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Nanophotonics, driven by low processing power and high density integration, is appearing as the next logical step for microwave photonics. Optical frequency combs (OFCs), which play a vital role in integrated microwave photonics, have not yet generated using nano-structured devices. In this paper, we propose OFC generation based on all-optical modulation of nanophotonic structures. A theoretical model based on temporal coupled mode theory is developed to describe cascaded all-optical photonic crystal intensity and phase modulators. Using a modulation light with a sinusoidal waveform, a separate carrier light is modulated to generate an OFC. By manipulating the modulation power and device dimensions, a flat OFC that spans over a 600 GHz is delivered. The proposed system offers OFC generation with tunable comb line spacing using devices with high density integration capabilities.

The performances of a fiber laser stabilized by a whispering-gallery-mode(WGM) resonator depends heavily on the coupling of the resonator and fiber system, and is labile due to the lasing mode competitions among excitable WGMs. Here, we propose a hybrid cavity where a linear fiber cavity is coupled by a WGM resonator for dual stabilizations of the laser mode, and experimentally demonstrate single-mode lasing emission with stable and high signal to noise ratio (up to 61 dB), narrow linewidth (low to ∼5 kHz) operations. By adjusting the coupling of the linear fiber cavity and the WGM resonator, the fiber laser can operate in two- to four- mode lasing without mode hopping as well.

Microcavity-feedback fiber-loop laser gives a promise for single-mode and tunable lasing. Here, a whispering gallery mode(WGM) microcavity-feedback fiber-loop laser is constructed and dynamic lasing mechanisms are investigated by rate equation models. For the single-mode lasing, the results show that the lasing efficiency can be maximized by tuning the coupling of waveguide and WGM microcavity, and two critical coupling rates exist for a fixed internal coupling coefficient of clockwise and counter-clockwise WGMs. By simply increasing the total length of fiber-loop laser, multi-mode lasing originated from one WGM feedback of a silica microsphere is explored, the lasing behaviors are well predicted by the rate equations and the WGM resonance linewidth can be effectively evaluated from the beat notes bandwidth of multiple lasings. We wish the results demonstrated here can be used for optimization on the lasing output of a fiber-loop laser with an external feedback mirror.

Optical resonances in a microcavity can be optically or thermally manipulated. Here, the tunings on optical resonances in silica microcavities with various dimensions are achieved by controlling the thermal dissipation with a thermal conductor. Finite-element thermal analyses show that the temperature in a mode volume of a microcavity can be definitely tuned, and the shifts of resonances near $1.55~\mu \text{m}$ are verified experimentally in a ~160- $\mu \text{m}$ -diameter cavity. In addition, the slight resonance shifts in a ~450- $\mu \text{m}$ -diameter cavity are examined indirectly from the output of single-mode Brillouin lasing. Compared to that of optical coupling, the thermal interaction space is much larger and fulfills a need to manipulate the high-quality resonances in a robust way.

Using cascaded intensity and phase modulators to achieve frequency combs is a common technique. However, this technique has not yet been employed to achieve optical frequency combs (OFCs) at the nanoscale. A theoretical model based on temporal coupled mode theory is developed to simulate an all-optical photonic crystal modulator. The concepts used to generate an OFC based on electro-optic modulators are then extended to the nanophotonic domain. It is theoretically proven that an OFC can be generated via all optical modulation of nanophotonic devices.

The integration of one more gain media in droplet microlasers with morphology-dependent modes, which can be employed in optofluidic systems as multi-wavelength lasing sources, is highly attractive and demands new cavity design and fabrication approaches. Here, cholesteric liquid crystal (CLC) droplets with an integrative triple-emulsion cavity are fabricated via glass-capillary-based microfluidic technologies and dual-gain lasing with variable modes, flexibly configured by the combination and incorporation of gain dyes and CLCs into both the core and shell. The distributed feedback (DFB) mode, formed by the feedback from the self-assembled helix periodic structure of CLCs, the whispering gallery (WG) mode, and the hybrid, is selectively excited by controlling the spatial coupling between the pump beam and the droplet with gain. With the merits of dual-gain and controllable lasing, a prototype dual-wavelength-ratiometric thermometer with self-calibration capability is expected to be developed. Furthermore, the anisotropic CLC core is substituted with an isotropic fluid and the gain from the CLC shell is additionally removed, DFB lasings in both shell and core are absent, and only Bragg-shell reflection-based hybrid modes are excited for lasing. The CLC droplet microlasers with an integrative cavity are expected to provide a new route to future lab-on-chip (LOC) applications.

