Narrow linewidth laser based on a sidewall grating active distributed Bragg reflector

We demonstrated a narrow linewidth semiconductor laser based on a deep-etched sidewall grating active distributed Bragg reflector (SG-ADBR). The coupling coefficients and reflectance were numerically simulated for deep-etched fifth-order SG-ADBR, and a reflectance of 0.86 with a bandwidth of 1.04 nm was obtained by the finite element method for a 500-period SG-ADBR. Then the fifth-order SG-ADBR lasers were fabricated using projection i-line lithography processes. Single-mode lasing at 1537.9 nm was obtained with a high side-mode suppression ratio (SMSR) of 65 dB, and a continuous tuning range of 10.3 nm was verified with SMSRs greater than 53 dB. Furthermore, the frequency noise power spectral density was characterized, from which a Lorentzian linewidth of 288 kHz was obtained.

Optical time domain reflectometry based on a self-chaotic circular-sided microcavity laser

A self-chaotic circular-sided square microcavity laser, with a chaos bandwidth of 12.9 GHz and a flatness of ±3d B, was applied in optical time domain reflectometry (OTDR). Using the broadband chaos laser, we demonstrated a range resolution of 4.5 mm and a 25-km detection distance experimentally. The solitary wide-bandwidth microcavity chaos laser, without the extra correlation peaks in optical feedback chaotic lasers, has shown potential advantages for correlation OTDR in practical application.

Feedback insensitivity in a self-chaotic microcavity laser

Insensitivity to external optical feedback is experimentally demonstrated in a self-chaotic deformed square microcavity laser for the first time, to the best of our knowledge. Both the optical and radio frequency (RF) spectra of the microlaser remain unaffected for external optical feedback with feedback strength as high as 9.9 dB. In addition, the autocorrelation function curve exhibits no time-delayed peaks. The insensitivity makes the self-chaotic microcavity laser promising for applications in feedback-insensitive optical sources.

Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser

Self-pulsing and dual-mode lasing in a square microcavity semiconductor laser are studied experimentally. Self-sustained pulses originating from undamped relaxation oscillation induced by a two-mode interaction are obtained, as the injection current is slightly above the laser threshold. A repetition frequency of 4.4 GHz and a pulse width of 30-40 ps are obtained at a current of 8 mA. The laser switches to continuous-wave operation when the injection current is higher than a certain value, and dual-mode lasing with 30.7 GHz at 16 mA and 10.7 GHz at 27 mA are observed in the lasing spectra. Furthermore, the relative intensity noise spectra are presented to reveal the relationship between the lasing states and the dynamics induced by relaxation oscillation and mode beating.

Yersiniabactin-Producing E. coli Induces the Pyroptosis of Intestinal Epithelial Cells via the NLRP3 Pathway and Promotes Gut Inflammation

The high-pathogenicity island (HPI) was initially identified in Yersinia and can be horizontally transferred to Escherichia coli to produce yersiniabactin (Ybt), which enhances the pathogenicity of E. coli by competing with the host for Fe3+. Pyroptosis is gasdermin-induced necrotic cell death. It involves the permeabilization of the cell membrane and is accompanied by an inflammatory response. It is still unclear whether Ybt HPI can cause intestinal epithelial cells to undergo pyroptosis and contribute to gut inflammation during E. coli infection. In this study, we infected intestinal epithelial cells of mice with E. coli ZB-1 and the Ybt-deficient strain ZB-1Δirp2. Our findings demonstrate that Ybt-producing E. coli is more toxic and exacerbates gut inflammation during systemic infection. Mechanistically, our results suggest the involvement of the NLRP3/caspase-1/GSDMD pathway in E. coli infection. Ybt promotes the assembly and activation of the NLRP3 inflammasome, leading to GSDMD cleavage into GSDMD-N and promoting the pyroptosis of intestinal epithelial cells, ultimately aggravating gut inflammation. Notably, NLRP3 knockdown alleviated these phenomena, and the binding of free Ybt to NLRP3 may be the trigger. Overall, our results show that Ybt HPI enhances the pathogenicity of E. coli and induces pyroptosis via the NLRP3 pathway, which is a new mechanism through which E. coli promotes gut inflammation. Furthermore, we screened drugs targeting NLRP3 from an existing drug library, providing a list of potential drug candidates for the treatment of gut injury caused by E. coli.

Unidirectional light emission in a deformed circular-side triangular microresonator

A waveguide-connected deformed circular-side triangular microresonator is proposed and fabricated. Room temperature unidirectional light emission is experimentally demonstrated in the far-field pattern with a divergence angle of 38°. Single mode lasing at 1545.4 nm is realized at an injection current of 12 mA. The emission pattern changes drastically upon the binding of a nanoparticle with radius down to several nanometers, predicting applications in electrically pumped, cost-effective, portable and highly sensitive far-field detection of nanoparticles.

