Programmable photonic circuits manipulate the flow of light on a chip by electrically controlling a set of tunable analog gates connected by optical waveguides. Light is distributed and spatially rerouted to implement various linear functions by interfering signals along different paths. A general-purpose photonic processor can be built by integrating this flexible hardware in a technology stack comprising an electronic monitoring and controlling layer and a software layer for resource control and programming. This processor can leverage the unique properties of photonics in terms of ultra-high bandwidth, high-speed operation, and low power consumption while operating in a complementary and synergistic way with electronic processors. This talk will review the recent advances in the field and it will also delve into the potential application fields for this technology including, communications, 6G systems, interconnections, switching for data centers and computing.
We introduce the emerging area of programmable integrated photonics highlighting the operation principles, basic component and subsystem arrangements and fabrication technologies. We describe the main present and future applications of this tecchnology.
An optoelectronic oscillator (OEO) is a microwave photonic system that produces microwave signals with ultralow phase noise using a high-quality-factor optical energy storage element. This type of oscillator is desired in various practical applications, such as communication links, signal processing, radar, metrology, radio astronomy, and reference clock distribution. Recently, new mode control and selection methods based on Fourier domain mode-locking and parity-time symmetry have been proposed and experimentally demonstrated in OEOs, which overcomes the long-existing mode building time and mode selection problems in a traditional OEO. Due to these mode control and selection methods, continuously chirped microwave waveforms can be generated directly from the OEO cavity and single-mode operation can be achieved without the need of ultranarrowband filters, which are not possible in a traditional OEO. Integrated OEOs with a compact size and low power consumption have also been demonstrated, which are key steps toward a new generation of compact and versatile OEOs for demanding applications. We review recent progress in the field of OEOs, with particular attention to new mode control and selection methods, as well as chip-scale integration of OEOs.
We review some of the basic principles, fundamentals, technologies, architectures and recent advances leading to thefor the implementation of Field Programmable Photonic Field Arrays (FPPGAs).
Programmable multifunctional integrated nanophotonics (PMIN) is a new paradigm that aims at designing common integrated optical hardware configurations, which by suitable programming can implement a variety of functionalities that can be elaborated for basic or more complex operations in many application fields. The strength of PMIN relies on the suitable interconnection of field-programmable waveguide arrays. Here, we review the recent advances reported in the field of PMIN, paying special attention to outlining the design principles, material platforms, synthesis algorithms and practical constraints of these structures. Finally, we discuss their applicability to different fields.
We review the recent advances reported in the field of integrated photonic waveguide meshes, both from the theoretical as well as from the experimental point of view. We show how these devices can be programmed to implement both traditional signal processing structures, such as finite and infinite impulse response filters, delay lines, beamforming networks as well as more advanced linear matrix optics functionalities. Experimental results reported both in Silicon and Silicon Nitride material platforms will be presented. We will also discuss the main programming algorithms to implement these structures and discuss their applications either as standalone systems or as part of more elaborated subsystems in microwave photonics, quantum information and machine learning.
This paper explores the use of honeycomb lattice waveguide meshes for universal linear operations and photonic
integrated circuit synthesis by programming a common hardware. We discuss the main photonic processor architecture,
the non-ideal effects to be considered and its application to different signal processing functionalities.
An optical fiber sensor composed of six standard FBGs in cascade is interrogated by use of a technique based on wavelength to delay mapping. A microwave-modulated optical signal enters the FBG cascade and, after being sliced and reflected, experiences dispersion in standard single-mode fiber. The Bragg wavelengths of the FBGs are mapped into the delays that determine the peaks in the system’s electrical impulse response. The Bragg wavelength shifts are calculated from the difference of the delays undergone by FBGs samples. A resolution of 9.2 pm in Bragg wavelength shift is demonstrated.
A system to interrogate photonic sensors based on long weak fiber Bragg gratings (FBGs) is presented and experimentally demonstrated, dedicated to measure the precise location of several spot events. The principle of operation is based on a technique used to analyze microwave photonics (MWP) filters. The long weak FBGs are used as quasi-distributed sensors. Several events can be detected along the FBG device with a spatial accuracy under 1 mm using a modulator and a photo-detector (PD) with a modest bandwidth of less than 500 MHz. The simple proposed scheme is intrinsically robust against environmental changes and easy to reconfigure.
