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This paper explores the data carrying capacity enhancement in free space optics (FSO) transmission systems by employing orbital angular momentum (OAM) multiplexing technique. Specifically, simulative investigation of OAM-FSO terrestrial transmission is carried out under varying weather conditions. A net data capacity of 40 Gb/s over free space transmission medium is demonstrated using four distinct OAM beams (LG0,0, LG0,13, LG0,40, and LG0,80). The performance is compared for alternate mark inversion (AMI), return-to-zero (RZ), and non-return-to-zero (NRZ) encoding schemes. The results showed that the best performance occurred when using NRZ modulation and a favorable 40 Gb/s transmission along a range varying from 64 to 800 m depending on the external weather conditions is reported.

A reconfigurable and application-specific tunable microwave photonic filter having finite impulse response is proposed. The filter exploits the differential mode group delays of linearly polarized modes in a multi-mode fiber to achieve single and multiple high-frequency passband response. The filter taps are realized using a single continuous wave laser source and differential delays among modes that are propagated through a single spool of graded index multi-mode fiber. Depending upon the application requirement, different values of free spectral range of the microwave photonic filter are obtained by employing fiber spools of different lengths. The reconfigurability of the microwave photonic filter is achieved by varying the number of linearly polarized modes. It has been shown that the passband ripple can be reduced by employing higher order spatial modes and unequal power ratio among different modes. The proposed filter enables application-specific free spectra range tunability and reconfigurability along with added advantages of easy implementation and passband optimization.

Numerical simulations for generating and transmitting four Laguerre-Gaussian (LG) modes over 100m of multimode fiber are conducted. Each LG mode is modulated using 10Gbps NRZ signal. Bit error rate (BER) and Q-factor performance metrics showed acceptable system performance as the worst mode has Q-factor of 9.1 and BER of 2.5E-20.

This paper investigates optimization and power/wavelength allocation of a RAMAN amplifier designed for Dense Wavelength Division Multiplexed (DWDM) Systems consisting of forty channels with frequency spacing 25 GHz at the edge of L and U wavelength bands (185 THz – 185.975 THz). Four pumps used in the forward direction with wavelengths at 1500, 1525, 1565, 1574 nm and four pumps in the backward direction with wavelengths at 1435, 1460, 1474, 1489 nm are used. The forward pumps power distribution and backward pump power distribution combinations are investigated for the Raman amplifier best performance. The performance of the system includes overall gain and flatness. The location of the wavelength in the forward or backward direction and the power distribution among each wavelength in an ascending or descending order is also investigated. It is found that the red shifted pump wavelengths should be used in the forward direction and the blue shifted pump wavelengths should be used in the backward direction for best performance.

Existing OPAs are typically based on 2D rectangular arrays or 1D linear arrays. Both approaches present a limited field-of-view (FOV) due to the presence of the grating lobes when the element spacing is larger than λ/2. To address the need for an increased steering range, we propose a new design strategy of an OPA system utilizing a 2D circular phased array, with a substantially increased FOV. We present a circular OPA using a demonstrated antenna element design, with an 820-element array. A steering range ΩSR calculated as a solid angle of 0.51π sr, and an angular beamwidth of 0.22°, was achieved. The array exhibits a sidelobe suppression larger than 10 dB, and a FOV of 2π sr. Although the performance is limited by the far field pattern of the individual antenna we chose, our circular OPA achieved, to the best of our knowledge, the largest steering range reported to date compared to the state-of-the-art integrated optical phased arrays reported in literature.

A comparison of different schemes to enhance stimulated Brillouin Scattering (SBS) in single-mode optical fiber is performed. Specifically, we evaluated SBS generation efficiency in a 3 km length fiber with and without power recycling versus the same fiber placed in a ring resonator and in a ring resonator in a recycling configuration. For the latter case, a large number of both odd and even higher-order Stokes and anti-Stokes harmonics is generated. We show that the choice of the scheme is dictated by specific application. In addition, when incorporating a ring resonator in a Sagnac loop, a flat optical frequency comb is generated.

