Single tone and multi tone microwave over fiber communication system using direct detection method

In this paper, an analog microwave over fiber link for long haul distance based upon Rate Equation Laser is demonstrated. This system uses the advantage of high potential bandwidth of fiber in transmission of microwave signal. The interface of the two systems needs an up-conversion of microwave band into baseband (at which fiber operates). An Intensity Modulation Direct Detection (IMDD) technique is used to achieve this purpose. The Rate Equation laser is operated in a dynamic state, where its intensity oscillates at a microwave frequency that varies with the input signal fed by wave generator. This system can also use for two modulating tones. The frequency of the first tone is varied from 1 to 20 GHz and second is set at 5 GHz. A data signal of 10 Gbps is transmitted over long haul single mode fiber by single tone system. A very good bit error rate (BER) 10^?40 performances for 100 km and 25 km fiber link is achieved for both single tone and two tones respectively in proposed microwave over fiber communication system.     

Inherently gain flattened S-band erbium doped fiber amplifier based on dual core resonant leaky fiber

A co-axial dual core resonant leaky optical fiber (DCRLF) is designed for inherent gain equalization of S-band erbium doped fiber amplifier (EDFA). Resonance tail of leakage loss of the fiber into the S-band region is utilized to flatten the gain. We have numerically studied the effect of various design parameters and their fabrication tolerances on gain flattening. We show 23.5 dB flat gain with ± 0.9 dB ripple over 30 nm bandwidth (1490–1520 nm) using 120 mW pump. The study should be useful in designing optical fiber amplifiers for optical communication system employing wavelength division multiplexing.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

All fiber passively mode locked zirconium-based erbium-doped fiber laser

All passively mode locked erbium-doped fiber laser with a zirconium host is demonstrated. The fiber laser utilizes the Non-Linear Polarization Rotation (NPR) technique with an inexpensive fiber-based Polarization Beam Splitter (PBS) as the mode-locking element. A 2 m crystalline Zirconia–Yttria–Alumino-silicate fiber doped with erbium ions (Zr–Y–Al-EDF) acts as the gain medium and generates an Amplified Spontaneous Emission (ASE) spectrum from 1500 nm to 1650 nm. The generated mode-locked pulses have a spectrum ranging from 1548 nm to more than 1605 nm, as well as a 3-dB bandwidth of 12 nm. The mode-locked pulse train has an average output power level of 17 mW with a calculated peak power of 1.24 kW and energy per pulse of approximately 730 pJ. The spectrum also exhibits a Signal-to-Noise Ratio (SNR) of 50 dB as well as a repetition rate of 23.2 MHz. The system is very stable and shows little power fluctuation, in addition to being repeatable.     

Experimental study on tandem pumped fiber amplifier

We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%.     

Wavelength tunable,high energy femtosecond laser pulses directly generated from large-mode-area photonic crystal fiber

Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494 fs (with 56 nJ pulse energy) to 1.24 ps (with 49 nJ pulse energy) at 55 MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation.     

A novel analytical model for intensity modulated and direct detected multiple-input–multiple-output system with time related zero forcing equalization over multimode fiber

In this paper, basing on tap delay lines filter model and model spatial coupling theory, we build up a novel analytical model for an intensity modulated and direct detected multiple-input–multiple-output (IM-DDMIMO) system over multimode fiber. At the receiver side, time related zero forcing (ZF) equalization was used to recover signals. With this model, we theoretically and by simulation analyzed a 2 × 2 multimode fiber MIMO system utilizing offset launching scheme. It's found that two received streams can be well recovered by equalization. Compared with traditional single-input–single-output (SISO) system, such 2 × 2MIMO system can provide at least 5 dB Bit error rate (BER) performance improvement.     

A 980 nm Yb-doped single-mode fiber laser pumped by a 946 nm Q-switched Nd:YAG laser

We demonstrate a 980 nm single-mode Yb-doped fiber laser with a 946 nm Q-switched Nd:YAG laser used as the pump source. The experimental arrangement exploited a 36.5 cm length of fiber and used the output from both ends of the cavity, providing a total average output power of 100 mW with a slope efficiency of 38%. In order to increase the coupling efficiency and the practicability of the fiber laser, another experimental setup with single ended output was studied, producing an average output power of 80 mW from a fiber length of 23.5 cm. The pulse duration is 10 ns at a repetition frequency of 16 kHz. The linewidth of the laser is 4 nm, ranging from 977 to 981 nm.     

