We investigate a two-wavelength method for recording a persistent hologram in a doped photopolymer. The recording method is based on two separated optical excitations of the four-energy-level system of the doped element, one at λ=325 nm as the sensitizing wavelength and the other at λ=647 nm as the writing wavelength, allowing for an experimental demonstration of nondestructive readout in phenanthrenequinone-doped poly(methyl methacrylate). Further, a four-energy-level rate equations model is proposed for describing the dynamics of hologram recording. The model successfully explains our experimental finding and further provides a general method to investigate such a two-wavelength holographic recording in photopolymer.
Two-wavelength holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) photopolymer is demonstrated. By using 325 nm laser as a gating illumination during the holographic recording with 647 nm laser, a volume hologram with diffraction efficiency of ∼ 4% can be recorded in a 2 mm thick sample. In addition, the Bragg selectivity curve with clear sinc nulls is demonstrated. These results support further applications as recording media for volume holographic device with extended spectral response and selective recording property.
As a type of optical measuring apparatus, the charge-coupled diode (CCD) camera provides the capability of increasing the speed of measurement by inspecting an area with only one shot. However, the CCD camera's high-variation range of reflectivity presents an exceptional challenge for the optical measurement established on the surface. We present a method that could enable one to acquire an image with a high-dynamic range in one shot without any reduction in spatial resolution. Because of the sufficient signal-to-noise ratio, the method presented could perform the robustness of the phase-retrieving algorithm, and the surface topography could be measured more accurately.
In this paper, we propose and experimentally demonstrate a simple self-restored architecture for WDM passive optical
network (PON) by only adding a novel 2x2 optical switch design in each optical networking unit (ONU). By using the
proposed protection architecture, the affected traffic will be restored immediately against fiber fault in the feeder and
distributed fibers. Moreover, the performance of proposed self-survivable WDM-PON is also discussed and analyzed.
In this investigation, an mm-wave RoF transmission link with dual beat-mode optical source is investigated. We
demonstrate a 170 GHz band millimeter-wave source using an external dual-mode-locked Fabry-Perot laser diode (FP-LD)
with a 1.38 nm mode-spacing. Two distributed feedback (DFB) lasers are used to inject the corresponding modes of
FP-LD to generate dual-beat-mode output. The proposed dual-mode laser is not only stable, but also has single-longitudinal-
mode (SLM) output characteristics. Moreover, we also investigate the relationship between two external-injected
wavelengths for the dual-wavelength output.
In an optical tweezers system, the force measurement with a resolution less than pico-Newton can
be achieved by precise measurement and analysis of the trapped particle trajectory. Typically, this
single particle tracking technique is realized by a quadrant position sensor which detects the scattering
lights of the trapping laser beam from the trapped particle. However, as the radius of the trapped
particle is larger than the wavelength of the trapped laser, the scattering pattern becomes complicated,
and it limits the tracking region and the signal sensitivity on the trapped particle. To solve this issue,
an extra probing laser with optimized focal offset according to the trapping laser is applied to improve
the flexibility and performance of our particle tracking system for each particle size. A rule of thumb
between the optimized focal offsets and particle size is also concluded from the experimental results
and theoretical simulations.
We propose a multiwavelength erbium-doped fiber (EDF) ring laser using a Fabry-Perot etalon inside the ring cavity
with optimal fiber length to satisfy the least common multiple number for generating multiwavelength at room
temperature.
KEYWORDS: Broadband telecommunications, WDM-PON, Orthogonal frequency division multiplexing, Fiber to the x, Passive optical networks, Digital signal processing, Single mode fibers, Semiconductor lasers, Wavelength division multiplexing, Modulation
We will introduce four related topics about fiber access network technologies for PONs. First, an upstream signal powerequalizer
is proposed and designed using a FP-LD in optical line terminal applied to the TDM-PON, and a 20dB
dynamic upstream power range from -5 to -25dBm having a 1.7dB maximal power variation is retrieved. The fiber-fault
protection is also an important issue for PON. We investigate a simple and cost-effective TDM/WDM PON system with
self-protected function. Next, using RSOA-based colorless WDM-PON is also demonstrated. We propose a costeffective
CW light source into RSOA for 2.5Gb/s upstream in WDM-PON together with self-healing mechanism against
fiber fault. Finally, we investigate a 4Gb/s OFDM-QAM for both upstream and downstream traffic in long-reach
WDM/TDM PON system under 100km transmission without dispersion compensation. As a result, we believe that these
key access technologies are emerging and useful for the next generation broadband FTTH networks.
