Mode-locking and frequency mixing at THz pulse repetition rates in a sampled-grating DBR mode-locked laser

Abstract

Abstract:We report a sampled grating distributed Bragg reflector (SGDBR) laser with two different gratings which mode-lock independently at respective pulse repetition frequencies of 640 and 700 GHz. The device operates in distinct regimes depending on the bias conditions, with stable pulse trains observed at 640 GHz, 700 GHz, the mean repetition frequency of 666 GHz, and the sum frequency of 1.34 THz (due to nonlinear mixing). Performance is consistent and highly reproducible with exceptional stability observed over wide ranges of drive bias conditions. Furthermore, a monolithically integrated semiconductor optical amplifier is used to amplify the pulse trains, providing an average output power of 46 mW at 666 GHz.

Mode-Locked Laser Diodes and Their Monolithic Integration

“…As anticipated, the equivalent laser fabricated using a 5-QW Al-quaternary structure [14] with a Γ value of 5% resulted in a less broad range for stable harmonic ML and a lower average output power. Pure ML with ∼100% modulation at ∼240 GHz was obtained with V S A = −2.0 V, 184 mA ≤ I Gain ≤ 196 mA.…”

“…An HML laser produces an optical pulse train at a harmonic of the fundamental round-trip frequency of the device. This can be achieved by methods including sub-harmonic optical injection [5], colliding pulse ML (CPM) [6]- [9], compound-cavity ML (CCM) [10]- [12], methods based on the selectivity of harmonic numbers related to the spectral-filtering properties of conventional distributed Bragg reflector (DBR) lasers [10], and techniques we proposed based on sampled grating DBRs (SGDBRs) [13], [14]. We have recently taken this concept further and demonstrated the use of novel SGDBRs in which a π-phase shifted grating is placed in the section where there would be no grating in a conventional SGDBR (C-SGDBR).…”

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.…”

A Molecularly Modulated Mode-Locked Laser

“…Theoretically, a 10-THz mode-locked pulse train would be emitted from a 30- μ m optical cavity. To achieve rates greater than 1 THz, several approaches have been proposed, such as harmonic mode-locking in semiconductor lasers or distributed Bragg reflector-structured lasers 17 , 18 , nonlinear modulation in optical fibers 19 , and phase-locking between multiple continuous lasers 20 . However, the bandwidth limits further increases in repetition rate, and new approaches are needed to reach 10 THz.…”