Chromatic Dispersion Of Optical Fiber Research Articles

EXPRESS: Feasibility of a Fiber-Dispersive Raman Spectrometer for Biomarker Detection.

Raman spectroscopy is among the top analytical techniques for ultra-low-dense organic matter, crucial to the search for life and analysis of celestial body surfaces in space exploration missions. Achieving the ultimate sensitivity in in situ Raman spectroscopy necessitates a breakthrough in detecting inelastically scattered light. Single-photon detectors (SPD) operating in photon counting mode, which can differentiate between Raman and luminescence responses, are promising candidates for the challenging scientific requirements. Since large SPD arrays are not yet commercially available, a dispersive element can be adapted to a single-pixel detector. By exploiting chromatic dispersion in optical fibers and picosecond-pulsed excitation, we delay the arrivals of different spectral components onto a single-pixel SPD. This method also separates weak Raman signals from stronger luminescence through correlated time-domain measurements. We study the impact of fiber properties and the excitation wavelength of a pulsed laser on the spectral resolution of the fiber-dispersive Raman spectrometer (FDRS). Additionally, we demonstrate the FDRS's potential for studying biomarkers and discuss its feasibility for analyzing inclusions in ice matrices.

A novel frequency 32-tupling ROF system without bit walk-off effect based on MZM with inserting pilot

A novel scheme for a frequency 32-tupling millimeter wave (MMW) radio over fiber(ROF) system without the bit walk-off effect is proposed. The operation principle and feasibility of our proposed scheme are theoretically analyzed and verified with simulation experiments. The main part of our scheme is a ±16th order sidebands generator (SG) which is constructed by eight Mach-Zehnder modulators (MZM) connected in parallel. In the back-to-back(BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±16th order sidebands are generated by the SG. In the data transmission case, the data signal is split into two beams first, one of which modulates the RF drive signal with an electrical phase modulator (PM), and the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can be modulated only to the +16th order sideband of the output of the SG. The optical carrier from the CW laser is split into two paths, one is sent into the SG, and the other is used as a pilot. The output signal of SG is combined with the pilot signal and is transmitted to the base station(BS) via optical fiber. In BS, the pilot signal is filtered out by an FBG and used as the carrier for uplink for carrier reuse. After filtering out the pilot, the signal from the FBG which is ±16th order sidebands is injected into the photodetector, and a frequency 32-tupling MMW with downlink data is generated. The influence on the bit error rate (BER) and Q factor by the key parameters in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the fiber transmission distance, but also effectively improve the performance of the downlink, it has important application prospects in ROF systems.

A Novel Inserting Pilot Radio over Fiber System without the Bit Walk-Off Effect for the Generation and Distribution of Frequency 16-Tupling Millimeter Waves by Mach–Zehnder Modulators

A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.

Dealing with Mathematically Difficult Topics in Electrical and Electronic Engineering

Due to insufficient mathematical background, electrical and electronic engineering students may have difficulties in handling essential concepts and processes related to their field. For example, it has been observed that students find it difficult to comprehend topics such as Fourier analysis, noise, Maxwell equations and wave propagation etc. The article describes an attempt to approach such concepts in a two-step manner, first the topics are addressed in an introductory way (by means of particular, yet representative, examples and simple mathematics) and, when the students have got the necessary background and confidence, the topics are addressed in a more formal manner. As a case-study, the proposed approach has been applied to topics such as basic signal quantities, Fourier analysis, noise and chromatic dispersion in optical fibers.

Chromatic dispersion dependence of GAWBS phase noise compensation with pilot tone

We describe experimental and numerical results regarding the influence of chromatic dispersion in optical fibers on guided acoustic-wave Brillouin scattering (GAWBS) phase noise compensation with a pilot tone (PT). We compared the compensation performance for GAWBS phase noise generated in an ultra-large-area fiber (ULAF) where DULAF = 21 ps/nm/km with that in a dispersion-shifted fiber (DSF) where DDSF = -1.3 ps/nm/km and found that the performance depends strongly on chromatic dispersion. The numerical analysis shows that the group delay between the signal and PT caused by chromatic dispersion reduces the GAWBS noise correlation between them, which degrades the compensation performance for GAWBS phase noise. It is clarified that a condition for effective GAWBS compensation is that the group delay between the signal and PT should be less than half the period of the GAWBS phase noise component.

