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(a) A cross-sectional scanning electron microscope image of a fabricated QD laser diode. (b) Optical microscope image to show four Fabry-Perot lasers from a cleaved laser bar. (c) Schematic cross-section of a ridge-waveguide QD laser on Si.
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We report the first demonstration of direct modulation of InAs/GaAs quantum dot (QD) lasers grown on on-axis (001) Si substrate. A low threading dislocation density GaAs buffer layer enables us to grow a high quality 5-layered QD active region on on-axis Si substrate. The active layer has p-modulation doped GaAs barrier layers with a hole concentra...
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A 25 Gbps limiting amplifier (LA) with loss of signal (LOS) detection is presented in this paper. The proposed LA is composed of an input buffer, three‐stage cascaded amplifier, an output buffer, a DC offset cancellation (DCOC) and a LOS circuit. The LA adopts single‐end input and differential output structure to reduce the complexity of optical re...
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... With the specific numerical parameters outlined in Ref. [42], where the depletion layer capacitance of the QW laser is around 280 pF, the calculated squeezing bandwidth is estimated to be around 1 GHz at 66 K. Meanwhile, QD lasers generally feature lower values of C dep , sometimes as low as 3.5 pF [43]. This would give rise to a scenario where τ te ≪ τ p , resulting in a calculated squeezing bandwidth of several tens of gigahertz at room temperature, given that τ p is in the order of a few picoseconds. ...
The generation of broadband squeezed states of light lies at the heart of high-speed continuous-variable quantum information. Traditionally, optical nonlinear interactions have been employed to produce quadrature-squeezed states. However, the harnessing of electrically pumped semiconductor lasers offers distinctive paradigms to achieve enhanced squeezing performance. We present evidence that quantum dot lasers enable the realization of broadband amplitude-squeezed states at room temperature across a wide frequency range, spanning from 3 GHz to 12 GHz. Our findings are corroborated by a comprehensive stochastic simulation in agreement with the experimental data. The evolution of photonics-based quantum information technologies is currently on the brink of initiating a revolutionary transformation in data processing and communication protocols [1, 2]. A cornerstone within this realm will be the quantum emitter. In recent years, there has been a substantial upsurge in both theoretical and experimental investigations centred around semiconductor quantum dot (QD) nanostructures [3]. A particular emphasis has been placed on self-assembled QDs embedded into microcavities, which facilitate the generation of single photons with high purity and indistinguishability [4-6]. As a result, such sources assume a pivotal role in quantum computing [7, 8] as well as the discrete variables (DV) quantum key distribution (QKD) [9]. In stark contrast to the DV QKD, which requires single-photon sources and detectors, continuous variable (CV) QKD leverages lasers and balanced detection to continuously retrieve the light's quadrature components during key distillation. This approach benefits from readily available equipment and seamless integration into existing optical telecommunications networks [10]. One of the CV QKD protocols, GG02 [11], is widely acclaimed for its security due to the no-cloning theorem of coherent states [12]. Nevertheless, a recent study has delved into the use of squeezed states to achieve even higher levels of security and robustness [13]. This innovative approach strives to completely eliminate information leakage to potential eavesdroppers in a pure-loss channel and to minimize it in a symmetric noisy channel. Within this cutting-edge protocol, information can be exclusively encoded through a Gaussian modulation of amplitude-squeezed states, which are commonly referred to as photon-number squeezed states. These states demonstrate reduced fluctuations in photon number ∆n 2 < n with respect to coherent states, albeit encountering enhanced phase fluctuations due to the minimum-uncertainty principle. Over the past years, squeezed states of light have been frequently generated using χ (2) or χ (3) nonlinear interactions via parametric down-conversion and four-wave mixing [14]. A variety of nonlinear materials have been applied in these processes, including LiNbO 3 (PPLN) [15], KTiOPO 4 (PPKTP) [16], silicon [17], atomic vapour [18], disk resonator [19], and Si 3 N 4 [20]. Recent advancements have also facilitated the transition from traditional benchtop instruments to a more compact single-chip design [21-25]. As opposed to that, Y. Yamamoto et al. [26] initially proposed an alternative to produce amplitude-squeezed states directly with off-the-shelf semiconductor lasers using a "quiet" pump, i.e. a constant-current source. A striking peculiarity of semiconductor lasers is their ability to be pumped by injection current supplied via an electrical circuit. Unlike optical pumping, electrical pumping is not inherently a Poisson point process due to the Coulomb interaction and allows for reducing pump noise below the shot-noise level [26]. Notably, this method can take full advantage of the mature fabrication processes in the semiconductor industry, thereby significantly boosting its feasibility. In other words, its efficacy hinges on the improved performance of recently developed semiconductor lasers, characterized by their compact footprint, ultralow intensity noise and narrow frequency linewidth. While subsequent experiments involving various types of laser diodes have gained widespread interest in this domain, including commercial quantum well (QW) lasers [27, 28], vertical-cavity surface-emitting lasers [29], and semiconductor microcavity lasers [30], the observed bandwidth has, until now, remained relatively limited. The broadest achieved bandwidth has reached 1.1 GHz with a QW transverse junction stripe laser operating at a cryogenic temperature of 77 K [31]. This limitation indeed poses strict constraints on the practical implementation of room-temperature conditions and hinders the realization of high-speed quantum communications. While a recent study did anticipate the theoretical potential of producing broadband amplitude-squeezed states in interband cascade lasers [32], it is worth noting that, prior to this Letter, no experimental demonstration of such phenomenon had been presented.
