Comparison of the radiation hardness of silicon Mach-Zehnder modulators for different DC bias voltages

Radiation hard optical links are the backbone of read-out systems in high-energy physics experiments at CERN. The optical components have to withstand large doses of radiation and provide high data rates. Silicon photonics is currently being considered a promising technology to replace electrical and optical links in future experiments. It has already been demonstrated that integrated silicon Mach-Zehnder modulators can withstand a high neutron fluence and large total ionizing doses. Before read-out systems based on these components can be taken into consideration, it has to be determined how biasing affects their radiation hardness. For this reason we prepared bonded and fiber-pigtailed prototypes and irradiated them with x-rays. We found that under reverse-bias the radiation hardness of the tested components is reduced in comparison to un-biased samples. However, we were able to show that one device type can withstand the radiation without phase shift degradation up to 1 MGy despite the accelerated degradation due to biasing

Investigation of the influence of temperature and annealing on the radiation hardness of silicon Mach-Zehnder modulators

Optical links are vital components in the data transmission systems of High Energy Physics (HEP) experiments at CERN. With the ever-higher beam fluxes achieved by the Large Hadron Collider (LHC) the optical components have to withstand higher radiation levels and handle ever-increasing data volumes. To face these challenges, the use of Silicon Photonics (SiPh) Mach-Zehnder modulators (MZMs) in the next generation of optical transceivers for HEP experiments is currently being investigated. In this work the dependence of the radiation hardness of custom-designed SiPh MZMs on temperature is reported, including the observed improvement in radiation tolerance at low operating temperatures that are closer to the typical temperatures found in HEP experiments. Furthermore, post-irradiation annealing measurements of the devices were performed. An effective annealing method has been found by applying a forward current to the MZMs, leading to an almost immediate and full recovery of the device after irradiation up to 3 MGy. This enhanced device recovery method could effectively increase the radiation hardness tremendously in applications with low dose rates and periodic shut-down times

Radiation tolerance enhancement of silicon photonics for HEP applications

Silicon photonics modulators and photodiodes are being investigated for use in optical links for High Energy Physics experiments. In order to withstand the harsh environment in the innermost detector regions of the Large Hadron Collider at CERN and in future High Energy Physics experiments beyond the Large Hadron Collider, components will have to be resistant against extreme levels of radiation. First, we show that Mach-Zehnder modulators, which lost their functionality after X-ray irradiation, can be fully recovered by applying a forward bias after irradiation. Devices irradiated and recovered withstand the same TID when re-irradiated. Furthermore, it is presented that by applying a forward bias already during irradiation, the irradiation-induced degradation can be compensated. The possibility of device recovery could lead to a tremendous increase of radiation resistance of the optical links. Additionally, the resistance against displacement damage and ionizing radiation of silicon germanium photodiodes is presented

The lpGBTIA, a 2.5 Gbps Radiation-Tolerant Optical Receiver using InGaAs photodetector

The Low Power GigaBit Transimpedance Amplifier (lpGBTIA) is the optical receiver amplifier in the lpGBT chipset. It is a highly sensitive transimpedance amplifier designed to operate at 2.56 Gbps. It is implemented in a commercial 65 nm CMOS process. The device has been designed for radiation tolerance and, in particular, to accommodate the radiation effects in photodiodes that manifest themselves as an increase of both their dark current and junction capacitance. The optical receiver consisting of the lpGBTIA connected to an InGaAs photodiode has been successfully tested and irradiation tests showed that the power penalty remains below 4 dBm for exposition to a very high neutron fluences of the order of 10$^{15}$ n/cm$^2$

Radiation hardness evaluation and phase shift enhancement through ionizing radiation in silicon Mach-Zehnder modulators

Data acquisition systems in High Energy Physics (HEP) experiments rely on tens of thousands of radiation hard optical links based on high data rate, low power transmitters which also have to be able to withstand high levels of different types of radiation. Radiation hardness is one of the requirements that becomes more demanding with every new generation of experiment. Previous studies have shown that there is currently no qualified technology for optical transmitters able to withstand operation in the innermost regions of upgraded LHC experiments at CERN. Silicon photonic Mach-Zehnder Modulators (MZMs) are being investigated as one of the promising technologies to address this challenge. We designed MZMs with different design parameters and exposed them to ionizing radiation in order to assess how their performance changes. We demonstrate that the etch depth of the MZM waveguides and the doping concentration in the waveguides strongly impact the response of the MZMs. In particular, a shallow etch depth and increased doping concentrations help to mitigate the detrimental effects of ionizing radiation. MZMs fabricated with these design parameters are found to show a post-irradiation phase shift enhancement compared to the pre-irradiation values. The improved radiation resistance is high enough that such devices could potentially be installed in future HEP experiments or in other fields of application sensitive to radiation

