DIRECT ANSWER / 01
Insertion loss and return loss describe different effects
Insertion loss (IL) describes reduced transmitted power; return loss (RL) is the incident-to-returned power ratio expressed in dB. Under matching conditions, lower IL and higher RL are desirable, but the numbers are not interchangeable and results from different conditions cannot be ranked directly.
Use this for RFQs, sample-report comparisons and incoming acceptance. IEC 61300-3-4 addresses component attenuation measurement and IEC 61300-3-6 addresses RL. Citing their public scope is not product certification. Distinguish a connector’s RL from whole-link optical return loss by defining the object under test.
SELECTION MATRIX / 02
Purchasing decision matrix
| Item | Identify | Correct action | Avoid |
|---|---|---|---|
| IL | Transmission attenuation, DUT and reference boundary | Specify a maximum and the corresponding method | Treating component loss as total link loss |
| RL | Returned power, port and wavelength | Specify a minimum and identify the DUT | Assuming a smaller RL is better |
| End face | APC/UPC, mating part and inspection state | Match end faces to equipment requirements | Treating a polish label as a measurement |
| Comparison conditions | Method, wavelength, cords and assembly revision | Align conditions before comparing results | Comparing numbers without methods |
| Report | Lane IL/RL, criteria and exceptions | Retain revision, ports, conditions and results | Providing only an average |
RFQ INPUTS / 03
Minimum inputs a supplier can verify
| Category | Required input or confirmation |
|---|---|
| Metric definition | IL maximum, RL minimum, DUT, wavelength and scope |
| Reference conditions | Method revision, mating part, reference setup and face condition |
| Deliverable record | Assembly/lane IDs, directions, results, verdict and report revision |
BUYER FAQ / 04
Purchasing FAQ
Does passing IL prove passing RL?
No. They describe different effects and need separate measurements and criteria.
What does a larger RL mean?
Under the same definition, less power returns relative to incident power; project criteria still apply.
Is APC suitable for every device?
No. Match the specified interface; do not substitute a polish solely to seek a desired RL number.
Are component RL and link ORL equivalent?
Do not assume equivalence. Identify the DUT, path and conditions to avoid comparing different scopes.
Can an RFQ start without numeric limits?
Yes. Provide application/equipment requirements and leave limits/methods open; catalogue values must not silently become guarantees.
SOURCES / 05
Sources and applicability
Sources checked: 2026-10-02. This guide clarifies purchasing fields; it does not replace current equipment data sheets, full standards or the approved project drawing.