Enter the optical input power, additional loss, and select a PLC splitter or tap ratio to estimate the output power (in dBm) on each branch.

Fiber Optic Split Ratio / Output Power Calculator

PLC Splitter (1:N) Tap Coupler (a:b)

Note: Adjust the additional loss as needed. The default (0.13 dB) is just an example value.

Note: Splitter/tap losses vary by product, wavelength, and specifications. For design work, use the device datasheet.

Related Calculators

Fiber Optic Split Ratio & Loss Formulas

In fiber optics, a “ratio” is commonly used to describe how a splitter or tap coupler divides optical power between outputs (for example, 1:4 or 10:90). For a given output branch, the linear power ratio is:

R=\frac{P_{out}}{P_{in}}

Variables:

  • R is the (dimensionless) power ratio for a specific output branch (sometimes expressed as a percentage)
  • Pout is the optical power at an output branch (use linear units such as mW or W)
  • Pin is the optical power at the splitter/tap input (use the same linear units such as mW or W)
  • When working in dB/dBm, total loss adds in dB, and output power is: Pout(dBm) = Pin(dBm) − Ltotal(dB)

Rule of thumb (ideal split only): for an ideal 1:N splitter, each output gets about 1/N of the input power (so R ≈ 1/N). The corresponding ideal “splitting loss” is 10·log10(N) dB, but real devices also have excess/insertion loss, so the actual loss is usually higher.

What is a Fiber Optic Split Ratio?

A fiber optic split ratio (or coupling ratio) describes how an optical splitter or tap coupler divides input power between its outputs. For example, a 1:4 PLC splitter is intended to split the input power evenly among four outputs, while a 10:90 tap coupler sends roughly 10% of the power to the tap port and 90% to the through port (before considering excess/insertion loss).

How to Estimate Splitter/Tap Output Power (dBm)

The following steps outline how to estimate output power when inputs are given in dBm and losses are in dB.

  1. Determine the optical input power Pin in dBm.
  2. Select the splitter type (PLC 1:N or tap coupler a:b) and obtain its loss (from the datasheet, or a typical value).
  3. Add any additional losses (fiber attenuation, connectors, splices, patch panels, etc.) in dB to get Ltotal.
  4. Compute output power: Pout(dBm) = Pin(dBm) − Ltotal(dB).
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Optical Input Power (Pin) = 0 dBm

PLC Splitter = 1:4 (typical per-output splitter loss ≈ 7.00 dB)

Additional Loss (cable, connectors, etc.) = 0.13 dB

Total Loss = 7.00 + 0.13 = 7.13 dB, so Output Power per port Pout ≈ 0 − 7.13 = −7.13 dBm