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Wavelength tunability of an all-optical clock recovery operation based on a quantum-dash mode-locked Fabry-Perot laser diode is experimentally investigated. Synchronization of the device to the injection of 40-Gb/s nonreturn-to-zero (NRZ) incoming data is assessed by analyzing both the carrier-to-noise ratio and the linewidth of the 40-GHz beat-tones measured at the mode-locked laser output. Under optical injection, beat-tone linewidths below 10 Hz are measured. Recovered clock pulses featuring a width of 1.6 ps are obtained irrespective of the wavelength detuning between the laser spectra and the optical carrier of the incoming data stream.

We propose a simple potentially integrable configuration for expanding a wavelength tunable comb by cascading gain switched Fabry-Pe´rot lasers. A 10GHz spaced comb, exhibiting 13 coherent low-linewidth tones within a 3 dB window, and tunable over 20 nm is demonstrated.

A passively mode locked extended cavity quantum well ring laser at 1.58 µm with repetition rate of 2.5 GHz in the form of a photonic integrated circuit is presented. The device is realized using InP based active-passive integration technology. The 33mm long cavity contains gain, saturable absorption and passive waveguide sections as well as a phase shifter sections to enable fine tuning of the spectral position of the lasing modes. Passive mode-locked operation and with wavelength tuning of the laser modes are experimentally demonstrated. This laser is the lowest reported repetition rate for a monolithically integrated ring laser.

Using monolithic integration technology we have designed and fabricated tunable lasers in the 1.5 µm region with a demonstrated tuning range of 60 nm and single mode operation. This performance is achieved using intracavity tunable Mach-Zehnder interferometers that use voltage controlled phase modulators. In this paper we will discuss design considerations and advantages of such tunable lasers.

A tunable laser operating from 2015 – 2040 nm realized as a monolithic InP photonic integrated circuit is presented. The laser uses an intracavity tuning mechanism based on parallel asymmetric Mach-Zehnder interferometers with electro-refractive modulators. The device is intended for a single line gas spectroscopy and was designed and fabricated using a generic integration technology platform.

Spectral phase control of optical pulses is often required to generate short pulses, and an important application of a pulse shaper is spectral chirp/dispersion (pre-) compensation. In this paper, we present the pulse shaping/compression capability of a monolithically integrated optical pulse shaper. Chip fabrication has been carried out in a standardized generic photonic integration platform which is available in the framework of European FP7 project EuroPIC. A key capability of this platform is the active-passive integration scheme which allows direct integration of active components such as semiconductor optical amplifiers (SOAs) with passive elements such as arrayed waveguide gratings (AWGs) and phase modulators (PMs) on a single photonic chip.

Modal gain characterization of mid-infrared semiconductor optical amplifiers intended for an active-passive integration platform is presented. Measured gain profiles reveal the peak values at around 2.07μm and 3dB bandwidth up to 27nm.

In this paper, we present the experimental investigation of the switching-on and passive mode-locking times of a Fabry-Perot quantum dash laser diode. Their values are 30ns and 8ns respectively. These times are measured in order to study the phenomenon of mode-locking in this device and its potential application for packet switching networks.

We experimentally investigate the locking/unlocking dynamics of a mode-locked QDash laser diode for packet-based clock-recovery applications. Results show 20 ns locking times for the passively and externally synchronized mode-locking mechanisms.

A wavelength tunable optical comb is generated based on the gain-switching of an externally seeded Fabry-Pérot laser diode. The comb consists of about eight clearly resolved 10 GHz coherent sidebands within 3 dB spectral envelope peak and is tunable over the entire C-band (1530 to 1570 nm). The optical linewidth of the individual comb tones is measured to be lower than 100 kHz, and the RIN of the individually filtered comb tones (-120 dB/Hz) is shown to be comparable to the entire unfiltered comb (-135 dB/Hz). Besides, expansion of the tunable gain switched comb is achieved with the aid of an optical phase modulator, resulting in near doubling of the number of comb tones.

A novel and cost effective long reach PON downlink scenario is proposed employing a multi-carrier transmitter and pilot tone aided direct detection at the receiver. Error free performance with QPSK and 50km transmission is presented.

