Microcavity Lasers Research Articles

Design optimization of silicon-based 1.55 μm InAs/InGaAs quantum dot square microcavity lasers with output waveguides

We optimize the structure of a silicon-based InAs/InGaAs quantum dot square microcavity laser with an output waveguide structure. By designing a new laser structure, the emission wavelength is extended to 1550 nm. We investigate the structure parameters that affect the quality factor and optical mode of the square microcavity, including the side length of the microcavity, the width of the output waveguide, the cladding layer thickness and the etching depth. By connecting the output waveguide at the edge-midpoint of the square microcavity, both the unidirectional emission and mode selectivity can be obtained, which avoids mode competition. The 1550 nm wavelength single-mode laser is beneficial and has reat significance for the development of silicon-based optoelectronic integration.

Optical frequency comb and picosecond pulse generation based on a directly modulated microcavity laser.

Optical frequency comb (OFC) and picosecond pulse generation are demonstrated experimentally based on a directly modulated AlGaInAs/InP square microcavity laser. With the merit of a high electro-optics modulation response of the microcavity laser, power-efficient OFCs with good flatness are produced. Ten 8-GHz-spaced optical tones with power fluctuation less than 3 dB are obtained based on the laser modulated by a sinusoidal signal. Moreover, the comb line number is enhanced to 20 by eliminating the nonlinear dynamics through optical injection locking. Owing to the high coherence of the OFC originating from the directly modulated microcavity laser, a 6.8 ps transform-limited pulse is obtained through dispersion compensation. The optical pulse is further compressed to 1.3 ps through the self-phase modulation effect in high nonlinear fiber.

Colloidal Gain Media: Single‐Mode Lasing from a Single 7 nm Thick Monolayer of Colloidal Quantum Wells in a Monolithic Microcavity (Laser Photonics Rev. 15(4)/2021)

In article number 2000479, Hilmi Volkan Demir and co-workers demonstrate single-mode lasing from an ultrathin self-assembled monolayer of colloidal quantum wells (CQWs) with a record thickness of 7 nm. The CQWs are integrated into a high-quality-factor microcavity with accurate spectral/spatial alignment of the cavity mode. By overcoming the long-pending problem of limited electrical conductivity in thicker colloidal films, such ultrathin colloidal gain media may enable electrically-driven colloidal lasers.

Single-resonator, stable dual-longitudinal-mode optofluidic microcavity laser based on a hollow-core microstructured optical fiber.

A single-resonator, stable dual-longitudinal-mode optofluidic microcavity laser based on a hollow-core microstructured optical fiber is proposed and experimentally demonstrated. The resonator and microfluidic channel are integrated in the hollow-core region of the fiber, inside which a hexagonal silica ring is used as the only resonator of the laser. Experimental results show that with mixing a small amount of Rhodamine B into a 1 mM Rhodamine 6G solution to form a dual-dye solution as a gain medium, the laser obtained by the method of lateral pumping can operate at dual longitudinal modes, with a threshold of 90 nJ/mm2. By adjusting the concentration of Rhodamine B, the lasing wavelength of the laser and the power ratio of the two wavelengths can be controlled. And because the laser emission is co-excited by different kinds of dye molecules, the mode competition is diminished, enabling the simultaneously efficient optical gain and therefore lasing at dual longitudinal modes stably with a maximum lasing intensity fluctuation of 3.2% within 30 minutes even if the dual longitudinal modes have the same linear polarization states. This work can open up promising opportunities for diverse applications in biosensing and medical diagnosis with high sensitivity and integrated photonics with compact structure.

