Nanocavity Laser Research Articles

Static and Dynamic Analysis of Lasing Action from Single and Coupled Photonic Crystal Nanocavity Lasers**Supported by the National Key Basic Research Special Fund/CNKBRSF of China under Grant Nos 2012CB933501, 2016YFA0301102, 2016YFB0401804 and 2016YFB0402203, the National Natural Science Foundation of China under Grant Nos 61535013, 61321063 and 61137003, the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant

The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing efficiency and generate an output power higher than the single-cavity lasers, results that are consistent with the theoretical results obtained by rate equations. In dynamic regime, the single-cavity lasers produce pulses as short as 113 ps, while the coupled-cavity lasers show a significantly longer lasing duration. These results indicate that the photonic crystal laser is a promising candidate for the light source in high-speed photonic integrated circuit.

Ultrahigh-speed Si-integrated on-chip laser with tailored dynamic characteristics.

For on-chip interconnects, an ideal light source should have an ultralow energy consumption per bandwidth (operating en-ergy) as well as sufficient output power for error-free detection. Nanocavity lasers have been considered the most ideal for smaller operating energy. However, they have a challenge in obtaining a sufficient output power. Here, as an alternative, we propose an ultrahigh-speed microcavity laser structure, based on a vertical cavity with a high-contrast grating (HCG) mirror for transverse magnetic (TM) polarisation. By using the TM HCG, a very small mode volume and an un-pumped compact optical feedback structure can be realised, which together tailor the frequency response function for achieving a very high speed at low injection currents. Furthermore, light can be emitted laterally into a Si waveguide. From an 1.54-μm optically-pumped laser, a 3-dB frequency of 27 GHz was obtained at a pumping level corresponding to sub-mA. Using measured 3-dB frequen-cies and calculated equivalent currents, the modulation current efficiency factor (MCEF) is estimated to be 42.1 GHz/mA1/2, which is superior among microcavity lasers. This shows a high potential for a very high speed at low injection currents or avery small heat generation at high bitrates, which are highly desirable for both on-chip and off-chip applications.

III–V-on-Si Photonic Crystal Nanocavity Laser Technology for Optical Static Random Access Memories

Heterogeneous integration of III-V semiconductors on silicon has gained considerable momentum fueled by the need to implement fully functional photonic devices and circuits in a CMOS compatible platform. In this communication, we report on a III-V photonic crystal (PhC) nanocavity, heterogeneously integrated on a silicon-on-insulator platform, to form a PhC nanocavity laser capable of exhibiting two elementary static random access memory (SRAM) cell functions individually, namely switching and latching operations under a high-speed, bit-level regime. As such, the PhC nanocavity laser is examined as a generic logic functions building block, suitable toward multiGb/s energy-efficient, optical SRAM cells with minimal device footprint. The proposed device occupies a total area of only 6.2 μm2 , rendering in this way the demonstrated memory element the smallest among the integrated optical memories presented so far. Bit-level SRAM cell operation requires two elementary functions: the access gate (AG) switching function and set-reset flip-flop (SR-FF) latching function. At first, AG switching operation is evaluated through successful wavelength conversion at 10 Gb/s, revealing a power penalty of 1 dB at 10–9 BER and a switching energy of only 4.8 fJ/bit. Then, fully functional SR-FF memory operation is successfully demonstrated, exhibiting error-free operation with negative power penalty at 5 Gb/s and switching energies of 6.4 fJ/bit. FF operation at higher speeds of 10 Gb/s with reduced switching energy levels of 3.2 fJ/bit is also experimentally investigated. Both logic operations were demonstrated separately with the same PhC nanocavity laser device exhibiting <50 ps switching times and evaluated under real-type data traffic patterns, raising expectations for beyond 20 Gb/s capabilities toward implementing energy-efficient, ultracompact and high-speed true optical SRAM setups for Datacom applications.

Modulation of carrier dynamics and threshold characteristics in 1.3-μm quantum dot photonic crystal nanocavity lasers

A self-consistent all-pathway quantum dot (QD) rate equation model, in which all possible relaxation pathways are considered, is used to investigate the influence of quality (Q) factor on the carrier dynamics of 1.3-μm InAs/GaAs QD photonic crystal (PhC) nanolasers. It is found that Q factor not only affects the photon lifetime, but also modulates the carrier occupation in QDs. About three times increases of carrier injection efficiency in QD ground state can be realized in nanocavity with high Q factor. However, it also reveals that over 90% improvement of threshold current happens when Q factor increases from 2000 to 7000, which means it might be not necessary to pursuit for ultrahigh Q factor for the purpose of low threshold current.

