Pascual Muñoz

Modeling and design of arrayed waveguide gratings

The purpose of this paper is twofold. First, a simple but comprehensive and powerful arrayed-waveguide grating (AWG) field model is presented which, based on Fourier optics, borrows some principles of that developed by Takeouchi and coworkers [see, Opt. Express, vol. 6, p. 124, 2000] for the analysis of reflective-type AWGs for optical signal processing, but at the same time adds more features, such as the calculation of device losses and the refinement of the mathematical model to obtain a simple expression for the output field for any input-output waveguide configuration where the meaning of the different high-level parameters of the AWG becomes very clear to the reader. Second, we elaborate on the model developed to present an useful design procedure of the AWG based on two steps illustrated by design flowcharts.

Optical microwave filter based on spectral slicing by use of arrayed waveguide gratings

We have experimentally demonstrated a new optical signal processor based on the use of arrayed waveguide gratings. The structure exploits the concept of spectral slicing combined with the use of an optical dispersive medium. The approach presents increased flexibility from previous slicing-based structures in terms of tunability, reconfiguration, and apodization of the samples or coefficients of the transversal optical filter.

Apodized coupled resonator waveguides.

In this paper we propose analyse the apodisation or windowing of the coupling coefficients in the unit cells of coupled resonator waveguide devices (CROWs) as a means to reduce the level of secondary sidelobes in the bandpass characteristic of their transfer functions. This technique is regularly employed in the design of digital filters and has been applied as well in the design of other photonic devices such as corrugated waveguide filters and fiber Bragg gratings. The apodisation of both Type-I and Type-II structures is discussed for several windowing functions.

Design, Fabrication and Characterization of an InP-Based Tunable Integrated Optical Pulse Shaper

In this paper a tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP-InGaAsP material for operation at wavelengths around 1.55 mum. Multimode inputs to the waveguide gratings are used to flatten their optical passband. We have used a new short-pulse characterization technique to fully characterize pulse shaping by the device, i.e., both the power and the phase profile. A fourfold decrease in pulse ringing was observed for the devices with flattened passbands. Moreover these devices showed a 25% increase in pulse peak power. The possibilities for using the device as a dispersion (pre-) compensator have been investigated. Pulse reconstruction could be obtained for dispersion values of up to 0.2 ps/nm. The fabrication technology of the pulse shaper is compatible with the fabrication of integrated mode-locked lasers, which makes further integration of complete arbitrary pulse generators possible.

Reconfigurable fiber-optic-based RF filters using current injection in multimode lasers

We propose and experimentally demonstrate the possibility of obtaining low-cost reconfigurable RF filters based on the combined use of multimode Fabry-Perot (FP) lasers and optical dispersive elements. The key to attain reconfigurability is the modification of the FP laser optical spectrum by means of changing the bias injection current to the device.

Silicon graphene waveguide tunable broadband microwave photonics phase shifter

We propose the use of silicon graphene waveguides to implement a tunable broadband microwave photonics phase shifter based on integrated ring cavities. Numerical computation results show the feasibility for broadband operation over 40 GHz bandwidth and full 360° radiofrequency phase-shift with a modest voltage excursion of 0.12 volt.

