The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry (BOTDR), where the simplex pulse codes are applied in the sensi...The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry (BOTDR), where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card (DAQ). A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator (LO) in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio (SNR) has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.展开更多
It has been proposed previously that the coherent detection of a terahertz(THz) pulse can be achieved based on the time-resolved luminescence quenching. In this paper, we investigate the frequency response range of ...It has been proposed previously that the coherent detection of a terahertz(THz) pulse can be achieved based on the time-resolved luminescence quenching. In this paper, we investigate the frequency response range of this novel detection technology by simulating the motion of carriers in gallium arsenide(GaAs) by the ensemble Monte Carlo method. At room temperature, for a direct-current(DC) voltage of 20 kV/cm applied to the semiconductor(GaAs) and sampling time o140 fs, the luminescence quenching phenomena induced by terahertz pulses with different center frequencies are studied The results show that the quenching efficiency is independent of the THz frequency when the frequency is in a range o0.1 THz–4 THz. However, when the frequency exceeds 4 THz, the efficiency decreases with the increase of frequency Therefore, the frequency response range is 0.1 THz–4 THz. Moreover, when the sampling time is changed to 100 fs the frequency response range is extended to be approximately 0.1 THz–5.6 THz. This study of the frequency-dependen characteristics of the luminescence response to the THz pulse can provide a theoretical basis for the exploration of THz detection technology.展开更多
Coherent change detection(CCD) is an effective method to detect subtle scene changes that occur between temporal synthetic aperture radar(SAR) observations. Most coherence estimators are obtained from a Hermitian prod...Coherent change detection(CCD) is an effective method to detect subtle scene changes that occur between temporal synthetic aperture radar(SAR) observations. Most coherence estimators are obtained from a Hermitian product based on local statistics. Increasing the number of samples in the local window can improve the estimation bias, but cause the loss of the estimated images spatial resolution. The limitations of these estimators lead to unclear contour of the disturbed region, and even the omission of fine change targets. In this paper, a CCD approach is proposed to detect fine scene changes from multi-temporal and multi-angle SAR image pairs. Multi-angle CCD estimator can improve the contrast between the change target and the background clutter by jointly accumulating singleangle alternative estimator results without further loss of image resolution. The sensitivity of detection performance to image quantity and angle interval is analyzed. Theoretical analysis and experimental results verify the performance of the proposed algorithm.展开更多
Non-uniform step-size distribution is implemented for split-step based nonlinear compensation in singlechannel 112-Gb/s 16 quadrature amplitude modulation (QAM) transmission. Numerical simulations of the system incl...Non-uniform step-size distribution is implemented for split-step based nonlinear compensation in singlechannel 112-Gb/s 16 quadrature amplitude modulation (QAM) transmission. Numerical simulations of the system including a 20 × 80 km uncompensated link are performed using logarithmic step size distribution to compensate signal distortions. 50% of reduction in number of steps with respect to using constant step sizes is observed. The performance is further improved by optimizing nonlinear calculating position (NLCP) in case of using constant step sizes while NLCP optimization becomes unnecessary when using logarithmic step sizes, which reduces the computational effort due to uniformly distributed nonlinear phase for all successive steps.展开更多