The rapid increase on the information sharing around the world, leads to an utmost requirement for capacity and bandwidth. However, the need for security in the transmission and storage of information is also of major importance. The use of quantum technologies provides a practical solution for secure communications systems. Quantum key distribution (QKD) was the first practical application of quantum mechanics, and nowadays it is the most developed one. In order to share secret keys between two parties can be used several methods of encoding. Due to its simplicity, the encoding into polarization is one of the most used. However, when we use optical fibers as transmission channels, the polarization suffers random rotations that may change the state of polarization (SOP) of the light initially sent to the fiber to a new one at the output. Thus, in order to enable real-time communication using this encoding method it is required the use of a dynamic control system. We describe a scheme of transmission of quantum information, which is based in the polarization encoding, and that allows to share secret keys through optical fibers without interruption. The dynamic polarization control system used in such scheme is described, both theoretically and experimentally. Their advantages and limitations for the use in quantum communications are presented and discussed.
In this work, both the design and experimental characterization of an InP photonic integrated circuit (PIC) working as a receiver for frequency-modulated microwave photonic links (MPWL) are presented. The PIC consists of three ring-assisted Mach-Zehnder interferometer (RAMZI) filters acting together as a complementary frequency discriminator, and includes a high-bandwidth balanced photodiode for on-chip signal detection. This is, to the best of our knowledge, the first PIC of this kind to be integrated in an active platform, and the first to include optical detectors. Designed as linear filter in optical intensity, the chip features SFDR values in the range of 78 dB.Hz2/3 and RF gains of -46 dB, partially limited by the high optical coupling losses of our experimental setup. Possible paths for further improvement of link figures of merit are also discussed.
In this paper, a novel technique to set the coupling constant between cells of a coupled resonator optical waveguide
(CROW) device, in order to tailor the filter response, is presented. It is known that using the same K value
for all the couplers produces filtering responses with significant side-lobes for the side-coupled integrated spaced
sequence of resonators (SCISSOR) or significant ripples in the pass-band for the direct coupled microrings
(CROW). It is also known that the side-lobes/ripples can be reduced, and the pass/reject bands can be made
wider, by apodizing the K value of each individual coupler in the structure, starting from a nominal K value
(either increasing or decreasing it). This technique consists on changing the effective length of the coupling
section by applying a longitudinal offset between the resonators. On the contrary, the conventional techniques
are based in the transversal change of the distance between the ring resonators, in steps that are commonly below
the current fabrication resolution step (nm scale), leading to strong restrictions in the designs. The technique has
been experimentally demonstrated employing a racetrack ring resonator geometry. The proposed longitudinal
offset technique allows a more precise control of the coupling and presents an increased robustness against the
fabrication limitations, since the needed resolution step is two orders of magnitude higher. Both techniques are
compared in terms of the transmission response of CROW devices, under finite fabrication resolution steps. The
offset technique presented is sufficient by itself for apodization, and optimized CROW's can be produced with a
fixed distance between the rings, solely by changing the offsets.
In this paper a novel microwave photonics beamformer device concept, for single side band (SSB) 40 GHz
modulated signals, is presented. The proposed device comprises tunable lasers, flat-top arrayed waveguide
gratings (AWG), a Mach Zender Modulator (MZM), an all-pass ring resonator and photodetectors. The device
can be produced as a photonic integrated circuit. The signals from the lasers (one for each beamformer radiant
element) are multiplexed by the first AWG, modulated, and passed through the all-pass ring resonator. The AWG
channel spacing and the ring resonator Free Spectral Range (FSR) are both set to be equal to 100 GHz. The signal
is demultiplexed by a second AWG and finally photodetected. By tuning each laser within its corresponding AWG
passband, the phase difference between the optical carrier and the 40 GHz microwave modulated signal for each
beamformer element can be controlled. The difference is determined by the phase response of the all-pass ring
resonator. A critical part of the design is the alignment between the resonances of the ring resonator and both
AWGs, but this can be alleviated by using a single AWG in fold-back configuration. The power provided to each
beamformer element is different due to the intrinsic non-uniform losses of the AWGs and the ring resonators, but
this can also be solved either by properly setting the lasers power, or by means of additional optical amplifiers.