In this paper, a novel method to generate optical frequency combs (OFCs) using nanoscale structures is explored. The growing demand for on-chip photonic processing dictates the need for multi-wavelength light sources, such as OFCs, that can be densely integrated with low processing power. Photonic crystal structues provide a viable method to generate all-optical modulation with sub-femto joule switching power and high density integration potential. This method of all-optical modulation is utilised here to generate an OFC from photonic crystal nanocavities and waveguides. Very- at-topped optical frequency combs with a small intensity variation can be generated based on theoretical predictions via detailed analysis of coupled mode theory for photonic crystal nanocavities and waveguides.

We propose and experimentally demonstrate a compact microresonator-feedback single-frequency fiber laser at 1.06 μm, and further initiating different-type nonlinear lasing based on stimulated Brilliouin scattering, stimulated Raman scattering, and four-wave mixing (FWM). A silica microsphere with an ultrahigh Q-factor is employed in our experiment as a narrow bandwidth cavity mirror around 1.06 μm, and a generator of nonlinear optical effects subsequently. With the help of mode selection both from the silica microsphere and a fiber Bragg grating, single-frequency lasing with a linewidth as narrow as 281 kHz is obtained at 1.06 μm by employing 974-nm laser diode pumped Ytterbium-doped fiber as a gain medium. By optimizing the polarization states, controlling the coupling position between the fiber taper and microsphere as well as the pump power, three-order cascaded Brilliouin Stokes lasings at 1.06 μm, and cascaded Raman lasing at 1.12, 1.18 and 1.23 μm are realized, respectively. An FWM-based optical frequency comb (OFC) with a bandwidth ∼31 nm is further realized with center wavelength of ∼1.06 μm. Interestingly, a 1.18-μm-centered OFC with ∼37-nm bandwidth is also generated assisted by the second-order Raman-gain.

A commercially available high-power GaN-based blue laser diode has been operated in a simple Littrow-type external cavity (EC). Two kinds of EC configurations with the grating lines perpendicular (A configuration) and parallel (B configuration) to the p-n junction are evaluated. Good performance has been demonstrated for the EC laser with B configuration due to the better mode selection effect induced by the narrow feedback wavelength range from the grating. Under an injection current of 1100 mA, the spectral linewidth is narrowed significantly down to ∼0.1 nm from ∼1 nm (the free-running width), with a good wavelength-locking behavior and a higher than 35 dB-amplified spontaneous emission suppression ratio. Moreover, a tuning bandwidth of 3.6 nm from 443.9 nm to 447.5 nm is realized with output power of 1.24 W and EC coupling efficiency of 80% at the central wavelength. The grating-coupled blue EC laser with narrow spectral linewidth, flexible wavelength tunability, and high output power shows potential applications in atom cooling and trapping, high-resolution spectroscopy, second harmonic generation, and high-capacity holographic data storage.

High Q microsphere optical cavity is usually fabricated from a single mode fiber. Here, we propose a new method to fabricate sphere-like cavity by melting the tip of rotating quartz-rod with a CO2 laser. The cavities with diameter from 200 µm to 700 µm and resonant Q factors above 108 are obtained. Due to the rich resonances of the sphere-like cavity, up to 15-order cascaded stimulated Brillouin lasings(SBL) near 1.55 µm are observed in a cavity with a diameter of ~760 µm by simply tuning the pump wavelength to a finely-selected resonance. We wish the ultra-high Q cavities with rich resonances and bulk rod mount can have practical applications in nonlinear optics and microwave photonics as an optical component.

