Pascal Landais

Phase Correlation and Linewidth Reduction of 40 GHz Self-Pulsation in Distributed Bragg Reflector Semiconductor Lasers

In this paper, self-pulsation (SP) in a distributed Bragg reflector (DBR) semiconductor laser without a saturable absorber is experimentally and theoretically investigated. Detailed experimental characterizations of the SP DBR laser are reported in the optical and radio-frequency domains. Phase correlation between the longitudinal modes selected by the DBR mirror has been experimentally demonstrated. A theoretical model based on coupled rate equations for three modes has been developed to study the time evolution of phases and amplitudes of the modes. The carrier density modulation, resulting from the beating between adjacent longitudinal modes generates four-wave mixing (FWM) and is responsible for mutual injection locking, leading to passive mode-locking. The calculated power spectral density of the frequency noise derived from the model is in agreement with experimental results and proves that the phases of the longitudinal modes are identically correlated through the FWM process in this type of SP lasers

InP-Based Integrated Optical Pulse Shaper: Demonstration of Chirp Compensation

We demonstrate dispersion compensation for highly chirped optical pulses with an ultracompact optical pulse shaper. The device integrates a 20-channel arrayed waveguide grating with 20 phase modulators and 20 semiconductor optical amplifiers on a single chip of 6 × 6 mm2. The chip has been realized in an InP-based generic photonic foundry process, which enables a significant reduction in design effort using standardized building blocks.

Sub-picosecond pulse generation by 40-GHz passively mode-locked quantum-dash 1-mm-long Fabry-Pérot laser diode

Optical pulses at a repetition rate of 39.8 GHz have been observed in a dc-biased passively mode-locked quantum-dash Fabry-Pérot laser diode. The pulses generated by this diode are studied in the temporal and spectral domains using a second harmonic generation frequency-resolved optical gating system. By using a tunable band-pass filter, it is observed that the pulse width decreases as the number of lasing modes selected by the filter increases. Furthermore, by controlling the phase difference of the modes using a 450 m-long single mode fibre, a passive compression of the pulses is obtained. A minimum pulse width of 720 fs has been measured with this type of mode-locked Fabry-Pérot laser.

Timing-jitter, optical, and mode-beating linewidths analysis on subpicosecond optical pulses generated by a quantum-dash passively mode-locked semiconductor laser

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.

Spectral amplitude and phase measurement of a 40 GHz free-running quantum-dash modelocked laser diode

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 diodes intracavity dispersion on the applied current.

Analysis of a narrowband terahertz signal generated by a unitravelling carrier photodiode coupled with a dual-mode semiconductor Fabry-Pérot laser

A narrowband terahertz signal generated by a unitravelling 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. 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.

Investigation on the origin of terahertz waves generated by dc-biased multimode semiconductor lasers at room temperature

A technique to measure a terahertz wave generated by spectrum tailored Fabry–Perot 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.

HOSA: hybrid optical switch architecture for data center networks

Optical interconnect is a fundamental requisite to realize Internet-scale data centers due to capabilities and benefits of optical devices. Optical interconnects are energy efficient and offer massive bandwidth support. State of the art interconnects can be divided into three types based on the optical technology used: 1) micro-electromechanical system (MEMS) optical cross connects (OXCs), 2) arrayed waveguide grating routers (AWGRs) and 3) semiconductor optical amplifiers (SOAs). MEMS switches are based on mature technology, have low insertion loss and cross-talk, and are data rate independent. They are also the most scalable and the cheapest class of optical switches. However, the reconfiguration time of these switches is in the order of tens of milliseconds. An AWGR switch is a passive device and works in conjunction with tunable wavelength converters (TWCs) or tunable lasers (TLs) while an SOA works as a gate element that manipulates light and also compensates for losses that occur during transmission of optical signals. AWGR and SOA switches have switching time in the range of nanoseconds but they are expensive as compared to MEMS. In this paper, we propose a novel all optical core interconnection scheme that utilizes potentials of both slow and fast optical switches. The core idea is to route traffic through slow or fast optical switch so that minimum end-to-end latency is achieved. Our architecture employs a single stage topology which allows our design to both incrementally scaled up (in capacity) and scaled out (in the number of racks) without requiring major re-cabling and network reconfiguration. We evaluate performance of the system using simulation and investigate a trade-off between cost and power consumption by comparing it with other well known interconnects. Our technique demonstrates a considerable improvement in power consumption and low latency with high throughput is achieved.

Terahertz wave generation from a dc-biased multimode laser

We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Perot 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 298K. The main two modes are separated by 3nm at 1550nm with a side-mode-suppression ratio of 25dB. Using a frequency resolved optical gating, evidence of mode beating at 373GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690GHz.

Linewidth Enhancement Factor of Semiconductor Lasers: Results from Round-Robin Measurements in COST 288

Round-robin measurements on the linewidth enhancement factor are carried out within several laboratories participating to EU COST 288 action. The alpha-factor is measured by applying up to 7 different techniques. The obtained results are compared.