AIM:To select the optimal edge detection methods to identify the corneal surface,and compare three fitting curve equations with Matlab software. METHODS:Fifteen subjects were recruited. The corneal images from optic...AIM:To select the optimal edge detection methods to identify the corneal surface,and compare three fitting curve equations with Matlab software. METHODS:Fifteen subjects were recruited. The corneal images from optical coherence tomography(OCT)were imported into Matlab software. Five edge detection methods(Canny,Log,Prewitt,Roberts,Sobel)were used to identify the corneal surface. Then two manual identifying methods(ginput and getpts)were applied to identify the edge coordinates respectively. The differences among these methods were compared. Binomial curve(y=Ax2+Bx+C),Polynomial curve [p(x)=p1xn+p2x(n-1)+....+pnx+pn+1] and Conic section(Ax2+Bxy+Cy2+Dx+Ey+F=0)were used for curve fitting the corneal surface respectively. The relative merits among three fitting curves were analyzed. Finally,the eccentricity(e)obtained by corneal topography and conic section were compared with paired t-test. RESULTS:Five edge detection algorithms all had continuous coordinates which indicated the edge of the corneal surface. The ordinates of manual identifying were close to the inside of the actual edges. Binomial curve was greatly affected by tilt angle. Polynomial curve was lack of geometrical properties and unstable. Conic section could calculate the tilted symmetry axis,eccentricity,circle center,etc. There were no significant differences between 'e' values by corneal topography and conic section(t=0.9143,P=0.3760 〉0.05).CONCLUSION:It is feasible to simulate the corneal surface with mathematical curve with Matlab software. Edge detection has better repeatability and higher efficiency. The manual identifying approach is an indispensable complement for detection. Polynomial and conic section are both the alternative methods for corneal curve fitting. Conic curve was the optimal choice based on the specific geometrical properties.展开更多
In this paper, we describe successful joint experiments with Deutsche Telecom on long-haul transmission of 100G and beyond over standard single mode fiber (SSMF) and with in-line EDFA-only amplification. The transmi...In this paper, we describe successful joint experiments with Deutsche Telecom on long-haul transmission of 100G and beyond over standard single mode fiber (SSMF) and with in-line EDFA-only amplification. The transmission link consists of 8 nodes and 950 km installed SSMF in DT' s optical infrastructure. Laboratory SSMF was added for extended optical reach. The first field experiment involved transmission of 8 x 216.8 Gbit/s Nyquist-WDM signals over 1750 km with 21.6 dB average loss per span. Each channel, modulated by a 54.2 Gbaud PDM-CSRZ-QPSK signal, is on a 50 GHz grid, which produces a net spectral efficiency (SE) of 4 bit/s/Hz. We also describe mixed-data-rate transmission coexisting with 1T, 400G, and 100G channels. The 400G channel uses four independent subcarriers modulated by 28 Gbaud PDM-QPSK signals. This yields a net SE of 4 bit/s/Hz, and 13 optically generated subcarriers from a single optical source are used in the 1T channel with 25 Gbaud PDM-QPSK modulation. The 100G signal uses real-time coherent PDM-QPSK transponder with 15% overhead of soft-decision forward-error correction (SD-FEC). The digital post filter and 1 -bit maximum-likelihood sequence estimation (MLSE) are introduced at the receiver DSP to suppress noise, linear crosstalk, and filtering effects. Our results show that future 400G and 1T channels that use Nyquist WDM can transmit over long-haul distances with higher SE and using the same QPSK format.展开更多
In this paper, we evaluate transmission in a 1 Tb/s (10 × 112 Gb/s) Nyquist WDM PMRZQPSK superchannel over a widelydeployed SMF-28 fiber with and without maximum aposteriori (MAP) equalization. Over 1000 km c...In this paper, we evaluate transmission in a 1 Tb/s (10 × 112 Gb/s) Nyquist WDM PMRZQPSK superchannel over a widelydeployed SMF-28 fiber with and without maximum aposteriori (MAP) equalization. Over 1000 km can be reached with BER below the HD FEC limit and with a spectral efficiency of 4 b/s/Hz.展开更多
This paper begins with Nyquist wavelengthdivision multiplexing (WDM) and then introduces fasterthanNyquist. In fasterthanNyquist a certain amount of intersymbol interference (ISI) is accepted, which violates the f...This paper begins with Nyquist wavelengthdivision multiplexing (WDM) and then introduces fasterthanNyquist. In fasterthanNyquist a certain amount of intersymbol interference (ISI) is accepted, which violates the fundamental principle of Nyquist WDM. This results in muchrelaxed transceiver bandwidth and simpler spectral design. However, in fasterthanNyquist, implementation complexity is shifted from the transmitter side to the receiver side. Therefore, successful application of fasterthanNyquist depends on innovation in the receiver structure. In this paper, we discuss the guidelines for implementing suboptimum, lowcomplexity receivers based on fasterthanNyquist. We suggest that duobinary shaping is a good technique for trading off achievable spectral efficiency, detection performance, and implementation complexity and might be preferable to Nyquist WDM. Experiments are conducted to verify robustness of the proposed technique.展开更多