Optical liquids can be used to engineer the dispersion characteristics of fibers by serving as
the core or cladding. The short-/long-pass filters are so made and concatenated to achieve
widely tunable Gaussian-shaped filters for bio-imaging.
We propose and investigate a new ring-based power-splitting passive optical network (PS-PON) with a self-healing mechanism that prevents fiber fault. Using our proposed Y-type passive component with bidirectional function in each remote node (RN), the proposed ring-based PS-PON can be retrieved directly under single fiber failure.
We investigate and demonstrate experimentally a two-stage erbium-based amplifier with a larger amplified-spontaneous-emission light source for a long-distance fiber sensor by using strain-induced fiber Bragg gratings in the fiber systems. In a 20-km-long fiber sensor system, the sensor has a maximal 2.28-nm wavelength shift under a 1500-µm/m strain.
To reduce the cost of optoelectronic modules, powder metallurgy (PM) and metal injection molding (MIM) are employed to fabricate metal housings for optoelectronic packages. During the laser welding of PM steel, the rising gas pressure pushes the molten metal out of the welding regions, resulting in weak and unstable joints. Metal parts fabricated by the MIM method provide good weldability, shape complexity, low cost, and long-term reliability. By using the MIM method, defect-free welding joints and postwelding-shifts of less than 1 µm are achieved, and the optoelectronic packages are reliable. Employment of MIM not only gives optoelectronic module designers more design flexibility due to the advantage of shape complexity, but also makes low-cost triple-directional optoelectronic modules realizable.
A novel fiber ring laser technique, which covers both C- and L-bands, with the function of wavelength tunability and single-longitudinal-mode oscillation, is proposed and demonstrated experimentally. We propose a two-stage hybrid amplifier, which consists of a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA) with cascade configuration, for the gain profile to achieve C- to L-band (1540 to 1610 nm). A saturated-absorber-based autotracking filter, which composes of an unpumped erbium-doped fiber (EDF) and an optical reflected mirror (ORM), is employed to provide fine mode restriction and guarantee the single-frequency operation. The unpumped EDF must use shorter length to retrieve the stabilized single-frequency operation while the EDF length is between 0.5 to 1 m long. The effectively operation range is from 1542 to 1618 nm. The maximal output power of 5.7 dBm is retrieved at near 1577 nm, and the output power will drop to 3.7 and -0.32 dBm at 1604 and 1616 nm, respectively. The SMSR can be up to 53.2 dB/ 0.05 nm at around 1577 nm. The performance of output power of > 2.1 dBm, power stability of ≤ 0.02 dB, wavelength variation of ≤ 0.01 nm and side-mode suppression ratio (SMSR) of > 31 dB / 0.05 nm has been demonstrated for this single-frequency fiber laser over the wavelength range of 1550 to 1608 nm. The linewidth (RF) spectrum of the proposed structure has also been studied.
An actively mode-locked fiber ring laser for generating wavelength-tunable optical pulses is demonstrated. An Er-Yb
doped waveguide amplifier is used as an optical amplifier, and a Fabry-Perot laser diode is used as a modulator in the
fiber laser. Moreover, we add a variable optical delay line to control the cavity length for maintaining a constant
repetition frequency and pulsewidth at different wavelengths. The optical side-mode-suppression-ratio is better than 33.5
dB over the wavelength-tunable range of 46 nm.
