Semiconductor Ring Laser Research Articles

单片集成微环反射器可调谐半导体环形激光器理论和数值模型

A novel and rapidly tunable laser was proposed, consisting of a semiconductor ring laser (SRL) formed by an active microring under constant current pumping and a monolithically integrated external tunable passive microring reflector. The geometry, therefore, enables very fast tuning by separating the mechanism (the active microring cavity) that defines stable lasing mode frequencies from the tuning mechanism (the passive microring) that only selects one of these stable frequencies. Furthermore, compared to the laser based on grating structures, this SRL offers many promising advantages including strong mode-selection and simple fabrication, which does not require phase matching sections and provides a strong immunity of the output wavelength to the thermal fluctuations of the tunable section. Theoretical simulations based on a multimode rate-equation model were used to study the performance of the laser. Numerical simulations demonstrate digital tuning of the laser across 15 cavity modes with reasonably low threshold current of about 40 mA and moderate side-mode suppression ratio (SMSR).

Theoretical and Numerical Investigations of Wavelength Bi/Multistability in Semiconductor Ring Lasers

Wavelength bi/multistability in semiconductor ring lasers is studied both theoretically and numerically based on a multimode model with nonlinear effects arising from carrier density pulsation, carrier heating, spectral hole-burning, and four-wave mixing included. Wavelength bi/multistability is explained theoretically, and conditions required for wavelength bi/multi-stable operation are derived analytically. It shows the dependence of wavelength bi/multistability on device size and other device and material properties. Radius range within which the device is wavelength bi/multistable is calculated based on the derived expressions. Both the theory and calculations are verified by numerical simulations and supported by previously reported experimental observations on wavelength bi/multistable semiconductor ring lasers. The results indicate that semiconductor microring/microdisk lasers with radius down to 10 μm could still support wavelength bi/multistable operation.

High-Speed Modulation Analysis of Strongly Injection-Locked Semiconductor Ring Lasers

A novel scheme for modulation bandwidth enhancement is presented, involving distributed Bragg reflector master laser monolithically integrated with strongly injection-locked whistle-geometry microring laser. Enhanced high-speed performance of the novel scheme is confirmed through numerical modeling by comparing it with an earlier scheme, where optical injection was provided by a waveguide directional coupler adjacent to the ring laser.

Solitary and coupled semiconductor ring lasers as optical spiking neurons

We theoretically investigate the possibility of generating pulses in an excitable (asymmetric) semiconductor ring laser (SRL) using optical trigger pulses. We show that the phase difference between the injected field and the electric field inside the SRL determines the direction of the perturbation in phase space. Due to the folded shape of the excitability threshold, this has an important influence on the ability to cross it. A mechanism for exciting multiple consecutive pulses using a single trigger pulse (i.e., multipulse excitability) is revealed. We furthermore investigate the possibility of using asymmetric SRLs in a coupled configuration, which is a first step toward an all-optical neural network using SRLs as building blocks.

All-Optical Directional Switching of Bistable Semiconductor Ring Lasers

All-optical directional switching of bistable semiconductor ring lasers is studied by numerical simulations of a traveling-wave model. We discuss how the reversal depends on the bias current applied to the laser as well as on the energy, duration, and wavelength of the trigger pulses. For pulse durations longer than the cavity roundtrip time, the reversal occurs smoothly with a transient that exhibits relaxation oscillations, otherwise, the transient is composed of large long-lived spikes that reveal its multimode character. In the former case, the switching speed can be defined like in electronics systems, but not in the latter, which requires an operational definition of the maximum speed based on, e.g., bit-error rate measurements. Our model includes the light extraction sections present in real devices, which allows us to discuss the experimental problems posed by the differences existing between intracavity fields and output fields.

Directional control of optical power in integrated InP/InGaAsP extended cavity mode-locked ring lasers

We report on a passively mode-locked InP/InGaAsP multiple quantum well semiconductor ring laser that operates at a 20 GHz repetition rate and around 1575 nm wavelength. The device has been realized using the active-passive integration technology in a standardized photonic integration platform. We demonstrate experimentally for the first time to our knowledge that the relative positioning of the amplifier and absorber in a monolithically integrated ring laser can be used to control the balance of power between counterpropagating fields in the mode-locked state. The directional power balance is verified to be in agreement with a model previously reported.

