JePPIX has integrated design, production and test for quality, reproducible, high-performance PICs. We show how manufacturing-grade process design kits created with in-line metrology are configured for test automation and accelerated time-to-market.
An InP integrated widely tunable laser is investigated for the use as a swept source in optical coherence tomography (OCT) applications. The laser is realized on a generic integration technology platform. It consists of a gain medium and a bandpass filter with 3 cascaded asymmetric Mach-Zehnder interferometers. The additional presence of a balanced Mach-Zehnder modulator as variable out-coupler is instrumental to increase the laser tuning range to 90 nm between 1480 and 1570 nm but can add to additional filtering effects in the laser cavity. In this work, we propose an optimized control strategy for the wavelength calibration of this widely tunable laser source, for a stepwise wavelength scan that is suitable for OCT. The aim is to obtain a wavelength scan with at least 1000 of 10 GHz equally spaced optical frequencies, having uniform power around 100 µW and 1 GHz accuracy. The control strategy is based on the a-priori knowledge of the coarse and the medium filter tuning and on an optimization of the fine filter tuning and the longitudinal cavity mode tuning that can be frequently updated. In this way, the calibration of the laser system can be kept sufficiently accurate and stability of the scan quality can be ensured. With this strategy, 10 GHz spaced optical lasing frequencies are obtained over 30 nm making the calibrated laser suitable as an OCT source
Modern IoT and 5G applications are driving the growth of Internet traffic and impose stringent requirements to datacenter operators for keeping pace with the increasing bandwidth and low-latency demands. At the same time, datacenters suffer from increasing number of interconnections dictating the deployment of novel architectures and high-radix switches. The ratification of 400 GbE standard is driving the market of optical transceivers nevertheless, a technology upgrade will be soon necessary to meet the tremendous traffic growth. In this paper, we present the development of 800 Gb/s and 1Tb/s optical transceivers migrating to 100 Gbaud per lane and employing wafer-scale bonding of InP membranes and InP-DHBT electronics as well as advanced co-packaging schemes. The InP membrane platform is also exploited for the development of novel ultra-fast optical space switches based on a modular architecture design for scaling to large number of I/O ports.
Publisher’s Note: This paper, originally published on 1 April 2020, was replaced with a corrected/revised version on 27 July 2020. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
We present results on the investigation of the dynamics of wavelength switching in a monolithically integrated widely tunable semiconductor ring laser for application in swept source optical coherence tomography. In this application wavelength switching within several tens of nanoseconds is desirable to reduce motion blur artefacts during imaging. The device under test is realized in an InGaAsP/InP platform, operates around 1530 nm wavelength and has been shown to have a tuning range over 50 nm. Both measurements and simulations of the wavelength switching behavior of the laser are presented. Tuning is achieved using voltage controlled electro-refractive phase modulators with a response faster than 1 GHz and negligible residual thermal tuning. The fastest switching strategy, of the three that we compare in our simulations, is shown to be the one that relies on rapid power-off of the origin wavelength. The longitudinal cavity mode position, that has an important impact on the switching time and switching stability, is shown to be hard to predict after switching due to gain-phase coupling in the amplifier.
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.
Indium Phosphide integrated photonics enables the combination of high-speed lasers and modulators with filters, detectors and multiplexers in one wafer-scale process flow. Low-voltage modulation at rates of 50Gigabit/second and above are feasible with combinations of semi-insulating substrates, optimised multi-quantum wells and high-speed electrical design. Advances in monolithic InP platform technologies have created a mechanism to rapidly introduce such high performance building blocks into sophisticated integration processes, enabling photonic integrated circuits with many tens of active components including distributed feedback lasers, tunable lasers and a range of passsive components. Our recent introduction of 192nm deep UV scanner lithography – believed to be a world first for InP integrated photonics – also enables a step change in the performance for the integrated filters and mode control.
In this paper, we present recent innovations in the creation of high performance transceiver technologies for optical interconnects. We showcase circuits using InP integrated photonics to create high-speed, energy-efficient, optically-multiplexed circuits. Monolithic polarization multiplexing and wavelength domain multiplexing are reviewed where all components, inclusive of the lasers, are created in the same wafer. Line-rates of up to 320 Gb/s are demonstrated for optically multiplexed circuits using a variety of open access fabrication platforms. The challenges and approaches for Terabit/second class transceiver chips will be addressed, addressing crosstalk management, component miniaturisation, and intimate electronic integration.
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.
