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In this work we present a study on teh Super Luminescent LIght Emitting Diodes (SLEDs) performance under high doses of gamma radiation. We investigate GaAs SLEDs with emission wavelengths around 830 nm. The devices were exposed to ionising radiation at a dose rate of about 4.7 Gy/s, up to a cumulated dose of 10.1 MGy in the CMF facility of the Belgian nuclear research centre SCK•CEN. We measured the device characteristics before adn after irradiation. We show that the SLED performance is only marginally affected.

International audience; In the framework of the fusion for energy radiation hard imaging system project, the main radiation effects affecting the image quality of a miniaturized complementary metal-oxide-semiconductor-based camera exposed to radiation doses up to 1 MGy(SiO 2 ) are investigated for ITER applications. The radiation effects related to two of the three subcomponents of the camera are investigated: the optical system (OS) and the illumination system (IS). Subsystem demonstrators have been manufactured selecting radiation tolerant or hardened materials and components to demonstrate the feasibility to withstand such high dose levels while fulfilling the ITER remote handling needs in terms of optical performances and miniaturization. Regarding the OS, the observed degradation of the radiation-hardened optical glasses used for the OS lenses is characterized in terms of both radiation-induced attenuation and radiation-induced refractive-index change. At the system level, impact of these phenomena on the OS demonstrator performances is discussed in terms of image contrast. Radiation test results highlight the high radiation tolerance of manufactured monochrome and color OS to both degradation mechanisms. Regarding the IS, the selected architecture consists in a ring of 20 commercially available light-emitting diodes (LEDs) with monochrome (amber) or white emissions. An appropriate choice for the LEDs allows designing an IS with the requested performances and slight degradation of its output power at the MGy dose levels. From the obtained results, developing miniaturized IS and OS subcomponents for MGy dose operation levels appears realistic using commercially available technologies and appropriate hardening procedures.

The ITER Neutral Beam cell will include a suite of Remote Handling equipment for maintenance tasks. This paper summarises the current status and recent developments in the design of the ITER Neutral Beam Remote Handling System. Its concept design was successfully completed in July 2012 by CCFE in the frame of a grant agreement with F4E, in collaboration with the ITER Organisation, including major systems like monorail crane, Beam Line Transporter, beam source equipment, upper port and neutron shield equipment and associated tooling. Research and development activities are now underway on the monorail crane radiation hardened on-board control system and first of a kind remote pipe and lip seal maintenance tooling for the beam line vessel, reported in this paper.

International audience; In this review paper, we present radiation effects on silica-based optical fibers. We first describe the mechanisms inducing microscopic and macroscopic changes under irradiation: radiation-induced attenuation, radiation-induced emission and compaction. We then discuss the influence of various parameters related to the optical fiber, to the harsh environments and to the fiber-based applications on the amplitudes and kinetics of these changes. Then, we focus on advances obtained over the last years. We summarize the main results regarding the fiber vulnerability and hardening to radiative constraints associated with several facilities such as Megajoule class lasers, ITER, LHC, nuclear power plants or with space applications. Based on the experience gained during these projects, we suggest some of the challenges that will have to be overcome in the near future to allow a deeper integration of fibers and fiber-based sensors in radiative environments.

The gamma radiation-induced variation of the transconductance in the subthreshold region is studied for different back-gate voltages and for different kinds of SOI MuGFETs: devices with and without selective epitaxial growth (SEG) and 45° rotated transistors. Wide fin devices show a larger degradation when the back-gate is grounded. The back-channel of narrow fin transistors, on the other hand, needs to be inverted before degradation in the transconductance is observed. The radiation behavior of the transconductance is similar for devices with and without SEG. It is shown that the maximum variation in transconductance correlates with the mobility for narrow fin devices. This mobility varies when the transistor is rotated. For wide fin devices this correlation is not as strong.

The effect of an airgap deep trench isolation on the gamma radiation behavior of a 0.13 mum SiGe NPN HBT technology is studied with the help of in-situ measurements. The incorporation of this deep trench isolation in the technology leads to a lower degradation of the transistor during irradiation as well in forward-mode as in reverse-mode operation. A possible explanation is briefly mentioned.

This paper describes the characterization and SPICE model adaptations for a SiGe Heterojunction Bipolar Transistor (HBT) with a characteristic emitter width of 0.4 mum, which is part of the device library in a commercial 0.35 mum SiGe BiCMOS technology. The developed model is used to design and validate the operation of an integrated driver for a 1550 nm Vertical Cavity Surface-Emitting Laser (VCSEL). The static measurements of the driver during irradiation up to 600 kGy correspond well with the simulations. A second irradiation experiment up to 1.6 MGy allowed us to verify the dynamic operation. Investigation of the eye diagram of the output signal both before and after irradiation revealed no significant signal degradation.