Demonstration of 200 Gbit/s Single λ Dual Band DMT Transmission With a SE of 6.29 bit/s/Hz

With the increasing demand of bandwidth, a higher capacity communication system is required for short-reach optical link. Intensity modulation/direct detection (IM-DD) is considered as a reasonable method, due to its low cost and power consumption. In the aspect of digital signal processing (DSP), discrete Fourier transform-spread (DFT-s) precoding can be used to reduce peak to average power ratio (PAPR) and average the noise among the subcarriers. In addition, probabilistic shaping (PS) turns out to further increase the system capacity. We experimentally demonstrated a 200 Gbit/s single λ dual band DMT transmission with a spectrum efficiency (SE) of 6.29 bit/s/Hz. The achievable information rate (AIR) of the proposed dual band signal increases about 30 Gbit/s compared with that of single band signal. Moreover, single-sideband (SSB) signal and signal with guard band are implemented to mitigate the frequency selective fading of optical fiber chromatic dispersion (CD). The performance of these two methods are quite closed for short reach transmission. Considering the signal-signal beat interference (SSBI) introduced by the SSB signal, an extra Volterra filter is applied in DSP. Besides, an extra optical filter is required to generate the SSB signal.

Experimental demonstration of a real-time hybrid optoelectronic analog-to-digital converter

A real-time hybrid optoelectronic analog-to-digital converter (HOE-ADC) based on optical sampling and electronic quantization is proposed and experimentally demonstrated. In the proposed HOE-ADC, a broadband semiconductor laser is intensity modulated by electronic pulses to generate an optical sampling pulse train. The optical sampling pulse is split into multiple channels with different optical fiber delay, and the analog signal is modulated on the multichannel optical sampling pulses using a Mach–Zehnder modulator array. By broadening the optical pulses, which can be done by employing optical-fiber chromatic dispersion, the bandwidth of the sampled pulse is reduced to match the sample rate of a low-speed electronic ADC, where the broadened optical sampling pulses are quantified. The nonlinearity of optical devices is calibrated through digital signal processing. A four-channel HOE-ADC is experimentally demonstrated. A sampling rate of 12 GS / s and a system bandwidth of 10 GHz are achieved. The effective number of bit (ENOB) for a 1.5-GHz target analog signal is measured to be 5.9 bit. Further, the primary influence factors, such as delay errors, for the performance of ENOB are also discussed.

Time Domain Equalization and Digital Back-Propagation Method-Based Receiver for Fiber Optic Communication Systems

Fiber optic communication systems (FOCSs) have attained a lot of attention by revolutionizing the telecommunication industry and offering new possibilities with the technical advancements in state-of-the-art high speed digital electronics. Advanced modulation formats make use of the phase, amplitude, and polarization of the optical signals at the same time to provide high spectral efficiency as compared with 1 bit/s/Hz for the intensity modulation direct detection system (IMDD), but are highly prone to transmission impairments. Thus, the effects that add up to the optical fiber impairments such as optical fiber chromatic dispersion (OFCD), polarization model dispersion (PMD), and phase offset and noise (POaN) need to be addressed at the receiver side. The development of components and algorithms to minimize these effects in next generation FOCSs with 100 Gbps data rate and beyond with long-haul transmission is still a challenging issue. In this paper, digital signal processing- (DSP-) assisted dispersion and nonlinear compensation techniques are presented to compensate for physical layer impairments including OFCD, PMD, and POaN. The simulations are performed considering Dual Polarization- (DP-) QPSK modulation format to achieve two-fold data rate to achieve spectral efficiency of 3.28 bits/s/Hz by making use of the polarization diversity and system performance is investigated in terms of bit error rate (BER), constellation diagrams, and quality factor (Q-factor) for different values of optical signal-to-noise ratio (OSNR), launch power (PL), and fiber length.

Centralized Fiber-Distributed Data Communication and Sensing Convergence System Based on Microwave Photonics

A unified data communication and radar sensing system towards millimeter-wave (mm-wave) applications with extended coverage is proposed and experimentally demonstrated. In the unified system, the transmission and reception of mm-wave signals are implemented by microwave photonics technologies, and the orthogonal frequency division multiplexing (OFDM) signal is employed for communications and radar sensing simultaneously. The superheterodyne optical carrier suppression (HeteroOCS) is used to up-convert the intermediate frequency (IF) OFDM signal to the mm-wave band in the central office (CO). The optical mm-wave signal is transmitted to the remote antenna units (RAUs) via optical fibers. The echo signal is received by the RAU which is remotely connected to the CO by an analog photonic link based on a polarization modulator (PolM). In the transmitter and receiver links, the chromatic dispersion of optical fibers is overcome by the HeteroOCS and the PolM, respectively. The baseband units (BBU) centralized in the CO is used to process the radar sensing signal. A pre-delayed trigger signal is proposed to overcome the fiber length limitation. A proof-of-concept experiment is performed. Two targets with distances of 1.64 m and 3.40 m are successfully detected separately. The communication function of the system is also verified. 1 m wireless transmission of 1.56 Gb/s data rate is achieved below the forward error correction limit.

