Safety Analysis for Laser-based Optical Wireless Communications: A Tutorial

Abstract

Light amplification by stimulated emission of radiation (laser) sources have many advantages for use in high data rate optical wireless communications. In particular, the low cost and high-bandwidth properties of laser sources such as vertical-cavity surface-emitting lasers (VCSELs) make them attractive for future indoor optical wireless communications. In order to be integrated into future indoor networks, such lasers should conform to eye safety regulations determined by the international electrotechnical commission (IEC) standards for laser safety. In this paper, we provide a detailed study of beam propagation to evaluate the received power of various laser sources, based on which as well as the maximum permissible exposure (MPE) defined by the IEC 60825-1:2014 standard, we establish a comprehensive framework for eye safety analyses. This framework allows us to calculate the maximum allowable transmit power, which is crucial in the design of a reliable and safe laser-based wireless communication system. Initially, we consider a single-mode Gaussian beam and calculate the maximum permissible transmit power. Subsequently, we generalize this approach for higher-mode beams. It is shown that the M -squared-based approach for analysis of multimode lasers ensures the IEC eye safety limits, however, in some scenarios, it can be too conservative compared to the precise beam decomposition method.Laser safety analyses with consideration of optical elements such as lens and diffuser, as well as for VCSEL array have been also presented. Skin safety, as another significant factor of laser safety, has also been investigated in this paper. We have studied the impacts of various parameters such as wavelength, exposure duration and the divergence angle of laser sources on the safety analysis by presenting insightful results.

Multi-User Rate Splitting in Optical Wireless Networks

“…We consider the use of VCSELs as transmitters under eye safety regulations [9], [10]. The beam profile of the VCSEL is Gaussian dictated by the DC bias current applied, and its transmitted power is determined based on the beam waist W 0 , the wavelength λ and the distance d through which the beam travels.…”

“…assuming photodiode m of user k is located right under transmitter l, more mathematical expressions and details on the received power calculations in different scenarios can be found in [9], [10].…”

“…The third constraint limits the power allocated to the private message intended to a certain user, k ∈ K g , where it must be less than or equal to the total power P T p devoted to send the private messages of the K g users. The last constraint defines the feasible region of the optimization problem, as well as ensures that the total power consumed by G groups is less than or equal to the maximum power consumption P T allowed in the network, which can be calculated according to [9] under eye safety regulations due to the use of the VCSEL as an optical transmitter.…”

“…However, the total radiated power of the VCSELs must be within eye safety regulations. It was shown that VCSEL-based OWC networks can provide up to terabits per second (Tbps) aggregate data rates [9]- [11].…”

Terabit Optical Wireless-Fiber Communication With Kramer-Kronig Receiver—Part II

“…As a consequence, the safety of people working around these systems is an important design factor. This is subject to existing standards for fiber and wireless systems [4]. The optical power that reaches the eyes and skin is limited to a level that cannot cause any health concerns.…”