Diode Laser Resonator
Fabry–Pérot diode laser: threshold modal gain, carrier density and current, differential and slope efficiency, front-facet share, far-field divergence and mode spacing.
Cavity
Active region (your epitaxy; defaults: three 8 nm InGaAs wells)
Near field (1/e² intensity radius of the guided mode)
Threshold modal gain Γg_th
47.98 1/cm
α_i + α_m, mirror loss α_m = 37.98 1/cm
Threshold carrier density
3.505 × 10¹⁸ cm⁻³
material gain g_th = 799.7 1/cm; lifetime 1.260 ns
Threshold current I_th
12.03 mA
J_th = 1337 A/cm²; radiative share 44.17 %
Differential efficiency η_d
63.33 %
η_i α_m/(α_i + α_m), both facets
Slope efficiency
0.8012 W/A
50.00 % of it from the front facet
Fast-axis divergence θ⊥
37.63° FWHM
1/e² half-angle 31.96°
Slow-axis divergence θ∥
10.44° FWHM
1/e² half-angle 8.865°
Longitudinal mode spacing
0.4104 nm
λ²/(2n_gL); c/(2n_gL) = 128.1 GHz
Γg_th = α_i + ln(1/(R₁R₂))/(2L); g = g₀ ln(N/N_tr) gives N_th = N_tr e^(g_th/g₀).
I_th = qwdL(AN_th + BN_th² + CN_th³)/η_i; above threshold P = η_d(hc/qλ)(I − I_th), η_d = η_i α_m/(α_i + α_m).
Front share (1 − R₂)√R₁/((1 − R₂)√R₁ + (1 − R₁)√R₂). Far field of a Gaussian near field: θ₀ = atan(λ/πw), FWHM = √(2 ln 2) θ₀; for w⊥ below λ it underestimates the true fast-axis divergence.
Default material: g₀ = 1200/cm, N_tr = 1.8 × 10¹⁸ cm⁻³, B = 10⁻¹⁰ cm³/s and C = 3.5 × 10⁻³⁰ cm⁶/s from the InGaAs/GaAs quantum-well laser model of De Koninck et al. (2025, Suppl. Table 1; g₀ after Tsvid et al. 2008, who measured dg/d ln J = 1130/cm at 0.98 µm, a current-density form; B and C after Strand et al. 1995); A = 4 × 10⁸/s and n_g = 3.9 from Wenzel et al. (2021, Table I). At threshold the radiative share BN²/(AN + BN² + CN³) is then 44 %, or 35 % of the injected current with η_i = 0.8. Tsvid et al. measured 40–54 % of the current as spontaneous emission at 0.98 µm, so this A is on the high side. Their g₀ is per ln J: with J ∝ N^1.55 at this threshold it would be ≈ 1750/cm in the carrier-density law.
Light–current curve
- Both facets
- Front facet (R₂)
Threshold current versus cavity length
- Threshold current
- This cavity
Far-field intensity
- Fast axis (⊥)
- Slow axis (∥)
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Γg_th = α_i + α_m with logarithmic gain g = g₀ ln(N/N_tr) and ABC recombination, uniform carriers in the active volume (no current spreading or leakage). Gain parameters and A, B, C are your epitaxy's; the defaults are a published InGaAs/GaAs quantum-well model set (g₀, N_tr, B, C: De Koninck et al. 2025; A, n_g: Wenzel et al. 2021), not a datasheet. De Koninck's g₀ is Tsvid et al.'s dg/d ln J = 1130/cm used as is; converted with J ∝ N^1.55 it would be ≈ 1750/cm. Far field from a Gaussian near field, paraxial.
- Coldren L. A., Corzine S. W., Mašanović M. L. (2012). Diode Lasers and Photonic Integrated Circuits, 2nd ed., ch. 2 and 4. Wiley. doi:10.1002/9781118148167
- De Koninck Y. et al. (2025). GaAs nano-ridge laser diodes fully fabricated in a 300-mm CMOS pilot line. Nature 637, 63–69. Supplementary Table 1 (arXiv:2309.04473): g₀ 1200 cm⁻¹, N_tr 1.8 × 10¹⁸ cm⁻³, B 10⁻¹⁰ cm³/s, C 3.5 × 10⁻³⁰ cm⁶/s. doi:10.1038/s41586-024-08364-2
- Wenzel H., Kantner M., Radziunas M., Bandelow U. (2021). Semiconductor Laser Linewidth Theory Revisited. Appl. Sci. 11, 6004. Table I (InGaAs quantum well, 1064 nm): A 4 × 10⁸ s⁻¹, n_g 3.9. doi:10.3390/app11136004
- Tsvid G. et al. (2008). Spontaneous Radiative Efficiency and Gain Characteristics of Strained-Layer InGaAs–GaAs Quantum-Well Lasers. IEEE J. Quantum Electron. 44, 732–739. Abstract: 40–54 % spontaneous radiative efficiency and g₀ = dg/d ln J = 1130 cm⁻¹ at 0.98 µm. doi:10.1109/JQE.2008.924242