Reduction of nonlinear impairments in fiber transmission system using fiber and/or transmitter diversity

A multi-fiber architecture is proposed to mitigate the nonlinear impairments in fiber-optic systems. The power launched to each fiber is reduced in multi-fiber architecture as compared to the case of single fiber leading to reduction in nonlinear impairments. The optical pulses propagating in the fibers undergo different amount of phase shifts and timing delays. Optical and electrical equalization techniques to compensate for these channel effects are discussed. Our numerical simulation results show that for unrepeatered systems, the performance (Q factor) is improved by 6.2 dB using 8-fiber configuration as compared to single-fiber system. In addition, for multi-span system, the transmission reach at a bit error rate (BER) of 2.1 × 10^? 3 is quadrupled in 8-fiber configuration.     

Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter

A dual-wavelength fiber laser with a narrow-linewidth, based on a P-F fiber filter has been proposed. Polarization-maintaining fiber Bragg grating (PM-FBG) and a F-P fiber filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device. The fiber F-P filter consists of two optical couplers and a section of un-pumped erbium-doped fiber (EDF). Due to the delay of cavity and the loss generated by the EDF, the filter has comb spectral response. The incorporation of the fiber F-P filter leads to the suppression of undesirable modes. At the room temperature, under 980 nm LD pumped, the maximum output of the two wavelengths is respectively ?2.259 dBm and 0.568 dBm, with the 3-dB bandwidth separately 0.1 nm and 0.14 nm, realizing the narrow linewidth and dual-wavelength output.     

A linearly-polarized tunable Yb-doped fiber laser using a polarization dependent fiber loop mirror

A Ytterbium-doped linearly-polarized fiber laser is constructed with a polarization maintaining fiber Sagnac loop mirror. The fiber loop mirror made of polarization maintaining fiber coupler has a polarization dependent reflectivity, which provides the necessary polarization discrimination between the slow and fast axes. With a fiber Bragg grating written in normal polarization maintaining fiber as an output coupler, laser output of up to 5.6 W at 1070 nm is generated with a polarization extinction ratio of > 20 dB and an overall efficiency of 55%. The broadband polarization dependent reflection of the fiber loop mirror offers advantages of easy spectral tuning and simple linearly-polarized laser generation.     

Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy

Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 μm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 °C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one well-defined glow peak at 327 ± 2 °C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4–6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.     

A novel OCS millimeter-wave generation scheme with data carried only by one sideband and wavelength reuse for uplink connection

We propose a novel optical carrier suppression (OCS) millimeter-wave generation scheme with data carried only by one sideband using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system, and the transmission performance is also investigated. As the signal is transmitted along the fiber, there is no time shifting of the codes caused by chromatic dispersion. Simulation results show that the eye diagram keeps open and clear even when the optical millimeter-waves are transmitted over 110 km and the power penalty is about 1.9 dB after fiber transmission distance of 60 km. Furthermore, due to the +1 order sideband carrying no data, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over a 40 km standard single mode fiber with less than 0.8 dB power penalty in the simulation. Both theoretical analysis and simulation results show that our scheme is feasible and we can obtain a simple cost-efficient configuration and good performance over long-distance transmission.     