Systematic study of thresholdless oscillation in high-β buried multiple-quantum-well photonic crystal nanocavity lasers

Buried multiple-quantum-well (MQW) 2D photonic crystal cavities (PhC) achieve low non-radiative recombination and high carrier confinement thus making them highly efficient emitters. In this study, we have investigated the lasing characteristics of high-β(spontaneous emission coupling factor) buried MQW photonic crystal nanocavity lasers to clarify the theoretically-predicted thresholdless operation in high-β nanolasers. The strong light and carrier confinement and low non-radiative recombination in our nanolasers have enabled us to clearly demonstrate very smooth lasing transition in terms of the light-in vs light-out curve and cavity linewidth. To clarify the thresholdless lasing behavior, we carried out a lifetime measurement and a photon correlation measurement, which also confirmed the predicted behavior. In addition, we systematically investigated the dependence of β on the detuning frequency, which was in good agreement with a numerical simulation based on the finite-difference time-domain method. This is the first convincing systematic study of nanolasers based on an MQW close to the thresholdless regime.

Monolithically Integrated High-β Nanowire Lasers on Silicon.

Reliable technologies for the monolithic integration of lasers onto silicon represent the holy grail for chip-level optical interconnects. In this context, nanowires (NWs) fabricated using III-V semiconductors are of strong interest since they can be grown site-selectively on silicon using conventional epitaxial approaches. Their unique one-dimensional structure and high refractive index naturally facilitate low loss optical waveguiding and optical recirculation in the active NW-core region. However, lasing from NWs on silicon has not been achieved to date, due to the poor modal reflectivity at the NW-silicon interface. We demonstrate how, by inserting a tailored dielectric interlayer at the NW-Si interface, low-threshold single mode lasing can be achieved in vertical-cavity GaAs-AlGaAs core-shell NW lasers on silicon as measured at low temperature. By exploring the output characteristics along a detection direction parallel to the NW-axis, we measure very high spontaneous emission factors comparable to nanocavity lasers (β = 0.2) and achieve ultralow threshold pump energies ≤11 pJ/pulse. Analysis of the input-output characteristics of the NW lasers and the power dependence of the lasing emission line width demonstrate the potential for high pulsation rates ≥250 GHz. Such highly efficient nanolasers grown monolithically on silicon are highly promising for the realization of chip-level optical interconnects.

Monolayer semiconductor nanocavity lasers with ultralow thresholds.

Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

Mode characteristics of subwavelength aluminum/silica-coated InAlGaAs/InP circular nanolasers

The mode characteristics are demonstrated for InAlGaAs/InP circular nanolasers bonded on silicon wafer, which consist of a core height of 800&#xA0;nm coated by silica/aluminum on the bottom and sidewalls. The lasing mode spectra agree well with the simulated mode spectra obtained by the 3D FDTD technique for 750 and 450&#xA0;nm radius nanolasers. For the 250&#xA0;nm radius nanoresonator, resonant modes with Q factors 400&#x2013;790 are numerically predicted with a mode wavelength interval up to 200&#xA0;nm. The mode selection related to the cavity size and location of the active region is critical for nanocavity lasers to operate over a wide temperature range. In addition, the size limit is estimated for high-Q dielectric mode in the nanoresonators. Finally, electric-injection circular nanolasers are discussed with the TE0,1,1 mode.

Frequency-doubled photonic crystal nanocavity lasers

Frequency-doubled photonic crystal nanocavity lasers

Self-frequency summing in quantum dot photonic crystal nanocavity lasers

We demonstrate self-frequency summing in photonic crystal nanocavity lasers with quantum dot gain. Two dipole modes and a hexapole mode, supported in the cavity, simultaneously showed lasing oscillation in the near infrared wavelength region under optical carrier injection. Meanwhile, within the same laser cavity, the internally generated three laser fields are up-converted to exhibit sharp visible emission lines via intra-cavity nonlinear frequency summing (and doubling) processes. This self-frequency summing process in active nanocavities will pave the way for developing nanoscale nonlinear optical light sources.

Publisher's Note: Self-pulsing nanocavity laser [Phys. Rev. A87, 041804(R) (2013)

Publisher's Note: Self-pulsing nanocavity laser [Phys. Rev. A<b>87</b>, 041804(R) (2013)

Few-fJ/bit data transmissions using directly modulated lambda-scale embedded active region photonic-crystal lasers

High-speed modulation and 4.4 fJ bit−1 data transmission is demonstrated using a photonic-crystal nanocavity laser. Its current threshold of 4.8 µA, modulation current efficiency of 2.0 GHz µA−0.5 and output power of 2.17 µW may enable on-chip photonic networks in combination with recently developed high-sensitivity receivers.

Self-pulsing nanocavity laser

We propose a scheme to achieve controllable self-pulsing operation in a semiconductor photonic-crystal nanolaser. The scheme is based on coupling two asymmetric nanocavities and pumping only one of them. As a result, either periodic or chaotic subnanosecond $Q$-switched pulses can emerge. A coupled-mode approach is used to model the system and study the bifurcation diagram. An experimental realization is proposed on the basis of two evanescently coupled photonic-crystal nanocavities.

Silicon-based three-dimensional photonic crystal nanocavity laser with InAs quantum-dot gain

We report on the demonstration of lasing oscillation in a silicon-based three-dimensional photonic crystal nanocavity using InAs quantum dots as gain material by pulsed optical pumping at 11 K. An active layer embedding InAs quantum dots was inserted in the cavity using micromanipulation technique. The highest quality factor for silicon-based three-dimensional photonic crystal cavities (∼22 000) was achieved. We also evaluated the spontaneous emission coupling factor of the laser to be ∼0.78 by fitting the experimental light-in light-out curve with coupled rate equations. This result would pave the way to the realization of CMOS-compatible high-density three-dimensional photonic integrated circuits.

