Muhammad Irfan Memon

All-Optical Response of Semiconductor Ring Laser to Dual-Optical Injections

The all-optical response of a semiconductor ring laser (SRL) to two optical injections is characterized. Once the lasing direction is locked by one optical injection, the SRL direction of operation can be switched by another optical injection into the counterpropagating direction. The switching process manifests a typical bistable hysteresis loop, with its width and switching thresholds variable by the first injection power. Extremely sharp transition has been measured which confirms the potential of the SRL for all-optical regeneration applications.

Generation and Modulation of Tunable mm-Wave Optical Signals Using Semiconductor Ring Laser

Optical injection locking and cavity enhanced four-wave mixing in semiconductor ring lasers have been used to generate data modulated millimeter (mm)-wave optical signals. The scheme is shown to have multigigahertz (multi-GHz) modulation bandwidth. The 4-Gb/s data is transferred directly from an intensity modulated optical signal onto an mm-wave optical signal with the mm-wave frequency tunable in steps of 62.5 GHz and with flexible radio-frequency modulation formats over the optical carrier. Bit-error-rate and eye-diagram measurements confirm excellent signal quality.

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.

Theoretical and Experimental Studies on Bistability in Semiconductor Ring Lasers With Two Optical Injections

Bistability in a semiconductor ring laser with two external optical injections is studied theoretically, numerically, and experimentally. Two optical injections are added to the two counterpropagating modes in the laser respectively. We first predicted theoretically that, with one of them acting as a static holding beam, the intensities of both modes will form a hysteresis loop as a function of the intensity of the second injection due to nonlinear mode competition. The bistability and the hysteresis characteristics such as its width depend heavily on the intensity of the holding beam. Average switching power will increase as the intensity of the holding beam is increased, accompanied by shrinking width of the hysteresis loop. Numerical simulations and experiment are then carried out to verify the theoretical prediction, and the hysteresis loops at different holding beam strength are plotted. The numerical results together with the qualitative experimental results demonstrate what has been predicted by the theoretical analysis, and a good agreement is obtained. The interaction between the two injections demonstrates potentials for application in all-optical digital signal processing.

Optically Triggered Monostable and Bistable Flip-Flop Operation of a Monolithic Semiconductor Ring Laser

A monolithic semiconductor ring laser (SRL) is demonstrated to operate as an optical monostable and bistable that can be triggered by an optical pulse, showing potential for all-optical 2R regeneration and all-optical Flip-Flop applications.

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.

All-optical digital logic XOR gate using bistable semiconductor ring lasers

All-optical XOR gate is an important function widely used in optical signal switching, data recognition and optical signal processing. Semiconductor ring laser (SRL) as a digital photonic device is attracting more and more attention for all-optical switching [1], signal regeneration, optical memory [2], and as a potential candidate for all-optical logic devices. In this paper, we propose and experimentally demonstrate a novel all-optical XOR gate using bistable SRLs. This is the first report to our knowledge that all-optical logic XOR gate is realized using the monolithically integrated bistable semiconductor ring lasers. In this initial experiment, we focus on demonstrating the novel principle of operation and logic XOR function that can be realized with a single device configuration as a basic logic unit. In future, these will be transferred to high data speed using the same operation and concept introduced here in high speed SRL devices.

Direct modulation of bistable semiconductor ring lasers

Semiconductor ring lasers (SRL) have received growing interest because of their potential as compact and coherent light source. Although intensive effort has been invested into the bistability of SRL under continuous wave operation, very little research has been conducted on the direct modulation of SRL[1]. We report the direct modulation of SRL at bit rates up to 1.5Gb/s. The experimental results show that the DC bias current is the key factor for direct modulation.

Cavity-enhanced four-wave-mixing in an integrated semiconductor ring laser for all-optical digital logic operations

All-optical digital logic AND and XOR gates based-on cavity-enhanced four-wave-mixing in an integrated semiconductor ring laser are demonstrated at 2.5Gb/s. Error free operation with ER >10dB is achieved.

Converting 4Gb/s IM data onto tunable 60GHz RF optical carrier using four wave-mixing in semiconductor ring laser

RF signals for Radio over fibre systems (RoF) can be generated optically by mode-locking (ML) in semiconductor lasers [1]. External optical injection at non-lasing cavity modes of semiconductor ring laser (SRL) generates strong cavity enhanced four-wave mixing(FWM)[2], that result in generation of optical waves modulated by high purity RF frequencies as a result of the mode-locking by way of such FWM. This makes the SRL very attractive for the generation of RF or millimetre wave modulated optical signals that may be used in RoF systems. We report, for the first time, the generation and wideband modulation of RF optical signals using a combination of optical injection locking (OIL) and FWM in the SRL. We demonstrate that ordinary intensity modulated optical data up to 4Gb/s can be converted onto RoF carrier, with the RF frequency widely tunable up to hundreds of GHz, with excellent data quality. We further demonstrate that this scheme is versatile in generating various modulation formats by simple filtering.