A hollow core fiber (HCF) link is characterized by structural properties selected to support and sustain light propagation in a fundamental mode and in at least one higher-order mode. Connected to a proximal end of the HCF link, there is a mode coupler configured to couple a data signal into the fundamental mode and to couple an obfuscating signal into the at least one higher-order mode for simultaneous propagation of the data signal and the obfuscating signal on the HCF link, where the obfuscating signal substantially overlaps the data signal in spectral content. At a distal end of the HCF link, there is a mode splitter configured to split a first optical signal detected in the fundamental mode from a second optical signal detected in the at least one higher-order mode.

A free-space optical communication system has a conversion assembly, a fiber array, and a wavelength selective switch (WSS) assembly. The conversion assembly converts circular polarization states of incoming optical signals to linear polarization states and converts linear polarization states to circular polarization states for outgoing optical signals. The fiber array has polarization-maintaining (PM) optical fibers arranged in optical communication between the conversion assembly and the WSS assembly to preserve the linear polarization states of the optical signals. The WSS assembly has free-space optics, such as dispersion element and beam-steering element, with optical axes arranged relative to the PM optical fibers. The WSS assembly selectively switches WDM channels of the optical signals relative to the PM optical fibers. Fast and slow axes of the PM optical fibers are aligned to the optical axes of the free-space optics.

Various embodiments relate to a method including: coupling one or more optical spatial pilot signals into a first end of optical fiber, wherein the optical fiber is a multimode optical fiber; Reflecting and modifying each mode of the optical pilot signals at a second end of the optical fiber; receiving a reflected portion of the one or more optical spatial pilot signals at the first end of the of the optical fiber in response to the reflected portion having propagated through the optical fiber in both directions; processing the reflected spatial pilot to determine components of one of a round-trip transfer matrix of the optical fiber and a single-direction transfer matrix of the optical fiber.

A system for enabling signal penetration into a building includes first circuitry, located on an outside of the building, for receiving signals at a first frequency that experiences losses when penetrating into an interior of the building and converting the received signals at the first frequency into a first format that overcome the losses caused by penetrating into the interior of the building over a wireless communications link. The first circuitry further includes a first transceiver, implementing a first transmission chipset for RF transmissions in the first format that counteracts losses occurring when penetrating into the interior of the building, for receiving the signals at the first frequency and converting the received signals at the first frequency into the first format that overcomes the losses caused by penetrating into the interior of the building. Second circuitry, located on the interior of the building is communicatively linked with the first circuitry for receiving and transmitting the converted received signals in the first format. The second circuitry further includes a second transceiver, implementing the first transmission chipset, for receiving and transmitting the converted signals in the first format from/to the first transceiver on the exterior of the building.

A communications device may include a local device, a remote device, and a multi-mode optical fiber coupled between the local device and the remote device. The local device may include a local spatial optical mux/demux coupled to the multi-mode optical fiber and having first and second local optical outputs and first and second local optical inputs, and a local electro-optic E/O modulator coupled to the second local optical input. The remote device may include a remote spatial optical mux/demux coupled to the multi-mode optical fiber, and a remote E/O modulator configured to generate a modulated signal onto a first remote optical output based upon modulating the first optical carrier signal from a first remote optical input responsive to a radio frequency (RF) electrical input signal.

An optical data transmitter includes vertical cavity surface-emitting lasers and an all-optical spatial mode multiplexer. Each vertical cavity surface-emitting laser is configured to output a data modulated optical carrier at a center wavelength of less than one micrometer. The all-optical spatial mode multiplexer has an optical output and optical inputs. Each vertical cavity surface-emitting lasers is optically connected to one or more of the optical inputs of the all-optical spatial mode multiplexer. The all-optical spatial mode multiplexer is configured to cause at least two of the vertical cavity surface-emitting lasers to excite linearly independent combinations of one or more optical spatial propagating modes of an optical fiber in response to the optical output being coupled to a near end of the optical fiber.

The present invention relates to a method for dual-polarisation SDM transmission over optical fibre. The transmission method uses specific I/Q coding for combating the effects of PDL. The modulation symbols to be transmitted on the 2N polarisation states of the N wavelengths are broken down into real values and imaginary values (220). A first orthogonal linear transformation (230-1) is applied to the vector of the real values thus obtained and a second orthogonal linear transformation (230-2), separate from the first, is applied to the vector of the imaginary values thus obtained. A complex scalar solving an irreducible polynome of [X] in is multiplied with the first or second transformed vector before the two transformed vectors are summed (240) in order to provide a vector of transmission symbols for modulating the different states of polarisation of the spatial elementary channels.

The invention relates to an optical link comprising N optical fibers, with N?2. Each optical fiber comprises an optical core and an optical cladding surrounding the optical core, the optical core having a single ?.sub.i graded-index profile with ?.sub.i?1, and the optical core having a radius R.sub.1i, where i E [1; N] is an index designating said optical fiber. Said optical cladding comprises a region of depressed refractive index n.sub.trenchi, called a trench, surrounding the optical core. According to embodiments of the invention, for all optical fibers in said link, said optical core radius R.sub.1i and said length L.sub.i are chosen such that R.sub.1i?13.5 ?m and so as to satisfy a criterion C of quality. Thus, the invention provides a few-mode optical fiber link, which allow guiding an increased number of LP modes as compared to prior art FMF links, while reaching low Differential Mode Group Delay.

A system includes a transmitter with multiple transmit devices each having an OAM multiplexer that converts multiple input signals into an OAM beam. Each transmit device outputs a coaxial group of orthogonal OAM beams. The system also includes a receiver that has multiple receive devices each having an OAM demultiplexer that receives the group of OAM beams from a corresponding transmit device. The OAM demultiplexer also converts the coaxial group of mutually orthogonal OAM beams into a plurality of received signals corresponding to input signals represented by the OAM beams. The receiver also includes a MIMO processor that has an equalizer that determines a transfer function corresponding to crosstalk of each of the plurality of received signals. The MIMO processor also reduces the crosstalk of each of the plurality of received signals based on the transfer function and updates the transfer function.

One aspect of the present invention is an optical transmission system including a transmitter connected to a transmission line having M spatial channels, and a receiver that receives a signal transmitted from the transmitter via the transmission line, wherein the transmitter includes: an allocator that allocates a transmission bit string transmitted to the transmission line into a bit string serving as a basic signal and a bit string serving as spatial channel information; a generator that generates N (M>N) signals from the bit string serving as the basic signal allocated by the allocator; and a selector that selects N spatial channels, through which the N signals generated by the generator are transmitted, from the M spatial channels on the basis of the bit string serving as the spatial channel information allocated by the allocator.