PARALLEL FIBER-OPTIC MODULES (PFOM) - THE ULTIMATE SOLUTION FOR YOUR HIGH-BANDWIDTH INTERCONNECTIONS!
Optical-based interconnections for high data rates are well known to offer key advantages over electrical cabling solutions. The prime motivation for optical interconnections is their extended reach.
For example, electrical CX-4 cabling, which provides a 4x2.5-Gbps and 4x3.125-Gbps solution for Infiniband and XAUI, respectively, generally offers a reach of less than 15m. In comparison, a PFOM (Parallel Fiber Optic Module) solution offers an extended reach in excess of 100m, at the same time providing excellent signal integrity and thus no requirement for signal pre- or postprocessing (e.g., pre-emphasis). Programming the signal in order to maximize reach, as is often required for electrical interconnections such as XAUI, is a power-hungry process. Eliminating this requirement by using a PFOM solution is therefore highly beneficial.
An optical solution also greatly simplifies cable management and system installation. High-performance electrical cabling, such as CX-4, is bulky, inflexible (large bending radius) and fragile. This makes handling, routing, installation and maintenance difficult. In addition, an MPO-based connector, as is used with PFOMs, doubles the achievable edge density.
Another advantage of optical over electrical solutions is the increased electromagnetic isolation of optical fiber, i.e., no EMI susceptibility and no radiated emissions, which particularly benefits harsh-environment applications (e.g., avionic, industrial, military).
As data rates increase, for example up to 5 Gbps and through to 10 Gbps, the limitations of electrical interconnections become even greater, in particular with respect to power consumption and achievable reach. Optical architectures, and especially PFOMs, offer direct scalability to the higher data throughputs, which means the investment in optical interconnections will pay dividends across several product generations.
ZL6030x: 4+4 2.7Gbps POF Transceiver
Serial Optical Interconnection Solutions
With respect to high data rate interconnections, a number of serial optical transceiver solutions are cited as competitors to PFOMs, with the following three commercially available solutions serving as prime examples: SFP, XFP and XENPAK. All three are transceiver solutions with a single optical input and output channel.
These three variants are briefly described as follows:
1. SFP
These small form-factor, serial, duplex, pluggable transceiver modules employ two LC fiber receptacles. They are widely used in the industry and are now becoming available in data-rates of up to 4.25-Gbps.
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ZL60101: 12 x 2.7Gbps POF Transmitter
2. XFP
This is a 10-Gbps, duplex, serial, LC-receptacle transceiver solution requiring 10-Gbps electrical I/Os. It is therefore normally used with an external PHY IC, which converts four lower data rate channels into a single 10-Gbps electrical input to the XFP module. The same IC thus converts both receive and transmit data.
3. XENPAK
This is similar in principle to the XFP, except that here the PHY IC is now an integral part of the module. Hence XENPAK has four lower data rate electrical I/Os that are multiplexed/de-multiplexed internally, with the optical I/O being 10 Gbps.
Although this sounds attractive, for many applications - in particular those where serial and parallel solutions stand in direct competition - such flexibility is not required. In these cases, the serial alternatives offer a less effective solution in terms of power dissipation, board and edge density, cable management and cost.
High data throughput interconnections:
Many applications require a simplex solution with separated transmit and receive functions and/or extremely high data throughput. In such cases, Zarlink PFOMs based on 12-channel simplex transmitters and receivers offer the most cost-effective solution. This case study will examine a high data throughput requirement of 30 Gbps duplex, i.e., in both directions. To do so, the use of 2.5-Gbps SFP modules will be compared with both an XFP solution and Zarlink's 12x2.5-Gbps PFOM pairs.
In this case, the PFOM solution offers reduced cabling requirements as compared to the alternative solutions.
Applications requiring high data throughout frequently find themselves limited by a finite board area or edge width. Hence the ability to increase the optical interconnection density is of particular importance, as this can have a significant impact on overall system cost.
It is thus clear that a PFOM solution offers significant savings at both the board and edge levels.
Simplex Interconnections
It should be noted that for pure simplex applications with a high data transfer rate, transceivers such as SFP or XFP modules are at a further disadvantage, since one part of the transceiver will not be utilized. In this case the use of simplex 12-channel transmit and receive PFOMs will provide further advantages in terms of cable management, power consumption, board and edge density and, ultimately, system cost.
Conclusion
PFOMs quite clearly provide the best solution for any application requiring high bandwidth interconnections. They provide savings of over 50% in power consumption, board real estate usage and edge density as compared to alternative optical solutions.
Have we piqued your interest? Then please don't hesitate to contact CODICO!
Ondrej Gavura, EXT 953
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