Realization of directional single-mode lasing by a GaN-based warped microring

Multimode and random directionalities are major issues restricting the application of whispering gallery mode microcavity lasers. We demonstrated a 40 μm diameter microring with an off-centered embedded hole and warped geometry from strained III-nitride quantum well multilayers. Single-mode directional whispering gallery mode lasing was achieved by the warped structure and high-order mode suppression induced by the off-centered hole. In addition, the introduction of the off-centered hole reduced the lasing threshold from 3.24 to 2.79 MW / cm 2 compared with the warped microdisk without an embedded hole while maintaining a high-quality factor of more than 4000. Directional light emission in 3D was achieved and attributed to the warped structure, which provides a vertical component of the light emission, making it promising for building multifunctional coherent light sources in optoelectronic integration.

Mode characteristics for gapless-coupled twin circular-side square microcavity lasers

We propose gapless-coupled twin circular-side square microcavities (TCSMs), and experimentally demonstrate the TCSM semiconductor lasers with weak mode coupling. The introduction of circular sides modifies the field distributions of the whispering-gallery modes and enables gapless coupling for the TCSMs without degrading the mode quality factors. Numerical simulation results show crossing and avoided crossing of the modes in the TCSMs with the variation of the wavelength difference and gain-loss contrast between the two cavities. By tuning the injection currents of the laser cavities, mode crossing is observed from the experimental lasing spectra of a TCSM laser. The realization of weak mode coupling in TCSM lasers indicates that the gapless-coupled deformed square microcavities provide a feasible robust coupling scheme for photonic integration.

Unusual Polarization Relation between Single-Mode Lasing Emission and Excitation Laser from an Evanescent-Wave Pumped Micro-Cavity Laser

Using a fiber of that is 125 μm in diameter in rhodamine 6G ethanol solution, controllable multi- and single-whispering-gallery-mode (WGM) optofluidic lasers based on evanescent-wave-coupled gain are both available. With multi-mode WGM emission, lasing emission with almost pure TM (transverse magnetic) or almost TE (transverse electric) modes can be obtained when the pump laser has an electric field parallel (perpendicular) to the fiber axis, i.e., the polarization direction of output laser is the same as that of the pump laser. On the other hand, when the laser emission is single-mode, the TE output laser always emerges firstly above lasing threshold, then keeps TE mode while the pump laser’s intensity increases with polarization direction perpendicular to the fiber axis; on the contrary, TE emission will dwindle relatively, while the TM emission emerges and dominates the spectra, when the pump laser’s intensity increases with polarization parallel to the fiber axis. Our work proves that controlling the leakage of the evanescent wave from high-Q microcavities is crucial for both modes of lasing emission and its polarization.

Dual-Passband Microwave Photonic Filter Based on a Directly Modulated Microcavity Laser

An approach to achieving a highly selective and stable dual-passband microwave photonic filter (MPF) is presented. The dual-passband MPF is realized based on the phase-to-intensity modulation conversion by stimulated Brillouin scattering (SBS). The core of the proposed scheme is a two-tone pump generation by a directly modulated microcavity laser instead of two individual lasers or electro-optic modulators (EOMs), which makes the system relatively simple and stable. The center frequency of the MPF can be tuned from 0 to 20 GHz by adjusting the modulation frequency of the microcavity laser, where the center frequencies of the two passbands are related. The 3-dB bandwidth and the out-of-band rejection ratio of each passband are about 38 MHz and lager than 28.5 dB, respectively. The frequency stability of the MPF is also verified experimentally.

Tunable WGM Laser Based on the Polymer Thermo-Optic Effect.

In this work, the thermo-optic effect in polymers was used to realize a temperature-tunable whispering-gallery-mode laser. The laser was fabricated using a capillary tube filled with a light-emitting conjugated polymer solution via the capillary effect. In the whispering-gallery-mode laser emission wavelength can be continuously tuned to about 19.5 nm using thermo-optic effect of polymer. The influence of different organic solvents on the tuning rate was studied. For a typical lasing mode with a bandwidth of 0.08 nm, a temperature-resolved tuning rate of ~1.55 nm/°C was obtained. The two-ring coupling effect is responsible for the suppression of the WGM in the micro-cavity laser. The proposed laser exhibited good reversibility and repeatability as well as a sensitive response to temperature, which could be applied to the design of photothermic and sensing devices.