International audience; We compare the visible and infrared luminescence spectra obtained by a green (514.5 nm) and infrared (830 nm) excitation of an erbium-doped fiber before and after irradiation with 105 MeV protons to an equivalent dose of 0.6 kGy(Si). For the irradiated fiber, we measured an increase of the luminescence intensity in this wavelength range due to the generation of additional color centers. Radiation defects such as Ge-NBOHC, Si-NBOHC are generated in both the fiber core and the cladding by the 105 MeV protons. They contribute through their luminescence bands at 1.84 eV (FWHM = 0 2 eV) and 2 eV (0.2 eV) to the fiber emission spectra. Two other pre-existing luminescence bands at 1.75 eV (0.32 eV) and 2.1 eV (0.37 eV), associated to host-matrix-point-defects, are enhanced by proton-irradiation. The Er3+ ions luminescence in both visible and infrared spectral ranges is also affected by the irradiation.

International audience; Abstract—The radiation responses of two erbium doped fibers are studied in harsh pulsed X-ray and gamma ray environments. Their transient and continuous responses were measured in the near-infrared spectral range. The online transmission measurements of Radiation-Induced Attenuation (RIA) show no detectable change in the 1450–1600 nm erbium-ions-absorption domain, whereas the background losses from the silica-based host matrix are strongly increased by the creation of point defects. For both harsh environments, the rare-earth doped samples exhibit higher RIA levels compared than standard passive optical fibers. From all our measurements, we proposed that the main contribution to the induced losses is due to the radiation-induced changes of the host matrix rather than changes related to erbium ions. Photo-luminescence analyses confirm the generation of NBOHC in erbium doped fibers and suggest the existence of energy transfer between the radiation-induced point defects and the Er3+ ions

The proton irradiation effects on n-MuGFET devices with three different geometries (single fin, wide fin and multiple fin) are studied. Also, the effect of tensile strain in the fin on the radiation behavior is investigated. A fundamental difference in the radiation behavior between the non-strained and the strained devices is found. The degradation of the strained devices is most affected by the mobility decrease of the backside transistor. The non-strained devices show a much lesser back gate mobility degradation. For these devices the creation of positive oxide traps is dominant. This shifts the onset of the back channel to lower gate voltages, inducing a transconductance increase at intermediate gate voltages. This effect is less pronounced for single fin MuGFETs. At higher gate voltage, the transconductance decreases for the strained and increases for the non-strained transistors.

International audience; Abstract—We characterized the responses of three erbium-doped fibers with slightly different concentrations of rare-earth ions (240–290 ppm) and Al2O3 (7–10 wt.%) during proton and gamma-ray exposures. We have simultaneously measured the radiation-induced attenuation (RIA) around the Er3+ ion pumping wavelength (980 nm) and the associated changes of the Er3+ emission around 1530 nm. The three erbium-doped fibers show similar radiation responses. All fibers exhibit RIA levels between 9 10-3 and 1.7 10-2 dB m-1 Gy-1 at 980 nm and between 4 10-3 and 1.1 10-2 dB m-1 Gy-1 at 1530 nm. Protons and gamma-rays lead to similar radiation damages, with small differences between the protons of different energies (50 MeV and 105 MeV). Furthermore, we have performed online measurements of the spectral dependence of RIA from 600 to 1600 nm and offline measurements from 1200 to 2400 nm. The three fibers exhibit the same spectral response. Losses decrease monotonically from the visible to the infrared part of the spectrum. We have performed spectral decomposition of these RIA curves with the help of absorption bands previously associated with radiation-induced point defects. Our analysis shows that the main part of the RIA (600–1700 nm) in erbium-doped glass can be explained by the generation of Al-related point defects. The other defects related to the germanium and phosphorus doping of the silica seem to have a lower contribution to the induced losses. The Er3+ ion properties seem to be mainly unaffected by proton exposure, suggesting a solvation shell around the Er3+ ion formed by Al2O3 species.

