FREE ENGINEERING TOOL
Micro Turning Mirror Acceptance Simulator
Enter the laser wavelength, fast/slow-axis divergence, submount height and emitting distance to estimate the collection efficiency of a 45° turning mirror and compare gold with aluminium.
Collection efficiency = geometric acceptance × mirror reflectance. Check with numbers whether the beam cone lands on the mirror before bringing package margins into an engineering evaluation.
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Defaults use the nominal geometry H 460, s 160, W 250 µm; results exclude manufacturing tolerances.
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METHOD
How collection efficiency is calculated
The 45° reflective face has an upper and a lower acceptance boundary. The tool integrates the laser’s angular distribution over the range that can hit the face, then multiplies by the mirror reflectance for the chosen wavelength, material and polarisation.
Scroll sideways to see the full drawing
L = H − s
αup = atan((H − h) / (d + L))
αdown = atan((s − h) / d)
symmetric equivalent acceptance angle = 2 × min(αup, |αdown|)
Five parameters to have ready
| Parameter | Source | Note |
|---|---|---|
| Wavelength λ | Laser datasheet | Decides the mirror material |
| Fast axis θ⊥ | Laser datasheet | Enter the full angle |
| Slow axis θ∥ | Laser datasheet | Enter the full angle |
| Height h | Package design | Typically 200–250 µm |
| Distance d | Package design | Recommended below 100 µm |
FWHM or 1/e²?+
FWHM is the contour where intensity falls to 50 % of peak; 1/e² is the contour at 13.5 %. Either definition works — what matters is consistency with the datasheet.
1/e² full angle = 1.699 × FWHM full angle
For example, an FWHM full angle of 20° corresponds to a 1/e² full angle of about 34.0°.
Gold or aluminium mirror?+
Below 500 nm use aluminium; between 600 and 1000 nm prefer gold; above 1000 nm the two are close and can be chosen by polarisation and cost.
At 808 nm, gold is 98.2 % (s) / 96.5 % (p) and aluminium 90.6 % (s) / 82.0 % (p). The p-polarised values are Fresnel estimates, not measurements.
TE/TM describe the laser mode; s/p describe the electric-field direction at the mirror surface. The two are not interchangeable.
REFERENCE CASES
Three typical package conditions
Calculated at nominal H 460, s 160, W 250 µm without manufacturing tolerances — a quick check of whether your fast-axis divergence falls within the acceptance range.
| Application | h | d | αup | αdown | Symmetric equivalent |
|---|---|---|---|---|---|
| 905 nm LiDAR | 200 µm | 80 µm | 34.4° | −26.6° | 53.1° |
| 808 nm LLLT | 250 µm | 100 µm | 27.7° | −42.0° | 55.4° |
| 1310 nm optical comms | 200 µm | 50 µm | 36.6° | −38.7° | 73.2° |
Model limitations
The result is an idealised upper-bound estimate for one set of package conditions, not a delivery guarantee.
- Excludes mirror-surface scattering, adhesive wicking and coating ageing.
- Excludes die-attach angle error, placement tolerance and process variation.
- Treats the source as an ideal point; emitter size and astigmatism are not included.
- Multimode slow-axis lasers may deviate from a Gaussian profile.
- p-polarised reflectance is a Fresnel estimate, not a measurement.
FAQ
Frequently asked questions
01How is the collection efficiency of a 45° turning mirror calculated?
Collection efficiency equals geometric acceptance multiplied by mirror reflectance. Geometric acceptance depends on the package position, mirror size and laser divergence; mirror reflectance depends on wavelength, gold or aluminium surface, and s/p polarisation.
02What happens if I mix up FWHM and 1/e² divergence?
The two full angles differ by a factor of 1.699. Use the same definition as the laser datasheet. Entering a 1/e² figure in the FWHM field makes the tool assume a broader beam and underestimate the collected fraction; entering an FWHM figure as 1/e² does the opposite and overestimates it.
03Gold or aluminium mirror?
Below 500 nm choose aluminium; between 600 and 1000 nm gold is usually preferred; above 1000 nm the two are close. When polarisation is uncertain, gold is generally less sensitive in the common near-infrared bands.
04Why is the measured collection lower than the tool predicts?
The tool is an idealised geometric model. It does not include mirror scattering, adhesive wicking, coating ageing, die-attach angle error, emitter size or astigmatism, so treat the result as an upper-bound estimate for the same package conditions.
05Which matters more, submount height or emitting distance?
Within the standard 200–250 µm submount range, the emitting distance d is usually the more sensitive parameter. At nominal geometry with h = 200 µm, reducing d from 100 µm to 50 µm raises the symmetric equivalent acceptance angle from 43.6° to 73.2°.
06Do manufacturing tolerances affect the result?
Yes. When the submount height is close to the mirror step, the emitting distance is very short, or several lasers must match each other, tolerance effects are amplified. Confirm the applicable tolerance and cleanliness grade during engineering evaluation.
Bring the numbers into an engineering discussion
Send the wavelength, divergence, submount height and emitting distance and we will confirm the mirror material, product grade and package margin. Inquiries from any country are welcome.