All-optical wavelength reuse with simultaneous upstream data and PPS timing signal transfer for flexible optical access networks

All-optical wavelength reuse is a viable approach for realization of low cost colourless ONUs. We experimentally demonstrate a novel all-optical wavelength reuse technique with simultaneous upstream data and pulse-per-second signal transfer, exploiting EDFA gain saturation with a holding beam. A DFB laser is modulated with 8.5 Gbps data and transmitted downstream over 24.7 km fibre. A saturated EDFA located at the ONU is adopted to reduce the extinction ratio of the downstream data from 6.2 dB to 839.1 mdB. This allows for data rewrite and wavelength reuse for upstream transmission. Receiver sensitivities of ?20.19 dBm and ?19.60 dBm are achieved at back-to-back analysis and 24.7 km downstream link respectively. A holding beam is further exploited to attain simultaneous carrier reuse and PPS clock upstream transfer. PPS jitter stability of 1.01 × 10^-08 ns and 6.64 × 10^-08 ns are attained respectively. This work offers a convenient all-optical wavelength reuse solutions for optical access networks.     

Dynamic O-band to C-band wideband wavelength converter for integrated VCSEL-based optical interconnects

ABSTRACT

Real-time wavelength conversion and traffic routing at key network nodes is a fundamental requirement for current optical interconnects. This work experimentally demonstrates a broadband wavelength conversion from O-band to C-band employing commercially available, power efficient VCSELs. A 1310?nm VCSEL is directly modulated with 8.5 Gbps data and transmitted over 22?km G. 652 fibre with a 0.53 dB penalty. The received data is used to run a 1550?nm VCSEL located at the network integration node, achieving the first reported wavelength conversion from O-to-C-band. VCSEL wavelength tuneability with changing bias current functionality is further exploited to route the converted wavelength over 400?GHz spectra range for integration into wavelength flexible networks. The newly converted wavelength is transmitted over 24.7?km of G. 655 fibre, incurring a maximum penalty of 1.86?dB. Results from this work proves an enabling development technology for wavelength converters for transparent contention resolution in current and future optical Interconnects.     

Wide-band flat-gain optical amplifier using Hafnia and zirconia erbium co-doped fibres in double-pass parallel configuration

ABSTRACT

A new compact and wide-band erbium-doped fibre amplifier (EDFA) was demonstrated by combining Hafnia-bismuth Erbium co-doped fibre (HB-EDF) and zirconia–yttria–aluminum Erbium co-doped fibre (Zr-EDF) as a hybrid gain medium, in parallel double-pass configuration. The proposed amplifier comprises a 0.5?m long HB-EDF and 4?m long Zr-EDF optimized for C- and L-band operations, respectively. The HB-EDF and Zr-EDF has erbium ion concentration of 12,500?ppm and 2800?ppm, respectively. At -10 dBm input signal, a wide-band flat gain of 15.7?dB is achieved with gain fluctuation of less than 1.5?dB within a wavelength region from 1525 to 1600?nm. Compared to same configuration of HB-EDF and Zr-EDF amplifiers which are using two pieces of HB-EDF and Zr-EDF, respectively with the same total amount of erbium ions, the proposed EDFA with hybrid gain medium provides even better performances in term of flat gain, bandwidth and noise figure.     

Self-seeded reflective semiconductor optical amplifier based optical transmitter for up-stream WDM-PON link

A novel up-stream transmitter for wavelength division multiplexed-passive optical network (WDM-PON) using a self-seeded reflective semiconductor optical amplifier (RSOA) was proposed. The RSOA was self-seeded by an amplified spontaneous emission itself using a fibre Bragg grating without an additional optical source. The side mode suppression ratio of self-seeded output signal and the extinction ratio were ~28 and 8.1 dB, respectively. Required power for 10^-9 BER at 622 Mb/s was about -28 dBm and the power penalty after 20 km transmission was <2 dB for 30 nm range of wavelength     

VCSEL-based differential modulation technique for high-speed gigabit passive optical networks

With the convergence towards 5G, optical networks need to be upgraded to support the emerging data tsunami. This work experimentally demonstrates the first real-time transmission of 20?Gbps over a class 10G 1550?nm vertical cavity surface emitting laser (VCSEL) in the context of on-off-keying (OOK) modulation format, by employing VCSEL differential drive mode technique, for adoption in high-speed gigabit passive optical networks (GPONs). Two OOK data streams each with 10?Gbps are differentially modulated onto a single VCSEL, therefore generating an aggregated data rate of 20?Gbps OOK signal. A receiver sensitivity of -13.36?dBm is experimentally achieved. Through extinction ratio optimization, an error free transmission over 24.7?km single mode fibre is attained, with a transmission penalty of 1.91?dB. Our proposed technique alleviates band-limitation of the VCSEL carrier, and doubles the channel data rate without replacing the transmitter optics.     