The radiation hard design of a 155 Mb/s, 0.7 mum CMOS driver for a vertical-cavity surface-emitting laser (VCSEL) is presented. The circuit features enhanced tolerance to radiation induced shifts in the device characteristics by employing a replica-based feedback mechanism. The layout was achieved using an in-house developed radiation hardened component library. At a low dose rate of 4.5 Gy/h or 450 rad/h, the output current remains constant up to at least 3.5 kGy. At a dose rate of 21 kGy/h, the output current of the driver drops by 10% at a dose of 3.5 MGy and breaks down completely at 5.5 MGy.

Several single mode silica-based fibers with different levels of erbium concentrations have been tested under Co-60 gamma radiation. Irradiation has been performed at a dose-rate of similar to 30 Gy/h to a total dose of similar to 2 kGy. Transmission spectra were measured in situ in a spectral range from 1250 to 1630 nm. The measurements show no detectable change in the Er-ions luminescence and absorption spectrum profiles, while a significant (similar to dB/m/kGy at 1530 nm) increase in transmission losses is attributed to the silica host matrix modifications. This conclusion is drawn based on the post-irradiation photo-luminescence analyzes realized with a confocal micro-spectrometer (514.5 nm excitation, P similar to 2 mW). (c) 2007 Elsevier B.V. All rights reserved.

Future maintenance tasks of the international experimental thermonuclear fusion reactor (ITER) will require communication links between the remotely operated equipment in the reactor vessel and the control room, that are radiation tolerant up to MGy dose levels. We therefore assessed the DC behaviour of a COTS SiGe heterojunction bipolar transistor (HBT) under gamma radiation up to more than 4 MGy. The DC current gain (beta) presents a limited loss of about 30% for a base current of 100 muA. Our in-situ measurements allowed us to adapt the manufacturer's SPICE model and account for these radiation effects. Circuit-hardened driving electronics for both photonic transmitters and receivers can hence be designed.

A digital VCSEL driver has been designed, simulated and assessed under radiation, using discrete SiGe HBT's. The circuit tolerates high levels of gamma radiation, up to 12 MGy, features less than 2% drift in the forward current of the VCSEL and operates well above 10 MHz. The output duty cycle shows no notable degradation at 200 kHz, enabling the design of robust analog and digital communication systems using pulse-width-modulation (PWM) schemes.

The radiation behavior of a commercially available Er-doped fiber is evaluated under varying gamma dose rates with in-situ spectral loss measurements. Complementary post-irradiation photoluminescence measurements allow us to better understand the radiation effects. Our results suggest that the microscopic environment of the Er/sup 3+/ ions is not much affected by the gamma irradiation, unlike the host matrix. We discuss the impact for potential applications of these commercially available fibers in radiation environments.

A first assessment of the total dose behavior of bulk p-multiple-gate field-effect transistors (MuGFETs) is reported, and special attention is given to the effect of the fin width on the radiation behavior. It was found that the effect of radiation-induced traps in the shallow trench isolation is larger when the fin width decreases. This is in contrast to the total dose behavior of SOI MuGFETs.

The basic components of fiberoptic links, such as light emitting diodes (LED), pin-type photodetectors (PD) and optical fibers are evaluated under (/sup 60/Co) /spl gamma/-ray irradiation, so as to ascertain their qualification for nuclear applications and to develop predictive models for their behavior under well defined environmental conditions, such as those encountered in nuclear power plants. This paper presents some results of irradiation tests, together with a discussion of proposals for optical fibers' behavioral models.

This paper presents the design of a radiation tolerant configurable discrete time CMOS signal conditioning circuit for use with resistive sensors like strain gauge pressure sensors. The circuit is intended to be used for remote handling in harsh environments in the International Thermonuclear Experimental fusion Reactor (ITER). The design features a 5 V differential preamplifier using a Correlated Double Sampling (CDS) architecture at a sample rate of 20 kHz and a 24 V discrete time post amplifier. The gain is digitally controllable between 27 and 400 in the preamplifier and between 1 and 8 in the post amplifier. The nominal input referred noise voltage is only 8.5 μV while consuming only 1 mW. The circuit has a simulated radiation tolerance of more than 1 MGy.

In this work the influence of Selective Epitaxial Growth (SEG), high- k gate-dielectric and rotation of the channel on the low frequency (LF)-noise is investigated. The carrier number fluctuations dominate the 1/ f noise for all the devices studied. An unusual effective trap density profile is found. It decays with a larger distance from the interface. This implies a higher trap density in the interfacial SiO 2 -layer, compared with the high- k dielectric. The shape of the profile is different for a HfSiON gate-dielectric compared with a HfO 2 gate-dielectric. Higher trap densities are found for the latter. The Selective Epitaxial Growth (SEG) and channel orientation show only a negligible impact on the noise behavior when a HfSiON-dielectric is used.