Novel implementations of fiber Bragg gratings (FBG) and phase shifter in loop mirror configurations enable monitoring of environmental conditions at both terminals of the loop. These implementations allow accessing the sensed signals in both directions (east and west) at locations far from the sensing position using regular fiber transmission schemes. Optical light of a 1550 nm wideband LED diode (100nm) is launched into the fiber loop that has the FBG and phase shifter. The center wavelength of the FBG varies with changes of conditions affecting the grating such as temperature, pressure, stress and strain. As a result, the center wavelength of the generated continuous wave (CW) optical signal in the fiber loop mirror sensor shifts based on these conditions at the sensing location. Controlling the phase of the phase shifter determines the direction of the generated CW sensed signal to the transmission path or reflection path of the optical loop mirror. Numerical simulations were conducted, which demonstrated the operation of the fiber sensor design.

A novel optical demultiplexer with auxiliary monitoring channel using multilayer dispersive material structure is proposed. A spatial shift among the different input wavelengths occurred due to the wavelength dependent of the dispersive material. The effect of the different design parameters such as number of layers, incidence angle of the optical beam, dispersive material of base layer, thickness, refractive index profile on the spatial shift between adjacent channels and size of the device are investigated.

A novel integrated demultiplexer and channel monitoring device is proposed and analyzed. The device uses multilayer graded index profile structure with α -parameter less than one. The effects of different relevant parameters such as refractive index profile parameter, thickness, input signal incident angle, number of layers and channel wavelength spacing on the structure are investigated. The component is recommended for course wavelength division multiplexing (CWDM) optical communication system applications.

Simple and fast algorithm for calculating spatially fiber chromatic dispersion is discussed. This method is applied on the data collected from measuring the Stokes wave of the back-reflected Rayleigh scattered signal in optical fiber under test. The data analysis is performed in the time domain contrary to already known analysis in frequency domain. The results achieved in the time domain match well with those in the frequency domain.

The design and performance of an all-optical wavelength converter based on a semiconductor optical amplifier (SOA) and a delay interferometer (DI) are presented for 10-Gb/s return-to-zero (RZ) transmission systems with pulsewidths of 25-45 ps. The performance of the wavelength converter is investigated in terms of the operating conditions for the SOA and DI, and the properties of the input signal. The regenerative characteristics of the wavelength converter are also examined for input signals degraded by amplified spontaneous emission noise and residual dispersion. With proper design, the SOA-DI structure provides a high-performance all-optical wavelength converter for 10-Gb/s RZ transmission with practical pulsewidths.

Linewidth measurements of a tuneable, high power, narrow linewidth semiconductor fiber ring laser are presented. The laser had a typical output power of 9.72 dBm with a corresponding 170 kHz FWHM and 311 kHz 20-dB linewidth. We demonstrate experimentally the dependence of laser's linewidth on SOP of the lasing light and polarization-dependent gain of semiconductor gain medium. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 31–34, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22984

Noise figure reduction of an erbium-doped fiber amplifier using loop mirror filter is demonstrated. Approximately 0.5-dB noise figure reduction is achieved at input signal power level below - 30dBm. Transferring energy from the amplifier spontaneous emission to the input signal compensates for the insertion loss of the loop mirror filter device. The insertion loss of the device approximately 1 dB.

The Raman time constant (T/sub R/) used in the generalized nonlinear Schrodinger equation is determined experimentally at 1550 nm based on the Raman self-frequency shift in a standard single-mode fiber. The effective value of the T/sub R/ as measured is found to be 3.0 fs. Detailed error analysis shows that the uncertainty in the measurement is less than /spl plusmn/1.0 fs. The measured value of the T/sub R/ is approximately half of what is commonly used at present in theoretical simulations. Determined experimentally in this work the accurate value of T/sub R/=3.0 fs is essential in modeling pulse propagation in optical fibers.

A comprehensive study for generating trains of ultra-high speed bright and dark soliton pulses at 1553 nm using comblike dispersion profile fiber structures is presented. The comblike structure employed for generating bright solitons uses the lowest average power for the input signal ever reported. The generated bright soliton pulses have a full width at half maximum (FWHM) of 2.2 ps at a repetition rate of 49.3 GHz, while the generated dark soliton pulses have a FWHM of 3.8 ps at 47.6 GHz. The experimental results agree well with performed numerical simulations.

