Seyed Reza Sandoghchi

Low-loss and low-bend-sensitivity mid-infrared guidance in a hollow-core–photonic-bandgap fiber

Hollow-core-photonic-bandgap fiber, fabricated from high-purity synthetic silica, with a wide operating bandwidth between 3.1 and 3.7 μm, is reported. A minimum attenuation of 0.13 dB/m is achieved through a 19-cell core design with a thin core wall surround. The loss is reduced further to 0.05 dB/m following a purging process to remove hydrogen chloride gas from the fiber-representing more than an order of magnitude loss reduction as compared to previously reported bandgap-guiding fibers operating in the mid-infrared. The fiber also offers a low bend sensitivity of <0.25 dB per 5 cm diameter turn over a 300 nm bandwidth. Simulations are in good agreement with the achieved losses and indicate that a further loss reduction of more than a factor of 2 should be possible by enlarging the core using a 37-cell design.

100 Gbit/s WDM transmission at 2 µm: transmission studies in both low-loss hollow core photonic bandgap fiber and solid core fiber

We show for the first time 100 Gbit/s total capacity at 2 µm waveband, using 4 × 9.3 Gbit/s 4-ASK Fast-OFDM direct modulation and 4 × 15.7 Gbit/s NRZ-OOK external modulation, spanning a 36.3 nm wide wavelength range. WDM transmission was successfully demonstrated over 1.15 km of low-loss hollow core photonic bandgap fiber (HC-PBGF) and over 1 km of solid core fiber (SCF). We conclude that the OSNR penalty associated with the SCF is minimal, while a ~1-2 dB penalty was observed after the HC-PBGF probably due to mode coupling to higher-order modes.

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

Abstract The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.

Efficient, Wide Angle, Structure Tuned 1

We propose a wide angle, efficient and low loss 1 × 3 power splitter based on triangular lattice air holes silicon slab Photonic Crystal (PhC). Desired power splitting ratio was achieved by altering the structure at the junction area of the power splitter. Simulation results obtained using 2-D finite difference time domain method show that for TE polarization incident signal, the power is distributed almost equally with total normalized transmission of 99.74% and negligible reflection loss at the 1550 nm optical operating wavelength. In addition, the power splitter can operate at 1388 nm and 1470 nm optical wavelengths.

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A glass-based substrate technology that fills the gap between a truly flexible extended length distributed sensor medium and the multifunctionality of optical chips is demonstrated. Flat fiber chips will open further degrees of freedom to control the behavior of light via mechanical manipulation. A flexible flat format will also allow straightforward incorporation into smart structures. Coupled with low manufacturing costs, these flexichips can also be a key enabler to disposable high-end sensing devices or fully distributed point sensors. In this study, Bragg gratings were used to demonstrate the optical flatness of the flat fiber core layer. Furthermore, the effective index values obtained from the grating experiment were input into a dynamic model, subsequently proving the influence of the dumbbell-shaped flat fiber cross section on the resultant UV written waveguides. Evanescent field sensing was also demonstrated by adopting a stepped Bragg approach.

3 Photonic Crystal Power Splitter at 1550 nm for Triple Play Applications

The low intrinsic nonlinearity and low signal latency characteristic of Hollow Core Photonic Bandgap Fibers (HC-PBGFs) have fueled strong interest for data transmission applications. Whereas most research to date has looked at improving the optical performance of HC-PBGFs (e.g., reducing the loss, increasing the transmission bandwidth and achieving well-tempered modal properties through the suppression of surface mode resonances). In this study, we address the challenging problem of scaling up the fabrication of these fibers to multi-kilometer lengths-an indispensable step to prove this fiber technology as viable. We report the fabrication of low loss, wide bandwidth HC-PBGFs operating both in the conventional telecoms window (1.55 μm) and in the predicted region of minimum loss (2 μm), in lengths that substantially exceed the state of the art. At 2 μm, we obtained a 3.85 km long fiber with ≈3 dB/km loss and >160 nm wide 3 dB bandwidth. Additionally, we report an HC-PBGF operating at 1.55 μm with a length of just over 11 km, transmission bandwidth in excess of 200 nm and a longitudinally uniform loss of ≈5 dB/km, measured via cutback and an integrated scattering method. We used the latter fiber to demonstrate error-free, low-latency, direct-detection 10 Gb/s transmission across the entire C-Band as well as 20 Gb/s quadrature phase shift keyed transmission. These represent the first demonstrations of data transmission over a length of HC-PBGF exceeding 10 km.

