In-line Optical Amplifiers Research Articles

Integrated optical phased array with on-chip amplification enabling programmable beam shaping

We present an integrated optical phased array (OPA) which embeds in-line optical amplifiers and phase modulators to provide beam-forming capability with gain and beam steering in the 1465–1590 nm wavelength range. We demonstrate up to 21.5 dB net on-chip gain and up to 35.5 mW optical output power. The OPA circuit is based on an InP photonic integration platform and features the highest measured on-chip gain and output power level recorded in an active OPA (i.e., with amplification), to the best of our knowledge. Furthermore, the OPA enables the independent control of both amplitude and phase in its arms and through this we demonstrate programmable beam shaping for two cases. First, we carried out a Gaussian apodization of the power distribution profile in the OPA emitter waveguides, leading to 19.8 dB sidelobe suppression in the far-field beam, which is the highest value recorded for active OPAs, and then we demonstrated beam forming of 0th, 1st, and 2nd order 1D Hermite–Gaussian beams in free-space.

Photon statistics and quantum phase distribution for coherent optical links in the presence of phase noise from both the laser source and the RF oscillator, and dispersion

A model of photon statistics and quantum phase distribution is analyzed for coherent optical communication links in the presence of quantum phase noise, dispersion and phase noise of the radio-frequency (RF) oscillator using an in-line optical amplifier. The quantum analysis of a dual drive Mach–Zehnder modulator and the quantum transfer function for an optical field mode across an in-line amplifier is performed by taking into account both the quantum and the classical phase noises. The resulting photon statistics are compared with the semiclassical model. We analyze the quantum phase distribution by considering the Wigner quasiprobability distribution for a coherent optical link. Here, we investigate the broadening of the quantum phase distribution due to quantum phase noise of the laser, the dispersive optical fiber, the phase noise of the RF oscillator and the inevitable noise coefficient of the optical amplifier for arbitrary amplified spontaneous emission (ASE) field modes. We analytically investigate the quantum analog to the bit error rate (BER) as a function of the laser’s linewidth, the linewidth of the RF oscillator and chromatic dispersion. The results of quantum models are compared with the semiclassical model. Quantum treatment of both the BER and variance is found to agree with prior results for a single-mode ASE field in the absence of phase noise but deviate when the effect of phase noise is considered. Including phase noise effects in the amplitude in the semiclassical treatment of the BER yields a new semiclassical expression that agrees with quantum expressions of machine precision for single-mode ASE fields.

Determination of the optimal input channel powers using particle swarm optimization algorithm in a WDM system with In-Line optical amplifiers

In this paper, a new application of the particle swarm optimization (PSO) algorithm has been carried out in the field of the optical fiber (OF) communication system. In this theoretical work, the most suitable input channel powers to reduce the disruptive effects of four-wave mixing (FWM) occurring in OF and amplified spontaneous emission (ASE) noise from optical amplifiers are determined with the help of two different particle swarm optimization (PSO) in terms of inertia weight. The figure of merit is the optical signal-to-noise ratio (OSNR) of each channel at the output end of OF. Each of the input channel powers is optimized to maximize the OSNR of the channel with the lowest OSNR. The values obtained by both optimization methods are well good compared to those obtained with equal powers allocation (EPA). The best improvement in OSNR with PSO is obtained as 1.105846 dB (2.762778 %). Moreover, the performances of both algorithms and EPA are also comparatively evaluated in the study.

Advanced DSP-Based Monitoring for Spatially Resolved and Wavelength-Dependent Amplifier Gain Estimation and Fault Location in C+L-Band Systems

The development of efficient anomaly detection schemes is a key element for the implementation of autonomous optical networks as they can help telecom operators to automate the location of defective devices and track the overall performance of the network infrastructure. In that regard, the exploitation of receiver based digital signal processing (DSP) for optical performance monitoring has shown to be a promising enabler for detection of spatially resolved and wavelength-dependent properties and anomalies in optical fiber links. In this work, we study the benefits of applying DSP-based longitudinal power estimation on multiple wavelength division multiplexing (WDM) channels allocated in the optical grid to infer wavelength-wise characteristics of a C+L-band optical line system. In that context, we show that the applied scheme can successfully recreate a visualization of the spatial evolution of the gain tilt imposed by in-line optical amplifiers. Additionally, we propose the utilization of advanced DSP tools based on wavelet-denoising to enhance the performance of an anomaly detection approach. The proposed method not only can improve accuracy of the fault location, by reducing positioning uncertainty, but it also delivers more uniform readings of the anomaly signatures.