A novel bidirectional 2×2 optical switch technique, based on the conventional erbium-doped fibers (EDFs) with an operation of pumped or unpumped power level, is proposed and demonstrated experimentally. By using the amplification and absorption function of EDFs and a simply architecture design, the input signals can be switched to a suitable position. The response time of wavelength switching will approach about 2 ms. Moreover, the behavior and system performance of the proposed configuration also have been studied.
The automation of a rapid and simple trapping-force calibration system is desired for optical tweezers to measure biological forces. One simple calibration method, the water-dragging-force method, is to calibrate the trapping force against a given water dragging force with an image-processing technique. However, the conventional image-processing technique is too slow because of the time it takes for image recording, transferring, storing, and retrieving. The pattern recognition technique of our automated calibration method is rapid and simple, because it directly processes the image signal without recording, storing, and retrieving any image. In an experiment, we have combined the dragging force method with the real-time pattern recognition technique to calibrate the relationship between the trapping force at a given laser power and a displacement of a bead. We demonstrate the calibration results of the trapping forces on two target beads 10 and 6.2 µm in diameter, separately, at two laser powers, 5 and 10 mW. Each calibration procedure is finished in 5 min at a pattern recognition rate of 10 Hz with a spatial resolution of 75 nm. We believe that this technique is reliable and rapid enough to be applied to biological force measurement.
Stabilized and tunable optical output are very necessary for fiber ring lasers applied to wavelength-division multiplexing (WDM) for communications and optical sensor systems. In general, a fiber Fabry-Perot (FFP) filter can provide wavelength tuning inside the ring cavity of the fiber ring laser. Because of the bandwidth limitation of erbium-doped fiber amplifiers (EDFAs), the operation region of erbium-doped fiber (EDF) ring lasers extends only from C to L band (1530 to 1610 nm)1- 2 and thus must be supplemented with the proposed S-band fiber ring laser.3 Actually, the wideband ring laser must use a long length of EDF even to approach C- plus L-band operation.1 However, that is insufficient to stabilize the lasing wavelength and power of a fiber ring laser. Recently, several remedial techniques, such as integrating two cascaded FFP filters of widely different free spectral ranges (FSRs) into a cavity,4- 5 using a compound ring resonator composed of a dual-coupler fiber ring and a tunable band pass filter,2 adding an extra ITU-grid periodic filter in the optical loop,6 and employing an integral saturable-absorber-based tracking narrowband filter,7 have been reported experimentally.
A stable and wavelength-tunable C- plus L-band fiber double-ring laser, which uses a two-stage hybrid amplifier with a semiconductor optical amplifier and an erbium-doped fiber amplifier, has been proposed and experimentally demonstrated. Based on the double-ring configuration, the proposed fiber ring laser exhibits more stable output wavelengths and powers than the single-ring laser. A wide tunable range of 1540 to 1620 nm, a side-mode suppression ratio (SMSR) of >31.2 dB/0.05 nm over a wide tuning range from 1550 to 1612 nm, and an output power of >2 dBm over the operation range of 1546 to 1608 nm have been achieved.
We have proposed and experimentally demonstrated a stabilized and tunable S-band erbium-doped fiber ring laser by using a Fabry-Perot laser diode (FPLD) and a fiber Fabry-Perot filter inside the ring cavity. Due to the bandwidth limitation of the FPLD, the effective operating range of the proposed laser is confined to 1490.28 to 1521.22 nm with a tuning step of 0.08 nm. A side-mode suppression ratio of >39.1 dB at 0.05 nm and an output power of >0.4 dBm can be achieved while this laser is tuned from 1490.28 to 1510.27 nm. Zero output wavelength variation and output power fluctuation 0.03 <= dB have also been obtained.
