Optical Waveguide Loss Calculator

This calculator models total attenuation as a sum of independent loss terms in decibels:

L_total = L_prop + L_bend + L_coupling + L_conn + L_splice + L_misc

• L_prop = (\u03b1_prop + \u03b1_abs + \u03b1_scat) \u00d7 L with all \u03b1 in dB/m and length L in meters.
• L_bend = N_b \u00d7 L_bend,per. In model mode, L_bend,per = A \u00d7 exp(-R/R0).
• Power ratio is Pout/Pin = 10^-Ltotal/10. If you provide input power, output power is computed in both dBm and mW.

The bend expression is an empirical placeholder. For high-accuracy work, fit A and R0 to your measured data or simulation at the target wavelength.

1. Enter the waveguide length and choose the correct unit.
2. Provide propagation, absorption, and scattering coefficients.
3. Select a bend loss mode and set bends and radius.
4. Add coupling, connector, splice, and miscellaneous losses.
5. Optionally enter input power to estimate output power.
6. Click Calculate to view results above the form.
7. Use the CSV and PDF buttons to export your run.

Tip: keep a small margin in Misc loss for contamination, packaging, and temperature effects.

1) Understanding a waveguide loss budget

Optical links built from integrated or fiber waveguides succeed or fail on margin. A good budget separates length-dependent attenuation from discrete events: bends, coupling interfaces, connectors, splices, and reserves. This calculator keeps every term in dB so contributions add and compare cleanly.

2) Typical propagation loss ranges

Propagation loss depends on platform, wavelength, and sidewall quality. Low-loss silica or SiN can be below 1 dB/m, while tighter silicon photonics often measures higher. Loss is often reported as dB/cm or dB/km and estimated via cutback, resonator Q, or transmission fitting. Enter your coefficient and length to estimate the distributed penalty and an effective attenuation in dB/m.

3) Absorption and scattering as separate knobs

Absorption comes from material chemistry and impurity bands, while scattering follows roughness and index contrast. Separating them helps when process changes affect one mechanism more than the other. Absorption can shift with temperature or contamination, so re-check it after packaging. Annealing may lower absorption, while optimized etch and smoothing may lower scattering.

4) Bend loss sensitivity to radius

Bend loss rises as radius shrinks and the mode radiates. The empirical model uses a per-bend exponential that is useful for early layout tradeoffs. Use manual mode when you already know per-bend loss from layout extraction. If you have a radius sweep, fit A and R0 to your data, then estimate penalties for layouts with many turns.

5) Coupling and interface penalties

Coupling loss bundles mode mismatch, alignment, facet or grating quality, and reflections into one value. For short links, this term can dominate. Use it to test improvements such as better couplers, tighter alignment tolerances, or cleaner facets.

6) Connectors, splices, and maintenance effects

Connectors and splices are count-based losses. Even 0.1 to 0.3 dB each becomes significant across patch panels, test fixtures, or repair points. Modeling them separately helps compare strategies: fewer interfaces versus slightly improved propagation.

7) Converting loss into received power

When input power is provided, total loss converts to output power in dBm and mW. That makes it easy to check detector sensitivity, amplifier headroom, and system margin. The power ratio is also useful for linear simulations.

8) Using results for design decisions

Focus on the largest term first. If bends dominate, relax radius or reduce turns. If coupling dominates, improve packaging and alignment. If propagation dominates, improve geometry or process. Export CSV/PDF so the budget stays traceable in reviews.

1) Which unit should I choose for loss coefficients?

Use the unit that matches your measurement report. The calculator converts dB/km, dB/cm, and dB/mm into dB/m internally, then multiplies by the waveguide length in meters.

2) Why are losses added in dB?

Decibels represent logarithmic power ratios. Independent attenuation factors multiply in linear power, which becomes simple addition in dB, making budgeting and comparisons much easier.

3) How do I set A and R0 in the bend model?

Measure loss per bend at several radii, then fit the curve to match those points. A sets the overall scale, while R0 controls how quickly loss decays as radius increases.

4) What does the power ratio mean?

Power ratio is Pout/Pin as a linear fraction. For example, 0.5 means half the input power remains after all modeled losses.

5) Can I account for wavelength dependence?

Yes. Enter coefficients measured at your operating wavelength. If you have multiple wavelengths, run the calculator separately for each set of wavelength-specific parameters.

6) What if my link has multiple waveguide sections?

Compute each section separately using its length and coefficients, then add the resulting dB totals. Alternatively, combine coefficients into an equivalent average if the sections are similar.

7) How much margin should I add in Misc loss?

Add a small reserve for contamination, packaging stress, aging, and temperature drift. The right margin depends on your environment and quality controls, but budgeting a dedicated term prevents surprises.