We present finite difference thermal modeling to predict temperature distribution, heat flux, and thermal resistance inside lasers with different waveguide geometries. We provide a quantitative experimental and theoretical comparison of the thermal behavior of shallow-ridge (SR) and buried-heterostructure (BH) lasers. We investigate the influence of a split heat source to describe p-layer Joule heating and nonradiative energy loss in the active layer and the heat-sinking from top as well as bottom when quantifying thermal impedance. From both measured values and numerical modeling we can quantify the thermal resistance for BH lasers and SR lasers, showing an improved thermal performance from 50K/W to 30K/W for otherwise equivalent BH laser designs.
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.
Sustained increases in capacity and connectivity are needed to overcome congestion in a range of broadband
communication network nodes. Packet routing and switching in the electronic domain are leading to unsustainable
energy- and bandwidth-densities, motivating research into hybrid solutions: optical switching engines are introduced for
massive-bandwidth data transport while the electronic domain is clocked at more modest GHz rates to manage routing.
Commercially-deployed optical switching engines using MEMS technologies are unwieldy and too slow to reconfigure
for future packet-based networking. Optoelectronic packet-compliant switch technologies have been demonstrated as
laboratory prototypes, but they have so far mostly used discretely pigtailed components, which are impractical for
control plane development and product assembly.
Integrated photonics has long held the promise of reduced hardware complexity and may be the critical step towards
packet-compliant optical switching engines. Recently a number of laboratories world-wide have prototyped optical
switching circuits using monolithic integration technology with up to several hundreds of integrated optical components
per chip. Our own work has focused on multi-input to multi-output switching matrices. Recently we have demonstrated
8×8×8λ space and wavelength selective switches using gated cyclic routers and 16×16 broadband switching chips using monolithic multi-stage networks. We now operate these advanced circuits with custom control planes implemented with
FPGAs to explore real time packet routing in multi-wavelength, multi-port test-beds. We review our contributions in the
context of state of the art photonic integrated circuit technology and packet optical switching hardware demonstrations.
We summarize the results of a European Project entitled WAPITI (Waferbonding and Active Passive Integration Technology and Implementation) dealing with the fabrication and investigation of active/passive vertically coupled ring resonators, wafer bonded on GaAs, and based on full wafer technology. The concept allows for the integration of an active ring laser vertically coupled to a transparent bus waveguide. All necessary layers are grown in a single epitaxial run so that the critical coupling gap can be precisely controlled with the high degree of accuracy of epitaxial growth. One key challenge of the project was to establish a reliable wafer bonding technique using BCB as an intermediate layer. In intensive tests we investigated and quantified the effect of unavoidable shrinkage of the BCB on the overall device performance. Results on cw-operation, low threshold currents of about 8 mA, high side-mode suppression ratios in the range of 40 dB and large signal modulation bandwidths of up to 5 GHz for a radius of 40 μm shows the viability of the integration process.
Optical interconnects are being considered for short link data networks as a solution enabling higher aggregate bit rates and lower power consumption. For short link length interconnects, as used in chip to chip interconnects, internal system backplanes and inter-system interconnects such as blade server backplanes, storage area networks and processing clusters, requirements are quite different to those for long distance telecommunications systems. Low power consumption, latency, and size become important criteria in addition to ultra high bandwidth. In order to achieve the projected ultra high capacity and low latency needs, we are considering optical switching fabrics. The optical switch, however, brings significant changes to the interconnect architecture in terms of how routing decisions are made and how contention resolution is managed. We discuss these issues and present our results for a multiwavelength optically switched interconnect.
We propose a device based on self-induced phase shifting to create a non-linear optical transfer function with a single optical access. The device is designed around the Nonlinear-Optical Loop Mirror (NOLM) principle. The device is a loop formed by four SOAs with a splitter/recombiner at one of the junctions for optical access. The device also includes a mirror inside one of the SOAs such that part of the light is transmitted around the loop and part is reflected. The dimensions of formed loop are kept below 4mm (1mm/SOA) to the requirement for integration. It is assumed the loop is based on a standard ridge waveguide design with InGaAsP/InGaAs quantum wells yielding a refractive index of 3.88. Also, the width of the waveguide is kept constant at 2μm to ensure single-moded operation.
