Frank Smyth

A Novel Two-Section Tunable Discrete Mode Fabry-PÉrot Laser Exhibiting Nanosecond Wavelength Switching

A novel widely tunable laser diode is proposed and demonstrated. Mode selection occurs by etching perturbing slots into the laser ridge. A two-section device is realized with different slot patterns in each section allowing Vernier tuning. The laser operates at 1.3 mum and achieves a maximum output power of 10 mW. A discontinuous tuning range of 30 nm was achieved with a side mode suppression greater than 30 dB. Wavelength switching times of approximately 1.5 ns between a number of wavelength channels separated by 7 nm have been demonstrated.

Effects of phase noise of monolithic tunable laser on coherent communication systems

We investigate the effects of different phase noise processes of SGDBR laser on coherent systems. The SGDBR device operated well with QPSK modulation at 5 Gbaud, while the performance of 16-QAM was significantly degraded due to excess noise. The white FM noise mainly defines the ultimate performance of coherent reception, but the low frequency excess noise can potentially degrade the performance of systems that employ 16-QAM format at 5 Gbaud.

Design, Characterization, and Applications of Index-Patterned Fabry–Pérot Lasers

The design and measured performance characteristics of a range of index-patterned diode laser sources are presented. These devices incorporate slotted regions etched into the laser ridge waveguide, which are formed in the same fabrication step as the ridge, thus avoiding the requirement for complex lithography and regrowth steps. We first demonstrate that the index profile of single and multimode devices can be obtained directly from an inverse problem solution based on a perturbative calculation of the threshold gain of the longitudinal modes of the cavity. Measurements of temperature stability, linewidth, and modulation bandwidth of single-mode devices obtained in this way are presented. It is then shown that the design of multimode devices including two-color and pulsed mode-locked devices designed to support a discrete comb of modes is also possible. We finally demonstrate a tunable source based on a multisection design defined using etched features. This device is shown to have wide tunability with narrow linewidth modes and fast wavelength switching speed.

Fast Wavelength Switching Lasers Using Two-Section Slotted Fabry–PÉrot Structures

Fast wavelength switching of a two-section slotted Fabry-Perot laser structure is presented. The slot design enables operation at five discrete wavelength channels spaced by 10 nm by tuning one section of the device. These wavelengths operate with sidemode suppression ratio in excess of 35 dB, and switching times between these channels of approximately 1 ns are demonstrated

Cross-Channel Interference Due to Wavelength Drift of Tunable Lasers in DWDM Networks

The authors present an investigation of the wavelength stability of a tunable laser (TL) transmitter and its impact on the performance of a 2.5-Gb/s dense wavelength-division-multiplexed (DWDM) system. Performance of a DWDM system, employing such a TL, is characterized by examining the cross-channel interference caused by this drift when the channel spacing is set to 12.5 and 25 GHz. Results obtained show that the wavelength drift affects the system performance by introducing an error floor in the case of 12.5-GHz spacing. This error floor can be mitigated by increasing the blanking time of the TL during the channel transition, in order to reduce the wavelength drift

Software reconfigurable highly flexible gain switched optical frequency comb source.

The authors present the performance and noise properties of a software reconfigurable, FSR and wavelength tunable gain switched optical frequency comb source. This source, based on the external injection of a temperature tuned Fabry-Pérot laser diode, offers quasi-continuous wavelength tunability over the C-band (30nm) and FSR tunability ranging from 6 to 14GHz. The results achieved demonstrate the excellent spectral quality of the comb tones (RIN ~-130dB/Hz and low phase noise of 300kHz) and its outstanding stability (with fluctuations of the individual comb tones of less than 0.5dB in power and 5pm in wavelength, characterized over 24hours) highlighting its suitability for employment in next generation flexible optical transmission networks.

All-Analogue Real-Time Broadband Filter Bank Multicarrier Optical Communications System

This paper studies the key aspects of an optical link which transmits a broadband microwave filter bank multicarrier (FBMC) signal. The study is presented in the context of creating an all-analogue real-time multigigabit orthogonal frequency division multiplexing electro-optical transceiver for short range and high-capacity data center networks. Passive microwave filters are used to perform the pulse shaping of the bit streams, allowing an orthogonal transmission without the necessity of digital signal processing (DSP). Accordingly, a cyclic prefix that would cause a reduction in the net data rate is not required. An experiment consisting of three orthogonally spaced 2.7 Gbaud quadrature phase shift keyed subchannels demonstrates that the spectral efficiency of traditional DSP-less subcarrier multiplexed links can be potentially doubled. A sensitivity of -29.5 dBm is achieved in a 1-km link.

Performance improvement of 10Gb/s direct modulation OFDM by optical injection using monolithically integrated discrete mode lasers

Performance improvement of a directly modulated 10Gb/s OFDM system by optical injection is shown experimentally over differing fibre lengths. The modulation and optical injection is performed using monolithically integrated Discrete Mode lasers.

On Bit and Power Loading for OFDM Over SI-POF

A new methodology is proposed for the modeling of practical uncoded bit and power loading schemes for OFDM, based on the assumption of a uniform transmit power spectrum. The accuracy of this technique, both in terms of predicted maximum data rate and occupied bandwidth, is demonstrated analytically for an Intensity Modulated/Direct Detected (IM/DD) system over Step Index Plastic Optical Fibers (SI-POF). It is shown that both this new methodology and the well known water pouring theorem accurately predict the maximum achievable data rate in practical uncoded systems; however, it is also demonstrated that the new methodology is a better predictor of the bandwidth occupied by the transmit signal, thus providing an important analytical tool for system designers. The analysis presented is also experimentally verified using an IM/DD optical system employing a directly modulated Resonant Cavity Light Emitting Diode (RCLED) light source and several lengths of 1 mm SI-POF.

Dynamic Linewidth Measurement Method via an Optical Quadrature Front End

This letter describes a dynamic linewidth characterization method using an optical quadrature front end. The phase noise of the laser is recorded using a real-time oscilloscope in the time domain and the linewidth of the laser can be estimated statistically offline. The major advantage of this technique compared with conventional linewidth measurements in the frequency domain, is that this method enables the dynamic phase noise characterization which is increasingly important for fast wavelength tunable and switched networks employing advanced modulation formats. The dynamic linewidth of an sampled grating distributed Bragg reflector (SG-DBR) laser is characterized by using this method.