We report the generation of tunable high-repetition-rate (0.1–1 THz) femtosecond pulses based on a quasi-continuous wave (CW) dual-pumped all-fiber cascaded four-wave-mixing (FWM) scheme without requiring a cavity resonator. By synchronously injecting two pulse-modulated lasers into an 85-m-long dispersion-flat highly nonlinear fiber, cascaded FWM processes under only ∼30-mW average pump power are efficiently initiated to form the Kerr frequency combs near 1.56 $\mu\text{m}$ . Phase locking of the Kerr combs is confirmed by real-time measurements using an autocorrelator, and stable ultrashort pulse trains are observed. The pulse repetition rate can be tuned continuously in the range of 0.1∼1 THz by controlling the wavelength spacing between the two pump lasers. The pulse duration can be correspondingly adjusted from 1.66 ps to 262 fs. Such quasi-CW dual-pumped all-fiber cascaded-FWM frequency combs with the advantages of compactness and flexibility could provide a practical solution for generating ultrahigh-repetition-rate femtosecond pulses.

Mid-infrared (mid-IR) lasers have great applications in bio-molecular sensing due to strong vibrational fingerprints in this wavelength range. However, it is a huge challenge to realize mid-IR lasers in conventional silica materials. Here, we demonstrate the generation of mid-IR Raman lasers and Kerr-frequency combs from an all-silica microresonator/fiber laser system. A single wavelength narrow-linewidth laser at ∼2 µm is first realized by using an ultrahigh Q-factor silica whispering-gallery-mode (WGM) microresonator as mode-selection mirror, and thulium-doped silica fiber as gain medium. Due to the strong intensity enhancement in the microresonator itself, multiple third-order nonlinear optical effects are observed, which include stimulated Stokes and anti-Stokes Raman scattering, and (cascaded) four-wave-mixing (FWM). The stimulated Stokes and anti-Stokes Raman scattering shift the initial 2 µm narrow-linewidth laser to as far as ∼2.75 µm and ∼1.56 µm, respectively. While the cascaded FWM helps to form a Kerr-frequency comb with a broad bandwidth of ∼900 nm and a mode spacing of twice of the microresonator free-spectral-range. This work offers a simple and effective route to realize all-silica mid-IR lasers based on enhanced optical nonlinearity in WGM microresonators.

A commonly used technique to generate an optical frequency comb (OFC) generation is to cascade intensity and phase electro-optical modulators [1]. Nanoscale all-optical devices can also achieve intensity and phase modulation, however the use of these modulators to generate OFCs has hitherto not been addressed. In this paper a mathematical model is introduced to simulate an all-optical modulator, based on temporal coupled mode theory. The techniques used in electro-optical modulators to generate an OFC are then extended to function on the nanoscale. Using this model, it is theoretically demonstrated that all-optical modulation of a nanophotonic device can generate an OFC.

In this paper, we investigate the thermal characteristics of Brillouin microsphere lasers. A mathematical model for Brillouin lasing in a waveguide coupled microcavity is constructed based on the coupled mode theory, the analytic correlation between lasing and thermal power is given. To track the thermal responses of Brillouin microlasers, we introduce two kinds of thermal perturbations on the packaged silica microspheres by either tuning the wavelength of pump wave or varying the surrounding temperature. It is shown that the output power of Brillouin lasers is sensitive to and linearly varied with the thermal change of the mode area and surroundings. The optical bistabilities induced by the resonances transitions of the pump wave and Brillouin lasing, and a single mode lasing with up to 41.7-dB side mode suppression ratio are demonstrated. Our results demonstrate that Brillouin microlasers with stable performances hold potential for sensor applications since thermal or optical perturbations on microcavity can be simply tracked by the variation of output power.