We present simulations results obtained with VPITransmissionMakerTM from VPIPhotonics. The software allows the simulation of optical modules such as Lasers, SOAs, Bragg Grating. The SOA and Laser modules exploit on the Transmission Line Laser Model (TLLM) model for solving the standard laser rate equations. For the Multi-Quantum Wells (MQW) SOAs, another set of equations are used to model the effects of carriers entering and exiting the quantum wells. The model is used to explore the tunability of the design and manufacturing parameters for optimal performance of the non-linear optical loop mirror. Design parameters include the size of the loop, drive current of each SOA, position and reflectivity of the mirror, number and size of the quantum wells and separate confinement height. To provide an efficient way of comparing different values for a given parameter, three figures of merits are chosen. The first one is the input dynamic range of the device in its current configuration, which corresponds to the area of the transfer function where the input signal will experience regeneration. The second parameter is the peak to trough ratio corresponding to the maximum possible output swing i.e. the maximum point of the transfer function less its corresponding minima. The final parameter named the regeneration slope is the division of the peak to trough ration by the input dynamic range.
The particularity of this loop is the mirror etched into one of the active waveguides to create self-induced phase shifts leading to non-linear transfer functions with a single optical input. Optimisation is explored for various design parameters that would need to be decided prior to manufacturing such a device. It is believed that such optimisation can provide a way to create all-optical signal processing devices created for a single application.
The input power dynamic range (IPDR) of a semiconductor optical amplifier (SOA) is extended using a moderate power holding beam, which could be readily achieved with a single DFB laser. The associated reduction of gain with improved IPDR is studied and assessed in parallel with power penalty to explore the optimum operating powers in switching applications. Holding beam powers of less than +10 dBm facilitate IPDR enhancement to 27 dB, representing an order of magnitude improvement. The achievable gain remains sufficiently high to find applications in a number of switching and routing applications.
KEYWORDS: Semiconductor lasers, Etching, Near field, Laser resonators, Fresnel lenses, High power lasers, Diodes, Lens design, Near field optics, Monochromatic aberrations
We demonstrate, for the first time, a monolithic integrated lens for wide aperture gain-guided tapered laser beam quality enhancement by compensating the quadratic phase curvature. The 3mm long tapered laser with an output aperture of 170μm adopted in this design consists of a gain-guided tapered section and an index-guided ridge section and operated at 980nm. The lens design is implemented by focus ion beam etching (FIBE) technique, whereby the laser diode is mounted p-side up in order to facilitate the etching process. The lens is located 600μm away from the junction of the tapered and ridge sections, and is 40μm wide and 300μm long with a focal length of 800μm. The laser diode is characterised by light-current characteristics together with near- and far- field measurements before and after etching. The device is biased by current pulses of 1μs width and 0.1% duty cycle. Light-current measurement shows a drop of 10.5% in threshold current from 380mA to 340mA after the inclusion of lens. This is an evidence that the lens effectively equalised the curved phase in order to reduce the laser cavity loss by improving the coupling efficiency of backward travelling wave at the output facet. Throughout the whole current range tested, the width of near-field at waist is broadened by an average of 36% after the inclusion of lens. By successfully compensating the quadratic phase curvature of the mode, the beam divergence in the far-field is significantly narrowed by an average of 28.5%. M2 factor is improved by an average of 12%.
With the continuous advent of new multimedia technologies, the local network bandwidth is getting closer and closer to limits set by electronic switching constraints. All-optical networks have long been demonstrated in the laboratory and rely on nonlinear switching devices such as Michelson Interferometers (MIs) for all-optical routing and all-optical digital processing. Hybrid integrated MIs allow for a greater electro-optical integration and thus easier packaging. It was recently published that multi-contact optical amplifiers provide a greater ease of use due to their greater flexibility in injecting current into the device. We have therefore investigated the optimisation of twin-contact SOAs for use in one arm of a Michelson device in order to provide the highest possible optically induced phase shift sine qua non for interferometry. The SOA section length as well as the corresponding injection currents were optimised and it was found that non-symmetrical sections (i.e. of different lengths and injection currents) produces best results with phase shifts up to 8.6 radians for 541μm (333μm + 208μm) long devices. This is explained by the non-symmetrical gains saturation effects created by the co-propagating pump and probe signal when passing through the various SOA sections. Multi-contact SOAs are hoped to provide a new ways of designing hybrid integrated interferometric devices by allowing greater control over the optical amplification process within the device.
Enhanced mode selection is facilitated by incorporating compact two dimensional photonic crystal gratings into Fabry-Perot lasers. The gratings are etched directly through the active layer and interact strongly with the guided mode. A high mode-selectivity 2D grating which is significantly wider than the ridge waveguide structure is investigated. The mode selectivity for the structure is -37 dB. The enhanced selectivity afforded by the broad 2D grating is attributable to a novel and robust photonic bandgap mechanism: transverse mode beating.
