X.J.M. Leijtens

Technische Universiteit Eindhoven, Eindhoven, North Brabant, Netherlands

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Publications (206)206.66 Total impact

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    ABSTRACT: Multimode Interference couplers (MMI) can have deviations in their amplitude and phase relations with respect to the ideal case. When using MMIs to construct a Mach-Zehnder interferometer (MZI), these deviations lead to non-ideal MZI behavior. In this paper, we introduce a correction algorithm that is able to strongly reduce amplitude and phase errors in 3 × 3 MMI based MZIs. Such MZIs are frequently used in phase estimation schemes in wavelength meters. Our method reduces the maximum phase estimation error to 2°, as measured in fabricated devices. This is two to three times better than the conventional method by Todd et al.
    Journal of Lightwave Technology 06/2015; 33(11):2233-2239. DOI:10.1109/JLT.2015.2409200 · 2.86 Impact Factor
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    ABSTRACT: We report the achievement of colliding pulse mode-locked (CPM) regimes on a novel on-chip mode locked laser diode (OCCP-MLLD). The advantage of the resonator structure that we present is that the end-mirrors are defined through multimode interference reflectors (MIRs), which provide precise control of the cavity length avoiding the need for cleaved facets. This simplifies positioning the saturable absorber at the center of the resonator to achieve the colliding pulse mode-locked regime and double the repetition rate, reaching the millimeter wave frequency range. An additional advantage is that the pulsed output is delivered within the Photonic Integrated Circuit chip for further processing (i.e. modulation). We demonstrate a colliding pulse passive mode locked regime with pulse widths below a picosecond (Δτ = 0.64 ps), timing jitter σ<sub>T</sub> = 75 fs and amplitude noise N<sub>AM</sub> = 0.012 dBc. The samples were fabricated in a generic InP foundry service through multi-project wafer (MPW) runs.
    Optics Express 06/2015; 23(11):14666. DOI:10.1364/OE.23.014666 · 3.49 Impact Factor
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    DESCRIPTION: Multi-wavelength laser sources based on Arrayed waveguide grating have been shown in order to provide simultaneously multiples wavelengths with a narrow optical linewidth. Two different laser structures have been developed for the millimeter wave signal generation, monolithically integrated using photonic integrated circuits. In this work we report the characteristics of the heterodyne signal in the millimeter wave range. The optical linewidth measured from the modes generated by different channels on each structure can become less than 150 KHz.
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    B Gargallo · Y Jiao · P Muñoz · J Van Der Tol · X Leijtens
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    ABSTRACT: We analyze the Arrayed Waveguide Grating (AWG) response on indium phosphide (InP) membranes on silicon (IMOS) technology. The model is based on an analytical approach [1] that provides a better performance than the Gaussian approximation and same time consumption. Introduction The IMOS photonic integration technique, based on the use of an indium phosphide membrane on top of a silicon chip, has shown some advantages as the possibility of integrating passive and active devices with approximately the same dimensions than silicon on insulator (SOI) technologies [2]. The cross-section consists of a silicon substrate, a 1850 nm height layer of silicon dioxide and the InP membrane (300 nm height) where the waveguides will be fabricated.
    Optical Wave and Waveguide Theory and Numerical Modelling Workshop (OWTNM 2015); 04/2015
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    ABSTRACT: We fabricated and experimentally tested a novel monolithically integrated Indium Phosphide optical circuit for differential phase-shift keying demodulation, which is robust to noise degradations of the received signal. The circuit consists of a one-bit-delay interferometer that demodulates the incoming signal and a semiconductor optical amplifier where the constructive and destructive demodulated outputs synchronously counter-propagate experiencing a reshaping effect. The novel optical circuit has been fabricated for 40 Gb/s signals, and the amplitude signal restoration is demonstrated by comparing the obtained output eye diagrams with those of a commercial fiber-based demodulator. We find a net improvement in the signal to noise ratio when the circuit is fed with a noisy input signal.