We report a magnetically transportable microlaser with cholesteric liquid crystal (CLC) core-shell structure, operating in band-edge mode. The dye doped CLC shells as a water-in-oil-in-water (W/O/W) double emulsion were fabricated by microfluidics. Water-dispersible Fe3O4 magnetic nanoparticles were incorporated in the inner aqueous phase by taking advantage of the immiscibility with the middle CLC oil phase. The influence of temperature and shell thickness on laser properties was discussed in detail. The non-invasive manipulation of microlasers was realized under a magnetic field. The dependence of velocity on the viscosity of the carrying fluid and size of the core-shell structure was theoretically analyzed and experimentally investigated using a prototype electromagnetic platform. We also discussed the design principles for this type of DDCLC core-shell structure. Such magnetically transportable microlasers offer promise in in-channel illumination applications requiring active control inside micro-channels.

Nd(TTA)3(TPPO)2 complex (HTTA: 2-thenoyltrifluoroacetone, TPPO: triphenylphosphine oxide) doped SU-8 polymer waveguide amplifiers were demonstrated. The absorption and photoluminescence spectra were observed on a 100-μm-thick film of the Nd(TTA)3(TPPO)2 complex doped SU-8 polymer. Under excitation at 808 nm, the fluorescence was obtained at 904 nm, 1068 nm, and 1346 nm wavelengths. The full-width at half-maximum bandwidth was about 25 nm wide around 1068 nm. Using reactive ion etching technology, optical waveguides were fabricated by taking the Nd(TTA)3(TPPO)2 complex doped SU-8 polymer and polymethylmethacrylate (PMMA) material as the core and cladding layers, respectively. According to fundamental rate equations and optical power propagation equations, the gain characteristic of the polymer waveguide amplifier was simulated to be 5.1 dB/cm. An experimental setup for the optical gain measurement was established. A relative optical gain of about 2.4 dB/cm at 1064 nm was obtained in a 20-mm-long multimode waveguide for an input signal power value of 0.1 mW and pump power of 140 mW.

Mode dynamics of metallic hybrid laser micro-resonator are investigated by the general waveguide theory. By tuning the thickness of sandwiched low refractive index dielectric layer, the lateral metal enables compression and release of the electric field into and from gain medium for both transverse electric and magnetic modes (TE/M), enhancing and weakening the coherent interaction of gain medium and quantized resonant mode. The mode quality (Q) factors depending on the geometric parameters are explored by power integration in waveguide and present different features for TE and TM polarizations. The influences of both cladding and dielectric layers on the gain threshold of passive micro-resonator are studied as well, showing that TE mode needs lower gain threshold than TM mode for compensating the overall dissipation of metal.

Stimulated Brillouin scattering (SBS) in a microcavity is usually realized by employing a wavelength tunable external cavity diode laser (TECDL) as the pump source. In this Letter, we report the observation of SBS in a high Q microcavity based on a TECDL-free scheme. The microcavity is employed as a mode-reflecting mirror for constructing a fiber-ring laser and, simultaneously, pumped by the fiber-ring lasing with intrinsic resonance latching. Several regimes are observed in a microcavity with a diameter of ∼215 μm, such as single lasing pumped SBS and multiple regular lasing pumped SBSs (single or cascaded). The microwave signals from the beat notes of the composite output lasing are measured with full-width at half-maximum on the scale of kilohertz at ∼11 and ∼22 GHz, indicating the high coherence between the pump and the Brillouin lasing.

