Monolithic Semiconductor Ring Laser Research Articles

Single-mode Bragg ring laser diodes.

We have designed and fabricated a monolithic semiconductor ring laser based on a Bragg waveguide structure. Through careful control of the waveguiding, we have overcome the inherent "leaky" nature of this waveguide mode and demonstrated a ring laser lasing in the Bragg mode. Best behavior was obtained from lasers with a diameter of 400 µm, where they exhibited output power ${ \gt }{1}\;{\rm mW}$>1mW, in continuous wave (CW) operation. A tangent waveguide provided access to the ring cavity using two ports through evanescent coupling. To meet the stringent waveguiding requirements imposed by the Bragg structure, a two-step etching process, consisting of a shallow-etched coupler and a deep-etched bend section of the ring, was developed in order to reduce the bend and scattering losses. The laser showed a threshold current density of ${\sim}{2.2}\;{{\rm kA/cm}^2}$∼2.2kA/cm2 in CW operation with single longitudinal mode operation with a signal-to-noise ratio of 30 dBm obtained at 1.5 ${I_{\rm th}}$Ith. Broadband phase-matching of $\chi ^{(2)}$χ(2) nonlinearity is observed, offering self-pumped parametric C-band conversion ${ \gt }{40}\;{\rm nm}$>40nm with efficiency of ${142}\% \;{{\rm W}^{ - 1}}\;{{\rm cm}^{ - 2}}$142%W-1cm-2.

All-Optical Toggle Flip-Flop Based on Monolithic Semiconductor Ring Laser

A novel monolithic all-optical flip-flop of the toggle type with two complementary outputs is demonstrated based on a semiconductor ring laser (SRL), where the intrinsic directional bistability of the SRL device is combined with the saturable absorption effect that takes place in the reverse-biased input waveguides. Toggle flip-flop (TFF) operation is experimentally demonstrated using optical trigger toggle pulses of 500 ps duration. The achieved bit-rate of 500 Mb/s is the highest reported so far for all-optical TFFs. The operational speed is limited by the carrier recovery time of the saturable absorbers; however, the proposed technology has potential for multi-gigabits per second operation.

Monolithic All-Optical Set-Reset Flip-Flop Operating at 10 Gb/s

A monolithic semiconductor ring laser is operated as an all-optical set-reset flip-flop triggered by external optical pulses. Bit-error-rate measurements of set-reset switchings under the injection of a pseudo-random-bit-sequence have been performed, showing reliable operation up to 10 Gb/s.

The frequency noise and spectral linewidth in semiconductor ring lasers

Numerical analyses for power spectral density of frequency noise (FN) and spectral linewidth in monolithic semiconductor ring laser (SRL) operating in the bistable unidirectional regime are performed in this paper. The Langevin noise sources for electric field and carrier density fluctuations are also taken into account in the frequency-domain theoretical model. The influences of several important physical parameters on the FN properties and laser linewidth are clearly demonstrated, including the injection current, linewidth enhancement factor and the particular backscattering coefficient. Due to the particular backscattering in SRLs, the calculated linewidths are relatively higher than that from the conventional Henry formula. The laser linewidth shows an exponential relationship with the backscattering strength.

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.

Linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers

We report linewidth properties of active-passive coupled monolithic InGaAs semiconductor ring lasers with various length of passive waveguide. It is experimentally confirmed that the linewidth of the lasers is proportional to the square of the ratio of the length of active part of the cavity over the total length of the cavity. The lasers are applicable for communication and sensing devices, which need the narrow linewidth.

All-optical Digital Logic Gates using Bistable Semiconductor Ring Lasers

This paper demonstrates all-optical digital logic gates using bistable monolithic semiconductor ring lasers (SRLs). With the flexible multi-functional experimental setup, we have experimentally demonstrated the application of SRLs to realize logic functions including: AND, OR, NOR, XOR and all-optical non-retum-to-zero (NRZ) to retum-to-zero (RZ) format conversion. Using bistable semiconductor ring lasers to fulfil all-optical logic functions have the advantages of high output extinction ratio, low switching energy, integration and the potential logic unit in the future.

Linewidth, autocorrelation, and cross-correlation measurements of counterpropagating modes in GaAs-AlGaAs semiconductor ring lasers

We perform an experimental investigation of the linear autocorrelation and cross correlation properties of the two counterpropagating modes of a monolithic semiconductor ring laser (SRL). The ring laser can operate in a bidirectional regime where the two modes are active at the same time and have equal power, and also in a unidirectional regime where one of the modes is suppressed. Autocorrelation measurements are carried out using an unbalanced optical fiber Mach-Zehnder interferometer that allows us to determine the linewidth of each mode of the ring laser. Cross correlation measurements are performed using a modified optical fiber interferometric setup where the two counterpropagating modes are directly superposed on a photodetector. This measurement reveals that in the bidirectional regime the two modes are phase-locked and allows us to evaluate the degree of their correlation.

Mode locking in large monolithic semiconductor ring lasers

A computer simulation based on a travelling-wave, distributed model of the ring laser has been sued to investigate the regimes of operation of passive mode-locked ring semiconductor lasers 2-3mm in circumference. Different configurations of intracavity saturable absorber have been employed and their relative merits determined. Experimental devices with similar configurations have been fabricated, and shown to exhibit mode-locked operation under similar conditions to those predicted by simulation.

Passive mode locking of monolithic semiconductor ring lasers at 86 GHz

We report the development of monolithic passively mode-locked semiconductor ring lasers. These direct-waveguide-coupled lasers with a ring radius of 150 μm emit a continuous train of 1.3 ps transform-limited lasing pulses at 86 GHz repetition rate with a peak power of 10 mW/pulse at the laser output facet. We also observe, under certain conditions, the presence of a second pulse in the ring cavity doubling the pulse repetition rate to 172 GHz.

A 1.54- mu m monolithic semiconductor ring laser: CW and mode-locked operation

The authors have fabricated a monolithic semiconductor ring laser with a diameter of 3.0 mm. A straight tangent waveguide provides two output ports through evanescent coupling. The laser, which exhibits a threshold current of 157 mA, operates in a single longitudinal mode with a linewidth of 900 kHz at a wavelength of 1.54 mu m. The device has been actively mode-locked at the fundamental resonance frequency of 9.0 GHz, yielding 27-ps pulses with a time-bandwidth product of 0.47. Differences in the characteristics of the pulses emitted from the two output ports indicate counterpropagating pulse trains, which because of the mode-locking scheme must collide in the modulated gain section. >