Fiber Sagnac Interferometer Research Articles

Soliton squeezing in a highly transmissive nonlinear optical loop mirror

A perturbation approach is used to study the quantum noise of optical solitons in an asymmetric fiber Sagnac interferometer (a highly transmissive nonlinear optical loop mirror). Analytical expressions for the three second-order quadrature correlators are derived and used to predict the amount of detectable amplitude squeezing along with the optimum power-splitting ratio of the Sagnac interferometer. We find that it is the number-phase correlation owing to the Kerr nonlinearity that is primarily responsible for the observable noise reduction. The group-velocity dispersion affecting the field in the nonsoliton arm of the fiber interferometer is shown to limit the minimum achievable Fano factor.

Temperature-Induced Changes of Sensitivity in the Unbalanced Hi-Bi Fiber Sagnac Interferometer

A temperature sensor based on the unbalanced Hi-Bi fiber Sagnac interferometer is analyzed in the temperature interval 15 250 C. It is shown that the sensitivity of such a sensor exhibits irreversible changes at temperatures higher than 200 C. To achieve this, it is proposed to anneal the fiber at 200 C for 1.5 h to avoid hysteresis and extend the measured temperature interval. Measurements were done for the polymer-coating-induced birefringence and the residual stresses causing hysteresis. It is also shown that the sensor sensitivity is reduced by 27 % when stresses are removed.

Fiber-optic gyroscope with suppression of excess noise from the radiation source

A new optical system is proposed and investigated experimentally for a Sagnac fiber interferometer in which the excess noise of the wide-band radiation source is suppressed. A tenfold improvement in the sensitivity of a fiber-optic gyroscope with an erbium/ytterbium fiber superfluorescent light source was achieved experimentally. It is shown that the identity of the polarization characteristics of the interferometer channels plays an important role.

Continuous-wave measurement of the fiber nonlinear refractive index

We propose a technique for measuring the nonlinear refractive index of fiber based on transmission-coefficient measurements in a fiber Sagnac interferometer. In contrast with traditional methods, the proposed method uses a single optical source operating in cw mode and direct intensity measurement, enabling one to avoid the errors caused by fiber dispersion and uncertainty of spectral peak difference measurements that occur with pulse-based methods. The nonlinear refractive index in 20-mol. % GeO(2) fiber was measured to be (3.1 +/- 0.2) x 10(-16) cm(2) W(-1) at 1064 nm.

Quantum statistics of fundamental and higher-order coherent quantum solitons in Raman-active waveguides.

The quantum dynamics of coherent optical pulses are studied using a nondiagonal coherent-state generalized $P$ representation including photon-phonon interactions. Photon-number squeezing of coherent quantum solitons using spectral filtering is theoretically predicted. It is shown that Raman noise does not significantly reduce photon-number squeezing produced by spectral filtering of 1-ps fundamental coherent quantum solitons in optical fibers. Coherent $Nsech$ pulses with $N>1$ can show a larger reduction in photon-number fluctuations even at room temperature. The reduction in quantum noise for $N>1$ is not restricted to photon number and an improvement of more than 3 dB is also found for the quadrature-phase squeezed soliton experiments using a fiber Sagnac interferometer at 77 K.

Inherently bias-drift-free amplitude modulator

The authors demonstrate an inherently bias drift free broadband amplitude modulator design based on an integrated optic travelling wave phase modulator in a fibre Sagnac interferometer. Operation is demonstrated over 0.5–20 GHz, and the bias is shown to be stable to better than 1° over a temperature range of 28°C.

Transient polarisation effects as the cause of the drift of a signal from a ring fibre interferometer

It is shown theoretically and experimentally that one reason for the appearance of a parasitic signal at the output of a fibre Sagnac interferometer, assembled in the conventional manner, may be the effects associated with the anisotropy of a phase modulator, which lead to modulation of the polarisation. These effects are transient. They depend on the delay of phase modulation of eigenwaves travelling in one direction, relative to the modulation of counterpropagating waves, because of an asymmetric position of the modulator in the fibre ring, which is typical of conventional configurations. The results obtained make it possible to explain the experimentally observed effects and to recommend ways of avoiding them.

Optical modulators using fibreoptic Sagnac interferometers

We propose, and present a theoretical and experimental investigation of optical modulators using fibreoptic Sagnac interferometers. Several possible modulator configurations have been investigated and compared. An optical modulator using the ceramic material PLZT as the electrooptic modulating element has been experimentally demonstrated to show the feasibility of this new type of modulator structure. Preliminary experimental results show that the optical modulators using fibre Sagnac interferometer have a number of useful features such as input polarisation independence, readily adjustable phase bias, and suitability for forming fibre-to-fibre devices.

All optical signal regularizing/regeneration using a nonlinear fiber Sagnac interferometer switch with signal-clock walk-off

All-optical signal regularizing/regeneration using a nonlinear fiber Sagnac interferometer switch (NSIS) that employs signal-clock walk-off is investigated. The NSIS realizes all-optical signal regeneration, including timing and amplitude regularizing, by switching clock pulses with amplified input signals using a walk-off-induced, wide, square switching window and intensity-dependent transmittance of the device. First, characteristics (in both the temporal and spectral domains) of the all-optical signal regeneration achieved with the NSIS are investigated theoretically and experimentally. They certify that if clock pulses are within the square switching window obtained with signal-clock walk-off, the clock pulses can be modulated according to the data that the input signals carry and retain their temporal and spectral profiles. This means that if clock pulses can be prepared that meet the system requirements, the NSIS can convert input signals that may not satisfy system requirements into high-quality output signals. Limitations on the switching contrast due to the cross-phase modulation of counterpropagating reference pulses is also discussed. Second, two possible applications of NSIS-based all-optical signal regularizing/regeneration, 1) an all-optical multiplexer with an optical clock and 2) an all-optical regenerative repeater, are discussed. Preliminary experiments with /spl sim/10-ps pulses at bit rates of /spl sim/5 Gb/s that use locally prepared optical clock pulses, show that the NSIS provides an error-free regeneration function with a certain tolerance for pulse-period irregularity if a proper optical clock is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of crosstalk and timing jitter on all-optical time-division demultiplexing using a nonlinear fiber Sagnac interferometer switch