Narrow linewidth optical frequency comb based on a directly modulated microcavity laser with optical feedback

A narrow linewidth optical frequency comb (OFC) based on a directly modulated microcavity laser with external optical feedback is investigated numerically and demonstrated experimentally. Based on the numerical simulations with rate equations, the evolution of the optical and electrical spectra is presented for the direct-modulated microcavity laser with increased feedback strength, and the linewidth property is improved at suitable feedback conditions. The simulation results also show good robustness for the generated OFC in terms of feedback strength and phase. Moreover, the OFC generation experiment is performed by combining with the dual-loop feedback structure to suppress the side mode, and an OFC with a side-mode suppression ratio of 31 dB is realized. Thanks to the high electro-optical response of the microcavity laser, a 15-tone OFC with a frequency interval of 10 GHz is obtained. Finally, the linewidth of each comb tooth is measured to be around 7 kHz under the feedback power of 47 µW, which indicates an enormous compression of approximately 2000 times compared with the free-running continuous-wave microcavity laser.

Highly efficient waveguide-coupled output in asymmetrically deformed square cavity microlasers

We propose and demonstrate deformed square cavity microlasers for realizing highly efficient output from a connected waveguide. The square cavities are deformed asymmetrically by replacing two adjacent flat sides with circular arcs to manipulate the ray dynamics and couple the light to the connected waveguide. The numerical simulations show that the resonant light can efficiently couple to the fundamental mode of the multi-mode waveguide by carefully designing the deformation parameter utilizing global chaos ray dynamics and internal mode coupling. An enhancement of approximately six times in the output power is realized in the experiment compared to the non-deformed square cavity microlasers, while the lasing thresholds are reduced by about 20%. The measured far-field pattern shows highly unidirectional emission agreeing well with the simulation, which confirms the feasibility of the deformed square cavity microlasers for practical applications.

Wideband multiwavelength Brillouin fiber laser with switchable channel spacing

A multiwavelength Brillouin fiber laser (MBFL) with a switchable channel spacing is demonstrated using a 1.55-µm single-mode AlGaInAs/InP hybrid square-rectangular laser as a seeding source. The scheme employs a highly nonlinear fiber loop with a feedback path to generate a 10-GHz-spacing MBFL. Then, assisted by a tunable optical bandpass filter, MBFLs with spacing from 20 GHz to 100 GHz at a step of 10 GHz are generated in another highly nonlinear fiber loop based on the cavity-enhanced four-wave mixing. More than 60 lasing lines with an optical signal-to-noise ratio over 10 dB are obtained successfully in all the switchable spacings. The total output power and the channel spacing of the MBFLs are proved to be stable.

Hemolysin Co-Regulatory Protein 1 Enhances the Virulence of Clinically Isolated Escherichia coli in KM Mice by Increasing Inflammation and Inducing Pyroptosis

Hemolysin-coregulated protein 1 (Hcp1) is an effector released by the type VI secretion system (T6SS) in certain pathogenic strains of Escherichia coli (E. coli) that causes apoptosis and contributes to the development of meningitis. The exact toxic consequences of Hcp1 and whether it intensifies the inflammatory response by triggering pyroptosis are yet unknown. Here, utilizing the CRISPR/Cas9 genome editing method, we removed the gene expressing Hcp1 from wild-type E. coli W24 and examined the impact of Hcp1 on E. coli virulence in Kunming (KM) mice. It was found that Hcp1-sufficient E. coli was more lethal, exacerbating acute liver injury (ALI) and acute kidney injury (AKI) or even systemic infections, structural organ damage, and inflammatory factor infiltration. These symptoms were alleviated in mice infected with W24Δhcp1. Additionally, we investigated the molecular mechanism by which Hcp1 worsens AKI and found that pyroptosis is involved, manifested as DNA breaks in many renal tubular epithelial cells. Genes or proteins closely related to pyroptosis are abundantly expressed in the kidney. Most importantly, Hcp1 promotes the activation of the NLRP3 inflammasome and the expression of active caspase-1, thereby cleaving GSDMD-N and accelerating the release of active IL-1β and ultimately leading to pyroptosis. In conclusion, Hcp1 enhances the virulence of E. coli, aggravates ALI and AKI, and promotes the inflammatory response; moreover, Hcp1-induced pyroptosis is one of the molecular mechanisms of AKI.

Nonlinear dynamics of a semiconductor microcavity laser subject to frequency comb injection

The nonlinear dynamical behaviors of a semiconductor microcavity laser with frequency comb injection have been experimentally and numerically investigated. The microcavity laser is harmonically locked to a unit fraction of the comb spacing due to the undamped relaxation oscillation at certain conditions, creating additional comb lines with reduced frequency spacing. The stability maps indicating various locking states are obtained based on rate equations, which demonstrates that the locking regions are closely related to the relaxation oscillation. Moreover, the microcavity laser with comb injection leads to spectral broadening of the original comb and the number of comb lines raises from 3 to 13. Owing to the large modulation bandwidth of the microcavity laser, the comb lines and the frequency spacing can be tailored over a wide range by varying the injection parameters.

