Erbium doped fibers (EDFs) based devices are widely employed in space for optical communication [1], remote sensing [2], and navigation applications, e.g. interferometric fiber optic gyroscope (IFOG). However, the EDF suffers severely radiation induced attenuation (RIA) in radiation environments, e.g. space applications and nuclear reactors [3].
An electrically controllable fiber Bragg grating (FBG) for working in the communication band is demonstrated by utilizing holographic polymer-dispersed liquid crystal (HPDLCs). PDLC is infiltrated in hollow-core fibers which are about 2μm and 5μm by means of capillarity. For the purpose of periodically separating polymer and liquid crystal to form an FBG, a two-beam interference system based on an argon laser (wavelength: 364nm) is used. To reduce coupling loss, we directly connect single-mode fibers (SMFs) to input and output ports. A maximum transmission loss dip of approximately 5-dB band rejection is obtained. After the cladding diameter is etched by buffered oxide etchant (BOE) solution to 12μm and a 150V external voltage is applied, a dip shift by ~ 15nm is measured
We demonstrate a novel method which is simple, real-time, and non-destructive to measure the core diameter of a coaxial cylinder. An optical fiber is an example of coaxial cylinder. The diameter measurement method is based on side-light-incidence scattering principle. For a cladding diameter 126μm coaxial fiber, our method could be used to measure core diameter ranging from 8 to 40μm. We could measure the core diameter of a coaxial cylinder for cladding diameter varying from 50 μm to 125 μm from our database. The accuracy of core diameter measurement could reach over 95%.
A corrugated long period microfiber grating (C-LPMFG) is fabricated by etching the corrugated LPFG down to tens of
micrometers in diameter with corrugated periodic structures made by using imprint lithography. It can be a grating
because of the periodic effective index difference caused by the corrugated structures without prestrain. During etching
of C-LPMFGs the in-situ monitoring of resonant wavelength shows that the wavelength shift varies rapidly with the
etching of fiber. The resonant dips are calculated and have similar trends compared with the experiment data. The
C-LPMFG is used as a temperature sensor with sensitivity of -146 pm/°C.
We demonstrated the splicing of 2 μm diameter microfibers by using a modified arc discharge device. Two microfibers
were aligned with the help of van der Waals forces before fusing them together by arc discharging. Most splicing losses
were below 1 dB, and the lowest was 0.16 dB. A spliced microfiber did not induce undesired wavelength selection
because arc splicing was a complete joining technique which is different from evanescent coupling. Simulation results
show splicing coupling has better averaged coupling efficiencies than evanescent one over various overlapping lengths,
and the measured results show consistency.
The dependence of radiation induced attenuation (RIA) on Al concentrations was investigated for
γ-irradiated EDFs doped with different Er, Al and Ge concentrations. The dependence of RIA on dose was
found well fitted by power law, and linear dependence of adjusted α on Al concentrations was verified. When
the Al concentration was as low as 0.11%, an unknown RIA band with absorption peak around 800 nm was
observed, which might be related to Erbium ions.
The performance of an FOG using a DPB SFS in a laboratory environment is reported, and compared with the one
using an SPB SFS. The result shows that the DPB SFS has a larger linewidth and a higher pump efficiency than the SPB
one. When measuring the earth rotation rate, the FOG using the DPB SFS has lower random noise and smaller bias drift
(0.019 deg/√h and 0.18 deg/h) than that using the SPB SFS (0.023 deg/√h and 0.47 deg/h). If a DPB SFS was applied in
the space, its output loss due to radiation damage could be smaller than an SPB one because a DPB SFS used a shorter
EDF so that the total radiation induced loss is reduced.
We demonstrate a new method that could make possible the mass production of symmetric and asymmetric corrugated long period fiber gratings (C-LPFG) by utilizing hot embossing and imprint lithography on polycarbonate (PC). The poly-dimethylsiloxane (PDMS) is imprinted on PC to create the periodic revealed region of fiber for hydrofluoric acid (HF) etching. The asymmetric C-LPFGs show some unique optical characteristics of two separate dips due to their asymmetric structures. After the torsion, the second dip would be gone and the first one would begin to shift toward shorter wavelength. It is assumed that the asymmetric C-LPFG behaves similar to the symmetric one with the torsion of a full circle. A C-LPFG was well packaged by fixing itself in the PC and having some open area close to the fiber to receive the liquid under test. The corrugated structures close to the fiber core were covered by the liquid that the packaged refractive index sensor has the sensitivity of 26.7 nm/RIU.
The assumption that a tapered fiber core diameter shrinks down as the same ratio to the cladding diameter was
examined by observing the refractive index profiles variation along the fiber. How small the cladding diameter be and the
core would still exist was also examined. Refractive index profiling method based on quantitative phase microscopy
(QPM) gives the ability to mapping the two dimensional refractive index profiles, and the tapering variation can be
obtained from this approach. A small amount of core germanium diffusion was observed, which suggests the non-ideal
fact of the core/cladding diameter ratio. The core can still be resolved when the cladding diameter is down to ~10μm,
proving the existence of the core down to this scale.