Discrete Mode Laser Diodes (DMLDs) present an economic approach with a focus on high volume manufacturability of single mode lasers using a single step fabrication process. We report on a DMLD designed for operation in the 1550 nm window with high Side Mode Suppression Ratio (SMSR) over a wide temperature tuning range of -20 °C < T < 95 °C. Direct modulation rates as high as 10 Gbit/s are demonstrated at both 1550 nm and 1310 nm. Transmission experiments were also carried out over single mode fibre at both wavelengths. Using dispersion pre-compensation transmission from 0 to 60 km is demonstrated at 1550 nm with a maximum power penalty measured at 60 km of 3.6 dB.

The authors present a multi-carrier transmitter based on a gain switched laser employed in a next generation access network. The simple, robust and cost efficient direct modulation based comb generation technique offers closely spaced coherent channels. Each of the channels is imposed with 2.5 Gbaud data using QPSK and 16-QAM formats. The authors also present a performance comparison between the commonly used coherent detection scheme and a novel receiver architecture based on a pilot tone aided direct detection scheme. The simplified low cost receiver, enabled by the phase correlated optical comb tones, eases the requirement for an expensive local oscillator (tunable laser), reduces the need for digital signal processing and also greatly enhances the phase noise tolerance of the system.

Linewidth narrowing of the radio frequency beat-tones and the optical-modes is experimentally investigated in a ∼40 GHz quantum-dash mode-locked laser diode subject to optical injection of 10 GHz pulses. In comparison to the 75 kHz linewidth exhibited by the beat-tones in passive mode-locking conditions, a remarkable reduction to less than 8 Hz is achieved when the laser is under optical injection. From this beat-tone signal, an integrated root-mean-square timing jitter of 64 fs is calculated. In addition, a quadratic profile of the optical linewidth with the wavelength is observed in active locking, reaching a minimum of 1.7 MHz for the longitudinal modes around 1530 nm and progressively increasing to 37.4 MHz for modes at 1525 nm.

In this paper, a detection scheme based on four wave mixing in a semiconductor optical amplifier (SOA) is used to measure the frequency and bandwidth of the optical terahertz beat-tone signal generated by a passively mode locked semiconductor laser. Two signals from external cavity lasers are injected into an SOA, which acts as a local oscillator at their detuning frequency. The device under test is a passively mode locked laser with a beat-tone frequency in the terahertz spectrum. Its optical signal is injected in the SOA, which also acts as a frequency mixer. The frequency and linewidth of the terahertz signal are then measured by retrieving the intermediate frequency detected by a low bandwidth photodiode and an electrical spectrum analyser.

We present a linear self-referenced measurement of the spectral amplitude and phase of a free-running quantum-dash modelocked laser diode. The technique is suitable for measuring optical signals with repetition rates up to 100 GHz. In contrast to many other linear techniques it requires no external electronic clock synchronized to the signal under test. Using this method we are able to compensate for the intracavity dispersion of the diode to demonstrate 500 fs pulses at a repetition rate of 39.8 GHz. We also use the technique to characterize the dependence of the diode’s intracavity dispersion on the applied current.

Beat-tones at 40-GHz from a QDash-ML laser under 10 to 160 Gb/s optical injection are analyzed. A FWHM linewidth less than 8 Hz is obtained regardless of the rate of injected data stream.

Optical frequency comb sources (OFCS) have recently attracted a lot of interest due to wide ranging applications such as optical arbitrary waveform generation [1], photonic microwave signal generation [2], optical signal processing [3] and multi-carrier spectrally efficient transmission techniques with the sub-channel spacing equal to the symbol rate of each sub-channel [4]. OFCS with good spectral flatness, stability and low linewidth are highly desirable for such applications. One of the conventional approaches used in realizing a comb source is based on mode-locked semiconductor and fibre lasers [5]. Although this technique can generate multi-carrier signals spanning over a wide bandwidth, it inherently suffers from cavity complexity and does not offer the free spectral range (FSR) tunability since the comb line spacing is fixed by the cavity length of the laser. Moreover, the optical linewidth of the individual comb lines can be relatively large (several MHz) preventing higher order (or low baud rate) advanced modulation formats to be imposed. Another technique that has been reported entails the use of a single, cascaded or dual drive Mach-Zehnder modulators (MZM) to generate the phase correlated optical frequency comb [6]. Although this technique provides a relatively flat optical comb, the large insertion loss of the modulator coupled with the modulation efficiency can prove prohibitive. The extra optical component also adds to the cost and complexity of the transmitter, rendering this technique unsuitable for short reach applications.