Novel CWDM multilayer structure demultiplexer in silica is proposed and investigated. The refractive index of each layer in the structure follows fiber graded index profile with a-parameter less than one. The demultiplexer structure depends on the refractive index profile parameter, thickness, incidence angle, number of layers and channel's spacing. The effect of all of these parameters on the amount of spatial shift and the separation between adjacent channels is investigated.

A novel scheme for measuring dispersion of chirped fiber Bragg gratings is demonstrated using loop mirror configuration. The measurement is insensitive to polarization or temperature variation. The technique is relatively simple, inexpensive, and requires only a broad-band light source.

The performance of optical telecommunication system is mainly limited by optical signal to noise ratio (OSNR) at the receiver, fiber dispersion and nonlinearities. The limiting factors of optical communication systems that employ pluggable XFPs are investigated experimentally by characterizing and correlating the information regarding pulses evolution of 10Gbps signals in optical fiber under the influence of dispersion and different nonlinear effects.

A novel, simple, and flexible WDM laser source is demonstrated using a loop erbium-doped fiber amplifier. Two configurations of the source are investigated where reflecting FBGs are cascaded in series or parallel at the loop outputs. High output power per channel with a signal-to-noise ratio better than 55 dB can be achieved. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 187–189, 2001.

Pluggable transceivers; either small form factor (SFP) that operates up to 2.5Gbps or XFPs that operates at 9.95Gbps, transmitter's laser characteristics are investigated experimentally. The laser linewidth and chirp in addition to stimulated Brillouin scattering (SBS) threshold for different transceivers are measured over many kinds of optical fiber. The measured transceiver's parameters are correlated and used to explain different system performance penalties encountered during data transmission over different kinds of optical fiber. This knowledge is valuable to system engineers as it is not available and not provided by transceivers' vendors. System performance penalties for different kind of fibers with positive and negative accumulative dispersion are measured experimentally at OC-192 and OC-48 modulated signals for different XFPs and SFPs, respectively.

Simple and relatively inexpensive in service optical fiber chromatic dispersion monitoring is demonstrated using supervisory channel. Modulating optical supervisory channel with frequency in the range of hundreds of MHz enables accurate measurement for lengths up to 80 km of SMF-28 fiber.

Stability and linewidth (FWHM & 20-dB) measurements of a tuneable, high power, narrow linewidth multiwavelength Hybrid Cavity Semiconductor Fibre Ring Laser (HC-SFRL) are presented. The laser incorporates a SOA, a polarization controller (PC), and a tuneable optical filter. The ring cavity itself is composed of Single Mode Fibre (SMF) and a 1-m long Polarization Maintaining Fibre (PMF). The laser is capable of single, dual and triple lasing wavelengths with ultra-narrow wavelength spacing (less than 30 pm) with good stability for periods over 2 hours.

Tunable fiber Bragg gratings (TFBGs) are investigated for single-channel and for dual-channels drop applications. The TFBGs are capable of dropping single DWDM channel or two consecutive DWDM channels in an 8-nm bandwidth in the C-band while allowing the rest of the C-band channels to passthrough. Extensive stability, reproducibility and system characterization in addition to numerical simulations were conducted to investigate the feasibility of using TFBG for ROADM applications in metro-edge optical communication networks.

We have investigated tunable fiber Bragg gratings (TFBGs) for single channel and for dual channels drop applications. The TFBGs are cable of dropping single DWDM channel or two consecutives DWDM channels in 8 nm bandwidth in the C-band. This feature is desirable in metro-edge network applications where low channel count (up to eight) dominates. Extensive stability, reproducibility and system characterization in addition to numerical simulations were conducted to investigate the feasibility of TFBG in optical communication networks.

