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Dispersion-induced Power Penalty In Fiber Bragg Grating-Based DWDM Network ElementsHuang, Ming-Hong 20 June 2001 (has links)
Optical add/drop multiplexer (OADM) and optical wavelength cross-connect (WXC) are two
key components to enable greater connectivity and flexibility in dense wavelength division
multiplexing (DWDM) networks. Fiber Bragg grating (FBG) based components have several
inherent advantages such as compact, low-insertion loss, high reflectivity, no-linearity
effect, polarization insensitivity and wavelength tunability.
We experimentally investigate the system power penalty induced by the chromatic dispersion
of the FBG as a function of the wavelength detuning of the reflection spectrum for 10 Gb/s
signals, which was reflected by cascade of FBGs. Such power penalty limits the number of
cascaded gratings and restricts the allowable range of wavelength detuning.
In our experiments, we have used several FBG filters with 3-dB bandwidth of 0.43 nm.
According to the experimental results, power penalty increases from the central wavelength
to the edge wavelength of the reflection spectrum. There are 0.4 dB and 7 dB power penalty
for one single FBG and ten cascaded-FBG filter, respectively, when the central wavelength
was detuned to ¡Ó0.2 nm and ¡V0.1/+0.14 nm. This study result may give a design guideline of
fiber grating-based optical add-drop multiplexers or optical wavelength cross-connects in DWDM
nodes.
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Fabrication and Characteristics of Fiber Grating External Cavity LasersYang, Huei-Min 02 June 2004 (has links)
A new scheme of fabricating the tapered hyperbolic-end fibers (THEFs)microlenses using unique etching and fusion techniques is proposed. TheTHEFs were fabricated by symmetrically tapering the fiber during theetching process and hyperbolically lensing the tip during the fusing process.The tapered hyperbolic microlenses have demonstrated up to 82% couplingefficiency for a laser with an aspect ratio of 1:1.5. The influence of the tapering asymmetry on the coupling has also been investigated
experimentally and theoretically. The axially symmetrical taperedmicrolenses of the THEFs showed that far-field profiles were well approximated to a Gaussian profile, while the asymmetric taper had deviated significantly from a Gaussian profile. A theoretical analysis illuminated a
larger wavefront transformation of the hemispherical microlenses. A lesser phase aberration of the normalized optical path difference (OPD) was found in the hyperbolic-end lens, and that resulted in more than 2 dB improvement
in the coupling efficiency when compared to the currently available hemispherical microlenses. The high-coupling performance of the hyperbolic microlens was due to an improved wavefront matching between the laser and
the fiber, which was one of the most important contributions in this study.The 1.55 µm fiber grating external cavity lasers (FGECLs), packaged with THEF microlens for coupling the fiber grating external cavity, have been investigated for different combinations of coupling efficiency (£b) and Bragg reflectivity (Rg). Various tapered hyperbolic-end fiber microlenses
with different coupling efficiency have been fabricated for this study. The FGL of higher £b = 72% and Rg = 0.52 has a stronger resonant feedback as the spectral output showed a single longitudinal mode with the side-mode-suppression-ratio (SMSR) greater than 45dB, a high output power of greater than 5mW, and a lower threshold current. However, for the case of £b = 68% and Rg = 0.35, the FGL exhibited a more stable SMSR against the variation of pumping current and temperature. Numerical simulations have also been performed on the SMSR at different coupling efficiencies and Bragg reflectivity for the FGLs. The high performance of the FGLs can be achieved through a higher coupling efficiency between a laser diode and a single-mode fiber. The calculated SMSR showed an excellent agreement with the measured data.
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Packaging of 2.5 Gb/s Directly-Modulated Non-AR Coated Fiber Grating External Cavity LaserWang, Shih-Hung 07 July 2004 (has links)
This study proposes a low cost potentiall with non-AR coated fiber grating external cavity laser (FGECL) module to apply the metro/access network.
The components inside the module include uncoated FP (Fiber-Perot) laser chip, PIN detector, substrate, and cooler. The processes of package are following: (1) to utilize the die-bonder to fix the FP laser and the PIN detector on the substrate, (2) to utilize the heating apparatus to make the cooler fixed on the butterfly housing and the substrate fixed on the cooler, (3) to utilize the 353ND paste to make the thermistor fixed on the substrate, and (4) to utilize the electrothermal heating machine to melt indium wire and then adjust the fiber lens provided with higher coupling efficiency of fiber pigtail by tweezer to couple light into the fiber inside the butterfly housing.
