Mid-infrared liquid sensing on the chip-scale is a newly emerging field of research, especially with respect to fully monolithic integrated devices. They enable addressing applications scenarios in chemical reaction monitoring and real-time sensing, which were so far prevented by the existing much more bulky technology (e.g. FTIR-based systems). In this work we present a quantum cascade laser (QCL), QC detector (QCD) and novel type of midinfrared plasmonic waveguide that are integrated into one substrate and which we use in real-time protein sensing and residual water in solvent measurements. Furthermore, we present how this rather simple linear geometry can be further improved by implementing other (more spectrally broadband) materials such as Germanium and integrating surface-passivation and -functionalization for improving sensing capabilities. In the last part we will demonstrate two pathways for introducing plasmonic mode-guiding along the chip-surface, which is the key to realizing much more complex geometries including integrating more active and passive elements into one PIC.
A 4-quadrant large area HgCdTe APD detector module have been developed and characterized in view of application in deep space optical communications. Single photon detection capacity has been demonstrated on each of the four channels of the detector module, associated with a bandwidth close to 400 MHz. The performance for pulse position modulation (ppm) has been estimated from the detection of strongly attenuated laser pulses and were found to be close to the system performance specifications given by ESA: the pulse detection probability in a time slot of 800 ps was measured to be higher about 90 % for a signal of 7 photons focused on the center on one channels, associated with a false alarm rate below 1 %, although the sensitivity of the full detector module was limited by a low quantum efficiency and a high dark count rate. With a 16-ary ppm modulation, this corresponds to a data rate of 320 Mbps at less than 2 photons per bit.
HgCdTe Avalanche Photo Diodes (APDs) are developed at CEA/Leti to enable applications that require the detection of information contained in a low number of photons in each spatial and/or temporal bin, such as LiDAR and free space optical communications. The requirements for such detectors are strongly application dependent, which is why both the HgCdTe APD technology and the proximity electronics, used to extract the detected photocurrent, needs to be optimized for each application. The present communication reports results obtained from the development of detectors for high dynamic range LiDAR applications, made within the scope of the H2020 project HOLDON, and high data rate FSO, made in collaboration with Mynaric Lasercom AG. For FSO applications, we have measured 10 GHz bandwidth at unity gain for APDs with 10 μm diameter. At higher APD gain and diameter, the BW is presently limited by carrier transit and by resistance-capacitance product in small and large area APDs, respectively. For LiDAR we have developed APDs with an made of an array of diodes in parallel with a diameter up to 200 μm and large avalanche gain, M<100, that will be hybridized with a dedicated CMOS amplifier. This circuit was designed to enable photon shot noise limited linear detection over a dynamic range of 6 order of magnitude of signal for observation times ranging from ns up to μs. First characterizations made at unity APD gain shows that the HOLDON detector will meet most of the required performance parameters in terms of sensitivity and linear dynamic range.
In the present communication, the characterization results of an in-house developed four-quadrants detection module based on HgCdTe APDs and a Si-CMOS ROIC pre-amplifier is discussed. The module has been designed to be employed as high data rate ground-segment detector for 1.55 μm long-distance free-space optical communication links in the framework of a project funded by the European Space Agency. The detector is characterized by a multiplication gain in excess of M = 150, a ROIC input referred noise of Ne = 45 electrons rms and a measured bandwidth of BW = 450 MHz. These characteristics enable the linear-mode detection of meso-photonic states ranging from tens of photons per pulse down to the single-photon level at high count rates exceeding 500 MHz per quadrant (and 2 GHz if the signal is dispatched over all four-quadrants). For the present module, the performance for PPM and OOK modulation formats was estimated and its potentiality for long-distance free-space optical communications employing these modulation formats was validated. In particular, for the PPM format, a detection probability of 0.9 and a false alarm probability of 10-2 , a minimum PPM slot width of 500 ps and a temporal jitter with a FWHM ~ 160 ps were estimated, for an incident photonic state with 10 photons/pulse. The potentiality of the detector for 625 Mbps OOK modulation format was also evaluated and compared with a quantum limited situation. In this case, a -3.9 dB penalty from the quantum limited BER was obtained. A new generation of detectors is currently in development, which is expected to further improve the performance.
In this work, we report InGaAs based photodiodes integrating liquid crystal (LC) microcells resonant microcavity on their surface. The LC microcavities monolithically integrated on the photodiodes act as a wavelength selective filter for the device. Photodetection measurements performed with a tunable laser operating in the telecom S and C bands demonstrated a wavelength sweep for the photodiode from 1480 nm to 1560 nm limited by the tuning range of the laser. This spectral window is covered with a LC driving voltage of 7V only, corresponding to extremely low power consumption. The average sensitivity over the whole spectral range is 0.4 A/W, slightly lower than 0.6 A/W for similar photodiodes that do not integrate such a LC tunable filter. The quality of the filter integrated onto the surfaces of the photodiodes is constant over a large tuning range (70 nm), showing a FWHM of 1.5 nm.
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