Wavelength conversion based on high nonlinear microstructured fiber

A wavelength conversion based on high nonlinear microstructured fiber is demonstrated. Core diameter and pitch of the microstructured fiber used in this wavelength conversion method are 2.05 μm and 5.0 μm, respectively. Diameter of the air-holes in the fiber cladding is 4.50 μm, the nonlinear coefficient of the microstructured fiber is 112.2 W^?1 km^?1 and it is 60 times higher than that of a conventional dispersion-shift fiber, the length of the fiber is 100 m. Four-wave-mixing effect is improved in the high nonlinear microstructure fiber and then the efficiency of the wavelength conversion is improved also. 10 Gbps Not-Return-to-Zero (NRZ) modulation format and 10 Gbps Return-to-Zero (RZ) modulation format are converted effectively by our method. This study can provide a new alternative solution for high effective all-light wavelength conversion in high speed optical communication systems with multi-wavelengths and all-light optical networks.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

Sub-200 fs microjoule pulses from a monolithic linear fiber CPA system

An all-fiber-integrated linear chirped-pulse amplifier system generating microjoule pulse energies is reported. It is seeded by an all-fiber dissipative-soliton laser and incorporates a newly developed fiber stretcher, whose dispersive properties match that of the grating compressor. Pulse durations of 189 fs with energies of 2.2 μJ were achieved after compression. The average power was 9.8 W at the repetition rate of 4.5 MHz.     

Optical millimeter-wave signal generation by frequency quadrupling using one dual-drive Mach–Zehnder modulator to overcome chromatic dispersion

We propose a novel approach to generate quadrupling-frequency optical millimeter-wave using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system. By properly adjusting the phase difference in the two modulation arms of MZM, the direct current (DC) bias, the modulation index and the gain of base-band signal, the quadrupling-frequency optical millimeter-wave with signal only carried by one second-order sideband is generated. As the signal is transmitted along the fiber, there is no time shift of the codes caused by chromatic dispersion. Theoretical analysis and simulation results show that the eye diagram keeps open and clear even when the quadrupling-frequency optical millimeter-wave are transmitted over 110 km and the power penalty is about 0.45 dB after fiber transmission distance of 60 km. Furthermore, due to another second-order sideband carrying no signals, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over 40 km standard single mode fiber with less than 0.6 dB power penalty in the simulation.     

Supercontinuum generation using a passive mode-locked stretched-pulse bismuth-based erbium-doped fiber laser

A Supercontinuum (SC) generation in photonic crystal fiber (PCF) is demonstrated using an amplified picosecond stretched-pulses from a passive mode-locked Bismuth-based Erbium-doped fiber laser (Bi-EDFL). The Bi-EDFL employs of a piece of a highly nonlinear 49 cm long Bismuth-based Erbium-doped fiber (Bi-EDF), an optical isolator and a polarization controller in a cavity to generate a mode-locked stretched-pulse via a nonlinear polarization rotation technique. It operates at 1560 nm with a repetition rate of 42 MHz and a pulse width of 131 fs. The SC lights, which extends from 1250 nm to 1910 nm as well as in the visible green wavelength region are obtained with a 100 m long PCF and the amplified pump power of 30 dBm.     

An all-fiber high resolution fiber grating concentration sensor

An all-fiber high resolution optical fiber grating concentration sensor has been studied theoretically and experimentally. A long period grating is used as the sensor head and a wavelength matched fiber Bragg grating is used as an interrogator to convert wavelength into intensity encoded information for interrogation. A concentration resolution of 0.104 g/L for NaCl solution is realized in experiment. The all-fiber sensor system, with the sensor head and the interrogator being all optical fiber components, is suitable for far-distance monitoring. The sensor system is with multifunction and can be used for temperature monitoring. A temperature resolution of 0.013 °C has realized in experiment.     

Widely tunable compact erbium-doped fiber ring laser for fiber-optic sensing applications

A compact erbium-doped ring-shaped fiber laser suitable for fiber-optic sensing applications has been developed. The fiber laser utilized a tunable fiber Fabry–Perot filter as the tuning element and had a moderate milli-Watt level power output over almost the whole tuning range from 1530 to 1595 nm with a power fluctuation of 0.15 dB. High repetition rate scanning of laser operation over the whole tuning range was achieved at rates of up to 200 Hz. Moreover, the performance of the ring-shaped fiber laser configured with a high-concentration erbium-doped fiber was investigated for its larger wavelength tunability of over 100 nm. Output power characteristics of this ring-shaped fiber laser were also investigated when it worked in a scanning mode. A distorted power wavelength dependence, as well as some pulsing phenomenon were observed in scanning mode.