Investigation of inline optical amplifiers in 2-D time-wavelength OCDMA systems

This paper introduces the first mathematical investigation on utilizing a single inline optical amplifier in the 2-D time-spreading wavelength-hopping (TW) code division multiple access (OCDMA) system. The study adopts a non-ideal erbium-doped fiber amplifier (EDFA), where the optical gain depends on the input power of the amplifier. Three en/decoders representing different loss levels are examined. In addition, the paper highlights the significance of the power budget in the amplified TW systems to ensure the accomplishment of two concurrent conditions. First, the total input power from all users to the inline amplifier should fall within the amplifier input power range to gain sufficient amplification. Hence, the transmitted chip power from users is the key contributor. The second condition is the ordinary case where the desired received power should meet the required bit error rate (BER). The number of central splitter/combiner ports (Nsys) is an additional important system parameter, representing the upper bound of the available number of simultaneous users (K). The analysis supported by the Optisystem simulation results shows that the best location for the inline amplifier is close to the central system’s combiner. The results also reveal that, for low-user system capacities, employing a single inline optical amplifier in the 2-D TW OCDMA system is effective for the low-loss TW en/decoders but with increased code weights (w). For an 8-user system (i.e., Nsys = 8), transmitted chip power of 15 dBm, and EDFA amplification gain of 28 dB, the system can support the full-user capacity (at a BER ≤ 10-9) when w = 29. On the contrary, the performance of the higher system capacities sustains only a particular number of simultaneous users, accommodating up to 60 % of the full-user capacity when Nsys = 16.

Experimental demonstration of single-span 100-km O-band 4×50-Gb/s CWDM direct-detection transmission.

We report on what is to the best of our knowledge the longest 50-Gb/s/λ O-band wavelength-division multiplexed (WDM) transmission. A pair of in-house built bismuth-doped fiber amplifiers (BDFAs) and the use of Kramers-Kronig detection-assisted single-sideband transmission are adopted to overcome the fiber loss and chromatic dispersion, respectively, in a reach-extended O-band coarse WDM (CWDM) system with a channel spacing of ∼10 nm. Through experiments on an amplified 4×50-Gb/s/λ direct-detection system based on booster and pre-amp BDFAs, we show the superior performance of single-sideband transmission in terms of both optical signal-to-noise ratio sensitivity and uniformity in performance amongst CWDM channels relative to double-sideband transmission after both 75-km and 100-km lengths of single-mode fiber. As a result, up to 100-km reach with comparable performance at all 50-Gb/s channels was achieved without the need for in-line optical amplification.

An approach for suppressing waveform distortion of SOAs by controlling the temperature on in-line optical amplifier systems

An approach for suppressing waveform distortion of SOAs by controlling the temperature on in-line optical amplifier systems

Large-capacity and long-distance distributed acoustic sensing based on an ultra-weak fiber Bragg grating array with an optimized pulsed optical power arrangement.

A large-capacity, long-distance distributed acoustic sensing (DAS) system without inline optical amplification was proposed and experimentally demonstrated using an ultra-weak fiber Bragg grating (UWFBG) array and coherent detection. The effect of the finite extinction ratio of an acousto-optic modulator and the Stokes signal of stimulated Brillouin scattering (SBS) in UWFBGs on the performance of DAS was simulated and revealed. A high extinction ratio and a balanced input pulsed optical power can improve the capacity and distance of the DAS. The dynamic acoustic signal can be well reconstructed for a serial array of 10828 near-identical UWFBG with a length of 54.14 km. An acoustic signal sensitivity of 189.54 pɛ/√Hz and a signal SNR of 40.01 dB with a spatial resolution of 5 m can be achieved at the far end.

Ultra-Low Crosstalk En/Decoder Using an Amplitude-Shaping Technique for 100 Gbps/λ OCDM-PAM-4 Transmission in O-Band

This paper proposes an optimized 16-chip multi-level phase-shifted optical code division multiplexing (OCDM) en/decoder for 4-level pulse amplitude modulation (PAM-4) format by using an amplitude-shaping (AS) technique. The optimized en/decoder can efficiently suppress the crosstalk and the primary beat noise (PBN). The code detection performance for 4-OCDM PAM-4 becomes the lowest to our knowledge. The numerical bit error rate analysis and the back-to-back simulation are shown. We also successfully demonstrate by computer simulation a 100 Gbps/λ enabling by 12.5 GBaud 4-OCDM PAM-4 transmission in O-band over 6×30 km with in-line optical amplifiers.

Phase-sensitively amplified wavelength-division multiplexed optical transmission systems.