Synchronization of a 40 GHz quantum-dash mode-locked Fabry-Perot laser diode with optically injected pulse streams is experimentally studied by analyzing the linewidth of the associated 40 GHz beat-tones. Injected signals consist of trains of 1.6 ps pulses at various repetition rates, spanning from 10 to 160 Gb/s of encoded or not with pseudo-random on-off key data sequence. Data injections at the fundamental bit-rate (40 Gb/s), harmonic at 80 and 160 Gb/s and sub-harmonic at 10 and 20 Gb/s are used to synchronize the mode-locked laser. The response is a stable 40 GHz clock pulse train featuring a width of 1.8 ps. Moreover, the 40 GHz beat-tones associated to the recovered clock pulses exhibit a full-width at half maximum smaller than 8 Hz regardless of the injected data rate. It is observed that frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses by the injection of data signals at 10 and 20 Gb/s. Similarly, synchronization of the quantum-dash laser with pulse streams at 80 and 160 Gb/s is sustained in spite of negligible components at and below 40 GHz are injected in these two data rates.

There is a vast interest in multi-wavelength light sources which can find applications in optical communications [1], and photonic generation of millimetre and terahertz signals [2]. For such applications highly coherent and stable optical comb sources, with uniform power distribution among frequency components are desirable. Conventional comb sources are mainly based on mode-locked semiconductor and fibre lasers. Both are penalized by fixed free spectral range (FSR), and complexity of the epitaxial growth in the first case, and stability issues due to long cavity lengths in the latter. Another technique, which offers the advantage of tuneable FSR, entails the use of electro-optic modulators. This however, requires the use of expensive dual drive modulators [3], or a series of cascaded modulators [4], in order to achieve a broad and relatively flat comb.

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.

Performance improvement of a directly modulated 10 Gb/s OFDM system by optical injection of monolithically integrated lasers is shown experimentally over differing fibre lengths. The modulation and optical injection is performed using monolithically integrated Discrete Mode lasers. It is shown that optical injection with this device reduces third order inter-modulation distortion by up to 10dB and this results in an improvement in system performance from above a forward error correction BER threshold of 1 × 10(-3) to significantly below it.

Quantum-dash modelocked laser diodes (QD-MLLD) are capable of producing short optical pulses at extremely high repetition rates. As such they are ideally suited to many telecommunications applications [1]. In this paper we present a linear self-referenced measurement of the spectral amplitude and phase of a free-running quantum-dash modelocked laser diode. The technique is suitable for measuring optical signals with repetition rates up to 100 GHz. In contrast to many other linear techniques it requires no external electronic clock synchronized to the signal under test. Using this method we show that compensating for the intra-cavity dispersion of the diode results in 500 fs pulses at a repetition rate of 39.8 GHz. The measurement technique is based on the stepped-heterodyne method presented in Ref. [2]. The signal under test is mixed with a CW narrowband optical local oscillator (LO) and the combined signal detected by a high-speed photodiode, mixed with an electronic LO, and then recorded on a real-time oscilloscope. When the optical LO is placed between two adjacent signal modes the resultant beat signals can be analysed to determine not only the power of each of the signal modes, but also the phase difference between them [2]. Stepping the optical LO across all signal modes allows for a complete measurement of the spectral amplitude and phase of the signal.

An all-optical approach based on nonlinear interactions inside a semiconductor optical amplifier for measuring the THz beat-tone of a passively mode-locked laser is proposed. This novel approach can be applied to beat-tones in the range from GHz to few THz.

