The comparison between linear cavity and ringcavity configuration observed that for types of variation, the linear cavity gives better performance output than ringcavity. It is also observed that the number of lasing lines and output power increased with increment of power of TLS and pump power for both linear and ringcavity configurations. This could be due to the power given is absorbed by the erbium ion within EDFA to be used as energy to amplify the input signal. The EDFA gain more energy when the power given higher. But at certain point of variation given, the number of lasing lines and output power remained constant at maximum value or continuously decreased. This is the point where the EDFA is fully inverted and exhibit the maximum gain to amplify wavelengths or the EDFA has reached gain saturation for the decrement situation. While when the effective area of HNLF is varied with an increment, the number of lasing lines and output power seems to be decreased. This is because the nonlinearity of HNLF is dependent to its effective area. This phenomenon is according to the equation of nonlinear parameter of HNLF,
The SOAs in any cases, having some of plus point as contradict to the EDFAs regarding the easiness of generating the DWFLs due to the of the control over the mode competition issue, which consequently, contribute to the incorporation of the gain medium using different cavity design [1-3]. Although the SOA have the upper hand in the production of DWFL, the EDFA is still being preferred due of it natural fiber-based waveguide that is well-matched to the cavity design, having size reduction, independent of polarization dependent loss and lower background noise. There are great deal of techniques utilized to unravel the mode-competition problem, for example, cooling the EDFA with fluid nitrogen[4,5], using a Distributed Fiber Bragg (DFB) fiber laser source , by utilizing a polarization maintaining Fiber Bragg Gratings (FBGs) , using a cavity frequency shifter , using the Four Wave Mixing (FWM) phenomenon to work as a stabilizer , using optical Fabry-Perot lasers in the DWFL, by utilizing cavity control  and notwithstanding utilizing double ringfiber laser design.
Erbium-doped fiber amplifier (EDFA) is a widely applied component, e.g., for wavelength division multiplexing (WDM) in modern optical communication systems, optical fiber sensing system, optical device testing system and optical instrumentation  . In addition, the application of EDFA is a main device for generation of multi wavelength laser  . The EDFA has gained spectrum operation range from 1525 nm to 1565 nm in the range of C-Band . The EDFA is used successfully due to a high gain, low insertion loss, high output power and po- larization-independent gain. There are many techniques of multi wavelength generation such as Fabry-Perot etalon inside cavity , fiber bragg grating , Sagnac interferometer , ring resonator , high nonlinear fi- ber , semi-conductor optical amplifier , LiNbO 3 . Most of these techniques are of high cost and re-
We build an optical set-up, see Figure. 4.3, that allows us to monitor the mi- cropillar cavity modes during the fiber coupling. If any misalignment arises during coupling we can correct for it immediately. The fiber is coupled by us- age of a bare fiber terminator to the SLEDs fiber, with a coupling efficiency of around 30%. The bare fiber is held by a bare fiber holder which is mounted onto a PI xyz motorized stage. The SLED light out of the bare fiber first hits, from above, our CQED device that is mounted on a xy-rotation stage. By usage of the other elements we focus the transmitted light onto a CCD, for positioning of the fiber, and on the Horiba FHR1000 spectrograph, for monitoring the spectrum. These remaining elements are all on the optical table, except for the spectrom- eter. We can see through the device because the SLED spectrum goes down to 900 nm and may have a tail even further down where the device is transparent. This can be seen from the simulations, see Fig. 2.4.
Abstract—We have developed the equations describing the interaction of light and matter. The Maxwell- Schrödinger equations were modified to be The Maxwell-Bloch equations by means of homogeneity and slowly varying wave approximation. The boundary conditions of a unidirectional ringcavity were performed to complete the analytical calculation. From this study, we observed the existence of a low-pass filter gain, parallel with the phenomenon which exists in op- amp circuit.