The throughput and reach in fiber-optic communication links are limited by in-line optical amplifier noise and the Kerr nonlinearity in the optical transmission fiber. Phase-sensitive amplifiers (PSAs) are capable of amplifying signals without adding excess noise and mitigating the impairments caused by the Kerr nonlinearity. However, the effectiveness of Kerr nonlinearity mitigation depends on the dispersion pre-compensation in each span. This paper investigates dense wavelength-division multiplexed PSA-amplified links using joint processing with a less complex digital domain Volterra nonlinear equalizer at the receiver. Both numerically and with experiments, it is shown that this significantly reduces the impact of the dispersion pre-compensation in each span. Also, with simulations, a substantial improvement in transmission reach is demonstrated for PSA links.

Security enhancement by swapping bits belonging to different data channels

A simple coding scheme is proposed to enhance information security in all-optical networks. It is based on swapping of data bits belonging to two different channels to form two garbled bit streams. The encryptor and decryptor designs used here can be implemented by using commercially available components. The performance of the proposed technique is evaluated at the system level by considering multiple spans of optical fibers with in-line optical amplifiers. Numerical simulations show that the decoded bit streams can be recovered with acceptable bit error rates after 500 km.

152 km-range single-ended distributed acoustic sensor based on inline optical amplification and a micromachined enhanced-backscattering fiber.

In this Letter, a distributed acoustic sensor (DAS) with a sensing range in excess of 150 km is reported. This extended sensing range is achieved by adding a low-loss enhanced-backscattering fiber at the far end of a standard single-mode fiber. A conventional DAS system along with inline optical amplifiers are used to interrogate the sensing fiber. The combined system exhibits a minimum detectable strain of 40 nε at 1 Hz over a spatial resolution of 5 m.

Comparative performance of optical amplifiers: Raman and EDFA

The in-line optical signal amplification is often used in optical communication systems to accomplish longer transmission distances and larger capacity. In this proposed paper, the operation of two types of optical amplifiers for 16×10 Gbps wavelength division multiplexing system had been examined by changing transmission distance from 10 to 200 km with a dispersion equals to 16.75 ps/nm/km. The analysis and design of such systems ordinarily includes many signal channels, nonlinear devices, several topologies with many noise sources, is extremely complex and effort-exhaustive. Therefore, theoretical studies with simulation CAD software of systems are become necessity to predict and optimize system performance. The comparison between EDFA and Raman has already explored by many researchers in varying ways in this work and to achieve obove objectives, the OptiSystem software was used to design the proposed fiber optic communications system and to simulate results. Performance for the present system was evaluated for parameters like bit error rate (BER), quality factor (QF), total gain with eye opening factor. It was saw that EDFA provides better results, in the maximal transmission distance 64% better than Raman amplifier, 57.5% for gain and 26.7% for maximum quality factor. As a future study a hybrid amplifier can produce better quality of amplification.

Hybrid-Integration of SOA on Silicon Photonics Platform Based on Flip-Chip Bonding

A precise flip-chip bonding (FCB) technology for indium phosphide semiconductor optical amplifiers (InP-SOAs) on a silicon photonics platform within less than ±1- μ m alignment accuracy was developed. For efficient optical coupling and a relaxed alignment tolerance, the mode field on both the InP-SOAs and the Si waveguides was expanded by spot-size converters (SSCs). On the InP-SOAs, width-tapered SSCs were used to obtain an isotropic mode-field having an approximately a 3- μ m diameter. On the silicon photonics platform, dual-core SSCs were used to expand the same mode-field size of 3 μ m as for the SSCs on SOAs. Using the FCB technology and the SSCs, an in-line optical amplification of 15 dB was achieved by in-line integrated SOAs with angled waveguides. The optical coupling losses were 7.7 dB, which included 5.1-dB excess losses by misalignment and a gap between InP-SOA and Si waveguides. A 4 × 4 Si switch with a hybrid-integrated 4-ch SOA array was fabricated, and achieved the first demonstration of a lossless Si switch.

Low-Power Consumption 28-Gb/s 80-km Transmission With 1.3-μm SOA-Assisted Extended-Reach EADFB Laser

We extend the transmission distance for 28-Gb/s optical links from 40 to 80 km in a single-mode fiber (SMF) in the 1.3-μm-wavelength window by using an intensity-modulation direct-detection scheme. To extend the link budget, and compensate for the optical loss of SMF, we try to increase the optical output power of an electroabsorption modulator integrated with distributed feedback (EADFB) laser. We apply a semiconductor optical amplifier (SOA)-assisted extended-reach EADFB laser (AXEL) to a 1.3-μm-wavelength light source. To increase the optical output power while using energy efficiently, we design the SOA length in terms of achieving a balance between the laser diode (LD) and the SOA length with a constant injection current of 160 mA. We fabricate an AXEL and an EADFB laser and compare their basic characteristics. By using the high-power AXEL, we achieve the first 28-Gb/s 80-km SMF transmission without the need for digital signal processing or an in-line optical amplifier. The AXEL consumes only 0.26 W and does not require any digital processing or an in-line amplifier and can, therefore, reduce the power needed for an optical network system by tens of watts.

