Semiconductor Microring Lasers Research Articles

Routes to chaos in a class-B laser coupled to a neutral resonator

We study the dynamics of a class-B semiconductor microring laser coupled to a neutral microring resonator for common fabrication parameters. For zero detuning between the resonators, we identify five dynamical regions controlled by the normalized pump rate of the laser and coupling strength between the resonators. These regions show stable lasing with phase locking for either sufficiently small or large coupling strength parameter values. Multistability and chaos arise in between these stable regions where at least one fixed point is attractive. The transition from stable to unstable lasing regions in the parameter space phase diagram is a crossover.

Backscattering Effects on High-Speed Modulation of Strongly Injection-Locked Whistle-Geometry Semiconductor Ring Lasers

An injection-locking scheme, involving a single-frequency master laser monolithically integrated with a unidirectional whistle-geometry semiconductor microring laser, has been proposed for enhanced ultra-high-speed performance. Greatly enhanced high-speed modulation performance of the strong-injection-locking scheme has been predicted in numerical calculations. In our previous analysis, however, linear coupling between the two counter-propagating modes due to light backscattering was not taken into account. In this work, we investigate the potential negative impact of light backscattering between the two counter-propagating modes on high-speed modulation performance of strongly injection-locked unidirectional whistle-geometry semiconductor microring lasers.

Epitaxially Grown InP Micro-Ring Lasers.

In the near future, technological advances driven by the Fourth Industrial Revolution will boost the demand for integrated, power-efficient miniature lasers, which are important for optical data communications and advanced sensing applications. Although top-down fabricated III-V semiconductor micro-disk and micro-ring lasers have been shown to be efficient light sources, challenges such as etching-induced sidewall roughness and poor fabrication scalability have been limiting the potential for high-density on-chip integration. Here, we demonstrate InP micro-ring lasers fabricated with a highly scalable epitaxial growth technique. With an optimized cavity design, the optically pumped micro-ring lasers show efficient room-temperature lasing with a lasing threshold of around 50 μJ cm-2 per pulse. Remarkably, through comprehensive modeling of the micro-ring laser, we demonstrate lasing mode engineering experimentally by tuning the vertical ring height. Our work is a major step toward realizing the high-density monolithic integration of III-V miniature lasers on submicrometer-scale optoelectronic devices.

Electrically Pumped Microring Parity-Time-Symmetric Lasers

Microscale and nanoscale electrically pumped lasers are expected to play an indispensable role in future photonic integrated circuits. Small footprint, low threshold, high efficiency, and large side-mode suppression ratio (SMSR) are among the most important characteristics that such on-chip emitters should exhibit—allowing for large-scale integrability, low energy consumption, and stable output power. Microring resonators are one of the main contenders for the realization of such compact light sources. However, the use of microring laser cavities has been so far hindered by their tendency to operate in multiple modes. Quite recently, several studies have shown that notions from parity-time (PT)-symmetry and non-Hermitian physics can be utilized to effectively enforce single-mode operation in semiconductor microring laser arrangements. However, as of now, most works in this area were mainly devoted to the proof of concept demonstrations, while the feasibility of practical implementation has remained largely unexplored. In this article, we demonstrate the first regrowth free, electrically pumped microscale PT-symmetric laser. Our results can pave the way toward the utilization of exceptional points in more diverse applications ranging from on-chip light sources and modulators to laser beam steering systems and active sensors.

Supersymmetric microring laser arrays

Coherent combination of emission power from an array of coupled semiconductor lasers operating on the same chip is of fundamental and technological importance. In general, the nonlinear competition among the array supermodes can entail incoherence and spectral broadening, leading to spatiotemporally unstable and multimode emission pattern and thus poor beam quality. Here, by harnessing notions from supersymmetric (SUSY) quantum mechanics, we report that the strategic coupling between a class III-V semiconductor microring laser array with its dissipative superpartner can be used to limit the number of supermodes available for laser actions to one. We introduce a novel approach based on second-order SUSY transformation in order to drastically simplify the superpartner array engineering. Compared to a conventional laser array, which has multimode spectrum, a SUSY laser array is observed to be capable of operating in a single (transverse) supermode. Enhancement of the peak output intensity of the SUSY laser array has been demonstrated with high-efficiency and lower lasing threshold, compared with a single laser and a conventional laser array. Our experimental findings pave the way towards broad-area and high-power light generation in a scalable and stable fashion.

Study of wavelength switching time in tunable semiconductor micro-ring lasers: experiment and travelling wave description

We report in this paper the wavelength switching features of semiconductor ring lasers that are wavelength tunable based on filtered optical feedback. The filtered feedback provides a wavelength dependent loss mechanism in these devices with which a particular longitudinal mode, and thus a particular wavelength, can be selected by changing the filter characteristics of the feedback channel. We investigate how the wavelength switching speed depends on the amplitude of the modulation of the switching driving signal and on the different phase factors within the filtering branches of the SRL. We compare qualitatively the experimental results with numerical simulations based on a travelling wave model. We also investigate the dynamical behavior of the lasing and nonlasing longitudinal modes in the two channels of the clockwise and the counter-clockwise directions. We show the crucial importance of various phase relation factors on the wavelength switching behavior. Finally, we discuss what limits the switching speed and how we can accelerate it.

Unidirectional lasing in semiconductor microring lasers at an exceptional point [Invited

Recent experiments demonstrated that chiral symmetry breaking at an exceptional point (EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model, we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, above a “second” laser threshold, unidirectional emission is restored.