Coronary artery bypass grafting versus percutaneous coronary intervention with stenting for multivessel coronary artery disease without left main coronary disease:reconstructed individual patient data

Background and aims

Data are emerging on 10-year mortality comparing coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI) with stenting for multivessel disease (MVD) without left main (LM) involvement. We conducted an updated two-stage meta-analysis using reconstructed individual patient data to compare long-term mortality between CABG and PCI for patients with MVD without significant LM coronary disease.

Methods

Medline and Embase databases were searched for articles comparing CABG with PCI for MVD. A two-stage meta-analysis was conducted using reconstructed patient level survival data for all-cause mortality with subgroups by SYNTAX score. The shared-frailty and stratified Cox models were fitted to compare survival endpoints.

Results

We screened 1496 studies and included six randomized controlled trials with 7181 patients. PCI was associated with greater 10-year all-cause mortality risk (HR: 1.282, CI: 1.118–1.469, p<0.001) compared with CABG. In patients with low SYNTAX score, 10-year all-cause mortality after PCI was comparable to CABG (HR: 1.102, 0.822–1.479, p=0.516). However, in patients with moderate to high SYNTAX score, 10-year all-cause mortality was significantly higher after PCI compared with CABG (HR: 1.444, 1.122–1.858, p<0.001; HR: 1.856, 1.380–2.497, p<0.001 respectively).

Conclusion

This updated reconstructed individual patient-data meta-analysis revealed a sustained lower cumulative all-cause mortality of CABG over PCI for multivessel disease without LM involvement.

Funding Acknowledgement

Type of funding sources: None.

Single-mode lasing in an AlGaInAs/InP dual-port square microresonator

Mode selection is crucial to achieving stable single-mode lasing in microlasers. Here, we demonstrate experimentally a dual-port square microresonator for single-mode lasing with a side-mode-suppression ratio (SMSR) exceeding 40 dB. By connecting waveguides at two opposite vertices, the quality factor for the antisymmetric mode (ASM) is much higher than that of the symmetric mode (SM), enabling single-mode lasing. Furthermore, far-field interference patterns similar to Young's two-slit interference are observed. This microlaser is capable of providing two optical sources simultaneously for optical signal processing in high-density integrated photonic circuits.

Chaotic microlasers caused by internal mode interaction for random number generation

Chaotic semiconductor lasers have been widely investigated for generating unpredictable random numbers, especially for lasers with external optical feedback. Nevertheless, chaotic lasers under external feedback are hindered by external feedback loop time, which causes correlation peaks for chaotic output. Here, we demonstrate the first self-chaotic microlaser based on internal mode interaction for a dual-mode microcavity laser, and realize random number generation using the self-chaotic laser output. By adjusting mode frequency interval close to the intrinsic relaxation oscillation frequency, nonlinear dynamics including self-chaos and period-oscillations are predicted and realized numerically and experimentally due to internal mode interaction. The internal mode interaction and corresponding carrier spatial oscillations pave the way of mode engineering for nonlinear dynamics in a solitary laser. Our findings provide a novel and easy method to create controllable and robust optical chaos for high-speed random number generation.

Wideband chaotic tri-mode microlasers with optical feedback

A tri-mode micro-square laser under optical feedback is proposed and demonstrated to generate chaos with the broadband flat microwave spectrum. By adjusting lasing mode intensities, frequency intervals, and optical feedback strength, we can enhance the chaotic bandwidth significantly. The existence of two mode-beating peaks makes the flat bandwidth much larger than the relaxation oscillation frequency. Effective bandwidth of 35.3 GHz is experimentally achieved with the flatness of 8.3 dB from the chaotic output spectrum of the tri-mode mode laser under optical feedback.

Manipulation of lasing modes in a circular-side octagonal microcavity laser with a spatially distributed current injection

We propose and demonstrate a circular-side octagonal microcavity (COM) semiconductor laser with a spatially distributed current injection for manipulating the lasing modes. There are two types of high-quality-factor whispering-gallery (WG) modes with distinct field patterns in a COM: the four-bounced quadrilateral modes and the eight-bounced octagonal modes. By designing two separated p-electrodes, the COM laser is divided into two regions that are pumped independently to select specific modes for lasing. The two types of WG modes lase simultaneously when the two regions are injected with equivalent currents. Degeneracy removal of the quadrilateral modes is observed in both simulation and experiment when the two regions are injected with inequivalent currents. The quadrilateral modes are suppressed when one of the two regions is un-injected or biased with a negative current, and single-octagonal-mode lasing is realized. The results show that the lasing modes can be efficiently manipulated with the spatially distributed current injection considering the distinct field patterns of different WG modes in the microcavities, which can promote the practical application of the microcavity lasers.