We have demonstrated the integration of supporting lasing at 1.88 µm for enhancing the gain in a thulium doped ZBLAN amplifier. The laser ringcavity has been created in order to reduce the bottleneck effect caused by the self- terminating nature of the amplifying transition. Two different types of fibre geometry and pumping scheme have been tested and the performance has been compared with a numerical model of the amplifier.
Following with the evolution of triple-play multimedia services, the explosive growth of the Internet and data traffics have placed huge bandwidth demands on current communication network systems . To deal with this tendency, all optical fiber optical transport systems are developed continuously to increase the overall network capacity, and fiber optical amplifiers are investigated widely to extend the network reach limit imposed by fiber attenuation and losses in optical networks. In this aspect, Erbium-doped fiber amplifier (EDFA) with high-gain, large output power and low noise figure (NF) characteristics has been designed widely to support data transmissions in fiber optical transport systems[2-5]. However, when the gain and NF performances in those EDFAs are promoted, their stability becomes another issue to limit the transmission performance. An in-line optical lightwave may obtain different gain values when other lightwaves are also fed into those EDFAs. These variations will make a difficulty to es timate power budget for each optical line in a multi-wavelength fiber optical transport system and will seriously reduce the overall transmission performance. This phenomenon in a long-distance transport system is more
Optical networks are telecommunication network with high capacity, which are basically based on optical technology and components .Such networks provides routing, restoration at wavelength level as well as wavelength based services. Having in mind that today telecommunication networks are facing with continuous problems for transmitting different class of services, operators always are looking for new alternatives or substitute, in order to transmit multimedia services with high quality. Due to the internet boom the demand for transmission capacity is growing rapidly day by day .So there is a tremendous growth of the Internet and the World Wide Web (www) both in terms of number of customers and amount of time and thus the bandwidth taken by each customer which is a major factor. Such factors have driven the development of high-capacity optical networks. Thus Optical data transmission is the key to meet this requirement. The demand for more bandwidth in telecommunication networks has rapidly expanded the development of new optical components and devices (especially Wavelength Division Multiplexers). Basically the origin of optical networks is associated to Wavelength Division Multiplexing (WDM) which leads to provide more and more capacity on existing fibers. The Dense WDM technique send multiple light waves at different wavelength onto single fiber and also increases the capacity of fiber because it multiplexed multiple signals and send it together. The major problem that DWDM network suffers is the problem of dispersion. This problem can be solved by using different dispersion compensation techniques, Dispersion compensation fiber etc. In history mostly the modulation formats used were NRZ and RZ but the results were not satisfactory. So now advanced are used like CSRZ (carrier suppressed return to zero), DRZ (duo-binary return to zero) and MDRZ (modified duo-binary return to zero). These advanced formats has given satisfactory results and worked well with DWDM transmission system.
As of late, examination on optical transmission frameworks has been centered on the expansion of their distance and capacity. Tight optical filtering (TOF) can enhance the transmission Capacity by expanding the spectral efficiency, prompting ultra-dense wavelength- division-multiplexing (UDWDM) frameworks , . For long-haul transmission frameworks, high powers are required at the fiber input to expand the optical signal-to- noise ratio (OSNR) lessened by collected amplified spontaneous emission (ASE) noise of optical Amplifiers. To keep up the OSNR in a point of confinement of loyal transmission, an option is boosting the signal control, yet high input optical power uncovered systems to the serious nonlinear impacts of the transmission fiber . Soliton pulse is another solution to transmit data over a long distance. Soliton is a kind of pulse for which dispersion is cancelled out by its self-phase modulation, so it can maintain its shape for long distance transmission.