Swimming activity of flagella is a main factor of the motility of bacteria. Flagella expressed on the surface of bacterial species serve as a primary means of motility including swimming. We propose to use optical tweezers to analyze the swimming activity of bacteria. The sample bacteria in the work is Pseudomonas aeruginosa, and it is a gram-negative bacterium and often causes leading to burn wound infections, urinary-tract infections, and pneumonia. The single polar flagellum of P. aeruginosa has been demonstrated to be important virulence and colonization factor of this opportunistic pathogen. We demonstrate a gene to regulate the bacterial swimming activity in P. aeruginosa PAO1 by biological method. However, the change of flagellar morphology was not observed by electron microscopy analysis, suggesting that the gene regulates the flagellar rotation that could not be detected by biological method. PFM exhibits a spatial resolution of a few nanometers to detect the relative position of the probe at an acquisition rate over 1 MHz. By binding a probe such as a bead or a quantum dot on the flagella, we expect the rotation of the probe due to the flagella could be detected. It is expected that the study of the swimming activity of P. aeruginosa provide potent method for the pathogenic role of the flagella in P. aeruginosa.
We demonstrate tunable single- and dual-wavelength fiber ring lasers using a compact Er-Yb doped waveguide amplifier. In the single-wavelength operation, a signal-to-noise ratio higher than 63 dB and an output power maintaining around 11 dBm in the operation range over 50 nm (from 1529.1 to 1579.43 nm) are achieved. In the dual-wavelength operation, lasing wavelengths with wavelength separation from 51.73 to 6.2 nm are demonstrated.
A system to generate wavelength-tunable optical short pulses with a constant repetition frequency and pulse width by a gain-switched Fabry-Pérot laser diode (FPLD) in a self-injection scheme is demonstrated. A variable optical delay line is used to control the self-injection scheme to maintain a constant repetition frequency and pulse width at different wavelengths. The optical sidemode suppression ratio (SMSR) of this system is better than 33 dB over the wavelength-tunable range of 33 nm.
A fiber Bragg grating (FBG) sensor system using a fiber ring laser with a hybrid amplifier is proposed and demonstrated. The hybrid amplifier comprises an erbium doped waveguide amplifier and a semiconductor optical amplifier. The experiment shows that such the hybrid amplifier has a high amplifier spontaneous emission power and gain spectrum. Moreover, this fiber ring laser can provide a stable multiwavelength output with an optical signal-to-noise ratio over 50 dB even if the FBGs are located at a 25 km remote sensing position.
A hybrid C- plus L-band fiber amplifier module with three amplifier stages, which provides an operation range of 1540 to 1600 nm, is proposed and experimentally demonstrated. The proposed amplifier consists of two erbium-doped fiber amplifier (EDFAs) and a semiconductor optical amplifier (SOA) in cascade. Compared with a traditional L-band EDFA having longer EDF length, this amplifier can reduce the total EDF length to 44 m. As a result, 41.5 dB gain and a 3.7-dB noise figure are achieved at 1562 nm over the bandwidth of 1540 to 1600 nm, while the input signal power is –30 dBm. In addition, the behavior and performance of the proposed gain-clamping amplifier module over the C- plus L-band is investigated experimentally under different operation conditions.
A novel S- to C-band erbium-doped fiber amplifier (EDFA) module over a 94-nm operation wavelength from 1476 to 1570 nm is experimentally investigated and demonstrated. This proposed module composes an S-band EDFA and a C-band erbium-doped waveguide amplifier (EDWA) with a coupled-structure. The 31.4-dB peak gain with 5.6-dB noise figure, and 30.5-dB peak gain with 4.7-dB noise figure are observed at 1506 and 1534 nm in this configuration when the input signal power is –30 dBm, respectively.
A stable and tunable fiber double-ring laser based on an erbium-doped waveguide amplifier (EDWA) is proposed and experimentally demonstrated. A widely tunable range from 1527 to 1567 nm, the side-mode suppression ratio (SMSR) of >45.6 dB/0.05 nm and the output power of >1.04 dBm in the operating range from 1535 to 1565 nm can be achieved for this ring laser. By applying the double-ring configuration, the ring laser is stabilized. The central wavelength variation of <0.02 nm and the power fluctuation of <0.03 dBm can therefore be retrieved.
The Raman effect influence on ultrashort pulse in optical fiber is investigated by using experimental data of delay response function. The frozen of the Raman effect is clarified by using nonlinear Schrodinger equation and finite difference time domain method. In Raman freezing region, a more stable soliton propagation is obtained when the initial power is enhanced.