All-optical time-division demultiplexing using a nonlinear fiber Sagnac interferometer switch (NSIS) is studied with respect to the two main causes that degrade the bit-error-rate (BER) performance: crosstalk and timing jitter. It is shown that unwanted cross-phase-modulation in the reference signal which counter-propagates to the control pulse, as well as the poor extinction of the switch itself, seriously degrades the extinction ratio of the switch, thus increasing the crosstalk from other channels. Numerical calculations clarify the effect of the switching window width, window shape, and the multiplexed channel number on the power penalty in terms of BER performance. Timing jitter between the signal and control pulses is investigated as another degradation factor that causes an error floor in BER performance. It is found that the minimum BER is obtained when the window width is set to the time slot width and the rms value of the jitter must be less than 1/14.1 times the time slot width to ensure that BER >

Effect of timing jitter on an optically controlled picosecond optical switch

Timing jitter between optical control and signal pulses seriously degrades the bit-error-rate (BER) performance of optically controlled optical switches in the picosecond region. BER's measured in a picosecond all-optical switch based on nonlinear fiber Sagnac interferometer switching reveal that the rms signal-to-control timing jitter must be less than 1/12 of the switching window to achieve BER &lt; 10−9.

Pump-induced frequency shifting of switched pulses in an interferometric all-optical switch

The induced frequency chirping of switched pulses in an interferometric all-optical switch that uses pump-induced nonlinear phase shifts is investigated. Using a nonlinear fiber Sagnac interferometer switch, it is shown that switched pulses suffer from frequency shift and broadening and can be compressed by using an anomalous group-velocity-dispersion fiber. It is also demonstrated that picosecond probe pulses can be switched while retaining their temporal and spectral profiles if pump-probe walk-off is employed.

Low-drift modulator without feedback

A low-drift amplitude modulator has been demonstrated using a fiber Sagnac interferometer with a lithium-niobate phase modulator. Although the fiber-loop length must be adjusted for the modulation rate, this type of modulator structure is inherently insensitive to variations in the voltage bias of the drive signal, as well as to temperature variations. >

All-optical analog-to-digital and digital-to-analog conversion implemented by a nonlinear fiber interferometer

We propose all-optical analog-to-digital and digital-to-analog converters using cross-phase modulation in a nonlinear interferometer. The proposed devices use the optical Kerr effect and are thus potentially very fast. Preliminary experimental results on 3-bit A/D and 2-bit D/A converters in a single-mode fiber Sagnac interferometer are presented. In the A/D conversion experiment, the interaction length of the fiber loop was 200 m and the input pump power was 1.55 W for bit 0 at the end of the dynamic range. In the D/A conversion, the interaction lengths were 100 m and 200 m for bit 0 and bit 1, respectively; when the bit value “1” of the input digital word was 0.26 W, the nonlinear phase shifts were π/3, 2π/3, and π for the input digital words 01, 10, and 11, respectively, demonstrating the linear phase response; we could linearize the output too by limiting and biasing the input pump power.

Polarization-independent all-optical switching

A polarization-independent all-optical switch has been demonstrated based on a nonlinear fiber Sagnac interferometer. The control signal is split and recombined with a time delay, producing two linearly polarized pulses that lie within the temporal switching window of the circuit. Less than 10% variation of the switched output signal was observed as the input polarization was varied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Diode-pumped nonlinear fibre sagnac interferometer switch with integrated silica-based planar lightwave circuit

A nonlinear fibre Sagnac interferometer switch with an integrated silica-based planar lightwave circuit is reported. Diode-pumped time-division demultiplexing is demonstrated at 50.4 Gbit/s with a 13 ps switching time and a 5.6 GHz repetition rate

All-optical regenerator based on nonlinear fibre sagnac interferometer

For the first time, all-optical regeneration using a nonlinear fibre Sagnac interferometer switch (NSIS) and pump-probe walk-off is demonstrated. In the NSIS, all-optical regeneration including timing and amplitude restoration is performed by switching clock pulses with amplified input signals. Timing restoration is evaluated by performing error-rate measurements at 5 Gbit/s. >

All-optical, all-fiber circulating shift register with an inverter

An all-optical fiber Sagnac interferometer switch and erbium amplifier have been combined to form an all-optical 254-bit circulating shift register with an inverter. This simple optical loop memory demonstrates the cascadability of Sagnac interferometer switches.

All-optical arbitrary demultiplexing at 25 Gbits/s with tolerance to timing jitter

All-optical demultiplexing has been shown with a full-duty-cycle 2.5-Gbit/s signal in a nonlinear fiber Sagnac interferometer. Complete switching of arbitrary pulse patterns in the data stream has been achieved by using two orthogonal polarization states for the switching and switched pulse trains. The polarization dispersion between the two fiber axes defines a window that allows for switching with timing errors as large as 350 ps.

Fiber gyro with squeezed radiation

A pulse-excited Sagnac fiber interferometer can perform squeezing. If this squeezed radiation is injected into a second Sagnac interferometer that is functioning as a fiber gyro that is itself nonlinear, additional unfavorable squeezing occurs in the gyro. By proper phase adjustment of the injected squeezed radiation it is possible to minimize this effect as long as the Sagnac interferometer that is performing the squeezing has a sufficiently large nonlinearity.