Feed-forward linearisation technique for impulse radar ultra-wideband over fibre

The authors present the linearisation of impulse radar ultra-wideband (IR-UWB) transmission system over fibre. The radio frequency signal of IR-UWB is transmitted over 50 km of the single mode fibre (SMF) using external Mach Zehnder modulator (MZM), amplified, linearised and detected by photodetector receiver. For improving the linearity and suppressing the four-wave mixing (FWM) caused by semiconductor optical amplifier (SOA) and 50 km SMF, the system uses feed-forward technique. Link performance was evaluated for two IR-UWB signals to suppress the FWM. The theoretical simulation results demonstrate a distortion cancellation that is produced by SOA of better than 25 dB over 1550 nm single mode optical fibre cable. In addition, the characteristic transmission of UWB pulse radio through 50 km single mode radio over fibre (RoF) system, such as BER measurements to evaluate the performance of the UWB with respect to different laser power output level, is investigated. This technique has been used to successfully transmit indirectly modulated data using laser diode at 10 GB/s light-wave transmission system.     

Maximizing capacity,flexibility and efficiency in G-PON networks using VCSEL-based OOK and 2/4-PAM formats

This work experimentally demonstrates the potential of multi-level pulse amplitude modulation with direct detection to maximize carrier spectral efficiency and double the Gigabit passive optical networks (G-PON) network data rate. Three scenarios have experimentally been exploited. First, a 1310?nm vertical surface-emitting laser (VCSEL) has directly been modulated with a 10?Gbps OOK data. A receiver sensitivity of ?19.11?dBm is attained, and a successful error free transmission over 22?km SMF fibre achieved, with a transmission penalty of 0.46?dB. To maximize carrier spectral efficiency, 2/4 PAM modulation formats are adopted respectively. A receiver sensitivity of ?14.64 and ?11.63?dBm is attained for 2-PAM and 4-PAM formats respectively. However, a 3.21?km fibre transmission introduces a penalty of 0.64 and 3.30?dB for 2-PAM and 4-PAM formarts respectively. 2/4-PAM modulation formats significantly increase the aggregated data rate at different ONUs within the G-PON without expensive optics investment, though at the cost of reduced transmission reach due to the high bitrate attained. We further demonstrate the design of a software defined digital signal processing assisted receiver to recover the 2/4 PAM transmitted signal without employing costly receiver hardware.     

Ultra-flattened negative dispersion for residual dispersion compensation using soft glass equiangular spiral photonic crystal fiber

Abstract

We present a numerical investigation of an equiangular spiral photonic crystal fibre (ES-PCF) in soft glass for negative flattened dispersion and ultra-high birefringence. An accurate numerical approach based on finite element method is used for the simulation of the proposed structure. It is demonstrated that it is possible to obtain average negative dispersion of –526.99 ps/nm/km over 1.05–1.70 μm wavelength range with dispersion variation of 3.7 ps/nm/km. The proposed ES-PCF also offers high birefringence of 0.0226 at the excitation wavelength of 1.55 μm. The results here show that the idea of using the proposed fibre can be potential means of effectively directing for residual dispersion compensation, fibre sensor design, long distance data transmission system and so forth.     

Bidirectional repeaterless transmission of 8 x 10 GE over 210 km of standard single mode fibre

Experimental results on error-free bidirectional transmission of 8times10 Gigabit Ethernet channels over 210 km of standard single mode fibre are presented here. Inexpensive XENPAKs transceivers, conventional unidirectional 1530-1560 nm (C-band) erbium-doped fibre amplifiers and fibre Bragg grating dispersion compensating modules have been used. The results are very promising, especially for operators of national research and educational networks     

Gain improvement in a dual-stage S-band EDFA by filtration of forward C-band ASE

Gain improvement in a dual-stage S-band erbium-doped fiber amplifier (S-band EDFA) is demonstrated using a broadband fiber Bragg grating (FBG) operating in the conventional-band (C-band) region or a C-band/S-band wavelength division multiplexing (WDM) coupler which filters out the forward C-band amplified spontaneous emission (ASE) in the amplifier system, thus increasing the population inversion in the S-band region. The gain for the amplifier with the WDM coupler increases by about 8.5 dB with an input signal power of ?40 dBm, compared to that of the conventional dual-stage amplifier. The gain improvement varies from 4.0–9.2 dB at a wavelength region between 1480 to 1512 nm without a significant noise figure penalty.     

