Coherence Multiplexing Research Articles

Corrigendum: A self-reference interference sensor based on coherence multiplexing

Corrigendum: A self-reference interference sensor based on coherence multiplexing

A Self-Reference Interference Sensor Based on Coherence Multiplexing.

Interferometry has been widely used in biosensing due to its ability to acquire molecular affinity and kinetics in real-time. However, interferometric-based sensors are susceptible to environmental disturbances, including temperature and non-specific binding of target molecules, which reduces their detection robustness. To address this shortcoming, this paper proposes a self-referencing interference sensor based on coherence multiplexing to resist environmental disturbances. The proposed sensor can address temperature and non-specific binding, but it is not limited only to these types of disturbances. In the proposed sensor design, each sensor signal is encoded using a specific optical path difference determined by the optical thickness of a sensor chip. In addition, two sensor signals for disturbances tracking and biomolecule detection are detected simultaneously without additional cost to the second spectrometer and then differenced to achieve real-time self-reference. The temperature fluctuations experiments and specific binding experiments of protein A to IgG are performed to verify the performance of the proposed sensor. The results demonstrate that the proposed sensor can eliminate non-specific binding and temperature disturbances in real-time during biomolecule detection, achieving higher detection robustness. The proposed sensor is suitable for applications that require large-scale testing of biomolecular interactions, such as drug screening.

Ultra-long (290 km) remote interrogation sensor network based on a random distributed feedback fiber laser.

In this work, an interferometric sensor has been interrogated 290 km away from the monitoring station, reaching the longest distance in fiber optic sensing up to date. This has been attained by employing a double-pumped random distributed feedback fiber laser as the light source for a fiber optic low-coherence interferometry scheme. Additionally, the capability of the system to achieve coherence multiplexing for ultra-long range measurements (up to 270 km) has been proved, without presenting crosstalk between the sensors. The use of coherence multiplexing together with a random distributed feedback fiber laser addresses two of the main limitations of long-range sensing setups: their limited multiplexing capability and the need to reach the maximum monitoring distance.

Coherence-multiplexed, label-free biomolecular interaction analysis

This Letter describes an interferometric technique based on the principle of coherence multiplexing for multichannel, label-free biosensing applications. Multiple biosensors can be interrogated simultaneously with a single spectral-domain, phase-sensitive interferometer by coding the individual sensograms in coherence-multiplexed channels. The experimental results demonstrate the multiplexed quantitative biomolecular interaction of antibodies binding to antigen-coated functionalized biosensor chip surfaces. The described technique also applies to a variety of other distributed and multiplexed sensing applications besides biosensing.

Performance of RF Signal Transmission Over Coherence Multiplexing Systems

Coherence multiplexing (CM) technique for analog signal transmission was proposed but has not been studied comprehensively. In this paper, we investigate RF signal transmission over CM systems (RF over CM) in theory, simulation, and experiments. The transmission performances are analyzed using a single-tone RF signal, and theoretical SNR is developed. It is found that RF over CM systems are limited in performance by both beat noise and fiber chromatic dispersion due to the use of a broadband light source. A broader light source improves the system performance only if fiber dispersion of the system is negligibly small. Otherwise, the performance is seriously degraded by fiber dispersion. The theoretical model is verified experimentally. Finally, an orthogonal frequency division multiplexing ultra-wideband wireless signal over a CM system is verified. It is concluded that CM systems cannot be used for high-frequency RF signal transmission.

Quasi-distributed sensing network based on coherence multiplexing and spatial division multiplexing for coal mine security monitoring

A low-cost fiber Bragg grating (FBG) sensing system for coal-mine security monitoring is proposed in this paper. Based on the coherence multiplexing (CM) and spatial division multiplexing (SDM) techniques, this hybrid sensing network can support more than 40 sensors for quasi-distributed detection. It is demonstrated experimentally that the multiplexed sensing signal of each sensor can be clearly distinguished by an optical low-coherence reflectometry (OLCR). Methane concentration is detected with maximum sensitivities of an intensity variation of 10.92% and a concentration variation of 1%, using a well-designed sensor structure. Strain and temperature are also detected by this system, which also exhibits good results in the experiment.

Coherence-Multiplexed Optical RF Feeder Networks

An optical RF feeding system for wireless access is proposed, in which the radio access points are distinguished by means of coherence multiplexing (CM). CM is a rather unknown and potentially inexpensive optical code division multiple access technique, which is particularly suitable for relatively short-range applications with moderate transmission bandwidth requirements. Subcarrier multiplexing (SCM) can possibly be used on top of CM, either as single-channel or multichannel SCM. The performances of the resulting distribution networks are analyzed, incorporating the effect of chromatic dispersion, optical beat noise, shot noise, thermal noise, and-in the case of multichannel SCM-intermodulation distortion. The results of the analyses are illustrated by using numerical examples, based on the IEEE 802.11b standard for wireless LAN.