Nyquist wavelength-division multiplexing (N-WDM) allows high spectral efficiency (SE) in long-haul transmission systems. Compared to polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK), m...Nyquist wavelength-division multiplexing (N-WDM) allows high spectral efficiency (SE) in long-haul transmission systems. Compared to polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK), multilevel modulation, such as PDM 16 quadrature-amplitude modulation (16-QAM), is much more sensitive to intrachannel noise and interchannel linear crosstalk caused by N-WDM. We experimentally generate and transmit a 6 x 128 Gbit/s N-WDM PDM 16-QAM signal over 1200 km single-mode fiber (SMF)-28 with amplification provided by an erbium-doped fiber amplifier (EDFA) only. The net SE is 7.47 bit/s/Hz, which to the best of our knowledge is the highest SE for a signal with a bit rate beyond 100 Gbit/s using the PDM 16-QAM. Such SE was achieved by DSP pre-equalization of transmitter-side impairments and DSP post-equalization of channel and receiver-side impairments. Nyquist-band can be used in pre-equalization to enhance the tolerance of PDM 16-QAM to aggressive spectral shaping. The bit-error ratio (BER) for each of the 6 channels is smaller than the forward error correction (FEC) limit of 3.8 × 10-3 after 1200 km SMF-28 transmission.展开更多
For the purpose of resolving the problem of performance deterioration introduced by inaccurate phase compensation in existing coherent averaging line spectrum detectors, a modified coherent detector is proposed. The t...For the purpose of resolving the problem of performance deterioration introduced by inaccurate phase compensation in existing coherent averaging line spectrum detectors, a modified coherent detector is proposed. The three point interpolation in frequency domain is applied to obtain accurate estimate of phase difference between segments when the segmented length is not an integral multiple of the signal period. Then the segmented data are multiplied by a complex coefficient to remove the phase difference and synchronize the phases of all the segments before coherent averaging. Theoretical analysis shows that there will be a gain of 3.9 dB at most by using the modified detector. The detection performance of the incoher- ent averaging power spectrum detector (AVGPR), the phase coherent averaging detector, the modified coherent averaging detector are compared with each other by computer simulations. The results coincide basically with the theoretical analysis, which show the superiority of the modified detector to the former two detectors.展开更多
Optical spectral measurements are crucial for optical sensors and many other applications,but the prevailing methods,such as optical spectrum analysis and tunable laser spectroscopy,often have to make compromises amon...Optical spectral measurements are crucial for optical sensors and many other applications,but the prevailing methods,such as optical spectrum analysis and tunable laser spectroscopy,often have to make compromises among resolution,speed,and accuracy.Optical frequency combs are widely used for metrology of discrete atomic and molecular spectral lines.However,they are usually generated by optical methods and have large comb spacing,which limits the resolution for direct sampling of continuous spectra.To overcome these problems,this paper presents an original method to digitally generate an ultrafine optical frequency comb(UFOFC)as the frequency ruler for spectral measurements.Each comb line provides one sampling point,and the full spectrum can be captured at the same time using coherent detection.For an experimental demonstration,we adopted the inverse fast Fourier transform to generate a UFOFC with a comb spacing of 1.46 MHz over a 10-GHz range and demonstrated its functions using a Mach–Zehnder refractive index sensor.The UFOFC obtains a spectral resolution of 0.01 pm and response time of 0.7 μs;both represent 100-fold improvements over the state of the art and could be further enhanced by several orders of magnitude.The UFOFC presented here could facilitate new label-free sensor applications that require both high resolution and fast speed,such as measuring binding kinetics and single-molecule dynamics.展开更多