Pre-Equalizing Electro-Optic Modulator Utilizing Polarization-Reversed Ferro-Electric Crystal Substrate

We have proposed and developed new electro-optic modulators for the pre-equalization of signal distortion caused by the optical fiber chromatic dispersion effect. We found that the synthesis of an almost arbitrary impulse response function is obtainable by utilizing an electro-optic modulator composed of a Mach-Zehnder waveguide and travelling-wave electrodes on a ferro-electric material substrate with polarization-reversed structures. In this paper, the operational principle, design and simulation results of the pre-equalization modulator are presented. Some preliminary experimental results are also shown with future prospects.

Extending the Reach of Short-Reach Optical Interconnects With DSP-Free Direct Detection

Coherent detection is the usual solution to achieve high bit rate transmission over long distance. However, it requires a local oscillator and energy consuming digital signal processing that make it not suitable for cost and energy sensitive interconnections and short haul links. In these applications, direct detection is the preferred solution and the main impairment is the chromatic dispersion of optical fibers. In theory, combined amplitude-phase shift (CAPS) codes are able to defeat any amount of chromatic dispersion. However, while they can be detected with a very simple direct detection receiver, their generation is not trivial. Their complexity grows with the order of the code which, in turn, increases with the chromatic dispersion. In this paper, the IQ-duobinary modulation scheme, a novel technique for approximating an order-3 CAPS code, is presented. Such a modulation scheme allows us to bridge up to 18 km at a bit-rate of 50 Gb/s over a standard single mode fiber using a simple direct-detection receiver without the need of any digital signal processing technique.

Fiber chromatic dispersion measurement with improved measurement range based on chirped intensity modulation

A novel method for accurately measuring chromatic dispersion of optical fibers is proposed based on the use of chirped intensity-modulated signals. Unlike the conventional method, the proposed method utilizes the configurable transfer function of optical fibers caused by the residual chirp of intensity modulation, which not only eliminates the chirp error but also improves the measurement range through adjusting the chirp parameter of the intensity modulator. Our method is applicable for measuring both the magnitude and sign of chromatic dispersion of optical fibers or other dispersive devices at different operating wavelengths by using a vector network analyzer.

Stable fiber-optic time transfer by active radio frequency phase locking.

In this Letter we demonstrate a fiber link capable of stable time signal transfer utilizing our active long-distance radio frequency (RF) stabilization technology. Taking advantage of the chromatic dispersion in optical fiber, our scheme compensates dynamically the link delay variation by tuning the optical carrier wavelength to phase lock a round-trip RF reference. Since the time signal and the RF reference are carried by the same optical carrier, a highly stable time transfer is achieved at the same time. Experimentally, we demonstrate a stability of the time signal transfer over 50-km fiber with a time deviation of 40 ps at 1-s average and 2.3 ps at 1000-s average. The performance of the RF reference delivery is also tested, with an Allan deviation of 2×10(-15) at 1000-s average. According to our proposal, a simultaneous stable time and frequency transfer is expected.

National primary special standard for the unit of chromatic dispersion in optical fibers

The national primary special standard for the unit of chromatic dispersion in optical fibers, a national verification scheme, and results of metrological studies of the standard are described.

Design of a continuously tunable delay line using vectorial modulational instability and chromatic dispersion in optical fibers

We design an all-optical tunable delay line based on both dispersive and wavelength conversion stages involving modulational instability of a two-frequency pump field propagating in a highly birefringent fiber. More precisely, we numerically show that, by varying the frequency separation between the two orthogonally polarized pump waves, we achieve a controllable and continuous delay of hundreds of picoseconds for signal pulse durations from picoseconds to nanoseconds, without pulse distortion and with only small peak power fluctuations. The proposed method does not require any tunable bandpass filter and can be applied to delay digital data streams at tens of Gbit/s depending on the pump power level.

