This work presents the designs and performance of a series of photonic integrated interrogators developed and investigated for the last few years by the Eastern Europe Design Hub team at Warsaw University of Technology. The interrogators were designed to monitor dynamic signals from fiber Bragg gratings (FBGs) and manufactured in the generic indium phosphide (InP) platform. In particular, the main design assumptions will be presented, along with parameters initially proven by versatile electrical and optical characterization. Possible applications and further development of solutions for integrated photonic interrogators will also be discussed.
This work presents and discusses the results of developing the first integrated photonic platform for the mid-IR spectral range, MIRPIC (Mid-IR Photonic Integrated Circuits). The platform is based on the heterogeneous integration of mid-IR light sources (QCLs), Ge-on-Si waveguiding components, and mid-IR photon detectors. We will present the platform's general concept along with the library of individual components developed and tested so far, discussing them in the context of operational parameters. Recent results will be showcased, documenting progress in MIRPIC platform development while pointing out the main challenges faced by the technology.
This work has received support from the National Centre for Research and Development through project MIRPIC (TECHMATSTRATEG-III/0026/2019-00).
We present a method of in-plane modification of the refractive index using ion implantation and electrochemical etching of GaN layers. Proposed method allows for the fabrication of embedded air-GaN channels that can be periodically arranged inside III-nitride heterostructures. Importantly, a flat top surface is preserved for further regrowth. High refractive index contrast between air and GaN makes the proposed technology attractive for the fabrication of embedded photonic structures such as diffraction gratings for distributed feedback laser diodes (DFB LDs). We discuss the impact of the different design of air-GaN channels on the properties of DFB LDs.
Recent advances in integration technologies enable constructing novel, highly complex and miniaturized photonic systems for a large variety of applications. A constantly increasing interest can be observed in implementing application specific photonic integrated circuits (ASPICs) in a new generation of optical sensing systems.
The InP platform allows to realize complete interrogators of sensing systems, comprising the light sources and photodetectors. An InP PIC can also be used as a sensing element itself. In this work we discuss the sensing systems addressing two different application fields, which can benefit from the recent developments of InP platforms - optical gyroscopes and interrogators of fiber Bragg gratings.
The principle of work of optical gyroscope is based on the Sagnac effect. Two typical configurations can be identified – interferometric fiber-optic gyroscope (IFOG) and ring laser gyroscope (RLG). An integrated interrogator unit of an IFOG system presented here was realized using a DBR laser, passive couplers and PIN photodiodes. Characterization results have proven the possibility of detection of the Sagnac signal for the length of the fiber loop of 1 km. We also discuss monolithic single-frequency lasers, which were realized in the framework of the development of an integrated optical gyro.
Also, the integrated interrogators of fiber Bragg gratings are presented and discussed. The investigated solutions are based on the interrogation scheme in which a broadband signal is coupled to a network of FBGs, and the reflected signals are analyzed using a spectrometer based on an arrayed waveguide grating. Several realized circuits are discussed with respect to their design, characterization results and potential for application in sensing systems.
Studies were funded by FOTECH-1 project granted by Warsaw University of Technology under the program Excellence Initiative: Research University (ID-UB). This work was partially supported by National Centre for Research and Development (PBS3/B9/41/2015).
Together with the development of fiber optic sensor networks the accurate and reliable operation of dedicated readout instruments became a critical issue. After years of optimizing the interrogating devices the use of photonic integrated circuits (PICs) has opened a new era of highly reliable, compact and versatile devices offering additionally advantages of low power consumption and cost-optimized design.
Considering the most commonly deployed fiber Bragg grating (FBG) based sensor systems/networks, typically two PICs-based solutions for interrogators may be used: an arrayed waveguide grating (AWG) spectrometer with a broadband SLED source or a set of tunable laser sources with a photodiode detector. Among commercially available PIC technologies the InP platform has a substantial advantage as it allows fabrication of both passive devices (waveguide circuitry) as well as active devices (photodiodes and light sources) in the same technological process.
In this work we investigate two different layouts of AWG-based integrated interrogators fabricated in generic technology of indium phosphide. We analyze the influence of crosstalk between AWG channels on operation of the device and possibility of interrogating narrow-band FBG reflection peaks as well as the influence of input polarization state on the AWG response, which is of fundamental importance for proper operation of an integrated FBG interrogator. As there is no polarization control elements available at present in the offer of generic InP technology providers we discuss the possibility of using off-chip solutions exploiting additional fiber-optic components. As a possible alternative to AWGbased interrogators, we discuss also the possibility of using integrated tunable lasers for FBG interrogation.
In this work we would like to present the results of low loss coupling of a novel soft glass fiber for super continuum generation with standard single mode fiber by a filament splicing method. For our experiment we used an all solid soft glass microstructured fiber (MSF) made from a composition of F2 lead-silicate glass and NC21 borosilicate glass. The structure and material properties of the fiber were optimized to achieve all normal dispersion (ND) flattened around 1560 nm, which offers two general advantages for supercontinuum generation. The ND supercontinuum avoids soliton dynamics, hence it is less sensitive to pump laser shot noise and has larger degree of coherence than supercontinuum in the anomalous dispersion range. Furthermore flattening around 1560 nm indicates optimal supercontinuum pump wavelength, which is readily available from erbium doped femtosecond fiber lasers. Using Vytran splicing station (GPX3400) we were able to achieve repeatable splice loss between a standard fused-silica single mode fiber (SMF28) and the low-melting-temperature soft glass MSF as low as 2.12 dB @1310 nm and 1.94 dB @ 1550 nm. The developed very low loss splicing technology together with the above mentioned all solid soft glass MSF advantages give very promising perspectives for commercial applications.
Phase sensitivities of temperature, longitudinal strain or pressure, are very important fiber features in sensing and
telecommunication applications. The most common ways to modify such sensitivities are to change the material
properties (by adjusting the core doping level) or employ microstructured fibers (which properties strongly depend on the
cross-section geometry). We decided to investigate strain sensitivity influenced by effective mode field area and mode
field diameter as clear consequence of fiber cross-section geometry.
In this paper we present the results of a three dimensional numerical analysis of the correlation between the fiber mode
field diameter and its longitudinal strain sensitivity. Both conventional and microstructured (commercially available and
custom designed) fibers are investigated. Furthermore we compare the theoretical results with experimental data. To
measure fiber sensitivity we developed a dedicated all-fiber Mach-Zehnder interferometer which enables the
measurement of strain induced phase changes in various fiber types (including conventional and microstructured fibers).
As a conclusion of our work we present relationship between strain sensitivity and MFD .
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