Optical Signal Power Research Articles

Optical filtering in directly modulated/detected OOFDM systems

This work presents a theoretical investigation on the performance of directly modulated/detected (DM/DD) optical orthogonal frequency division multiplexed (OOFDM) systems subject to optical filtering. The impact of both linear and nonlinear distortion effects are taken into account to calculate the effective signal-to-noise ratio of each subcarrier. These results are then employed to optimize the design parameters of two simple optical filtering structures: a Mach Zehnder interferometer and a uniform fiber Bragg grating, leading to a significant optical power budget improvement given by 3.3 and 3dB, respectively. These can be further increased to 5.5 and 4.2dB respectively when balanced detection configurations are employed. We find as well that this improvement is highly dependent on the clipping ratio.

Formal Worst-Case Analysis of Crosstalk Noise in Mesh-Based Optical Networks-on-Chip

Crosstalk noise is an intrinsic characteristic as well as a potential issue of photonic devices. In large scale optical networks-on-chips (ONoCs), crosstalk noise could cause severe performance degradation and prevent ONoC from communicating properly. The novel contribution of this paper is the systematical modeling and analysis of the crosstalk noise and the signal-to-noise ratio (SNR) of optical routers and mesh-based ONoCs using a formal method. Formal analytical models for the worst-case crosstalk noise and minimum SNR in mesh-based ONoCs are presented. The crosstalk analysis is performed at device, router, and network levels. A general 5 × 5 optical router model is proposed for router level analysis. The minimum SNR optical link candidates, which constrain the scalability of mesh-based ONoCs, are identified. It is also shown that symmetric mesh-based ONoCs have the best SNR performance. The presented formal analyses can be easily applied to other optical routers and mesh-based ONoCs. Finally, we present case studies of mesh-based ONoCs using the optimized crossbar and Crux optical routers to evaluate the proposed formal method. We find that crosstalk noise can significantly limit the scalability of mesh-based ONoCs. For example, when the mesh-based ONoC size, using optimized crossbar, is larger than 8 × 8, the optical signal power is smaller than the crosstalk noise power; when the network size is 16 × 16 and the input power is 0 dBm, in the worst-case, the signal power is -24.9 dBm and the crosstalk noise power is -11 dBm.

Photon shot noise limited detection of terahertz radiation using a quantum capacitance detector

We observed a sweep rate dependence of the quantum capacitance in a single Cooper-Pair box used as the readout of a Quantum Capacitance Detector. A model was developed that fits the data over five orders of magnitude in sweep rate and optical signal power and provides a natural calibration of the absorbed power. We are thereby able to measure the noise equivalent power of the detector as a function of absorbed power. We find that it is shot-noise-limited in detecting 1.5 THz photons with absorbed power ranging from 1 × 10−22 W to 1 × 10−17 W.

QoS-driven multicast routing in sparse-splitting optical networks

This paper investigates the quality-of-service (QoS)-driven multicast routing problem in a sparse-splitting optical network. The main objective is to minimize the total cost of wavelength channels utilized by the light-tree while satisfying required QoS parameters. In this paper, both the optical-layer constraints (e.g., optical signal power) and application-layer requirements (e.g., end-to-end delay and inter-destination delay variation) are considered as the QoS parameters. First, integer linear programming (ILP) formulations to solve the optimal multicast routing problem with the given QoS parameters are presented. Solving the ILP formulations for large-scale networks can easily overwhelm the capabilities of state-of-the-art computing facilities, and hence, a heuristic algorithm is proposed to construct a feasible light-tree that satisfies the required QoS parameters in large-scale networks. Simulation results demonstrate the performance of the proposed heuristic algorithm in terms of the cost of utilized wavelength channels.

Computational Simulation of Ultraviolet ZnO Diode Laser

This article deals with a mathematical technique for the study of functionality of semiconductor laser, by its rate equations, to be used in the simulation of high speed optical systems. We describe the development of numerical simulation model of a p-ZnO laser emitting in UV optical wavelength. A powerful dynamic algorithmical model is used to study the p-ZnO active region waveguide laser. It is based on time dependant rate equations of a quasi two levels system for the population density and time dependant for the pump and optical signal power. The model is sufficient to account for many of the observed dynamics in a single mode semiconductor laser in response to a dynamic drive current, such as relaxation oscillations and frequency chirping.

Optimization of free space optics parameters: An optimum solution for bad weather conditions

Free Space Optics Systems (FSO) is one of the most effective solutions, especially for atmospheric turbulence due to the weather and environment structure. Free space optics system suffers from various limitations. A well-known disadvantage of FSO is its sensitivity on local weather conditions-primarily to haze and rain, resulting in substantial loss of optical signal power over the communication path. The main objective of this article is to evaluate the quality of data transmission using Wavelength Division Multiplexing (WDM) with highlighting several factors that will affect the quality of data transmission. The results of these analyses are to develop a system of quality-free space optics for a high data rate transmission. From the result analysis, FSO wavelength with 1550nm produces less effect in atmospheric attenuation. Short link range between the transmitter and receiver can optimize the FSO system transmission parameters or components. Based on the analysis, it is recommended to develop an FSO system of 2.5Gbps with 1550nm wavelength and link range up to 150km at the clear weather condition of bit-error-rate (BER) 10−9.