    Optics Communications 04/2015; 340. DOI:10.1016/j.optcom.2014.11.097 · 1.54 Impact Factor
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    C. Gordón · R. Guzmán · X. Leijtens · G. Carpintero
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    ABSTRACT: We report, for the first time to our knowledge, an on-chip mode-locked laser diode (OCMLLD) that employs multimode interference reflectors to eliminate the need of facet mirrors to form the cavity. The result is an OCMLLD that does not require cleaved facets to operate, enabling us to locate this OCMLLD at any location within the photonic chip. This OCMLLD provides a simple source of optical pulses that can be inserted within a photonic integrated circuit chip for subsequent photonic signal processing operations within the chip (modulation, optical filtering, pulse rate multiplication, and so on). The device was designed using standardized building blocks of a generic active/passive InP technology platform, fabricated in a multi-project wafer run, and achieved mode-locking operation at its fundamental frequency, given the uncertainty at the design step of the optical length of these mirrors, critical to achieve colliding pulse mode-locked operation.
    Photonics Research 02/2015; 3(1). DOI:10.1364/PRJ.3.000015
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    ABSTRACT: This study presents the recently developed monolithic photonic-integrated circuits that provide efficient amplitude modulation for wavelength division multiplexed optical channels. The circuits were designed for application as a read-out unit in a high-energy physics experiment, and are sufficiently general to be applied in various types of high-speed photonic transmitters. They were constructed using basic building blocks provided in an indium phosphide-based generic integration technology process and fabricated in a multi-project wafer run. Two variants of the circuits, utilizing modulators in Mach–Zehnder and Michelson interferometer configuration, are discussed. A modulation bandwidth of 18.6 GHz was measured and error-free transmission of a 10-Gb/s signal through 85 km of optical fiber was achieved.
    Journal of Lightwave Technology 12/2014; 32(23). DOI:10.1109/JLT.2014.2354240 · 2.86 Impact Factor
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    ABSTRACT: We numerically and experimentally investigate an on-chip solution to reduce the thermal crosstalk in indium phosphide-based photonic integrated circuits. We introduce deep trenches, fabricated through wet etch, between active and passive components. The current injected in active components and the geometry of the trenches are the parameters considered in our analysis. The trenches thermally isolate the passive components from the heat generated by active components. The thermal crosstalk is quantified by measuring the effects on the electro-optical response of an MZ modulator considered as a test structure. The heat sources are represented by semiconductor optical amplifiers placed at different distances with respect to the position of the MZ. Our experiments show how both the geometry and the position of the trenches, play a role in the reduction of the thermal crosstalk.
    Journal of Lightwave Technology 12/2014; 32(24):4262-4268. DOI:10.1109/JLT.2014.2366781 · 2.86 Impact Factor
  • M Khoder · R M Nguimdo · J Danckaert · X J M Leijtens · J Bolk · G Verschaffelt
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    ABSTRACT: We investigate the wavelength tuning speed in semiconductor ring lasers with filtered optical feedback. The device consists of a micro ring laser and a feedback section which contains two arrayed waveguide gratings and four semiconductor optical amplifiers. The wavelength tuning and switching are controlled by changing the injected currents into the gates. We obtained a wavelength transition time of a few nano seconds together with a substantial delay time of several nano seconds in the switching event.
    Annual Symposium of IEEE Photonics Society Benelux Chapter, Enschede- The Nederlands; 11/2014
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    ABSTRACT: Multi-wavelength laser sources based on Arrayed waveguide grating have been shown in order to provide simultaneously multiples wavelengths with a narrow optical linewidth. Two different laser structures have been developed for the millimeter wave signal generation, monolithically integrated using photonic integrated circuits. In this work we report the characteristics of the heterodyne signal in the millimeter wave range. The optical linewidth measured from the modes generated by different channels on each structure can become less than 150 KHz. Beating the two wavelengths from any of these chips on a high speed photodiode resulted in a beat note having a linewidth less than 250 kHz, which is the narrowest beat-note measured from free running monolithic semiconductor dual wavelength sources.
