The backward cascaded stimulated Brillouin scattering in a backward pumped S band distributed fiber Raman amplifier
was researched. The gain medium is G652 fiber. The Raman pump laser is a 1428 nm fiber Raman laser whose power is
tunable between 0 and 1W. The signal source is a frequency tunable narrow spectral bandwidth (<100 MHz) external
cavity laser. The thresholds of first order and second order stokes SBS are measured as 5mW and 67.6 mW
respectively. The stimulated Brillouin scattering lines are amplified by both fiber Raman amplifier and fiber Brillouin
amplifier. The saturation gain of first and second stimulated stokes Brillouin lines are about 50 dB and 65dB
respectively and the saturation gain of 25 km G652 backward fiber Raman amplifier is about 25 dB, so the gain of first
and second stimulated stokes Brillouin lines are about 25 dB and 40 dB respectively. It was shown that the fiber Raman
amplifier can assist the stimulated Brillouin scattering greatly. If used Raman amplification in BODTR, the measure
range of BOTDR can be extended.
The forward and backward cascaded stimulated Brillouin scattering(SBS) in the backward pumped S band distributed G652 fiber Raman amplifier have been researched, pumped by the tunable power at 1428nm fiber Raman laser and signal source is a tunable power external cavity laser (ECL) with narrow spectral bandwidth (<100MHz). The threshold power of backward Stokes the first and second stimulated Brillouin scattering SB1- and SB2- in the backward pumped S band distributed fiber Raman amplifier is 5mW and 67.6mW, respectively. The Stokes stimulated Brillouin scattering lines is amplified by fiber Raman amplifier and fiber Brillouin amplifier. The total GA is production of the gain of Raman GR and the gain of Brillouin amplifier GB. GA=GR×GB. In experimental work, the saturation gain of SB1- and SB2- is about 50dB and 65dB respectively and the saturation gain of 25km G652 backward FRA is about 25dB, so the gain of backward fiber Brillouin amplifier SB1- and SB2- are about 25dB and 40dB, respectively. The forward SBS does not obey the common theory that only weakening backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide characters weaken the wave vector rule, but the forward transmit sound wave-guide forward Brillouin scattering lines are generated and amplified in S band G652 FRA. The stimulated threshold power of the forward first Stokes SBS (SB1- ) in the backward pumped FRA is 6.6mW. In experimental work, the saturation gain of SB1- is about 49dB and the saturation gain of 25km G652 backward FRA is about 10dB, so the gain of SB1- in the forward fiber Brillouin amplifier is about 39dB.
Now the communication band of fiber focuses on C-band, but with increasing demand of fiber communication capacity, the communication band will extend to the S-band and L-band and fiber Raman amplifier will play a very important role in this process. In this paper, actual fiber Raman gain spectrum using single high power fiber Raman laser as pump was tested and the proper chirped Bragg fiber grating as gain flattening filter was designed to flatten actually tested gain spectrum. Besides, FWDM (film wavelength division multiplexer) is used as the multiplexer of signals and 1427nm/1505nm CWDM (coarse wavelength division multiplexer) is used as pump-signal coupler. The gain media are 50 km G652 fiber and 5km DCF (dispersion compensation fiber). The gain is 10dB of S-band fiber dispersion compensation Raman amplifier from1487.88nm~1541.88nm (total 53nm bandwidth) with gain ripple ± 0.6dB was successfully obtained. Besides, the effect caused by different location ways of different type fibers was also discussed. It is very significant for extending range of communication band of fiber and increasing the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system.
