Binary and multilevel optical polarization modulation (POLSK) is an innovative transmission technique, suitable for both coherent and direct detection. To prove its feasibility, we have built a flexible polarization modulator based on a specifically designed LiNbO/sub 3/ device. We show that it can generate any state of polarization and therefore it is suitable for transmission of any binary or multilevel POLSK constellation. Once electrically equalized, the modulator has a 4 GHz bandwidth. To test the modulator with actual digital modulation, we set up a coherent binary experiment at 800 Mbit/s, and attained a sensitivity 1.5 dB away from the noise limit of the receiver.
In this letter, we introduce time domain hybrid quadrature amplitude modulation (TDHQ) for the single sideband (SSB) discrete multi-tone (DMT) systems. Experimental results reveal that with a single precoding set and the proposed adaptive loading algorithm, the TDHQ scheme can achieve finer granularity and therefore smoother continuous growth of data rate than that with the conventional quadrature amplitude modulation (QAM). Besides, thanks to the frame construction and the tailored mapping rule, the scheme with TDHQ has an obviously better peak to average power ratio (PAPR).
The use of a micro-ring resonator (MRR) to enhance the modulation extinction ratio and dispersion tolerance of a directly modulated laser is experimentally investigated with a bit rate of 25 Gb/s as proposed for the next generation data center communications. The investigated system combines a 11-GHz 1.55-μm directly modulated hybrid III-V/SOI DFB laser realized by bonding III-V materials (InGaAlAs) on a silicon-on-insulator (SOI) wafer and a silicon MRR also fabricated on SOI. Such a transmitter enables error-free transmission (BER < 10-9) at 25 Gb/s data rate over 2.5-km standard single mode fiber without dispersion compensation nor forward error correction. As both laser and MRR are fabricated on the SOI platform, they could be combined into a single device with enhanced performance, thus providing a cost-effective transmitter for short reach applications.
A novel linearization concept to reduce the distortion products from integrated-optic modulators is proposed and analyzed. The proposed linearization concept could be used on any type of modulator with an odd transfer function. A dual parallel Mach-Zehnder modulator was linearized, and the results are compared to those obtained using a conventional linearization concept. The proposed concept gives a 40% higher modulation index compared to a concept based on reduction of the cubic nonlinearity of the modulator
The proposed modulation scheme enables us to combine the advantages of the duobinary modulation, i.e., reduced transmission bandwidth compared to traditional intensity modulation, together with the advantages of prechirped modulation. Below, a theoretical investigation is presented where four different methods of modulating a double electrode Mach-Zehnder modulator is compared. It will be shown that the proposed prechirped duobinary modulation scheme will have the best performance in terms of power penalty.
The authors have analyzed and measured the dispersion effects of residual chirp arising from asymmetry in field overlap in Mach-Zehnder structures. A clear influence of chirp was seen at 7 Gb/s and a propagation length of 75-km nondispersion shifted fiber at lambda =1.55 mu m. It is shown that a MZ-modulator with field overlap in one arm only and operated in the blue-shift mode is the best choice for single coplanar stripline (CPS) electrode MZ-modulators in this case. Calculations have shown good agreement with measured results. This indicates that a simple model for fiber mode propagation have shown good agreement with measured results. This can be used together with a FFT-algorithm for calculating the effect of residual chirp from external modulators in multigigabit dispersive fiber-optic systems.
The behavior of the differential group delay (DGD)root-mean-square (rms) value is investigated for a buried G.652fiber line in a metropolitan fiber plant outside Stockholm, Sweden.This study presents measurement results from two different mea-surement periods where the same fiber and the same measurementequipment was used. In total,2800 hours of measurements wereperformed. As expected, the recorded DGD rms-value variedwith time. The measured standard deviation for the statistics ofthe DGD rms-value fits reasonably well with values presentedin literature. The fiber line, which showed a DGD rms-value of0.45 ps in average, had an extremely long time constant. Evenafter2800 hours of measurements we have not closed in on theexpected asymptotic distribution of the measured DGD rms-value
We demonstrate experimentally as well as numerically that the alternate-phase return-to-zero modulation format increases the nonlinear tolerance of strongly dispersion-managed 40-Gb/s transmission. An analysis of phase misalignment is also presented.
We use the cost-effective APM technique to increase the non-linear tolerance of NRZOOK, and we demonstrate, in a recirculating loop experiment, the transmission over 2800 km SSMF of 16 NRZ-OOK 40 Gb/s channels with 100 GHz spacing.