Reading lamp-based visible light communication system for in-flight entertainment

This paper explores the use of a reading lamp as an access point for a Visible Light Communications (VLC) downlink channel. We have established an infrared uplink channel based on a network adapter, supporting both a VLC receiver and an infrared emitter. The optical signal power distribution over the passenger area has been also studied using a Monte Carlo Ray-Tracing algorithm. The hardware implementation and testing results are also presented.

Experimental demonstration of high-speed free-space reconfigurable card-to-card optical interconnects

In this paper, we experimentally demonstrate a high-speed free-space reconfigurable card-to-card optical interconnect architecture employing MEMS-based steering mirror arrays for simple and efficient link selection. A printed-circuit-board (PCB) based interconnect module is developed and 3 × 10 Gb/s reconfigurable card-to-card optical interconnect with a bit-error-rate (BER) of ~10(-6) for up to 30 cm is realized using a 250 μm pitch-size micro-lens array. In addition, due to the usage of MEMS steering-mirrors, larger lenses can be employed at the receiver side for collecting stronger optical signal power to increase the achievable interconnect range or to improve the BER performance. Experimental results show that with 1-mm diameter lenses the interconnect distance can exceed 80 cm.

Force-induced optical nonlinearity and Kerr-like coefficient in opto-mechanical ring resonators

This paper demonstrates the optical nonlinearity in opto-mechanical ring resonators that consist of a bus waveguide and two ring resonators, which is induced by the optical gradient force and characterized by the Kerr-like coefficient. Each ring resonator has a free-hanging arc that is perpendicularly deformable by an optical gradient force and subsequently this deformation changes the effective refractive index (ERI) of the ring resonator. The change of the ERI induces optical nonlinearity into the system, which is described by an equivalent Kerr coefficient (Kerr-like coefficient). Based on the experimental results, the Kerr-like coefficient of the ring resonator system falls in the range from 7.64 × 10(-12) to 2.01 × 10(-10) m(2)W(-1), which is at least 6-order higher than the silicon's Kerr coefficient. The dramatically improved optical nonlinearity in the opto-mechanical ring resonators promises potential applications in low power optical signal processing, modulation and bio-sensing.

Bias-free, low power and optically driven membrane InP switch on SOI for remotely configurable photonic packet switches

A small footprint integrated Membrane InP Switch (MIPS) on Silicon-On-Insulator (SOI) is demonstrated for use in all-optical packet switching. The device consists of an optically pumped III-V membrane waveguide of only 100 nm thick, coupled to the underlying SOI waveguide circuit. Because of its limited thickness, the optical confinement in the active layers is maximized, allowing for high extinction ratio of over 30 dB when applying a low power optical pump signal, over the entire C-band. The switch has 400/1300 ps on/off switching times and no measurable pattern dependence or switching related power penalties for a bitrate up to 40 Gb/s, using a switching power of only 2 dBm.

Free Space Optics: Atmospheric Effects & Back U

The Free space optical communication technology tries to fulfill rising need for high bandwidth transmission capability link along with security and ease in installation. Due to their high carrier frequency in the range of 300 THz, it provides highest data rates of 2.5 Gbps which can be increased to 10 Gbps using Wavelength Division Multiplexing (WDM). FSO link is license free, secure, and easily deployable and offers low bit error rate link. These features motivate to use FSO as a solution to last mile access. Along with these attractive features of FSO, a well-known disadvantage of (FSO) is its sensitivity on local weather conditions which results in loss of optical signal power. In this paper we will discuss performance analysis of FSO in different weather conditions..

Performance Analysis of Electrical MMSE Linear Equalizers in Optically Amplified OOK Systems

We analyze the linear equalizers used in optically amplified on-off-keyed (OOK) systems to combat chromatic dispersion (CD) and polarization mode dispersion (PMD), and we derive the mathematical minimum mean squared error (MMSE) performance of these equalizers. Currently, the MMSE linear equalizer for optical OOK systems is obtained by simulations using adaptive approaches such as least mean squared (LMS) or constant modulus algorithm (CMA), but no theoretical studies on the optimal solutions for these equalizers have been performed. We model the optical OOK systems as square-law nonlinear channels and compute the MMSE equalizer coefficients directly from the estimated optical channel, signal power, and optical noise variance. The accuracy of the calculated MMSE equalizer coefficients and MMSE performance has been verified by simulations using adaptive algorithms.

