An optical data link includes first and second pluralities of transmission devices, at least one of which is configured as an array. A multichannel transmission link has a first end connected to the first plurality of transmission devices and a second end connected to the second plurality of transmission devices so as to form a plurality of parallel transmission channels therebetween. The multichannel transmission link includes a multicore fiber with a plurality of individual cores having a configuration matching the array configuration of the at least one plurality of transmission devices. The multicore fiber has an endface connected directly to the at least one plurality of transmission devices, with the individual cores of the multicore fiber aligned with respective devices in the at least one plurality of transmission devices. Further described are access networks and core networks incorporating a transmission link comprising at least one span of a multicore fiber.

Multicore fiber transmission systems and methods

In recent years, free space optical (FSO) communication has gained significant importance owing to its unique features: large bandwidth, license free spectrum, high data rate, easy and quick deployability, less power and low mass requirement. FSO communication uses optical carrier in the near infrared (IR) and visible band to establish either terrestrial links within the Earths atmosphere or inter-satellite or deep space links or ground to satellite or satellite to ground links. However, despite of great potential of FSO communication, its performance is limited by the adverse effects (viz., absorption, scattering and turbulence) of the atmospheric channel. Out of these three effects, the atmospheric turbulence is a major challenge that may lead to serious degradation in the bit error rate (BER) performance of the system and make the communication link infeasible. This paper presents a comprehensive survey on various challenges faced by FSO communication system for both terrestrial and space links. It will provide details of various performance mitigation techniques in order to have high link availability and reliability of FSO system. The first part of the paper will focus on various types of impairments that poses a serious challenge to the performance of FSO system for both terrestrial and space links. The latter part of the paper will provide the reader with an exhaustive review of various techniques used in FSO system both at physical layer as well as at the upper layers (transport, network or link layer) to combat the adverse effects of the atmosphere. Further, this survey uniquely offers the current literature on FSO coding and modulation schemes using various channel models and detection techniques. It also presents a recently developed technique in FSO system using orbital angular momentum to combat the effect of atmospheric turbulence.

Free Space Optical Communication: Challenges and Mitigation Techniques

Next-generation high-end data processing systems such as Internet switches or servers are approaching aggregate bandwidths in excess of 1 Terabit per second. In the case of Internet switches, the increase of fiber bandwidth that is caused by the introduction of Dense Wavelength Division Multiplexing leads to an increase of system size from single-shelf to multi-rack configurations. Intra-system interconnects will therefore span from centimeters (on-board) up to tens of meters (rack-to-rack). The task of providing hundreds of individual links at speeds in excess of 10 Gigabit per second over these distances becomes increasingly difficult for conventional copper-based technology. Using a packet switch system as an example application, we define a set of interconnect requirements for future large-scale systems. Distinguishing three interconnect classes (on-board, card-to-card over a backplane, rack-to-rack), we study the expected limits of copper-based solutions from an application point of view. After an overview of the state of the art in optical interconnect technology, we compare available technologies with the initially defined requirements. From this, we deduct key focus areas for future optical interconnect research. Finally, we present some of our recent activities in the field of waveguide and free-space based board-to-board interconnects.

High-density optical interconnects within large-scale systems

Optical backplanes with integrated polymer waveguides

Active alignment of a 1 x 8 free-space optical switch was studied experimentally. Optical signals, carried on single-mode fibers, were switched by a ferroelectric liquid-crystal-on-silicon spatial light modulator. Continuous measurement of the in-coupled power to the fibers provided feedback for the switch control. The switch automatically located and locked to the output fibers. An advantage with adaptive switches of a similar kind is relaxed geometrical tolerances in the switch assembly. Further, such switches can adapt to possible geometrical changes and light wavelength drift during operation.

Adaptive beam steering implemented in a ferroelectric liquid-crystal spatial-light-modulator free-space, fiber-optic switch.