Near UV-visible absorption coefficients of an erbium-doped optical fiber were investigated through an original technique based on a transverse cw UV-laser irradiation operating at 244 nm. Such irradiation leads to the generation of a quite intense guided luminescence signal in near UV spectral range. This photoluminescence probe source combined with a longitudinal translation of the fiber sample (at a constant velocity) along the UV-Iaser irradiation, presents several major advantages: (i) we bypass and avoid the procedures classically used to study the radiation induced attenuation which are not adapted to our case mainly because the samples present a very strong absorption with significant difficulties due to the injection of adequate UV-light levels in a small fiber diameter: (ii) the influence of the laser irradiation on the host matrix of the optical fiber is directly correlated to the evolution of the generated photoluminescence signal and (iii) in our experimental conditions, short fiber sample lengths(typically 20-30 cm) suffice to determine the associated absorption coefficients over the entire studied spectral domain. The generated photoluminescence signal is also used to characterize the absorption of the erbium ions in the same wavelength range with no cut-back method needed. (C) 2008 Elsevier B.V. All rights reserved.

This paper describes the characterization and SPICE model adaptations for a SiGe Heterojunction Bipolar Transistor (HBT) with a characteristic emitter width of 0.4μm, which is part of the device library in a commercial 0.35μm SiGe BiCMOS technology. The developed model is used to design and validate the operation of an integrated driver for a 1550nm Vertical Cavity Surface-Emitting Laser (VCSEL). The static measurements of the driver during irradiation up to 600 kGy correspond well with the simulations. A second irradiation experiment up to 1.6 MGy allowed us to verify the dynamic operation. Investigation of the eye diagram of the output signal both before and after irradiation revealed no significant signal degradation.

We evaluated the radiation tolerance of volume holographic elements written in photo-thermo refractive glass. To do so these elements were exposed to Co-60 gamma-radiation and 60 MeV protons. At 10 kGy dose levels a high stability has been observed. Our results confirm that such components can operate in a space radiation environment.

We compare the visible and infra-red luminescence spectra obtained by a green (514.5 nm) and infra-red (830 nm) excitation of an erbium-doped fiber before and after irradiation with 105 MeV protons to an equivalent dose of 0.6 kGy(Si). For the irradiated fiber, we measured an increase of the luminescence intensity in this wavelength range due to the generation of additional color centers. Radiation defects such as Ge-NBOHC, Si-NBOHC are generated in both the fiber core and the cladding by the 105 MeV protons. They contribute through their luminescence bands at 1.84 eV (FWHM=0.2 eV) and 2 eV (0.2 eV) to the fiber emission spectra. Two other pre-existing luminescence bands at 1.75 eV (0.32 eV) and 2.1 eV (0.37 eV), associated to host-matrix-point-defects, are enhanced by proton-irradiation. The Er3+ ions luminescence in both visible and infra-red spectral ranges is also affected by the irradiation.

The effect of airgap deep trench isolation on the radiation behavior of a 0.13 mum NPN SiGe:C HBT is studied and compared with standard components with conventional junction isolation. Proton and gamma irradiations are performed. The only effect discerned on this technology after a proton irradiation of 7 kGy is a decrease in collector current at higher base-emitter voltages. After 100 kGy gamma irradiation, no change in collector current is observed. However, the base current increases severely at lower base-emitter voltages. In forward-mode the base current degradation of devices featuring deep trench isolation is higher compared to conventional devices. In reverse-mode the effect is opposite: degradation is higher for conventional devices. The difference in degradation between the two isolation types is smaller in forward-mode operation.

We discuss on-going reliability studies of micro-optical components and assemblies as conducted in the EU FP6 Network of Excellence on Micro-Optics "NEMO". We focus on three case studies including first biaxial fatigue testing of micro-optical components, second reliability testing and quality control of MEMS and third micro-interferometric tomography for measuring optical fibre refractive index changes. For each of these case studies we discuss the dedicated measurement and characterization methods as well as first results and the perspectives for future research.

This paper presents the first results of long term experiments conducted within the SOFTI (Study of Optical Fibres and components under Thermal ageing and Irradiation) project. This on-going 6-years study is intended to determine the effects of ageing on the behaviour of optical fibres and their fibre-end components submitted to harsh environments, with respect to the safety of nuclear facilities. The test program consists of irradiations at low dose rates with different thermal constraints and spool radius. After completion, these tests will enable us to write a guideline for qualification procedures related to future fibre-optic systems, for their applications in nuclear facilities. The observations of these first results show a clear dependence of the radius of curvature for the radiation induced loss. To our knowledge, it is the first time that this was experimentally verified for a radius of curvature superior to 6 cm.

