[Show abstract][Hide abstract] ABSTRACT: We report on extensive studies of the frequency and intensity noise spec.tra in discrete-mode AlGaInAs multiple QW lasers at 1.55 µm wavelengths. Our final goal is to understand the mechanism of 1/f flicker noise build up that leads to linewidth broadening at high currents.
European Semiconductor Laser Workshop - ESLW 2015, Madrid, Spain; 09/2015
[Show abstract][Hide abstract] ABSTRACT: We show, for the first time, dense WDM (8×20 Gbit/s) transmission at 2 μm enabled by advanced modulation formats (4-ASK Fast-OFDM) and the development of key components, including a new arrayed waveguide grating (AWGr) at 2 μm. The AWGr shows -12.8±1.78 dB of excess loss with an 18-dB extinction ratio and a thermal tunability of 0.108 nm/°C.
[Show abstract][Hide abstract] ABSTRACT: Optical injection locking is used to increase the modulation bandwidth and suppress chirp in a single-channel, single-polarization discrete multi-tone bit-loading-optimized transmitter. Transmission through a hollow-core photonic bandgap fiber with negligible signal degradation and distortion is demonstrated.
[Show abstract][Hide abstract] ABSTRACT: We show for the first time 100 Gbit/s total capacity at 2 µm waveband, using 4 × 9.3 Gbit/s 4-ASK Fast-OFDM direct modulation and 4 × 15.7 Gbit/s NRZ-OOK external modulation, spanning a 36.3 nm wide wavelength range. WDM transmission was successfully demonstrated over 1.15 km of low-loss hollow core photonic bandgap fiber (HC-PBGF) and over 1 km of solid core fiber (SCF). We conclude that the OSNR penalty associated with the SCF is minimal, while a ~1-2 dB penalty was observed after the HC-PBGF probably due to mode coupling to higher-order modes.
[Show abstract][Hide abstract] ABSTRACT: The ability to generate high-speed on-off-keyed telecommunication signals by directly modulating a semiconductor laser's drive current was one of the most exciting prospective applications of the nascent field of laser technology throughout the 1960s. Three decades of progress led to the commercialization of 2.5 Gbit s(-1)-per-channel submarine fibre optic systems that drove the growth of the internet as a global phenomenon. However, the detrimental frequency chirp associated with direct modulation forced industry to use external electro-optic modulators to deliver the next generation of on-off-keyed 10 Gbit s(-1) systems and is absolutely prohibitive for today's (>)100 Gbit s(-1) coherent systems, which use complex modulation formats (for example, quadrature amplitude modulation). Here we use optical injection locking of directly modulated semiconductor lasers to generate complex modulation format signals showing distinct advantages over current and other currently researched solutions.
[Show abstract][Hide abstract] ABSTRACT: Progress on advanced active and passive photonic components that are required for high-speed optical communications over hollow-core photonic bandgap fiber at wavelengths around 2 mu m is described in this paper. Single-frequency lasers capable of operating at 10 Gb/s and covering a wide spectral range are realized. A comparison is made between waveguide and surface normal photodiodes with the latter showing good sensitivity up to 15 Gb/s. Passive waveguides, 90 degrees optical hybrids, and arrayed waveguide grating with 100-GHz channel spacing are demonstrated on a large spot-size waveguide platform. Finally, a strong electro-optic effect using the quantum confined Stark effect in strain-balanced multiple quantum wells is demonstrated and used in a Mach-Zehnder modulator capable of operating at 10 Gb/s.
[Show abstract][Hide abstract] ABSTRACT: An all-optical switching mechanism via optical injection of an InAs/GaAs quantum dot laser is presented. Relative state suppression in excess of 40 dB is achieved, and experimental switching times of the order of a few hundred picoseconds are demonstrated.
[Show abstract][Hide abstract] ABSTRACT: The dynamic characteristics of a discrete mode laser diode fabricated in the InGaAs/InP multiple quantum well material system and emitting single mode at λ ~ 2.0 μm are reported. Results are presented on the electro-optical bandwidth, direct modulation and gain switched performance.
[Show abstract][Hide abstract] ABSTRACT: We report on high-energy nanosecond-pulsed fiber master oscillator power amplifier (MOPA) systems seeded by semiconductor laser diodes at 2 μm incorporating arbitrary pulse-shaping capabilities. Two MOPA systems, one based on direct diode modulation and the second using additional electro-optic modulator (EOM) based shaping, are investigated, with up to 0.5 mJ (25 kHz) and 1.0 mJ (12.5 kHz) pulse energies achieved, respectively, for 100 ns pulses with user-defined pulse shapes. Our results indicate that further energy scaling with shaped output pulses is primarily limited by the maximum pulse peak power available from the seed laser diode and the dynamic range offered by the first generation of EOMs at 2 μm.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate compact multi-carrier transmitters based on 2 types of monolithically integrated lasers. A 2-section discrete mode laser and a passive feedback laser are gain switched resulting in 5-15GHz FSR tunable combs
[Show abstract][Hide abstract] ABSTRACT: We discuss a technique that allows for flexible synthesis of square QAM constellations via the direct modulation of tunable, injection locked, semiconductor lasers. The approach uses optical coherent multiplexing and we demonstrate full C-band tuning.