Extensive mode-locking investigations are performed in InGaAs/InAs/GaAs quantum dot (QD) lasers. Monolithic mode-locked lasers are fabricated using QD material systems grown by MOCVD and MBE techniques and emitting at 1.1μm and 1.3μm, respectively. The mode-locking performance is evaluated using a variety of laser designs, with various ridge waveguide geometries, cavity and absorber lengths. Passive and hybrid mode-locking are studied and compared in 3.9mm long devices emitting at 1.1μm and operating at a repetition rate of 10GHz. Using 2.1mm long devices emitting at 1.3μm, 18GHz passive mode locking with 10ps Fourier transform limited pulses is demonstrated. This confirms the potential of quantum dot laser for low chirp, short optical pulse generation. Preliminary investigation of the timing jitter of QD passively mode-locked lasers and the behaviour of the QD absorber are also presented. Finally, we report 36GHz passive mode-locking with 6ps optical pulse obtained using 1.1mm long QD lasers emitting at 1.3μm.
We have investigated the characteristics of 1550 nm GaInAsP/InP multiple quantum well (MQW) structures to be used as the gain medium in monolithic mode-locked lasers. For this purpose, a series of laser structures with 3 QWs, 5 QWs and 8 QWs were grown and processed into ridge waveguide lasers. The impact of the quantum well number was studied by analyzing the changes in threshold current, external quantum efficiencies, gain-spectra and linewidth enhancement factors, which are valuable in design and modeling of the mode-locked lasers. Monolithic 20 GHz mode-locked lasers were fabricated. Pulse trains with a good extinction ratio of 14.8 dB and less than 14 ps in width were demonstrated, and an average power of 1 mW could be coupled into an optical fiber.
It is desirable for data networks to have low transmission latency. This may be achieved by exploiting the short packet lengths and the high bandwidths that can be achieved using multi-wavelength operation. Semiconductor optical amplifiers (SOAs) have been demonstrated as building blocks for optical switches and have also been shown to be well suited to the fast switching required for optical packet switching [1]. We have realised an InP based add-drop multiplexer (ADM) integrated on a single 850 μm x 850 μm chip. The bit error penalty performance has previously been shown to be below 1.2 dB for each of the operating paths through the device: add, drop and through modes at 2.5 Gbit/s data rates. Further, low penalty operation has previously been demonstrated experimentally with 4 simultaneous wavelengths [2].
It is known that the dynamic range of an SOA can limit the number of wavelengths supported and that the pattern sensitivity in SOAs increases their operating penalty [3]. We investigate the multi-wavelength operation of our ADM device and show that a power penalty of less than 0.8 dB is maintained over a 20 dB input power dynamic range. We also show a -3 dB optical bandwidth of 30 nm suitable for multi-wavelength operation of cascaded ADMs. Finally we present experimental results to show that the pattern dependent operating penalty of the ADM is reduced as the number of wavelengths of asynchronous data is increased. This result may be exploited in our proposed optical data network to produce an improved optical penalty.
We describe a photonic bandgap polarization selector based on a photonic crystal placed at junction of two 90° intersecting waveguides to form an ultra-compact device. The photonic crystal consists of 7 layers of a triangular lattice with a radius to pitch ratio (r/a) of 0.24 and a lattice constant of 0.386μm. The PBG is orientated so that the light is incident and collected at 45° to the Γ-K crystallographic direction. Modeling of the PBG shows that TM polarized light is strongly reflected while TE light passes largely into the crystal. Measurements of the fibre-to-fibre transmitted power of the device for each polarization show that the TM collected power is ~6dB higher than the TE light for equal input polarization powers. Further evidence of the strong reflection of TM light comes from an equivalent sample without a 2-D lattice at the waveguide junction. In these samples, no TM light is detected at the output. Furthermore, by taking into account the TE and TM gains within the active waveguides, the TM to TE polarization selection of the PBG is estimated to be up to 22dB.
In this work we present a detailed study of picosecond optical pulse generation using high-repetition rate mode-locked quantum dot lasers. MOCVD-grown quantum dot lasers emitting at 1.1μm and MBE-grown quantum dot lasers emitting at 1.3μm are investigated. Passive mode-locking at 10GHz, 18GHz and 36GHz with pulse widths in the 6-12ps range are reported. Hybrid mode-locking is demonstrated at 10GHz, showing a significant improvement in the RF spectral characteristics when compared with passive mode-locking. A timing jitter of 600fs (2.5MHz to 50MHz) is measured in the 18GHz passively mode-locked laser. Autocorrelation techniques are used to characterise the high repetition rate mode-locked lasers as well as the time-bandwidth product of the optical pulses. Fourier-transform
limited pulses are obtained from passively mode-locked QD lasers.