A network meta-analysis on the vasomodulators for portopulmonary hypertension

Background

In patients with portopulmonary hypertension (PoPH) who are eligible and awaiting liver transplant, guidelines recommend lowering pulmonary pressures with vasomodulators as a bridge to transplant. However, efficacy of each vasomodulator class as a bridge to transplant remains unknown.

Purpose

This review compares the use of endothelin receptor antagonists (ERA), phosphodiesterase type-5 inhibitors (PDE5-I), prostacyclin (PC) and combination therapy in its pulmonary pressure-lowering effects and pre-transplant mortality in this strictly selected subset of patients.

Methods

A search conducted on Medline and Embase on articles relating to vasomodulator use in PoPH for pulmonary pressure-lowering effects and mortality. Network analysis was conducted to summarize the evidence. Surface under the cumulative ranking curve (SUCRA) was used to rank treatments.

Results

Ten studies with 180 patients were included. SUCRA analysis demonstrated largest mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR) lowering effects in ERA and combination therapy, followed by PDE5-I and PC. mPAP-lowering effects were largest in ERA (MD −19.440, CI: −62.280 to 23.400) and combination therapy (MD −18.223, CI: −29.677 to −6.770) when compared to PDE5-I (table 1). Pre-transplant mortality were comparable between ERA, PDE5-I and combination therapy. Both ERA (RR:0.349. CI: 0.137–0.891) and PDE5-I (RR: 0.279, CI: 0.091–0.854) had significantly lower mortality than PC (table 2).

Conclusion

This meta-analysis provides preliminary evidence that ERA have shown larger pulmonary pressure-lowering effects than PDE5-I in PoPH patients who were eligible for LT. Both ERA and PDE5-I have comparable mortality outcomes, with unfavorable outcomes in PC users.

Funding Acknowledgement

Type of funding sources: None.

Numerical simulation of all-optical logic gates based on hybrid-cavity semiconductor lasers

All-optical switch and multiple logic gates have been demonstrated using a hybrid-cavity semiconductor laser composed of a square microcavity and a Fabry-Perot cavity experimentally. In this paper, two-section tri-mode rate equations with optical injection terms are proposed and applied to study all-optical logic gates of NOT, NOR, and NAND operations utilizing the hybrid-cavity laser. Steady-state and dynamical characteristics of all-optical multiple logic gates are simulated, taking into account the influence of mode frequency detuning, gain suppression coefficients, mode Q factor, injection energy, and biasing current. All-optical logic NOT, NOR, and NAND gates up to 20, 15, and 20 Gbit/s are obtained numerically with dynamic extinction ratios of over 20, 20, and 10 dB, respectively, which are potential response speeds of the all-optical logic gates based on the hybrid-cavity semiconductor lasers.

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.

207 Laparoscopic versus Open Surgery for Locally Advanced Colon Cancer: A Retrospective Cohort Study

Introduction

While an increasing number of studies substantiate the non-inferiority of laparoscopy to open surgery for pT4 colon cancer, studies investigating its value specific to the subgroup pT4a in right hemicolectomies remain scarce.

Method

We performed a retrospective cohort analysis in National University Hospital of Singapore of patients who underwent a right hemicolectomy for pT4 colon cancer. Statistical analysis was performed using Wilcoxon rank sum test and chi square/fisher exact.

Results

In total, 65 patients had T4 colon cancer. 55 underwent right hemicolectomy and 10 underwent extended right hemicolectomy. Baseline demographics were similar in laparoscopic (n = 27) and open (n = 38) groups, with no significant difference in proportion of pT4a patients (p = 0.724). For pT4, 30-day mortality (7%, 5% respectively, p = 0.723), overall survival (p = 0.1903) and disease-free survival (p = 0.3476) did not differ significantly between laparoscopic and open groups. R0 resection rates were significantly higher in laparoscopic group (p = 0.039). pT4a subgroup analysis found similar observations. Other complications including postoperative wound infection and anastomotic bleed were not significantly different for both T4 and T4a analysis.

Conclusions

This study presented comparable safety and oncological outcomes between the two surgical methods for right hemicolectomy, suggesting laparoscopy to be a viable alternative approach for locally advanced right colon cancer.

Comparison of single- and dual-mode lasing states of a hybrid-cavity laser under optical feedback

In this Letter, we design and realize a hybrid-cavity laser with single- or dual-mode lasing states and study the nonlinear states of the laser under external optical feedback (EOF). The laser at a dual-mode state easily and directly enters the chaotic state without periodic oscillation states and display chaos for a much wider range of the EOF magnitude than the laser at a single-mode state. A flat chaotic signal is obtained for the laser at a dual-mode lasing state under a weak EOF benefitting from the low-frequency energy enhancement caused by mode competition between the dual modes.