Random optical pulse generation with bistable semiconductor ring lasers

We experimentally show that a random optical pulse train can be generated by modulating a bistable semiconductor ring laser. When the ring laser is switched from the monostable to the bistable regime, it randomly selects one of two different stable unidirectional lasing modes, clockwise or counterclockwise modes. Non-deterministic random pulse sequences are generated by driving the switch parameter, the injection current, with a periodic pulse signal. The origin of the nondeterministic randomness is the amplified spontaneous emission noise coupled to the counter-propagating lasing modes. The statistical randomness properties are optimized by adjusting the relative strength of amplified spontaneous emission noise sources for the two lasing modes. It is also shown that it is possible to generate optical pulse sequences which pass a standard suite of statistical randomness tests.

A semiconductor ring laser: study of its characteristics as a rotation sensor

A semiconductor ring laser (SRL) with a radiation wavelength of 1540 nm and a fibre ring cavity is developed and studied in several main lasing regimes. An SRL design based on a semiconductor optical travelling-wave amplifier and a ring cavity, composed of a single-mode polarisation-maintaining fibre, is considered. The SRL is studied in the regime of a rotation speed sensor, in which the frequency shift of counterpropagating waves in the SRL is proportional to its rotation speed. The minimum rotation speed that can be detected using the SRL under consideration depends on the cavity length; in our experiment it turned to be 1deg s-1. The changes in the threshold current, emission spectrum, and fundamental radiation wavelength upon closing and opening the SRL ring cavity and with a change in its radius are also investigated.

Error-Free 10-Gb/s All-Optical Switching Based on a Bidirectional SRL With Miniaturized Retro-Reflector Cavity

The retro-reflector structure of semiconductor ring laser (RR-SRL) has been further miniaturized by redesigning its total-internal-reflection parabolic mirrors. The SRL device with new RR structures is fabricated successfully and identical output properties have been observed from the clockwise and the counterclockwise directions. The static stably switching and locking regions of both the main-mode and first sidemode have been measured, which are ~ 5 and ~ 6 GHz, respectively. The fast switching speed of ~ 40 ps and error-free 10-Gb/s all-optical switching is achieved, which confirms the potential of these SRLs for high-speed all-optical digital applications.

Optical injection in semiconductor ring lasers

We theoretically investigate optical injection in semiconductor ring lasers and disclose several dynamical regimes. Through numerical simulations and bifurcation continuation, two separate parameter regions in which two different injection-locked solutions coexist are revealed, in addition to a region in which a frequency-locked limit cycle coexists with an injection-locked solution. Finally, an antiphase chaotic regime without the involvement of any carrier dynamics is revealed. Parallels are drawn with the onset of chaos in the periodically forced Duffing oscillator.

Multistable and excitable behavior in semiconductor ring lasers with broken Z2-symmetry

We study the bifurcation scenario and the evolution of the counter-propagating modes in a semiconductor ring laser when their symmetry is broken. We show how a two-dimensional asymptotic model for this asymmetric ring laser can be used to interpret and predict regions of multistability and excitability in the laser. The theoretical predictions and insights in these different dynamical regimes of the asymmetric semiconductor ring laser are confirmed and further explored experimentally in a semiconductor ring laser set-up that allows to controllably break the Z2-symmetry of the laser.

Noise transfer functions of mode-locked semiconductor laser

The noise behavior of mode-locked semiconductor ring laser, including timing jitter, and pulse energy fluctuation are investigated using the notion of a noise transfer function. Numerical simulation predicts that semiconductor mode-locked lasers have very complex structure in the transfer function which is confirmed experimentally by corresponding noise measurements.

All-optical functions based on semiconductor ring lasers (Invited Paper)

Semiconductor ring laser (SRL) has been shown to possess robust bistability between its two possible directions, i.e., clockwise (cw) and counter-clockwise (ccw) lasing, routinely demonstrating directional extinction ratio (DER) of > 25 dB. In this paper, experimental schemes and results using the SRL as a universal photonic digital element to form all-optical logic, memory, and signal processing circuits are summarized. It is demonstrated that the SRL can be used for both combinatorial and sequential logic functions, and as all-optical regeneration devices. Furthermore, it is shown that a SRL logic circuit can be all-optically reconfigured to perform different all-optical logic functions.

Modulation Bandwidth Enhancement in Optical Injection-Locked Semiconductor Ring Laser

The modulation bandwidth of a optical injection-locked (OIL) master-slave configuration using a semiconductor ring laser (SRL) as the slave laser is investigated. The modulation bandwidth depends on the detuning frequency, input optical power into the slave SRL, and the bias current to the SRL in the master-slave configuration. Modulation bandwidth of >40 GHz has been achieved when modulating the master laser, in contrast to the 15-GHz modulation bandwidth of the free-running SRL. The unidirectional operation of the SRL as a slave laser allows monolithic integration of such OIL scheme as it produces little feedback to the master laser.