Simulation and experiment of packaging of the fibre Bragg grating sensors using brazing/soldering methods

Abstract

To manufacture fibre Bragg grating (FBG) transducer, finite element model simulation and experimental verification of packaging of the FBG by brazing/soldering were investigated. The packaging processes and their impacts on the wavelength change of FBG were analysed. Simulation results showed that the Bragg wavelength of packaged FBG shifted down a level of ~10 nm. For experimental verification, temperature sensitivity of the packaged FBG was enhanced about twice of the bare FBG, while its spectrum was well preserved. The Bragg wavelength was shifted down a level of ~10 nm which was in accordance with the simulation.     

Design of ultra-flattened nearly zero dispersion and ultrahigh non-linear slot microfibres with ultrahigh birefringence

We proposed a new simple design of microfibre employing an elliptical silica rod in the centre of fibre core region as a slot core for the purpose of controlling the chromatic dispersion properties of the microfibre and enhancing the performance of non-linearity and birefringence. The simulation results show that the proposed slot microfibre has ultra-flattened near-zero dispersion of 0.94 ps/(nm km) for quasi-TE mode over a 50-nm wavelength range, ultrahigh birefringence up to the order of 10^?1, and ultrahigh non-linear coefficients of 38.35 and 37.92 W^?1 m^?1 for the fundamental quasi-TE mode and quasi-TM mode at the wavelength of 1.55 μm. The outstanding advantage of this new design is that nearly zero ultraflattened dispersion, ultrahigh modal birefringence and ultrahigh non-linearity can be realized simultaneously simply using a slot fibre core. Benefiting from its excellent performance, the proposed slot microfibre will have great potential for all-optical signal processing applications.     

Purely axial compression of fiber Bragg gratings embedded in a highly deformable polymer

We demonstrate a tuning device for fiber Bragg gratings with a wavelength tuning range in excess of 65 nm. A purely axial tuning technique using a highly deformable polymer molded in a cylinder shape is used to embed a fiber Bragg grating and to achieve a wavelength tuning range from 1551.7 to 1485.5 nm. The tuning curve is highly linear with a tuning rate of 9.6 nm for every percent of applied strain. The insertion losses of the device, the variations of the full width at half maximum, and the stability of the Bragg wavelength over a working day have been studied and shown to be less than 0.02 dB, 0.14, and 0.2 nm, respectively.     

All-fibre Mach–Zehnder interferometer based on seven-core and coreless fibres for generating stable wavelength-switchable laser

In order to realize a wavelength-tuneable fibre-laser output, a ring-cavity erbium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer (MZI) is proposed and experimentally tested. The MZI consists of a single-mode fibre, two segments of coreless fibre, and a seven-core fibre. For the proposed fibre laser, the length of the gain medium is 4?m and the lasing threshold is 75?mW. By adjusting the loss of the laser cavity, switchable single-wavelength laser emission is realized across the range of 1527.6–1549.9?nm and the wavelength interval is less than 2.4?nm; the peak power difference of each lasing wavelength is less than 7.9?dB. Tuneable dual- and three-wavelength laser outputs were obtained by adjusting the polarization controller. The 3-dB linewidth was less than 0.57?nm. The single- and dual-wavelength laser output power fluctuations were less than 1.4 and 1.7?dB, respectively, when monitored over a period of 30?min.     

Dual wavelength fibre laser with tunable channel spacing using an SOA and dual AWGs

In this paper, we propose and demonstrate a dual wavelength fibre laser (DWFL) based on the use of an inhomogeneously-broadened semiconductor optical amplifier (SOA) gain medium as well as two arrayed waveguide gratings (AWGs) together with two optical channel selectors (OCSs) and a broadband fibre Bragg grating (FBG) to generate dual wavelength output at variable channel spacings. The widest spacing obtained from the DWFL is 12.21 nm, while the narrowest spacing is 1.16 nm. The DWFL has good stability with only minor power fluctuations of less than 2 dB and a side mode suppression ratio (SMSR) of approximately 38.5 dB with fluctuations of less than 0.5 dB.     