Mode control through anti-Hermitian coupling in regular-polygonal microcavities with non-uniform gain and loss

We theoretically and numerically study optical modes in regular-polygonal microcavities with non-uniform gain and loss, where high quality (Q) whispering-gallery-like modes typically appear as superscar states. High Q superscar modes can be described by the propagating plane waves in an effective rectangle formed by unfolding the periodic orbits and exhibit regular and predictable spatial field distributions and transverse-mode spectra. With non-uniform gain and loss, anti-Hermitian coupling between the transverse modes with close frequencies occurs according to the mode coupling theory, which results in novel mode properties such as modified mode spectra and field patterns, and the appearance of exceptional points. Numerical simulation results are in good agreement with the theoretical analyses, and such analyses are also suitable for other kinds of high Q microcavities with non-uniform gain and loss. These results will be highly useful for studying non-Hermitian physics in optical microcavities and advancing the practical applications of microcavity devices.

Wideband multiwavelength Brillouin fiber laser based on dual-mode AlGaInAs/InP microcavity lasers

A multiwavelength Brillouin fiber laser (BFL) is demonstrated using a 1.55-µm AlGaInAs/InP microcavity laser as a seed source. The combination of a nonlinear fiber cavity and a feedback loop leads to multiwavelength generation with a channel spacing of double-Brillouin-frequency assisted by cavity-enhanced four-wave mixing. The amplified output of a dual-mode lasing square microcavity laser with a wavelength interval of 1.5 nm is applied as the pump source for the broadband multiwavelength generation. A wideband multiwavelength BFL covering from 1490 nm to 1590 nm is successfully generated at an optimized pump power of 25 dBm and a feedback power of -17.2dBm. The power stability of 0.82 dB over a 60 min duration of the multiwavelength BFL can satisfy the demands for the optical fiber sensing and microwave photonic systems.

Wideband frequency-tunable optoelectronic oscillator with a directly modulated AlGaInAs/InP integrated twin-square microlaser

We propose and demonstrate an optoelectronic oscillator with a directly modulated AlGaInAs/InP integrated twin-square microlaser for generating wideband frequency-tunable microwave signals with low phase noise. Apart from the relaxation oscillation peak, the modulation response of the twin-square microlaser working at the mutual optical injection state exhibits a significant enhancement around the beating frequency of the lasing modes in the two square cavities owing to the photon-photon resonance. A self-sustaining oscillation can be generated around the modulation response peak with the lowest loop loss occurring at the relaxation oscillation frequency or the beating frequency, depending on the practical state of the twin-square microlaser. High-quality tunable microwave signals ranging from 2.22 to 19.52 GHz are generated with single sideband phase noises below -110 dBc/Hz at the 10 kHz offset frequency and side-mode suppression ratios of approximately 40 dB by tuning the injection currents of the twin-square microlaser.

Single-transverse-mode waveguide-coupled deformed hexagonal resonator microlasers

AlGaInAs/InP waveguide-coupled deformed hexagonal resonator microlasers with enhanced mode quality (Q)-factors are demonstrated for realizing single-transverse-mode operation. A circular hole is introduced to the center of the hexagonal resonators with rounded corners to enhance the mode Q-factors and suppress high-order transverse modes simultaneously. Single-mode lasing with side-mode suppression ratios up to 40 dB is obtained for the 10-μm-sidelength hexagonal microlasers with a center hole. All the lasing spectra demonstrate pure single-transverse-mode properties within the whole tuning range of injection current, and mode hopping with one, two, and three longitudinal-mode intervals is observed due to the mode Q-factor modification by the center holes. To further reduce the device size and threshold current, the deformed hexagonal resonator microlasers with the flat sides replaced by circular arcs are analyzed and demonstrated experimentally. The Q-factors of the fundamental transverse modes can be enhanced by two orders of magnitude due to the convergence effect of the circular sides by optimizing the deformation amplitude, while the single-transverse-mode property is still maintained. A threshold current of 2.4 mA is realized for a circular-side hexagonal microlaser with the side length of 8.5 μm and the deformation amplitude of 0.55 μm.

Low-phase-noise microwave generation using dual-mode microsquare laser phase locking by modulated sidebands

An effective method for millimeter-wave (mmW) carrier generation from a dual-transverse-mode microsquare laser is experimentally demonstrated. By directly modulating the dual-mode microsquare laser at 6.7 GHz, multiple sidebands are generated due to enhanced modulation nonlinearity, and the lasing modes with an interval of 40 GHz are phase-locked. MmW carriers up to 47 GHz, corresponding to seven times that of the modulation frequency, are achieved with a linewidth below 10 Hz. The single-sideband phase noises of the signals keep the same level after transmission over 2.5 km of optical fiber.