Increasing the system capacity and spectral efficiency(SE)per unit bandwidth is one of the ultimate goals for data network designers,especially when using technologies compatible with current embedded fiber infrastruc...Increasing the system capacity and spectral efficiency(SE)per unit bandwidth is one of the ultimate goals for data network designers,especially when using technologies compatible with current embedded fiber infrastructures.Among these,the polarizationdivision-multiplexing(PDM)scheme,which supports two independent data channels on a single wavelength with orthogonal polarization states,has become a standard one in most state-of-art telecommunication systems.Currently,however,only two polarization states(that is,PDM)can be used,setting a barrier for further SE improvement.Assisted by coherent detection and digital signal processing,we propose and experimentally demonstrate a scheme for pseudo-PDM of four states(PPDM-4)by manipulation of four linearly polarized data channels with the same wavelength.Without any modification of the fiber link,we successfully transmit a 100-Gb s−1 PPDM-4 differential-phase-shift-keying signal over a 150-km single-mode fiber link.Such a method is expected to open new possibilities to fully explore the use of polarization freedom for capacity and SE improvement over existing fiber systems.展开更多
In this paper,a novel birefringence measurement method through the Rayleigh backscattered lightwave within single-mode fiber is proposed,using a single chirped-pulse with arbitrary state of polarization.Numerical anal...In this paper,a novel birefringence measurement method through the Rayleigh backscattered lightwave within single-mode fiber is proposed,using a single chirped-pulse with arbitrary state of polarization.Numerical analysis is carried out in detail,then pulse-compression phase-sensitive optical time domain reflectometry(PC-O-OTDR)with polarization-diverse coherent detection is employed to verify this method.A 2 km spun single-mode fiber is tested with 8.6cm spatial resolution,and the average birefringence of the fiber under test is measured as 0.234rad/m,which is consistent with previous literatures about single-mode fiber.Moreover,the relationship between the measured birefringence and the spatial resolution is also studied for the first time,and the results show that spatial resolution is crucial for fiber birefringence measurement.展开更多
A few-mode fiber (FMF) is designed to support three spatial modes (LP01, LP 11a, and LP 11 b) and fabricated through plasma chemical vapor deposition (PCVD)and rod-in-tube (RIT) method. Using PDM-DFTS-OFDM- 32...A few-mode fiber (FMF) is designed to support three spatial modes (LP01, LP 11a, and LP 11 b) and fabricated through plasma chemical vapor deposition (PCVD)and rod-in-tube (RIT) method. Using PDM-DFTS-OFDM- 32QAM modulation, wavelength division multiplexing, mode multiplexing, and coherent detection, we successfully demonstrated 200Tb/s (375× 3 × 178.125Gb/s) signal over 1 km FMF using C and L bands with 25 GHz channel spacing. After 1 km FMF transmission, all the tested bit error rates (BERs) are below 20% forward error correction (FEC) threshold (2.0 × 10-2). Within each sub-channel, we achieved a spectral efficiency of 21.375 bits/Hz in the C and L bands.展开更多
A flow measurement system consisting of an optical fiber Fabry–Perot(F-P) sensor and an elbow tube is proposed and demonstrated to realize flow measurements and eliminate thermal disturbance.Two F-P sensors are sym...A flow measurement system consisting of an optical fiber Fabry–Perot(F-P) sensor and an elbow tube is proposed and demonstrated to realize flow measurements and eliminate thermal disturbance.Two F-P sensors are symmetrically mounted on the inner-wall surface of the elbow of 90° in order to eliminate the effect of thermal disturbance to the flow measurement accuracy.Experimental results show that the absolute phase difference is the square root of the fluid flow.It is consistent with the theoretical analysis,which proves that the flow measurement method can measure flow and eliminate the influence of thermal disturbance simultaneously.展开更多
基金supported by the National High Technology Research and Development Program of China(Grant No.2012AA041203)the National Natural Science Foundation of China(Grant Nos.61377062 and 31201377)+1 种基金the Program of Shanghai Excellent Technical Leaders,China(Grant No.13XD1425400)the Doctorial Fund of Zhengzhou University of Light Industry,China(Grant No.2013BSJJ012)
文摘The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry (BOTDR), where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card (DAQ). A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator (LO) in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio (SNR) has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.
