A new underwater optical modem based on highly sensitive Silicon Photomultipliers

Abstract

Silicon Photomultipliers (SiPMs) have recently been recognized as an interesting alternative to photomultiplier tubes (PMTs) thanks to their high sensitivity and time resolution. They can closely approach quantum-limited sensitivity in the detection of weak optical signals. Ifremer (French Research Institute for Exploitation of the Sea) and Institut Fresnel research lab have been investigating appropriate alternative solutions for PMTs in the context of underwater optical communications, and have for the first time used these new photodetector components for signal detection. A novel prototype of an optical modem based on SiPM receivers was realized with support from Osean SAS Co., a French instrumentation company. A number of lab experiments and sea trials in turbid waters and clear open sea were conducted using this modem to evaluate the practical interest of SiPMs. This paper studies the feasibility of using SiPMs for underwater optical communications. It outlines the description of the transmitter and the receiver of the modem prototype, the different techniques used to take advantage of this new technology and solutions to possible practical challenges. It also presents the methodology of the conducted sea trials and the performance evaluations in terms of range and data rate.

Silicon-Photomultiplier-Based Underwater Wireless Optical Communication Using Pulse-Amplitude Modulation

“…O-OFDM could be a solution to this problem [20], however, the limited DR of power LEDs and the NLD introduced by SiPMs suggests using more appropriate signaling schemes with a lower PAPR. In this work, we consider the use of simple non-return-to-zero (NRZ) PAM that can be readily employed at the Tx by simply switching on and off a set of LEDs (usually multiple LEDs are used at the Tx in order to increase the transmit power [9]). Note that NRZ signaling occupies a slightly larger BW (compared to root raised cosine filtering, for instance), but it has the advantage of removing the need to digital filtering at the Tx and the Rx, decreasing hence system implementation complexity and circuit power consumption.…”

“…Allowing operation over relatively long range underwater links, SiPMs have the advantages of lower cost and operating bias voltage, reduced size, weight, and power (SWaP), mechanical robustness, and insensitivity to magnetic fields, as compared with PMTs. Although currently available components suffer from limited dynamic range (DR) and relatively small active areas, due to their operational flexibility, SiPMs are likely candidates to extend the range of current UWOC systems and their use is foreseen in next generation underwater communication systems [9].…”

“…In practice, the increase in the transmit power can be achieved using multiple LEDs at the Tx, see for instance the use of 100 LEDs in a recent prototype in[9]. This way, the response time of the Tx is not affected, as compared to the case of using a high-power LED with a higher parasitic capacitance.…”

Optical OFDM for SiPM-Based Underwater Optical Wireless Communication Links

“…Since the limited LED DR constrains the transmit power, a rational solution for increasing the link span is to use multiple LEDs by putting them into an array, thus increasing the effective transmit optical power [9,53]. Consider 100 LEDs at the Tx, modulated simultaneously, and set the transmit power per LED to P Tx,e = 50 mW (this way, the total transmit electrical power is 5 W).…”

Effects and Constraints of Optical Filtering on Ambient Light Suppression in LED-Based Underwater Communications

“…In contrast to stationary applications, mobile ones generally require wider field of views (FOVs) for transmitting and receiving. To achieve a hemispherical or even spherical characteristic, it is self-evident to combine segments comprising off-the-shelf parts with limited FOV [ 3 , 4 , 5 , 6 ]. Alternatively, an appropriate optical concentrator could be used to extend the FOV of a single detector.…”