A novel SOA based fibre ring laser is presented. An S-band optimized SOA is added to the cavity of a C-band SOA fibre ring laser resulting in significant improvements in the ring laser characteristics. Three main linewidth control parameters are identified: 1) Bias current of C-band SOA, 2) Bias current of S-band SOA, and 3) SOP of lasing light in ring's cavity. Experimental measurements suggest the SOP of the lasing light to be the dominant control parameter for reduction or enhancement of the laser's linewidth. An output power level of 5.27 dBm (corresponding to 10.54 dBm cavity power) and less than 20 kHz FWHM (limited by equipment resolution) and 190 kHz 20-dB linewidth at 1558 nm is demonstrated. The measured 20-dB linewidths displayed stronger variations to changes in the bias currents of the ring lasers compared to variations in the FWHM. This suggests that the optical spectrum of the ring lasers becomes asymmetric at high bias currents and is no longer pure Lorentzian.

We report an experimental demonstration of an all optical demultiplexing a burst of 4/spl times/10-Gb/s multilevel TDM soliton signal using the soliton effect pulse compression and soliton self-frequency shift in a silica fiber.

Small form factor pluggable (SFPs) transceivers have been used to demonstrate that legacy optical networks operating in the metro-core-edge region of the network can be upgraded cost effectively through optical-electrical-optical (OEO) wavelength translation (WT). The WT technique involves detection of the original communication signal, re-timing and retransmission at a new laser wavelength and linewidth. The change is a deliberate one and gives rise to better optical transmission characteristics, resulting in longer system reach. In this paper, we present experimental results that demonstrate how WT can be used to upgrade existing optical fiber communication systems through improvements in system dispersion by using dense wavelength division (DWDM) SFPs and single-channel dispersion-compensation modules (DCM).

The dominant limiting factors affecting the performance of an amplified 10-Gbps CWDM data transmission system with an inline semiconductor optical amplifier (SOA) are investigated. More than 3 dB of system penalty at a BER of 1x10 -9 can be attributed to ASE and cross-gain-modulation (XGM) effects.

We report an extremely flat (better than 3-dB), ultra-wide band (over 160-nm) supercontinuum source for use ni the C and L wavelength bands. The supercontinuum is generated using approximately 2.2 Km of commercially available single mode non-zero dispersion shifted fiber by exploiting soliton decomposition and Raman self-frequency shift nonlinear effects. A supercontinuum spectral flatness of better than 1-dB over a 115-nm wavelength range is achieved.

Numerical simulations predict the generation of a 50 GHz train of optical dark soliton pulses at 1553 nm. The generated pulses have a full width at half maximum of 4.7 ps and continuous background power of 70 mW.

A novel simple passive narrow-band tunable filter using chirped fiber Bragg gratings in loop mirror is proposed. The filters have 3-dB bandwidth of approximately 7% of the grating bandwidth. Bandpass and notch filter characteristics are available at the device output terminals.

A novel scheme for measuring the dispersion of chirped fiber Bragg gratings is demonstrated using loop mirror configuration. The technique is relatively simple and requires only a broadband light source.

Two novel simple and flexible WDM laser sources are demonstrated using loop erbium-doped fiber amplifier configuration. The loop serves as a mirror and as an amplification medium. The laser cavity was made form loop mirror and either a set of fiber Bragg gratings (FBGs) in the first design, or a 100 percent reflecting mirror in the second scheme. The FBGs select the proper lasing wavelengths in the first technique, while a combination of stress induced effect of erbium-doped fiber and the presence of fused fiber filter in the laser cavity determine the lasing wavelengths in the second design. The FBGs can be placed either in parallel or in series at the input of the loop configuration. Optical attenuators are placed in front of the FBG to control the flatness of the laser source output and determine the required lasing condition for each wavelength to avoid competition of the different lasing wavelengths. This configuration is flexible for adding any number of wavelengths as long as enough amplified spontaneous emission is generated in the loop. Signal to noise ratio as high as 55-dB can be achieved.

All-optical automatic gain control in loop erbium-doped fiber amplifiers is investigated using single Bragg reflecting fiber grating. Reflecting back part of the filtered amplifier spontaneous emission to the loop mirror generates a lasing signal. The lasing wavelength is selected at 1525 nm, which is outside the amplifier bandwidth, to avoid interference between the signal and laser oscillation, and away from the amplifier surveillance wavelength at 1510 nm. This technique avoids tapping part of the amplifier output signal for generating the lasing signal. The loop amplifier has 20 nm flat gain spectrum with peak to peak gain variation less than 0.5 dB. Adjusting the lasing threshold using variable optical attenuator placed before the fiber Bragg grating controls the achieved gain clamping. An input signal consists from 8 channels picked up on the ITU frequency grid in the range from 1540 nm to 1560 nm and two laser diode pumps at 980 nm each with 60 mW pumping power are used in the experiments. The power excursion when adding or dropping any number of the 8 channels with -25 dBm input power per channel is less than 0.3 dB. The transient response time of the surviving channel(s) is measured to less than 200 microsecond(s) .

