Model stimulated Raman gain for fiber-based amplifiers quickly. Switch between effective-length modes and units easily. Validate designs using realistic parameters and clear outputs today.
This tool uses a common small-signal Raman gain estimate for a fiber with an undepleted pump:
G = exp\( (gR · Pp · Leff · Γ · P) / Aeff \)
When attenuation is provided, effective length is computed as:
Leff = (1 − e−αL) / α
| Case | Pump Power | gR | Aeff | Length | Loss | Overlap | Pol. | Estimated Gain (dB) |
|---|---|---|---|---|---|---|---|---|
| Silica example | 2 W | 1.0×10−13 1/(W·m) | 80 µm² | 10 km | 0.2 dB/km | 1.0 | 0.5 | ~7.8 dB |
| Higher overlap | 1.5 W | 0.9×10−13 1/(W·m) | 60 µm² | 5 km | 0.25 dB/km | 0.9 | 0.7 | ~8.5 dB |
| Short fiber | 1 W | 1.1×10−13 1/(W·m) | 90 µm² | 2 km | 0.2 dB/km | 1.0 | 0.5 | ~1.9 dB |
Stimulated Raman scattering transfers energy from a higher-frequency pump to a lower-frequency signal through molecular vibrations. In a fiber, long interaction length and tight confinement make the effect useful for distributed amplification, especially in silica telecom fibers.
The Raman gain coefficient depends on material, polarization, and frequency shift. For standard silica, peak small-signal values are commonly on the order of 10−13 1/(W·m) near the Raman gain peak, while off-peak values can be significantly lower. The gain spectrum is broad, so multi-pump schemes are often used to flatten gain across wide telecom bands.
This calculator uses the proportionality γ ∝ Pp/Aeff. Doubling pump power doubles the exponent, while doubling Aeff halves it. Typical single‑mode fibers have Aeff roughly 50–100 µm², whereas large‑mode‑area fibers may exceed that range.
Fiber loss limits how much of the physical length contributes to gain. Using Leff = (1 − e−αL)/α, a low-loss link (for example ~0.2 dB/km) can still provide multiple kilometers of effective interaction, but Leff eventually saturates as length increases.
Real systems rarely achieve perfect alignment between pump and signal. The overlap factor Γ captures spatial mode matching (0–1). The polarization factor accounts for relative polarization states; values around 0.5 are often used for random polarization, while polarization-maintaining setups can approach 1.
The tool reports G = exp(γ) and converts to GdB = 10·log10(G). A linear gain of 2 corresponds to about 3.01 dB, while a gain of 10 corresponds to 10 dB. Use dB for cascade budgeting and link analysis.
For watt-level pumps, kilometer-scale fibers, and realistic factors, small-signal on-off gains of a few dB to low tens of dB are common in preliminary designs. If you obtain thousands of dB, re-check units, Aeff magnitude, and whether gR represents peak or average gain.
This is a steady, undepleted-pump estimate. It does not model pump depletion, amplified spontaneous emission, double Rayleigh scattering, gain bandwidth, transient effects for short pulses, or counter‑propagating pump geometry. Use it as a first-pass sizing tool before detailed numerical simulations. For higher fidelity, solve coupled pump/signal power equations along the fiber and include noise sources to estimate OSNR and saturation behavior.
It quantifies how efficiently pump power transfers to the signal per unit length. It depends on material and the pump–signal frequency shift, so values vary with wavelength and fiber composition.
Compute Leff when you know physical length and attenuation. Enter Leff directly when it is measured, simulated elsewhere, or already includes additional loss or geometry effects.
Large gain usually comes from unit mistakes or very small Aeff. Confirm that gR is in 1/(W·m), lengths are realistic, and overlap/polarization factors are not accidentally above 1.
Use about 0.5 for random relative polarization in standard fibers. Use values closer to 1 when pump and signal polarizations are actively aligned or the link uses polarization-maintaining fiber components.
Use the manufacturer’s mode-field or effective area specification when available. If not, estimate from the mode-field diameter: Aeff ≈ π·(MFD/2)², with units converted consistently.
It can provide a rough average estimate if you use average launched power, but short pulses require transient modeling. Pulse walk-off, peak power, and gain dynamics can change results significantly.
Yes. Counter‑propagating pumps change local gain distribution along the fiber, and multiple pumps broaden usable bandwidth. This calculator approximates net small-signal gain, not the full spatial gain profile.