In this paper, we propose an optical method for sorting micro-particles with holographic optical tweezers. By projecting an optical pattern onto the sample plane of a microscope via its objective, we can separate the sample particles of different sizes flowing to different directions.
The conformational change of integrin αIIbβ3 plays an important role in clot formation. However, the correlation between the structure and the function of integrin αIIbβ3 in interacting with its ligand is still not clear. In this report, we focus on the dynamic variation of the binding between integrin αIIbβ3 and its ligand, rhodostomin by using a photonic force microscopy (PFM). The PFM is used to trap a rhodostomin-coated bead and, then, shift it to bind a surrounding CHO αIIbβ3 cell. Meanwhile, it tracks, with a resolution of 1MHz, the Brownian fluctuations of the trapped bead. Theoretically, the smaller the amplitude of the Brownian fluctuations, the stronger the stiffness of the binding force between the rhodostomin and the CHO αIIbβ3 cell. Experimentally, a significant decrease of the Brownian fluctuations was observed during the interval between the 360th seconds and the 400th seconds after the trapped rhodostomin-coated bead contacted an integrin-expressed CHO αIIbβ3 cell. This observation reveals that it takes the rhodostomin 360 seconds to seek the correct position to bind to the integrin αIIbβ3. After 400 seconds, the rhodostomin has bound rigidly with the integrin αIIbβ3. We presume that the integrin αIIbβ3 has reached its final stage of conformational change.
Integrin receptors serve as both mechanical links and signal transduction mediators between the cell and its environment. Experimental evidence demonstrates that conformational changes and lateral clustering of the integrin proteins may affect their binding to ligands and regulate downstream cellular responses; however, experimental links between the structural and functional correlations of the ligand-receptor interactions are not yet elucidated. In the present report, we utilized optical tweezers to measure the dynamic binding between the snake venom rhodostomin, coated on a microparticle and functioned as a ligand, and the membrane receptor integrin alpha(IIb)beta(3) expressed on a Chinese Hamster Ovary (CHO) cell. A progressive increase of total binding affinity was found between the bead and CHO cell in the first 300 sec following optical tweezers-guided contact. Further analysis of the cumulative data revealed the presence of "unit binding force" presumably exerted by a single rhodostomin-integrin pair. Interestingly, two such units were found. Among the measurements of less total binding forces, presumably taken at the early stage of ligand-receptor interactions, a unit of 4.15 pN per molecule pair was derived. This unit force dropped to 2.54 pN per molecule pair toward the later stage of interactions when the total binding forces were relatively large. This stepped change of single molecule pair binding affinity was not found when mutant rhodostomin proteins were used as ligands (a single unit of 1.81 pN per pair was found). These results were interpreted along with the current knowledge about the conformational changes of integrins during the "molecule activation" process.
A novel wavelength-tunable add-drop multiplexer (ADM) using fiber Fabry-Pérot tunable filters (FFP-TFs) for the bidirectional wavelength division multiplexing (WDM) network is proposed and demonstrated. The wide tuning range, low loss, and low polarization dependence properties of the FFP-TFs are used for the ADM operation. The experimental results show that the wavelength tuning range of this wavelength-tunable ADM can be up to 40 nm. The bit-error-rate performance of the dropped and pass-through channels for a 2.5 Gbit/s system shows the feasibility of ADM.
Three new design waveguides for adiabatic directional full couplers are studied. We theoretically and numerically show that the performance of new full couplers is improved. Whe the length of the coupler is 4mm (the minimum local beat length is 2mm) at 1.57μm wavelength, the crosstalk is smaller than -35dB. For the length of the coupler is 4mm, the crosstalk is smaller than -20dB in the 1.5μm ~ 1.7μm range. For the length of the couplers is 7mm, we find that the crosstalk is smaller than -35dB in the 1.5μm ~ 1.7μm range. The same as the requirement of the maximum crosstalk, the corresponding wavelength is between 1.42μm to 1.7μm when the lenght of the couplers is 12mm.