Spectral engineering for circular-side square microlasers

Spectral engineering has been demonstrated for the circular-side square microlasers with an output waveguide butt-coupled to one vertex. By carefully optimizing deformation parameter and waveguide connection angle, undesired high-order transverse modes are suppressed while the mode Q factors and the transverse-mode intervals are enhanced simultaneously for the low-order transverse modes. Dual-mode lasing with pure lasing spectra is realized experimentally for the circular-side square microlasers with side lengths of 16 μm, and the transverse mode intervals can be adjusted from 0.54 to 5.4 nm by changing the deformation parameter. Due to the enhanced mode confinement, single-mode lasing with a side-mode suppression-ratio of 36 dB is achieved for a 10μm-side-length circular-side square microlaser with a 1.5μm-wide waveguide.

Narrow-linewidth microwave generation by an optoelectronic oscillator with a directly modulated microsquare laser

A simple dual-loop optoelectronic oscillator using a 16 μm side length AlGaInAs/InP directly modulated microsquare laser is proposed and investigated without an external modulator. High-performance first harmonics are realized, with 3 dB linewidth, less than 200 Hz, and a frequency-tunable range from 2 to 8 GHz. Meanwhile, a side-mode suppression ratio of 60 dB is obtained for the microwave by the dual-loop structure. Within the whole tuning range, the measured single-sideband phase noises of the first harmonics are about -110  dBc/Hz at 10 kHz frequency offset. Furthermore, the second and third harmonics with frequency-tunable ranges from 4 to 16 GHz and 6 to 24 GHz are achieved as well.

Modulation bandwidth enhancement for coupled twin-square microcavity lasers

Modulation bandwidth enhancements are investigated for coupled twin-square microcavity lasers due to photon-photon resonance effect. For a coupled twin-square microcavity laser with the square side length of 20 μm, we demonstrate the increase of 3-dB modulation bandwidth from 9.6 GHz to 19.5 GHz, by adjusting the resonance mode wavelength interval between two square microcavities. The enhanced modulation bandwidth is explained by rate equation analysis, and numerical simulations are conducted for large signal modulation with improved eye-diagrams at 40 Gbit/s.

All-optical flip-flop based on hybrid square-rectangular bistable lasers

A compact, simple, and bistable hybrid square-rectangular laser is experimentally demonstrated as an all-optical flip-flop memory. Controllable bistability is induced by two-mode competition, together with the saturable absorption at the square microcavity section. The all-optical set and reset operations are realized by injecting signal pulses at two-mode wavelengths, with the response times of 165 and 60 ps at the triggering pulse width of 100 ps and switching energies of 2.7 and 14.2 fJ, respectively. The robust hybrid-cavity design has an active area of 660  μm² and permits efficient unidirectional single-mode lasing, low-power flip-flop operation, and superior fabrication tolerance for monolithic photonic integration.

Single-mode unidirectional-emission circular-side hexagonal resonator microlasers

Circular-side hexagonal resonator (CSHR) microlasers connecting an output waveguide are proposed and demonstrated for enhancing the mode Q factor and realizing single-mode operation. Three-dimensional simulation results indicate that the CSHRs with an optimized deformation can greatly enhance mode Q factors. The CSHR microlasers with output waveguides are fabricated using a planar technology process. For a CSHR microlaser with a side length of 7.5 μm and an output waveguide width of 2 μm, single-mode operation is realized with a side-mode suppression ratio of 43 dB and a threshold current of 2.5 mA. Furthermore, flat small-signal modulation responses are obtained with a 3 dB bandwidth of 13 GHz.

Multicoherence wavelength generation based on integrated twin-microdisk lasers

An effective method for multicoherence wavelength generation is experimentally demonstrated using an integrated twin-microdisk laser as a seeding source. Dual-wavelength lasing with variable wavelength spacing is achieved by adjusting injection currents independently. Using the integrated laser as a pump seed, we obtain multicoherence wavelength in a nonlinear optical fiber, which has a tunable frequency interval from 50 to 300 GHz. Ten waves with optical signal to noise ratio from 28 to 10 dB are produced at the frequency interval of 200 GHz and a pulse width of 1.2 ps. The high extinction ratio of the pulse trace indicates the high coherence in the mode-locked multiwavelength light source.

Locally deformed-ring hybrid microlasers exhibiting stable unidirectional emission from a Si waveguide

We propose and demonstrate a locally deformed-ring (LDR) hybrid microlaser to realize stable unidirectional emission from a silicon waveguide. The coupled modes eliminate the competition between clockwise (CW) and counter-clockwise (CCW) modes, and the highly unidirectional characteristics are achieved with an enhanced mode quality factor based on a locally deformed notch in the LDR resonator. Using a divinylsiloxane-benzocyclobutene bonding technique, a LDR hybrid microlaser is fabricated vertically coupled to a silicon waveguide with a radius of 20 μm, a ring width of 4 μm and a notch width of 500 nm. The threshold current is 7 mA, and single-mode lasing is achieved with the side-mode suppression ratio of 27 dB. Nearly total unidirectional output from the CCW direction of a Si waveguide is demonstrated with a unidirectional ratio of 0.053.