Excitability in optical systems close to [formula omitted]-symmetry

We report theoretically and experimentally on excitability in semiconductor ring lasers in order to reveal a mechanism of excitability, general for systems close to Z 2 -symmetry. The global shapes of the invariant manifolds of a saddle in the vicinity of a homoclinic loop determine the origin of excitability and the features of the excitable pulses. We show how to experimentally make a semiconductor ring laser excitable by breaking the Z 2 -symmetry in a controlled way. The experiments confirm the theoretical predictions.

Noise spectra of a semiconductor ring laser in the bidirectional regime

Fluctuations in ring lasers (RLs) are widely studied e.g. because they determine the performance [1] of Ring Laser Gyroscope. Spontaneous emission [2] yields fluctuations of the emitted intensity and frequency in Semiconductor ring lasers (SRLs). SRLs show different operating regimes [3] depending on the pump current, ranging from bidirectional-continuous wave, to bidirectional with alternate oscillations, to a bistable regime. In this contribution, we calculate the noise spectra as function of pump current and complex backscattering coefficients when the SRL is biased in the bidirectional-continuous wave regime. We consider a two mode rate equation model in the Langevin formulation. Within linear approximation, perturbations concerning the total intensity and carrier inversion dynamics decouple from the energy distribution processes between the two modes. This fact permitted a full analytic analysis, well confirmed by numerical simulations of the complete non linear system. We reinterpreted the two counterpropagating lasing modes in terms of mode-intensity sum (I-Spectrum) and difference (D-Spectrum). The I-Spectrum reflects the energy exchange between the total field and the medium and behaves similarly to the standard relative intensity noise for single-mode semiconductor lasers (see Fig. 1 a). The I-Spectrum is characterized by a resonance that corresponds to relaxation oscillations.

Characterization of All-Optical Regeneration Potentials of a Bistable Semiconductor Ring Laser

All-optical pulse reamplification, reshaping (2R), and retiming (3R) using a monolithic bistable semiconductor ring laser (SRL) is demonstrated for the first time. The regeneration performance of the SRL is characterized with an all-optical settable switching threshold, achieving significant increases in the extinction ratio (ER) of the output pulse for input ER as low as 1 dB. For retiming, a rectangular retiming window generated by a clean clock signal is used to eliminate the timing jitter in the input pulse. For input pulse with peak-to-peak timing jitter as high as ~ 12% of the bit period, the timing jitter in the retimed output pulse is reduced to < 2% of the bit period. The pulsewidth of the final regenerated data can be controlled by changing the width of the retiming window. The SRL is, therefore, shown to have a hard digital performance in both amplitude and time domain suitable for all-optical 3R.

AlGaInAs multi-quantum wells ring laser with optical coupling waveguides

Based on InAlGaAs multi-quantum wells epitaxy structure for Fabry-Pero laser diode, a multi-quantum wells semiconductor ring laser is realized using ICP dry etching process and polyimide planarization process. The laser is generated in a semiconductor resonator ring and is output by two coupled integrated bus waveguides. The ring diameter is 700 µm and the width of the waveguide is 3 µm. The output optical power-current (P-I) characteristic and the wavelength spectra of the ring laser are measured using a fiber coupled to the cleaved facet of the bus waveguide. The threshold current of the device is 120 mA and the wavelength is 1602 nm at an injected current of 160 mA. In addition, the operation mode for the laser in the resonator ring is roughly discussed based on the P-I characteristic plot.

Asymptotic approach to the analysis of mode-hopping in semiconductor ring lasers

We investigate the directional mode-hopping in semiconductor ring lasers in the limit of small noise intensity. We show how only long time scales are involved in the hopping process. In such limit, the initial stochastic rate equations can be reduced to an auxiliary Hamiltonian system, and the dependence of the hopping on the laser parameters can be investigated. The predictions made from the reduced model agree well with the results obtained by simulating the full rate-equation system.

Theoretical Analysis of a New Technique for Inertial Rotation Sensing Using a Semiconductor Ring Laser

We introduce a new technique for the measurement of inertial rotations using a semiconductor ring laser. Inertial rotation introduces a frequency deviation of the optical frequency of the two counterpropagating waves in the laser cavity, whereas mode coupling causes frequency attraction (frequency pushing) and finally locking at low rotation rates, washing out the small Sagnac frequency difference to be measured. Here we propose to measure inertial rotation whitin the so-called locking band using the phase/amplitude dependence on detuning found for the oscillating modes under the gain line. The dephasing accumulated by the two counterpropagating waves unbalances the fields' amplitudes within the locking region. We analytically derive the responsivity function quantifying the two-mode power unbalance versus rotation rate, by means of a two-mode rate equations model. Noise performance of a possible rotations sensor are also discussed by calculating the noise equivalent rotation rate.