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Broadband Parallel-Fiber Optical Link for Short-Distance Interconnection with Multimode Fibers
Abstract
In a multimode step-index fiber the propagation angle of a beam is conserved over short distances even if the fiber is bent slightly. This behavior can be exploited for a multiplexed signal transmission by the assignment of different channels to different propagation angles [angle-division multiplexing (ADM)]. Thus parallel transmission can be achieved. Because each channel occupies only a subrange of the fiber's numerical aperture, modal dispersion is reduced compared with single-channel transmission through the same fiber. The transmission properties of an ADM-based transmission line are analyzed for short propagation distances. Passive all-optical setups for multiplexing and demultiplexing operations are proposed. Cross-talk measurements are shown for a transmission with a length of 8 m and 13 multiplexed channels.
... Involving the spatial dimension seems one of the mainstream and promising directions for a substantial increase in the capacity of optical communication channels by transmitting several data channels through a single data link [1][2][3][4][5][6][7][8]. Angular multiplexing [7,8] and mode-division multiplexing (MDM) [1,2,5,6] are some of recently discussed options for space-division multiplexing (SDM). ...
... Involving the spatial dimension seems one of the mainstream and promising directions for a substantial increase in the capacity of optical communication channels by transmitting several data channels through a single data link [1][2][3][4][5][6][7][8]. Angular multiplexing [7,8] and mode-division multiplexing (MDM) [1,2,5,6] are some of recently discussed options for space-division multiplexing (SDM). In particular, the multimode (MM) free-space optical schemes resorting to orbital angular momentum were demonstrated in [9][10][11][12][13][14][15][16]. ...
... The design was done per Eqs. (3), (8), and (11) with m n 2, a 0, b 0, l 0, ν ζ;y 10 lp∕mm in the y-axis direction, and options of design parameters jζj 0.15, jζj 0.33, and jζj 0.42; the last value was actually used in our experiments. ...
Optical aspects of space-division multiplexing with orthogonal modes of coherent light were considered in theory and experiments with the coherent optical correlator. We resorted to the mathematical tool of generating functions and technologies of diffractive optical elements to implement complex spatial filters matched to rotationally symmetrical transverse modes. Successful multiplexing and demultiplexing in free-space transmission of low-frequency temporally modulated signals through different spatial modes was demonstrated. Experimental results show low cross talk between different mode channels and feasibility of further applications in multimode fiber optical communication data links.
The switching backplane of fiber array has a great prospect in large-scale multi-rack connection system as connecting equipments. In order to conquer the difficulties in producing the backplane of dense fiber array, starting from the traditional structure of Crossbar of switching backplane, an original method of programming the structure of backplane by gradual routing is adopted, and applied to the preparation of backplane. A set of outfit and the flow of producing are also proposed to predigest the process of producing. The advantage of this method is testified through the preparation of a sample backplane and its experimental results.
One half decade after the first edition the book is now published in a completely new revision, updated and doubled in size. The Polymer Optical Fiber Application Center of the University of Applied Science was responsible for this second edition. A huge number of measurements of bandwidth, optical properties and the possible transmission capacities of more than a dozen large diameter fiber versions are included. Many internationally published results are shown in the new edition. The POF was a niche technology only a few years ago. In the meantime, millions of cars drive with POF onboard networks. Due to the rapidly growth of the number of private broadband access lines and the increase in the available bit rate at the same time, mainly driven by IP TV applications, the POF will be used in home networks more and more. This handbook shows available commercial solutions as well as the potentials for future applications. Further application areas are optical waveguides, POF as low cost sensors and multi parallel data connections. More than 1000 figures, 600 references and numerous tables complete the text.
Capabilities and limitations of diffractive optics in mode division multiplexing for optical communications are investigated theoretically and experimentally. Computer generated multichannel matched optical spatial filters provided low cross-talks in de-multiplexing of several Laguerre-Gaussian modes.
Angle division multiplexing (ADM) is a multiplexing scheme which is applicable to optical signal transmission through multimode step-index fibers. ADM allows for parallel and high-bandwidth transmission by using passive components, i.e. no external control is necessary. The fiber quality limits the simultaneous optimization of transmission distance, number of channels and cross-talk. This paper reports on first experiments with an ADM based data link over 10 m between workstations with 8 Gigabit-Ethernet channels at a cross-talk of better than -10 dB. For a micro-optical integration of the ADM system design rules and tolerance considerations are discussed.