This study achieves a FGECL module with the output power of larger than 2mW and the side-mode suppression ratio (SMSR) of more than 38dB. Finally, we measure eye diagram and bit-error-rate at 2.5Gb/s of the FGECL module to analyze the impedance matching of laser diode, current signal and the limit of the dispersion to the optical communication system. The performance of the FGECL module can meet the ITU-T G.957 standard.
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Packaging and Characteristics of AR-Coated Fiber Grating LaserTsai, Zong-jin 11 July 2005 (has links)
The fiber grating external cavity laser (FGECL) module packaged with fiber bragg grating and FP laser diode is investigated. The optical spectrum of FGECL is single longitudinal mode. In order to get stable single longitudinal mode, the FP laser diode coated with an AR-coating (reflectivity is 0.5%).
To achieve higher coupling efficiency between laser diode and fiber, the hyperbolic-end lensed fiber is used. A coupling efficiency of up to 86% has been demonstrated. The alignment and fix between laser diode and fiber are accomplished by laser welding technology.
The results of FGECL module show that the output power and side-mode suppression ratio (SMSR) are more than 2mW and 44dB, respectively. Comparing to the non-AR coated FGECL, the result of SMSR is 5 dB improved. Dynamic tests of the FGECL module operate at 2.5Gbps, including the eye diagram, bit error rates, impedance matching of laser diode, signal current, and the limit of the dispersion in the optical communication system has been measured. The FGECL module can meet the ITU-T G.957 standard.
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The Study of Spectral Characteristics for Non-AR Coated Fiber Grating LasersChen, Ming-Hung 24 June 2001 (has links)
ABSTRACT
The spectral characteristics for non-AR coated fiber grating lasers were studied theoretically and experimentally. The lensed fiber was used to improve coupling efficiency between laser and fiber. The tapered fibers were fabricated by using the mixture of HF and oil with different density to increase etched taper angle. The coupling efficiency could reach more than 60%. A single-mode operation for a fiber grating external cavity laser (FGECL) was simulated. The results showed that the SMSR, emitted power, and wavelength drift were dependent on the related device parameters. Our calculations showed that the strong current-dependent SMSR oscillation was from the mode selection by the fiber grating external cavity and the heating effect in the Fabry-Perot (FP) laser. A 1.55mm FP laser chip that one facet was coated a high reflectivity (HR) of 90% and another facet was uncoated. In our experiment and simulation of FGECL, the reflectivity of fiber gratings were 50% and 70% and 86%, and the length of external cavity was about 0.9cm. The measured result of FGECL showed that the side-mode suppression ratio (SMSR) was more than 35dB and the output power was larger than 1.5mW at the injected current 2 to 3 times of threshold current. Furthermore, the spectrums of fiber grating external cavity lasers were studied in order to understand the external laser characteristics.
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UV-Induced Long Period Fiber Gratings in Gel-Filled Photonic Crystal FibersChen, Chi-Ping 28 July 2010 (has links)
A long period fiber grating (LPFG) is formed by inducing the periodic refractive index variation along a fiber. A lot of work has been done to fabricate the LPFGs in the photonic crystal fibers (PCFs) to function as all-fiber band-rejection filters, interferometers, and sensing applications.
In this thesis, we propose a novel LPFG based on the gel-filled PCF. The PCF filled with the UV gel was exposed to the high-intensity UV light through the mask. The periodic index variation is formed along the fiber in the cladding region, resulting in the LPFG. By measuring the propagation losses of our LPFG, three spectral dips in the transmission bands are observed at 872 nm, 1309 nm, and 1418 nm as the grating period is 600 £gm, which indicates the mode coupling from the fundamental core mode to the higher order modes (HOMs) of the gel-filled PCFs. By using a full-vector finite-difference frequency-domain (FDFD) method, we numerically calculate the phase match condition for our LPFGs. The calculated resonant wavelengths are 875
nm, 1319 nm, and 1415 nm. Very good agreement between the measured resonant wavelengths and the numerical results is obtained. We also fabricate the selectively gel-filled LPFGs to reduce the propagation losses by utilizing a simple selectively blocking technique. In addition, we measure and discuss the sensing sensitivities of
the UV-induced LPFGs, including the temperature, strain, curvature, torsion, and surrounding refractive index (SRI) sensitivities. The measured sensitivity to temperature is 1.7 nm/¢XC from 25 ¢XC to 45 ¢XC. As the surrounding refractive index is increased to 1.377, the dip position has a maximum shift of 2 nm. Compared with other LPFGs, the UV-induced LPFGs are more insensitive to bending and strain due
to the complete cladding structure. This could benefit the stability of the temperature
sensors, based on our UV-induced LPFGs.
