Photonic Crystal Nanocavity Laser Research Articles

Observation of unique photon statistics of single artificial atom laser

We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain and its unique photon statistics. Gain tuning measurements and photon correlation measurements indicated that a single quantum dot plays a substantial role in the laser oscillation. Photon correlation measurements showed a distinct transition from anti-bunching to Poissonian via photon bunching around the threshold with the increase of the excitation power. Numerical simulations, including contributions of other light sources besides a single quantum dot, indicated that the photon bunching feature around the threshold can be enhanced by the interfusion of incoherent photons into the cavity mode.

High-peak-power efficient edge-emitting photonic crystal nanocavity lasers

Record-high edge-emitted peak power was collected from L3 and finite-waveguide two-dimensional photonic crystal nanocavity quantum well membrane lasers at room temperature under single-mode operations. Peak power levels of 230 microW and 540 microW were collected from L3 and finite-waveguide edge-emitters, and their quantum differential efficiencies are 11% and 27%, respectively, limited by their collection efficiencies in free space.

Photonic crystal nanocavity laser with a single quantum dot gain

We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10(8) cm(-2)) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require ~145 nW for lasing. This spectral detuning dependence of laser threshold indicates substantial contribution of the single quantum dot to the total gain. Moreover, photon correlation measurements show a distinct transition from anti-bunching to Poissonian via bunching with the increase of the excitation power, which is also an evidence of laser oscillation using the single quantum dot gain.

Room temperature continuous wave operation of InAs/GaAs quantum dot photonic crystal nanocavity laser on silicon substrate

Room temperature, continuous-wave lasing in a quantum dot photonic crystal nanocavity on a Si substrate has been demonstrated by optical pumping. The laser was an air-bridge structure of a two-dimensional photonic crystal GaAs slab with InAs quantum dots inside on a Si substrate fabricated through wafer bonding and layer transfer. This surface-emitting laser exhibited emission at 1.3 microm with a threshold absorbed power of 2 microW, the lowest out of any type of lasers on silicon.

120 μ W peak output power from edge-emitting photonic crystal double-heterostructure nanocavity lasers

As an attempt to collect more in-plane emission power out of wavelength size two-dimensional photonic crystal defect lasers, edge-emitting photonic crystal double-heterostructure quantum well membrane lasers were fabricated by shortening the number of cladding periods on one side. 120μW peak output power was collected from the facet of the single mode laser at room temperature. Laser efficiencies were analyzed and agree very well with three-dimensional finite-difference time-domain modeling.

Ultrafast photonic crystal lasers

AbstractWe describe recent progress in photonic crystal nanocavity lasers with an emphasis on our recent results on ultrafast pulse generation. These lasers produce pulses on the picosecond scale, corresponding to only hundreds of optical cycles. We describe laser dynamics in optically pumped single cavities and in coupled cavity arrays, at low and room temperature. Such ultrafast, efficient, and compact lasers show great promise for applications in high‐speed communications, information processing, and on‐chip optical interconnects.

Ultra-low threshold photonic crystal nanocavity laser

We demonstrate that continuous-wave (CW) photonic crystal (PhC) nanocavity laser operates at room temperature with a very low effective threshold power of ∼375 nW. The CW lasing was achieved at 1.3 μm with InAs/GaAs self-assembled quantum dots (QDs) and high-quality PhC nanocavity with a quality factor of 87,000. The light-in versus light-out curve shows no sharp threshold unlike conventional lasers with pronounced kinks around the thresholds. This near-thresholdless behavior with smooth transition from thermal to coherent light region indicates that this nanocavity laser has a very high spontaneous emission coupling efficiency. We also discuss the characteristics of background noise of QD-based PhC nanocavity lasers compared with quantum well based PhC nanocavity lasers.

Low-threshold surface-passivated photonic crystal nanocavity laser

The efficiency and operating range of a photonic crystal laser is improved by passivating the InGaAs quantum well (QW) gain medium and GaAs membrane using an (NH4)S treatment. The passivated laser shows a four-fold reduction in nonradiative surface recombination rate, resulting in a four-fold reduction in lasing threshold. A three-level carrier dynamics model explains the results and shows that lasing threshold is as much determined by surface recombination losses as by the cavity quality factor (Q). Surface passivation therefore appears crucial in operating such lasers under practical conditions.

Efficient terahertz room-temperature photonic crystal nanocavity laser

The authors describe an efficient surface-passivated photonic crystal nanocavity laser, demonstrating room-temperature operation with 3ps pulse duration (detector response limited) and low-temperature operation with an ultralow threshold of 9μW.

Temporal coherence of a photonic crystal nanocavity laser with high spontaneous emission coupling factor

Temporal coherence of a continuous-wave photonic crystal nanocavity laser is investigated in detail using interference experiments at room temperature. The nanocavity laser operates at $1.3\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ with InAs quantum dot gain material and has a very high spontaneous emission coupling factor $\ensuremath{\beta}=0.9$ with a threshold absorbed pump power of $\ensuremath{\sim}375\phantom{\rule{0.3em}{0ex}}\mathrm{nW}$. The coherence around the laser threshold of such a high-$\ensuremath{\beta}$ laser is not obvious because spontaneous emission efficiently couples to the lasing mode. The output power dependence of the coherence length shows linearity at and above threshold. This result indicates that the first-order coherence is not greatly reduced even at threshold, where the cumulative power of spontaneous emission of other wavelengths cannot be negligible when compared with the laser power. This can be attributed to the fact that the lasing mode of a high-$\ensuremath{\beta}$ laser has a relatively large portion of the total power compared to lasers with lower $\ensuremath{\beta}$'s due to efficient coupling of the spontaneous emission to the cavity mode.