Experimental measurements on a quantum dash mode-locked Fabry-Perot laser are presented. Its potential for clock recovery at 40 Gb/s in an all-optical 3R regeneration with an NRZ-to-RZ format conversion and wavelength offset of 23 nm is demonstrated.

A narrowband terahertz signal generated by a uni-travelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry-Perot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. All components involved in this experiment operate at room temperature. The terahertz signal at a frequency of 372 GHz is recorded, and the linewidth is 17 MHz. The linewidth and the tunability of the emitted terahertz wave are analyzed, as a function of the laser bias.

An experimental analysis of the timing jitter associated with sub-picosecond pulses produced from a quantum dash passively mode-locked Fabry-Perot laser is produced. Moreover, application as an all-optical clock recovery function for a 40Gb/s data rates with non-return-to-zero (NRZ) modulation format is demonstrated using this laser.

A bulk semiconductor optical amplifier (SOA) utilizing a multi-contact biasing method is characterized as a function of the bias current supplied to each section Firstly, amplified spontaneous emission spectra and characteristic light-current profiles are analyzed. Single-pass gain and noise figure of the SOA are then assessed by injecting a continuous wave input beam. Finally, the amplification of a 10 Gb/s (215-1) long pseudo random bit sequence signal is analysed. The obtained results, particularly at a bias condition of 90mA-50mA-10mA, reveal the potential of this device as a low noise figure in-line amplifier.

Timing-jitter measurements in optically generated subpicosecond pulses by a quantum-dash passively mode-locked semiconductor laser as a function of the bias current are reported. All the measurements are retrieved from a second-harmonic-generation frequency-resolved optical gating system. A decreasing trend in the pulse width and the associated timing jitter is found with the bias current. Additionally, the optical and mode-beating linewidths are analyzed in terms of both the mode wavelength and the bias current. From our results, we can conclude that once the optical modes are phase locked, the optical linewidth associated to every individual longitudinal mode of the device under test does not have a significant impact on the mode-beating signal on neither the pulse width nor its respective timing jitter.

Wave-mixing at 370-GHz in a SOA and FP semiconductor laser is investigated by using a FROG-system. A comparison of the optical time-fluctuations measured at their output stresses the importance of a resonant cavity in THz-signals generation from semiconductor optical devices.

International audience; A narrowband terahertz signal generated by a unitravelling carrier photodiode (UTC-PD) interfaced with a dual-mode Fabry–Pérot laser diode is demonstrated. A beat tone corresponding to the free spectral range is generated on the UTC-PD, and radiated by a transverse-electromagnetic-horn antenna. A terahertz signal at a frequency of 372 GHz, featuring a linewidth of 17 MHz is recorded by a subharmonic mixer coupled to an electrical spectrum analyzer. All components involved in this experiment operate at room temperature. The linewidth and the frequency of the emitted terahertz wave are analyzed, along with their dependency on dc-bias conditions applied to laser diode.

An experimental analysis on the quality of 40-GHz radio-frequency signals generated by various passively mode-locked semiconductor lasers is addressed. The analysis is performed considering the frequency linewidth of 40-GHz optically generated signals and the number of longitudinal modes selected by the cavity of each laser under study. Four of these devices are multi-quantum wells InAlGaAs Fabry–Perot lasers. They have been engineered to exhibit a specific number of longitudinal modes: 4, 5, 10, and 22 modes, respectively. Another device under test is a bulk distributed Bragg reflector laser exhibiting 3 lasing modes. The last device under study is a quantum-dash Fabry–Perot laser characterized by 40 lasing modes. From our experimental results it appears that, regardless the nature of the device cavity and active media, the strength of the passively mode-locked mechanism might be enhanced with the number of longitudinal modes oscillating into the laser cavity, allowing a reduction in the frequency linewidth.

Generation of sub-picosecond pulses by a dc-biased passively mode-locked Fabry-Perot laser is demonstrated. By using a tunable band-pass filter, it is observed that the width of the generated pulses decreases in direct proportion to the optical modes emitted by the laser. Furthermore, performing a passive compression by a piece of single mode fiber, we demonstrate the generation of 720 fs pulses by this type of mode-locked Fabry-Perot laser.