C-band and S-band fiber Raman gain spectrum pumped by single wavelength high power fiber Raman laser were tested and the proper chirped Bragg fiber grating as gain flattening filter was designed to flatten actually tested gain spectrum. Besides, FWDM (filter wavelength division multiplexer) and 1427nm/1505nm CWDM (coarse wavelength division multiplexer) are used as C-band and S-band fiber Raman amplifier pump-signal couplers respectively. The gain media are 50 km G652 fiber and 5km DCF (dispersion compensation fiber). C-band fiber dispersion compensation Raman amplifier with bandwidth from 1519nm to 1574nm (55nm) and average gain 15.2dB and ripple ±0.8dB was successfully obtained. S-band fiber dispersion compensation Raman amplifier with bandwidth from 1488nm to 1541nm (53nm) and average gain 10.1dB and ripple ±0.9dB was successfully obtained. During the test of C-band fiber Raman amplifiers, broadband ASE light source and WDM-emulator were used to simulate the DWDM (dense wavelength division multiplexing) signal source that can make the whole test more accurate. It is very significant for extending range of communication band of fiber and increasing the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system. At last, the result of experiment using these setup and influence caused by gain flattening filter and different type fibers location arrangements (G652 fiber and DCF) and corresponding solutions were also discussed.
The amplification effect on forward and backward stimulated Brillouin scattering lines in the forward pumped S band discrete DCF fiber Raman amplifier (FRA) has been studied. The pumped threshold power of the forward first order Stokes SBS (FSB1- ), second order Stokes SBS (FSB2-) and third order SBS (FSB3-) in the forward pumped FRA are 1.5 mW, 1.4 mW and 1.7 mW respectively. The Stokes SBS lines are amplified by FRA and fiber Brillouin amplifier (FBA) at the same time. The gain of amplification is given as GA=GR multiplied by GB where GR is Raman gain and GB is Brillouin gain. In the experiments, the saturation gain of FSB1-, FSB2- and FSB3- are about 52dB, 65dB and 65dB respectively. The saturation Raman gain of 10km DCF forward FRA is about 14dB, so the Brillouin gain of FSB1- , FSB2- and FSB3- are about 38dB, 51dB and 51dBrespectively. There are pumped threshold power of the first order, second order and third order Stokes backward SBS (B-SBS) line BSB1-, BSB2- and BSB3- in the forward pumped discrete DCF FRA, and they are about 4.7mW, 17.1mW and 67mW respectively. The saturation gain of the first order, second and third Stokes backward SBS line BSB1-, BSB2-and BSB3- are about 60dB and the saturation gain of 10km DCF forward pumped FRA is about 27dB, so the gain of FBA is about 33dB. The forward and backward cascaded SBS lines have been observed.
The forward and backward cascaded stimulated Brillouin scattering (SBS) in the backward pumped S band distributed G652 fiber Raman amplifier have been researched, pumped by the tunable power 1428nm fiber Raman laser and signal source is a tunable narrow spectral bandwidth (<100MHz)ECL. The forward SBS does not obey the common theory, that only weaken backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide character weaken the wave vector rule, the forward transmit sound wave-guide forward Brillouin scattering lines are generated and amplified in S band G652 FRA. Forward SBS that is amplified phenomena of transmit sound wave Brillouin scattering in the G652 FRA, during pump power is larger than the threshold value of SBS in a S band G652 FRA. Two-order SBS in the Stokes region is observed during the pump power is increased. When the FRA pump power is further increased, Cascaded SBS lines and comb profile are observed.
KEYWORDS: Optical fibers, Raman spectroscopy, Photons, Fiber lasers, Raman scattering, Temperature metrology, Signal to noise ratio, Laser scattering, Signal processing, Temperature sensors
A 30km long distance distributed optical fiber Raman temperature sensor (DOFRTS) system has been made, it use new measuring temperature principle of optical fiber amplified anti-Stokes Raman spontaneous scattering. In the system, 1550nm erbium-doped optical fiber laser, a highness speed data acquisition card and signal processing technique are used. By using these technique, the problem of weak signal detection is resolved and signal to noise ratio is increased. All components of system are put into an intellectualized constant temperature box and work in constant temperature condition. Stability and environment adaptability are improved. By appraisal, performance of the system is listed as follows: length of single mode fiber: 31km, temperature rang:0-100°C (can be expanded), temperature measuring uncertainty:±2°C, temperature resolution:0.1°C, measurement time:432s, spatial resolution :3m.