Grating integrated single mode microring laser

Microring and microdisk lasers are potential candidates for small footprint, low threshold in-plane integrated lasers; however, they exhibit multimode lasing spectra and bistability. Here, we theoretically propose and experimentally demonstrate a novel approach for achieving single mode lasing in microring lasers. Our approach is based on increasing the radiation loss of all but one of the resonant modes of microring resonators by integrating second order gratings on the microrings' waveguide. We present single mode operation of electrically pumped semiconductor microring lasers whose lasing modes are lithographically selected via the second order grating. We also show that adding the grating does not increase the lasing threshold current significantly.

All-optical flip-flop and inverter using adjacent lasing wavelengths by semiconductor microring laser

We demonstrated an all-optical flip-flop and inverter using two adjacent lasing wavelengths (FSR = 1.7 nm) from an InGaAs/InGaAsP multiple quantum well (MQW) microring laser. The main lasing wavelength (1567.54 nm) and both side adjacent lasing wavelengths (1565.84 and 1569.24 nm) were used as the injection light wavelength. These operations were realized in the same device with different injected currents. The injected light power and detuning dependence of the inverter operation were clarified.

Design and Investigation on Characteristics of a Semiconductor Micro-Ring Laser with Retro-Reflector Cavity

A miniaturized semiconductor micro-ring laser with retro-reflector cavity is investigated. By introducing higher order aspheric terms, miniaturized parabolic mirrors are designed and optimized. A Retro-Reflector based semiconductor micro-ring laser with equivalent radius of 38μm and low threshold current of 60mA is realized. The free-running wavelength is 1541.04 nm when the injection current is increased to 140mA.

Analysis of High-Frequency Modulation Response of Strongly Injection-Locked Cascaded Semiconductor Ring Lasers

A novel scheme for modulation bandwidth enhancement and tailoring is presented. This scheme involves a distributed Bragg reflector master laser monolithically integrated with two cascaded strongly injection-locked whistle-geometry semiconductor microring lasers. Enhanced high-speed performance of the novel scheme is confirmed through numerical modeling.

Theoretical description of spontaneous pulse formation in a semiconductor microring laser

We theoretically describe the spontaneous formation of stable pulses in a GaAs bulk semiconductor microring laser. These pulses are obtained without active or passive mode locking. We show that the parameter regime associated with their existence is limited on one side by the phase instability of the continuous-wave solution, and on the other side by the failure of Lamb's mode-locking criterion. Bistability between the continuous-wave solution and the spontaneous pulses is observed.

Excitability in semiconductor microring lasers: Experimental and theoretical pulse characterization

We characterize the operation of semiconductor microring lasers in an excitable regime. Our experiments reveal a statistical distribution of the characteristics of noise-triggered optical pulses that is not observed in other excitable systems. In particular, an inverse correlation exists between the pulse amplitude and duration. Numerical simulations and an interpretation in an asymptotic phase space confirm and explain these experimentally observed pulse characteristics.

Investigation on a microring laser coupled with phase-section bus waveguide as a tunable transmitter for application in future optical/wireless hybrid networks

In this paper, semiconductor microring lasers with integrated phase sections in the bus waveguide are numerically evaluated, using a dynamic multimode laser model, and investigated as low-cost, integrated, potential tunable directly modulated transmitters for future hybrid optical–wireless networks. The effect of optical feedback through bus waveguide is revealed as a promising mechanism for improving nonlinear distortion. Additionally, tunability is achieved with the aid of phase-tuning. The underlying laser dynamics beyond this behavior are analyzed.

Bistable self-starting pulses with terahertz repetition rate in a semiconductor microring laser

We report on the prediction of stable self-starting pulses in a GaAs bulk semiconductor microring laser with terahertz repetition rate. The pulses are obtained without active or passive mode locking. Especially interesting for practical applications is the bistability between pulses and continuous waves.

All-optical set–reset flip-flop based on frequency bistability in semiconductor microring lasers

The electric field of the modes of semiconductor microring lasers (SMRLs) in the presence of bus waveguide reflections are linear combinations of the clock wise (CW) and the counter clock wise (CCW) electric fields. The mode structures can be controlled by the waveguide reflection coefficients. The power ratio and phase difference of the CW and CCW fields of one mode is proportional to the ratio of the reflection coefficients of the left and right waveguides. It is shown that the degenerate CW and CCW modes in the presence of bus waveguide reflections are split into two modes with different frequencies. Employing these new modes, SMRL can be used as an element to design flip-flops used in photonic integrated circuits. For a symmetric structure, the inter-frequencies of CW and CCW waves relating to each mode can be considered as the output of the optical flip-flop. Output of asymmetric mode is zero while the symmetric mode has a nonzero output.

Storing 2 Bits of Information in a Novel Single Semiconductor Microring Laser Memory Cell

An optical memory cell that has four distinctive states, therefore storing 2 bits of information optically, is demonstrated by utilizing a novel single semiconductor microring laser with a retro-reflector cavity. To our best knowledge, it is the first time the combination of two directional and two wavelength states with a single semiconductor ring laser of only 20 times 62 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in size has been demonstrated in which room-temperature continuous-wave operation is realized. These states can be easily written by corresponding optical inputs with low optical energy of ~ 1.56 fJ and rapid access time of ~70 ps suitable for 10 Gb/s or higher data rates.

Mode emission characteristics of semiconductor microdisc and microring lasers

We fabricate both microdisc and microring InGaAsP-InGaAs quantum well semiconductor lasers using an etching-and-bonding technique. Their emission properties are studied by optical pumping at 77 K. Single mode lasing is achieved for discs with a diameter of 5 μm. Multimode emission is observed for rings with larger diameters. Both fundamental and higher order lasing modes are observed and are found to exhibit interesting emission characteristics.