—The authors propose a modulation format in which the phase of the signal pulses alternates, in order to reduce the intrachannel four-wave mixing. They demonstrate numerically that the performance of a 40-Gb/s transmission link can be substantially improved.
A free-space optical (FSO) transmission system is experimentally demonstrated in the long-wave infrared (LWIR, 9.15μ m ) using a directly modulated quantum cascade laser (DM-QCL) and a commercial mercury-cadmium-telluride infrared photovoltaic detector. At room temperature, the DM-QCL is current-modulated by discrete multitone signals pre-processed with bit-/power-loading. Up to 5.1 Gbit/s data rate is achieved with bit error rate performance below the 6.25% overhead hard-decision forward error correction limit of 4.5× 10-3 , enabled by a frequency domain equalizer. The stability study of the FSO system is also performed at multiple temperature values. This study can provide a valuable reference for future terrestrial and space communications.
We numerically compare the performance of a bidirectionally pumped Raman- and an erbium-doped fiber amplifier (EDFA) system in a 40-Gb/s dispersion-managed return-to-zero (RZ) transmission. The Raman amplifier system shows a substantially higher Q-value compared to that of the EDFA.
A method for mitigating local oscillator (LO) phase noise-induced impairment, also known as equalization-enhanced phase noise, in coherent optical systems is discussed. The method is suitable for real-time implementation and requires hardware with a bandwidth much lower than the signal baud rate, even for a system utilizing conventional semiconductor laser as LO. We evaluate the required parameters like interpolation technique, electrical signal-to-noise ratio at digital coherence enhancement (DCE) front end, for long haul transmission links having quadrature phase shift keying and 16-quadrature amplitude modulation formats. We show that the method can be implemented using a low-speed DCE front end and a simple digital linear interpolator with small (<1 dB) implementation penalty even in cases that would otherwise result inerror floor.
The relatively high phase noise of coherent optical systems poses unique challenges for forward error correction (FEC). In this letter, we propose a novel semianalytical method for selecting combinations of interleaver lengths and binary Bose-Chaudhuri-Hocquenghem (BCH) codes that meet a target post-FEC bit error rate (BER). Our method requires only short pre-FEC simulations, based on which we design interleavers and codes analytically. It is applicable to pre-FEC BER similar to 10(-3), and any post-FEC BER. In addition, we show that there is a tradeoff between code overhead and interleaver delay. Finally, for a target of 10(-5), numerical simulations show that interleaver-code combinations selected using our method have post-FEC BER around 2x target. The target BER is achieved with 0.1 dB extra signal-to-noise ratio.
We demonstrate the addition of time gating to a standard optical spectrum analyzer (OSA) operating in the spectral region ∼ 1.06 μm. This is accomplished by opening for 7 ns the optical input to the OSA with an electrically driven poled fiber in a Sagnac loop. The sequential interrogation with nanosecond resolution of the reflection from three fiber Bragg gratings along a piece of fiber allows distinguishing the spectral peaks created with a minimum separation of 85 cm. The passive extinction ratio of this device is >40 dB and returns to >40 dB from >23 dB on a 35-ns time scale directly after time gating.
Integrated polymer photonics brings low cost and high fabrication flexibility to optoelectronic industry. However, this platform needs to overcome several issues to be effective enough for practical applications. In this work, we experimentally demonstrate a decrease of propagation losses and polarization sensitivity of polymer waveguide-based devices as a result of thermal treatment. Heating of poly(methyl methacrylate) strip optical waveguides above the glass transition temperature initiates a waveguide surface reflow due to a decrease of the polymer viscosity and surface tension energy. This results in a decrease of surface roughness and shape change from rectangular to cylindrical. Thus, scattering losses and polarization sensitivity are minimized. IEEE
The use of dispersion-managed (DM) solitons for 160-Gb/s data transmission in fiber lines where the period of dispersion management is much shorter than the amplifier spacing is investigated through numerical simulations. It is shown that DM solitons outperform both standard solitons and “quasi-linear” return-to-zero (RZ) pulses. The dispersion tolerance is limited by pulse-to-pulse interactions and Gordon–Haus jitter and decreases with increasing transmission distance.
