Temperature grades: commercial, extended, industrial

Every datasheet specifies a case-temperature range, and the same PMD is sold in two or three grades that differ in that range alone — and in laser selection, screening and price. Choosing the wrong grade is invisible in the lab and expensive in an outdoor cabinet in January. This page defines the grades, explains what changes inside the module across temperature, shows how to recognise the grade from the part number, label and EEPROM, and lists where each grade belongs.

The grades

Grade	Marking	Operating case temperature	Storage	Where used
Commercial (C-temp)	none, `-C`, "standard"	0 … +70 °C	−40 … +85 °C	data centres, offices, climate-controlled rooms
Extended (E-temp)	`-E`, `-X`, sometimes `-T`	−5 … +85 °C (some −20 … +85)	−40 … +85 °C	telecom rooms without tight climate control, dense line cards, PON OLT
Industrial (I-temp)	`-I`, `-IND`, `-40/85`	−40 … +85 °C	−40 … +85 (−55 … +100 some)	outdoor cabinets, base stations, industrial switches, PON ONU outdoors, vehicles, energy
Hardened / special	vendor	−40 … +95 °C, −40 … +105 °C	—	fronthaul RRU, military, rail

"Case temperature" is measured at a defined point on the module shell, not ambient: inside a switch the case runs 10–25 °C above the room, and the DDM temperature sensor sits on the PCB or in the laser driver, reading another few degrees higher (Temperature & voltage).

What changes with temperature inside the module

Effect	Mechanism	Consequence
Laser wavelength drift	DFB ≈ +0.08–0.1 nm/°C, VCSEL ≈ +0.06 nm/°C, FP ≈ +0.4 nm/°C	uncooled CWDM lasers need the ±6.5–7 nm channel window; DWDM lasers need a TEC (Lasers)
Threshold current rises, slope efficiency falls	semiconductor physics	bias climbs, Tx power drops unless the APC loop compensates — up to the driver's limit (Tx bias & ageing)
Extinction ratio and eye margins shrink	slower carrier dynamics at high T; higher RIN	link penalty of 0.5–2 dB at the extremes
Receiver sensitivity degrades	higher dark current, TIA noise	0.5–1.5 dB at +85 °C
Cold start	laser below threshold, TEC needs time	slow bring-up at −40 °C; some modules delay Tx enable
Electronics timing	CDR/DSP margins	at extremes of a C-temp part, LOL or FEC errors appear
Mechanical	solder, optics alignment, adhesives	thermal cycling ages joints; I-temp parts are screened for it
Lifetime	Arrhenius acceleration	laser wear-out roughly halves for every +10–15 °C of junction temperature (Failures)

An I-temp module is not just "tested colder": it uses lasers selected for a wide window, a TEC where the PMD needs wavelength stability, a firmware calibration table covering the full range and often a different DSP power profile.

Recognising the grade

Where	What to look for
Part number	suffix `-I`, `-X`, `-E`, `-T`, `-IND`, "(I)" — vendor grammars in Part numbering; Cisco `-I` (industrial), HPE/Aruba separate J-numbers, Huawei/H3C `-I`, Nvidia usually commercial only
Label	"−40~85°C" or "I-temp" printed; often nothing for commercial (Labels)
Datasheet	"Case operating temperature" in Absolute Maximum / Recommended Operating Conditions (Reading a datasheet)
EEPROM	no standard grade field. Hints: DDM temperature thresholds — commercial parts typically set HA ≈ +80…+85 °C / LA ≈ −5…−10 °C, industrial HA ≈ +95…+100 °C / LA ≈ −45…−50 °C (Thresholds); some vendors encode the grade in the vendor-specific area or the PN itself
Behaviour	a commercial module in a cold cabinet shows low bias, low Tx power and LOS on cold start; in a hot one, high bias and rising temperature alarms

Typical DDM thresholds by grade

Threshold	Commercial	Industrial
Temperature high alarm	+75 … +85 °C	+90 … +100 °C
Temperature high warning	+70 … +80 °C	+85 … +95 °C
Temperature low warning	0 … −5 °C	−35 … −40 °C
Temperature low alarm	−5 … −10 °C	−40 … −50 °C

Vendors differ; the pairs above are what makes a module "look" I-temp in a DDM readout.

Where each grade belongs

Environment	Grade	Why
Data-centre switch, controlled room	commercial	case stays 30–60 °C
Dense 400G/800G line card, hot aisle marginal	extended or commercial with derated reach	inlet 35–40 °C → case near 70
Telecom room, no air conditioning	extended	summer peaks
Outdoor street cabinet, pole-mounted ONU, RRU fronthaul	industrial	−40 in winter, +60 ambient in a sun-heated box
Industrial plant, rail, energy substation	industrial	temperature plus vibration and dust
Home ONT/ONU	commercial (indoor)	—
DWDM/ER/ZR in any environment	check TEC and grade together	TEC range limits the usable ambient

Cost and availability

Industrial parts cost more (selected dies, longer screening, TEC) and exist for fewer PMDs: 1G/10G/25G SR-LR-ER-BiDi-CWDM, PON, 100G LR4/ER4 and fronthaul 25G/50G are common in I-temp; 400G+ and coherent modules are almost always commercial. Where an I-temp optic is not available, the fix is environmental: heated/cooled enclosures or an extended-grade module with margin (Power & consumption).

In CodingBox

The DDM temperature and thresholds are on the Check screen: an unexpectedly wide threshold pair is the fastest hint that a module is industrial grade, a narrow pair on a module labelled -I is a coding or labelling question. The vendor PN and date code show which grade was actually shipped (Check transceiver, DDM in the app).

Industrial switches, their ambient limits and fanless designs — the boxes that need these grades: Switch classes & form factors.