[Show abstract][Hide abstract] ABSTRACT: The first demonstration of a hollow core photonic bandgap fiber (HC-PBGF) suitable for high-rate data transmission in the 2 µm waveband is presented. The fiber has a record low loss for this wavelength region (4.5 dB/km at 1980 nm) and a >150 nm wide surface-mode-free transmission window at the center of the bandgap. Detailed analysis of the optical modes and their propagation along the fiber, carried out using a time-of-flight technique in conjunction with spatially and spectrally resolved (S<sup>2</sup>) imaging, provides clear evidence that the HC-PBGF can be operated as quasi-single mode even though it supports up to four mode groups. Through the use of a custom built Thulium doped fiber amplifier with gain bandwidth closely matched to the fiber's low loss window, error-free 8 Gbit/s transmission in an optically amplified data channel at 2008 nm over 290 m of 19 cell HC-PBGF is reported.
[Show abstract][Hide abstract] ABSTRACT: We report on the generation of picosecond pulses at 2 μm directly from a gain-switched discrete-mode diode laser and their amplification in a multistage thulium-doped fiber amplifier chain. The system is capable of operating at repetition rates in the range of 2 MHz-1.5 GHz without change of configuration, delivering high-quality 33 ps pulses with up to 3.5 μJ energy and 100 kW peak power, as well as up to 18 W of average power. These results represent a major technological advance and a 1 order of magnitude increase in peak power and pulse energy compared to existing picosecond sources at 2 μm.
[Show abstract][Hide abstract] ABSTRACT: Directly modulated lasers provide simple, and cost efficient, optical transmitters for use in optical networks. However, chirp limits the bit rate distance product achievable in such systems, with transmission distances limited to around 10 km when operating at 10 Gbit/s in the 1550 nm window [1, 2], and thereby limiting their suitability as optical transmitters in next generation access networks operating at 10 Gbit/s, where transmission distances of 20 km and beyond will be required. External modulation of lasers is currently the most common method to modulate a light-wave signal in optical communication systems. Although this technique provides high speed and stable data modulation, the large insertion losses and the polarization dependence of the modulator can prove to be cumbersome. The extra optical component also adds to the cost and complexity of the transmitter, rendering this technique unsuitable for cost-sensitive applications.
The European Conference on Lasers and Electro-Optics; 05/2013
[Show abstract][Hide abstract] ABSTRACT: High power fibre laser sources in the 2 μm wavelength region with picosecond-scale pulse durations have attractive applications such as materials processing, eye-safe radar and nonlinear frequency conversion to mid-infrared wavelengths. Current implementations are typically based on the amplification of picosecond pulses obtained from a mode-locked oscillator, and pulse energies of several hundred nano-Joule and peak powers of the order of 10 kW have been achieved [1, 2].
The European Conference on Lasers and Electro-Optics; 05/2013
[Show abstract][Hide abstract] ABSTRACT: The most cost-effective solution for modulating data onto an optical
carrier is via direct modulation of a semiconductor laser.
Unfortunately, this approach suffers from high chirp. The chirp can be
reduced by reducing the on/off modulation contrast ratio (i.e. by
keeping the signaling laser well above threshold when generating both
logical `0' and `1' bits), but the low contrast ratio itself compromises
performance. Other techniques can better suppress chirp, e,g., based on
selfinjection or optical injection locking of the directly-modulated
laser (slave) to another laser (master) that emits CW light. However,
this technique although very efficient at eliminating chirp, also
requires the slave laser be operated well above threshold. We show
however that the issue of the limited on/off modulation contrast can be
addressed in this instance by subtraction of the carrier using a
component of the master beam and an interferometric arrangement.
Proceedings of SPIE - The International Society for Optical Engineering 05/2013; DOI:10.1117/12.2017230 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An edge-coupled high-speed photodiode based on strained InGaAs quantum wells for detection at 2000nm is demonstrated. The fabricated device shows a leakage current as low as 120nA at -3V bias voltage and a responsivity of around 0.3A/W at 2000nm. The high-speed butterfly packaging of the device is presented which shows a 3dB bandwidth of more than 10GHz. The device shows similar high-speed performance at 1550nm.
[Show abstract][Hide abstract] ABSTRACT: BPSK modulation tunable over 30 nm is obtained, highlighting the practicality of a recently-demonstrated new scheme for direct synthesis of phase and amplitude modulated signals. Experiments are carried out at 12 and 24 Gbit/s.
OptoElectronics and Communications Conference held jointly with 2013 International Conference on Photonics in Switching (OECC/PS), 2013 18th; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Our recently-developed QAM synthesis using direct modulation of injection locked semiconductor lasers is analyzed in terms of the optical and RF power requirements and compared with IQ modulation and multiple binary modulator schemes.
Optical Communication (ECOC 2013), 39th European Conference and Exhibition on; 01/2013
[Show abstract][Hide abstract] ABSTRACT: A new scheme for direct and tunable (30nm shown here) QAM synthesis from binary RF data streams is demonstrated with up to 48Gbit/s QPSK, including propagation over 75km SMF-28. Preliminary 16QAM (60Gbit/s) results are shown.
Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference (OFC/NFOEC), 2013; 01/2013