Two EDFs with different radiation sensitivities were used in the photo-annealing tests. We compared photo-annealing
efficiencies obtained by using 532 nm and 976 nm lasers. The 532 nm laser with 10 mW showed better efficiency than
976 nm laser with 290 mW in a ~30 cm EDF. The recovery rate was 5.6 seconds of the half-height recovery time. The
532 nm laser possibly excited the defects and provided some thermal energy so that the defects could be recovered. The
annealing efficiency from using the 976 nm laser was close to the one purely from thermal annealing at ~330 °C. For
practical tests, we also built two SPB SFSs and a bidirectional SFS and measured the output power loss dependence on
pump power. Under the dose rate of 129.2 krad/hr, the recovery rate of output power loss was 0.009 dB/min when a 2.8
m EDF#1 co-pumped by both the 532 nm and the 976 nm lasers.
Mean-wavelength stable superfluorescent fiber sources composed of three kinds of EDFs were irradiated by a 60Co
source up to 2000Gy to compare their mean-wavelength drifts and output power losses.
We report bubble scattering effects on photoresist when a 193nm immersion interferometric lithographic system is employed. According to Mie theory and FDTD simulation, the scattering effect of a bubble becomes significant and may cause defects on a resist pattern when its diameter is greater than 60nm. Some preliminary experimental results are also included.
The chemistry of acid-catalyzed dehydration reaction and followed by crosslinking of the tert-alcohol group in the cycloolefin photoresists was used to tailor the performance of the photoresists for 193nm lithography. A radiation- sensitive photoacid generator (PAG) in this chemically amplified photoresist (CAMP) can change the polarity of the exposed area of the resist and exhibit a negative-tone behavior. The cycloolefin resists are synthesized by the free radical copolymerization of alicyclic monomer and maleic anhydride, and/or by the cationic polymerization of alicyclic monomer via Pd catalyst followed by the attaching of tert-alcohol group in to the resist. The side reaction of cycloolefin copolymer was observed at the temperature below the post exposure baking (PEB) temperature, but this problem can be eliminated by the introduction of isobornyl methacrylate into the polymer. The lithographic performance of the resists was investigated by using isopropyl alcohol as a developer under various processing conditions. The results demonstrate that these resists are the promising candidates for being used in 193nm lithography.
A novel torsion sensor is made of a corrugated long period fiber grating whose shift of peak resonant wavelength is directly sensitive to the applied torsional angle per length.
Suitable silicon-oxynitride films for constructing the attenuated phase shifting masks to be operated in the 157 nm excimer laser regime are obtained by varying the gas flow rations in a RF sputtering process. Characteristics of the films such as optical constants, material compositions, etching selectivity, surface profiles, and adhesion strength are experimentally analyzed. These results indicate that he silicon-oxynitride films thus fabricated can meet the requirements for building such APSM's working in the wavelength of 157 nm.
We have simulated the optical behavior of a new reflective APSM by utilizing the optical multilayer thin film theory. In a typical Mo/Si multilayer structure, we show that the requirement of a reflective APSM can be met simply by adjusting the thickness of the over-coated Ge layer. A phase shift of 180 degrees results when compared light reflected from a Ge absorption layer to that form a Mo/Si multilayer, and the resultant reflectance ratio is in the range of 4-15 percent. No additional phase shifting layer is needed.
The effects of optical feedback on the characteristics of a double pass backward (DPB) superfluorescent fiber source (SFS) are demonstrated and compared to those of the single pass backward (SPB) SFS. The major effects of the optical feedback are the formation of resonance cavity for a DPB SFS and the reduction of output power for an SPB one. An isolator with an isolation loss larger than 50 dB should be used for both backward SFSs to maintain a stable mean wavelength operation, large output power and broad linewidths.
An appropriate analytical model which deals with out-of- plane coupling between an elliptical Gaussian beam and an angled single mode fiber is developed and utilized for two potential applications. The first one is for fast search of the optimal coupling efficiency in an optical sub-assembly packaging process while the second one is for the inspection of concentricity between the up and low tooling in an optical sub-assembly packaging system.
Fiber Bragg gratings were fabricated by utilizing high pressure deuterium loading for photosensitivity enhancement and a phase mask for holographic exposure. The absorption peak near 1.71 micrometers was used as an indicator to monitor the evolution of deuterium diffusion into and out of a fiber, and the results were consistent with the theoretical modeling. Thermal hysteresis of the fiber Bragg grating was greatly reduced and thermal reliability was increased when annealing was applied.
We demonstrate a four-channel WDM network at 622 Mb/s with 1 .3 xm multifrequency Fabry-Perot laser diodes. A channel spacing of only 15 nm was achieved by using a WDM component consisting of interference filters of special design. Results of laser-filter misalignment measurements suggested that more channels could be implemented without serious power penalties from mode-partition noise. Higher bit rate transmission in such a medium-density WDM system was also shown.
An efficient holographic optical element that combines the beammultiplexing properties of binary-phase computer-generated holograms with the efficiency of volume holograms formed in dichromated gelatin is described. Experimental results for an element that improves both the efficiency and the signal-to-noise ratio of a computer-generated hologram
are presented. The possibility of using this element as an optical interconnect is discussed.
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