Coherence Multiplexing of Distributed Sensors Based on Pairs of Fiber Bragg Gratings of Low Reflectivity

A coherence multiplexing scheme for distributed sensors based on fiber Bragg grating (FBG) pairs is introduced. Each pair of identical FBGs forms a Fabry-Perot (FP) interferometer (FPI) and induces an additional optical path difference (OPD) that is proportional to the center-to-center interval between the two FBGs (one for sensing and the other for reference). The interference intensity reaches its maximum when the FPI-induced OPD is compensated by scanning one arm of a Michelson interferometer to a certain position. The variation of the measurand induces a mismatch between the central reflection wavelengths of two FBGs and consequently reduces interference intensity. To separate the interferometric signals for demultiplexing, the intervals between the two FBGs are preset to different values for different sensors. In order to improve the multiplexing ability of the system and reduce the crosstalk among the sensors, we use gratings of low reflectivity. Temperature sensing is demonstrated to show the high sensitivity (-1.92%/degC) and low crosstalk of our distributed sensing system.

Quasi-Distributed Absorption Sensing System Based on a Coherent Multiplexing Technique

A coherence multiplexing scheme for quasi-distributed absorption sensors is introduced. The sensing units are designed with different optical path lengths, and the signals from the inline sensing array can be demultiplexed by a path-scanning Michelson interferometer. Intracavity absorbance in each unit can be deduced from the corresponding signal and the signals of the previous sensing units

Coherence Multiplex System Topologies

Coherence multiplexing is a potentially inexpensive form of optical code-division multiple access, which is particularly suitable for short-range applications with moderate bandwidth requirements, such as access networks, LANs, or interconnects. Various topologies are known for constructing an optical transmission system in which several channels are coherence-multiplexed in one optical fiber. In this paper, the parallel array, the intrinsic reference ladder (IRL), and the discontinuous series system topologies will be further considered and compared with respect to code orthogonality requirements, theoretical performance, and some practical implementation aspects. A modification to the IRL system is proposed, resulting in a significant improvement in the theoretical performance.

Multichannel Temperature Sensing by Differential Coherence Multiplexing

The method of differential coherence multiplexing is demonstrated for multichannel temperature sensing. The idea of the method is to introduce into the conventional coherence-multiplexed sensor array a chain of stable etalon interferometers connected to the interrogating interferometer in parallel to the sensor chains. Optical delays of sensor interferometers are obtained from the phase shift of the interference maximums of the etalon and sensor coherence peaks. The technique is inherently insensitive to low-frequency phase noise in the interrogating interferometer and does not require any means for measurement of the optical path difference of the interrogating interferometer. Multiplexed temperature sensing is demonstrated in a chain of four extrinsic Fabry–PÉrot temperature sensors in the range of 400 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ hboxC$</tex> with a root-mean-square noise of 0.005 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ hboxC$</tex> . Theoretical estimations show a possibility of increasing the dynamic range to the units of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10^5$</tex> .

Balanced Optical Phase Diversity Receivers for Coherence Multiplexing

Coherence multiplexing (CM) is a specific form of CDMA that is particularly suitable for optical communication systems for medium data rates and small distances. By virtue of its potentially simple implementation, it is particularly useful for bridging the last mile to the subscribers, which is an issue that is receiving considerable attention in optical communication research nowadays. The receivers in coherence multiplex systems published so far were all based on either self-homodyne or self-heterodyne detection. Both solutions are rather complicated, and therefore, expensive. In this paper, a new CM receiver concept is proposed, based on optical phase diversity detection. Theoretical performance results are derived for several modulation formats and receiver structures.

Analysis of Optical Coherence Multiplexing Networks for Satellite Communication

Free-space optical communication between satellites networked together can enable a high data rate between the satellites. Coherence multiplexing (CM) is an attractive technique for satellite networking due to its ability to cope with the asynchronous nature of communication traffic and the dynamic changes taking place in the satellite constellation. The use of optical radiation for intersatellite links creates very narrow beam divergence angles. Due to the narrow beam divergence angle, the vibration of the pointing system, the movement of the satellite, and the large distance between them the pointing from one satellite to another is a complicated task. The vibration of the pointing system is caused by two stochastic fundamental mechanisms: 1) tracking noises created by the electrooptic tracker and 2) vibrations created by internal satellite mechanical mechanisms and external environments. We derive mathematical models of signal, noise, the approximate signal-to-noise ratio, and the approximate bit-error rates of optical communication satellite networks as functions of the system's parameters, the number of satellites, and the vibration amplitude for frequency-shift keying coherence multiplexing (FSK-CM). Based on these models, we can calculate the negative impact of both the number of satellites and the optical terminal vibration on the system's performance.

