Extending the continuous tuning range of an external-cavity diode laser

Abstract

The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.

Building a better atomic clock

“…Spurred by some curious effects we observed in the photodiode signal we started looking into active injection locking servos. Before much research had been done into the subject, Igor Teper and Tom Loftus from AOsense pointed out three very useful papers on the matter of optimum current set point servos in various diode laser configurations [51,52,53]. For the purpose of explaining how these servos derive their error signal, let us take the example of an uncoated diode placed inside an external cavity diode laser setup.…”

“…The photodiode current signal is then demodulated at f m , and the voltage output from a lock-in amplifier gives the phase relationship between the induced amplitude noise and the current driving signal. The phase relationship depends on the transfer function of the laser diode, and not only is it stable, but it smoothly changes with the current of the laser near the optimal setting [51,53]. In essence, one is just measuring the frequency modulation to amplitude modulation transfer function of the laser at one specific frequency, f m .…”

Development of a widely tunable amplified diode laser differential absorption lidar for profiling atmospheric water vapor

“…A feedback loop using a wavemeter, described in Refs. 54 and 55, tuned the laser wavelength until the on-line wavelength was reached and held it to within +/-88 MHz (the frequency accuracy of the wavemeter) for the duration of the measurement [54,55]. This wavelength and the reference power were measured.…”

Modified grating-based external cavity diode laser for simultaneous dual-wavelengths operation

“…Diode lasers in an external cavity [3][4][5] are known to be efficient and compact and have achieved dual-wavelength operation in several approaches. Most of these include an apodizing holographic grating [6] as well as dual-period holographic element [7] in a Littrow configuration of an external cavity.…”