Superimposed Bragg Gratings Research Articles

Superimposed Bragg gratings and entangled biphoton dispersion management

Quantum optical integrated circuits have heralded a paradigm shift in the realm of quantum information processing. Integrated photonics technology now empowers the creation of intricate optical circuits on single chips. While optical integrated circuits used to pose formidable challenges for numerous quantum applications, they have, in recent times, evolved to satisfy stringent requirements across a spectrum of research and industrial domains. Today, it is imperative to delve into research aimed at both crafting and preserving quantum properties within photonic substrates. Superimposed Bragg grating structures have emerged as valuable components within optical applications, poised to play pivotal roles in the development of integrated circuits. Nevertheless, these structures exhibit an inherent drawback in the form of dispersion, which can potentially compromise the preservation of quantum states. In this study, we meticulously scrutinize the physical attributes of these structures to elucidate the factors contributing to undesirable dispersion effects. We also investigate the correlation between two photons at the termination point of the structure. The superimposed Bragg grating structure under scrutiny boasts periods of both 1 and 3 micrometers, an overall length of 100 micrometers, and radiates at a wavelength of 1.55 micrometers. By subjecting photons to this medium individually or in tandem and analyzing their correlation function, we aim to pinpoint elements that effectively safeguard the quantum properties inherent in the system. This research endeavor is poised to yield valuable insights that will substantially influence the design of quantum integrated circuits, enhancing their efficacy in computational tasks and quantum information processing.

Reflectivity of Superimposed Bragg Gratings Induced by Longitudinal Mode Instabilities in Fiber Lasers

We report on reflectivity of transient Bragg gratings created in the active medium of a fiber laser with longitudinal mode instability. Despite the long history of laser physics, reflectivities of such gratings were theoretically studied and experimentally measured only recently. Based on the coupled-mode theory, we derived a theoretical model of superimposed Bragg gratings for a special case of mode instability known as spontaneous laser line sweeping (SLLS). SLLS fiber lasers exhibit a periodic wavelength drift over an interval of several nanometers, followed by a quick bounce backward, narrowband, and mostly single-frequency operation as well as pulsed output with pulse lengths on the order of microseconds. The refractive index modulation inside the active fiber is given by the Kramers–Kronig relations. For ytterbium, the refractive index change in the 1060-nm band is directly proportional to the metastable level population with a factor of ${\text{2.1}}\times {\text{10}}^{- 31}\,{\text{m}}^{3}$ . Taking into account realistic values of temporal damping of the gratings, significant reflectivity on the order of units to tens of percent is estimated. The reflectivity can be controlled by setting the SLLS laser parameters. Effect of the resonator length is shown as an example.

Inscription of superimposed fiber Bragg gratings using a Talbot interferometer

In this paper, we present results on the inscription of superimposed Bragg gratings in various optical fibers, including specialized light guides produced in Russia, using an inscription setup based on the Talbot interferometer. A KrF excimer laser system of the master oscillator type—an Optosystems CL-7550 power amplifier—is used as the source of ultraviolet radiation for the experimental stand. The spectral characteristics of superimposing a different number of fiber Bragg gratings are demonstrated and the inscription of several Bragg gratings in the same region of the optical fiber is investigated.

Highly efficient volume hologram multiplexing in thick dye-doped jelly-like gelatin.

Dye-doped jelly-like gelatin is a thick-layer self-developing photosensitive medium that allows single and multiplexed volume phase holograms to be successfully recorded using pulsed laser radiation. In this Letter, we present a method for multiplexed recording of volume holograms in a dye-doped jelly-like gelatin, which provides significant increase in their diffraction efficiency. The method is based on the recovery of the photobleached dye molecule concentration in the hologram recording zone of gel, thanks to molecule diffusion from other unexposed gel areas. As an example, an optical recording of a multiplexed hologram consisting of three superimposed Bragg gratings with mean values of the diffraction efficiency and angular selectivity of ∼75% and ∼21', respectively, is demonstrated by using the proposed method.

All‐optical multi‐wavelength header recognition using superimposed Bragg gratings based correlators

SUMMARYWe have demonstrated that an optical correlator, based on superimposed Bragg gratings, can be used as all‐optical multi‐wavelength header recognition in optical packet switching networks. The proposed correlator is composed of two superimposed gratings in conjunction with variable delay lines. These superimposed Bragg gratings are used to demultiplex and multiplex the wavelength components of multi‐wavelength header bit patterns. The variable delay lines create a wavelength profile that can be matched with any arbitrary bit patterns. Simulation results for all optical recognition of four‐bit patterns at 10 Gbps are reported. The results show that when the header bit pattern matches the wavelength profile of the correlator, the generated auto‐correlation function will include a high amplitude peak; otherwise, a cross‐correlation function with low amplitude peaks will be generated in the output of the correlator. Considering this idea, multi‐wavelength header is recognized by using all‐optical processing method. Copyright © 2012 John Wiley & Sons, Ltd.