cavity excited by a cw laser will exhibit high energy build-up when the laser frequency is resonant with a cavity mode, and a near-zero cavity transmission when off-resonance. Attempting to simply match the laser frequency with a cavity mode can suffer from significant noise. Because of the narrow linewidths associated with high-finesse optical cavity (~ 10 kHz), any noise in the resonance of the laser frequency with the cavity mode will result in large fluctuations (~100 %) in cavity transmission, making direct absorption spectroscopy nearly impossible. In cw-ICOS this cavity frequency to transmission noise is significantly reduced by effectively randomizing the cavity mode structure on a time scale faster than the scanning rate of the light source. In off-axis ICOS, the laser is aligned to the cavity in an off-axis arrangement (similar to a Herriot cell) such that the ray paths of the laser are spatially separated over multiple reflections within the cavity before retracing the original path. A cavity aligned in such an off-axis arrangement can be theoretically treated as a cavity that is m time longer, where m is the number of roundtrips before the beam retraces itself. Therefore, a 0.5 m cavity in a 100-pass off- axis alignment will have an effective free spectral range (FSR =
Tehran in 1989. Later on, the solar cell production line was founded and the company name changed to “Optical Fiber and Solar Cell Fabrication Company (OFFC)”. The company has two hydrogen and oxygen and one nitrogen generator, two de-ionized water production machine, one tube washing machine, two MCVD systems (lathes and gas delivery systems), one sleeving machine, one preform analyzer system, two twelve meter height fiber drawing tower, one proof testing system, one fiber coloring machine and one complete set of test equipments for measuring all necessary parameters such as, loss, geometry of the fiber, attenuation spectrum, cutoff wavelength, dispersion, real length, etc. The preform fabrication was started in 1994. The preform fabrication by MCVD technique and incorporation of the erbium ions by solution doping can easily be performed in the factory. The drawing of the sintered preform and characterization of the preform and fiber can easily be carried out in the company.
Residual powers of an erbium-doped fiber amplifier (EDFA) and a Raman pump are utilized effectively for pumping a 0.45 m long bismuth-based EDF (Bi-EDF) in linear-cavity L-band multi-wavelength fiber laser generation. A 7.7 km dispersion compensating fiber (DCF) operates as both Brillouin and Raman gain media and a 6.5 dBm fixed-power tunable laser source (TLS) amplified by an EDFA works as a Brillouin pump (BP). By inserting the Bi-EDF in the linear cavity and using the EDFA and the fixed Raman pump residual powers 13.6 mW and 64 mW, at wavelengths 978.8 nm and 1490.6 nm respectively, the gain spectrum is inhomogeneously broadened so that linewidth of the gain spectrum is expanded from 3.4 to 12.3 nm. As a result, the number of lines of an L-band multi-wavelength fiber laser (MFL) is increased noticeably. In addition, the number of lines at a BP wavelength 1590.6 nm decreased from 38 to 32 by using the maximum EDFA pump residual power of 44 mW due to a reduction in the quantum coefficient efficiency. However, flatness and stability characteristics of the MFL are improved. The MFL can be generated in the wavelength region 1570–1610 nm with the signal to noise ratio of about 42. Keywords: stimulated Brillouin scattering, fiber lasers, Raman amplifier, EDFA
Debye carried out a theoretical study and in 1920 Schriever reported an experimental work. Although in the early part of twentieth century optical communication was going through some research work but it was being used only in the low capacity communication links due to severe affect of disturbances in the atmosphere and lack of suitable optical sources. However, low frequency (longer wavelength) electromagnetic waves like radio and microwaves proved to be much more useful for information transfer in atmosphere, being far less affected by the atmospheric disturbances. The relative frequencies and their corresponding wavelengths can be known from the electromagnetic spectrum and it is understandable that optical frequencies offer an increase in the potential usable bandwidth by a factor of around 10000 over high frequency microwave transmission. With the LASER coming into