Free-space supercontinuum coherence data packets multiplexing and demultiplexing for ultrafast laser communication

The multiplexing and ultrafast multichannel spatially-resolved demultiplexing of supercontinuum (SC) coherence data packets using a coherent time-to-space conversion is proposed as a novel approach for free-space ultrafast laser communication. The femtosecond coherence time of spectrally extended SC pulses is used on the femtosecond time scale without the need for femtosecond pulses. The proposed scheme for data packets coherence multiplexing and demultiplexing is experimentally demonstrated. This SC approach has the capability of processing multigigabits per second information for free-space laser communication applications.

Multiplexed fiber Fabry–Perot temperature sensor system using white-light interferometry

A novel monitoring system for a fiber Fabry-Perot interferometer (FFPI) temperature sensor has yielded a resolution of 0.013 degrees C (0.0025 fringe). Light from a broadband source passes through a scanned Michelson interferometer and is reflected from a FFPI to produce a fringe pattern, the temporal position of which is proportional to a change in the optical length of the fiber interferometer. A second Michelson interferometer with a distributed-feedback laser source is used to correct for variations in the translation rate of the motor-driven scanning mirror. Coherence multiplexing of three such sensors has also been demonstrated.

A simple broad-band coherence multiplexed optical access network and its scalability

This paper proposes a novel and simply configured broad-band optical access network that uses coherence multiplexing (CM) and half-duplex bidirectional transmission. It allows the on-demand use of broad bandwidth on existing fiber-to-the-home (FTTH) access lines. The design of the proposed CM network considers degradation factors in CM systems. This paper introduces two analyses. The first one is a numerical simulation to optimize the tradeoff between available user number and fiber dispersion degradation, and the second estimates acceptable access-line loss in the network. These analyses show that 16 users/spl times/100 Mb/s (or 12 users/spl times/155 Mb/s) bandwidth Is possible on a standard single-mode fiber access line whose loss and length are under 9 dB and 10 km (and 7 km), respectively. The feasibility and scalability of the proposed network are verified by an experiment in which eight-channel 155-Mb/s half-duplex optical packet transmission is successfully demonstrated on a 7-km standard fiber access line with bit error rates better than 1/spl times/10/sup -9/. This study shows that the capacity of existing FTTH access lines that employ star couplers can be significantly enhanced.

Coherence multiplexing of fiber-optic pressure and temperature sensors based on highly birefringent fibers

In this paper, we present several coherence-based configurations of sensor systems that have been designed and studied specifically for multiplexing of white-light interferometric pressure and temperature transducers based on highly birefringent optical fibers. The first discussed is a serial system that may be composed of up to four pressure (range 0-20 MPa) and temperature (range -50/spl deg/C-+50/spl deg/C) sensors powered by a single broadband laser source. An electronically scanned interferometer based on a Wollaston prism with a step-delay line and a CCD array was used as a decoding unit. To increase the number of multiplexed sensors we also proposed a mixed serial-parallel configuration in which two serially connected sensors for measuring pressure and temperature are further arranged in parallel branches powered by several independent sources. The absolute system accuracy is about 0.5% of full scale. In addition to the full characterization of all multiplexed pressure sensors against a primary pressure standard, system response to fast temperature changes, to connecting additional cables, to input-output replacing, and to exchanging sources is also presented.

Noise in coherence-multiplexed optical fiber systems

We present measurements, in good agreement with theory, of the noise power spectral density at the outputs of a coherence-multiplexed system employing a low-coherence source. We investigate correlations in the noise between outputs and confirm that differential detection can be used to improve the signal-to-noise ratio of sensor and communication systems based on coherence multiplexing.

Capacity of coherence-multiplexed CDMA networks

We determine the capacity and numbers of users that can be supported by CDMA networks that use coherence multiplexing. The analysis takes into account reduced optical beat noise due to differential detection of the decoder outputs. The analysis also includes the effect of fibre dispersion and shows that there is an optimum source linewidth for a given link length and user bit rate. We confirm that the capacity is severely restricted by optical beat noise. However, our calculations show that performances achievable may be adequate for certain local area and access network type applications. For example, at 40 Mb/s per user a maximum of 50 users can be supported over 12 km. We compare our calculations with the measured performance of our recent network demonstration and find good agreement.

Hybrid coherence multiplexing/coarse wavelength-division multiplexing passive optical network for customer access

We propose a passive optical network for customer access based on a hybrid coherence multiplexing/coarse wavelength-division multiplexing (WDM) technique. Coherence multiplexing provides asynchronous multichannel transmission, and coarse WDM provides bidirectional transmission. A cost-shared superfluorescent source is used for downstream transmission, and inexpensive lightemitting diodes are employed for upstream transmission. Asynchronous two channel transmission at 40 Mb/s per channel is demonstrated for both upstream and downstream. Our experiment indicates that upstream and downstream aggregate bit rates of 640 Mb/s are feasible based on current commercially available components.