Excess Relative Intensity Noise Research Articles

Dual-polarization interferometric fiber optic gyroscope based on a four-port circulator.

The dual-polarization interferometric fiber optic gyroscope (IFOG) has been studied for many years and achieved remarkable performance. In this study, we propose a novel dual-polarization IFOG configuration based on a four-port circulator, in which the polarization coupling errors and the excess relative intensity noise are well handled meanwhile. Experimental measurements of the short-term sensitivity and long-term drift using a fiber coil with a length of 2 km and a diameter of 14 cm show that the angle random walk of 5.0×10-5∘/h and bias instability of 9.0 × 10-5 °/h are achieved. Moreover, the root power spectrum density of 20n r a d/s/H z is almost flat from 0.001 Hz to 30 Hz. We believe this dual-polarization IFOG is a preferred candidate for the reference-grade performance IFOG.

Self-Adaptive Suppression of the Excess Relative-Intensity-Noise in Fiber Optic Gyroscopes

The excess relative intensity noise (RIN) in the fiber optic gyroscope (FOG) can be suppressed by the balanced intensity addition of the interferometer output signal and the RIN reference. In practice, the suppression effect will be ruined by the mismatching of the intensities at addition induced by external environments, resulting in the degradation of the angular-random-walk (ARW) coefficient of the FOG. In this work, we propose a self-adaptive scheme to keep the excess-RIN suppressed at the lowest level. The multiple roles that the modulation depth plays in the loss of the interferometer output signal and the amplitude of each noise component are analyzed, theoretically. Based on this, the modulation depth is designed to be self-adjusted in a closed-loop scheme so as to keep intensity balancing and to maintain the total noise at the lowest level in real time. Experiments show that, under the manually adjusted intensity ratios between the interferometer output signal and the RIN reference from 0.42 to 3.25, the proposed self-adaptive scheme reduces the ARW to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.24\times 10^{-{3}}$ </tex-math></inline-formula> deg/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{h}^{\text {1/2}}$ </tex-math></inline-formula> with respect to the conventional case of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.27\times 10^{-{3}}$ </tex-math></inline-formula> deg/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{h}^{\text {1/2}}$ </tex-math></inline-formula> . With this technique, the robustness of the excess-RIN suppression is significantly improved without the need of modifying the typical simplest optical configuration or adding any extra device. The lowest ARW for the FOG can be guaranteed in long-term operations and under different environments.

High Optical Feedback Tolerance of a Detuned DBR Laser for 10-Gbps Isolator-Free Operation

The optical feedback tolerance (OFT) of a distributed Bragg reflector (DBR) laser was investigated experimentally. The static and modulation performance of the DBR laser under optical feedback was examined by evaluating its relative intensity noise (RIN) and bit error rate (BER). It is shown that the OFT of the DBR laser is closely related to its peak wavelength detuning relative to the Bragg wavelength. A high tolerance to optical feedback was demonstrated, both in the continuous wave (CW) and the direct modulation (DM) states, when the DBR laser was red-detuned relative to the Bragg wavelength. The excess RIN induced by optical feedback was well suppressed to a level of −140 dB/Hz at a feedback level of −9 dB in the CW state. In a 10 Gbps direct modulation state, bit error rates (BER) below 1 × 10−9 and 3 × 10−7 were obtained under a feedback level of −15 dB and −9 dB, respectively, for the case of back-to-back transmission. After 20 km fiber transmission, the BER still maintained below 1 × 10−7 under a feedback level of −15 dB, with a power penalty of less than 1 dB.

Reduction of relative intensity noise in a broadband source-driven RFOG using a high-frequency modulation technique.

A broadband source-driven resonant fiber-optic gyroscope (RFOG) can reduce coherence-related noise, thus achieving a better sensitivity with a much simpler configuration than the traditional system with a coherent source. Its detection sensitivity, however, is still limited by the excess relative intensity noise (RIN) of the broadband source. In this paper, the RIN error mechanism in this broadband source-driven RFOG is revealed and countermeasures are presented. We demonstrate that the use of a high-finesse fiber-optic ring resonator and a high-frequency modulation-demodulation technique can reduce the RIN-induced error. It is indicated that the optimal modulation parameters can provide a RIN-induced error reduction of 6.1 dB, allowing the broadband source-driven RFOG to operate near the shot-noise-limited theoretical sensitivity. With the optimal high-frequency modulation-demodulation technique, an angle random walk of 0.0013°/√h is achieved with a 200-m-long fiber-optic ring resonator of 7.6 cm diameter. This is the best result reported to date, to the best of our knowledge, for fiber-optic gyroscopes of this size.

Sensitivity enhancement through RIN suppression in dual-polarization fiber optic gyroscopes for rotational seismology.

Portable sensors with a sufficiently high sensitivity in detecting small rotational motions have attracted significant attention in the field of rotational seismology. In this study, we propose and demonstrate a dual-polarization fiber optic gyroscope (IFOG) with a portable-sized fiber coil. Excess relative intensity noise (RIN) is effectively compensated for owing to the opposite parities and strong correlation of the two orthogonal polarized light, whereas other noises including coherent phase noise and thermal phase noise have also been handled well. In a test on detecting the rotation rate of the Earth, an enhanced sensitivity of 20nrad/s/Hz over a frequency range of 0.01 Hz to 30 Hz was demonstrated using the proposed design with an enclosed area of only 68 m2.