The cascaded forward stimulated Brillouin scattering (SBS) in the S band distributed G652 fiber Raman amplifier forward pumped and backward pumped by the tunable power fiber laser and signal source is a tunable narrow spectral bandwidth(<100MHz)ECL have been studied. Forward SBS does not obey the common theory, that only weaken backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide character weaken the wave vector rule. The forward transmit sound wave-guide Brillouin scattering lines are generated and amplified in FRA. Forward SBS that is amplified phenomena of transmit sound wave Brillouin scattering in the FRA, during pump power is larger than the threshold value of SBS in a S band G652 FRA. The 2 orders Stokes forward Brillouin lines are present during forward pump power of FRA is 920mW, the pump power of BP line is 7.7dBm and the FRA gain is 15.05dB, the power of first order Brillouin lines is smaller than the second Brillouin scattering line. When pump power is further increased, cascaded SBS lines and comb profile are observed. The even order SBS lines is stronger than odd order SBS lines, The odd order SBS lines are named Brillouin- Rayleigh scattering lines.
DCF optical fiber Stokes Raman forwrad scattering and backward scattering gain spectrum have been measured by Raman laser as a pump source and high spectral resolution four grating spectrometer. There are 15 phonon modes in the Stokes forward scattering region and 18 phonon modes in the Stokes backward scattering region. In the low frequency region, there are 3 characteristic phonon modes they are 41.4 cm-1, 68.0 cm-1 and 96.7 cm-1. The characteristic Raman peaks of DCF fiber is 434.7 cm-1 and 455.4 cm-1 that are correspond to 440 cm-1 and 490 cm of normal single mode fiber as a function of pump power has been measured. Measured DCF Raman gain spectrum is different from that in common reference and books. The reasons are the high Ge02 concentration in DCF fiber and the developing of measuring technology.
The backscattering spectrum of optical fiber has been measured by use 1427 nm Raman laser and Q8384 optical spectrum analyzer and Stokes and anti-Stokes ZX band backscattering spectrum has been first observed and discussed, ZX band frequency shift is 1THz, bandwidth 3THz(3dB). Optimum design of S-band negative dispersion DCF discrete fiber Raman amplifier has been researched by OPTIAMP DESIGN 3.3 SOFTWARE (made in Canada Optiwave Corporation) and gain spectrum and gain vs. power of DCF discrete fiber Raman amplifier have been measured, practical including Stokes ZX band backscattering gain effect. Pump on/off small signal gain is 13dB (pump power 700mw; fiber 5.1km) and gain band width is 88nm (1440nm-1528nm). The operation principle, configuration and performance of distributed fiber Raman temperature sensors system has been researched. Amplification of anti-Stokes spontaneity Raman scattering (ARS) effect of fiber and its temperature effect has been first observed and discussed. It has been applied to 30km distributed FRS system.
The optical fiber Raman temperature (OFRT) Lidar is a real time, on line and multi-point temperature measurement system. 30k spot temperature information on space field can be measured and located the position by 30km OFRT Lidar It is a new technology integration of optical-mechanic-electric and computer. The system can take real time, on line measurement of spatial temperature field. In the system, optical fibers are both transmission media and sensing media. The intensity of anti-stokes Raman backscattering of optical fiber is modulated by the spatial temperature field where the optical fiber is laid. After signal processing and demodulation, the information of temperature can be extracted from the noise and can be displayed in real time. In time domain, using the velocity of light wave in optical fiber, the time interval ofback-direction light wave and optical fiber OTDR technology The amplification of anti-stokes Rairan spontaneous scattering (ARS) and the temperature effect have been first observed and applied to OFRT Lidar. The performance of OFRT Lidar is following: fiber length : 25.2km; temperature measuring range: O-lOOC(can be expand) temperature uncertainty: 2 C : temperature resolution: 0. 1 ; spatial resolution: Sm: measurement time: 5mm; Main unit operation temperature range: O—40t .The optical fiber sensor probes and the software for signal processing are also discussed. Keywords: Optical Fiber Raman Temperature (OFRT) Lidar, Optic Time Domain Reflection (OTDR),distributed optical fiber Raman photons temperature sensors, the temperature effect of Raman backscattering, Rayleigh backscattering, ZX band backscattering spectrum, optical fiber sensor probe.
