Abstract
A two-sectioned quantum dash laser structure based on an InAs/InP chirped active region medium is investigated as a monolithic broadband tunable laser. A thorough parametric analysis on the effect of three tuning parameters ( viz. injection current, cavity length, absorber-to-device length ratio) on the optical power-injection current (L-I) and spectral characteristics, particularly wavelength tunability and bandwidth broadening, is performed. A total emission wavelength tunability of ~20 nm is demonstrated in the mid-L-band (~1600 to ~1620 nm) window and ~2 times enhancement in the 3dB bandwidth. Furthermore, optical bistability in the two-sectioned InAs/InP quantum-dash laser device is observed at near room temperature in the form of L-I curve hysteresis. Further investigation displayed a direct relation between the absorber length and the hysteresis loop width with a maximum value of ~40 mA is demonstrated; a potential platform in fast optical switching and modulation applications. Finally, the two-sectioned structure is also proposed and investigated as a monolithic two-segment contact spectrum shaper to manipulate the lasing spectrum profiles to attain flat tops and effectively increase the spectrum 3dB bandwidth. As such, a maximum 3dB bandwidth was able to be pushed up to ~20 nm from ~7 nm by proper tuning of the current density distribution across the two segments of the device.
Highlights
A tunable optical source, by definition, is one whose emission wavelength can be manipulated or adjusted through different mechanisms
Though the tunability of optical sources can be achieved through different mechanisms, monolithic tunable semiconductor sources offer an extra edge over external cavity tuning structures for their compactness, reliability, ease in tuning, and integrability with other optoelectronic components
A Quantum-dash laser diode (QD-LD) was selected with a cavity length (L) of 760 μm, a gain section length (Lg) of 660 μm, and an absorber section length (La) of 100 μm, absorber-todevice length ratio (La/L) of ∼13%
Summary
A tunable optical source, by definition, is one whose emission wavelength can be manipulated or adjusted through different mechanisms. Though the tunability of optical sources can be achieved through different mechanisms, monolithic tunable semiconductor sources offer an extra edge over external cavity tuning structures for their compactness, reliability, ease in tuning, and integrability with other optoelectronic components. In such monolithic configurations, the tunability is achieved over a single device either via altering the wavelength selectivity of distributive feedback (DFB) structure [8], employing segmented two or more sections where one acts as a gain medium section while the other(s) acts as a saturable absorber [1], [2], partially-injected section [9], [4], etc. The DFB approach yields high-performance tunable devices, suffers from the cost issues and
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