This paper describes the current status of Coarse Wavelength Division Multiplexing (CWDM), and then progresses to discuss how it may evolve in networking applications in the future. As WDM can enhance not only transmission but also networking systems, the paper reports a potentially low cost WDM based access node architecture, particularly suited for routing optical data packets on nanosecond timescales. The scheme is cascadable and involves the use of a simple semiconductor optical amplifier (SAO) based add-drop switch. Preliminary results concerning the operation of the add-drop switches under multi-wavelength operation are reported.
KEYWORDS: Waveguides, Wave propagation, Refractive index, High power lasers, Waveguide modes, Optical simulations, Near field, Waveguide lasers, Beam propagation method, Near field optics
A finite difference beam prop0agation mode is used in conjunction with laser rate equation simulations to study the inclusion of an intracavity lens in a high-power tapered ridge waveguide laser diode emitting at 980 nm. A parabolic lens is introduced in the top of the ridge near the front facet via a change in the waveguide effective refractive index profile. The inclusion of the lens has led to 13 percent reduction in the threshold current and an improved power slope efficiency from 0.4 W/A up to 0.8 W/A. The lens has caused near field broadening of 2 micrometers at full width half maximum power, indicating more efficient use of the cavity. The far field has narrowed by 1 degree indicating higher brightness. The model uses a mesh for reach of its points the standard carrier rate equation is solved across the active layer. The 2D wave equation is solved for the two counter propagating fields using a finite difference algorithm. The result of the does how good agreement with experiment.
Requirements for directly modulated semiconductor lasers are investigated in terms of directly measurable laser and link parameters. Data rates comparable to the bandwidth imposed by the active layer design are considered, and performance is assessed in terms of laser resonance frequency and damping. Link critical variables such as contrast ratio, fall time and error rate are thereby related directly to parameters extracted from static measurements. To allow error free operation, a resonance frequency equal to the data rate is acceptable, but to ensure a fast fall time, resonance frequencies exceeding one and a half times the data rate are necessary.
All-optical 2R regeneration and wavelength conversion is demonstrated in a simple SOA/DFB laser device. A regenerated Q factor improvement of 2.5 is reported.
In this paper, the static and dynamic performance of multi quantum-well (MQW) 1.3 micrometer InGaAsP Fabry Perot lasers is assessed experimentally and theoretically to identify the mechanisms responsible for impaired high speed performance at elevated temperature. Initially, threshold currents and spontaneous emission spectra are characterized for a range of temperatures from room temperature to 85 degrees Celsius to indicate a significant increase in non-radiative current contributions. Preliminary estimates are made for the contributions of leakage and Auger recombination rates, found from the dependence of integrated spontaneous emission with carrier density. Drift-diffusion modeling is found to accurately predict the trend of threshold currents over temperature. Using gain modeling good agreement is found between the measured and predicted integrated spontaneous emission intensity. Gain measurements at 85 degrees Celsius indicate a reduction in RIN frequency to 63% of the 25 degree Celsius value which matches well with experimental small signal performance.
Polarization control is reported for a 2-D independently addressable VCSEL array. Polarization pinning for emitters on the same die at several orientations is achieved by etching trenches close to the contact metallization of each emitter in the array using focused ion beam etching. Polarization extinction ratios in excess of 50 are achieved over a wide range of orientations and bias currents. No significant effects are observed on threshold current subsequent to the etching of polarization pinning trenches.
Uncooled direct modulation of a 1.55 micrometers distributed feedback (DFB) laser is demonstrated at 10 Gbit/s is demonstrated. The small signal performance of the laser at 25 degree(s)C gives rise to a -3 dB bandwidth in excess of 9 GHz, reducing to 8 GHz at 55 degree(s)C. Under uncooled, direct modulation at 10 Gbit/s the back-to-back eye diagrams obtained at temperatures up to 55 degree(s)C are found to be open, with extinction ratios of 6 dB for a peak-to-peak current swing of 40 mA. Transmission at 10 Gbit/s over standard singlemode fiber, is demonstrated over 12 km with the uncooled device. Using this device, multi-level coding is demonstrated at 20 Gb/s, and transmission at 5 Gb/s over 700 m of multi-mode fiber at 60 degree(s)C.
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