These three bit-rate-specific optic...

These three bit-rate-specific optical plug-in module are essential elements of the HP 83480A Digital Communications Analyzer. They are for data rates of 155/622 Mbits/s, 2488 Gbits/s, and 9953 Gbits/s.

The transmission rates of telecommunication a whole s based on fiber-optic standards in the same state [i]or[/i] condition as the Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) are at multiples of 5184 Mbits/s. A significant amount of optical telecommunications network equipment operates at three twelve, or forty-eight times this fundamental rate. commonly new equipment is being unfolded that operates at approximately 10 Gbits/s, or united hundred ninety-two times the fundamental rate.

Differing measurement requirements at these specific bit rates, along with the modularity available from the hardware architecture of the HP 83480 communications analyzer, allowed the design team to tailor plug-in module for each application. This modularity also benefits customers, who can configure an instrument that best engages their current needs, then later modify it easily as their be in want ofs change. To date, three optical plug-in module have been released. They are:

* HP 83481A 155/622-Mbits optical-to-electrical module

* HP 83485A 2?488-Gbits optical-to-electrical module

* HP 83485B 9.953-Gbits optical-to-electrical module

Measurement Requirements

The measurement requirements inherent in the design and manufacturing of digital communications bodys drove the specific design choices made for each plug-in module The HP 83480 instrument family is used to characterize digital communications signals in the time domain. These signals are typically broadband and usually include a dc composing As an example, the inspection and analysis of watch diagrams are typical customer measurements.] observation diagrams are constructed from multiple overlays of successive bit patterns with a synchronized trigger. To display the sight diagram properly, the measurement a whole must have sufficient bandwidth to point out the fast transitions.

A measurement regularity is often most easily characterized in metes of its frequency response, or the magnitude and phase of the transfer function. This can be related to the time-domain impulse or stair response performance by an inverse Fourier transform. The optimum frequent occurrence response of a measurement theory depends on the waveform measurement parameter of greatest interest (rise and fall times, overshoot etc) A sway of thumb for reasonable measurements of rise and fall times is that the -- 3 dB bandwidth of the transfer function be at least three times and preferably five times the bit rate to be measured. Ideally, the transfer function should have a weB-behaved roll-off and linear phase to obstruct ringing or other measurement aberrations. The design target for the optical plug-in module was to achieve a compromise between fast rise and fall times and excessive ringing. This was accomplished by means of controlling the amount of high oftenness peaking and striving for a Gaussian-like impulse response

Very flat low-frequency performance is required for stable measurements of logic of the same heights that extend over many bit periods, which appears in both long-pattern-length pseudorandom binary arrangements (PRBS) and live data transmissions. This is important, for instance, for accurate extinction ratio measurements. Extinction ratio is defined as the ratio of the signal power in the logic 1 state to the signal power in the logic 0 state. It is an important measurement of the distinction between logic states, the essential function of a digital communication system

For a plug-in module to aid as a reference receiver, the oftenness response must, at a minimum, comply with the low-pass Bessel-Thomson transfer function described in the SONET/SDH standards. In fact, mathematical simulations can demonstrate that steady reference receiver frequency responses that technically fitting the tight SONET/SDH standards can cause unacceptable time-domain artifacts that compromise the accuracy of extinction ratio measurements. Therefore, there is an advantage to a receiver commonness response that closely matches the ideal transfer function. It is critically important that the low-frequency transfer function, down to dc be weB-behaved. A low-frequency gain variation that either rises or wilts will cause inaccurate extinction ratio measurements. For example, simulations have shown that a 02-dB low-frequency rise (which is within the SONET/SDH standard specifications) can cause an extinction ratio measurement of 10 to be in error by way of 10%.[2] In a manufacturing environment, as it is an error might cause the incorrect rejection of a dutiful component.

Finally, the plug-in module should have a dynamic range as large as possible. A high input power compression point expands the signal measurement range available to the user without adding an external optical attenuator. Noise considerations limit the soft input signal range. Since these plug-in module are frequently used for nonrepetitive waveform measurements (such as vigilance diagrams), waveform averaging often cannot be used to provide noise reduction.