Mode locking at terahertz frequencies using a distributed Bragg reflector laser with a sampled grating

Abstract

We present a highly reproducible method of producing terahertz (THz) optical pulses using a class of mode-locked AlGaInAs/InP laser operating in the 1.55 μm wavelength range. The device uses a sample grating distributed Bragg reflector to provide strong frequency selectivity at the mode-locked frequency while the distributed reflectors relax the fabrication tolerances and ensure the cavity can self adjust to being an integral number of mode-locked periods in length. The measured devices provide nearly transform-limited pulse trains at 640 GHz or 1.28 THz with a high degree of controllability and operate with consistent performance over a wide range of drive conditions. Being low cost and compact sources of THz radiation, these lasers will open up many applications, including systems for high-speed optical communication and THz imaging.

THz repetition frequency mode-locked laser using novel sampled gratings

“…Conventional sampled grating distributed-Bragg-gratings (C-SGDBRs) are widely used in tunable DBR lasers [1], and more recently have been used to precisely control the wavelength spacing in arrays of DBR lasers for use in WDM systems [2], and as the reflectors in THz repetition frequency (Fr) semiconductor mode locked lasers (SMLLs) [3]. However, the effective coupling coefficient, κ, of a C-SGDBR ( Fig.…”

Integrated gratings for novel photonic integrated circuits

“…However, fabrication tolerances make it difficult to obtain reliable ML at Fr >~200 GHz. We have therefore proposed techniques based on SGDBRs [2,3]. The SGDBR provides strong frequency selectivity at the modelocked frequency while the 'soft walls' of the reflectors relax the tight fabrication tolerances required by other designs and ensure the long cavity can self-adjust to supporting an integral number of mode-locked periods.…”

“…Using this approach, we have obtained pure ML operation at around 640 GHz with nearly transform limited pulse characteristics. By tuning the bias parameters, operation at the second harmonic, with Fr=1.28 THz, was also achieved [2].…”

A High Power and Ultrahigh Frequency Mode-Locked Laser Monolithically Integrated with an SOA

“…We have previously reported [3] a sampled-grating DBR (SGDBR) MLL in which the DBR section acts as an optical filter to mode-lock the laser at sub-THz repetition frequencies, i.e., ~640 GHz. Due to the nonlinear effects in the cavity, pulse trains at double the 640 GHz pulse repetition rate, i.e., ~1.2 THz, were observed as well.…”

“…The epitaxial structure and fabrication processes used to develop the device are similar to those described in [3]. An optical microscope picture of the top view (p-side) of the fabricated device along with its dimensions is shown in Fig.…”