Edge-emitting photonic crystal double-heterostructure nanocavity lasers with InAs quantum dot active material

We report what is, to the best of our knowledge, the first demonstration of an edge-emitting photonic crystal nanocavity laser that is integrated with a photonic crystal waveguide. This demonstration is achieved with a double-heterostructure photonic crystal nanocavity incorporating an InAs quantum dot active region.

A photonic crystal nanocavity laser with ultralow threshold

Confining photons in a small space is a difficult task. Recent nanotechnology advances now enable their confinement in a cubic wavelength volume for as long as 1 nanosecond in semiconductors when using 2D photonic crystal (PhC) structures. As shown in Figure 1, a PhC is a periodic optical structure whose periodicity is on the order of the wavelength of light. PhCs are designed to affect the motion of photons1 because they have the optical equivalent of the energy gap of conventional semiconductors. The possibility to manipulate photons in solid materials offers many attractive applications such as nanocavity lasers, tunable slow light devices, and optical integrated circuits. The PhC nanocavity laser is considered one of the best candidates to achieve ultra-low threshold lasing due to its small mode volume and high quality factor (Q, which expresses the ability of an oscillating system to keep oscillating before running out of energy). The first reported PhC laser (1999) used multiple quantumwells (QWs) as the gain material at low temperature in pulsed operation.2 Recently, continuous wave (CW) laser operation at low temperature was also reported. However, CW lasing is inherently difficult to achieve at room temperature due to fast non-radiative losses that translate into very high Q nanocavity requirements. Our group was the first to demonstrate room temperature operation of a high-Q PhC nanocavity CW laser.3 Further improvement of the cavity Q reduced the optical pumping threshold down to the microwatt level.4 3D photon confinement can be achieved by fabricating the PhC slab structure with a nanocavity (see Figure 1). The 2D triangular lattice confines photons in the plane of the slab. The excitation beam generates excitons in quantum dots (QDs) embedded into the slab layer and the excitons recombine with photon emission. Our PhC nanocavity was designed to have its resonant wavelength at the excitonic photoluminescence (PL) peak, allowing CW lasing at 1.33μm at room temperature with Figure 1. Scanning electron micrographs of a photonic crystal nanocavity structure. Top (a) and cross sectional (b) views. QD: quantum dot.

Lasing characteristics of InAs quantum dot microcavity lasers as a function of temperature and wavelength

A Strong temperature dependence of microdisk lasers and photonic crystal nanocavity lasers with InAs quantum dot active regions is reported. These lasers operate at 1.3 microm at room temperature under optical pumping conditions. T(0, microdisk) = 31 K. T(0, photonic crystal nanocavity) = 14 K. The lasing threshold dependence on the lasing wavelength is also reported. We observe a minimum absorbed threshold pump power of 9 microW. This temperature and wavelength dependent lasing behavior is explained qualitatively by a simple model which attributes the experimental observations predominantly to surface recombination at threshold and the high quality factors of these cavities.

Highly efficient optical pumping of photonic crystal nanocavity lasers using cavity resonant excitation

The authors demonstrate highly efficient optical pumping of photonic crystal (PhC) nanocavity lasers with InGaAs single quantum wells (QWs) using cavity resonant excitation at 10K. The laser threshold power is largely reduced when the central wavelength of the excitation pulse is resonant with a higher-order cavity mode. The localized excitation by the cavity resonant effect increases the effective absorption of the QW region in the nanocavity. The direct photocarrier generation in the QW also results in the highly efficient optical pumping. This cavity resonant excitation technique can lower the laser threshold of PhC nanocavity lasers and avoid detrimental device heating.

Ultrafast photonic crystal nanocavity laser

Spontaneous emission is not inherent to an emitter, but rather depends on its electromagnetic environment. In a microcavity, the spontaneous emission rate can be greatly enhanced compared with that in free space. This so-called Purcell effect can dramatically increase laser modulation speeds, although to date no time-domain measurements have demonstrated this. Here we show extremely fast photonic crystal nanocavity lasers with response times as short as a few picoseconds resulting from 75-fold spontaneous emission rate enhancement in the cavity. We demonstrate direct modulation speeds far exceeding 100 GHz (limited by the detector response time), already more than an order of magnitude above the fastest semiconductor lasers. Such ultrafast, efficient, and compact lasers show great promise for applications in high-speed communications, information processing, and on-chip optical interconnects.

Low-threshold photonic crystal laser

We have fabricated photonic crystal nanocavity lasers, based on a high-quality factor design that incorporates fractional edge dislocations. Lasers with InGaAsP quantum well active material emitting at 1550 nm were optically pumped with 10 ns pulses, and lased at threshold pumping powers below 220 μW, the lowest reported for quantum-well based photonic crystal lasers, to our knowledge. Polarization characteristics and lithographic tuning properties were found to be in excellent agreement with theoretical predictions.