Optical transceiver module (SFP, SFP+, QSFP)

01

Check transmit power, sensitivity and the link budget

ETU-Link's datasheet for its 10G SFP+ LR module (ESP31X-10D) states compliance with IEEE 802.3ae 10GBASE-LR optically and SFF-8431 electrically, a 1310 nm DFB transmitter with a PIN receiver, data rates to 10.3125 Gb/s over 10 km of single-mode fibre, and average output power of −8.2 to +0.5 dBm, extinction ratio at least 3.5 dB, transmitter and dispersion penalty of 3.2 dB, receiver sensitivity of −14.4 dBm, overload of +0.5 dBm and a damage threshold of +1.5 dBm. It lists a 3.13–3.47 V supply, 1 W power, and case temperature ranges of 0 to 70 °C (commercial) or −40 to 85 °C (industrial). [1]

Editorial calculation: the worst-case difference between minimum transmit power and receiver sensitivity is −8.2 − (−14.4) = 6.2 dB; subtracting the listed 3.2 dB transmitter and dispersion penalty leaves about 3.0 dB for fibre attenuation, connectors and splices. Ask the supplier how its 10 km reach rating is budgeted and compare it with your measured or calculated link loss. [1]

The same datasheet shows the receiver saturates at +0.5 dBm, equal to the maximum transmit power, so very short single-mode links between two such modules sit at the overload limit; ask whether an attenuator is recommended for short runs. [1]

Give the supplier the host equipment and port type, protocol and data rate, form factor, fibre type and length, wavelength (or CWDM/DWDM channel), connector, measured or estimated link loss, temperature grade, diagnostic and coding (host compatibility) requirements, power limits per port, and quantity.

02

Compare two LR datasheets line by line before mixing vendors

A network-equipment maker's LR SFP+ specification shows which figures can differ between modules that both claim 10GBASE-LR. Extreme Networks lists its LR SFP+ module (part numbers 10302 and AA1403011-E6) for single-mode fibre with LC connectors up to 10 km, and states that transmission distances are a nominal guide only; achievable distance depends on the device's optical specifications and the fibre installation. [4]

Editorial calculation: both sheets give the same 6.2 dB between minimum launch power and minimum receive power (−8.2 − (−14.4)). The upper receive limit differs: if an ETU-Link module at its +0.5 dBm maximum launch power feeds an Extreme receiver, the received power must drop by at least 1.5 dB to reach −1 dBm, so a very short patch link may need a fixed attenuator; in the opposite direction the ETU-Link receiver accepts up to +0.5 dBm. [1] [4]

The Extreme sheet states sensitivity two ways, as a −14.4 dBm average power and as −12.6 dBm optical modulation amplitude (OMA); ask every supplier which basis its sensitivity figure uses before comparing modules. [4]

03

Check digital diagnostics and their accuracy

SNIA's SFF-8472 Rev 12.5a defines the management interface and memory map for SFP+ transceivers, with ID data at 2-wire address A0h and diagnostics at A2h. When a module declares digital diagnostic monitoring, it must report received power, transmitted power, laser bias current, supply voltage and temperature, and write alarm and warning thresholds. [2]

The specification sets minimum accuracies for internally calibrated values: temperature better than ±3 °C over the operating range, supply voltage better than ±3% of nominal, transmitter bias current better than ±10% of nominal, and transmitted and received optical power better than ±3 dB, with power reported from 0 to 6.5535 mW (about −40 to +8.2 dBm). [2]

Editorial calculation: a ±3 dB reporting accuracy means a module reading −10 dBm may actually receive anywhere from about −13 to −7 dBm — wider than the 3 dB margin calculated above, so use DDM readings for trends and alarms and an optical power meter for link acceptance. [2] [1]

04

Compare what suppliers offer

Suppliers linked to this page list optical transceiver modules; each card links to the page reviewed.

Listings include SFP to QSFP-DD Ethernet transceivers, CWDM and DWDM modules, PON and data-centre optics, video SDI optical transceivers, and SFP modules sold with industrial switches; ask each for datasheets with optical budget, DDM support, temperature grade and host coding.

05

Check the fibre's attenuation and dispersion against the module budget

A module's reach rating assumes a fibre, so check the cable data as well. Prysmian's datasheet for its G.652.D, OS2 single-mode cable lists conformity with ITU-T G.652.D, IEC/EN 60793-2-50 category B.1.3 and IEEE 802.3ae, and gives a maximum cable attenuation of 0.36 dB/km at 1310 nm and 0.22 dB/km at 1550 nm, measured to IEC/EN 60793-1-40. Chromatic dispersion is no more than |3.5| ps/km·nm from 1285 nm to 1330 nm, 18 ps/km·nm at 1550 nm and 22 ps/km·nm at 1625 nm, and the cabled PMD coefficient no more than 0.2 ps/√km. Mode field diameter is 9.2 ± 0.4 μm at 1310 nm. [3]

Editorial calculation: at the 0.36 dB/km cable maximum, 10 km of this cable can lose 10 × 0.36 = 3.6 dB at 1310 nm before any connectors or splices, which is more than the 3.0 dB left in the worst-case budget calculated above for the 10 km LR module. Ask the module supplier which fibre attenuation its reach rating assumes, and measure the installed link rather than relying on length alone. [3] [1]

The same datasheet limits added loss from bending to 0.05 dB for 100 turns on a 25 mm radius mandrel at 1310 and 1550 nm, and OTDR trace inhomogeneity to 0.1 dB/km between any two 1000 m lengths. [3]

06

Trace the module parts

This is a functional reference built from the sources cited; it is not one maker's specification.

07

Fill the specification fields with values for your link

A transceiver quotation needs values for your link. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

08

Send the host, link and diagnostic needs together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Host: [equipment; port; coding]
Link: [protocol; rate; fibre; length; measured loss]
Optics: [wavelength or channel; Tx power; sensitivity]
Form factor: [SFP; SFP+; SFP28; QSFP]
Grade: [commercial; industrial]
Diagnostics: [SFF-8472 DDM; alarms]
Documents: [datasheet; test report]

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