GaInNAs microspheres for wavelength division multiplexing

We report on the use of a frequency-rnodulated continuous wave (FMCW) technique for multiplexing fiber Bragg grating (FBG) sensors. This technique is based on the modulation of light intensity from a broadband source by a linear swept-frequency RF carrier. Signals from the FBG sensors located at different positions in an array are separated in frequency-domainand demodulated using a tunable optical filter. The potential and limitation of the technique are discussed. A 3-sensor FMCWmultiplexed FBG array of parallel topology and a 6-sensor hybrid FMCWIWDM system were experimentally demonstratedwith -30 dB crosstalk between sensors and 2 tc resolution in terms ofroot-mean-square strain value.Keywords: optical fiber sensors, fiber Bragg grating sensors, frequency-modulated continuous wave, strain measurements. 1. Introduction Fiber Bragg gratings (FBGs) have been identified as an enabling technology for a variety of applications from aerospace, marine, to civil engineering structural monitoring, from medical, nuclear power industry, to electrical power industry[1]. In many applications such as condition monitoring of civil structures such as highways, bridges and buildings. FBG sensorsneed to be multiplexed in order to achieve quasi-distributed measurement and to reduce cost per sensing point to compete withconventional electrical or optical sensors.The most popular technique for multiplexing FBG sensors is the wavelength division multiplexing (WDM) technique[2,3]. The maximum sensor number that can be multiplexed using the WDM technique is determined by the ratio ofthe sourcespectral width over the spacing between the Bragg wavelengths of the FBGs. For applications requiring a larger multiplexinggain, a combination ofthe WDM and time-division multiplexing (TDM) techniques [3] may be used.A TDM system employs a pulsed or gated CW source to illuminate gratings in sequence as the pulse travels along thefiber, the reflected signals from the gratings are separated in time domain [4]. The physical separation between the gratings isdetermined by the input pulse width. A fast time-gated photodetector can be used to select the signal from an individual grating

To develop polarization-insensitive semiconductor optical amplifier (SOA) gates into more efficient and functional optical components by using hybrid integration with a planer lightwave circuit (PLC) platform, vertical tapered spot-size converters were integrated into a SOA gate with a narrow mesa-stripe structure of submicrometer width leading to low coupling loss (2.6 dB). Very-low polarization dependence of gain ( 30 dB) were achieved in a wide wavelength range (40 nm). High-speed (<1 us) gate operation was also demonstrated. These results indicate that the spot-size converted SOA integrated on a PLC platform will perform well in wavelength-division-multiplexing (WDM) applications.

Wavelength division multiplexing (WDM) systems are widely deployed in high-capacity long-haul transmission systems. They can provide cost-effective additional capacity on fibers overloaded by the increase in data traffic. Current WDM systems are used mainly for point-to-point transmission links. Next generation WDM technologies are expected to provide full functionality at both the system and network levels. Next generation WDM system will require many optical components, including optical filters, add/drop multiplexers, circuit switches and wavelength converters. Optical components using planar lightwave circuits (PLCs) are now widely used in WDM systems. Arrayed waveguide gratings (AWGs), in particular, play an important role in current WDM systems. In the next generation system, optical components using PLCs are expected to provide many functions that counterparts cannot. In this paper, we will describe the current and future WDM components using PLCs, focusing on AWGs and switchable add/drop filters.

An optical fiber sensor system with multichannel fiber Bragg gratings (FBGs) is proposed. The gratings are designed and fabricated by phase sampling technique within strongly chirped phase masks. The sensing application can be realized at multiple points through wavelength division multiplexing (WDM) technique. It means that the different point can be monitored by different gratings, which occupies different wavelength region, according to the central pitch and chirp coefficient of phase masks. The heating position with high resolution can be analyzed through three corresponding channel shifts in the multichannel profile. In our experiment, the two multichannel gratings with channel spacing of 0.8 and 1.6 nm, respectively, are fabricated and used to sensing in two points. At last, the 400 μm accuracy of localizing the heating position is achieved.

Measurement device independent quantum key distribution (MDI QKD) has attracted growing attention for its immunity to attacks at the measurement unit, but its unique structure limits the secret key rate. Utilizing the wavelength division multiplexing (WDM) technique and reducing error rates are effective strategies for enhancing the secret key rate. Reducing error rates often requires active feedback control of wavelengths using precise external references. However, for a multiwavelength laser, employing multiple references to stabilize each wavelength output places stringent demands on these references and significantly increases system complexity. Here, we demonstrate a stable, wavelength-tunable multiwavelength laser with an output wavelength ranging from 1270 to 1610 nm. Through precise temperature control and stable drive current, we passively lock the laser wavelength, achieving remarkable wavelength stability. This significantly reduce the error rate, leading to an almost doubling of the secret key rate compared to previous experiments. Furthermore, the exceptional wavelength stability offered by our multiwavelength laser, combined with the WDM technique, has further boosted the secret key rate of MDI QKD. With a wide wavelength tuning range of 5.1 nm, our multiwavelength laser facilitates flexible operation across multiple dense wavelength division multiplexing channels. Coupled with high wavelength stability and multiple wavelength outputs simultaneously, this laser offers a promising solution for a high-rate MDI QKD system.

In all-optical Wavelength Division Multiplexing (WDM) technique, data contention is an inevitable challenge. For reliable data transmission, contention resolution is very much essential. There are different contention resolution techniques that are used in optical WDM network. In this paper, wavelength converter is used for contention resolution in optical WDM network. Here Semiconductor Optical Amplifier (SOA) is used to implement wavelength converter based on a special third-order nonlinear susceptibility phenomenon of silica fiber, called Four-Wave Mixing (FWM) technique. Realization of wavelength converter is done for two different sets of WDM networks. Performance of the wavelength converter was estimated in terms of number frequencies generated, number of new wavelength generated, its corresponding power, etc. Result shows that four-wave mixing is a very effective technique to generate new wavelengths at the output to overcome the problems due to contention in an optical WDM network. OptiSystem of Optiwave is used to design schematic layout for the wavelength converter using SOA.