A monolithic integrated photonic microwave filter

Meeting the ever increasing demand for transmission capacity in wireless networks will require evolving towards higher regions in the radiofrequency spectrum, reducing cell sizes as well as resorting to more compact, agile and power efficient equipment at the base stations, capable of smoothly interfacing the radio and fiber segments. Photonic chips with fully functional microwave photonic systems are promising candidates to achieve these targets. Over the last years, many integrated microwave photonic chips have been reported in different technologies. However, and to the best of our knowledge, none of them have fully integrated all the required active and passive components. Here, we report the first ever demonstration of a microwave photonics tunable filter completely integrated in an Indium Phosphide chip and packaged. The chip implements a reconfigurable RFphotonic filter, it includes all the required elements, such as lasers, modulators and photodetectors, and its response can be tuned by means of control electric currents. This demonstration is a fundamental step towards the feasibility of compact and fully programmable integrated microwave photonic processors. Emerging information technology scenarios, such as 5G mobile communications and Internet of Things (IoT), will require a flexible, scalable and futureproof solution capable for seamlessly interfacing the wireless and fiber segments of communication networks [1,2,3]. Microwave photonics (MWP) [4,5],the interdisciplin ary approach that combines radiofrequency and photonic systems, is the best positioned technology to achieve this target. A very relevant example is 5G wireless communications, which targets an extremely ambitious range of requirements including [6,7], a 1000-fold increase in capacity, connectivity for over 1 billion users, strict latency control, as well as network flexibility via agile software programming. These objectives call for a paradigm shift in the access network to incorporate smaller cells, exploit the millimeter wave regions of the radiofrequency spectrum and implement massive multiple-input multipleoutput at the base stations (BTSs) [7]. The successful integration of the wireless and fiber segments thus relies on the possibility of implementing agile and reconfigurable MWP subsystems, featuring broadband operation, as well as low space, weight and power consumption metrics. The solution consists in resorting to integrated microwave photonics (IMWP) [8,9] chips allocated either in the BTS and/or the central office in combination with radio over fiber transmission in the fiber segment connecting them [10,11]. The two fundamental issues to be solved in IMWP are related respectively to technology and architecture. First, there is the need to identify the best material platform where to implement MWP chips. Second, whether it would be better to follow an application specific photonic integrated circuit (ASPIC) approach, where a specific architecture is employed to implement a specific functionality, or to resort to a generic programmable architecture. IMWP ASPICs with certain complexity have been reported to date mainly in four material platforms: indium phosphide (InP) [1214], Silicon-on-Insulator (SOI) [15-21], silicon nitride (Si3N4) [22-26] and chalcogenide glass [27,28]. Several functionalities have been demonstrated with a variable degree of photonic (20-60%) integration, as shown in Table 1. A different approach is based on generic processors [29,30], where a common architecture implements different functionalities by suitable programming. A recent paper [31] reported the design of a programmable optical core inspired by the concept of electronic field programmable gate arrays. This approach is based on an optical core composed implemented by a 2D waveguide mesh where the connections between waveguides 1 ar X iv :1 61 2. 06 99 9v 1 [ ph ys ic s. op tic s] 2 1 D ec 2 01 6 are controlled by means of tunable Mach-Zehnder interferometers (MZIs). Researchers fabricated a simplified version of the processor composed of two mesh cells, using a commercial Si3N4 waveguide technology known as TriPleX [32]. The reported processor featured a free spectral range of 14 GHz and is fully programmable. A band-pass filter with a tunable centre frequency that spans two octaves (1.6-6 GHz) and a reconfigurable band shape (including a notch filter and a flat-top resonance) was demonstrated. A reconfigurable processor implementing signal integration, differentiation and Hilbert transformation has also been recently reported in InP technology [33]. To the best of our knowledge however, none of the above contributions has reported to date the integration of all the required active (sources, modulators and detectors) and passive (splitters, optical filters and waveguides) photonic components in a single chip, either monolithically or following a hybrid approach. Here we report, , the design, fabrication, packaging and experimental demonstration of the first monolithic IMPW filter that integrates all these elements in the same substrate. The chip implements a reconfigurable RF-photonic filter that employs a tunable distributed Bragg reflector laser (DBR); a singlesideband optical modulator; a tunable optical filter based on a ring assisted Mach Zehnder interferometer (RAMZI)[34]; and an on-chip optical detector. This demonstration constitutes a fundamental step forward in the implementation of a fully integrated MWP filter, and opens the path for compact and programmable MWP signal processors, where the RAMZI filter will be replaced by a 2D reconfigurable mesh and multiple functionalities will be implemented by suitable programming of the mesh interconnections. Table 1: Overview of reported IMWP chips. AWG: Arbitrary waveform generation. BFM: Beamforming. TBPS: Tunable broadband phase shift. TTTD: Tunable true-time delay. IFM: Instantaneous frequency measurement. ADC: Photonic analog-to-digital conversion.

Photonics-based microwave frequency measurement using a double-sideband suppressed-carrier modulation and an InP integrated ring-assisted Mach Zehnder interferometer filter

A photonic system capable of estimating the unknown frequency of a CW microwave tone is presented. The core of the system is a complementary optical filter monolithically integrated in InP, consisting of a ring-assisted Mach-Zehnder interferometer with a second-order elliptic response. By simultaneously measuring the different optical powers produced by a double-sideband suppressed-carrier modulation at the outputs of the photonic integrated circuit, an amplitude comparison function that depends on the input tone frequency is obtained. Using this technique, a frequency measurement range of 10 GHz (5-15 GHz) with a root mean square value of frequency error lower than 200 MHz is experimentally demonstrated. Moreover, simulations showing the impact of a residual optical carrier on system performance are also provided.

All silicon waveguide spherical microcavity coupler device

A coupler based on silicon spherical microcavities coupled to silicon waveguides for telecom wavelengths is presented. The light scattered by the microcavity is detected and analyzed as a function of the wavelength. The transmittance signal through the waveguide is strongly attenuated (up to 25 dB) at wavelengths corresponding to the Mie resonances of the microcavity. The coupling between the microcavity and the waveguide is experimentally demonstrated and theoretically modeled with the help of FDTD calculations.

Graphene Integrated Microwave Photonics

This paper proposes and analyzes the incorporation of graphene to integrated waveguides and circuits for application to the field of microwave photonics (MWP). We discuss the main optical and electronic properties of graphene in connection to its operation in the optical region of the spectrum, including their tunability by electrical means. We use numerical techniques to evaluate the impact of graphene on the effective index and absorption of the propagating modes in several waveguide designs and use these results to design several fundamental building components that are instrumental in the implementation of several key MWP functionalities including tunable phase-shifters, true time delay lines and Bragg grating filters. Our results suggest that the incorporation of graphene to silicon waveguides can bring important potential benefits, especially in terms of modest power consumption, high tuning speed with respect to other techniques used for current tuneable MWP devices and increased operation bandwidth.