Monolithic dual mode lasers
Monolithic dual-mode lasers are beneficial for THz systems due to their compact, integrated design, which enables stable and coherent THz signal generation through phase-locked modes and adjustable beat frequencies. At PTT, two different laser types with a Y-shaped cavity are tested.
Y-DFB laser:
This laser features a Y-shaped resonator with a shared gain segment (combiner segment) and two separate gain segments for selective feedback at 1536 nm and 1544 nm with top-etched slots selecting a single mode from the available Fabry-Perot modes in the cavity. This allows oscillation of two distinct modes in the same cavity. Both modes can be tuned by adjusting the chip temperature and individually via the gain current in each segment, offering high spatial overlap, reduced inter-mode noise, and significant potential for on-chip integration. The laser chip is enclosed in a butterfly package, ensuring temperature control, mechanical protection, and stable coupling into a polarization-maintaining (PM) fiber. This laser features fast modulation performance while being limited in modulation bandwidth of the beating signal. In a single frequency CW-THz system, which is employing this laser as the beating source, measurement rates in the high kHz range of thin film thicknesses with micrometer precession can be achieved.
Y-DBR laser:
The Y-DBR laser is a micro-integrated dual-wavelength master oscillator power amplifier (MOPA) designed and fabricated by our cooperation partner Ferdinand-Braun Institute. The laser has two-color emission in the regime of 785 nm with up to 600 mW optical power, thanks to the integrated tapered amplifier section. Originally designed for Raman Spectroscopy, the MOPA laser are now being used for CW THz generation due to its compact size and optical spectra tunability. Being integrated in a turn-key system, the laser has a potential to be used in on-site measurements with its robust housing and all-software-based source control.