Wavelength demultiplexing with layered multiple Bragg gratings in LiNbO_3:Fe crystal

Dense wavelength division multiplexing (DWDM) is an important technology for expanding the capacity of optical network. The optical component based on the superimposed Bragg gratings shows that it can be used as one of advantageous multichannel components because of its excellent angle and wavelength selectivities. An optimized method for recording multiple Bragg gratings for wavelength demultiplexing in optical telecommunication band is proposed to achieve gratings with equal diffraction efficiency. A structure of three layers with twenty four gratings is demonstrated in a LiNbO(3):Fe crystal by employing the optimized recording method. Then an initial wavelength demultiplexing experiment based on the formed gratings is carried out in optical telecommunication C-band. The results obtained by measuring and analyzing the transmitted spectra of the fabricated gratings show that the diffraction efficiencies of the gratings are uniform. It is suggested that this kind of multiple gratings can be used for increasing the number of the demultiplexed wavelengths in recording medium with unit volume for WDM.

Study of Multichannel Parallel Anti-Symmetric Waveguide Bragg Gratings for Telecom Applications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We theoretically demonstrate the viability of parallel anti-symmetric waveguide Bragg gratings within a two-mode waveguide. These gratings produce reflections with mode conversions. This is the functional equivalent of superimposed Bragg gratings in silica-on-silicon without requiring multilevel etches. Also, due to their weaker coupling constant, these gratings allow for devices with narrow spectral full-width at half-maximum that can process multiple wavelength channels for applications such as optical add–drop multiplexers and optical encoders in optical communication systems. </para>

Generalized Fibonacci quasi photonic crystals and generation of superimposed Bragg Gratings for optical communication

In optical fiber communication, usually, optical signals are communicated around 1.35 or 1.55μm. All optical active and passive devices should operate in these wavelengths or in a bandwidth close to these wavelengths. In this paper, it is shown that the Fibonacci-class (FC(J,n)) one-dimensional quasi-periodic dielectric stack for [1.2–2μm] bandwidth duration shows superimposed Bragg Gratings behavior. Thus, a new method will be presented to approximate these structures with superimposed Bragg Gratings in this wavelength duration. For the approximated superimposed Gratings the number of Gratings, the index of refraction contrasts, number of layers and related period of Gratings are calculated in terms of original system parameters. The proposed idea will open applicable analytical methods for investigation of quasi crystals in optical communication. Also, using presented approach nature of light propagation and physical interactions through these structures can be better described. In this work, using simulation of original Fibonacci quasi structure some of important parameters are extracted. Then, all parameters for construction of the superimposed Bragg Gratings using basic relations in integrated optics and extracted information will be calculated. Finally, constructed model is simulated and compares with original case. We show that our constructed superimposed Bragg Gratings closely follows original curve.

Superimposed Bragg gratings in high-birefringence fibre optics: three-parameter simultaneous measurements

We used a pair of Bragg gratings written in high birefringence fibre optics to measure, simultaneously, longitudinal and transverse strain and temperature. The Bragg gratings are superimposed in the same position of the fibre optic, so as to behave as a punctual sensor. The sensitivity of the spectral response of the device to longitudinal strain, transverse strain and temperature are all characterized, and the results of its application as a three-parameter sensor are also presented.

Fabrication of high-reflectivity superimposed multiple-fiber Bragg gratings with unequal wavelength spacing

We report the inscription of as many as 10 superimposed Bragg gratings of high reflectivity in a 25-mm segment of fiber. Using hydrogenated boron codoped and germanosilicate fibers, we inscribed 10 superimposed gratings with reflectivities above 80% and 6 superimposed gratings with reflectivities above 98%, respectively. The superimposed gratings had unequal wavelength spacing and were written over a 20-nm wavelength span in the region of 1530 nm. The inscription of each new grating caused an increase in the FWHM linewidth of the existing gratings, while their reflectivity was unaffected.

Superimposed Bragg gratings on semiconductor material

The authors report the transfer of six Bragg gratings at the same location into semiconductor material. Measurements on an active device demonstrate that all the gratings have the same efficiency for guided light. This technology is an attractive alternative to the sampling effect for providing multiwavelength filter functionality at predefined wavelengths.

Superimposed multiple Bragg gratings

The authors demonstrate the inscription of seven Bragg gratings at the same location on a photosensitive fibre. These superimposed Bragg gratings were written over a 60 nm span in the region of 1530 nm with reflectivities better than 45%. Effects due to the inscription of multiple gratings within the same location on the fibre such as wavelength shifting and linewidth narrowing are studied.