Optical fiber channels are used as media to transfer the information globally. This paper presents an implementation of a novel procedure using which a secured communication between two parties can be carried out using polarized beam of light over an optical fiber. The paper presents the experimental results obtained of the procedure in the lab environment and a security analysis of the same. It is observed that polarization state of a light pulse cannot be retained as it travels over an optical fiber because of the birefringence phenomenon. Multiple environmental factors such as pressure, vibration, temperature, etc. also add a non-linearity to the birefringence of an optical fiber leading towards an unpredictable polarization state changes over the course of an optical fiber. The proposed procedure helps the receiving party to successfully retrieve the data in the form of a polarization state transmitted by the sending party without having any knowledge about the state of polarization at the transmitting end. The paper also explains an added layer of security the procedure provides to the communicating parties to make it difficult for an adversary to fetch the data being transferred. The proposed system does not depend on the wavelength of the light being used, nor does it depend upon the type of the optical fiber used for the communication. Using this procedure, multiple bits of secured information can be sent over an optical fiber in a single polarized pulse and retrieved at the receiving end, also known as <i>Polarization Shift Keying</i>.
We describe a layer-1-based intrusion detection system for fiber-optic–based networks. Layer-1-based intrusion detection represents a significant elevation in security as it prohibits an adversary from obtaining information in the first place (no cryptanalysis is possible). We describe the experimental setup of the intrusion detection system, which is based on monitoring the behavior of certain attributes of light both in unperturbed and perturbed optical fiber links. The system was tested with optical fiber links of various lengths and types, under different environmental conditions, and under changes in fiber geometry similar to what is experienced during tapping activity. Comparison of the results for perturbed and unperturbed links has shown that the state of polarization is more sensitive to intrusion activity than the degree of polarization or power of the received light. The testing was conducted in a simulated telecommunication network environment that included both underground and aerial links. The links were monitored for intrusion activity. Attempts to tap the link were easily detected with no apparent degradation in the visual quality of the real-time surveillance video.
This paper proposes and analyzes the potential of a multi-photon tolerant quantum communication protocol to secure satellite communication. For securing satellite communication, quantum cryptography is the only known unconditionally secure method. A number of recent experiments have shown feasibility of satellite-aided global quantum key distribution (QKD) using different methods such as: Use of entangled photon pairs, decoy state methods, and entanglement swapping. The use of single photon in these methods restricts the distance and speed over which quantum cryptography can be applied.<p> </p> Contemporary quantum cryptography protocols like the BB84 and its variants suffer from the limitation of reaching the distances of only Low Earth Orbit (LEO) at the data rates of few kilobits per second. This makes it impossible to develop a general satellite-based secure global communication network using the existing protocols. The method proposed in this paper allows secure communication at the heights of the Medium Earth Orbit (MEO) and Geosynchronous Earth Orbit (GEO) satellites. The benefits of the proposed method are two-fold: First it enables the realization of a secure global communication network based on satellites and second it provides unconditional security for satellite networks at GEO heights. The multi-photon approach discussed in this paper ameliorates the distance and speed issues associated with quantum cryptography through the use of contemporary laser communication (lasercom) devices. This approach can be seen as a step ahead towards global quantum communication.
This paper proposes a quantum secure communication protocol using multiple photons to represent each bit of a message to be shared. The multi-photon tolerant approach to quantum cryptography provides a quantum level security while using more than a single photon per transmission. The protocol proposed is a multi-stage protocol; an explanation of its operation and implementation are provided. The multi-stage protocol is based on the use of unitary transformations known only to Alice and Bob. This paper studies the security aspects of the multi-stage protocol by assessing its vulnerability to different attacks. It is well known that as the number of photons increases, the level of vulnerability of the multi-stage protocol increases. This paper sets a limit on the number of photons that can be used while keeping the multi-stage protocol a multi-photon tolerant quantum secure method for communication. The analysis of the number of photons to be used is based on the probability of success of a Helstrom discrimination done by an eavesdropper on the channel. Limiting the number of photons up to certain threshold per stage makes it impossible for an eavesdropper to decipher the message sent over the channel. The proposed protocol obviates the disadvantages associated with single photon implementations, such as limited data rates and distances along with the need to have no more than a single photon per time slot. The multi-stage protocol is a step toward direct quantum communication rather than quantum key distribution associated with single photon approaches.