Nonreciprocal Morphology-Dependent Resonance in Stacked Spinning Microresonators

As is well known, Sagnac-Fizeau light dragging effect may serve as the fundamental nonreciprocal mechanism for photonic devices. In this study, we theoretically analyze nonreciprocal morphology-dependent resonance in spinning stacked microresonators (SSμRs) based on this effect. A theoretical model is set up to analyze the impact of Sagnac-Fizeau effect on resonance characteristics of SSμRs. Two typical morphology-dependent resonances, i.e., Fano resonance and mode splitting resonance, have been discussed for the microresonators operating at different rotation frequencies. The simulation results presented in this work would provide significant guidance for the design of nonreciprocal photonic devices based on non-magneto-optical approach. Our proposed SSμRs are expected to find promising applications in unidirectional microcavity laser, quantum light chiral control and quantum optical communications.

Research progresses of microcavity lasers based on lithium niobate on insulator (Invited)

Research progresses of microcavity lasers based on lithium niobate on insulator (Invited)

The Applications of Microcavity Lasers in Multimodality Imaging

The Applications of Microcavity Lasers in Multimodality Imaging

Genetic Algorithm Applied to the Optimized Design of Semiconductor Microcavity Lasers

Semiconductor microcavities have been used in important studies of several areas for technological or purely scientific purposes. However, the definition of the optimal parameters for the fabrication of microcavities is a difficult task. Moreover, some uncertainties related to the growth process can change the device features. These problems cannot be experimentally controlled, hindering the development of theoretical models. In this work we present a theoretical model to simulate the microcavities and also propose an evolutionary approach to optimize the device under uncertainty in order to ensure the growth with the desired features. Thus, based on the reflectance spectra of a AlxGa1-xAs semiconductor microcavity, the aluminum concentrations, x, and the number of layers that compose the heterostructure were optimized. This set of parameters may offer increased robustness in the growth process, while providing a considerable quality factor and the desired position of the cavity resonance, achieving the device’s operation limits. The device was optimized considering the cavity resonance between 700nm and 2000nm, where the results indicate that the proposed algorithm is able to find satisfactory solutions, minimizing the problems caused by inaccuracy in the growth process.

Dynamical tuning for single mode whispering gallery mode microcavity lasing

The dynamically modulated lasing mode is extremely significant for laser applications in optical interconnections, on-chip communications and trace detection. However, tunable micro/nano laser (especially for single mode laser) is still a challenge although enormous efforts have been devoted. The coexisting modes could be selected out through light field coupling between two adjacent cavities based on Vernier effect, which could provide a compact and suitable approach for single mode lasing operation in various kinds of compound microcavity. Herein, a spherical whispering gallery cavity with small size and low threshold was rolled along a hexagonal tapered microrod to adjust the lasing mode. The coupling mechanism was explored based on static and time-resolution photoluminescence measurements in situ. The tunable lasing mode mainly derives from resonant mode of microsphere according to carrier recombination analysis. Such a spectral control establishes to realize a lasing mode selection flexibly in real-time micromanipulation.

An erbium-doped lithium niobate micro-cavity laser

An erbium-doped lithium niobate micro-cavity laser

On-chip erbium-doped lithium niobate microcavity laser

The commercialization of lithium niobate on insulator (LNOI) wafer has sparked significant on-chip photonic integration application due to its remarkable photonic, photoacoustic, electro-optic and piezoelectric nature. A variety of on-chip LNOI-based optical devices with high performance has been realized in recent years. Here we developed 1 mol\% erbium-doped LN crystal and its LNOI wafer, and fabricated an erbium-doped LNOI microdisk with high quality ($ \sim $ 1.05$\times 10^{^5}$ ). C-band laser emission with $ \sim $1530 nm and $ \sim $1560 nm from the high-Q erbium-doped LNOI microdisk was demonstrated both with 974 nm and 1460 nm pumping, and the latter has better thermal stability. This microlaser would play an important role in the photonic integrated circuits of lithium niobate platform.