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Gain Flattening Design For Optical Fiber Amplifier By Long-Period Fiber GratingsKe, Chun-Hao 20 August 2004 (has links)
Using Long-Period Fiber Gratings as component of Gain-Flattening filter ofOptical Amplifier, and discuss spectrum of different struture of Long-Period Fiber Gratings. To investigate the spectra characteristics of Long-Period fiber Gratings for designing reference resources. Aiming at different Gain-Flattening filter uses different struture of fiber grating, and the decision of parameter of fiber grating using Genetic Algorithm. Finally delcaring the dataflow of designing filter using Long-Period Fiber
Grating and conclusion.In this paper , gain flatttening Cr:YAG optical amplifier spectrum and Erbium-doped optical amplifier spectrum,one achieve 300nm bandwidth and
another achieve 40nm.
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Coupling between Ultra High-Power Laser Diodes and FibersWang, Kuo-liang 11 July 2005 (has links)
The width of an ultra high-power laser diode is greater than 50 £gm and more than 20 times of low-power laser diode.The core diameter of Erbium Doped Fiber Amplifier fiber (EDFA) is 4~6 £gm and it is a single-mode fiber (SMF).However¡Athe ultra high-power laser diode is multi-mode laser. Therefore¡Athe mismatch between high-power laser and SMF resulting in low coupling efficiency.
We improve coupling efficiency by using a wedge-shaped graded-index fiber (GIF) tip spliced to a SMF then fused a fiber bragg grating (FBG) to form an external cavity laser. The GIF is a focusing action like a graded-index fiber. From near-field pattern (NFP)¡Awe find the best GIF length is 400 £gm. The coupling efficiency between ultra high-power laser diode and wedge-shape lensed fiber is only 5% .
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Optically Controllable Long-Period Fiber Gratings in Photonic Liquid Crystal FibersChang, Ting-Hao 12 July 2011 (has links)
Recently, long-period fiber gratings (LPFGs) based on PCFs have been demonstrated by using heating or a mechanically pressure to induce periodic index variations along the fibers. However, LPFGs fabricated by these two methods suffer the structure damage. In this thesis we propose novel optically controllable LPFGs based on the photoresponsive photonic liquid crystal fibers (PLCFs) and no structure damage occurs during the fabrication process.
The photoresponsive PLCF was filled with a LC mixture consisting of the nematic LC E7 and the photoresponsive 4MAB. The properties of the photoresponsive PLCF can be modulated by using laser irradiation. In addition, the transmission bands of the photoresponsive PLCF can also be tuned by controlling the 4MAB concentration or operation temperature. An optically controllable LPFG was fabricated based on the photoresponsive PLCF by using blue-laser irradiation through a mask with 700-£gm grating period. The measured resonant wavelength appeared at 1539 nm with the FWHM was 27 nm, and the maximum dip depth was about −15 dB with a 6.5-dB insertion loss. The LPFG was shown to be erasable by using a green laser. In addition, we have also investigated the effects of the number of grating period, 4MAB concentrations, operation temperatures, thermal recovery properties, and irradiation intensity on the LPFGs. Our proposed optically controllable LPFGs possess reversible property and are quite useful to be applied in tunable optical devices.
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Vláknové difrakční struktury Point-by-Point / The Point-by-Point fiber diffraction structuresValášek, Martin January 2017 (has links)
The diploma thesis described the basic principles and characters of the long period fiber gratings (LPFGs). Our concern was to describe basic mathematical description of these gratings needed to their modelation and simulation. Consequently some exact models leading to changes in the shape of the spectrum LPFGs were suggested, these methods were the chirping, apodization and changes in the average refractive index navg. In the Matlab environment, programes for counting the important parametres LPFGs were created and meanwhile each model leading to the change in the shape of the spectrum was simulated.
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