Abstract
We describe mode locked laser diodes (MLLDs) operating from 40 GHz to >1 THz. Below 40 GHz, operation at the fundamental cavity frequency is appropriate, but at higher frequencies harmonic mode-locking (HML) is used. To increase output power and control nonlinear behavior, the gain needs to be modified, and an AlGaInAs/InP structure with a three-quantum-well active layer and passive far-field reduction layer is presented. In 40-GHz all-active MLLDs, this structure offers improvements in internal loss, slope efficiency, mode locking (ML) range, RF linewidth, timing jitter, far field pattern, and coupling efficiency to a single-mode fiber. By creating a transparent passive waveguide in part of the cavity, a 490-fs pulse width was achieved, the shortest reported from any quantum well MLLD. Several approaches are described for HML: colliding pulse ML operating up to 240 GHz, coupled cavity ML up to 160 GHz, and sampled Bragg grating constructions up to 1.28 THz. This latter approach offers stable HML over a wide range of bias conditions. Finally, we report a synchronized multicolor ML laser array, containing four 40-GHz lasers with designated wavelength registration for optical code division multiple access or optical time division multiple access applications.
Highlights
G ENERATION of ultrafast and ultrashort optical pulses is of great interest for future large capacity optical communication networks, including high-bit-rate optical timedivision-multiplexing systems and ultrafast data processing
Mode-locked laser diodes (MLLDs) are very attractive and promising candidates for this purpose because they have excellent pulse characteristics compared to other optical pulse sources and can produce short pulse widths ranging from picoseconds to sub-picoseconds with small frequency chirp
An harmonic mode-locking (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 mode locking (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]
Summary
G ENERATION of ultrafast and ultrashort optical pulses is of great interest for future large capacity optical communication networks, including high-bit-rate optical timedivision-multiplexing systems and ultrafast data processing. 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].
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