Direct UV Written Optical Waveguides in Flexible Glass Flat Fiber Chips

We report a novel approach to reconstruct the cross-sectional profile of fabricated hollow-core photonic bandgap fibers from scanning electron microscope images. Finite element simulations on the reconstructed geometries achieve a remarkable match with the measured transmission window, surface mode position and attenuation. The agreement between estimated scattering loss from surface roughness and measured loss values indicates that structural distortions, in particular the uneven distribution of glass across the thin silica struts on the core boundary, have a strong impact on the loss. This provides insight into the differences between idealized models and fabricated fibers, which could be key to further fiber loss reduction.

Multi-kilometer Long, Longitudinally Uniform Hollow Core Photonic Bandgap Fibers for Broadband Low Latency Data Transmission

First experimental wavelength scaling in 19-cell core HC-PBGF indicates that the minimum loss waveband occurs at longer wavelengths than previously predicted. Record low loss (2.5dB/km) fibers operating around 2μm and gas-purging experiments are also reported.

Accurate modelling of fabricated hollow-core photonic bandgap fibers

The modal content of 7 and 19 cell Kagomé anti resonant hollow core fibers (K-ARF) with hypocycloid core surrounds is experimentally investigated through the spectral and spatial (S2) imaging technique. It is observed that the 7 and 19 cell K-ARF reported here, support 4 and 7 LP mode groups respectively, however the observation that K-ARF support few mode groups is likely to be ubiquitous to 7 and 19 cell K-ARFs. The transmission loss of the higher order modes (HOMs) was measured via S2 and a cutback method. In the 7 cell K-ARF it is found that the LP11 and LP21 modes have approximately 3.6 and 5.7 times the loss of the fundamental mode (FM), respectively. In the 19 cell it is found that the LP11 mode has approximately 2.57 times the loss of the FM, while the LP02 mode has approximately 2.62 times the loss of the FM. Additionally, bend loss in these fibers is studied for the first time using S2 to reveal the effect of bend on modal content. Our measurements demonstrate that K-ARFs support a few mode groups and indicate that the differential loss of the HOMs is not substantially higher than that of the FM, and that bending the fiber does not induce significant inter modal coupling. A study of three different input beam coupling configurations demonstrates increased HOM excitation at output and a non-Gaussian profile of the output beam if poor mode field matching is achieved.

Understanding Wavelength Scaling in 19-Cell Core Hollow-Core Photonic Bandgap Fibers

Specialty optical fibers, in particular microstructured and multi-material optical fibers, have complex geometry in terms of structure and/or material composition. Their fabrication, although rapidly developing, is still at a very early stage of development compared with conventional optical fibers. Structural characterization of these fibers during every step of their multi-stage fabrication process is paramount to optimize the fiber-drawing process. The complexity of these fibers restricts the use of conventional refractometry and microscopy techniques to determine their structural and material composition. Here we present, to the best of our knowledge, the first nondestructive structural and material investigation of specialty optical fibers using X-ray computed tomography (CT) methods, not achievable using other techniques. Recent advances in X-ray CT techniques allow the examination of optical fibers and their preforms with sub-micron resolution while preserving the specimen for onward processing and use. In this work, we study some of the most challenging specialty optical fibers and their preforms. We analyze a hollow core photonic band gap fiber and its preforms, and bond quality at the joint between two fusion-spliced hollow core fibers. Additionally, we studied a multi-element optical fiber and a metal incorporated dual suspended-core optical fiber. The application of X-ray CT can be extended to almost all optical fiber types, preforms and devices.