基金supported by the Wuhan Applied Basic Research Project,China(Grant No.20140101010009)the National Natural Science Foundation of China(Grant Nos.61405063,61475054,11574105,and 61177095)+1 种基金the Hubei Science and Technology Agency Project,China(Grant No.2015BCE052)the Fundamental Research Funds for the Central Universities,China(Grant No.2017KFYXJJ029)
文摘It has been proposed previously that the coherent detection of a terahertz(THz) pulse can be achieved based on the time-resolved luminescence quenching. In this paper, we investigate the frequency response range of this novel detection technology by simulating the motion of carriers in gallium arsenide(GaAs) by the ensemble Monte Carlo method. At room temperature, for a direct-current(DC) voltage of 20 kV/cm applied to the semiconductor(GaAs) and sampling time o140 fs, the luminescence quenching phenomena induced by terahertz pulses with different center frequencies are studied The results show that the quenching efficiency is independent of the THz frequency when the frequency is in a range o0.1 THz–4 THz. However, when the frequency exceeds 4 THz, the efficiency decreases with the increase of frequency Therefore, the frequency response range is 0.1 THz–4 THz. Moreover, when the sampling time is changed to 100 fs the frequency response range is extended to be approximately 0.1 THz–5.6 THz. This study of the frequency-dependen characteristics of the luminescence response to the THz pulse can provide a theoretical basis for the exploration of THz detection technology.
文摘Coherent change detection(CCD) is an effective method to detect subtle scene changes that occur between temporal synthetic aperture radar(SAR) observations. Most coherence estimators are obtained from a Hermitian product based on local statistics. Increasing the number of samples in the local window can improve the estimation bias, but cause the loss of the estimated images spatial resolution. The limitations of these estimators lead to unclear contour of the disturbed region, and even the omission of fine change targets. In this paper, a CCD approach is proposed to detect fine scene changes from multi-temporal and multi-angle SAR image pairs. Multi-angle CCD estimator can improve the contrast between the change target and the background clutter by jointly accumulating singleangle alternative estimator results without further loss of image resolution. The sensitivity of detection performance to image quantity and angle interval is analyzed. Theoretical analysis and experimental results verify the performance of the proposed algorithm.
基金funding of the Erlangen Graduate School in Advanced Optical Technologies (SAOT) by the German National Science Foundation(DFG) in the framework of the excellence initiative
文摘Non-uniform step-size distribution is implemented for split-step based nonlinear compensation in singlechannel 112-Gb/s 16 quadrature amplitude modulation (QAM) transmission. Numerical simulations of the system including a 20 × 80 km uncompensated link are performed using logarithmic step size distribution to compensate signal distortions. 50% of reduction in number of steps with respect to using constant step sizes is observed. The performance is further improved by optimizing nonlinear calculating position (NLCP) in case of using constant step sizes while NLCP optimization becomes unnecessary when using logarithmic step sizes, which reduces the computational effort due to uniformly distributed nonlinear phase for all successive steps.