Zusammenfassung
Die stetig wachsende Anforderung an Rechenleistung hat neben der Leistungssteigerung von Einzelsystemen auch zur Nutzung verteilter Ressourcen geführt. Im LAN-Bereich wird die Rechenaufgabe partitioniert und auf mehrere Workstations in einem Netzwerk verteilt (Cluster-Computing). Auf der Systemebene (SAN) werden einzelne spezialisierte Sub-Systeme auf einer Platine (board-to-board) oder in einem Raum (rack-to-rack) verbunden. Die Begrenzung verteilter Systeme ist nicht mehr durch die Rechenleistung, sondern durch die Übertragungsbandbreite und die Kommunikationslatenz gegeben. Es werden für die elektrische bzw. optische Übertragung stellvertretend zwei Systeme beschrieben, die breitbandige Verbindungen mit geringer Latenz ermöglichen und keine externe Steuerung bzw. Überwachung benötigen. Für die elektrische Übertragung ist dies die in Entwicklung befindliche Netzwerkkarte "ATOLL" (Atomic low Latency), die das gesamte Protokollmanagement einschließlich Fehlerkorrektur wie auch das Routing vollkommen autonom übernimmt. ATOLL bietet einen bidirektionalen 4×4-Kreuzschienenverteiler mit Übertragungsbandbreiten von bis zu 2 GByte/s. Als optisches Übertragungssystem für Board-to-Board- oder Rack-to-Rack-Anwendungen wird ein faserbasiertes Multiplex-Übertragungssystem vorgestellt. Die Multiplexfunktion wird rein passiv optisch realisiert; externe Steuersignale entfallen somit. Das System erlaubt die Übertragung von typischerweise 12 bis 16 logischen Kanälen durch eine einzige Faser und über Entfernungen von einigen cm bis zu einigen Metern mit akkumulierten Bandbreiten im Bereich von 1 THz×m. Es wird ein System mit mikrointegrierten optischen Modulen und Schnittstellen in Form von standardisierten Fasersteckern vorgestellt.
Optical interconnection and signal distribution at the backplane, board, and substrate level can be implemented using thin-film active optoelectronic devices embedded in polymer waveguide structures. These active embedded devices eliminate the need for optical beam turning to and from photodetectors and emitters, respectively, for inputs and outputs to the substrate waveguides. In this paper, optical interconnections using fully embedded thin-film metal-semiconductor-metal (MSM) photodetectors in polymer optical waveguides are demonstrated, and the experimental characterization of these thin-film MSMs embedded in polymer waveguides is reported. To illustrate the potential for high-level signal distribution at the backplane, board, and substrate levels, a 1×4 balanced multimode interference (MMI) coupler has also been demonstrated in a photoimageable polymer for the first time. Finally, a 1×4 thin-film MSM photodetector array has been embedded in the output arms of the a photoimageable polymer MMI for the first time, and the MSM array photocurrent outputs from the 4 arms show that highly balanced optical signal distribution has been achieved.
Angular division multiplexing (ADM is an optical multiplexing technique that offers an important option on for attaining multichannel transmission on a single fiber required in local networks, industrial control systems and using other fiber applications.
In this paper the applications of a photopolymerizable holographic recording material are discussed. The holographic recording characteristics of the photopolymer include very high diffraction efficiency in transmission mode and relatively low exposure energy, typically tens of milliJoules. The recording material has a resolution of 3000 lines/mm and there is not distortion of slanted gratings. This allows high inter-beam angles in transmission recording and makes the material particularly suitable for the holographic recording of diffractive optical elements. The implications of the resolution limit and other material properties for DOE fabrication are discussed in some detail and results for the recording of on- and off-axis focusing and beam splitting diffractive optical elements are presented. One of the most significant advantages of this material is that it is self-developing. As well as making ordinary transmission holography and DOE recording more convenient, this makes the material particularly useful for both live fringe and double exposure holographic interferometry. Live fringes can be viewed as soon as any stress is applied to the object. This material's unique self-developing properties also mean that the growth of the diffraction efficiency of a holographically recorded DOE can be monitored as it is being recorded. This type of on-line control is extremely useful in DOE fabrication particularly when controlling the ratio of beam splitters.
