Direct modulation of excited state quantum dot lasers

Stevens, B.; Childs, David; Shahid, Hifsa; Hogg, R. A.

doi:10.1063/1.3193664

Cited by 42 publications

(35 citation statements)

References 13 publications

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“…However, it has to be noted that the shapes of the gain spectra of both lasers may also affect the dynamics. 15,34 To this end, the ES laser under study might be more sensitive to optical feedback also because of a stronger modal competition as compared to the GS laser, which has a rather flat optical spectrum around the central lasing wavelength (not shown here). The different dynamics can also be attributed to the ES degeneracy where the existence of two closely spaced p-levels can lead to more radiative transitions.…”

confidence: 99%

“…13 Owing to the faster carrier capture from the surrounding carrier reservoir as well as a higher saturated gain, 14 ES QD transmitters have been touted to be a promising solution for high-speed applications. 15,16 The larger degeneracy of the ES translates into a larger differential gain and smaller nonlinear gain compression than to those of the GS. The first successful investigation at the link level was realized with 1.…”

confidence: 99%

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Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

et al. 2016

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Quantum dot lasers are envisioned to be the next generation of optical transmitters used for short-reach communication links, owing to their low threshold current and high temperature operation. However, in a context of steady increase in both speed and reach, quantum dot lasers emitting on their upper energy levels have been recently of greater interest as they are touted for their faster modulation dynamics. This work aims at further evaluating the potential impact of such lasers in communication links by characterizing their long-delay optical feedback responses as well as the role of the lasing states on the multimode dynamics of InAs/GaAs quantum-dot Fabry-Perot devices sharing the same design. Results unveil that the excited-state laser shows a much larger sensitivity to optical feedback, with a more complex route to chaos, and a first destabilization point occurring at lower feedback strengths than for a comparable ground-state laser, which remains almost unaffected.

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confidence: 99%

Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

et al. 2016

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“…22 The advantage of an ES laser is that the net modal gain is increased without increasing the QD layer number. Indeed, the scattering time is expected to be reduced 8 due to the higher density of final scattering states, leading to an increase in the predicted K-factor limited bandwidth (see Fig. 4, G sat ¼ 18 cm À1 , s 0 ¼ 3 ps, G sat ¼ 18 cm À1 , s 0 ¼ 1.5 ps).…”

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confidence: 99%

“…7 It has recently been demonstrated that operation using the excited state (ES) of the QDs exhibit much higher damping limited bandwidths as compared to ground state (GS) lasers. 8,9 This enhancement was attributed to higher saturated gain (double) and lower scattering time (half) compared to the ground state. However, this is achieved at the expense of higher operating currents and shorter operating wavelengths that may be impractical for fiber-optic based optical communications applications.…”

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confidence: 99%

O-band excited state quantum dot bilayer lasers

Majid

Childs

Kennedy

et al. 2011

Applied Physics Letters

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Bilayer InAs/GaAs quantum dot (QD) lasers operating in the excited state at wavelengths that span the O-band are demonstrated. The higher saturated gain and lower scattering time of the excited states of the ensemble of QDs offers the opportunity for fast direct-modulation lasers. We predict an increase in K-factor limited modulation bandwidth from QD lasers operating in the excited state due to a reduction in carrier transport and scattering times whilst maintaining high peak modal gain. Semiconductor diode lasers incorporating self-assembled quantum dots (QDs) on GaAs substrates accessing the International Telecommunication Union (ITU) O-band (1.26-1.36 lm) have received considerable attention, to the point of their current commercialization, 1,2 with recent performance milestones reached including high-speed, temperature-insensitive 3 operation around room temperature (RT) at 1.3 lm through the use of p-type doping. 4 In contrast to quantum well lasers, the modulation dynamics of QD lasers are limited by damping, 5 and in order to achieve high modulation rates, low carrier scattering times into the lasing state and high saturated modal gains are required. Possible routes to increase saturated gain include careful optimization of growth conditions to increase QD areal density 6 or to increase differential gain by increasing p-doping, but this has practical limit in terms of additional loss. 7 It has recently been demonstrated that operation using the excited state (ES) of the QDs exhibit much higher damping limited bandwidths as compared to ground state (GS) lasers. 8,9 This enhancement was attributed to higher saturated gain (double) and lower scattering time (half) compared to the ground state. However, this is achieved at the expense of higher operating currents and shorter operating wavelengths that may be impractical for fiber-optic based optical communications applications.Here, we demonstrate that the technologies to realize long wavelength QD GS emission can be applied to realize QD ES emission spanning the O-band. In this paper, we report on the fabrication of QD bilayer 10,11 materials where ES lasing is demonstrated between 1.26 lm and 1.33 lm spanning the ITU O-band. This is achieved by using QD material comprising closely stacked layers of QDs, which are strain and electronically coupled, consisting of a seed layer that determines the areal density and an upper emission layer. The wavelength coverage is made possible by utilizing both GaAs and InGaAs capping of the emission layer. Measurement of multi-section lasers containing these QD bilayers allows the peak modal gain of the ES as a function of current density to be deduced, 12 and this is comparable to commercially available 1.3 lm QD laser samples operating in the GS.

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“…Although a direct modulation rate of as high as 25 Gb/s for a GS lasing QD laser has been reported recently, there is still a large gap between practical and theoretical values. 4 On the other hand, the excited-state (ES) lasing QD lasers have recently shown to have greater modulation potential than the GS lasing QD lasers, [5][6][7][8][9] because of their higher modal gain and shorter carrier capture time. [9][10][11] Thus, ES lasing is expected to enhance the modulation performance of the QD lasers.…”

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confidence: 99%

Dynamic characteristics of two-state lasing quantum dot lasers under large signal modulation

Luo

et al. 2015

AIP Advances

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Large signal modulation characteristics of the simultaneous ground-state (GS) and excited-state (ES) lasing quantum dot lasers are theoretically investigated. Relaxation oscillations of ‘0 → 1’ and ‘1 → 0’ in the GS lasing region (Region I), the transition region from GS lasing to two-state lasing (Region II) and the two-state lasing region (Region III) are compared and analyzed. It is found that the overshooting power and settling time in both Regions I and III decrease as the bias current increases. However, there exist abnormal behaviors of the overshooting power and settling time in Region II owing to the occurrence of ES lasing, which lead to fuzzy eye diagrams of the GS and ES lasing. Moreover, the ES lasing in Region III possesses much better eye diagrams because of its shorter settling time and smaller overshooting power over the GS lasing in Region I.

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Direct modulation of excited state quantum dot lasers

Cited by 42 publications

References 13 publications

Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

O-band excited state quantum dot bilayer lasers

Dynamic characteristics of two-state lasing quantum dot lasers under large signal modulation

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