基金Supported by the National Natural Science Foundation of China(No.81400428)Science and Technology Commission of Shanghai Municipality(No.134119b1600)
文摘AIM:To select the optimal edge detection methods to identify the corneal surface,and compare three fitting curve equations with Matlab software. METHODS:Fifteen subjects were recruited. The corneal images from optical coherence tomography(OCT)were imported into Matlab software. Five edge detection methods(Canny,Log,Prewitt,Roberts,Sobel)were used to identify the corneal surface. Then two manual identifying methods(ginput and getpts)were applied to identify the edge coordinates respectively. The differences among these methods were compared. Binomial curve(y=Ax2+Bx+C),Polynomial curve [p(x)=p1xn+p2x(n-1)+....+pnx+pn+1] and Conic section(Ax2+Bxy+Cy2+Dx+Ey+F=0)were used for curve fitting the corneal surface respectively. The relative merits among three fitting curves were analyzed. Finally,the eccentricity(e)obtained by corneal topography and conic section were compared with paired t-test. RESULTS:Five edge detection algorithms all had continuous coordinates which indicated the edge of the corneal surface. The ordinates of manual identifying were close to the inside of the actual edges. Binomial curve was greatly affected by tilt angle. Polynomial curve was lack of geometrical properties and unstable. Conic section could calculate the tilted symmetry axis,eccentricity,circle center,etc. There were no significant differences between 'e' values by corneal topography and conic section(t=0.9143,P=0.3760 〉0.05).CONCLUSION:It is feasible to simulate the corneal surface with mathematical curve with Matlab software. Edge detection has better repeatability and higher efficiency. The manual identifying approach is an indispensable complement for detection. Polynomial and conic section are both the alternative methods for corneal curve fitting. Conic curve was the optimal choice based on the specific geometrical properties.
文摘In this paper, we describe successful joint experiments with Deutsche Telecom on long-haul transmission of 100G and beyond over standard single mode fiber (SSMF) and with in-line EDFA-only amplification. The transmission link consists of 8 nodes and 950 km installed SSMF in DT' s optical infrastructure. Laboratory SSMF was added for extended optical reach. The first field experiment involved transmission of 8 x 216.8 Gbit/s Nyquist-WDM signals over 1750 km with 21.6 dB average loss per span. Each channel, modulated by a 54.2 Gbaud PDM-CSRZ-QPSK signal, is on a 50 GHz grid, which produces a net spectral efficiency (SE) of 4 bit/s/Hz. We also describe mixed-data-rate transmission coexisting with 1T, 400G, and 100G channels. The 400G channel uses four independent subcarriers modulated by 28 Gbaud PDM-QPSK signals. This yields a net SE of 4 bit/s/Hz, and 13 optically generated subcarriers from a single optical source are used in the 1T channel with 25 Gbaud PDM-QPSK modulation. The 100G signal uses real-time coherent PDM-QPSK transponder with 15% overhead of soft-decision forward-error correction (SD-FEC). The digital post filter and 1 -bit maximum-likelihood sequence estimation (MLSE) are introduced at the receiver DSP to suppress noise, linear crosstalk, and filtering effects. Our results show that future 400G and 1T channels that use Nyquist WDM can transmit over long-haul distances with higher SE and using the same QPSK format.
文摘In this paper, we evaluate transmission in a 1 Tb/s (10 × 112 Gb/s) Nyquist WDM PMRZQPSK superchannel over a widelydeployed SMF-28 fiber with and without maximum aposteriori (MAP) equalization. Over 1000 km can be reached with BER below the HD FEC limit and with a spectral efficiency of 4 b/s/Hz.
文摘This paper begins with Nyquist wavelengthdivision multiplexing (WDM) and then introduces fasterthanNyquist. In fasterthanNyquist a certain amount of intersymbol interference (ISI) is accepted, which violates the fundamental principle of Nyquist WDM. This results in muchrelaxed transceiver bandwidth and simpler spectral design. However, in fasterthanNyquist, implementation complexity is shifted from the transmitter side to the receiver side. Therefore, successful application of fasterthanNyquist depends on innovation in the receiver structure. In this paper, we discuss the guidelines for implementing suboptimum, lowcomplexity receivers based on fasterthanNyquist. We suggest that duobinary shaping is a good technique for trading off achievable spectral efficiency, detection performance, and implementation complexity and might be preferable to Nyquist WDM. Experiments are conducted to verify robustness of the proposed technique.