Cost-effective and dispersion-tolerant cascade modulation for millimeter-wave-over-fiber applications

In millimeter-wave-over-fiber (MWoF) feeder systems, the received millimeter-wave signals at the remote antennas (RAs) can suffer from signal fading by chromatic dispersion of optical fiber. This can be substantially mitigated by Mach–Zehnder modulator (MZM) based photonic up-conversion technique. In this technique, the data signals at intermediate frequency (IF) are frequency up-converted to millimeter-wave frequency by an MZM biased at its transmission null point. However, this scheme requires a costly, high-speed MZM, which will hinder the widespread of this technique for cost-sensitive MWoF applications. Hence, we propose and demonstrate a cost-effective way of reducing the cost of MWoF optical transmitters based on photonic up-conversion technique. We employ a dual wavelength source composed of a directly modulated laser and a polarimetric filter. This source is used to generate a millimeter-wave tone signal and to frequency up-convert the IF data signals to millimeter-wave frequency. The dual wavelength source is also shared with numerous RAs for further cost reduction. Our experimental demonstration performed with 30Msymbol/s 16-quadrature amplitude modulation signals shows that we can transmit the 20GHz millimeter-wave signals over 25km standard single-mode fiber without any transmission penalty.

Modeling the Longitudinal Temperature Evolution of a Chirped Fiber Bragg Grating Submitted to Temperature Gradients

The chromatic dispersion of optical fiber is a limiting factor in the increase of optical communications transmission bitrates. Chirped Fiber Bragg Gratings submitted to temperature gradients can provide tuneable dispersion compensation, being the tuneability achieved by an appropriate control of the applied temperature gradient. In this work we propose a numerical model that describes heat transfer mechanisms along the fiber grating and its surroundings to obtain a temperature distribution along the fiber grating longitudinal axis. This model, which enables the subsequent modeling of the grating dispersion, demonstrated that the temperature distribution in a steady state is linear. The subsequent modeling of the fiber grating chromatic dispersion agreed with experimental results.

A PRINCIPAL INVESTIGATION OF THE GROUP VELOCITY DISPERSION (GVD) PROFILE FOR OPTIMUM DISPERSION COMPENSATION IN OPTICAL FIBERS: A THEORETICAL STUDY

In this paper, an analytical method for management of optimum group velocity dispersion (GVD) for compensation of chromatic dispersion in optical fibers is proposed. The proposed method mathematically is based on the Volterra series as alternative method for solution of the nonlinear Schrodinger equation (NLS). Based on analytical solution of the nonlinear equation in pulse propagation, we propose a differential equation including optimum GVD for complete dispersion compensation for given dispersion coefficient and fiber length. The obtained integro-differential equation is solved for special cases and it is shown that the obtained results are so better than traditional dispersion compensation cases. Also, the proposed technique can be applied to fiber design to introduce an especial GVD profile for dispersion less transmission.

Analysis of optical fiber chromatic dispersion in noisy interferometric systems

In this paper an analysis of optical fiber chromatic dispersion in noisy interferometric system is introduced. The interferometric relative intensity noise (IRIN) is derived in interferometric systems, by considering all effects such as the optical fiber chromatic dispersion and white noise applied to light from a laser diode. The direct relative intensity noise (RIN) is compared with the RIN caused by phase-to-intensity noise conversion. Numerical calculations reveal that the optical fiber chromatic dispersion can enhance significantly the IRIN magnitude and lead to a shift of the IRIN dips. The results can be employed to estimate the influence of the chromatic dispersion in phase-to-intensity noise conversion, which use either self-delayed interferences or interferometers.

Measuring chromatic dispersion of optical fiber using time-of-flight and a tunable multi-wavelength semiconductor fiber laser

We have developed a tunable multi-wavelength semiconductor fiber laser (SFL) for chromatic dispersion measurements of optical fiber based on the time-of flight (TOF) or pulse-delay technique. The SFL incorporates a programmable high-birefringence fiber Sagnac loop to select the separation of the lasing wavelengths between 3.2 and 1.6 nm. The SFL emits 5 and 11 wavelengths for separations of 3.2 and 1.6 nm, respectively, all within the C-band and with an output power uniformity within 3.2 dB. Results from TOF measurements are compared with standard phase-shift techniques; the percent differences between the two methods are within ±1.34% for measurements on various lengths of standard single mode fiber.