Optical Preamplifier and Inline Amplifiers Comparison Based Raman-EDFA Hybrid Amplifiers in 40 × 10 Gb/s DWDM System

his paper presents forty channels dense wavelength-divisionmultiplexing (DWDM) system using a hybrid optical amplifiercomposed of Raman optical amplifiers and erbium doped fiberamplifier (EDFA). The forty channel DWDM system have beendesigned and simulated to study the behavior of the proposedRaman-EDFA amplifier as preamplifier and in-line amplifier toselect one which have better performance with maximumtransmission distance. These configurations are transmitted andmeasured over different distances. The optical link composed ofdispersion compensated fiber (DCF) and single mode fiber (SMF)to limit the chromatic dispersion. The performance of the proposedhybrid optical amplifier as preamplifier and as in-line amplifier wereevaluated by bit error rate (BER), output power, gain and qualityfactor (QF). Moreover, it calculate the number of spans and thelength of each span which give maximum transmission distance forRaman-EDFA hybrid amplifier using the two positions as in-lineamplifier along the fiber and as preamplifier at the end of the fiber.It is found that Raman-EDFA hybrid amplifier as preamplifierperformed better than in-line optical amplifier.

Off-set Filtering Effect in SOA Based Optical Access Network

In-line and reflective semiconductor optical amplifiers (SOA and RSOA) can be effectively utilized as external optical intensity modulators. However the limited modulation bandwidth affects the application possibilities, because next generation access networks desire high trans- mission speed. Bandwidth enhancement can be achieved by means of optical equalization thanks to the chirping char- acteristics of semiconductor optical amplifier. The limited modulation transfer function can be combined with the converted phase modulation transfer function. Investiga- tion of optical filter with optimal slope is a crucial chal- lenge in this approach. The presented simulations describe the slope dependence of the modulation band. The model can take into account the different type of realizable opti- cal filters. However there is a trade-off between modula- tion efficiency and modulation bandwidth due to the extra insertion loss of the set-off optical filter. In the paper theo- retical and simulation investigations are presented with the result of improved modulation bandwidth.

Transmission of 2 × 56 Gb/s PAM-4 signal over 100 km SSMF using 18 GHz DMLs.

We experimentally demonstrate C-band 2 × 56 Gb/s pulse-amplitude modulation (PAM)-4 signal transmission over 100 km standard single-mode fiber (SSMF) using 18 GHz direct-modulated lasers (DMLs) and direct detection, without inline optical amplifier. A delay interferometer (DI) at the transmitter side is used to extend the transmission reach from 40 to 100 km. A digital Volterra filter at the receiver side is used to mitigate the nonlinear distortions. We obtain an average bit error ratio (BER) of 1.5 × 10(-3) for 2 × 56 Gb/s PAM-4 signal after 100 km SSMF transmission at the optimal input power, which is below the 7% forward error correction (FEC) threshold (3.8 × 10(-3)).

Generation of carrier-envelope phase-stable mid-infrared pulses via dual-wavelength optical parametric amplification.

Carrier-envelope phase-stable mid-infrared pulses spanning from 5 μm to 11 μm with a pulse energy of 5 μJ were produced by difference frequency generation of two-color near-infrared pulses that were produced in a novel inline optical parametric amplifier. The mid-infrared electric waveform was characterized by electro-optic sampling using 6.5-fs pulses at 620 nm.

Experimental Demonstration and Field-Trial of an Improved Optical Fast OFDM Scheme Using Intensity-Modulation and Full-Field Detection

We experimentally investigate an improved fast orthogonal frequency division multiplexing (OFDM) scheme using intensity modulation and full-field detection. This new fast OFDM algorithm exhibits better back-to-back and transmission performance than the conventional one, and is shown to support a 40-Gb/s signal over a 480-km re-circulating loop-based single-mode fiber (SMF) with 1-dB penalty. We compare this scheme with the direct-detection (DD) system using the same algorithm, and show that the DD system cannot support 60-km SMF at 40 Gb/s. Finally, we demonstrate the proposed scheme over 124 km of BT Ireland's field-installed fiber without inline optical amplification. The results show that this scheme can be a promising solution to address the gap between direct detection and coherent detection for applications in short metro networks and long-reach Ethernet and access networks.