    XXIX SIMPOSIUM NACIONAL DE LA UNIÓN CIENTÍFICA INTERNACIONAL DE RADIO, Valencia, Spain; 09/2014
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    ABSTRACT: We report on an integrated approach to achieve fast wavelength switching in a semiconductor ring lasers using on-chip filtered optical feedback. The feedback section consists of two arrayed waveguide gratings and four semiconductor optical amplifiers. The wavelength tuning and switching are controlled by changing the injected currents into the semiconductor optical amplifiers. Experimental observations and numerical simulations show a wavelength switching speed of few nano seconds. We also investigate the effect of the feedback parameters and the noise strength on the wavelength switching speed.
    International Conference on Transparent Optical Networks (ICTON), GRAZ; 07/2014
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    ABSTRACT: In Europe a number of technology platforms for generic integration are being created for photonic integrated circuits (PICs); in Silicon, in passive dielectrics, and in Indium Phosphide. Such platforms are on the brink of commercialization, they offer a range of calibrated building blocks from which application specific PICs can be built and allow simplified, reduced cost access to a standardised technology, but presently only InP based platforms allow the integration of optical gain blocks; the essential feature of a semiconductor laser. The wavelength is constrained by the platform, usually C-band, but in the near future we expect other wavelengths in the 1.3μm-2.0μm range will be addressed. A frozen platform technology may not seem an ideal starting point for novel laser research but for what may be appear to be lost in epitaxial and process flexibility, much more is gained through a new-found ability to build up complex circuits quickly to deliver new and interesting laser based functionality. Building blocks such as reflectors (a distributed Bragg reflector (DBR) or a multimode interference reflector (MIR)), an amplifier section, and passive waveguides, can be built up by designers into integrated semiconductor lasers of a wide variety of types. This ready integration of novel sources with other circuit functionality can address a wide range of applications in telecoms, datacoms, and fibre based sensing systems. In this paper we describe a number of recent developments on generic InP-based platforms ranging from the fabrication of simple Fabry-Perot lasers, through tuneable DBR lasers, multi-wavelength comb lasers, picosecond pulse lasers and ring lasers.
    SPIE Photonics Europe; 05/2014
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    ABSTRACT: Semiconductor ring lasers are promising sources in photonic integrated circuits because they do not require cleaved facets or mirrors to form a laser cavity. In this work, we characterize the wavelength switching speed of a tunable semiconductor ring lasers using filtered optical feedback. The filtered optical feedback is realized by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback of each wavelength channel independently. The wavelength switching is achieved by changing the currents injected in the semiconductor optical amplifier gates. Experimentally, we observe a wavelength transition time of 5 ns. However, we also noticed a non-negligible delay in the switching process. [ Khoder et al, IEEE Photon. Technol. Lett. 26, 520{523, 2014]. We numerically reproduce the experimental results using rate equations taking into account the effect of spontaneous emission. The simulations further elaborate on the effect of the noise strength on the wavelength transition time and the delay time. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    SPIE PHOTONICS EUROPE Silicon Photonics and Photonic Integrated Circuits IV, Brussels; 04/2014
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    ABSTRACT: Laser diodes that emit multiple wavelengths simultaneously are needed in a range of applications including wavelength division multiplexing, high speed optical networks and tera-hertz generation. In this work we report on an integrated approach to obtain multi-wavelength emission from a semiconductor ring laser based on on-chip filtered optical feedback. Semiconductor ring laser have the advantage that they can be easily integrated with other optical components as they do not require mirrors to form the cavity. Moreover, no thermal control of the wavelength emission is needed and therefore the device can be in principle fast. The filtered optical feedback is realized by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback strength of each wavelength channel independently. Experimental observations [Khoder et al, Optics. Lett. 38, 2608-2610, 2013] have shown that the effective gain is the key parameter that has to be balanced using the feedback in order to achieve multi-wavelength emission. This can be achieved by tuning the injection current in each amplifier which will change the feedback phase and strength. Numerical simulations using rate equations reproduce the experimental results and show the effects of feedback phase and strength on the multi-wavelength emission.