Raman and Brillouin lasers based on a high-quality (high-Q) whispering gallery mode microresonator (WGMR) are usually achieved by employing a tunable single-frequency laser as a pump source. Here, we experimentally demonstrate visible Raman and Brillouin lasers using a compact microresonator/ZrF4−BaF2−LaF3−AlF3−NaF (ZBLAN)-fiber hybrid system by incorporating a WGMR with a fiber-compatible distributed Bragg reflector/fiber Bragg grating to form a Fabry–Perot (F-P) fiber cavity and using a piece of Pr:ZBLAN fiber as gain medium. The high-Q silica-microsphere not only offers a Rayleigh-scattering-induced backreflection to form the ∼635 nm red laser oscillation in the F-P fiber cavity, but also provides a nonlinear gain in the WGMR itself to generate either stimulated Raman scattering or stimulated Brillouin scattering. Up to six-order cascaded Raman lasers at 0.65 μm, 0.67 μm, 0.69 μm, 0.71 μm, 0.73 μm, and 0.76 μm are achieved, respectively. Moreover, a Brillouin laser at 635.54 nm is clearly observed. This is, to the best of our knowledge, the first demonstration of visible microresonator-based lasers created by combining a Pr:ZBLAN fiber. This structure can effectively extend the laser wavelength in the WGMR to the visible waveband and may find potential applications in underwater communication, biomedical diagnosis, microwave generation, and spectroscopy.

The non-local optical interaction of two semiconductor microdisks with a waveguide bridged at radial direction is proposed and studied by three dimensional finite-difference time-domain (FDTD) electromagnetic simulations. The strong and weak optical interactions between two microdisks are observed and ascribed to the internal coupled modes with different coupling ratios. The vertical radiation losses and the related mode quality factors are modulated by waveguide length and present oscillation characteristics for the resonant modes. In addition, the optical leakage of coupling system is affected by the etching depth of disks due to the emission of minor components of electric field.

We propose and experimentally demonstrate a simple scheme for generating optical frequency combs (OFCs) in a fiber-ring/microresonator laser system. The ultrahigh Q whispering gallery mode microresonator is employed both as a mode reflection mirror to generate erbium lasing and as a Kerr-nonlinearity initiator that introduces optical parametric oscillation signals to form OFCs. By controlling the coupling position between the fiber taper and microresonator, optimizing the fiber polarization, as well as the pump power from a 974 nm laser diode (LD), versatile OFCs can be tuned out from single-wavelength states. The OFCs have single, multiple, or combined free spectral ranges. In addition, a Raman-gain-assisted OFC is also observed with a bandwidth of ∼230 nm. This LD-pumped and multifunctional laser system could find applications in precision spectroscopy, biochemical sensing, and optical fiber communication systems.

National Natural Science Foundation of China [50802080]; Natural Science Foundation of Fujian Province, China [2010J01349]; Open Foundation Project of the State Key Lab of Silicon Materials [SKL2010-12]

Multiple-port semiconductor microlasers can be used as the light sources in photonic integrated circuits through on-chip waveguide connection. By directly jointing two and four coupling waveguides at vertices, two- and four-port electrically pumped InP/InGaAsP square-resonator microlasers are proposed and fabricated by standard photolithography and inductively coupled plasma etching techniques. The mode characteristics of square resonators with two and four coupling waveguides are investigated by 2-D finite-differences time-domain (FDTD) simulation. The influences of the thickness of insulating layer SiO2 and the width of coupling waveguides on the mode Q factors are studied for the square resonators laterally confined by an insulating layer SiO2 and p-electrode layers Ti/Au. Room-temperature continuous-wave operations are achieved for a square microlaser with a side length of 15 μm and two 1-μm-wide coupling waveguides at threshold current of 26 mA. In addition, a 20-μm-side microlaser connected with four 1-μm-wide bus waveguides is realized at 270 K. At last, the four-port square resonator with the same size as the fabricated lasers is studied by FDTD simulation, which yields the mode Q factors at the same magnitude as that measured result of 1.34 × 104.

Microsquare resonators laterally confined by SiO2/Au/air multilayer structure are investigated by light ray method with reflection phase-shift of the multiple layers and two-dimensional (2-D) finite-difference time-domain (FDTD) technique. The reflectivity and phase shift of the mode light ray on the sides of the square resonator with the semiconductor/SiO2/Au/air multilayer structure are calculated for TE and TM modes by transfer matrix method. Based on the reflection phase shift and the reflectivity, the mode wavelength and Q factor are calculated by the resonant condition and the mirror loss, which are in agreement well with that obtained by the FDTD simulation. We find that the mode Q factor increases greatly with the increase of the SiO2 layer thickness d , especially as d < 0.3 ?m . For the square resonator with side length 2 ?m and refractive index 3.2, anticrossing mode couplings are found for confined TE modes at wavelength about 1.6 ?m at d = 0.11 ?m, and confined TM modes at d = 0.71 ?m, respectively.