We have proposed and experimentally demonstrated a new tunable laser structure, which is based on Fabry-Perot (FP) lasers with external lightwave injection. The wavelength tuning can be obtained by adjusting the bias currents of FP lasers. The wavelength tuning time of <2 ns, 3.3-nm tuning range, and the side-mode suppression ratio (SMSR) of >19 dB have been achieved experimentally. In addition, the SMSR performance has also been investigated. This tunable laser has the advantage of simple architecture, potentially low cost, data direct modulation, and fast wavelength tuning, and is expected to benefit the applications of fast wavelength tuning.
A two-level bidirectional path-protected ring (BPR) architecture for the dense wavelength division multiplexing/subcarrier multiplexing (DWDM/SCM) broadband fiber-wireless access network is proposed and experimentally verified. This architecture can perform self-healing function that utilizes a distributed controller placed at each remote node (RN) and each concentration node (CN) under link failure. If fiber cut occurs between two RNs or CNs, two separate rings are constructed and the up/downstream signals can be delivered adequately. Consequently, the BPR is a reliable architecture for fiber-wireless network. Moreover, we employ a 16-quadrature amplitude modulation (16-QAM) modulated scheme to achieve better spectral efficiency on both up/downstream subcarrier channels. The data rate for each channel is up to 12 Mbit/s for a 3 MHz bandwidth. According to simulated and analyzed results, this architecture can provide large bandwidth, high reliability and excellent flexibility for future broadband wireless networks. Finally, we set up an experimental fiber-wireless network to demonstrate the feasibility of the proposed architecture.
The prior artwork for a Dot-matrix hologram is always animated by a computer instead of a man made sculptured model. For a computer graphic software, it is very easy to interlace several bitmap graphics ona small area. So, if we generate an interlaced graphic and transfer the bitmaps to corresponding gratings which diffract the illumination light to a specific direction with respect to each individual graphic, then it will have several viewing images in different view angles. Hologram has special light characteristics that are difficult to duplicate, so it has intrinsic advantage for anti-counterfeiting application. For more guarantee of security to protect the value paper from the fraud activity. We use a more complex and delicate multi-image hologram to hold back the ambition of copycat. In this paper, will describe how to transfer the images that generated by computer to a hologram. The concept for interlace graphics, and the apparatus that is easy to generate the dot grating with respect to each bitmap in the image, and the practical samples that made by this technology for anti-counterfeiting purpose.
For solving the problem of poor stability that exists in most of the optical dot-matrix hologram fabrication systems. We are now developing a non-optical manner for making dot- matrix hologram by using a pin with a small metal mold made of diamond ruled or electroformed grating on the tip. By rotating the pin and pressing it on a heating plastic plate dot by dot, we can compose a dot-matrix hologram. That's an easy way to make a hologram with the same quality as that resulted from optical interference methodology. We need only a simple motorized rotational stage to rotate the pin that fixed on it instead of using complex optical interference method. The method, which employs mechanical devices, will offer a new concept of implementing a high quality dot- matrix hologram.
A new dispersion slope compensator by writing the Bragg gratings at different positions in a dispersion compensation fiber is proposed for the WDM transmission system to compensate for the accumulated dispersion of each channel.
An iterative algorithm for multiple incoming wavelengths considering divergent sources is proposed to design a computer-generated holographic diffuser (CGHD) with high light utilization efficiency and uniform color mixing. We modified the conventional G-S algorithm when its input wavefront is divergent and consists of more than one wavelength. This diffuser is designed according to the Fresnel diffraction theory and can uniformly spread the different input light as far field distribution. The amplitude transmittance of this CGHD is a constant, while the phase transmittance consists of multiple phase levels. An example of designed CGHD with two divergent wavefronts is illustrated and simulated. The proposed algorithm can be used to design diffractive device for applications such as wavefront multiplexing and demultiplexing.