文摘Nyquist wavelength-division multiplexing (N-WDM) allows high spectral efficiency (SE) in long-haul transmission systems. Compared to polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK), multilevel modulation, such as PDM 16 quadrature-amplitude modulation (16-QAM), is much more sensitive to intrachannel noise and interchannel linear crosstalk caused by N-WDM. We experimentally generate and transmit a 6 x 128 Gbit/s N-WDM PDM 16-QAM signal over 1200 km single-mode fiber (SMF)-28 with amplification provided by an erbium-doped fiber amplifier (EDFA) only. The net SE is 7.47 bit/s/Hz, which to the best of our knowledge is the highest SE for a signal with a bit rate beyond 100 Gbit/s using the PDM 16-QAM. Such SE was achieved by DSP pre-equalization of transmitter-side impairments and DSP post-equalization of channel and receiver-side impairments. Nyquist-band can be used in pre-equalization to enhance the tolerance of PDM 16-QAM to aggressive spectral shaping. The bit-error ratio (BER) for each of the 6 channels is smaller than the forward error correction (FEC) limit of 3.8 × 10-3 after 1200 km SMF-28 transmission.
文摘For the purpose of resolving the problem of performance deterioration introduced by inaccurate phase compensation in existing coherent averaging line spectrum detectors, a modified coherent detector is proposed. The three point interpolation in frequency domain is applied to obtain accurate estimate of phase difference between segments when the segmented length is not an integral multiple of the signal period. Then the segmented data are multiplied by a complex coefficient to remove the phase difference and synchronize the phases of all the segments before coherent averaging. Theoretical analysis shows that there will be a gain of 3.9 dB at most by using the modified detector. The detection performance of the incoher- ent averaging power spectrum detector (AVGPR), the phase coherent averaging detector, the modified coherent averaging detector are compared with each other by computer simulations. The results coincide basically with the theoretical analysis, which show the superiority of the modified detector to the former two detectors.
基金Zhaohui Li acknowledges the support of the National Basic Research Programme of China(973)(Project No.2012CB315603)National High Technology 863 Research and Development Program of China(Nos.2013AA013300 and 2013AA013403)+5 种基金the Research Fund for the Doctoral Program of Higher Education of China(20124401110003)National Natural Science Foundation of China(NSFC)(Grant No.61435006)the Program for New Century Excellent Talents in University(NCET-12-0679)in ChinaXuming Zhang acknowledges the NSFC(Grant No.61377068)the Hong Kong Research Grant Council(Grant Nos.PolyU 5327/11E and N_PolyU505/13)the Hong Kong Polytechnic University(Grant Nos.G-YN07,4-BCAL and G-YBBE).
文摘Optical spectral measurements are crucial for optical sensors and many other applications,but the prevailing methods,such as optical spectrum analysis and tunable laser spectroscopy,often have to make compromises among resolution,speed,and accuracy.Optical frequency combs are widely used for metrology of discrete atomic and molecular spectral lines.However,they are usually generated by optical methods and have large comb spacing,which limits the resolution for direct sampling of continuous spectra.To overcome these problems,this paper presents an original method to digitally generate an ultrafine optical frequency comb(UFOFC)as the frequency ruler for spectral measurements.Each comb line provides one sampling point,and the full spectrum can be captured at the same time using coherent detection.For an experimental demonstration,we adopted the inverse fast Fourier transform to generate a UFOFC with a comb spacing of 1.46 MHz over a 10-GHz range and demonstrated its functions using a Mach–Zehnder refractive index sensor.The UFOFC obtains a spectral resolution of 0.01 pm and response time of 0.7 μs;both represent 100-fold improvements over the state of the art and could be further enhanced by several orders of magnitude.The UFOFC presented here could facilitate new label-free sensor applications that require both high resolution and fast speed,such as measuring binding kinetics and single-molecule dynamics.