Studying the rate of data transfer through an optical communication channel with a detector based on a photon counter

The rate of data transfer through an optical communication channel with a photon counter based on an avalanche photodiode being used as a detector in this channel is studied. The rate of data transfer through the optical channel is found as a function of the reverse bias voltage of the photodiode, the optical signal power, and the threshold level of detection.

The dressed atom as binary phase modulator: towards attojoule/edge optical phase-shift keying

We use a single 133Cs atom strongly coupled to an optical resonator to induce random binary phase modulation of a near infra-red, ∼ 500 pW laser beam, with each modulation edge caused by the dissipation of a single photon (≈ 0.23 aJ) by the atom. While our ability to deterministically induce phase edges with an additional optical control beam is limited thus far, theoretical analysis of an analogous, solid-state system indicates that efficient external control should be achievable in demonstrated nanophotonic systems.

Sensitivity of High-Speed Lightwave System Receivers Using InAlAs Avalanche Photodiodes

Calculations based on a rigorous analytical model are carried out to compare the sensitivity of optical receivers that use InP and In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As avalanche photodiodes (APDs). The model includes the effects of intersymbol interference, tunneling current, avalanche noise and its correlation with the stochastic avalanche duration, dead space, and transimpedance amplifier noise. For a 10-Gb/s system with a bit-error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> , the optimum receiver sensitivity predicted for In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As and InP APDs is -28.6 and -28.1 dBm, respectively, corresponding to a reduction of 11% in optical signal power for receivers using In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As APDs. Thus, considering overall receiver sensitivity, the improvement offered by In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As APDs over InP is modest.

Impact of GVD and SPM on the Performance of DS-OCDMA

The bit error rate (BER) performance of direct sequence optical code division multiple access with cascaded optical amplifiers is analytically investigated in presence of fiber group velocity dispersion (GVD) and self phase modulation (SPM). Super Gaussian-shaped optical orthogonal codes are employed as address sequence for intensity modulation direct detection technique. The signal to noise power ratio for the proposed system is calculated on account of receiver, optical amplifier, and multiuser access interference noises. The system performance is determined as a function of optical signal power, code length, code weight, number of simultaneous users, fiber length, and order of Super Gaussian. The power penalty suffered by the system is evaluated at BER of 10-9. The numerical results show that the BER performance of the proposed system is highly dependent on the input signal power, bit rate, fiber length, and shape of the chip. It is found that the performance of the proposed system can be improved significantly in presence of GVD and SPM using Gaussian shaped chip.

Influence of optical simple pulse coding on the Brillouin optical time domain analyzer based on bi-directional Raman amplification

We report the influence of optical simple pulse coding on the Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification. This method is proposed to reduce the frequency uncertainty in long-distance BOTDA under higher spatial resolution. The experimental characterization of 49.6 km temperature sensing with a measurement accuracy of ~1 ℃ under ~2.5 m spatial resolution over the whole length of sensing fiber is demonstrated. The signal-to-noise ratio (SNR) and the optical signal power distribution characteristics of the system are studied experimentally in this paper.

A Study for Stable Measurement of Optical Signal Power in an Optical Fiber Using an Improved Optical Fiber Identifier

Optical signal power estimation utilizing an improved optical fiber identifier is experimentally evaluated. In order to realize fine measurement, a mechanical bend adjuster and fiber guides attached to both side of the identifier are introduced. The former is useful for stabilizing the identifier operation in consequence of well controlled bend of the test fiber. The latter is effective for eliminating influence of fiber handling. As a result, standard distribution of the measured optical power of less than 0.16dB is obtained, which seems to be enough small for the field use.

Brillouin optical time domain analyzer based on bi-directional Raman amplification

We report a Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification in this paper. With the bi-directional Raman amplification, the loss of the optical fiber and the depletion of Brillouin pump light can be compensated for efficiently, hence the measurement resolution is improved at the end of the optical fiber significantly. The detected signal is stable along the whole length of the sensing fiber, free from the spectral broadening caused by the modulation instability and the problem of uneven ness of detected signals of the conventional BOTDA. The Raman amplification is very useful for enhancing the measurement accuracy. With the bi-directional Raman pump, a temperature resolution of 0.6 ℃ was achieved over a sensing distance of 50 km with a 50 m spatial resolution. The signal-to-noise ratio and the optical signal power distribution characteristics of the system have been studied by experiment.

Proposal of super low power consumption detector for emergency communication downstream system in FTTH

This paper discusses an optical access system that enables emergency voice communication when a power failure occurs in a user's house, and we also propose a super low power consumption detector that consists entirely of passive devices. And we present applied techniques that comprise sub-carrier multiplexing for user multiplexing/demultiplexing and a new passive detector for signal regeneration driven solely by the transmitted optical signal power. Then we confirm the feasibility of the system experimentally by using a prototype detector that has 8-channel selectivity. We report the realization of the intended detector functions that we achieved by back-to-back simulated voice signal regeneration.