The characteristics of whispering-gallery-like modes in the equilateral triangle and square microresonators are introduced, including directional emission triangle and square microlasers connected to an output waveguide. We propose a photonic interconnect scheme by connecting two directional emission microlasers with an optical waveguide on silicon integrated circuit chip. The measurement indicates that the triangle microlasers can work as a resonance enhanced photodetector for optical interconnect.

The characteristics of equilateral-triangle resonator (ETR) and square resonator microlasers are reported, which are potential light sources in the photonic integrations. Based on the numerical simulations, we find that high-efficiency directional emission can be achieved for the triangle and square microlasers by directly connecting an output waveguide to the resonators. The electrically injected InP/InGaAsP ETR and square resonator microlasers with a 2-mum-wide output waveguide were fabricated by standard photolithography and inductively coupled plasma etching techniques. Room-temperature continuous-wave (CW) operations were achieved for the ETR microlasers with the side length from 10 to 30 mum and the square resonator microlasers with the side length of 20 mum. The output power versus CW injection current and the laser spectra are presented for an ETR microlaser up to 310 K and a square resonator microlaser to 305 K. The lasing spectra with mode wavelength intervals as that of whispering-gallery-type modes and Fabry-Parot modes are observed for two square lasers, which can lase at low temperature and room temperature, respectively.

We demonstrate the first observation of stimulated Brillouin scattering (SBS) in a high-Q whispering gallery mode tellurite microsphere. Tellurite glass with composition of 70TeO₂-20ZnO-5Na₂O-5La₂O₃ (molar ratio) was prepared in-house using a melt-quenching technique. Moreover, tellurite microspheres with Q in excess of 13 millions at 1550 nm were fabricated by melting tellurite microwires using a CO₂ laser. By pumping the tellurite microspheres with a tunable single frequency laser, SBS is further realized with a threshold as low as 0.58 mW. At last, the beat notes between the pump and the Stokes signals were measured, which indicated the Brillouin frequency shift is at the 8.2 GHz band for our tellurite glass. Our results could propel significant applications utilizing SBS by employing tellurite microspheres.

The double transfer matrix method (DTMM) is proposed for calculating the eigenvalues of the resonant mode of a metallically coated dielectric rectangle resonator. Two-dimensional electromagnetic analyses are performed to investigate the optical influences induced by planar structure parameters. The results show that there theoretically exists a highest Q-factor resonance for both TE and TM modes at a certain length-width ratio with fixed resonant wavelength and resonator area. Due to the influence of surface plasma polaritons (SPPs) trapped at the corners of the resonator which is not considered in DTMM, the TM mode resonances are deformed and deviate severely from that of the analytical model. The geometric deformation on the resonator is introduced by replacing the four right angles with circular boundaries, and the SPP accompanied mode behaviors are corrected to the standing waves.

We examined the end-pumped lasing behaviors of dye doped cholesteric liquid crystal (DDCLC) microshells which were fabricated by glass capillary microfluidics. Several kinds of mode resonances, including distributed feedback, Fabry–Perot (FP), and whispering gallery (WG) modes, can be robustly constructed in each individual DDCLC microshell by varying the beam diameter, namely, tuning the DDCLC gain area. The FP and WG modes were further confirmed experimentally, and the corresponding lasing mechanisms are clearly revealed from the unique material characteristics of DDCLC and the geometrical structure of the microshell. Additionally, we demonstrated that the osmotic pressure can be used to shrink/expand the microshell, productively tuning the excitation of lasing modes in a controlled manner. We wish our findings can provide a new insight into the design of DDCLC microlasers with tunable optical properties.