Hybrid spiral-ring microlaser vertically coupled to silicon waveguide for stable and unidirectional output

A hybrid spiral-ring laser vertically coupled to a silicon waveguide is demonstrated to achieve stable and unidirectional output theoretically and experimentally. The mode competition between clockwise (CW) and counter-clockwise (CCW) modes is eliminated due to the mode coupling in a spiral resonator. The simulation results indicate that the CCW and CW direction traveling waves are dominant components, respectively, for the spiral resonator without and with an output waveguide. A hybrid AlGaInAs/Si spiral-ring laser is designed and fabricated vertically coupled to a silicon waveguide. For a spiral-ring laser with a radius of 30 μm and a ring width of 5 μm, the continuous-wave lasing threshold of 9.5 mA is obtained with the threshold current density of 1.1  kA/cm(2) at a temperature of 285 K. The output power fluctuations due to the mode competition between CW and CCW modes are eliminated. The output power from CCW direction is five times that from CW direction.

Mode selection in square resonator microlasers for widely tunable single mode lasing

Mode selection in square resonator semiconductor microlasers is demonstrated by adjusting the width of the output waveguide coupled to the midpoint of one side. The simulation and experimental results reveal that widely tunable single mode lasing can be realized in square resonator microlasers. Through adjusting the width of the output waveguide, the mode interval of the high-Q modes can reach four times of the longitudinal mode interval. Therefore, mode hopping can be efficiently avoided and the lasing wavelength can be tuned continuously by tuning the injection current. For a 17.8-μm-side-length square microlaser with a 1.4-μm-width output waveguide, mode-hopping-free single-mode operation is achieved with a continuous tuning range of 9.2 nm. As a result, the control of the lasing mode is realized for the square microlasers.

Narrow-linewidth microwave generation using AlGaInAs/InP microdisk lasers subject to optical injection and optoelectronic feedback

Narrow-linewidth and low phase noise photonic microwave generation under sideband-injection locking are demonstrated using an 8-μm-radius AlGaInAs/InP microdisk laser subject to optical injection and optoelectronic feedback. Microdisk laser subject to external optical injection at the period-one state provides the microwave subcarrier seed signal, and the optoelectronic feedback serves as direct current modulation to stabilize and lock the generated microwave signal without using the electrical filter. High-quality photonic microwave signals are realized with the 3-dB linewidth of less than 1 kHz and the frequency tunable range from 8.8 to 17 GHz. Single sideband phase noise of -101 dBc/Hz is obtained at a frequency offset of 10 kHz for the generated 14.7 GHz signal. Furthermore, the dependences of photonic microwave signal on the optical injection and optoelectronic feedback parameters are investigated.

Dual-transverse-mode microsquare lasers with tunable wavelength interval

A dual-transverse-mode microsquare laser with a tunable wavelength interval is designed and realized by using a square-ring-patterned contact window. For a 30-μm-side-length microsquare laser with the square-ring width of 4 μm, the wavelength interval varies from 0.25 to 0.37 nm with the intensity ratio less than 2.5 dB as the injection current increases from 89 to 108 mA. Based on the dual-transverse-mode microsquare laser, the microwave signals with the frequencies of 30.56, 32.70, 35.12, and 39.51 GHz and the 3-dB bandwidths of 47, 53, 54, and 47 MHz are obtained at the injection currents of 90, 95, 100, and 105 mA, respectively.

Thermal and high speed modulation characteristics for AlGaInAs/InP microdisk lasers

Thermal and high speed modulation characteristics are investigated for a unidirectional-emission microdisk laser with a radius of 7 μm surrounded by BCB-cladding layer, with a threshold current of 1.5 mA at the temperature of 287 K. The lasing spectra under different widths of pulsed current are measured to characterize the temperature rise during the pulse period, and the thermal distribution in the microdisk laser is simulated by the finite-element modeling technique. A temperature rise of 25 K is estimated for the microdisk laser biased at 20 mA. Furthermore, small signal modulation response with 3dB bandwidth up to 20 GHz is obtained for the microdisk laser at the biasing current of 18 mA, and eye-diagrams at the modulation bit rates of 20, 25, and 30 GHz are also measured at the temperature of 287 K.