We present a double time-multiplexed interferometer based on Faraday mirrors, which can be used for two quantum cryptography channels. Two channel operation with "star" configuration, 1km + 1km telecom optical fibers, was demonstrated. Experiments show a fringe visibility of 0.96 for both channels. Crosstalk attenuation more than 70dB was observed.
The distributed optical fiber Raman Photons Temperature Sensors (DFRS) is a real time, on line and multi-point (30k points) measuring system for multi-parameter measurement of temperature etc. According to temperature effect of optical fiber Raman backscattering, the intensity of anti-stokes Raman backscattering of optical fiber is modulated by the spatial temperature field where the optical fiber is laid. Then after signal processing and demodulation, the information of temperature can be extracted from the noise and can be displayed in real time. It is a typical optical fiber sensors measuring network. In time domain, using the velocity of light wave in optical fiber, the time interval of back-direction light wave and optical fiber OTDR technology, the DFRS can locate the temperature spots. In this case, it is a typical optical fiber laser temperature radar system as well. The backscattering spectrum of optical fiber has been measured by fiber laser and optical spectrum analyzer. Raman backscattering spectrum and ZX band backscattering spectrum has been first observed. The amplification of anti-stokes Raman spontaneous scattering (ARS) and the temperature effect have been first observed and applied to DFRS. The performance of DOFS is following: fiber length : 25.2km;temperature measuring range: 0-1000C(can be expand) temperature uncertainty: ±200C : temperature resolution: 0. 1; spatial resolution: 5m: measurement time: 10mm; Main unit operation temperature range: 0—400C . The optical fiber sensor probes and the software for signal processing are also discussed.
This paper briefly introduces the operation principle and configuration of distributed optical fiber sensor (DOFS) system. A new demodulation method that uses Rayleigh back scattering photon flux to demodulate Raman back scattering photon flux is put forward, and the advantages of this new method are discussed. Methods to measure temperature, strain and pressure at the same time are researched. The performance of DOFS is following: fiber length: 10.2 km; temperature uncertainty: +/- 2 degree(s)C: temperature resolution: 0.1 degree(s)C; spatial resolution: 4m: measurement time: 5 min; Main unit operation temperature range: 0 - 40 degree(s)C. The DOFS system have been applied to coal mine.
The operation principle of distributed optical fiber Raman gain amplifier has been discussed. The amplification phenomena have been observed in the 1410-nm wavelength range pumped by the 1320-nm solid laser using 23-km single-mode GI optical fiber. The Raman gain is depending on optical fiber interaction length . The optical fiber effective interaction lengths are 15.5 km and 10.5 km when pump pulse peak power are 50W and 30W. The relation between the gain of Raman amplifier and pump power at different effective interaction length of optical fiber is discussed. The Raman gain of optical fiber is 0.62x10-15 m/W during 50W pump power and the effective interaction area of optical fiber is 30 micrometers 2. The effective interaction area of optical fiber is 41.4 micrometers 2 during the pump power is 30W.
In this paper a new structure all fiber Q-switched Erbium-doped fiber laser by using all-fiber wavelength selective intensity modulator based on fiber grating loop mirror (FGLM) was reported. This Q-switched scheme not only modulates loss of the cavity but also selects wavelength. Stable optical pulse with 3 dB linewidth of 0.07 nm, pulse width of 1.4 microsecond(s) , average power of 14.2 mW, and peak power of 1.267 W at 80 mW pump power and 8 KHz repetition rates was obtained in experiments. The generation of single laser pulses and its stability were discussed.
