Semiconductor lasers subject to optical injection exhibit both stable locking regime and unstable locking regime. Inside the stable locking regime, various laser performances can be improved. Outside the stable locking regime, the lasers produce rich nonlinear dynamics. However, very few dynamics are known when the QCLs are subject to optical injection. This work reports the measured dynamics of a QCL subject to optical injection, both within and outside the stable locking regime. In the experimental setup, the master QCL is injected into the slave QCL through a unidirectional isolator. Both QCLs are single-mode distributed feedback lasers, and emit around 2182.5 /cm. The lasing threshold of the master laser is 385 mA and the threshold of the slave laser is 425 mA. The detuning frequency between the two lasers is adjusted by tuning the pump current of the master laser, and the frequency tunability is -776.5 MHz/mA. In the experiment, the slave laser is fixed at 435 mA with an output power of 2.9 mW. The slave laser is stably locked by the master laser when decreasing the pump current from 429.2 mA down to 426.1 mA, which corresponds to a detuning frequency from -0.85 GHz up to +1.42 GHz. Meanwhile, the injection ratio slightly reduces from 4.24 dB down to 4.02 dB. Therefore, the stable locking frequency range is as large as 2.27 GHz. Within the stable locking regime, the optical power rises almost linearly with increasing detuning frequency. Interestingly, the injection-locking boundary exhibits clear hysteresis phenomenon when increasing the pump current of the master laser, where the stable-locking range shrinks to 1.03 GHz. Outside the stable-locking regime, the QCL mostly produces period-one oscillations. Besides, we also observe quasi-periodic oscillations and spiking pulsations, although the occurrence of both dynamics is rare.
Gas sensing based on modulation spectroscopy requires sinusoidal modulation of the laser sources. This work proposes a modulation scheme for quantum cascade lasers, using the period-one (P1) oscillations. The P1 oscillations are introduced by the tilted optical feedback. Although the optical linewidth of the laser is around 15.0 MHz, the beat-note electrical linewidth of the modulation is less than 2.0 kHz, which suggests that the optical sidebands induced by the P1 oscillations are highly coherent with the main optical mode. In addition, the modulation frequency can be simply tunned by adjusting the feedback length, and the modulation depth of the optical signal is in the range of 1.0 % to 3.0 %. In contrast to the direct modulation scheme and the external modulation scheme, the proposed P1 modulation method does not require any radio-frequency electronics.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.