... Microlasers based on whispering gallery modes [3,4] are one of the promising light sources for the implementation with photonic integrated circuits. Such microlasers supplemented with a III-V quantum dot (QD) active region demonstrate operating characteristics of low-threshold currents and, good thermal stability, together with a high-speed modulation and low lateral dimensions [5][6][7][8]. It should also be noted that QD-based microlasers can be monolithically grown on silicon [9][10][11], as well as transferred to silicon from the native substrate [12,13] without performance degradation [14]. ...
One-state and two-state lasing is investigated experimentally and through numerical simulation as a function of temperature in microdisk lasers with Stranski–Krastanow InAs/InGaAs/GaAs quantum dots. Near room temperature, the temperature-induced increment of the ground-state threshold current density is relatively weak and can be described by a characteristic temperature of about 150 K. At elevated temperatures, a faster (super-exponential) increase in the threshold current density is observed. Meanwhile, the current density corresponding to the onset of two-state lasing was found to decrease with increasing temperature, so that the interval of current density of pure one-state lasing becomes narrower with the temperature increase. Above a certain critical temperature, ground-state lasing completely disappears. This critical temperature drops from 107 to 37 °C as the microdisk diameter decreases from 28 to 20 µm. In microdisks with a diameter of 9 µm, a temperature-induced jump in the lasing wavelength from the first excited-state to second excited-state optical transition is observed. A model describing the system of rate equations and free carrier absorption dependent on the reservoir population provides a satisfactory agreement with experimental results. The temperature and threshold current corresponding to the quenching of ground-state lasing can be well approximated by linear functions of saturated gain and output loss.
... Recently, these lasing parameters were significantly improved to 160 A/cm 2 and 52°C, respectively, by the same group, optimising the buffer design and growth condition [44]. Besides intensively studied broad area lasers, narrow ridge lasers that guarantee fundamental transverse electronic mode lasing are now garnering more attention [82][83][84]. Reducing the ridge width down to a few microns, a lower threshold current and better heat dissipation are also expected due to the reduced injection area and efficient current confinement. However, the sidewall recombination effect becomes significant along with the increase in series resistance. ...
With continuously growing global data traffic, silicon (Si)-based photonic integrated circuits have emerged as a promising solution for high-performance Intra-/Inter-chip optical communication. However, a lack of a Si-based light source remains to be solved due to the inefficient light-emitting property of Si. To tackle the absence of a native light source, integrating III-V lasers, which provide superior optical and electrical properties, has been extensively investigated. Remarkably, the use of quantum dots as an active medium in III-V lasers has attracted considerable interest because of various advantages, such as tolerance to crystalline defects, temperature insensitivity, low threshold current density and reduced reflection sensitivity. This paper reviews the recent progress of III-V quantum dot lasers monolithically integrated on the Si platform in terms of the different cavity types and sizes and discusses the future scope and application.
... In contrast to QW lasers, the direct modulation performance in terms of the modulation rate is not satisfactory enough in QD lasers, due to the strongly limited carrier capture and relaxation processes as well as the Pauli blocking (direct consequence of Pauli exclusion principle) that lead to a large damping factor (Malic et al., 2007). In general, the -factor of QD laser is ≈0.9 ns (Arsenijević and Dieter Bimberg, 2016;Inoue et al., 2018), whereas that of QW laser is below 0.2 ns (Keating et al., 1999). It is worth stressing that the gain broadening mechanisms in QDs play a crucial role in affecting the relaxation oscillation frequency and the damping (Fiore and Markus, 2007). ...
... Therefore, it is of importance to minimize the OWD or to apply the p-modulation doping to the active region to ensure an optimum laser performance in terms of the K-factor. The second statement comes from the fact that the differential gain can be increased by the p-doping technique (Inoue et al., 2018;. Moreover, these results demonstrate that a large OWD at room temperature is an efficient technique to develop a high-performance laser source for high-temperature applications. ...