InGaAsP-InP square microlasers with a vertex output waveguide are fabricated by planar processes, and the etched sidewalls of the lasers are confined by insulating layer SiO2 and p-electrode Ti-Au metals. For a square microlaser with a side length of 30 μm and a 2-μm -wide output waveguide, a continuous-wave threshold current is 26 mA at room temperature and output power is 0.72 mW at 86 mA. The mode interval of 21 and 7.4 nm is observed for the microlasers with the side length of 10 and 30 μm , respectively. Finite-difference time-domain (FDTD) simulations indicate that the lasing modes have incident angles of about 45 ° at the boundaries of the resonator. In addition, square resonators surrounded by air, SiO2-Ti-Au, and SiO2-Au are compared by FDTD simulations.

We theoretically present in-plane multiple guided emissions of metallically confined microdisk lasers which can be applied to drive multiple elements in compact photonic integration at the same time. Two to four-port microdisks with transverse magnetic and electric polarizations are investigated based on finite difference time domain simulation and pade approximation. Modes filtering of coupling ports are verified by the calculated mode quality factors (Q) which are decided by the matching of coupling ports with the energy density distribution of corresponding modes. Single mode lasing operation of semiconductor microdisk with guided emissions is possibly realized by selectively pumping.

Multiple-port microlasers can be used to driver several optical elements as the light or signal sources in photonic integrated circuits through optical interconnection. Using simple planar technique process, four-port square-resonator microlasers are proposed and fabricated by directly four coupled waveguides at vertices. Continuous wave lasing is realized at room temperature with a threshold current of 65 mA for GalnAsP/InP square microlaser with a side length of 15 μm and the width of coupled waveguides 1.5 μm. The mode Q-factors of 6.9 × 10 3 and 1.3 × 10 4 are estimated near the threshold at the mode wavelengths of 1521.2 and 1524.2 nm. In addition, the mode characteristics of four-port square-resonator are investigated by FDTD simulation.

Multiple-port directional emission microlasers are potential light sources and optical signal processing units in photonic integrated circuits. Connecting bus waveguides to a microresonator is a simple method to realize directional emission microlasers. In this paper, we investigate square and circular resonator microlasers connected with multiple bus waveguides. The mode characteristics of the microresonators connected with multiple bus waveguides are simulated by finite-difference time-domain technique, and the numerical results of mode Q factors and output coupling efficiencies show that high efficiency directional emission microresonator lasers can be realized. Furthermore, the microcylinder laser connected with a bus waveguide fabricated by planar technology processes is reported, and the lasing spectra of square microlasers with four vertices connected to bus waveguides are analyzed.

CW Electrically injected AlGaInAs/InP microcylinder lasers are realized with 10µm radius and a 2µm-wide output waveguide at room temperature. High output efficiency is predicted for coupled microcylinders with an output waveguide by 2D FDTD simulation.

Microcavity lasers with whispering-gallery modes (WGMs) ar e potential light sources for photonic integrated circuits. However, the direction emission and output power are greatly limited for microdisks with the WGMs confined by total internal reflection. Deformed microdisk with chaos mode light rays or evanescently coupled waveguide were used to realize directional emission microlasers. Different from the microdisk with traveling wave WGMs, confined modes in triangle and square microcavities are standing wave WGMs. So the confined modes can still have high Q-factors if an output waveguide is directly connected to triangle and square microcavities at the position with weak mode field distribution. Based on theoretical analys is and numerical simulation of the mode characteristics, we fabricate directional emission triangle and square InGaAsP/InP microcavity lasers with an output waveguide directly connected to the resonators by standard photolithography and inductively coupled plasma etching technique. Continuous-wave (CW) electrically-injected InGaAsP triangle and square microlasers are realized at room temperature for the triangle microlasers with side length from 10 to 30 P m and the square microlaser with the side length of 20 P m. Keywords: Optical microcavity, semiconductor lase rs, whispering-gallery modes, InGaAsP