We propose a method for cycle-slip mitigation in circular multilevel quadrature amplitude modulation (C-mQAM) coherent optical systems, with constellation rotational asymmetry, based on an adaptive boundaries approach. The impact of cycle-slips in C-mQAM coming from Viterbi-Viterbi algorithm limits the phase noise tolerance. By introducing adaptive boundaries and a differential coding scheme, the ambiguity of asymmetrical rotation of constellation can be effectively removed. Performance of the proposed method is evaluated for a C-16QAM and C-64QAM for various laser linewidths. Results show a noticeable improvement in linewidth symbol duration product (Δν · TS) tolerance compared with the previous studies on C-mQAM and mQAM constellations. The Δν · TS tolerance reaches 4 × 10 -4 and 1.1 × 10 -4 for C-16QAM and C-64QAM, respectively, for 1 dB penalty at a symbol error rate of 10 -3.
Transmission of 86 dense wavelength division multiplexed channels on a 50-GHz grid, carrying 112-Gb/s radio-frequency-assisted dual-channel dual-polarization 16-QAM (8.6-Tb/s), was successfully demonstrated in a straight-line transmission link. Required bit-error rate before forward error correction was obtained after 1200 km of ultralow-loss G.652 fiber (0.17-dB/km attenuation) and after 881 km of conventional G.652 fiber (0.21-dB/km attenuation).
We experimentally evaluate high-speed intensity modulation/direct detection (IM/DD) transmissions with a 1.55-μ text broadband electro-Absorption modulated laser and pulse amplitude modulations (PAM). We demonstrate 80 Gb/s/ λ PAM-4 and 96 Gb/s/ λ PAM-8 transmissions with low-complexity digital equalizers at the receiver. Performance comparison with different types of equalizers are performed, including linear symbol-spaced feed-forward equalizer (FFE), fractional (half-symbol) spaced FFE and decision feedback equalizer (DFE), with different tap number. It is found that for both cases, a 6-Tap symbol-spaced FFE is sufficient to achieve a stable performance with bit-error-rate below the 7% overhead hard decision forward error correction (7%-OH HD-FEC) threshold over a 4 km standard single mode fiber link. Practical considerations including comparison between adaptive and static equalizer implementation and tolerable fiber chromatic dispersion are discussed.
Short reach optical communication technologies are increasingly demanded in several fast-evolving application scenarios in both telecom and datacom. Low-cost and low-complexity intensity modulation and direct detection (IM/DD) technologies are challenged to scale up the link rate beyond 400 Gbps by increasing the single-lane rate towards 200 Gbps, to maintain a low lane count in client-side optics. Limited by the bandwidth of both electronics and optoelectronics, and the more pronounced chromatic dispersion in the fiber, such high baud rate systems require the use of digital signal processing techniques with forward error correction (FEC) coding. Therefore, in this work, we first summarize a few potential alternative technologies to the IM/DD for future development and then focus on extending the IM/DD systems towards 200 Gbps lane rate. We study both their capability and their performance limits using numerical simulations and transmission experiments. CCBY
In this letter, we present the design and implementation of a pixelated electro-absorption modulator-based modulating retroreflector (MRR) for high-speed optical wireless communications. The modulator is based on a multiple quantum well structure embedded in an asymmetric Fabry-Perot cavity. This MRR was used in an outdoor link, operating at 150 Mb/s with a bit error rate (BER) of 1.22 × 10-6 at a range of 200 m. The system was also tested in laboratory-controlled conditions achieving a data rate of 200 Mb/s with a BER of 2 × 10-4. To the best of our knowledge, this is the fastest retroreflective free-space optics demonstration in both the indoor and outdoor environments.
A component is presented that combines light and fluid in an optical fiber arrangement for optofluidics. The component couples light from a standard telecom fiber (STF) to the solid-core of a microstructured fiber, and delivers fluid from a capillary to the holes of the same microstructured fiber. The light is then made to interact longitudinally with the delivered fluid in a hollow-core fiber or capillary. The component is all-spliced, hermetic and allows for fluid flow without interrupting the optical beam. Light is brought from the STF to the solid-core/fluid interface with a loss <0.1 dB.
By solving the two-dimensional Poisson equation for fibers with circular internal electrodes, we show that the parallelplate approximation incurs significant error in the determination of the electric field applied to the fiber core. This also affects the value of χ(3) measured in electro-optical fibers. The exact solution of Poisson's equation is used to solve the field applied to the core of a photonic crystal fiber, where the many holes screen the field. A universal curve is derived to allow using the simplifying parallel plate approximation and correcting for the error in symmetric fibers with round holes.
Measurements and numerical simulations of the noise statistics after a semiconductor optical amplifier (SOA) demonstrate nonlinear noise redistribution. The redistribution, which relies on self-modulation due to gain saturation and carrier dynamics, shows a strong power and bandwidth dependence and can be important for SOA-based regenerators. © 2005 IEEE.