Silicon photonics is promising for high-speed communication systems, short-reach optical interconnects, and quantum technologies. Direct epitaxial growth of III-V materials on silicon is also an ideal solution for the next generation of photonic integrated circuits (PICs). In this context, quantum-dots (QD) lasers with atom-like density of states are promising to serve as the on-chip laser sources, owing to their high thermal stability and strong tolerance for the defects that arise during the epitaxial growth. The purpose of this dissertation is to investigate the nonlinear properties and dynamics of QD lasers on Si for PIC applications. The first part of this thesis investigates the dynamics of epitaxial QD lasers on Si subject to external optical feedback (EOF). In the short-cavity regime, the QD laser exhibits strong robustness against parasitic reflections hence giving further insights for developing isolator-free PICs. In particular, a near-zero linewidth enhancement factor is crucial to achieve this goal. The second part is devoted to studying the static properties and dynamics of a single-frequency QD distributed feedback (DFB) laser for uncooled and isolator-free applications. The design of a temperature-controlled mismatch between the optical gain peak and the DFB wavelength contributes to improving the laser performance with the increase of temperature. The third part of this dissertation investigates the QD-based optical frequency comb (OFC). External control techniques including EOF and optical injection are used to optimize the noise properties, reduce the timing-jitter, and increase the frequency comb bandwidth. In the last part, an investigation of the optical nonlinearities of the QD laser on Si is carried out by the four-wave mixing (FWM) effect. This study demonstrates that the FWM efficiency of QD laser is more than one order of magnitude higher than that of a commercial quantum-well laser, which gives insights for developing self-mode-locked OFCs based on QD. All these results allow for a better understanding of the nonlinear dynamics of QD lasers and pave the way for developing high-performance classical and quantum PICs on Si.
... Table 1 summarizes the room-temperature device parameters of this work aggregated with those previously reported in 1.3 μm InAs QD lasers grown on either native GaAs substrate or silicon substrate (with sole ground-state lasing). It is worth stressing that a low K-factor typically below 1 ns is desired to ensure a large maximum 3 dB bandwidth f 3 dB, max 2 ffiffi ffi 2 p π∕K [39,41]. To increase the modulation capabilities, shortening the cavity length below 500 μm is preferred. ...
... To increase the modulation capabilities, shortening the cavity length below 500 μm is preferred. The modulation bandwidth can also be increased with p-modulation doping of the active region in order to improve the carrier transport across the barrier [41]. In this study, the large K-factor is attributed to the low differential gain at room temperature [42,43]. ...
This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.
... Si x Ge 1−x based lattice-graded buffers were adopted as a buffer layer to release the lattice mismatch [11,12]. GaP on Si was also used as a buffer layer and GaAs was epitaxially grown on the GaP/Si [13,14]. And the threading dislocations or stacking faults can be reduced by growing GaAs on an inclined facets of patterned Si substrate [15,16]. ...
A GaAs quantum-well laser diode was directly grown on silicon (001) substrate by a hybrid technique comprising AlAs nucleation and thermal cycle annealing. The hybrid technique provided the advantages of superior surface roughness, high quantum efficiency, and low threading dislocation density (TDD) of a thin buffer. The TDD was quantitatively characterized through the electron channeling contrast imaging method. Directly grown GaAs on Si exhibited a TDD of 5.45 × 10⁷ /cm² with small thickness of approximately 1.5 µm. The roughness and quantum efficiency of GaAs on Si was enhanced by adopting the nucleation layer of AlAs. We found that there exists an optimal thickness of AlAs nucleation to be 1.68 nm through structural and optical analysis. Based on optimized GaAs on Si, the GaAs quantum-well laser diode was directly grown with a TDD of 2.5 × 10⁷ /cm². Whole epitaxial layers were grown by metalorganic chemical vapor deposition. An edge-emitting broad stripe laser diode was successfully fabricated with a cavity length and width of 1120 µm and 60 µm, respectively. The continuous-wave lasing at room temperature was realized with a threshold current density of 643 A/cm² and maximum output power of 19.7 mW at a single facet, where a threshold current density of 317 A/cm² was obtained under pulsed operation condition. This result would constitute a building block to realize silicon-based on-chip light sources.
... Compared to heterogeneously integrated QW lasers, QD lasers show a nearly 20 dB reduced sensitivity to feedback with total system RIN below -140 dBc/Hz from 100 to 10 GHz [100]. At the system level, the use of onchip QD lasers without optical isolation gives rise to a low power penalty of 1 dB at 5 Gb/s after a 12-km transmission distance [101], a penalty-free operation for BER < 10 −12 at 10 GHz external modulation with 100% (i.e., -7.4 dB) optical feedback [94], error-free operation at 25 Gb/s and more than 70 °C in a chipscale Si-photonics optical transmitter [102], and negligible signal degradation by optical feedback within the transmitter for an optical input-output core [103]. ...