Recently, photonic networks based on wavelength division multiplexing (WDM) systems have developed considerably in response to the explosive growth of the Internet. Devices with novel functions are required for photonic networks, and planar lightwave circuits (PLCs) are being considered to meet this need. This paper reports recent progress on PLC- type devices with advanced functions developed for the photonic networks. We describe fabrication techniques and device applications for silica and silicone polymer based PLC technologies.

Silica-based planar lightwave circuit (PLC) devices are starting to be introduced into commercial optical communication systems. PLC devices such as optical splitters, wavelength-insensitive coupler (WINC) arrays, and hybrid- integrated wavelength-division-multiplexing (WDM) transceivers are used to construct cost effective optical access systems. In trunk lines, on the other hand, arrayed-waveguide gratings (AWG) are employed for dense WDM systems to increase the transmission capacity. This paper reviews the current status and recent progress on these practical PLC devices.

An FSO system can provide a solution to the problem of last-mile connectivity while also offering a high degree of security and a large capacity for high-speed information transmission, making it a versatile and powerful option for data communication. Despite the above-mentioned advantages, some factors have to be considered when establishing long-range communication, one such factor is atmospheric turbulence (haze, light fog, moderate fog) which degrades the ideal characteristics of the FSO channel and causes a loss in the signal’s power. This loss of power during transmission can be improved by using suitable amplifiers (hybrid optical amplifier, semiconductor optical amplifier) to provide better performance. The next-generation networks must be capable of supporting a significant amount of backhaul data traffic, accommodating a larger number of users, and increasing channel capacity to meet the demands of modern data communication. By implementing wavelength division multiplexing (WDM) and free space optical (FSO) communication techniques, the capacity of the channel can be increased, and more users can be accommodated. The maximum link length offered by the FSO–WDM system has been investigated with hybrid optical amplifier considering the minimum bit error rate, which can provide reliable and long-distance communication.

Evolution of the optical fiber systems is currently seeing the general acceptance of wavelength division multiplexing (WDM) as the best mechanisms in increasing the transmission capacity of fiber optics. However, there are problems associated with WDM technique such as wavelength drifts, wavelength inventory and management and stringent demultiplexing requirements that tend to either limit the system's performance or increase the cost. Also, it is difficult to construct a WDM system for a dynamic set of multiple users because of the significant amount of coordination among the nodes required for successful operation. Optical Code Division Multiplexing (OCDM) provides some solutions to the problems. This simple technique operates on a single broadband light source, thus alleviating the problems and cost of handling multiple lasers as in WDM systems. This paper elaborates the working principle of the OCDM technique and provides some proofs on its viability.

A 20Gb/s polarization-insensitive all-optical wavelength switching system for high-speed free-space optical communication (FSO) network is experimentally demonstrated All-optical wavelength conversion (AOWC) is implemented using four-wave mixing (FWM) by highly-nonlinear fiber (HNLF). In the experimental setup, a simple actively mode-locked fiber ring laser (AML-FRL) with repetition frequency from 1 to 15 GHz is used to generate eight 2.5Gb/s tributary signals, which are multiplexed into one 20Gb/s optical data stream. At the receiver, the 20 Gb/s OTDM data stream is demultiplexed down to 2.5 Gb/s via a polarization-insensitive FWM scheme. The whole space communication distance is over 10 meters in building hallway. The experimental results show that this system can stably run over 24 hours at 10-9 BER level, thus the proposed architecture can work at higher rate with wavelength-division multiplexing (WDM) and high order modulation schemes.

Silica-based planar lightwave circuits (PLC) provide various important devices for both optical wavelength division multiplexing (WDM) networks and optical access networks. This paper is an overview of recent progress in PLC technology including optical power splitters, arrayed-waveguide gratings, thermo-optic switches, and hybrid integrated PLCs.

Planar lightwave circuits (PLCs) are waveguide devices that integrate fiber-matched optical waveguides on Silicon or glass substrate to provide an efficient means of interaction for the guided-wave optical signals. The most prominent feature of the silica waveguides is their simple and well defined waveguide structures. This allows us to fabricate multi-beam or multi-stage interference devices such as arrayed-waveguide gratings and lattice-form programmable dispersion equalizers. PLCs provide various important and functional devices for optical wavelength division multiplexing (WDM), time division multiplexing (TDM) systems and subscriber networks. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add/drop multiplexers, programmable dispersion equalizers and hybrid optoelectronics integration technologies.

A simple theory for the crosstalk in multichannel wavelength-division multiplexing (WDM) communication systems caused by the cross gain saturation in semiconductor optical amplifier (SOA) is developed. It is shown that increasing the carrier recombination lifetime while reducing the differential gain in the SOA greatly mitigates the crosstalk. An SOA using type-II quantum wells with reduced recombination probability is designed, and its characteristics are numerically modeled for a number of different WDM systems. It is shown that when used as a preamplifier or in local/metro networks with a small number of amplifiers, error-free transmission can be achieved with the type-II SOA.

Optical fibers can be used as promising sensors in smart structures due to their novel characteristics. This paper presents a wavelength division multiplexing (WDM) technique in order to improve the application capacity of single reflective grating based fiber optic sensors to monitor large industrial structures at multiple points. The models are appropriate for the general extrinsic fiber optic sensors such as the grating panel-based fiber optic sensor. The manufactured WDM fiber optic sensor system was examined in order to demonstrate the feasibility for two parameter detections at two points using mirror mounted grating based fiber optic sensor. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.