Kaitlyn Morgan

Multi-gigabit/s underwater optical communication link using orbital angular momentum multiplexing.

In this work we experimentally demonstrated an underwater wireless optical communications (UWOC) link over a 2.96 m distance with two 445-nm fiber-pigtailed laser diodes employing Orbital Angular Momentum (OAM) to allow for spatial multiplexing. Using an on-off keying, non-return-to-zero (OOK-NRZ) modulation scheme, a data rate of 3 Gbit/s was achieved in water with an attenuation coefficient of 0.4128 m-1 at an average bit error rate (BER) of 2.073 × 10-4, well beneath the forward error correction (FEC) threshold.

Spatial multiplexing for blue lasers for undersea communications

Space division multiplexing of optical beams has recently been demonstrated for improving the bandwidth of optical communication links. This paper will explore the use of space division multiplexing utilizing blue lasers for potential undersea applications. Experimental results will be shown for optical vortices utilizing a range of charge numbers corresponding to various Orbital Angular Momentum states.

Free Space Propagation of Concentric Vortices through Underwater Turbid Environments

The propagation of concentric vortex beams for communication through turbid water is studied and temporally modulated. Experiments show the spatial profile is maintained over 11.2 attenuation lengths using commercial antacids as a scattering agent.

Attenuation of beams with orbital angular momentum for underwater communication systems

Beams carrying orbital angular momentum (OAM) have been shown to possess unique properties in scattering environments. However, a limited source of quantifiable data is available on the propagation properties of these beams through turbid water in the context of underwater optical communication systems. In this work we investigate differences in attenuation between beams with and without OAM in line-of-sight geometries.

Free space propagation of concentric vortices through underwater turbid environments

Concentric optical vortex beams of 3-petal, 5-petal, and 6-petal spatial profiles are generated at 450 nm using a single diffractive optical element. The spatial and temporal propagation characteristics of these beams are then studied in a scattering underwater environment. Experimental results demonstrate a less than 5% reduction in the spatial pattern for turbidities in excess of 10 attenuation lengths. The temporal properties of concentric vortex beams are studied by temporally encoding an on-off keyed, non-return-to-zero (OOK-NRZ) data stream at 1.5 GHz.

Design and fabrication of diffractive optics for orbital angular momentum space division multiplexing

This work presents the design and fabrication of diffractive optical elements for use in optical communication systems. The device geometry uses a vortex pattern to impart orbital angular momentum (OAM) onto an incident beam, providing a robust method for transmitting information through free space. Two refractive elements were designed and fabricated to use log-polar coordinate transformation of an incident OAM beam at 1550 nm for communications systems. Furthermore, diffractive elements were designed based on the phase profile of this refractive element. Fabrication of the devices uses conventional photolithography on a fused silica substrate.

The detection of objects in a turbid underwater medium using orbital angular momentum (OAM)

We present an investigation of the optical property of orbital angular momentum (OAM) for use in the detection of objects obscured by a turbid underwater channel. In our experiment, a target is illuminated by a Gaussian beam. An optical vortex is formed by passing the object-reflected and backscattered light through a diffractive spiral phase plate at the receiver, which allows for the spatial separation of coherent and non-coherent light. This provides a method for discriminating target from environment. Initial laboratory results show that the ballistic target return can be detected 2-3 orders of magnitude below the backscatter clutter level. Furthermore, the detection of this coherent component is accomplished with the use of a complicated optical heterodyning scheme. The results suggest new optical sensing techniques for underwater imaging or LIDAR.

Underwater optical communication link using Orbital Angular Momentum space division multiplexing

This work demonstrates an underwater optical link utilizing Orbital Angular Momentum (OAM). Space division multiplexing is used to increase the data rate over a range of modulation frequencies.

Blue-light digital communication in underwater environments utilizing orbital angular momentum

Underwater optical communication has recently become the topic of much investigation as the demands for underwater data transmission have rapidly grown in recent years. The need for reliable, high-speed, secure underwater communication has turned increasingly to blue-light optical solutions. The blue-green visible wavelength window provides an attractive solution to the problem of underwater data transmission thanks to its low attenuation, where traditional RF solutions used in free-space communications collapse. Beginning with GaN laser diodes as the optical source, this work explores the encoding and transmission of digital data across underwater environments of varying turbidities. Given the challenges present in an underwater environment, such as the mechanical and optical turbulences that make proper alignment difficult to maintain, it is desirable to achieve extremely high data rates in order to allow the time window of alignment between the transmitter and receiver to be as small as possible. In this paper, work is done to increase underwater data rates through the use of orbital angular momentum. Results are shown for a range of data rates across a variety of channel types ranging in turbidity from that of a clear ocean to a dirty harbor.

Propagation and dynamic manipulation of coherent orbital-angular-momentum modes through underwater turbid environments

This work demonstrates the propagation and dynamic manipulation of composite vortex beams through an underwater turbid environment. These profiles are generated through the coherent superposition of several different optical orbital-angular momentum modes using a 543.5 nm HeNe laser with a coherence length of 58.5 mm. The spatial coherence is maintained after propagation through 0.508 m of water with a scattering coefficient of 9.57m-1.