Multi-mode Optical-to-Electrical Converters
950-1630 nm ProLink BMA Connector

These wide- band multi-mode optical-to-electrical converters are designed for measuring optical communications signals. They connect to Teledyne LeCroy real-time oscilloscopes and provide capability for physical layer signal assessment using a variety of oscilloscope tools, such as SDAIII-CompleteLinQ Serial Data Eye, Jitter, Noise and Crosstalk Analysis, mask testing, serial triggering and decoding, and other compliance and debug tools. Maximum data rate test capability is >11.317 Gb/s with reference receiver, or 12.5 Gb/s without.

Teledyne LeCroy’s wide-band multi- mode optical-to-electrical converters are designed for measuring optical communications signals. Their broad wavelength range and multi-mode input optics make these devices ideal for appli cations including Gigabit Ethernet and Fibre Channel, as well as SONET/SDH up to 2.5 Gb/s.

The OE425 and OE455 are ProBus modules compatible with WavePro ® oscilloscopes, as well as WaveMaster ® when used with a LPA-BNC adapter.

The OE525 and OE555 are ProLink modules compatible with WaveMaster, SDA models, and DDA oscilloscopes.

Universal Calibrated Reference Receivers 
The O/E converters contain calibration data that can be used to create optical reference receivers for SONET/SDH (up to OC48/STM16), Fibre Channel, Gigabit Ethernet, and other optical standards. This feature is available when the O/E is used on a WaveMaster Series oscilloscope. The universal reference receiver supports any data rate up to 3 GHz and remains calibrated on any channel of any WaveMaster.

Cleaning
Clean only the exterior of the converter with a soft cloth moistened with water or 75% isopropyl alcohol solution. Under no circumstances should moisture be allowed to penetrate the converter. The fiber connectors can be cleaned by blowing residue-free air into the connector to remove loose particles.
  Application
The OE4x5 and OE5x5 are optical-to-electrical converters with multimode fiber inputs. They are specifically designed for the measurement of optical telecommunication signals. DC, AC, and impulse light intensities can be measured (with the oscilloscope automatically converting units to Watts) as cursor or parameter measurements are being made.

The OE4x5 and OE5x5 converters are compatible with Teledyne LeCroy WavePro® and WaveMaster® series oscilloscopes:

• OE4x5 models fit BNC (ProBus) connectors or ProLink connectors when using a BNC adapter (TPA-BNC).
• OE5x5 models fit ProLink connectors.

CAUTION. The fiber cable is fragile, handle with care.

Application as Optical Reference Receiver
With the OE4x5 and OE5x5, you can filter the optical signal in a precise way, in accordance with ITU-T G.957 and other optical standards (such as IEEE802.3) so that the scope and probe chain will constitute an Optical Reference Receiver, per Annex B of G.957.

When used with a WaveMaster or WavePro series oscilloscope, the converters have a response vs. frequency that follows a 4th order Bessel-Thompson lowpass filter whose -3 dB cutoff frequency is set by the user-adjustable data rate. This filter adapts to the probe automatically, so it remains calibrated regardless of the channel on which it is used.

Quantity of Light
What the scope displays is actually the voltage resulting from the conversion of the light signal by an optical-to-electrical converter. The efficiency of this conversion (V/W) depends on the wavelength of the incident light.

The OE4x5 and OE5x5 are designed to operate optimally over different wavelengths:

• OE455 and OE555 operate over the 950 to 1630 nm range
• OE425 and OE525 operate over the 500 to 870 nm range

The probes are calibrated at 1550 nm and 800 nm, respectively.

Therefore, when other wavelengths of light are measured, the power displayed by the scope will differ slightly from the actual value.

The detectors are “multimode”; they will remain accurate when used with either single or multimode optical fibers.

Another factor affecting the measurement of power is the insertion loss of cables chained between the light source and the probe. Each optical connection will typically cost between 0.3 and 0.5 dB (7% to 12%) of light output. Scope calibration is based on light at the probe FC connector.

Measurements of Small Amounts of Light
Through “Enhanced Resolution” and “Averaging” of mathematical functions, it is possible to measure very small signals that represent minute amounts of light. However, the offsets generated by temperature changes can become significant. If the absolute amount of light is to be measured, you should plan for frequent scope re-calibrations, or minimize temperature variations. But if only the amplitude of light modulation is to be measured, this is not critical.

Operation with Oscilloscope
The OE4x5 probes use ProBus style connectors. Therefore, a BNC-BMA adapter is required when they are to be used with a WaveMaster oscilloscope.

The probe response can be read directly from the oscilloscope Probe dialog, which will have the same name as the connected converter. From the Vertical drop-down menu, select the channel to which the OE is connected, then click the tab. The probe information is listed at the right of the dialog and the reference receiver filter selection is shown at the left. The reference receiver is set to a given standard by selecting it from Receiver Standard.

You can also select a user-defined filter from Receiver Standard, then enter either the Receiver Bandwidth or Data Rate in the appropriate field. These two values are related in that the receiver bandwidth is 75% of the data rate. Only one of the two parameters need be entered; the other will be computed automatically.

A selection is also available for disabling the reference receiver filter.

When the probes are used with the WaveMaster or WavePro series oscilloscope in combination with the universal reference receiver, the probe response is automatically matched to the scope and channel, and the bandwidth response is adjusted to the user-selected data rate.

Optical Reference Receiver Background Information
An Optical Reference Receiver has a filter that implements the transfer function:

Where y is defined as:

and ƒr is the reference frequency (chosen as 0.75ƒ0) and ƒ0 is the bit rate (for example, 2.4488 GHz for OC48/STM4). The form of the transfer function is the inverse of a Bessel Polynomial (see Krall, H. L. and Fink, O., “A New Class of Orthogonal Polynomials: The Bessel Polynomials,” Trans. Amer. Math. Soc. 65, 100-115, 1948). Filters implementing Bessel polynomials as denominators of the transfer function are called Thompson filters, hence the name “fourth order Thompson-Bessel” for the transfer function. The order n Bessel polynomial is simply given by the formula:

The factor 2.114 in Equation 2 simply ensures that the norm squared of the transfer function reaches (the “-3 dB point”) at the reference frequency. The main property of the Bessel- Thompson filter is a minimal group delay distortion. The group delay is defined by the derivative of the phase delay with respect to the frequency of an input sine wave. When quoted in “UI,” the group delay is normalized to the bit rate’s period. The group delay of the fourth-order Bessel-Thompson filter at low frequencies is:

The group delay diminishes monotonically, reaching 0.1512 UI at a frequency of two times the bit rate. The difference between the group delay at zero frequency and the group delay at a given frequency is called the group delay distortion. The conformity of the response to the specifications for the combination of probe and scope channel is verified in detail on a clean optical impulse at the factory.