基金supported by the Natural Science Foundation of China(Nos.61335005,61325023,61275068 and 61401378)the National Basic Research Program of China(2012CB315704)。
文摘Increasing the system capacity and spectral efficiency(SE)per unit bandwidth is one of the ultimate goals for data network designers,especially when using technologies compatible with current embedded fiber infrastructures.Among these,the polarizationdivision-multiplexing(PDM)scheme,which supports two independent data channels on a single wavelength with orthogonal polarization states,has become a standard one in most state-of-art telecommunication systems.Currently,however,only two polarization states(that is,PDM)can be used,setting a barrier for further SE improvement.Assisted by coherent detection and digital signal processing,we propose and experimentally demonstrate a scheme for pseudo-PDM of four states(PPDM-4)by manipulation of four linearly polarized data channels with the same wavelength.Without any modification of the fiber link,we successfully transmit a 100-Gb s−1 PPDM-4 differential-phase-shift-keying signal over a 150-km single-mode fiber link.Such a method is expected to open new possibilities to fully explore the use of polarization freedom for capacity and SE improvement over existing fiber systems.
文摘In this paper,a novel birefringence measurement method through the Rayleigh backscattered lightwave within single-mode fiber is proposed,using a single chirped-pulse with arbitrary state of polarization.Numerical analysis is carried out in detail,then pulse-compression phase-sensitive optical time domain reflectometry(PC-O-OTDR)with polarization-diverse coherent detection is employed to verify this method.A 2 km spun single-mode fiber is tested with 8.6cm spatial resolution,and the average birefringence of the fiber under test is measured as 0.234rad/m,which is consistent with previous literatures about single-mode fiber.Moreover,the relationship between the measured birefringence and the spatial resolution is also studied for the first time,and the results show that spatial resolution is crucial for fiber birefringence measurement.
基金Aeknowledgements This work was supported by the Major Scientific and Technological hmovation Projects of Hubci Province (No. 2014AAA001), the National Basic Research Program of China (Nos. 2014CB340100, 2014CB340101, and 2014CB340105). and the Natural Science Foundation of Hubei Prov incc (No. 2015CFA056).
文摘A few-mode fiber (FMF) is designed to support three spatial modes (LP01, LP 11a, and LP 11 b) and fabricated through plasma chemical vapor deposition (PCVD)and rod-in-tube (RIT) method. Using PDM-DFTS-OFDM- 32QAM modulation, wavelength division multiplexing, mode multiplexing, and coherent detection, we successfully demonstrated 200Tb/s (375× 3 × 178.125Gb/s) signal over 1 km FMF using C and L bands with 25 GHz channel spacing. After 1 km FMF transmission, all the tested bit error rates (BERs) are below 20% forward error correction (FEC) threshold (2.0 × 10-2). Within each sub-channel, we achieved a spectral efficiency of 21.375 bits/Hz in the C and L bands.
基金supported by the National Instrumentation Program of China(No.2013YQ030915)the National Natural Science Foundation of China(Nos.61675152,61227011,61378043,61475114,61505139,and 61505138)+2 种基金the open project of Key Laboratory of Micro Opto-electro Mechanical System Technology,Tianjin University,Ministry of Education(No.MOMST2016-3)the Shenzhen Science and Technology Research Project(No.JCYJ20120831153904083)the SEM Soft Science Research and Development Project of Ministry of Housing and Urban-Rural Development of China(No.2016-K4-087)
文摘A flow measurement system consisting of an optical fiber Fabry–Perot(F-P) sensor and an elbow tube is proposed and demonstrated to realize flow measurements and eliminate thermal disturbance.Two F-P sensors are symmetrically mounted on the inner-wall surface of the elbow of 90° in order to eliminate the effect of thermal disturbance to the flow measurement accuracy.Experimental results show that the absolute phase difference is the square root of the fluid flow.It is consistent with the theoretical analysis,which proves that the flow measurement method can measure flow and eliminate the influence of thermal disturbance simultaneously.