External Modulation Scheme Research Articles

A prior-guided deep network for real image denoising and its applications

Recently, the popularity of deep learning in computer vision has brought about a rapid development of deep convolutional neural network (CNN)-based image denoising algorithms. Most of the existing methods have shown their superiority in removing additive white Gaussian noise (AWGN) with a specific noise level, but have limited performance in handling much more complicated real noise. To address this problem, we develop a novel prior-guided dynamic tunable network (PDTNet) for real image denoising. Firstly, we break up the image denoising optimization problem into noise estimation and image reconstruction sub-problems, and employ the inference process to guide the architecture design of PDTNet. Then, we exploit an internal and external dual modulation (IEDM) scheme to achieve real image denoising. Specifically, a designed global spatial and channel attention (GSCA) is embedded in the external estimator and internal stacked dynamic residual blocks (DRBs) to extract global features from the noise prior and iterative image features, respectively. Next, a dynamic weight generator block (DWGB) is leveraged to adaptively combine external and internal features at each DRB. In addition, we also analyze a realistic real noise model from the physical perspective to generate synthetic noisy images for model training. Experimental results show the superiority of PDTNet over state-of-the-arts both quantitatively and visually and its applications on different networks and tasks.

Single-tone mid-infrared frequency modulation spectroscopy for sensitive detection of transient species.

A single-tone mid-infrared frequency modulation (MIR-FM) spectrometer consisting of a cw-OPO-based laser system, a 500 MHz LiTaO 3 electro-optical modulator (EOM), and a high-bandwidth GaAs mid-infrared detector has been developed. In order to assess the instrument's sensitivity and time resolution, FM spectra of selected CH 4 transitions around 3070 cm -1 were measured and the reaction Cl + CH 4 following the 193 nm excimer laser photolysis of oxalyl chloride was investigated by recording concentration-time profiles of HCl at 2925.90 cm -1 in a low-pressure slow-flow reactor. Furthermore, OH radicals were generated by UV photolysis of H 2O 2 and its transients were recorded at 3447.27 cm -1. The minimal detectable absorption of the spectrometer was determined to be A min=4⋅10-4 (Δ f BW=1 MHz, ν~=3447 cm -1) by using the Allan approach. Mainly due to thermal noise contributions of the easy-to-saturate photodetector, the detection limit is about a factor of 4 above the shot-noise limit. To the best of our knowledge, this work reports the first implementation of a single-tone MIR-FM spectrometer based on an external EOM modulation scheme and its use for the detection of transient molecular species.

First demonstration of Brillouin optical correlation-domain reflectometry based on external modulation scheme

We demonstrate basic operation of Brillouin optical correlation-domain reflectometry (BOCDR) based on an external modulation scheme, which can mitigate three demerits of a conventional direct modulation scheme. A 0.8 m long strain in a 2.8 m long silica fiber is successfully detected in a distributed manner. This scheme can be employed not only in BOCDR but also in Brillouin optical correlation-domain analysis.

Performance Analysis of Single Side Band Orthogonal Frequency Division Multiplexing in Radio over Fiber System with Direct and External Modulation Schemes

Abstract Radio over fiber is a technology in which the light signals at the central station are modulated by a radio frequency signal, and by using the optical fiber it is transmitted to base stations. The data stream being sent is separated into subcarrier frequencies by the technique of orthogonal frequency division multiplexing. The orthogonality between the sub-carriers is provided by FFT modulation, which avoids the demodulators from accepting other frequencies. It is possible to transmit high-data rate signals over short and long distance by implementing orthogonal frequency division multiplexing with radio over fiber system along with the optical fiber. This enhances the system with more coverage area, and without increasing the cost of the system it provides the flexibility. The proposed work is to investigate the performance analysis of single side band orthogonal frequency division multiplexing in radio over fiber system with external and direct modulations using spectral analysers and constellation visualizers. The Mach-Zender modulator is proposed for external modulation, the vertical cavity surface emitting laser is used in direct modulation. The simulations were carried out by using Optisystem Software version 15.0 with global parameters for both intensity modulation schemes.

Optical millimeter wave generation utilizing stimulated brillouin scattering for radio over fiber system

<span>Optical millimeter-wave signal generation in Radio over Fiber (RoF) based on external modulators using different modulation schemes such as Single-Sideband (SSB), Double-Sideband (DSB) are experimentally compared. The major fallout for external modulation scheme system performance to downgrade is due to dispersion and the fading effect in optical signal generation while generating high Bit Error Rate (BER) when involving long distance delivery. In this work, we proposed mm-wave signal utilize Stimulated Brillouin Scattering (SBS) scheme which indicates the best performance amongst the scheme based on simulation that it achieves to propagate longest of distance over fiber, highest receiver sensitivity, the lowest BER and coherence of Mach-Zehnder Modulator (MZM) extinction ratio. Mm-wave signal of 40 Ghz and 10 Gb/s data rate was generated with the plotting of eye diagram.</span>

Proposal of external modulation scheme for fiber-optic correlation-domain distributed sensing

All the previous configurations of optical correlation-domain reflectometry (OCDR) have been based on the direct modulation of laser driving current. However, some lasers are not designed for high-speed large-amplitude modulation, and the modulation amplitude and frequency are mutually dependent. In this work, to mitigate these drawbacks, we propose an external modulation scheme for OCDR. After confirming its basic operation, we show that a non-specially designed laser can be employed. We also clarify that the interdependence of the modulation amplitude and frequency is negligibly small in this scheme, which is not the case for the conventional direct modulation scheme.