Low noise all-fiber amplification of a coherent supercontinuum at 2 \xb5m and its limits imposed by polarization noise

We report a low noise, broadband, ultrafast Thulium/Holmium co-doped all-fiber chirped pulse amplifier, seeded by an Erbium-fiber system spectrally broadened via coherent supercontinuum generation in an all-normal dispersion photonic crystal fiber. The amplifier supports a − 20 dB bandwidth of more than 300 nm and delivers high quality 66 fs pulses with more than 70 kW peak power directly from the output fiber. The total relative intensity noise (RIN) integrated from 10 Hz to 20 MHz is 0.07%, which to our knowledge is the lowest reported RIN for wideband ultrafast amplifiers operating at 2 µm to date. This is achieved by eliminating noise-sensitive anomalous dispersion nonlinear dynamics from the spectral broadening stage. In addition, we identify the origin of the remaining excess RIN as polarization modulational instability (PMI), and propose a route towards complete elimination of this excess noise. Hence, our work paves the way for a next generation of ultra-low noise frequency combs and ultrashort pulse sources in the 2 µm spectral region that rival or even outperform the excellent noise characteristics of Erbium-fiber technology.

Excess Relative-Intensity-Noise Reduction in a Fiber Optic Gyroscope Using a Faraday Rotator Mirror

The fiber optic gyroscope (FOG) suffers from the excess relative intensity noise (RIN) caused by the broadband light source, which significantly impacts the angular random walk (ARW) of the FOG. The existing suppression methods for the excess RIN usually require complex configuration or devices with big volume, and thus are not suitable for practical applications especially in small-sized FOGs. What is more, as the key parameters or components, that determine the practical suppression effects of the excess RIN, and the corresponding impacting mechanisms are not clarified, there is no efficient way in evaluating or optimizing the excess-RIN reduction configuration in practice. In this work, we propose a simple but effective method to achieve the reduction of the excess RIN at the demodulation frequency, in which a Faraday rotator mirror is inserted to the dead arm of the source coupler to realize the delay line filter for the excess RIN. Experimental results show that the ARW is improved from 1.70 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> to 0.58 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> for a navigation-grade FOG. More importantly, this work provides a comprehensive understanding on how the main defects in the excess-RIN reduction scheme impact the practical excess-RIN suppression effects both theoretically and experimentally, which demonstrates the inherent robustness of the proposed scheme against internal and external influencing factors. This method is especially suitable for realizing the excess-RIN reduction in small-sized FOGs and upgrading the existing FOG products with minimal modifications, and is also potentially referable in evaluating and optimizing other similar excess-RIN reduction schemes.

Excess relative intensity noise suppression in depolarized interferometric fiber optic gyroscopes

Excess relative intensity noise (excess RIN) is one of the major factors that degrade the short-term performance of interferometric fiber optic gyroscopes (IFOGs). We theoretically and experimentally investigate the correlation of excess RIN between interferometric and reference signals in depolarized IFOGs in which single-mode fiber coils are adopted to make them cost-effective. The Lyot depolarizers decrease the correlation coefficient to about 81%, giving a lower limit that excess RIN can be suppressed to 59%. Then, an excess RIN suppression method by co-processing interferometric and reference signals electronically is proposed that works well with the open-loop demodulation. Experimental results show the proposed method compensates the excess RIN to 60.4% compared to original, almost achieve the noise limit of the depolarized configuration.

Influences of optical-spectrum errors on excess relative intensity noise in a fiber-optic gyroscope

The excess relative intensity noise (RIN) generated from broadband sources degrades the angular-random-walk performance of a fiber-optic gyroscope dramatically. Many methods have been proposed and managed to suppress the excess RIN. However, the properties of the excess RIN under the influences of different optical errors in the fiber-optic gyroscope have not been systematically investigated. Therefore, it is difficult for the existing RIN-suppression methods to achieve the optimal results in practice. In this work, the influences of different optical-spectrum errors on the power spectral density of the excess RIN are theoretically analyzed. In particular, the properties of the excess RIN affected by the raised-cosine-type ripples in the optical spectrum are elaborately investigated. Experimental measurements of the excess RIN corresponding to different optical-spectrum errors are in good agreement with our theoretical analysis, demonstrating its validity. This work provides a comprehensive understanding of the properties of the excess RIN under the influences of different optical-spectrum errors. Potentially, it can be utilized to optimize the configurations of the existing RIN-suppression methods by accurately evaluating the power spectral density of the excess RIN.

Active intensity noise suppression for a broadband mid-infrared laser source.

Excess relative intensity noise (RIN) constitutes one of the major limitations of most spectroscopic methods involving lasers. Here, we present an active RIN suppression scheme for a coherent mid-infrared (MIR) light source (8.4-11 µm), based on intra-pulse difference frequency generation (DFG). Three different stabilization concepts that rely on modulating the intensity of the driving near-infrared (NIR) pulse train with an acousto-optic modulator are investigated and compared. By using the wings of the NIR spectrum to generate the error signal, a RIN suppression of the MIR pulse train of up to a factor of 20 was achieved in the band between 1 Hz and 100 kHz, resulting in a total integrated RIN of 0.07%.

Compensation of excess RIN in fiber-optic gyro

The paper describes the sources of fundamental noises in FOG measurement signal. Methods of excess relative intensity noise (RIN) compensation are considered. Technique improving the compensation method using division of signals from two photodetectors for noise suppression is proposed and implemented. Functional simulation is conducted, which estimates the limiting theoretical value of noise suppression by the selected compensation method with the photodetector power of min 10 µW. Test results for FOG experimental prototype are presented. Allan variance plots for the cases with and without compensation are constructed.