Directional emission semiconductor microcavity lasers integrated with semiconductor planar technique are potential light sources for photonic integrated circuits. In this article, we investigate mode characteristics for equilateral triangle and square microcavities for realizing directional emission microcavity lasers. The analytical mode field distributions and mode wavelengths are presented for two-dimensional (2D) triangle and square resonators, and directional emission are simulated by finite-difference time-domain (FDTD) technique. The numerical results of mode Q-factors and output coupling efficiencies for the triangle and square resonators show that high efficiency directional emission microcavity lasers can be realized by directly connected an output waveguide to the resonators, because the mode field patterns are standing distributions in the triangle and square resonator. Laser output spectra of fabricated InGaAsP/InP triangle lasers are compared with the analytical results.

InP/GaInAsP square-resonator microlasers with an output waveguide connected to the midpoint of one side of the square are fabricated by standard photolithography and inductively-coupled-plasma etching technique. For a 20-mu m-side square microlaser with a 2-mu m-wide output waveguide, cw threshold current is 11 mA at room temperature, and the highest mode Q factor is 1.0 X 10(4) measured from the mode linewidth at the injection current of 10 mA. Multimode oscillation is observed with the lasing mode wavelength 1546 nm and the side-mode suppression ratio of 20 dB at the injection current of 15 mA. (C) 2008 Optical Society of America

Theoretical analysis and numerical simulation are presented for triangle and of square optical microcavities connected with an output waveguide. The mode behaviours are also simulated for an equilateral triangle resonator confined by metal layers. Furthermore, triangle and square InP/InGaAsP microcavity lasers are fabricated by ICP etching technique, and room temperature CW operation are realized.

Directional emission triangle and square InGaAsP/InP lasers have been fabricated by standard photolithography, inductively coupled plasma etching technique combined with wet chemical etching process. In this article, the characteristics of the microcavity lasers are presented. For an equilateral triangle microcavity laser with the side length of 30 mum, we got the laser spectra fitted very well with the mode wavelength formulate up to the 8th transverse mode at room temperature. But the laser spectra are usually more complex than the formulae for the lasers, especially for the lasers with a smaller side length. For a square microcavity laser with side length of 20 mum, we observed the mode competition between the Fabry-Perot (FP) modes and whispering-gallery (WG) modes at 200 K. The output spectra below the threshold have the mode interval of FP modes with a large mode interval, and the laser spectra agree very well with the WG modes, which have mode interval less than the FP modes. The output spectra are dominated by the FP modes below the threshold, because the FP modes have a higher output coupling efficiency than the WG modes.

We experimentally demonstrate an ultralow-threshold cascaded Brillouin microlaser for tunable microwave generation in a high-Q silica microsphere resonator. The threshold of the Brillouin microlaser is as low as 8 μW, which is close to the theoretical prediction. Moreover, the fifth-order Stokes line with a frequency shift up to 55 GHz is achieved with a coupled pump power of less than 0.6 mW. Benefiting from resonant wavelength shifts driven by thermal dynamics in the microsphere, we further realized tunable microwave signals with tuning ranges of 40 MHz at an 11 GHz band and 20 MHz at a 22 GHz band. To the best of our knowledge, it was the first attempt for tunable microwave source based on the whispering-gallery-mode Brillouin microlaser. Such a tunable microwave source from a cascaded Brillouin microlaser could find significant applications in aerospace, communication engineering, and metrology.

Plasmonic whispering gallery (WG) modes confined in metal-coated resonators are theoretically investigated by electromagnetic analyses. The resonance can be tuned from internal surface plasmonic WG modes to the hybrid state of the plasmonic mode by an introduced isolation layer. As the coated metal is reduced in size, the optical resonance is shifted out by the mode coupling of the internal and external surface plasmonic WG modes. Based on the optical leak of the plasmonic WG mode, the optical influences led by the surroundings with a variable refractive index are considered. Device performance criteria such as optical power leak, resonant wavelength shift, and threshold gain are studied. Full wave simulations are also employed and the results present good consistency with analytic solutions. The metal-coated resonator assisted by an active material is expected to provide promising performance as a refractometric sensor.