The deployment of optical fibre networks for communication and monitoring in nuclear environments, including nuclear power plants, future thermonuclear power reactor buildings and even spacecrafts is a very particular issue. A major reliability problem when dealing with photonics in these environments is the presence of nuclear radiation fields. It is well known that electronic or photonic components may suffer from exposure to high-energy radiation. Any resulting system malfunctions might have dramatic consequences on safety and cost and it is therefore essential to investigate the reliability of optical communication devices exposed to radiation. In this paper, we try to summarize the degradation mechanisms of state-of-the-art fibre optic components. We illustrate these findings with recent results obtained on commercially available optical fibre components.

We design and test a radiation tolerant opto-electronic transmitter based on vertical-cavity surface-emitting lasers (VCSELs) and dedicated driver electronics consisting of discrete components. VCSELs have already demonstrated their good radiation tolerance level. We confirm this by on-line irradiation experiments on such devices up to a 10 MGy total dose. For the design of the driver circuit, we rely on discrete commercial-off-the-shelf (COTS) bipolar transistors. When the radiation induced degradation of these components is considered within the design of the circuits, total dose levels larger than 1 MGy can be tolerated. The driver uses standard TTL input signals and delivers a forward current of 12 mA to a pigtailed 840 nm VCSEL. SPICE simulations show that the driver still delivers a sufficient forward current to the VCSEL, in spite of the radiation induced degradation of the h/sub fe/ and V/sub CEsat/ values of the transistors. These simulations are verified by our experiments. At a total dose of 1 MGy, the measured decrease of the forward current is only about 8 %, as measured for three driver circuits This induces an optical output power decrease that can still be tolerated with irradiated VCSELs, as shown by our experiments. We conclude that a high total dose hardened optical transmitter for use in nuclear instrumentation systems can be fabricated using discrete COTS bipolar transistors, COTS vertical-cavity surface-emitting lasers and COTS optical fiber.

We measure the ionizing radiation induced optical loss in different fiber-optic communication devices and evaluate the total optical loss in a multimode fiber link for application in high total dose nuclear environments.

The conceptual design of a MGy tolerant configurable discrete time signal conditioning circuit in a 130nm and 700nm CMOS technology is presented, for use with resistive sensors like strain gauge pressure sensors. The design features a differential preamplifier using a Correlated Double Sampling (CDS) architecture at a sample rate of 20kHz. Furthermore, a high voltage buffer and level shifter is presented in the 0.7μm design. The gain is digitally controllable between 27 and 400. The nominal input referred noise voltage is only 8.6μV at room temperature. The circuits have a simulated radiation tolerance of more than 1MGy. Simulations of the radiation behaviour are based on results obtained from [1],[2].

We have studied the effect of gamma-radiation on the small signal gain and on the noise figure of several EDFAs with similar characteristics and based on special highly Er-doped fibers. Those fibers were fabricated using direct nano-particle deposition technology, with different Er3+ doping levels. The results show that the use of this technology allows improving the EDFA's radiation tolerance by increasing the concentration of Er3+ ions provided this is not accompanied with higher concentrations of other dopants, which influence the radiation sensitivity of the fiber.

Optical plasma diagnostic systems often require a complex optical path involving mirrors, lenses and windows. The use of optical fibres could significantly simplify the design of such a system. Radiation-induced effects, namely induced absorption and luminescence, may compromise the integration of optical fibres in the diagnostic system. However, recent developments of new fused silica glass types open perspectives to use optical fibres as a wave-guide device. In this paper, we present the common European, Japanese and Russian efforts in setting up a standardized round-robin procedure to test the optical fibres under relevant ITER conditions. The round-robin procedure should allow to select the most appropriate optical fibre. We briefly illustrate the discussion with results of an in-core reactor irradiation of pure silica optical fibres in the BR2 material testing reactor of the Belgian Nuclear Energy Research Centre.