Narrow linewidth operation of buried-heterostructure photonic crystal nanolaser

We investigate the spectral linewidth of a monolithic photonic crystal nanocavity laser. The nanocavity laser is based on a buried heterostructure cavity in which an ultra-small InGaAsP active region is embedded in an InP photonic crystal. Although it was difficult to achieve narrow linewidth operation in previously reported photonic crystal nanocavity lasers, we have successfully demonstrated a linewidth of 143.5 MHz, which is far narrower than the cold cavity linewidth and the narrowest value yet reported for nanolasers and photonic crystal lasers. The narrow linewidth is accompanied by a low power consumption and an ultrasmall footprint, thus making this particular laser especially suitable for use as an integrated multi-purpose sensor.

Quantum-dot nano-cavity lasers with Purcell-enhanced stimulated emission

We present a rate equation model for quantum-dot light-emitting devices that take into account Purcell enhancement of both spontaneous emission and stimulated emission as well as the spectral profile of the optical and electronic density-of-states. We find that below threshold the β-factor in a quantum-dot nanolaser depends strongly on the pump. For quantum dots with linewidth comparable to that of the cavity, we then show that an otherwise non-lasing device can lase due to Purcell enhancement of the stimulated emission. Finally, we compare the rate equation model to a microscopic model and obtain good agreement.

표면 플라즈몬-폴라리톤의 외부-전반사에 의해 도파되는 나노 크기 모드의 특성

Total external reflection (TER), which does not occur on a dielectric interface, is a unique feature of surface plasmon-polaritons (SPP). We propose an SPP-TER waveguide structure consisting of low-index dielectric nanocore covered with high-index dielectric on a flat metal surface. The SPP mode confined in the nanocore by the TER effect has a mode size much smaller than wavelength scale. Numerical comparison of mode characteristics between the SPP-TER waveguides and other total-internal-reflection-based waveguides such as metal or high-index dielectric nanowires show that the SPP-TER structures can possess higher modal gain for applications of nanocavity lasers.

Photonic crystal nanocavity laser in an optically very thick slab

A photonic crystal (PhC) nanocavity formed in an optically very thick slab can support reasonably high-Q modes for lasing. Experimentally, we demonstrate room-temperature pulsed lasing operation from the PhC dipole mode emitting at 1324 nm, which is fabricated in an InGaAsP slab with thickness (T) of 606 nm. Numerical simulation reveals that when T≥800 nm, over 90% of the laser output power couples to the PhC slab modes, suggesting a new route toward an efficient in-plane laser for photonic integrated circuits.

High-Temperature Operation of Photonic-Crystal Lasers for On-Chip Optical Interconnection

SUMMARY To meet the demand for light sources for on-chip optical interconnections, we demonstrate the continuous-wave (CW) operation of photonic-crystal (PhC) nanocavity lasers at up to 89.8 ◦ Cb y using InP buried heterostructures (BH). The wavelength of a PhC laser can be precisely designed over a wide range exceeding 100 nm by controlling the lattice constant of the PhC. The dynamic responses of the PhC laser are also demonstrated with a 3-dB bandwidth of over 7.0 GHz at 66.2 ◦ C. These results reveal the laser’s availability for application to wavelength division multiplexed (WDM) optical interconnection on CMOS chips. We discuss the total bandwidths of future on-chip optical interconnections, and report the capabilities of PhC lasers.

유전체 판과 금속 나노선 사이에 구속된 표면 플라즈몬 모드

회절한계 이하의 모드 크기를 가지는 금속-유전체 혼합 광도파로 구조를 제안하고자 한다. 제안된 혼합 광도파로는 금속 나노선이 유전체 평면 위에 놓인 구조로서, 금속선과 유전체 사이에 구속된 파장보다 작은 크기의 표면-플라즈몬 모드의 특성을 기존의 유전체 나노선을 이용하는 구조와 비교 분석하였다. 두 도파로의 모드 크기와 전파 거리는 나노선의 직경이 큰 경우에는 비슷한 경향을 보이나, 직경이 작아짐에 따라 서로 상이한 값을 가진다. 회절 한계보다 100배 이상 작은 모드를 갖는 파장길이의 나노 공진기 구현을 위해서는 제안된 금속 나노선-유전체 광 도파로 구조가 적합함을 보였다. We propose a metal-dielectric hybrid waveguide structure consisting of a single metal nanowire placed on a flat dielectric slab. Mode size and propagation loss of the surface-plasmons confined in the metal-dielectric gap are compared with those of the complementary structure with a dielectric nanowire on a metal surface. In the case of the nanowire's diameter much smaller than the wavelength the two structures reveal quite different characteristics; the dielectric nanowire-on-metal has longer propagation distance, but only the metal nanowire-on-dielectric exhibits a mode size two fold smaller than the diffraction limit. The proposed hybrid structure may therefore be more suitable for realization of nanocavity lasers.