A technique to measure a terahertz wave generated by spectrum tailored Fabry–Pérot lasers (FP) is assessed. A dc-biased and 25 °C temperature controlled FP is probed by a continuous wave signal, tuned at 20 nm away from its lasing modes. With a 0.02 nm resolution optical spectrum analyzer (OSA), the terahertz generated signal frequency is measured from the interval between the probe and its side-band modulations. The terahertz waves emitted by these FPs are measured at 370±5 GHz and at 1.157±0.005 THz, respectively, within a precision set by our OSA. The origin of the terahertz wave is due to passive mode-locked through intracavity four-wave-mixing processes.

Generation of narrow microwave signals produced from the mode beating of a DBR laser is presented. The application of this process to the cw-THz wave generation is also demonstrated using a slotted FP laser.

We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Pérot based device with shallow grooves implemented on its p-side to engineer the longitudinal mode spectrum. The laser is dc-biased and temperature controlled at 298 K. The main two modes are separated by 3 nm at 1550 nm with a side-mode-suppression ratio of 25 dB. Using a frequency resolved optical gating, evidence of mode beating at 373 GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690 GHz.

In this paper, Cassidy's method is presented and is applied to measure the linewidth enhancement factor (LEF) of a 370 GHz self-pulsating Fabry-Perot laser. The importance of the LEF is addressed, the method is detailed, and the device under test is presented. It exhibits a self-modulation at 370 GHz even though it is DC biased. The measured LEFs vary according to the wavelength, values of 4 have been measured at threshold current, which is typical in the case of multi-quantum well lasers. In this paper we propose to present measurement of the linewidth enhancement factor (LEF) in semiconductor laser based, 370 GHz source generator. First we explain the origin of LEF in semiconductor material, then we present several techniques to measure it. We present a computational simulation using modelled ASE spectra, and in part 4, we detail our device and experimental set-up and provide some results. The linewidth enhancement factor (LEF) or alpha parameter is a distinguishing feature of semiconductor devices. Semiconductor devices generally have a larger linewidth than other solid state lasers. This broadened linewidth leads to effects such as mode instability, filementation in broad area devices and frequency chirping under modulation. This last effect is of particular interest, especially in the field of optical communications. It can be suppressed if the LEF is reduced. Therefore in the design of semiconductor lasers or semiconductor amplifiers (SOA), a number of factors have to be taken into consideration, but one of the most important of these is the linewidth enhancement factor. For instance, when the gain of an SOA is affected by the injection of a pulsed source, refractive index changes caused by changes in carrier density will lead to an instantaneous variation of the frequency. This effect is exacerbated as the gain is saturated.

In this paper we present some characterizations of passively mode-locked semiconductor lasers. These lasers are multimode and they exhibit a modulation of their output power even though they are DC-biased. The modulation frequency corresponds to their free-spectral range. We demonstrate their potential: for generation of ultra-fast modulation for THz wave generation at room temperature without any direct modulations applied, in the radio frequency range they synchronise their modulation to the bit-rate of an incoming signal used for clock extraction. Therefore these devices can be used for all-optical clock recovery.

Characterizations of passively mode-locked semiconductor lasers will be presented in following paper. These lasers are able to operate in multimode regime and to exhibit a modulation of output power even though they are DC-biased. A frequency of the modulation corresponds to their free-spectral range associated with optical longitudinal modes. Some potential applications for devices of that type will be disclosed: in THz frequency range for terahertz wave generation at room temperature without any direct modulations applied, in the radio frequency range ability to synchronise their modulation to the bit-rate of an incoming signal makes them suitable for all-optical clock extraction.

Multimode semiconductor lasers under certain DC bias conditions generate electromagnetic waves from the beating between the longitudinal lasing modes. The frequency of those waves is directly related to the free spectral range of the involved modes. Our recent experimental work is carried out on slotted Fabry-Perot lasers with mode separation of 330 GHz. The devices are at room temperature biased at 3 times the threshold current. Using a bolometer coupled to an FT-IR interferometer we are able to observe radiation at 660 GHz, in the terahertz range.