A novel transmission structure of holographic color filters is introduced. The device is based on the natural characteristics of angular color dispersion in transmission holograms, and the optical reciprocity interacting with two same transmission structure. The type of holographic color filters, differed from before, is composed of two same structure of transmission holograms which are laminated on the both side of transparent substrate. The first transmission hologram diffract normally incident white light, generally emitted from metal halide lamp, into transparent substrate with angular color separation. The diffracted beams transmitted through substrate and are separated for different R, G, B wavelengths. At last, the different R, G, B beams normally couple out with the second hologram as same structure as first one due to optical reciprocity. A light beam matrix mask (LBM) is presented to produce R, G, B pixel, and provided an approach in LCD application.
Optical birefringence of volume photopolymer holograms could be applied as polarization elements and an important compensated device for display. In this paper, an analysis of the optical birefringence in volume photopolymer hologram is given. This characteristic analysis is mainly based on the Kogelnik's coupled wave theory. These characteristic properties for index modulation and optical birefringence in hologram formation are theoretically analyzed with respect to the parameter of diffraction efficiency, film thickness, angular and wavelength selectivity. This paper is also considered the holograms in slanted and nonslanted structures. Results of the characteristics of optical birefringence is provided an approach to realize as an optical compensation. This study shows that the property of negative birefringence in volume photopolymer will give a newer application in liquid crystal display technology.
Reductions of the soliton interactions by using the optical sliding-frequency filters and optical phase conjugation are numerically studied. For the filters, the second-order Butterworth filters can more effectively reduce the soliton interactions than the Fabry- Perot filters or the third-order Butterworth filters, and the zigzag-sliding case is better than the up-sliding or the down-sliding cases. It is shown that, by properly applying the conjugators and choosing the filter bandwidth, the soliton transmission can be significantly improved.
Temporal effects of the optical phase conjugation in dispersion-shifted fibers and in semiconductor laser amplifiers are numerically shown. In dispersion-shifted fibers, the frequency chirping is induced in the conjugate pulse by the signal pulse and pump wave through the cross-phase modulation, which increases with the signal power. In semiconductor laser amplifiers, the conjugate pulse has distortion and frequency chirping due to the amplified spontaneous emission noise and the carrier depletion induced by the signal pulse. These effects can be reduced by increasing the pump power. By properly choosing the signal power and pump power, for both conjugators, the optical phase conjugations can be nearly ideal. Finally, the performances of the two conjugators are compared.
The optical phase conjugation is numerically shown to reduce the soliton interaction and the timing jitter of the soliton caused by the Gordon-Haus effect. With the conjugator, both the bit rate and the transmission distance of the soliton communication system can be improved. The criteria for applying the conjugation are discussed.
The retinal image quality in the human eye have been measured by using a hybrid optical digital method, consisting in the recording and processing of retinal images of a point test after reflection in the retina. The method allows one to obtain accurate data on the modulation transfer function of the eye, which can be directly used in vision research and practical optical engineering studies. The technique has been used to obtain image quality results both in the fovea and the periphery under different experimental conditions. These results have some implications to retinal sampling: in natural viewing the eye's optics provides a good protection against aliasing (spatial undersampling) in the fovea, but leaving the cone mosaic least protected at eccentricities around 10 to 20 degrees. Experimental systems based on this optical digital technique might have potential applications to obtain high resolution fundus images in the living eye.
The optimal pump period for the least total pump power required for the long-haul transmission system with periodically pumped distributed erbium-doped fiber amplifier is studied numerically. The pump power of the distributed erbium-doped fiber amplifier is minimized with the optimal doping density. It is found that the optimal pump period depends only slightly on the total transmission length.
Effects of stimulated Raman scattering on the distributed erbium-doped fiber amplifier are studied numerically. The pump wavelength is 1.48 micrometers and the signal wavelength lies between 1.52 micrometers and 1.57 micrometers . The competition between the gain from stimulated Raman scattering and the gain from the pumped erbium ions is shown. It is found that the signal gain is enhanced by SRS except for the signal near 1.53 micrometers .
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