Nenad Bozinovic

Terabit-Scale Orbital Angular Momentum Mode Division Multiplexing in Fibers

A Twist on the Capacity Crunch The rate at which data can be transmitted down optic fibers is approaching a limit because of nonlinear optical effects. Multiplexing allows data to be encoded in different modes of light such as polarization, wavelength, amplitude, and phase and to be sent down the fibers in parallel. Optical angular momentum (OAM) can provide another degree of freedom whereby the photons are given a well-defined twist or helicity. Bozinovic et al. (p. 1545) were able to transmit high-bandwidth data using OAM modes in long lengths of optical fibers, thus providing a possible route to get yet more capacity through optic fiber networks. Encoding data in the twist, or helicity, of photons provides a route to increase optical communication rates in fibers. Internet data traffic capacity is rapidly reaching limits imposed by optical fiber nonlinear effects. Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capacity. We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber. Over 1.1 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 1.6 terabits per second using two OAM modes over 10 wavelengths. These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks.

Control of orbital angular momentum of light with optical fibers

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1ℏ to +1ℏ per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states.

Fluorescence endomicroscopy with structured illumination

We present an endomicroscope apparatus that utilizes structured illumination to produce high resolution (approximately 2.6 microm) optically sectioned fluorescence images over a field of view of about 240 microm. The endomicroscope is based on the use of a flexible imaging fiber bundle with a miniaturized objective. We also present a strategy to largely suppress structured illumination artifacts that arise when imaging in thick tissue that exhibits significant out-of-focus background. To establish the potential of our endomicroscope for preclinical or clinical applications, we provide images of BCECF-AM labeled rat colonic mucosa.

Optically sectioned fluorescence endomicroscopy with hybrid-illumination imaging through a flexible fiber bundle

We present an endomicroscope apparatus that exhibits out-of-focus background rejection based on wide-field illumination through a flexible imaging fiber bundle. Our technique, called HiLo microscopy, involves acquiring two images, one with grid-pattern illumination and another with standard uniform illumination. An evaluation of the image contrast with grid-pattern illumination provides an optically sectioned image with low resolution. This is complemented with high-resolution information from the uniform illumination image, leading to a full-resolution image that is optically sectioned. HiLo endomicroscope movies are presented of fluorescently labeled rat colonic mucosa.

Multimode Communications Using Orbital Angular Momentum

In this chapter, we provide a comprehensive review of multimode communications using OAM. The fundamentals of OAM are introduced first followed by the techniques for OAM generation, multiplexing/demultiplexing, and detection. We then present recent research efforts to free-space communication links and fiber-based transmission links using OAM multiplexing together with optical signal processing using OAM (data exchange, add/drop, multicasting, monitoring, and compensation). Future challenges of OAM communications are discussed at the end.

Fibers Supporting Orbital Angular Momentum States for Information Capacity Scaling

A novel mode-division-multiplexing scheme would be provided by fibers supporting stable orbital angular momentum states. We present a new class of air-core fibers that achieves this goal through enhancement of vector propagation effects.

Complex mode amplitude measurement for a six-mode optical fiber

We propose a measurement protocol and parameter estimation algorithm to recover the powers and relative phases of each of the vector modes present at the output of an optical fiber that supports the HE₁₁, TE₀₁, HE₂₁, and TM₀₁ modes. The measurements consist of polarization filtered near-field intensity images that are easily implemented with standard off-shelf components. We demonstrate the accuracy of the method on both simulated and measured data from a recently demonstrated fiber that supports stable orbital angular momentum states.

Are Orbital Angular Momentum (OAM/Vortex) States of Light Long-Lived in Fibers?

We study the evolution of OAM states in fibers, showing that they can be maintained over km-lengths with purity levels exceeding 94%. This suggests a novel means for encoding information in fiber-based quantum encryption links.

Efficient crosstalk mitigation of OAM based 400-Gbit/s QPSK data transmission in 1.1-km vortex fiber by using soft-decision LDPC codes

The efficient mitigation of crosstalk-induced “error floor” in system performance by using soft-decoding LDPC codes in an OAM-based four modes multiplexed fiber transmission system is experimentally demonstrated. A significant coding gain of >15.5 dB is achieved, depending on the amount of crosstalk from other channels.

Record-length transmission of entangled photons with orbital angular momentum (vortices)

We demonstrate, for the first time, transmission of entangled photons carrying orbital angular momentum, over km-lengths of a specially designed optical fiber, representing a thousand-fold improvement of transmission-distance over previous reports.