The future International Thermonuclear Experi- mental Reactor (ITER) is a complex installation that will require permanent monitoring and frequent maintenance operations. The high-gamma dose rates, the high neutron fluence, and other radiological hazards call for the use of remote-handled equipment. The management of heavy umbilicals connecting the control systems with the remote tools is therefore a key issue. Multiplexing signals can relieve the cable-handling difficulties. In this respect, the intrinsic wavelength division multiplexing (WDM) capabilities of fiber-optic technology make it a very promising candidate for integration in ITER instrumentation links. However, the radiation hardness of a complete WDM optical link still needs to be assessed. In this paper, as a first step toward the development of a rad-hard WDM optical link, we report on irradiations of different parts of a typical WDM optical link. We present our irradiation results on COTS fiber-optic devices, including WDM single-mode couplers, which remain operational up to MGy dose levels while the channel drift observed in narrow-band couplers compromises their use in WDM multiplexers. The intrinsic wavelength encoding of fiber Bragg grating (FBG) sensors makes them ideal candidates for WDM fiber-optic sensor networks. Therefore, we also investigated the -radiation response of FBGs written in germanosilicate fibers. We irradiated such sensors up to MGy dose levels. At a total dose of 0.1 MGy, saturation of the radiation-induced Bragg peak shift has been observed, evidencing the potential radiation hardness of FBG-based devices in highly radioactive environments. To illustrate wavelength multiplexing in sensing, we discuss our preliminary results on a new multicomponent force sensor design based on eight multiplexed FBG sensors intended for use at the end effector wrist of remote-controlled robots. Finally, we present the in-reactor irradiation results of standard Corning Ge-doped fiber up to GGy dose levels. Index Terms—Fiber Bragg grating (FBG) sensor, gamma radia- tion, International Thermonuclear Experimental Reactor (ITER), nuclear robotics, optical fiber sensor, radiation effects, wavelength division multiplexing (WDM).

We have developed an industry-aimed pragmatic method based on a known model for the prediction of radiation induced losses in single mode optical fibers exposed to /sup 60/Co gamma rays. When environmental and measurement conditions are well defined, long-term losses could be predicted with a precision of about 15%, provided a sufficiently large data-set is available. From an interpretation of these results, we discuss its applicability and potential further improvements.

Up to now, fiber optics and several photonic components have been considered for space and nuclear power plant applications, mainly at relatively low dose rates and total doses. In this paper, we present our recent results of particularly high dose gamma irradiation tests performed with different fiber-optic components intended for applications in enhanced radiation environments such as ITER (International Thermonuclear Experimental Reactor), We present a radiation induced loss at 1310 nm as low as 30 dB/km, measured at a cumulated dose of 3 MGy for a pure-silica core single mode fiber. On-line measurements with commercially available vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm confirmed their excellent radiation hardness. Furthermore, we demonstrated that an initial power loss of about 6 dB is caused by an early degradation of a focusing lens in these connectorized components. A combined effect of dose rate, cumulated dose and temperature on the degradation of our devices under test (DUT) is evidenced.

In this paper, we design and test a radiation-tolerant opto-electronic transmitter based on vertical-cavity surface-emitting lasers (VCSELs) and dedicated driver electronics consisting of discrete components. VCSELs have already demonstrated their good radiation tolerance level. We confirm this by on-line irradiation experiments on such devices up to a 10-MGy total dose. For the design of the driver circuit, we rely on discrete commercial-off-the-shelf (COTS) bipolar transistors. When the radiation induced degradation of these components is considered within the design of the circuits, total dose levels larger than 1 MGy can be tolerated. The driver uses standard Transistor-Transistor Logic TTL input signals and delivers a forward current of 12 mA to a pigtailed 840-nm VCSEL. SPICE simulations show that the driver still delivers a sufficient forward current to the VCSEL in spite of the radiation induced degradation of the h/sub FE/ and V/sub CESat/ values of the transistors. These simulations are verified by our experiments. At a total dose of 1 MGy, the measured decrease of the forward current is only about 8%, as measured for three driver circuits. This induces an optical output power decrease that can still be tolerated with irradiated VCSELs, as shown by our experiments. We conclude that a high total dose hardened optical transmitter for use in nuclear instrumentation systems can be fabricated using discrete COTS bipolar transistors, COTS vertical-cavity surface-emitting lasers, and COTS optical fiber.

We studied long-wavelength vertical-cavity surface-emitting laser diodes (LW-VCSELs) emitting in the 1.4-1.7 mum range under gamma radiation up to 9 MGy and 36 MeV protons up to 1013p/cm2, in order to compare the impact of both ionizing and displacement damage on their optical and electrical properties. The limited threshold shift and slope efficiency degradation of these state-of-the-art electrically-pumped laser diodes allow us to envisage data and sensor applications in various radiation environments.