    SPIE Photonics Europe, Brussels; 04/2014
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    ABSTRACT: In this letter, we demonstrate a novel monolithically integrated photonic multiwavelength transmitter that was realized by integrating an arrayed waveguide grating-based laser with selective distributed Bragg reflector mirrors and Mach-Zehnder modulators. The integrated circuit was designed according to a generic integration model, by utilizing standardized photonic building blocks, and was fabricated on an InP-based platform in a multiproject wafer run. The device delivers above 1 mW of optical power into the fiber with a side mode suppression ratio better than 40 dB. The linewidth of the generated signals is 275 kHz. We achieved error free 50-km transmission at the modulation data rate of 10 Gb/s per channel, for a received power of ${-}{26.5}~{rm dBm}$ .
    IEEE Photonics Technology Letters 04/2014; 26(7):710-713. DOI:10.1109/LPT.2014.2303496 · 2.18 Impact Factor
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    ABSTRACT: A ring mode-locked laser fabricated as a monolithic photonic integrated circuit using a InP based integration technology is presented. It generates an optical coherent comb around 1546 nm with a record 11.5 nm 3 dB bandwidth.
    Optical Fiber Communication Conference; 03/2014
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    ABSTRACT: We report a novel narrow-linewidth WDM transmitter operating at 10Gbps per transmission channel with 275kHz optical linewidth. The device was fabricated in generic InP-based foundry process and integrates AWG-laser with selective DBR-mirrors and Mach-Zehnder modulators.
    Optical Fiber Communication Conference; 03/2014
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    ABSTRACT: We experimentally and numerically characterize the wavelength switching speed of a tunable semiconductor ring laser using filtered optical feedback. The feedback is realized employing two arrayed-waveguide gratings to split/recombine light into different wavelength channels. The wavelength tuning and switching is controlled by changing the currents injected in semiconductor optical amplifiers in the feedback section. A wavelength switching speed of a few ns is achieved.We investigate also the effect of the feedback parameters and noise strength on the wavelength switching speed
    IEEE Photonics Technology Letters 03/2014; 26(5):520-523. DOI:10.1109/LPT.2013.2296398 · 2.18 Impact Factor
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    ABSTRACT: Parasitic reflections can deteriorate the performance of a photonic integrated circuit. This is especially true in circuits containing amplifiers, but even in passive circuits, small reflections can already have a strong influence on circuit performance. It is known that strong reflections can be present when using a 2$,times,$1 multimode interference coupler (MMI) as a combiner. We investigate methods for reducing these spurious reflections in a generic integration technology. We present a novel MMI shape whose measurements show reduced reflections by 17.5 dB.
    IEEE Photonics Technology Letters 02/2014; 26(4):408-410. DOI:10.1109/LPT.2013.2295624 · 2.18 Impact Factor
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    ABSTRACT: We present the calibration method and characterization of a monolithically integrated semiconductor optical pulse shaper. The photonic integrated circuit has been realized in an InP-based generic photonic foundry process. In this circuit, a 20-channel arrayed waveguide grating filter with 50-GHz channel spacing and 20 phase modulators and semiconductor optical amplifiers are combined on the InP chip. By calibrating the device, a mathematical description of the pulse shaper is obtained. The theoretical procedure for complete calibration of the device is presented, and the details of the experiments and measurement setups are given. We demonstrate that the frequency response of the pulse shaper can be calculated from the response of the individual channels in a reference state of the control signals and a separate mask function that describes the effect of a change in the control signals.
    IEEE Photonics Journal 12/2013; 5(6):6602317-6602317. DOI:10.1109/JPHOT.2013.2289945 · 2.33 Impact Factor