Mable P. Fok

Optical Layer Security in Fiber-Optic Networks

The physical layer of an optical network is vulnerable to a variety of attacks, including jamming, physical infrastructure attacks, eavesdropping, and interception. As the demand for network capacity grows dramatically, the issue of securing the physical layer of optical network cannot be overlooked. In this survey paper, we discuss the security threats in an optical network as well as present several existing optical techniques to improve the security. In the first part of this paper, we discuss various types of security threats that could appear in the optical layer of an optical network, including jamming, physical infrastructure attacks, eavesdropping, and interception. Intensive research has focused on improving optical network security, in the above specific areas. Real-time processing of the optical signal is essential in order to integrate security functionality at the physical layer while not undermining the true value of optical communications, which is its speed. Optical layer security benefits from the unique properties of optical processing-instantaneous response, broadband operation, electromagnetic immunity, compactness, and low latency. In the second part of this paper, various defenses against the security threats outlined in this paper are discussed, including optical encryption, optical code-division multiple access (CDMA) confidentiality, self-healing survivable optical rings, anti-jamming, and optical steganography.

Waveband-switchable SOA ring laser constructed with a phase modulator loop mirror filter

An electrically tunable multiwavelength source has been developed using a birefringence-based optical comb filter in a semiconductor optical amplifier ring laser. The filter is constructed with an electrooptic phase modulator placed inside a fiber loop mirror. By controlling the birefringence of the modulator through the applied bias, the radio-frequency power, or the modulation frequency, we achieve a continuous shift of the spectral comb to access different interleaved wavebands. Electrical waveband switching has been successfully demonstrated for 21 wavelengths at 100-GHz grid spacing with an optical signal-to-noise ratio over 40 dB.

4 /spl times/ 2.5 GHz repetitive photonic sampler for high-speed analog to digital signal conversion

This letter presents a 10-gigasample/s (GS/s) photonic analog-to-digital converter (ADC) system constructed using a four-wavelength picosecond pulsed source. The lasing-to-nonlasing modes suppression ratio of the optical source is over 24 dB. By using the 10-GHz optical source, a 10-GS/s photonic ADC has been demonstrated and was used to sample an arbitrary radio-frequency signal. The system was further investigated by sampling a 2.4-GHz sinusoidal signal. Important parameters including the signal-to-noise and distortion ratio and the spurious-free dynamic range have been determined.

Multipump Four-Wave Mixing in a Photonic Crystal Fiber for 6

We demonstrate differential phase-shift keying wavelength multicasting using four-wave mixing in a 64-m dispersion-flattened highly nonlinear photonic crystal fiber. The power penalty is less than 2.9 dB for all the 10-Gb/s multicast channels spaced at 200 GHz.

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We propose a new type of dynamically tunable birefringence comb filter based on a semiconductor optical amplifier Sagnac loop interferometer. By optically modulating the birefringence of the amplifier, we demonstrate a tuning of the output wavelengths. The shift of wavelength increases monotonically with the power of the control light until saturation occurs. The tuning relation is independent of the comb spacing governed by the length and birefringence of the polarization maintaining fiber inside the loop. A tuning range up to 59% of the comb spacing has been achieved at 18.5 dBm input power.

10 Gb/s Wavelength Multicasting of DPSK Signals

In this paper, we demonstrate for the first time an ultrafast fully functional photonic spiking neuron. Our experimental setup constitutes a complete all-optical implementation of a leaky integrate-and-fire neuron, a computational primitive that provides a basis for general purpose analog optical computation. Unlike purely analog computational models, spiking operation eliminates noise accumulation and results in robust and efficient processing. Operating at gigahertz speed, which corresponds to at least 108 speed-up compared with biological neurons, the demonstrated neuron provides all functionality required by the spiking neuron model. The two demonstrated prototypes and a demonstrated feedback operation mode prove the feasibility and stability of our approach and show the obtained performance characteristics.

Optically controlled Sagnac loop comb filter

Phase mask encryption is proposed to improve the transmission privacy of an optical steganography system. The stealth signal carried by amplified spontaneous emission noise is encrypted by a fast changing code.

Ultrafast all-optical implementation of a leaky integrate-and-fire neuron

We demonstrate room-temperature operation of a spacing-adjustable multi-wavelength erbium-doped fiber laser using stimulated Brillouin scattering. With the use of an intra-cavity birefringent loop mirror filter, the laser output wavelengths can be well defined without applying an external Brillouin pump. By adjusting the comb spacing of the filter, a wide range of mode spacings can be obtained to support the oscillations of up to 49 output wavelengths.

Optical steganography based on amplified spontaneous emission noise

Using four-wave mixing in a 35-cm highly nonlinear bismuth-oxide fiber incorporated in an erbium-doped fiber laser, a stable dual-wavelength output is obtained. The spectral spacing has been tuned from 1.3 to 7.2 nm with a tunable fiber Bragg grating. Simultaneous tuning of the two wavelengths over 20 nm is also demonstrated using a tunable bandpass filter together with a birefringent filter defining a 100-GHz frequency comb. The output stability has been experimentally analyzed. An abrupt reduction in the intensity fluctuation is observed when the amplifier output power reaches 22.0 dBm. At 22.3 dBm, the fluctuation attains a lower limit of approximately 1 dB.

Spacing-adjustable multi-wavelength source from a stimulated Brillouin scattering assisted erbium-doped fiber laser.

We demonstrate an approach that allows a good flexibility in controlling the spectral spacing in a birefringent comb filter. Our scheme exploits the bidirectional transit of light in a polarization-maintaining fiber (PMF). The light polarization between the two transits is adjusted to change the equivalent propagation distance. The number of achievable spectral spacings is substantially larger than those demonstrated by previous approaches. Using two segments of PMFs, 12 different spacings that span from 0.27 to 6.08 nm have been demonstrated. The experimental data agree well with our calculated results. The approach is easily cascadable and the number of combinations scales up very rapidly with the fiber segments used in the setup