We have designed an optical backplane with free-space optical interconnections using tunable beam deflector arrays and a mirror for terabit per second class bookshelf-assembled asynchronous transfer mode (ATM) switches. Optical beam transmitter arrays and optical beam receiver arrays are placed on the edges of a printed circuit board. Optical beams are deflected individually by the tunable deflector arrays, emitted obliquely and downward, and reflected at the mirror placed on the backplane, passing through some printed circuit boards, and reach the targeted receivers on the edges of printed circuit board. As a preliminary experiment, we show that board-to-board free-space arbitrary optical interconnections are possible using a tunable beam deflector array and 1-mm-pitch 2×2 optical beam array provided with a vertical cavity surface emitting laser diode, we also show that these optical interconnections are made very stable by attaching reinforcing frames to the printed circuit board. Furthermore, we show that more than 1000 channel interconnections per printed circuit board are possible using a 1-mm-pitch optical beam array. As the speed per channel may be more than 1 Gbit/s, the throughput of the interconnection per board reaches almost the terabit/s level. Using this optical interconnection system is used, ATM switches with a huge capacity of 1.0 to 10 Tbit/s will be possible. © 1998 Society of Photo-Optical Instrumentation Engineers.

Optical backplane with free-space optical interconnections using tunable beam deflectors and a mirror for bookshelf-assembled terabit per second class asynchronous transfer mode switch

We propose free-space optical interconnections for a
bookshelf-assembled terabit-per-second-class ATM switch. Thousands
of arrayed optical beams, each having a rate of a few gigabits per
second, propagate vertically to printed circuit boards, passing through
some boards, and are connected to arbitrary transmitters and receivers
on boards by polarization controllers and prism arrays. We describe
a preliminary experiment using a 1-mm-pitch 2 × 2 beam-collimator
array that uses vertical-cavity surface-emitting laser
diodes. These optical interconnections can be made quite stable in
terms of mechanical shock and temperature fluctuation by the attachment
of reinforcing frames to the boards and use of an autoalignment
system.

Board-to-Board Free-Space Optical Interconnections Passing through Boards for a Bookshelf-Assembled Terabit-Per-Second-Class ATM Switch.

PURPOSE: To eliminate the need of an electric connector and mechanical alignment, to enhance economization, and to realize ultra high-speed, ultra high- density and ultra large-capacity optical connection between boards by connecting a surface light emitting laser array, an optical fiber optical connection circuit and a surface detector array by a light beam in free space without bringing them into contact with each other. CONSTITUTION: Optical interconnection between the boards is performed by using a surface light emitting laser 1-3 and a surface detector 1-4 on the board and connecting them through an optical fiber. They are connected by the light beam in the free space. Namely, the optical fiber, the laser 1-3 and the detector 1-4 are coupled by the light beam in optical contact with each other without using a connector. By such optical contact, trouble on the damage caused by the mechanical contact of the fiber, the laser array and the detector array in the case of drawing and inserting the board is avoided. By providing a guide pin 1-6, the fiber array and the surface light emitting laser array 1-3, the surface detector 1-4 are connected.

Inter-board optical interconnection device

PROBLEM TO BE SOLVED: To provide an inter-board optical interconnection equipment capable of easily adjusting deviation with an optical system even when the position of board is deviated, and correctly aligning light beams between adjacent boards. SOLUTION: A variable apex angle prism 2-7 is arranged between adjacent boards 2-1 and the signal from light beam detection sensor 2-5 is fed back to the variable apex angle prism 2-7 so that an optical signal beam from a planar light emitting laser array 2-2 on one board can be made incident on any desired detector array 2-4 on the other board. Thus, the advancing direction of optical signal beam from the planar light emitting array 2-2 on one board to the detector array 2-4 on the other board is controlled through the variable apex angle prism.

Inter-board optical interconnection equipment

PROBLEM TO BE SOLVED: To provide an optical interconnection device between boards economically and exactly performing optical connection without necessitating exact control of the wavelength of a light source. SOLUTION: Light beam arrays 2-7 generated from surface light emitting arrays 2-2 having lens arrays 2-3 mounted on the end parts of the respective boards 2-1, are received by light deflection control array elements 2-5, the traveling direction of the light beam array is variably controlled for every individual beam and is made obliquely incident on mirrors 2-6. The light beam arrays 2-7 reflected by the mirrors 2-6 are received by photodetector arrays Z-4 having the lens arrays 2-3 and a light beam from a desired board is connected to the photodetector of the desired board.

Hino Shigeki

Papers

Optical backplane with free-space optical interconnections using tunable beam deflectors and a mirror for bookshelf-assembled terabit per second class asynchronous transfer mode switch

Board-to-Board Free-Space Optical Interconnections Passing through Boards for a Bookshelf-Assembled Terabit-Per-Second-Class ATM Switch.

Inter-board optical interconnection device

Inter-board optical interconnection equipment

Optical interconnection device between boards