The presented analysis is independent of the integration technology. In Silicon photonics, the AWGs and ring
resonator can be produced, while the (hybrid) integration of lasers, modulator, photodetectors (and eventually
amplifiers) is a challenge. The device can be monolithically integrated on semi-insulating InP technology.
We review the theory of slow and fast light effects due to coherent population oscillations in semiconductor waveguides,
and potential applications of these effects in microwave photonic systems as RF phase shifters. In order to satisfy the
application requirement of 360° RF phase shift at different microwave or millimeter-wave frequency bands, we present
several schemes to increase the achievable RF phase shift by enhancing light slow-down or speed-up. These schemes
include integrating gain and absorption sections, optical filtering and the exploitation of the initial chirp effects. As a real
application in microwave photonics, a widely tunable microwave photonic notch filter with 100% fractional tuning range
is also proposed and demonstrated.
A new amplified CWDM (Coarse Wavelength Division Multiplexing) self-referencing sensor network using phase-shifted
fiber Bragg gratings (PS-FBGs) is experimentally demonstrated in this work. The network uses the PS-FBGs to
address intensity sensors in a transmissive configuration, obtaining simultaneously in reflection a wavelength encoded
reference signal. In order to enable the remote operation of the sensors, we have introduced optical amplification at the
interrogation header of the network, using highly doped erbium fiber.
The application of transversal strain on an optical fiber leads to an asymmetry of the fiber section that locally induces
fiber birefringence. In this paper, we show that it is possible to use FBG as a probe to obtain the amount of this induced
birefringence. We describe two techniques able to get the birefringence value. They are both based on differential group
delay (DGD) measurement. The first technique makes use of the comparison between the measurement and the
simulation of the wavelength dependency of grating DGD. Considering that all grating parameters are known, we adjust
the birefringence value to obtain the best fit between experiment and simulation. For the second technique, we first
demonstrate that the wavelength dependencies of chromatic dispersion (CD) and DGD parameters differ in their
amplitude by a quantity proportional to the birefringence. We exploit this relationship to get the birefringence value by
separately measuring the DGD and CD spectral evolutions. The birefringence value is adjusted to obtain the best fit
between the two measurements. These two techniques are discussed and experimental results are finally reported.
Birefringence in fiber Bragg gratings (FBGs) can result from two distinct effects that combine with the intrinsic fiber
birefringence: the birefringence induced by the UV photo-writing and the birefringence due to a transversal load. In both
cases, it leads to polarization dependent loss (PDL) and differential group delay (DGD) inside gratings. Although these
parameters are not desired for optical telecommunications applications, we demonstrate here that they can be
advantageously used to obtain temperature-insensitive transverse strain measurements with uniform FBGs written into
standard single mode fiber, which is not possible through conventional amplitude spectral measurements. Simulated
results obtained by means of the coupled mode theory and the Jones formalism as well as experimental results measured
by means of a tunable laser source and a polarimeter are presented.
Birefringence in fiber Bragg gratings can result from two distinct effects that combine with the intrinsic fiber birefringence: the birefringence induced by the UV photo-writing and the birefringence due to a transversal load. In both cases, it leads to polarization dependent loss and differential group delay inside gratings. This paper aims to provide a characterization, both theoretically and experimentally, of the polarization dependent loss and the differential group delay generated by uniform Bragg gratings written into single mode optical fibers. We demonstrate that the measured polarization properties can be accurately reconstructed by means of the coupled mode theory and the Jones formalism. We also demonstrate that the PDL and DGD evolutions contain information about birefringence and can thus be used for transverse force sensing purposes. Experimental results obtained on fiber Bragg gratings transversally loaded by an external force confirm the simulated evolutions.
We propose a new structure for sensing variations in the refraction index independent of fluctuations in temperature. The scope of applications is very wide and can be used to detect electromagnetic, biochemical and even radiation changes. Also, it can be applied to the telecommunications field.
A new interrogation system for a large number of strain sensors is presented. In the residential building sensor market some facts have to be dealt with: low cost, networks with a large number of sensors, reliability, passive devices, amongst others. We have accomplished all of these with the new interrogation system we are going to present.
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