Photonic integration technologies allow for fabrication of on-chip laser sources and systems that provide functionalities for applications beyond telecommunications, such as sensing, healthcare, millimeter and terahertz generation and quantum technologies. New applications impose a different range of demands regarding performance of such semiconductor laser sources. All characteristics of the optical output signal, output power, wavelength tuning range and mechanism, long and short term stability as well as the energy footprint have to be considered. Monolithic integration technologies on indium phosphide substrates natively support an on-chip combination of active and passive functions that enable development of a new class semiconductor lasers with complex cavities. Such lasers can be tailored to achieve optimum performance with respect to a specific application. A number of single frequency, tunable laser sources in form of photonic integrated circuits for applications in gas sensing, optical coherence tomography, millimeter and terahertz generation and quantum applications have been developed at Eindhoven University of Technology. Ongoing research and development activities that address challenges related to addressable wavelength bands, wavelength tuning and stability imposed by specific applications are enabled by mature generic monolithic technology on indium phosphide. In parallel to those efforts, extensive research works towards expansion of accessible wavelength bands. Tunable and mode-locked leaser geometries and challenges related to unique performance expectations are presented.
Step-wise tuning of a monolithically integrated widely tunable continuous wave semiconductor ring laser is investigated, for application in Fourier domain optical coherence tomography (OCT). The device operates around 1530 nm and was realized on an InP generic photonic integration technology platform. The laser is tuned using voltage-controlled electrooptic phase modulators with <100 μW thermal dissipation, which reduces time dependent thermal effects in the filter. Here we present a calibration method with progressively finer wavelength control steps and discuss the limits of wavelength accuracy and repeatability with respect to OCT requirements. It is shown that thermal effects due to light absorption in the phase modulators have a negligible effect on the tuning of the laser for six out of seven phase modulators. To bring the thermal dissipation of the seventh phase modulator in line with the others a design change is proposed. Wavelength switching dynamics are investigated with a numerical model of the laser. A simulation based on this model shows that it takes around 50 ns from the wavelength switching instant to establish a single mode operation with side mode suppression ratio of 30 dB.
RF frequency downconverters are of key importance in communication satellites. Classically, this is implemented using an electronic mixer. In this paper we explore the use of photonic technology to realize the same functionality. The potential advantages of such an approach compared to the classical microwave solutions are that it is lighter weight, has lower power consumption and can be made smaller if photonic technology is used. An additional advantage is the fact that the optical local oscillator (LO) reference can easily be transported over longer distances than the equivalent LO signal in the microwave domain due to the large bandwidth and low loss and dispersion of optical fiber. Another big advantage is that one can envision the use of short pulse trains as the LO – starting off from a sinusoidal RF reference – in order to exploit subsampling. Subsampling avoids the need for high frequency LO references, which is especially valuable if a downconversion over several 10s of GHz is required. In this paper we present the operation principle of such a photonic frequency downconverter and describe the performance of the developed micro-photonic building blocks required for this functionality. These micro-photonic building blocks are implemented on a III-V semiconductor-on-silicon photonic platform. The components include a micro-photonic hybridly modelocked laser, a 30GHz electroabsorption modulator and an intermediate frequency (1.5GHz) photodetector.
In this paper an overview is presented of results obtained with mode-locked semiconductor laser systems that are monolithically integrated using a standardized photonic integration platform based on InP. The laser systems are operating around 1550nm. In this technology platform the basic components that form the laser circuits such as amplifiers, passive waveguides and filters, as well as the semiconductor processing are standardized. Several of the possibilities that such a standardized technology offer are demonstrated by a number of examples of realized devices such as low repetition rate mode-locked lasers, a stabilized comb system and a wide frequency comb source.
In this paper a generic monolithic photonic integration technology platform and tunable laser devices for gas sensing applications at 2 μm will be presented. The basic set of long wavelength optical functions which is fundamental for a generic photonic integration approach is realized using planar, but-joint, active-passive integration on indium phosphide substrate with active components based on strained InGaAs quantum wells. Using this limited set of basic building blocks a novel geometry, widely tunable laser source was designed and fabricated within the first long wavelength multiproject wafer run. The fabricated laser operates around 2027 nm, covers a record tuning range of 31 nm and is successfully employed in absorption measurements of carbon dioxide. These results demonstrate a fully functional long wavelength photonic integrated circuit that operates at these wavelengths. Moreover, the process steps and material system used for the long wavelength technology are almost identical to the ones which are used in the technology process at 1.5μm which makes it straightforward and hassle-free to transfer to the photonic foundries with existing fabrication lines. The changes from the 1550 nm technology and the trade-offs made in the building block design and layer stack will be discussed.
In this paper we report on the progress in the development of modelocked ring lasers that are integrated on a single chip in the InP/InGaAsP material system. With the current optical integration technology it is possible to integrate quantum well optical amplifiers, phase modulators and passive optical components such as waveguides, splitters and spectral filters as standardized building blocks on a single chip. Using such standardized components a number of passively modelocked ring laser devices have been realized in a standardized fabrication process. Results from a few of these devices are presented here. We have observed a record width of the frequency comb from a modelocked quantum well ring laser operating at a 20 GHz repetition rate. The optical coherent comb is centered around 1542 nm and has a 3 dB bandwidth of 11.5 nm. A minimum pulse width of 900 fs was observed. A second device that is highlighted is a modelocked ring laser with a 2.5 GHz repetition rate. Its 33 mm long cavity is fitted onto a chip of 2.2x1.9 mm2. One of the goals of this work is to make such designs available in device libraries for use in more complex integrated optical systems using standardized technology platforms.
In this paper we present recent results obtained in the area of monolithically integrated modelocked semiconductor laser systems using generic InP based integration platform technology operating around 1550nm. Standardized components defined in this technology platform can be used to design and realize short pulse lasers and optical pulse shapers. This makes that these devices can be realized on wafers that can contain many other devices. In the area of short pulse lasers we report design studies based on measured optical amplifier performance data. This work has the ultimate goal to establish a library of widely applicable short pulse laser designs. Such lasers can include components for e.g. wavelength control. An important boundary condition on the laser design is that the laser can be located anywhere on the InP chip. In the area of pulse shaping we report on a 20 channel monolithic pulse shaper capable of phase and amplitude control in each channel. Special attention is given to the calibration of the phase modulator and amplifier settings. Pulse compression and manipulation of pulse generated from modelocked semiconductor lasers is demonstrated using a 40 GHz quantum dash modelocked laser.
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.