A figure-eight fiber laser is used to generate continuum in the L-band wavelength range (1565 nm-1610 nm). The continuum is flat with peak to peak variation better than 3.5 dB within 31 nm spectral width.

Summary form only given.Passive mode-locking schemes have been used extensively for generating soliton pulses around 1550 nm in the past couple of years. One of the configurations used is the figure-eight fiber laser (F8-L). These fiber lasers have used standard erbium-doped fiber amplifiers (EDFA). Stable subpicosecond soliton pulses are generated in the L-band wavelength range using passive mode-locked F8-L without any environment control. An L-band EDFA is placed asymmetrically in the nonlinear loop. Soliton pulses with full width at half maximum as short as 200 fs are generated around 1590 nm.

The Raman time constant (T R ) used in the generalized nonlinear Schrodinger equation is determined experimentally to be around 1550 nm, based on the Raman self-frequency shift in standard single mode fibre. The measured effective value of the T R is found to be 3.0 fs. Detailed error analysis shows that the uncertainty in the measurement is less than ±1.0 fs. Accurate knowledge of the value of the T R is essential in modeling subpicosecond pulse propagation in optical fibres.

Future optical communication systems will have to provide ultra-high speed transmission rates over long distances. An important limitation for such systems is imposed by the fiber nonlinearity typically described by the coefficient: $$\gamma = \frac{{2\pi {n_2}}}{{\lambda {A_{eff}}}}$$ (1) where n2is the nonlinear refractive index of the fiber, A eff is the fiber effective core area, and X is wavelength of the propagating signal. To design systems for such applications, it is necessary to determine the ratio n 2/A eff with high accuracy. The nonlinear properties of the fibers have been determined recently by measuring the self-phase modulation (SPM) effect using propagation of a short pulse at 1.3 μn through the tested fibers [1]. A different technique was employed in reference [2], where cross-phase modulation effect between a low power probe signal at 1550 nm and a high power pump signal at 1540 nm was used to find the nonlinear characteristics of the fiber. The ratio n 2/A eff was also measured based on the generation of beating frequency components through four-wave mixing (4WM) of two DFB laser diodes operating around 1555 nm [3]. In this scheme, two cw laser beams with frequencies v1 and v2 are launched into the fiber under test. The two beams with different power levels generate new beat frequencies (2V1-V2) and (2 V2-2V1) through 4WM process. All these schemes measure the nonlinear ratio of the fiber and an independent measurement of the effective core area enables the estimation of the nonlinear refractive index.

A novel all-optical demultiplexing system which is insensitive to the state of polarization of the input signals as well as to their drift in polarization is simulated. The technique employs a modified nonlinear optical loop mirror configuration to demultiplex 50 GHz pulse train into 10 GHz. The gain of an erbium-doped fiber amplifier is varied between 14 dB and 21 dB using a feedback signal from the loop output ports to achieve polarization independent complete switching.

Phase effect of the optical duobinary (ODB) modulation on the chromatic dispersion (CD) tolerance is more important than the ODB modulation-induced bandwidth effect. To show this, we evaluate, respectively, the filter bandwidth effect and the phase effect of the partial bit delay correlative modulation (PBDCM) on the CD tolerance. Due to the cancellation between the CD-induced and the PBDCM-induced phase effects, the PBDCM method can increase the CD-limited transmission to 2 ??? 3 times of that using standard 1-bit delay modulation, while the optimized filter bandwidth method can increase the transmission by 50% or less, depending on the input signal format. The PBDCM can be physically realized by adjusting the delay time of the delay-and-add circuit in the conventional duobinary transmitter (without lower-pass filter). These conclusions are also valid for systems having non-negligible polarization-mode dispersion (PMD) and polarization dependent loss (PDL).