Loss, coupling, and delay differences among the modes of multimode fibers influence their transmission characteristic in a complicated way. An approximation of the modes by a continuum leads to a comprehensive description of these interrelations. We relate the mode power distribution to the far-field output and calculate these distributions as functions of the fiber length and the input. We report measurements of the far-field distributions at various lengths of a cladded low-loss multimode fiber. A comparison of theory and experiment yields a quantitative estimate of the mode coupling involved. We associate this coupling with random irregularities of the fiber configuration and straightness, and construct a quantitative model of such irregularities.
We propose a scalable bit-parallel optical interconnect method for use in large-bandwidth interprocessor communications. Flexible fiber image guides are used to transmit spatially parallel optical data between a vertical-cavity surface-emitting laser array and a photodetector array. We have studied a lens-based and a fiber-image-taper-based input-output coupling scheme and have modeled power-loss mechanisms and resolution-degradation mechanisms associated with the schemes. We have also performed some experiments to confirm the operational principles of the proposed schemes and to investigate the power efficiency and imaging-resolution performance of the interconnect schemes. Our study indicates that the proposed interconnects can offer a scalable method to transmit hundreds of channels of multigigabyte per second per channel optical data in parallel.
We report the fabrication of planar microlenses with numerical apertures (N.A.'s) of 0.2 by field-assisted Ag-Na ion exchange in glass. To measure the N.A. of microlenses, different definitions can be used. We discuss the issue of measuring the N.A. and suggest an additional definition based on diffraction-limited performance. According to a simple model, the N.A. of a spherical lens is limited by the maximum index difference. Owing to this model, the N.A. for Ag-Na ion exchange is limited to a value of ~0.1. From measurements of microlenses, fabricated by field-assisted ion exchange, we obtained N.A.'s as high as 0.2, providing for diffraction-limited performance within the whole aperture.
A simple method has been devised for the experimental determination of mode conversion coefficients in multimode fibers and involves only the observation of the far-field output as the angle of incidence of a collimated input beam is changed. The normalized mode coupling coefficient in a liquid-core fiber is D = 3 x 10(-6) rad(2) m(-1) and increases by as much as a factor of 10 when transverse pressure is applied. Values some 2 orders of magnitude larger are found in glass-core fibers. There is good agreement between the theory presented and experiment.
Experimental measurements of the spatial and temporal transfer of power of a 225-m length of low-loss optical waveguide have been made. In particular, measurement of the angular attenuation showed substantial loss of the high order modes, which reflected itself in an ~8.2 nsec/km decrease in measured dispersion. Additionally there was a reduction of the effective numerical aperture from 0.15 to 0.12. Negligible mode coupling was observed in this particular waveguide, which allowed a phenomenological calculation of temporal output for an assumed uniform excitation of all modes. This agreed well with experimental measurements. Calculation of this output from knowledge of the index profile is presently not in agreement, and some possible reasons are indicated.
A concept of angular multiplexing of several communication channels in a relatively short step-index fiber is described. The angular dependence of the outgoing light flux and the temporal impulse response are calculated for slab waveguides and round fibers in terms of the fiber's length and the excitation conditions. Calculations of the inpulse response in the presence of mode coupling are based on a simple model which is found to be adequate for short fibers. Crosstalk levels are calculated by integrating the flux over the aperture of the detectors. Measurements of angular flux distribution, temporal impulse response, and crosstalk levels agree with theoretical prediction and validate the proposed concepts. To increase light levels, parallel excitation of each channel by several light sources is suggested and tested. Also, light collection efficiency is increased by employing lenses and annular mirrors to deflect and focus the light from each channel to small-area detectors. Given a 25 m long fiber with a coupling constant of 10<sup>-5</sup>rad<sup>2</sup>/m, it is possible to multiplex four channels with cross-talk of about -25 dB and information rates ranging from 10<sup>9</sup>bits/s to 10<sup>10</sup>bits/s for each channel.
Angular divi-sion multiplexing in optical fibers
- G J Herskowitz
- H Kobrinsky
- U Levy
G. J. Herskowitz, H. Kobrinsky, and U. Levy, " Angular divi-sion multiplexing in optical fibers, " Laser Focus 19, 83– 88 ͑1983͒.
Numerical Recipes in C ͑Cambridge U. Press, Cam-bridge
- Flannery
Flannery, Numerical Recipes in C ͑Cambridge U. Press, Cam-bridge, 1992͒, p. 236.