Although self pulsating (SP) lasers are DC biased, they feature a modulation of the output power. For the results presented in this paper, the SP frequency corresponds to the frequency spacing between longitudinal modes or its second harmonic. The performances of both a 40 GHz self pulsating distributed Bragg reflector laser and of a 660 GHz slotted laser are presented. For the first laser, the radio frequency (RF) signal was analysed on electrical spectrum analyser and its linewidth was smaller that the sum of the main optical modes, proving a passive modelocking of the mode phases. For the slotted laser, a bolometer interfaced to a FT IR spectrometer is used for the terahertz (THz) detection. A signal 10 times larger than the noise level was measured with this set up. Both lasers have demonstrated to be an easy solution to produce RF or THz signal generator.

A compact and fabrication-tolerant integrated remotely tunable optical delay line is proposed for millimeter-wave beam steering and is fabricated in an InP generic foundry. The proposed delay line is based on a spectrally cyclic-arrayed waveguide grating feedback loop. Its major features include the tolerant architecture with reduced chip size, and bi-directional operation with simplified remote tuning. Moreover, its cyclic feature guarantees further cascaded operations either for 2D radio beam steering or for high-resolution delay generation. The experimental results show less than 6.5-dB insertion loss of the integrated delay line. Five different delays from 0 to 71.6 ps are generated with less than 0.67-ps delay errors.

A mode-locked extended cavity quantum well ring laser at 1.58 μm with a repetition rate of 2.5 GHz in the form of a photonic integrated circuit is presented. The device is realized using InP-based active-passive integration technology. The 33 mm long cavity contains gain, saturable absorption, and passive waveguide sections as well as phase shifter sections to enable fine tuning of the spectral position of the lasing modes. Passive and hybrid mode-locked operation, along with the wavelength tuning of the laser modes, are experimentally demonstrated. In the passive mode-locking regime, a beat signal at the fundamental round trip frequency with a 3 dB bandwidth of 6.1 kHz is produced on a fast photo diode.

An all-optical heterodyne approach based on a room-temperature controlled semiconductor optical amplifier (SOA) for measuring the frequency and linewidth of the terahertz beat-tone signal from a passively mode-locked laser is proposed. Under the injection of two external cavity lasers, the SOA acts as a local oscillator at their detuning frequency and also as an optical frequency mixer whose inputs are the self-modulated spectrum of the device under test and the two laser beams. Frequency and linewidth of the intermediate frequency signal (and therefore, the beat-tone signal) are resolved by using a photodiode and an electrical spectrum analyzer.

Mode-locked fiber and solid state lasers have played an essential role in several scientific and technological developments. The integration of mode-locked lasers on chips could enable their use in a wide range of applications. The advancement of semiconductor mode-locked laser diodes has been going on for several decades, but has recently seen the development of novel devices based on generic InP and III-V-on-silicon photonic integration platforms. These photonic integration platforms enable the use of standardized components and low-loss waveguides within the laser cavity, allowing for the design of advanced extended cavities. In this manuscript we give a review of these novel devices and compare their performance.

Linewidth narrowing of the radio frequency beat-tones and the optical-modes is experimentally investigated in a ∼40 GHz quantum-dash mode-locked laser diode subject to optical injection of 10 GHz pulses. In comparison to the 75 kHz linewidth exhibited by the beat-tones in passive mode-locking conditions, a remarkable reduction to less than 8 Hz is achieved when the laser is under optical injection. From this beat-tone signal, an integrated root-mean-square timing jitter of 64 fs is calculated. In addition, a quadratic profile of the optical linewidth with the wavelength is observed in active locking, reaching a minimum of 1:7 MHz for the longitudinal modes around 1530 nm and progressively increasing to 37:4 MHz for modes at 1525 nm.

We report first demonstration of quantum dash mode-locked laser based open-loop optical clock recovery of 160 Gb/s RZ-OOK after 52 km transmission with 102 fs timing jitter 40 GHz clock and 2 dB BER penalty.