A self-assembled quantum dot (QD) gain medium has multiple favorable material properties over conventional quantum well (QW) structures and bulk materials, including a large tolerance for material defects, reduced reflection sensitivity, nearly zero linewidth enhancement factor, low transparency current density, high temperature operation, and ultrafast gain dynamics useful for semiconductor mode-locked lasers and amplifiers. Here, we review the recent advances in the field of QD lasers and amplifiers with a focus on the direct growth on silicon (Si). Si photonics has found widespread application, particularly for high volume applications and for co-integration with CMOS electronics.
... However, they suffer from insufficient performance in most applications, such as low performance and vulnerability to moisture, and thus are unsuitable for longterm exposure in vivo. Recently, as an alternative approach, the high-performance and long-term operational stability of inorganic electronics with III-V compound semiconductors are being utilized in lasers, [10][11][12] photodetectors (PDs), [13][14][15] and a broad range of optoelectronic applications. [16][17][18] Despite the superior characteristics of these devices over their organic counterparts, they are limited by the thick, rigid, and brittle substrates used in growing them. ...
In this paper, we first demonstrated an approach to form high‐quality GaAs‐based flexible photodetectors (PDs) by metal wafer bonding (MWB) and high‐throughput epitaxial lift‐off (ELO) with encapsulated thermally grown silicon dioxide (t‐SiO2) for chronic biomedical implants. The flexible GaAs PDs demonstrate responsivity over a wide range of visible and near‐infrared wavelengths. Regarding certain diagnoses, high‐performance PDs are essential for precise treatments with long‐term optoelectronic implants, and the long‐term stability and reliable encapsulation of GaAs PDs will play a major role when optoelectronics are injected into biofluids. t‐SiO2, as an encapsulation barrier, is stable without increasing the leakage current for over 120 hours in phosphate‐buffered saline at 70°C. By Arrhenius scaling, the device shows a 700‐day lifetime with stable operation in a biofluid at 37°C. Finally, by measuring the mass of arsenic using an inductively coupled plasma mass spectrometer (ICP/MS), the t‐SiO2 encapsulation barrier is capable of preventing toxic elements from leaching out to surrounding tissues. Our technology may provide approaches based on III‐V materials for expanding high‐performance optoelectronic devices to biomedical implants, namely, a broad range of high‐resolution retinal prostheses for blindness or the integration for measuring physiological parameters, such as tissue oxygenation and neural activity in the cerebral cortex.
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... A number of studies have demonstrated the growth of high quality III-V materials on Si. To avoid the high density of threading dislocations (TD) that arise from the lattice mismatch between silicon and the epitaxial layers, various groups employ a combination of two-step growth, dislocation filter layers, thermal cyclic annealing, and aspect-ratio trapping [24][25][26][27][28]. To further drive down the cost associated with the substrate and leverage the mature Si CMOS industry in the future, we propose to eliminate the use of III-V wafer altogether and grow the PDs on on-axis Si wafer. ...
We demonstrate flexible GaAs photodetector arrays that were hetero-epitaxially grown on a Si wafer for a new cost-effective and reliable wearable optoelectronics platform. A high crystalline quality GaAs layer was transferred onto a flexible foreign substrate and excellent retention of device performance was demonstrated by measuring the optical responsivities and dark currents. Optical simulation proves that the metal stacks used for wafer bonding serve as a back-reflector and enhance GaAs photodetector responsivity via a resonant-cavity effect. Device durability was also tested by bending 1000 times and no performance degradation was observed. This work paves a way for a cost-effective and flexible III-V optoelectronics technology with high durability.
... The f 3dB of the un-doped device and p-doped device are 3.7 and 7.8 GHz, respectively. The p-doped device obtains a flat frequency response corresponding to the higher γ of 39.31 ns −1 , which is attributed to the strong damping characteristics of the p-doped QD active layers [20]. ...
Aiming to realize high-speed optical transmitters for isolator-free telecommunication systems, 1.3 μm p-modulation doped InGaAs/GaAs quantum dot (QD) lasers with a 400 μm long cavity have been reported. Compared with the un-doped QD laser as a reference, the p-doped QD laser emits at ground state, with an ultra-low threshold current and a high maximum output power. The p-doped QD laser also shows enhanced dynamic characteristics, with a 10 Gb/s large-signal direct modulation rate and a 7.8 GHz 3dB-bandwidth. In addition, the p-doped QD laser exhibits a strong coherent optical feedback resistance, which might be beyond −9 dB.
