 1.3 μm wafer-fusion vertical-cavity surface-emitting lasers (VCSELs) for single-channel short-reach optical interconnects. O-band wafer-fusion VCSELs combine high optical gain from InP-based active regions with high-reflectivity, low-absorption, and high-thermal-conductive GaAs-based distributed Bragg reflectors. VCSELs offer a low-cost and low-power-consuming light source for optical interconnects in data centers and fiber-based local-area networks, presenting an attractive alternative to common edge-emitting lasers. Our investigation focuses on the highest error-free bit rates and energy efficiency of OOK and PAM4 signaling. We achieved an error-free bit rate of 38 Gbit/s with PAM4 for devices having a small-signal bandwidth of 9.9 GHz, presenting a spectral efficiency of 3.8 bit/s/Hz. These PAM4 values offer an improved error-free bit rate of 26% and consume 32% less energy-per-bit when co...

Nanoscale Light Sources for Optical Interconnects

Nanoscale Light Sources for Optical Interconnects

Electro-absorption Modulated Lasers with High Immunity to Residual Facet Reflection by Using Lasers with Partially Corrugated Gratings

Residual facet reflection can significantly degrade the performance of electroabsorption modulated lasers (EMLs) operating at high data rates. This issue also complicates the fabrication and characterization of the highly demanded light sources for optical interconnects and transmission. It is desired to optimize the device structure to make EMLs robust and immune to residual facet reflection. EMLs with a partially corrugated-grating DFB section are designed and optimized to have much improved tolerance to the residual optical reflection from the modulator output facet. By designing the laser section with an appropriate grating length and linear gain coefficient, the EML can have good tolerance to residual facet reflection. The analysis indicates that 100% yield can be obtained with the optimal design. If the EML needs to operate over a wide ranges of gain coefficient and facet reflection, >70% of yield can still be obtained.

Four-wavelength Microdisk Lasers Laterally Coupling to an Output Bus Waveguide

A multiple-wavelength GaInAsP/InP microlaser with microdisk radiuses from 10 m to 10.6 m laterally coupled into a bus waveguide are fabricated by standard photolithygraphy and inductively coupled-plasma (ICP) etching techniques. The lasing wavelengths are 1533 nm, 1541 nm, 1551 nm and 1555 nm at the CW injection current of 10 mA for the four microlasers. The proposed multiple-microlaser array would be useful for realizing compact wavelength division multiplexing (WDM) light source for optical interconnects.

Room temperature all‐silicon photonic crystal nanocavity light emitting diode at sub‐bandgap wavelengths

AbstractSilicon is now firmly established as a high performance photonic material. Its only weakness is the lack of a native electrically driven light emitter that operates CW at room temperature, exhibits a narrow linewidth in the technologically important 1300–1600 nm wavelength window, is small and operates with low power consumption. Here, an electrically pumped all‐silicon nano light source around 1300–1600 nm range is demonstrated at room temperature. Using hydrogen plasma treatment, nano‐scale optically active defects are introduced into silicon, which then feed the photonic crystal nanocavity to enhance the electrically driven emission in a device via Purcell effect. A narrow ( nm) emission line at 1515 nm wavelength with a power density of is observed, which represents the highest spectral power density ever reported from any silicon emitter. A number of possible improvements are also discussed, that make this scheme a very promising light source for optical interconnects and other important silicon photonics applications.

GaInAsP/InP Membrane Lasers for Optical Interconnects

In this paper, the state-of-the art of long-wavelength GaInAsP/InP membrane semiconductor lasers, one of the most promising candidate light sources for optical interconnects and on-chip optical wiring between large-scale integrated circuits, is described. After an extensive review of research activities focused on laser preparation on either Si or Si-on-insulator substrate, the findings of our recent research activities on low power consumption lasers are presented. Specifically, our interest was set on the low-damage fabrication of strongly index-coupled grating, which is generally opted forDFB and distributed reflector (DR) lasers consisting of wire-like active regions, as well as of high index-contrast membrane waveguides. A submilliampere threshold current and a differential quantum efficiency close to 50% from the front facet were achieved in the case of the DR laser. On the other hand, a lateral current injection (LCI) structure, which can be combined with the membrane laser, was adopted for the realization of an injection-type membrane laser. The successful continuous wave operation of LCI lasers, prepared on a semiinsulating InP substrate, was achieved with moderately low threshold current at room temperature.

High Coupling Efficiency of Microcavity Organic Light-Emitting Diode with Optical Fiber for as Light Source for Optical Interconnects

We investigated directional characteristics of the electroluminescence (EL) from microcavity organic light-emitting diodes (MOLEDs) to examine applicability of these diodes as a light source for optical interconnects. By measuring the angular dependence of a EL emission, we estimated the coupling efficiency between a MOLED and an optical fiber. The coupling efficiency was enhanced by 1.4-fold compared with that of a non cavity organic light-emitting diode (OLED), and reached 85% for an optical fiber with a numerical aperture (NA) of 0.5. The current efficiency of the MOLED also increased optimizing the device structure, and its maximum was 18.4 cd/A.

Bias-free 2.5 Gbit/s data transmission using polyimidepassivated GaAs VCSELs

GaAs based selectively oxidised VCSELs are being investigated as light sources for optical interconnects. Bias-free 2.5 Gbit/s NRZ PRBS transmission with 2/sup 31/-1 word length at a BER of better than 10/sup -11/ is reported for transmission over 500 m of graded index multimode fibre.