This paper presents the concept and implementation of a <i>Braided Single-stage Protocol </i>for quantum secure
communication. The braided single-stage protocol is a multi-photon tolerant secure protocol. This multi-photon tolerant
protocol has been implemented in the laboratory using free-space optics technology. The proposed protocol capitalizes
on strengths of the three-stage protocol and extends it with a new concept of braiding. This protocol overcomes the
limitations associated with the three-stage protocol in the following ways: It uses the transmission channel only once as
opposed to three times in the three-stage protocol, and it is invulnerable to man-in-the-middle attack. This paper also
presents the error analysis resulting from the misalignment of the devices in the implementation. The experimental
results validate the efficient use of transmission resources and improvement in the data transfer rate.
This paper introduces an m-ary version of the Three-stage Quantum Cryptography protocol. The three-stage protocol was first proposed in 2006 and implemented in 2012. The m-ary version of the three-stage protocol proposed in this paper results in enhanced data transfer between a sender Alice and a receiver Bob since each pulse carries more than one bit of information. An experimental realization of the m-ary three-stage protocol is also reported in this paper. The implementation has used free-space optics as the transmission medium and passive optical components controlled through LabView. Furthermore, analytical results that address the impact of the noise factor and its trade-off with data rate are presented. This analysis includes a study of the probability of errors and channel capacity variations in terms of the noise variance factor for the m-ary three-stage protocol using two, four and eight levels. Limits within which the m-ary three-stage protocol can be used with higher performance efficiency compared to its original version counterpart are set.
We present new results on cryptography and system state estimation using polarization states of photons. Current
quantum cryptography applications are based on the BB84 protocol which is not secure against photon siphoning
attacks. Recent research has established that the information that can be obtained from a pure state in repeated
experiments is potentially infinite. This can be harnessed by sending a burst of photons confined to a very narrow time
window, each such burst containing several bits of information. The proposed method represents a new way of
transmitting secret information. While polarization shift-keying methods have been proposed earlier, our method is
somewhat different in that it proposes to discover the polarization state of identical photons in a burst from a laser
which codes binary information. We also present results on estimating the state of a system based on the polarization of
the received photons which can have applications in intrusion detection.
Generation of chaos from nonlinear optical systems with an optical or electronic feedback has been studied for several
years. Such chaotic signals have an important application in providing secure encryption in free-space optical
communication systems. Lyapunov exponent is an important parameter for analysis of chaos generated by a nonlinear
system. The Lyapunov exponent of a class of a nonlinear optical system showing a nonlinear transfer characteristics of
the form sin<sup>2</sup>(x) is determined and calculated in this paper to understand the dependence of the chaotic response on the
system parameters such as bias, feedback gain, input intensity and initial condition exciting the optical system. Analysis
of chaos using Lyapunov exponent is consistent with bifurcation analysis and is useful in encrypting data signal.
Generation of chaos from acousto-optic modulators with an electronic feedback has been studied for several years. Such chaotic signals have an important application in providing secure encryption in free-space optical communication systems. Lyapunov exponent is an important parameter for analysis of chaos generated by a nonlinear system. The Lyapunov exponent of an acousto-optic system is determined and calculated in this paper to understand the dependence of the chaotic response on the system parameters such as bias, feedback gain, input intensity and initial condition exciting the cell. Analysis of chaos using Lyapunov exponent is consistent with bifurcation analysis and is useful in encrypting data signals.
Propagation of a monochromatic Gaussian beam through a stack of alternating layers of positive-refractive-index
dielectrics and negative-refractive-index metamaterials is analyzed using paraxial ray-optics approach.
Expressions for the change of the spot-size of the Gaussian beam are derived. Sensors for measuring parameters
that affect the thickness or refractive index of the metamaterials can be developed based on the change of the
In this paper we describe a free-space optics (FSO) based mobile sensor network that is not subject to RF interference
common to wireless sensor networks. FSO-based mobile sensor networks can potentially be used in applications where
security of communication, including freedom from susceptibility to jamming, is important. The design of nodes
containing multiple transceivers each composed of an LED and an angle-diversity array of identical photo detectors is
discussed in this paper. Depending on the number of photodetectors in the array and the angular field of view of each
photo detector we may obtain an increase in the signal to noise ratio of the overall optical communication system.
