DFB Thermal / Current Tuning Calculator (Target Wavelength → TEC)

Reference point & tuning coefficients

Ref. wavelength λ₀ (nm) Ref. temperature T₀ (°C) Ref. current I₀ (mA) k_T (nm/°C, typical) k_I (nm/mA, typical)

Forward · Settings → wavelength

TEC temperature T (°C) Operating current I (mA)

—Output wavelength λ

Reverse · Target wavelength → suggested settings

Target λ (nm)

—Suggested TEC (current held at I₀)

λ = λ₀ + k_T·(T−T₀) + k_I·(I−I₀) k_T ≈ 0.09 nm/°C and k_I ≈ 0.005 nm/mA are typical values; exact coefficients per unit are in its factory report

λ–T tuning line (15–45 °C window); orange dot = forward-card operating point

Division of labor between the two knobs

A DFB's wavelength is locked to the Bragg condition of its built-in grating. Temperature changes both the refractive index and the grating pitch, giving a smooth ≈0.09 nm/°C (typical) tuning — single-mode, mode-hop-free, which is the DFB's core advantage over FP lasers. Injection current acts mainly through self-heating at ≈0.005 nm/mA (typical): fast response, ideal for scanning and modulation, at the cost of a coupled power change.

The standard TDLAS recipe: use the TEC to coarse-tune near the target absorption line (the temperature suggested by the reverse card), then sweep across the line with a current ramp plus high-frequency modulation (2f detection). The usual TEC window of 15–45 °C corresponds to about ±1.35 nm of single-device tuning — beyond that, choose an adjacent-wavelength model; DFB grating wavelengths can be customized on request.

DFB Thermal / Current TuningWavelength Tuning

Division of labor between the two knobs