To reduce the ever-increasing energy consumption in datacenters, one of the effective approaches is to increase the ambient temperature, thus lowering the energy consumed in the cooling systems. However, this entails more stringent requirements for the reliability and durability of the optoelectronic components. Herein, we fabricate and demonstrate silicon-polymer hybrid modulators which support ultra-fast single-lane data rates up to 200 gigabits per second, and meanwhile feature excellent reliability with an exceptional signal fidelity retained at extremely-high ambient temperatures up to 110 °C and even after long-term exposure to high temperatures. This is achieved by taking advantage of the high electro-optic (EO) activities (in-device n3r33 = 1021 pm V−1), low dielectric constant, low propagation loss (α, 0.22 dB mm−1), and ultra-high glass transition temperature (Tg, 172 °C) of the developed side-chain EO polymers. The presented modulator simultaneously fulfils the requirements of bandwidth, EO efficiency, and thermal stability for EO modulators. It could provide ultra-fast and reliable interconnects for energy-hungry and harsh-environment applications such as datacentres, 5G/B5G, autonomous driving, and aviation systems, effectively addressing the energy consumption issue for the next-generation optical communication. Information and communication datacentres require a large amount of energy for their cooling systems, which could be decreased by working at higher temperatures. Here, the authors introduce a silicon-polymer hybrid modulator that maintains high data rates for long periods at high temperatures that could be used under such conditions, to reduce energy consumption.

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High-temperature-resistant silicon-polymer hybrid modulator operating at up to 200 Gbit s-1 for energy-efficient datacentres and harsh-environment applications.

Electrically pumped on-chip C-band lasers provide additional flexibility for silicon photonics in the design of optoelectronic circuits. III–V quantum dots, benefiting from their superior optical properties and enhanced tolerance to defects, have become the active medium of choice for practical light sources monolithically grown on Si. To fully explore the potentials of integrated lasers for silicon photonics in telecommunications and datacenters, we report the realization of 1.5 μm room-temperature electrically pumped III–V quantum dot lasers epitaxially grown on complementary metal-oxide-semiconductor (CMOS)-standard (001) Si substrates without offcut. A threshold current density of 1.6 kA/cm2, a total output power exceeding 110 mW, and operation up to 80 °C under pulsed current injection have been achieved. These results arose from applying our well-developed InAs/InAlGaAs/InP QDs on low-defect-density InP-on-Si templates utilizing nano-patterned V-grooved (001) Si and InGaAs/InP dislocation filters. This demonstration marks a major advancement for future monolithic photonic integration on a large-area and cost-effective Si platform.

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1.5 μm quantum-dot diode lasers directly grown on CMOS-standard (001) silicon

With a new generation of quantum dot (QD) optical gain material comprising atom-like features, the fundamental spectral characteristics of laser emission have been improved significantly. We describe the spectral and power characteristics of continuous wave (CW) single-mode InAs/AlGaInAs/InP QD distributed feedback lasers operating at 1.5 μm. Linewidths as narrow as 60 kHz (30  kHz±10  kHz intrinsic linewidth) at 20°C, which broadens to only 280 kHz (80  kHz±10  kHz intrinsic linewidth) at 80°C, have been achieved. The laser exhibits high output powers of 58 mW at 20°C and 26 mW at 80°C with side mode suppression ratios exceeding 50 dB. These record values stem from high uniformity of the QDs and a large dot density. The linewidth was measured by two techniques that confirm each other: delayed self-heterodyne interferometry and optical frequency comb interferometry. A model fits the experimental results well and enables extraction of the bias and temperature dependent α parameter. At 20°C, α is less than 0.5 at threshold and increases to only 0.9 at 150 mA above threshold. The corresponding values at 80°C are 2 and 2.5. These results imply a great potential of QD lasers for the most demanding applications in terms of spectral purity, such as coherent optical communication systems and optical metrology.

Large linewidth reduction in semiconductor lasers based on atom-like gain material

Realization of fully integrated silicon photonics has been handicapped by the lack of a reliable and efficient III-V light source on Si. Specifically, electrically pumped continuous wave (CW) lasing and operation sustainable at high temperatures are critical for practical applications. Here, we present the first electrically pumped room temperature (RT) CW lasing results of 1.55 μm quantum dash (QDash) lasers directly grown on patterned on-axis (001) Si using metal organic chemical vapor deposition (MOCVD). Adopting a dash-in-well structure as the active medium, the growth of QDash was optimized on an InP on Si template. Incorporating the advantages of the optimized material growth and device fabrication, good laser performance including a low threshold current of 50 mA, a threshold current density of 1.3 kA/cm2 and operation at elevated temperature up to 59 °C in CW mode was achieved. Comparison of lasers grown on Si and native InP substrates in the same growth run was made. Based on the laser characteristics measured at room temperature and elevated temperatures, the QDash quality on the two substrates is comparable. These results suggest that MOCVD is a viable technique for lasers on Si growth and represent an advance towards silicon-based photonic-electronic integration and manufacturing.

1.55 µm electrically pumped continuous wave lasing of quantum dash lasers grown on silicon.

O-band InAs/GaAs quantum dot laser monolithically integrated on exact (0 0 1) Si substrate

Static and dynamic properties of InP-based 1.55 µm quantum dot (QD) lasers were investigated. Due to the reduced size inhomogeneity and a high dot density of the newest generation of 1.55 µm QD gain materials, ridge waveguide lasers (RWG) exhibit improved temperature stability and record-high modulation characteristics. Detailed results are shown for the temperature dependence of static properties including threshold current, voltage-current characteristics, external differential efficiency and emission wavelength. Similarly, small and large signal modulations were found to have only minor dependences on temperature. Moreover, we show the impact of the active region design and the cavity length on the temperature stability. Measurements were performed in pulsed and continuous wave operation. High characteristic temperatures for the threshold current were obtained with T0 values of 144 K (15 - 60 °C), 101 K (60 - 110 °C) and 70 K up to 180 °C for a 900-µm-long RWG laser comprising 8 QD layers. The slope efficiency in these lasers is nearly independent of temperature showing a T1 value of more than 900 K up to 110 °C. Due to the high modal gain, lasers with a cavity length of 340 µm reached new record modulation bandwidths of 17.5 GHz at 20 °C and 9 GHz at 80 °C, respectively. These lasers were modulated at 26 GBit/s in the non-return to zero format at 80 °C and at 25 GBaud using a four-level pulse amplitude format at 21 °C.

I Kalifa

Papers

Temperature stability of static and dynamic properties of 1.55 µm quantum dot lasers.