Transmission and reflection spectra of periodic and random stacks comprising positive index materials and
metamaterials have been extensively studied. In this paper we investigate the effectiveness of periodic stacks of
PIM/NIM for use as a sensor. The transfer matrix method is used to find the transmittance and reflectance.
Differences between the zero average refractive index bandgap and Bragg bandgap are illustrated. It is shown how
these bandgaps can be used as the basis for designing sensors with minimal cross-sensitivity.
We discuss the design of an acousto-optic cell based free space optical communication link where the data
beam is made secure through chaos encryption. Using external signal modulation of the diffracted light from
a hybrid acousto-optic cell chaos (or directly via incorporation in the sound-cell driver's bias voltage)
encryption of data is possible. We have shown numerically that decryption of the encoded data is possible by
using an identical acousto-optic system in the receiver.
This paper proposes an FSO-based mobile sensor network that is not subject to RF interference common to wireless
sensor networks. FSO-based mobile sensor networks can potentially be used in a battlefield where security of
communication, including freedom from susceptibility to enemy-induced jamming, is important. The paper discusses the
design of nodes containing multiple transceivers composed of LEDs and photo detectors. Results of initial experiments
are included. The work reported in this paper is part of an ongoing investigation on mobile FSO networks, including the
design of efficient protocols that can allow the mobile sensor nodes to function as a mesh network permitting
information exchange among nodes directly and, possibly, through an intermediate node.
A non-contact and low-cost nanomaterial based fiber-optic sensor is developed for measuring large values of electric
currents. The magnetic field, generated by the electric current, changes the refractive index of a liquid in which
nanomaterial particles are suspended. The change of refractive index is converted to a change in the intensity of light
transmitted in an evanescent field based fiber optic sensor. The change in the intensity is proportional to the magnitude
of the electric current and thus the current can be measured by measuring the resultant change in the intensity of light.
A free space optics based identification and interrogation system has been designed. The applications of the proposed
system lie primarily in areas which require a secure means of mutual identification and information exchange between
optical readers and tags. Conventional RFIDs raise issues regarding security threats, electromagnetic interference and
health safety. The security of RF-ID chips is low due to the wide spatial spread of radio waves. Malicious nodes can read
data being transmitted on the network, if they are in the receiving range. The proposed system provides an alternative
which utilizes the narrow paraxial beams of lasers and an RSA-based authentication scheme. These provide enhanced
security to communication between a tag and the base station or reader. The optical reader can also perform remote
identification and the tag can be read from a far off distance, given line of sight. The free space optical identification and
interrogation system can be used for inventory management, security systems at airports, port security, communication
with high security systems, etc. to name a few. The proposed system was implemented with low-cost, off-the-shelf
components and its performance in terms of throughput and bit error rate has been measured and analyzed. The range of
operation with a bit-error-rate lower than 10-9 was measured to be about 4.5 m. The security of the system is based on the
strengths of the RSA encryption scheme implemented using more than 1024 bits.
Free Space Optical (FSO) communication has evolved to be applied to the mobile network, because it can provide up to 2.5Gbps or higher data rate wireless communication. One of the key challenges with FSO systems is to maintain the Line of Sight (LOS) between transmitter and receiver. In this paper, the feasibility and performance of applying the FSO technology to the mobile network is explored, and the design plan of the attitude positioning and tracking control system of the FSO transceiver is investigated. First, the system architecture is introduced, the requirements for the control system are analyzed, the involved reference frames and frame transformation are presented. Second, the control system bandwidth is used to evaluate the system performance in controlling a positioning system consisting of a gimbal and a steering mirror, some definitions to describe the positioning accuracy and tracking capacity are given. The attitude control of a FSO transceiver is split into 2 similar channels: pitch and yaw. Using an equivalent linear control system model, the simulations are carried out, with and without the presence of uncertainties that includes GPS data errors and sensor measurement errors. Finally, based on the simulation results in the pitch channel, the quantitative evaluation on the performance of the control system is given, including positioning accuracy, tracking capability and uncertainty tolerance.