The temperature effect of fiber optics Raman back-scattering have been researched at high temperature (1000 degree(s)C) condition. A distributed fiber optics Raman and Rayleigh back-scattering sensor measuring network have been design and fabricated. The performance of high temperature measuring network is following: temperature measuring range: 0-1000 degree(s)C; temperature uncertainty: <+/- 30 degree(s)C; temperature resolution: 1 degree(s)C; Spatial resolution: 8<m Measuring time: 40s; Fiber length: 100m-10km (according to user need). The stress change of optical cable can be toke out by the measuring network.
The miniature fiber optic Fabry-Perot pressure sensor with a silicon diaphragm was developed for medical applications. The configuration of this sensor was a 1-mm long fiber optic Fabry-Perot interferometer bonded to an 80 micrometers -thick diaphragm. The length of the sensor was about 1.5 mm and the area of the diaphragm was 1 mm x 1 mm. The phase shift of the interferometric sensor was proportional to the applied pressure. The relationship between the applied pressure and the phase change was nonlinear.
A new sampling correct technology of distributed optical fiber temperature sensor (DOFTS) has been researched to eliminate the instability of DOFTS system that caused by the change of environment temperature, gain of amplifier and voltage of power supply. Put the optical sampling loop into a constant temperature thermostat. A computer automatically corrects signal voltage of every point. Thus the stability of the system is improved.
KEYWORDS: Optical fibers, Temperature metrology, Time metrology, Photons, Raman spectroscopy, Temperature sensors, Signal detection, Spatial resolution, Raman scattering, Signal to noise ratio
The operation principle, technique character and measuring method of 10 km LDOFTS are discussed. The testing result of 10 km LDOFTS is given in this paper.
Self-stabilizing modulation scheme is described for fiber optical gyroscope, which can be used in car navigation system. Resonance properties of cylinder piezo-electric modulator were tested, which was used as a resonant element for sine generator. Proper modulation index was calculated in case of second harmonic feedback loop for minimum nonlinearity.
The DOFTS system that has applied to temperature automatically alarm system of coal mine and tunnel has been researched. It is a real-time, on line and multi-point measurement system. The wavelength of LD is 1550 nm, on the 6 km optical fiber, 3000 points temperature signal is sampled and the spatial position is certain. Temperature measured region: -50 degree(s)C--100 degree(s)C; measured uncertain value: +/- 3 degree(s)C; temperature resolution: 0.1 degree(s)C; spatial resolution: <5 cm (optical fiber sensor probe); <8 m (spread optical fiber); measured time: <70 s. In the paper, the operated principles, underground test, test content and practical test results have been discussed.
This paper presents a methodology to suppress the vibration of thin rectangular plate clamped all edges. Intelligent materials such as the piezoelectric ceramic are used as actuators and sensors. The experimental modeling technique, i.e., the state-space frequency domain identification, is introduced to model the complex shaped structures bonded with noncollocated actuators/sensors. This method is much free from the Multi-Input Multi-Output (MIMO) model order problem caused at the digital implementation and also reduces distortion of the signal. In control scheme, the adaptive feedforward with feedback control algorithm is adopted since it is robust for both the transient and persistent external disturbances. The adaptive feedforward control uses the well known Multiple filtered-x LMS (least mean square) algorithm. The MIMO error path dynamics is controlled by the feedback loop which is constructed by multivariable digital LQG (Linear Quadratic Gaussian) controller composed of the regulator and Kalman filter. Experiment results demonstrate the effective reduction of the vibration label and the robustness for both the transient and persistent external disturbances.
We present a dynamic scheme north finder using a low accuracy fiber optic gyroscope which the random walk noise is around 1.5 deg/h/(root)Hz. North finder accuracy has been estimated and experimental data also are presented and error sources are discussed. Two lock-in-amplifier algorithm is proposed for signal processing.
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