Gariano John, Djordjevic Ivan B
Opt Express. 2019 Feb 4;27(3):3055-3064. doi: 10.1364/OE.27.003055.
Due to the absorption of water, communication between two parties submersed below the water is normally performed with acoustic waves. However, with the need for higher data rates, the use of RF or optical frequencies is needed. Currently, optical wavelengths have been demonstrated for classical communication over short distances. For these short distances, if a large amount of data needs to be transmitted securely, it is not feasible for both parties to return to the surface to communicate. Additionally, it can be assumed that a third party (Eve) is located in the channel trying to gather information. The solution is to use quantum key distribution (QKD) to generate the secure key, allowing the parties to continuously encrypt and transmit the data. It is assumed the BB84 protocol using pairs of polarization entangled photons generated from a spontaneous parametric down conversion (SPDC) source of Type-II. By using entangled photons, Eve is not able to gain information without being detected. In this work, horizontal oceanic channel is studied for various distances ranging from 10 m to 100 m, depth ranging from 100 m to 200 m, and surface chlorophyll-a concentrations at a wavelength of 532 nm. The secure key rates are calculated, assuming that a low-density parity check (LDPC) error correction code is used for information reconciliation. The maximum secure key rate and optimal number of average entangled photons transmitted are then studied for the various channels.
由于水的吸收作用，水下两方之间的通信通常通过声波进行。然而，随着对更高数据速率的需求，需要使用射频或光频率。目前，光波长已被证明可用于短距离的经典通信。对于这些短距离，如果需要安全地传输大量数据，双方返回水面进行通信是不可行的。此外，可以假设第三方（伊芙）位于信道中试图收集信息。解决方案是使用量子密钥分发（QKD）来生成安全密钥，使各方能够持续加密和传输数据。假设使用基于II型自发参量下转换（SPDC）源产生的偏振纠缠光子对的BB84协议。通过使用纠缠光子，伊芙在不被检测到的情况下无法获取信息。在这项工作中，研究了水平海洋信道，其距离范围为10米至100米，深度范围为100米至200米，以及波长为532纳米时的表面叶绿素a浓度。假设使用低密度奇偶校验（LDPC）纠错码进行信息协调，计算安全密钥率。然后研究各种信道的最大安全密钥率和平均传输的最佳纠缠光子数。