the picture the research interest of optical communication got a stimulation. A powerful coherent light beam together with the possibility of modulation at high frequencies was the key feature of LASER. Kao and Hockham proposed the transmission of information via dielectric waveguides or optical fiber cables fabricated from glass almost simultaneously in 1966. In the earlier stage optical fibers exhibited very high attenuation (almost 1000 dB/km) which was incomparable with coaxial cables having attenuation of around 5 to 10dB/km. Nevertheless, within ten years optical fiber losses were reduced to below 5dB/km and suitable low loss jointing techniques were perfected as well. Parallely with the development of the optical fibers other essential optical components like semiconductor optical sources (i.e. injection LASERs and LEDs) and detectors (i.e. photodiodes and phototransistors) were also going through rigorous research process. Primarily the semiconductor LASERs exhibited very short lifetime of at most a few hours but by 1973 and 1977 lifetimes greater than 1000 hr and 7000 hr respectively were obtained through advanced device structure. ( Prasenjit,2000)
The increasing promise of using fiber optical CATV networks for broadband communications stems from the fact that the introduction of 1550 nm technology has been enhanced. The advantages make 1550 nm transmission particularly attractive for long-haul fiber optical CATV applications. However, when multiple CATV channels are transmitted through a nonlinear device such as an optical amplifier, nonlinear distortions like composite second order (CSO) and composite triple beat (CTB) will be generated [1–3]. Dispersion accumulates rapidly over long-haul transmission; therefore, it is important that some ways be taken to reduce the fiber dispersion when transmitting CATV signals, leading to better CSO and CTB performance. Several ways have been proposed to improve CSO and CTB performance of systems. However, sophisticated optical single sideband modulation
CRDS is an ultra-sensitive laser-based absorption technique, which may be used to measure trace species in the gas phase (Busch and Busch, 1999; Berden et al., 2000; Berden and Engeln, 2009; Gagliardi and Loock, 2014). The technique is seeing growing use in a range of fields including combustion diagnostics, plasma diagnostics, basic spectroscopic stud- ies, and atmospheric trace gas detection. In the cw-CRDS technique, a high-finesse optical cavity is pumped with a continuous-wave (cw) single-mode narrow-linewidth laser (Lehmann, 1996; Romanini et al., 1997; He and Orr, 2002; Dudek et al., 2003). In a typical setup, the laser is scanned over a spectral line of the analyte, as the laser frequency over- laps with a resonance of the static cavity, significant intra- cavity power is built up. A piezoelectric transducer can also be used to achieve spectral overlap between the cavity and the laser, though that approach is not used here. Once such a resonance is detected with a photodetector placed after the cavity, an acousto-optic modulator is triggered to quickly ex- tinguish the incoming laser beam. The same photodetector measures the subsequent exponential decay of light leaking out from the cavity, termed a ring down. The time constant of the ring down gives the total loss within the cavity. When the laser is tuned to resonance with the analyte, there will be additional loss, causing a faster decay (ring down). Using known line strength parameters for the specific spectral line, and the change in ring-down time, the species concentration can be calculated. The details of this procedure will be given later in this section.
Coarse wavelength division multiplexing (CWDM) is a method which will combine multiple signals on laser beams at various wavelengths for transmission along fiber optic cables, such that the number of channels is fewer than in dense wavelength division multiplexing (DWDM) but more than in standard wavelength division multiplexing (WDM). CWDM systems have channels at wavelengths spaced 20 nanometers (nm) apart, compared with 0.4 nm spacing for DWDM. This allows the use of low-cost, uncooled lasers for CWDM. In a typical CWDM system, laser emissions occur on eight channels at eight defined wavelengths: 1610 nm, 1590 nm, 1570 nm, 1550 nm, 1530 nm, 1510 nm, 1490 nm, and 1470 nm. But up to 18 different channels are allowed, with wavelengths ranging down to 1270 nm.