Application of macro-bending for flat and broad gain EDFA

Gain flattened C-band erbium-doped fiber amplifier (EDFA) is demonstrated using a macro-bending method. Various bending diameter and length of high concentration aluminosilicate EDFA are theoretically and experimentally analyzed. By varying the bending radius and the length of the doped fiber, the gain saturation effect as well as the energy transfer from shorter wavelength to a longer wavelength can be controlled to obtain a flattened and broadened gain profile in the C-band region. The amplifier uses a 9 m long erbium-doped fiber (EDF) with erbium ion density of 1.6 × 10²⁵ ions m^?3 and bending radius of 6.5 mm as a gain medium. The gain variation of the EDFA is obtained within ±1 dB over 25 nm bandwidth of C-band region.     

High-birefringence dual-wavelength single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance

A dual communication band single-polarization photonic crystal fibre polarizing filter based on surface plasmon resonance is presented in this paper. Numerical simulation results demonstrate that the resonance strength of x- and y-polarized direction can reach 569.83 and 719.25?dB.cm^?1 simultaneously at the communication wavelength of 1.31 and 1.55?µm. By filling liquid analyte, the confinement loss of x- and y-polarized direction can simultaneously reach 831.7 and 580.53?dB.cm^?1 at the wavelength of 1.31 and 1.55?µm. Furthermore, when the fibre length L is equal to 700?µm, the peak value of the crosstalk can reach 493.86 and ?323.67?dB at the same time at the wavelength of 1.31 and 1.55?µm, and when the length of the fibre L is 400?µm, the bandwidths of the crosstalk better than 20?dB and less than ?20?dB are about 160 and 210?nm, respectively. These performances make it an ideal candidate for designing dual-band polarization filter equipment.     

Gain-clamped erbium-doped fibre amplifier for wavelength division multiplexed systems

Abstract

Amplification of multiwavelength signals by an erbium-doped fibre amplifier (EDFA) is becoming critical, due to the proliferation of wavelength division multiplexed systems. However, when a standard EDFA is employed, dissimilarities between signal gains may prove unacceptable. Thus, a novel gain-clamped EDFA is proposed here to tackle the issue of gain tilt, a measure of maximum gain difference. The suitability of the configuration is then investigated through a numerical model, which is developed based on the standard EDFA and fibre laser models.     

Wavelength switchable L-band erbium-doped fiber laser employing C-band EDFA as gain medium

A new structure for the L-band multiwavelength switchable erbium-doped fiber laser is proposed. Overlapping laser cavities are formed by cascading fiber Bragg gratings as reflectors in a ring structure with a C-band EDFA as a common gain medium. The proposed laser is made to be wavelength-switchable by individually adjusting the loss of each overlapping cavity. Instead of using an L-band EDFA as the gain medium in the L-band fiber laser, we have experimentally demonstrated that by tailoring the gain of the C-band EDFA to have a significant gain tilt in the L-band, a lasing power efficiency of 26% can be achieved over a wide range of switchable lasing wavelengths. Following this optimal design, the side-mode suppression ratio and the minimal separation between two switchable lasing wavelengths were found to be over 42 dB and 0.33 nm, respectively.     

Characterization of a broadband all-optical ultrasound transducer-from optical and acoustical properties to imaging

A broadband all-optical ultrasound transducer has been designed, fabricated, and evaluated for high- frequency ultrasound imaging. The device consists of a 2-D gold nanostructure imprinted on top of a glass substrate, followed by a 3 microm PDMS layer and a 30 nm gold layer. A laser pulse at the resonance wavelength of the gold nanostructure is focused onto the surface for ultrasound generation, while the gold nanostructure, together with the 30 nm thick gold layer and the PDMS layer in between, forms an etalon for ultrasound detection, which uses a CW laser at a wavelength far from resonance as the probing beam. The center frequency of a pulse-echo signal recorded in the far field of the transducer is 40 MHz with -6 dB bandwidth of 57 MHz. The signal to noise ratio (SNR) from a 70 microm diameter transmit element combined with a 20 microm diameter receive element probing a near perfect reflector positioned 1.5 mm from the transducer surface is more than 10 dB and has the potential to be improved by at least another 40 dB. A high-frequency ultrasound array has been emulated using multiple measurements from the transducer while mechanically scanning an imaging target. Characterization of the device's optical and acoustical properties, as well as preliminary imaging results, strongly suggest that all-optical ultrasound transducers can be used to build high-frequency arrays for real-time high-resolution ultrasound imaging.