A tellurite glass optical microbubble resonator.

We present a method for making microbubble whispering gallery resonators (WGRs) from tellurite, which is a soft glass, using a CO2 laser. The customized fabrication process permits us to process glasses with low melting points into microbubbles with loaded quality factors as high as 2.3 × 106. The advantage of soft glasses is that they provide a wide range of refractive index, thermo-optical, and optomechanical properties. The temperature and air pressure dependent optical characteristics of both passive and active tellurite microbubbles are investigated. For passive tellurite microbubbles, the measured temperature and air pressure sensitivities are 4.9 GHz/K and 7.1 GHz/bar, respectively. The large thermal tuning rate is due to the large thermal expansion coefficient of 1.9 × 10-5 K-1 of the tellurite microbubble. In the active Yb3+-Er3+ co-doped tellurite microbubbles, C-band single-mode lasing with a threshold of 1.66 mW is observed with a 980 nm pump and a maximum wavelength tuning range of 1.53 nm is obtained. The sensitivity of the laser output frequency to pressure changes is 6.5 GHz/bar. The microbubbles fabricated using this method have a low eccentricity and uniform wall thickness, as determined from electron microscope images and the optical spectra. The compound glass microbubbles described herein have the potential for a wide range of applications, including sensing, nonlinear optics, tunable microcavity lasers, and integrated photonics.

Observation of gain-pinned dissipative solitons in a microcavity laser

We demonstrate an experimental approach to create dissipative solitons in a microcavity laser. In particular, we shape the spatial gain profile of a quasi-one-dimensional microcavity laser with a nonresonant, pulsed optical pump to create spatially localised structures, called gain-pinned dissipative solitons that exist due to the balance of gain and nonlinear losses and are confined to a diffraction-limited volume. The ultrafast formation dynamics and decay of the gain-pinned solitons are probed directly, showing that they are created on a picosecond timescale, orders of magnitude faster than laser cavity solitons. All of the experimentally observed features and dynamics are reconstructed by using a standard complex Ginzburg-Landau model.

Complex coupling coefficient in laterally coupled microcavity laser diode arrays

The complex component of the coupling coefficient κ=κr+iκi, used to describe the coupling between adjacent semiconductor microcavity laser diodes, is studied. The complex component κi represents the gain or loss difference between the coherent in-phase and out-of-phase array supermodes obtained from two laterally coupled lasers. Steady-state analysis reveals that the threshold of the preferred coherent supermode is lower than that of an individual laser mode in proportion to κi. We show that the complex component κi can be experimentally extracted from a simple output power vs current measurement. Furthermore, the change in the lasing threshold at the onset of optical coupling perturbs the differential resistance of the coupled lasers. Therefore, an electrical signature of optical coupling can be detected in the diode array series resistance.

Numerical modeling of on-threshold modes of eccentric-ring microcavity lasers using the Muller integral equations and the trigonometric Galerkin method

We analyze on-threshold mode characteristics of eccentric-ring microcavity lasers, i.e. two-dimensional (2-D) models of thin circular disks made of gain material and pierced with circular air hole. As a tool of computational electromagnetics, we use the Muller boundary integral equations, discretized with trigonometric Galerkin method. This enables us to reduce the lasing eigenvalue problem to an infinite matrix equation with elements having explicit form as combinations of the cylindrical functions. Then the Fredholm second-kind nature of this equation guarantees the convergence of its eigenvalues, with greater matrix-truncation numbers, to exact values. Using the proposed algorithm, we calculate frequencies, threshold values of material gain index and directivities of emission of laser modes on threshold. Numerical experiments demonstrate that, by varying the location and size of the piercing hole, one can increase the directivity while preserving the threshold gain as low as in unperturbed circular cavity.