| Parameter | Value | Unit | Comment |
|---|---|---|---|
| Wavelength | 1550 | nm | Common single‑mode band |
| Input Power | 1.00 | mW | Reference injected power |
| Output Port 1 | 0.48 | mW | Through path measurement |
| Output Port 2 | 0.47 | mW | Coupled path measurement |
- dBm to mW: P(mW) = 10^(P(dBm)/10)
- mW to dBm: P(dBm) = 10·log10(P(mW))
- Split percentage (per port): Splitᵢ(%) = Poutᵢ / ΣPout · 100
- Excess loss: EL(dB) = 10·log10(Pin / ΣPout)
- Insertion loss (per port): ILᵢ(dB) = 10·log10(Pin / Poutᵢ)
- Imbalance (1×2): IMB(dB) = |10·log10(P1 / P2)|
- Coupling ratio (1×2): CR = P2 / P1 and CR(dB) = 10·log10(CR)
- Select your coupler configuration (1×2, 1×3, or 1×4).
- Enter measured output power for each active port (mW or dBm).
- Optionally enter input power to compute insertion and excess loss.
- For 1×2 couplers, set a target split to see deviations.
- Press Calculate to display results above the form.
- Use Download CSV or Download PDF for reporting.
Why splitting ratio matters
Optical couplers divide one input signal into multiple outputs, and the split drives link budgets and receiver sensitivity. A nominal 50/50 device should deliver about 50% power per output, before losses, which corresponds to 3.01 dB ideal splitting loss per port.
Choosing measurement units
Field meters often report dBm, while datasheets may list mW or percent. This calculator converts every entry to mW first, then reports both mW and dBm. For example, −3 dBm equals about 0.50 mW, and 0 dBm equals 1.00 mW. Keep the reference plane and launch conditions consistent.
Interpreting insertion loss
Insertion loss (IL) compares the injected power to a single output and includes splitting plus internal losses. For a measured Pin of 1.00 mW and Pout of 0.48 mW, IL = 10·log10(1.00/0.48) ≈ 3.19 dB. Values close to the ideal splitting loss indicate a healthy coupler and clean connectors. If IL drifts upward, inspect endfaces and confirm source power.
Estimating excess loss
Excess loss quantifies energy lost inside the component beyond splitting and is independent of which port you examine. It uses the total output sum: EL = 10·log10(Pin/ΣPout). With Pin 1.00 mW and ΣPout 0.95 mW, EL ≈ 0.22 dB. Higher EL can signal microbends, contamination, tight radius routing, or wavelength mismatch. Track EL over temperature if the coupler is used in outdoor enclosures.
Evaluating imbalance and uniformity
Imbalance expresses how evenly power is shared. In 1×2 mode it is |10·log10(P1/P2)|. If P1 = 0.48 mW and P2 = 0.47 mW, imbalance is about 0.09 dB, typically within tight production specs. For 1×3 or 1×4, the calculator also reports max–min imbalance across active ports, helping you spot a weak branch quickly. Use the split table to check that each port stays within your tolerance band.
Reporting results for acceptance
Use the split percentages to verify targets such as 90/10 or 70/30 and to document compliance against purchase specifications. An ideal 90/10 coupler yields about 0.46 dB on the 90% port and 10.00 dB on the 10% port, before excess loss. Export CSV for traceability, and attach the PDF report to test records with wavelength, device ID, and notes. Recording both linear power and dB values makes audits and troubleshooting faster.
What is the difference between split percentage and coupling ratio?
Split percentage shows each port’s share of total output power. Coupling ratio is a two-port comparison, often P2/P1, and can also be expressed in dB using 10·log10(P2/P1).
Can I mix mW and dBm inputs in one calculation?
Yes. Each entered value is converted to mW internally, so you can type Port 1 in dBm and Port 2 in mW. The results are reported in both units for easy comparison.
Why does the calculator sometimes show efficiency above 100%?
Efficiency uses ΣPout divided by Pin. If instruments are not referenced to the same plane, or if units are misread, ΣPout can appear larger than Pin. Recheck connectors, calibration, and whether any values were entered in the wrong unit.
Do I need to enter input power to get a valid ratio?
No. Ratios and split percentages only require output powers. Input power is optional and is only used to compute insertion loss and excess loss.
How should I test a 1×4 coupler for uniformity?
Measure all four outputs under the same launch condition, then compare split percentages. The max–min imbalance value highlights the spread across ports, helping you detect a weak branch or a connector problem.
Does wavelength change the calculations?
The math is power-based and does not directly use wavelength. Wavelength is recorded for reporting and sanity checks, because coupler loss and split can vary between 1310 nm and 1550 nm in real devices.