Typical DDM values by module type

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A DDM reading is only meaningful against an expectation. "Rx −12 dBm" is excellent for an 80 km ZR module and alarming for a 300 m SR module. This page collects the expected windows per interface type — transmit power, receive window, bias current, temperature — drawn from the IEEE/ITU/MSA specifications and typical datasheets. Use it to judge a reading before you have a baseline of your own. All values are average optical power in dBm as DDM reports it, not OMA; specification sensitivities quoted in OMA have been converted approximately.

Single-lane Ethernet (SFP class)

Interface	Reach	λ, nm	Tx power, dBm	Rx window (sensitivity … overload), dBm	Bias, mA (typ.)
1000BASE-SX	550 m MMF	850	−9.5 … 0	−17 … 0	4–8 (VCSEL)
1000BASE-LX	10 km	1310	−9.5 … −3	−20 … −3	15–35 (FP/DFB)
1000BASE-EX (MSA)	40 km	1310	−3 … +2	−23 … −3	30–60
1000BASE-ZX (MSA)	80 km	1550	0 … +5	−24 … −3	40–80
1000BASE-BX10 U/D	10 km, 1 fibre	1310 / 1490	−9 … −3	−19.5 … −3	15–35
10GBASE-SR	300 m OM3	850	−7.3 … −1	−11 … −1	5–9 (VCSEL)
10GBASE-LRM	220 m MMF	1310	−6.5 … +0.5	−8.5 … +0.5	20–40
10GBASE-LR	10 km	1310	−8.2 … +0.5	−14.4 … +0.5	20–50 (DFB)
10GBASE-ER	40 km	1550	−4.7 … +4	−15.8 … −1	40–80 (cooled EML often)
10GBASE-ZR (MSA)	80 km	1550	0 … +4	−24 … −7 (APD)	50–90
10G CWDM (MSA)	40 / 80 km	1270–1610	0 … +5	−18 … −1 / −24 … −7	40–80
10G DWDM (MSA)	80 km	C-band	0 … +4	−24 … −7 (APD)	60–100, cooled (TEC)
25GBASE-SR	100 m OM4	850	−8.4 … +2.4	−10.3 … +2.4	5–9
25GBASE-LR	10 km	1310	−7 … +2	−12 … +2	25–55
10G/25G BiDi (MSA)	10–40 km	1270 / 1330	−5 … +2	−15 … 0	25–55

Multi-lane Ethernet (QSFP class, per lane)

Interface	Lanes	Tx per lane, dBm	Rx per lane, dBm	Notes
40GBASE-SR4	4 × 10G, 850 nm	−7.6 … +2.4	−9.9 … +2.4	VCSEL array, bias 5–9 mA each
40GBASE-LR4	4 × 10G LAN-WDM	−7 … +2.3	−13.7 … +2.3	1271–1331 nm, DFB
100GBASE-SR4	4 × 25G, 850 nm	−8.4 … +2.4	−10.3 … +2.4	70 m OM3 / 100 m OM4
100GBASE-LR4	4 × 25G LAN-WDM	−4.3 … +4.5	−10.6 … +4.5	1295–1310 nm, cooled or uncooled DFB
100G CWDM4 (MSA)	4 × 25G CWDM	−6.5 … +2.5	−11.5 … +2.5	1271–1331 nm, 2 km
100G PSM4 (MSA)	4 × 25G, 1310 nm	−6 … +3	−11 … +3	parallel SMF, MPO
100GBASE-DR / 400GBASE-DR4	100G PAM4 per lane	−2.9 … +4	−5.9 … +4	500 m; narrow window — attenuator rarely needed but overload is close
400GBASE-FR4	4 × 100G PAM4 CWDM	−3.3 … +3.5	−7.3 … +3.5	2 km
400GBASE-LR4-6 / LR4-10	4 × 100G PAM4	−2.5 … +3.5	−9 … +3.5	6 / 10 km
800G DR8 / 2×FR4	8 × 100G PAM4	−2.9 … +4	−5.9 … +4	as DR4 per lane

PAM4 receivers have small windows (≈ 10 dB) compared with NRZ (15–20 dB): both a dirty connector and a too-short link can push them out of range.

Access, storage and fabric

Interface	Side	Tx, dBm	Rx, dBm	Notes
GPON class B+	OLT (1490 down)	+1.5 … +5	−28 … −8 (1310 up, burst)	OLT Rx from DDM is a burst average — use per-ONU figures
GPON class B+	ONU (1310 up)	+0.5 … +5	−27 … −8	ONU Rx is the number that matters in the field
GPON class C+	OLT / ONU	+3 … +7 / +0.5 … +5	−32 … −12 / −30 … −8	4 dB more budget
XGS-PON N1	OLT (1577) / ONU (1270)	+2 … +6 / +4 … +9	−28 … −9 / −28 … −9	—
8/16/32GFC SW	850 nm MMF	−8 … +2	−10 … +2	per Fibre Channel PI
16/32GFC LW	1310 nm 10 km	−5 … +2	−12 … +2	—
InfiniBand EDR/HDR/NDR optics	as 100G/200G/400G Ethernet PMDs	see above	see above	same components, different protocol
AOC (any rate)	each end	−6 … +1 (internal VCSEL)	−8 … +1	DDM present at both ends, levels are "internal" and rarely diagnostic
Passive DAC	—	none	none	no A2h; identity only
1000BASE-T / 10GBASE-T SFP	—	none	none	temperature (and sometimes Vcc) only

PON specifics: PON transceivers, PON problems.

Bias current by laser type

Laser	Typical bias	Threshold	Behaviour
850 nm VCSEL	4–9 mA	~1 mA	very low bias; rises slowly with age; thermal roll-over at high temperature
1310 nm FP	15–40 mA	5–10 mA	cheap 1G LX/PON; mode hops
1310/1550 uncooled DFB	20–60 mA	8–15 mA	10G LR/ER, CWDM; bias climbs ~1 %/°C
Cooled DFB / DWDM	40–100 mA	10–20 mA	TEC keeps temperature; bias stable, TEC current varies
EML (10G ER/ZR, 100G+ LR)	40–100 mA	—	DDM reports the DFB section bias; modulator bias is not shown
Silicon-photonics CW source (DR4/FR4)	60–150 mA	—	one shared laser; the bias field may mirror to all lanes

Why bias matters more than its absolute value: Tx bias & laser ageing.

Temperature and voltage

Parameter	Normal	Watch	Notes
Module temperature	25–55 °C in a switch, 20–35 °C on the bench	> 65 °C	commercial parts are rated 0–70 °C case; see Temperature & voltage
Vcc	3.20–3.40 V	< 3.13 or > 3.47 V	3.3 V ± 5 % is the specification
Laser temperature (cooled)	set point, often 25–45 °C	drift > ±1 °C	reported in the optional A2h 106–107 / CMIS Aux
TEC current	±20–60 % of max	near ±100 %	sign shows heating vs cooling

How to use the tables

Identify the interface from the module's codes (Check transceiver), not from the label.
Compare Tx with the Tx column: below range → laser fading or fake constant value (DDM levels).
Compare Rx with the window: below → budget problem, above → attenuate (Rx power & link budget).
Compare bias with the laser type and, better, with the module's own history.
Remember the ±3 dB accuracy of DDM (Accuracy & limits) — a reading 1 dB outside a window is not a verdict.

Values in this page are typical windows, not guarantees; the datasheet of the specific module and the IEEE/MSA table for the PMD are authoritative (PMD reference).

Where the datasheet numbers behind these values come from, and how to compare min/typ/max between vendors: Reading a datasheet.

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