In this post, we present the wavelength calibration of a narrow-linewidth DFB laser using a fiber coupled gas cell from Wavelength References. The gas cell contains carbon 13 hydrogen cyanide (H13CN) at 20 Torr pressure with 5.5 cm absorption path. The figure below shows the transmission spectrum of an H13CN cell (15 cm aborption path, 25 Torr) measured by the NIST :
The wavelength of each absorption line is insensitive to environmental conditions and is known very accurately. For instance, the wavelength of the P2 line center is at 1543.80967(18) nm .
The optical power at the output of the gas cell is monitored with a Thorlabs PM100D power meter. The analog output of the power meter is measured with the analog-to-digital converter of a Red Pitaya board. The Red Pitaya controls the DRV100 laser driver via a Serial Peripheral Interface. A 16-bit PWM signal between 0 and 1.8 V is used to control the laser temperature via the TSET pin of the TEC100L temperature controller.
The figure below shows the optical power (in decibel scale) measured at the output of the gas cell for 500 currents x 500 temperatures:
We observe 3 strong and 5 weak absorption lines. Thanks to the weak absorption lines, we can say that the 3 strong lines corresponds to the lines P1, P2 and P3 of the H13CN spectrum.