Mohammed Al-Mumin

All-optical clock recovery from RZ-format data by using a two-section gain-coupled DFB laser

High-speed all-optical clock recovery using a two-section gain-coupled distributed feedback laser is demonstrated operating in the coherent and the incoherent modes. It is found that the coherent mode has a much better performance compared with the incoherent mode. The performance of the coherent clock recovery scheme at 12 and 40 Gb/s, including wavelength and polarization insensitivity, timing jitter, and phase noise; power penalty; sensitivity; dynamic range; locking bandwidth; detuning range of the injection wavelength; and lockup time are described in detail. A comparison between the performances of the two modes of operation is also presented.

All-optical clock recovery for both RZ and NRZ data

An all-optical clock recovery scheme for both the nonreturn-to-zero and the return-to-zero formats has been proposed and successfully demonstrated. Clock extraction, enhancement, and clock-to-data suppression were realized by a semiconductor optical amplifier and a fiber Bragg grating. Clock recovery was achieved using a two-section gain-coupled distributed-feedback laser. The scheme has large dynamic range of input power for both formats.

Optical generation of microwave/millimeter-wave signals using two-section gain-coupled DFB lasers

We report the first analysis and experimental demonstration of tunable microwave/millimeter-wave signal generation in two-section gain-coupled distributed-feedback (DFB) lasers. Continuous tuning from 20 to 64 GHz was directly observed and characterized both in the electrical and optical domain. The mechanism of microwave generation in two-section gain-coupled DFB lasers is different from that of two-section index-coupled DFB lasers previously reported. As a result, gain coupling can lead to simultaneous large modulation indexes and high frequencies in two-section DFB lasers.

All-optical enhancement of clock and clock-to-data suppression ratio of NRZ data

A scheme for all-optical enhancement of clock and clock-to-data suppression ratio of nonreturn-to-zero (NRZ) data based on self-phase modulation is proposed and demonstrated. More than 3-dB clock enhancement and 11-dB clock-to-data suppression ratio enhancement has been realized by a semiconductor optical amplifier (SOA) and fiber Bragg grating (FBG) in reflection. Clock enhancement of more than 6 dB is possible using a FBG in transmission. Using this technique, all-optical clock recovery from NRZ data has been demonstrated.

Self-consistent Simulation of self-pulsating two-section gain-coupled DFB lasers

The role of cavity conditions in the dynamics of two-section gain-coupled distributed feedback (DFB) lasers is investigated using a self-consistent model. Self-sustained pulsation (SSP) exists only for devices with strongly coupled DFB gratings. As the coupling strength increases, multiple SSP regimes are developed. The SSP frequency tuning range increases as cavity length decreases. The frequency and modulation index predicted by the model agree well with experimental results. The facet condition of each section is found to affect SSP differently because of the asymmetrical behavior of the modes responsible for SSP.

Optical generation and self subharmonic injection locking of tunable 10-100 GHz microwave/millimeter signals

Summary form only given.Optical techniques for generation of RF signals are becoming increasingly important in applications requiring very high frequencies and narrow linewidth microwave/millimeter signals such as fiber-radio systems for broadband wireless. Two-section distributed-feedback (DFB) lasers exhibiting high frequency self-pulsation signals up to 80 GHz has been reported. The frequency of microwave/millimeter signals from the two-section DFB lasers is controlled via the bias current of the two section. We report on a continuous RF tuning from 10 to a 100 GHz measured electronically by optical downconversion. These microwave/millimeter wave signals have a free running linewidth in the order of a few MHz, unacceptable for many applications. We achieved stabilization and linewidth-reduction by using self subharmonic locking technique, different from ordinary subharmonic injection locking. In ordinary subharmonic locking, frequency multiplication of the subharmonic is achieved by over modulating a master laser with a high-power subharmonic signal. In self subharmonic locking, frequency multiplication of subharmonic is achieved via intracavity nonlinearity. The self subharmonically locked signals have linewidths comparable to that of the injecting subharmonic signal.

Millimeter-wave fiber optic links using two-section gain-coupled DFB lasers

The potential use of two-section gain-coupled distributed feedback lasers as a source for the generation and distribution of millimeter-wave signals for wireless applications is demonstrated. First we report on the dependence of the tuning range on the device structure and the use of two injection techniques to reduce the linewidth of the millimeter-wave signals generated at 40GHz. The first technique is self sub-harmonic injection locking using a 5GHz signal and the second is direct side-band injection locking using a 20GHz to lock a 40GHz signal. The phase noise is measured and the jitter is calculated. Secondly the fiber-based network architecture of a wireless system based on the two-section DFB laser is proposed. The aim of the networks is to expand the bandwidth for each base station, maximize sharing of the mm-wave source and fiber, reduce the number of active devices at the base and the mobile unit, and expand the role of photonics in the network design. The system we propose is WDM-SCM network architecture.

High frequency intensity oscillations in the multi-section gain-coupled DFB lasers

Summary form only given. Intensity oscillations in multi-section semiconductor laser diodes have been investigated for applications such as all-optical clock recovery and microwave fiber-optic links. Self-pulsation of laser intensity has been observed in both bulk and quantum-well laser diodes as well as in both Febry-Perot and distributed feedback (DFB) type laser diodes. We report here the first observation of widely tunable self intensity oscillations in multi-section gain-coupled DFB lasers.

Assessment of amplitude and phase modulation performance of high-frequency subcarrier optical communication systems based on heterodyning of sideband injection-locked semiconductor lasers

This paper present a theoretical assessment of the performance of subcarrier optical communication systems using sideband-injection locking and heterodyning. In this scheme, a master laser is strongly intensity modulated. The modulation sidebands of the master laser are injected into two slave lasers for the production of the subcarrier. One of the slave lasers is directly modulated to produce the amplitude and phase modulation on the subcarrier. First, using the Van der Pol equations for coupled oscillators, the small-signal response of the output power and phase of injection-locked semiconductor lasers was derived. Then the performances of the subcarrier optical communication systems based on amplitude modulation and phase modulation were assessed in terms of optimum power injection ratio and phase detuning between the master and slave lasers. For phase modulation, the performance was limited for two cases: lowest AM to PM conversion and highest PM modulation efficiency. The distortion and noise were calculated assuming coherent detection for phase modulation and envelope detection for amplitude modulation. Finally the signal to noise ratio is calculated and plotted.