Filter Bank Multicarrier (FBMC) for long-reach intensity modulated optical access networks

Filter Bank Multi Carrier (FBMC) is a modulation scheme which has recently attracted significant interest in both wireless and optical communications. The interest in optical communications arises due to FBMC's capability to operate without a Cyclic Prefix (CP) and its high resilience to synchronisation errors. However, the operation of FBMC in optical access networks has not been extensively studied either in downstream or upstream. In this work we use experimental work to investigate the operation of FBMC in intensity modulated Passive Optical Networks (PONs) employing direct detection in conjunction with both direct and external modulation schemes. The data rates and propagation lengths employed here vary from 8.4 to 14.8Gb/s and 0–75km. The results suggest that by using FBMC it is possible to accomplish CP-Less transmission up to 75km of SSMF in passive links using cost effective intensity modulation and detection schemes.

20 Gbps Bidirectional Transmission via Four Channels over Long-haul SMF in a WDM-PON Architecture using External Modulation Scheme

Abstract A novel architecture of bidirectional gigabit signal transport system over long-haul single-mode fiber (SMF) using wavelength division multiplexed passive optical network technique is proposed and demonstrated. In order to offer multimedia services of high bandwidth, four signals of 5 Gbps data rates are externally modulated and transmitted through four channels over 100-km SMF in uplink and downlink. In our proposed scheme, an excellent bit error rate, good Q-factor and clear eye diagrams are observed for both 100-km uplink and downlink transmission. This architecture has potential to transmit 4×5 Gbps over long-haul fiber backbone and it will be useful in future broadband communications.

Chromatic Dispersion Induced Second-Order Distortion in Long-Haul Photonic Links

Closed form expressions for the theoretical photocurrent of a photonic link with a dispersive fiber are derived for multiple external modulation schemes. These expressions are used to derive the link's output power at both the fundamental and second-order frequencies. Expressions for phase modulation (with and without an asymmetric Mach–Zehnder Interferometer), and both X- and Z-cut LiNO3 intensity modulation are presented and compared.

Reduction of Four Wave Mixing Nonlinearity Effect in WDM Radio over Fiber Systems

The optical networks are fast, robust and error-free, but there are some nonlinearity hindrances which prevent them from being a perfect medium. The performance of wavelength division multiplexing (WDM) in radio over fiber (RoF) systems is found to be intensely influenced by nonlinearity characteristics within the fiber. In this paper, the performance of WDM network is analyzed using optical filter and various external modulation schemes under FWM nonlinearity effect. Here, the effect of input signal power on FWM is studied. Also, the threshold value of input power for different external modulation technique is calculated and hence duobinary modulation is found to be optimal technique for reducing FWM effect in WDM networks.

28 Gb/s duobinary signal transmission over 40 km based on 10 GHz DML and PIN for 100 Gb/s PON.

In this paper, we demonstrate the direct modulation and direct detection of 28-Gb/s duobinary signal for the future downstream capacity upgrade in next generation passive optical network (PON). Commercial 10-GHz directly modulated laser (DML) and PIN with a combined modulation bandwidth of ~7 GHz are used as transmitter and receiver respectively. In order to mitigate the chromatic dispersion induced signal distortion, an optical delay interferometer (DI) is employed to narrow down the signal spectrum, thereby realizing 40-km single mode fiber (SMF) transmission in C-band. Besides, the chirp-induced spectral broadening of the directly modulated signal enables a higher launch power than external modulation schemes, which increases the loss budget of the system. As a result, 31-dB loss budget is achieved, supporting 64 users with 40-km reach. Also, as the transceivers in both optical line terminal (OLT) and optical network unit (ONU) are commercial l0-GHz devices, the proposed scheme is compatible with 40-Gb/s time and wavelength division multiplexing passive optical network (TWDM-PON) systems, providing a cost-efficient alternative for the development of 100G PON.

RSOA-Based Full-Duplex WDM-PON for 20 Gbps Transmission in Two Channels Over a Long-Haul SMF Using External Modulation Scheme

AbstractWe have proposed and demonstrated a full-duplex wavelength division multiplexed passive optical network (WDM-PON) configuration based on reflective semiconductor optical amplifier (RSOA). RSOA is used for reusing and remodulate the downlink signal in the uplink. We have used external modulation scheme for transmitting 20 Gbps data rates in two channels over a 40 km single mode fiber (SMF). The uplink and the downlink performances are checked by the bit error rate (BER) and the eye diagrams.