Four-wavelength microdisk laser array laterally coupled with a bus waveguide

A four-wavelength microdisk laser array laterally coupled with a bus waveguide is demonstrated numerically and experimentally. The coupled-mode characteristics as well as scattering loss in the bus waveguide caused by the connected microdisks are simulated by a 2D finite-difference time-domain technique. An AlGaInAs/InP microdisk laser array with circular radii of 10.1, 10.2, 10.3, and 10.4 μm is designed and fabricated by common photolithography and an inductively coupled-plasma etching technique. Continuous-wave electrically injected operation is realized at room temperature with the lowest threshold current of 3 mA. Four-wavelength lasing operation is realized with wavelength intervals of 3-4 nm and side mode suppression ratios larger than 25 dB. Finally, the influences of heating effect and thermal cross talk on lasing mode wavelength tuning are investigated experimentally.

Analysis of vertical radiation loss and far-field pattern for microcylinder lasers with an output waveguide

Vertical radiation loss and far-field pattern are investigated for microcylinder lasers by 3D FDTD simulation and experimentally. The numerical results show that an output waveguide connected to the microcylinder resonator can result in additional vertical radiation loss for high Q coupled modes and affect the far field pattern. The vertical radiation loss can be controlled by adjusting the up cladding layer thickness. Furthermore, two lobes of vertical far-field patterns are observed for a 15-μm-radius microcylinder laser connected with an output waveguide, which confirms the vertical radiation loss.

High-Q modes in defected microcircular resonator confined by metal layer for unidirectional emission

Defected circular resonators laterally confined by a metal layer with a flat side as an emitting window are numerically investigated based on the boundary element method for realizing unidirectional emission microlasers. The results indicate that Fabry-Pérot (FP) modes become high Q confined modes in the defected circular resonator with a metallic layer. The mode coupling between the FP mode and chaotic-like mode can result in high Q confined mode for unidirectional emission with a narrow far field pattern.

Wide-angle emission and single-mode deformed circular microlasers with a flat side

We demonstrate wide-angle emission and single mode operation in deformed circular microlasers with a flat side. The mode characteristics of a metallic confined deformed circular resonator with a flat side are investigated by finite-difference time-domain simulation. The numerical results indicate that this structure is suitable to realize wide-angle emission. Furthermore, metallic confined deformed circular microlasers with a flat side are fabricated using common photolithography and inductively coupled-plasma etching techniques. A continuous-wave single-mode operation with a side mode suppression ratio of 25 dB is achieved at an injection current of 4 mA for an 8 μm radius microlaser with a flat side. Additionally, wide angle emission over 120° is observed from the far-field pattern.

Coherence of a single mode InAlGaAs/InP cylinderical microlaser with two output ports

We experimentally investigate the coherence of a single mode InAlGaAs/InP cylindrical microlaser with two output waveguides. For a cylindrical microlaser with a radius of 15 μm and two 2 μm-wide output waveguides, single mode operation with a side mode suppression ratio of 30 dB is realized, and a far-field interferometric pattern similar to a Young's interferometer is observed. The results indicate that the microlasers with two output waveguides can be used as the light source for an optical sensor by monitoring the phase change of the output emission from one port versus that of the other port.

Reduced linewidth enhancement factor due to excited state transition of quantum dot lasers

The carrier induced refractive index change and linewidth enhancement factor α due to ground-state (GS) and excited-state (ES) transitions have been compared by measuring the optical gain spectra from an InAs/GaAs quantum dot (QD) laser structure. It is shown that the ES transition exhibits a reduced α-factor compared to the value due to the GS transition. This result can be explained by the α-factor due to the ES transition having a smaller increase from the non-resonant carriers in the combined state of the wetting layer and InGaAs strain reducing layer than the α-factor increase due to the GS transition, since the relaxation time for carriers from the combined state of the wetting layer and InGaAs strain reducing layer to the ES is shorter than to the GS. The result reported here shows another advantage of using ES QD lasers for optical communication, in addition to their higher modulation speed.

Optical bistability in GaInAsP/InP coupled-circular resonator microlasers

Optical bistability is realized in GaInAsP/InP coupled-circular resonator microlasers, which are fabricated by planar technology. For a coupled-circular resonator microlaser with the radius of 20 μm and a 2 μm-wide bus waveguide, hysteresis loops are observed for the output power coupling into an optical fiber versus the cw injection current at room temperature. The laser output spectra of the upper and lower states of the hysteresis loop indicate that the bistability is related to mode competitions. The optical bistability can be explained as the mode competition between the symmetry and antisymmetry coupled modes relative to the bus waveguide.

Optical bistability in InP/GaInAsP equilateral-triangle-resonator microlasers

Optical bistability is reported in InP/GaInAsP equilateral-triangle-resonator (ETR) microlasers, which are fabricated by planar technology. For a 30 mum side ETR microlaser with a 2-mum-wide output waveguide connected to one of the vertices of the ETR, hysteresis loops are observed for the output power versus the injection current from 215 to 235 K. The laser output spectra are measured in the upper and lower states of the hysteresis loop, which show strong mode competition among transverse modes. The hysteresis loops are demonstrated by two-mode rate equations with asymmetric cross gain saturation and different output efficiencies.