Abstract: - It is difficult in optical communication systems to predict the final signal at the customer side because of using various components and the effect of many features. Simulation helps to analyze and expect the performance before any actual hardware is done. In the proposed research, Optisystem 12 th version software is used in order to analyze transmitting 40Gb/s, 10Gb/s for each channel, in four channels of coarse wavelength division multiplexing (CWDM) from the transmitter to the receiver based on extinction ratio and the distance of the optical fiber until 100km. An Erbium-Doped Fiber Amplifier (EDFA) is used for long distances. The objective of the simulation is to certify that the received signals are not affected by the noise and attenuation so they are undamaged and in good condition by using bit error rate (BER) analyzer. From the simulation obtained, maximum Q factor, eye height, and threshold decreased as the fiber length increased, and as the value of the extinction ratio increased, the eye height increased but threshold decreased. The results of the CWDM are presented in this paper.
The advantages of EW-CRDS compared to other surface sensitive techniques are its moderate cost (relatively cheap CW diode lasers) and its possibility to measure kinetic processes on surfaces very accurately and at the same time, time resolved. The principle of EW-CRDS is based on the measurement of the decay constant of light trapped in the optical cavity rather than the measurement of the light intensity. In this way, the sensitivity is not compromised by temperature or pressure changes and intensity fluctuations of the laser source. Both ATR and EW-CRDS provide measurements of optical losses originating from molecular absorption or scattering caused by local changes in the refractive index within the region of the evanescent field. However, a particular benefit of EW-CRDS is the increased pathway of light which enables much higher sensitivity compared to ATR and also provides spatial resolution since the surface is always probed in the same spot as well as operating on a faster timescale. It is also possible to investigate surface reactions in real time and monitor polarisation dependencies of adsorbed molecules simultaneously without having to make compromises in terms of sensitivity. Combinations with other techniques such as electrochemistry, SECM and flow techniques are very easy and convenient to implement.
fiber refractive index and non-linear phase shift for each beam respectively. As mentioned by Liu et.al , FWM effect in the cavity is related to three parameters of optical fiber; the length, the dispersion and the nonlinearity coefficient. Phase matching is a group of applied technique to generate efficient nonlinear interactions in a medium. It is ensuring that a proper phase relationship between the interacting waves is maintained along the propagation direction in an optical transmission system .
work demonstrates for modest concentrations of organic pre- cursor. Based solely on the precision of the extinction co- efficient measurements, the respective limits of detection (3σ ) of the three systems were respectively 1.2, 2.1, and 1.2 Mm −1 for the BBCRDS and CE-DOAS systems over 60 s, and for the IBBCEAS system over 5 s. Other recently developed broadband systems by Washenfelder et al. (2013) and Zhao et al. (2013) have reported somewhat lower preci- sions of around 0.2 Mm −1 (corresponding to a detection limit of 0.6 Mm −1 ). These figures represent the best case perfor- mance of the instruments and do not take into account any drift in the instruments’ baselines. Such instrumental drift was generally a larger source of uncertainty and limited the accuracy at small aerosol extinctions. Engineering improve- ments since the NO3Comp campaign, including more fre- quent re-calibration of the baseline spectrum, have produced performances much closer to the best case values (Kennedy et al., 2011). Zhao et al. (2013) report a long-term stabil- ity of around 1 Mm −1 , which is only slightly worse than the detection limit of their instrument. The detection limits we report are well sufficient for monitoring aerosol extinction in polluted atmospheres (for instance, mean aerosol extinction coefficients are 121 Mm −1 in Atlanta, and over 300 Mm −1 in Beijing) and are possibly low enough for measurements in pristine environments (Carrico et al., 2003; He et al., 2009). If necessary, the detection limits of these broadband systems could be improved by increasing the cavity length or by using higher reflectivity cavity mirrors. As a point of comparison, a recently-developed broadband aerosol extinction spectrome- ter using a multipass White cell had a higher detection limit of 33 Mm −1 (albeit over a very wide spectral range of 250– 700 nm) compared to the optical cavity instruments in this work (Chartier and Greenslade, 2012). It should be noted that detection limits of cavityring-down systems are typi- cally well below 1 Mm −1 (Moosmüller et al., 2009); never- theless, for the broadband instruments, the aerosol extinction is typically obtained in addition to the quantification of trace gases.