Thermal Characterisation of the Versatile Link+^+ Transceiver

The miniaturised optical transceiver module, developed in the framework of the Versatile Link$^+$ project (VL$^+$) will be installed in the upgraded detector front-ends at the HL-LHC. The modules will have to operate over a wide temperature range (-35 °C to +60 °C). We describe the impact of the temperature on the performance of the transceiver and we present simulation and measurement results obtained during the thermal characterisation of different transceiver prototypes

High-Speed, Radiation-Tolerant Laser Drivers in 0.13 μ\mum CMOS Technology for HEP Applications

The gigabit laser driver (GBLD) and low-power GBLD (LpGBLD) are two radiation-tolerant laser drivers designed to drive laser diodes at data rates up to 4.8 Gb/s. They have been designed in the framework of the gigabit-transceiver (GBT) and versatile-link projects to provide fast optical links capable of operation in the radiation environment of future high-luminosity high-energy physics experiments. The GBLD provides laser bias and modulation currents up to 43 mA and 24 mA, respectively. It can thus be used to drive vertical cavity surface emitting laser (VCSEL) and edge-emitting laser diodes. A pre-emphasis circuit, which can provide up to 12 mA in 70 ps pulses, has also been implemented to compensate for high external capacitive loads. The current driving capabilities of the LpGBLD are 2 times smaller that those of the GBLD as it has been optimized to drive VCSELs in order to minimize the power consumption. Both application-specific integrated circuits are designed in 0.13 m commercial complementary metal-oxide semiconductor technology and are powered by a single 2.5 V supply. The power consumption of the core circuit is 89 mW for the GBLD and 55 mW for the LpGBLD

Ionizing Radiation Effects in Silicon Photonics Modulators

Silicon photonics (SiPh) shows considerable potential as a radiation-hard technology for building the optical data transmission links for future high-energy physics (HEP) experiments at CERN. Optical modulators are a key component of optical links, which will need to withstand radiation doses in excess of 10 MGy. The geometrical parameters and doping concentrations of two popular types of SiPh modulators, Mach–Zehnder and ring modulators (RMs), have been varied in order to study their impact on the device radiation tolerance. They were exposed to an X-ray beam to test their resistance to ionizing radiation. The RM with the highest doping concentration is shown to be the most tolerant, showing no degradation in performance up to the highest dose of 11 MGy. Moreover, we report first evidence of the dependence of the radiation tolerance on the RM operating temperature.Silicon photonics (SiPh) shows considerable potential as a radiation-hard technology for building the optical data transmission links for future high-energy physics (HEP) experiments at CERN. Optical modulators are a key component of optical links, which will need to withstand radiation doses in excess of 10 MGy. The geometrical parameters and doping concentrations of two popular types of SiPh modulators, Mach–Zehnder and ring modulators (RMs), have been varied in order to study their impact on the device radiation tolerance. They were exposed to an X-ray beam to test their resistance to ionizing radiation. The RM with the highest doping concentration is shown to be the most tolerant, showing no degradation in performance up to the highest dose of 11 MGy. Moreover, we report first evidence of the dependence of the radiation tolerance on the RM operating temperature

Radiation Effects on High-Speed InGaAs Photodiodes

International audiencePhotodiodes are important components in optical data links, and their performance degradation under irradiation has to be understood in order to guarantee the long-term functionality of the data links in radiation environments of high-energy physics experiments. Indium gallium arsenide (InGaAs) on indium phosphide (InP) photodiodes are attractive candidates for these applications, thanks to their relatively modest radiation-induced responsivity loss when operated at 850 nm. In this paper, we present the results that confirm earlier observed additional sensitivity penalties in InGaAs-based receivers. This behavior is further investigated by carrying out several proton tests where InGaAs photodiodes are irradiated together with alternative photodiode types. The critical parameters—responsivity, dark current, and capacitance—are measured up to fluences exceeding ${1\times 10^{16}}$ p/cm2. Radiation-induced dark current is shown to be orders of magnitude higher in InGaAs photodiodes than in GaAs and InGaAs on GaAs photodiodes. However, instead of the dark current increase, the additional losses with InGaAs photodiodes are shown to arise from strongly increased capacitance, which is a dominant feature only in InGaAs photodiodes. This is confirmed with simulations where the measured capacitance characteristics are used in the device model. Our results show that without precautions in the receiver design, radiation-induced capacitance can limit the use of InGaAs photodiodes in harsh radiation environments