1.5-$\mu$m Frequency-Stabilized $\lambda/4$-Shifted DFB LD Employing an External Fiber Ring Cavity With a Linewidth of 2.6 kHz and an RIN of $-$135 dB/Hz

We present a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> frequency-stabilized λ/4-shifted distributed feedback laser diode (DFB LD) with an external fiber ring cavity. By controlling the λ/4-shifted DFB passband to track one Fabry-Pérot mode associated with the fiber ring cavity, the oscillation frequency was continuously tuned over 1.2 GHz without mode-hopping. The optical frequency was stabilized to a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line with an external frequency modulation scheme that enabled us to realize an output beam without additional modulation. As a result, we obtained a frequency stability as high as 1.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> for τ = 1 s and 1.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> for τ = 100 s. In addition, we simultaneously achieved a linewidth of 2.6 kHz and a relative intensity noise of less than -135 dB/Hz.

A Multi-Channel Correlative Vector Direction Finding System Using Active Dipole Antenna Array for Mobile Direction Finding Applications

A fast correlative vector direction finding(CVDF) system using active dipole antenna array for mobile direction finding(DF) applications is presented. To develop the CVDF system, the main elements such as active dipole antenna, multi-channel direction finder, and search receiver are designed and analyzed. The active antenna is designed as composite structure to improve the filed strength sensitivity over the wide frequency range, and the multi-channel direction finder and search receiver are designed using DDS-based PLL with settling time of below 35 us to achieve short signal processing time. This system provides the capabilities of the high DF sensitivity over the wide frequency range and allows for high probability of intercept and accurate angle of arrival(AOA) estimation for agile signals. The design and performance analysis according to the external noise and modulation schemes of the CVDF system with five-element circular array are presented in detail.

Continuous-phase frequency-shift keying with external modulation

A high-speed external modulation scheme for optical continuous-phase frequency-shift keying (CPFSK) is presented. In external frequency-shift keying (FSK) modulation using single-sideband modulation technology, an optical upper/lower sideband (USB/LSB) component with respect to a carrier frequency is selectively generated. However, the FSK-modulated signal has phase discontinuities at the timings of frequency shifts. To overcome the problem, we propose a synchronous control technique that enables continuous phase modulation. In the external CPFSK modulation, the USB/LSB is allowed to shift to the other state when their phases coincide with each other. It is shown that CPFSK with a zero-to-peak frequency deviation of 0.5times(bit rate) is achieved with this synchronous control. Occupant bandwidth is less than half that of the externally modulated incoherent FSK with phase discontinuities. At a modulation speed of 10 Gb/s, higher order sidelobes are highly suppressed by more than 20 dB at the 20-GHz offset, comparing to a conventional binary phase-shift keying (BPSK). By the use of a Mach-Zehnder interferometer with balanced photodetection, receiver sensitivity is 3-dB greater than that of an on-off keying, as well as a BPSK. In this paper, we report on the experimental demonstration of CPFSK modulation/demodulation. A six-channel wavelength-division-multiplexed, 10-Gb/s CPFSK modulation/demodulation was successfully demonstrated

Optical minimum-shift keying with external modulation scheme

We propose an optical initial phase control technique for external modulation in the format of minimum-shift keying (MSK). In this scheme, the optical phase discontinuities inherent to external frequencyshift- keying (FSK) modulation are compensated by use of an initial phase controller in conjunction with a FSK modulator. We present the principle of the control method and then numerically and experimentally prove that the signal has a modulation spectrum more compact than that of conventional binary phase-shift keying. 10-Gbit/s external modulation in MSK format was experimentally demonstrated.

Distortion and noise properties of a praseodymium-doped fluoride fiber amplifier in 1.3 /spl mu/m AM-SCM video transmission systems

The distortion and noise of a praseodymium-doped fluoride fiber amplifier (PDFA) are measured in two 40-channel AM-SCM video transmission systems. While it is already known that with direct modulation a PDFA leads to increased composite second-order distortion (CSO) and cross-modulation distortion (XM), this letter introduces an external modulation scheme that completely eliminates both problems. One PDFA is examined and found to yield low distortion and high CNR, but this is offset by a low-frequency noise. This noise is significant and the resulting picture quality is "annoying" in subjective tests.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency stabilization of an InGaAsP distributed feedback laser to an NH3 absorption line at 15137 Å with an external frequency modulator

The oscillation frequency of a 1.5-μm InGaAsP distributed feedback laser is stabilized to an NH3 linear absorption line at 15137 Å. A LiNbO3 external frequency modulator is used instead of direct frequency modulation of the laser to extract error signals. An effective bandwidth of 100 kHz for the feedback loop is obtained through this external modulation scheme. Frequency stability of σ(2,τ)=4×10−11 is achieved for an averaging time of 1 s≤τ≤100 s.