DFB FL Research Articles

Power equalization method of a DFB fiber laser sensor array.

To reduce the output power ununiformity mainly caused by the exponential attenuation of pump power in a distributed feedback fiber laser (DFB FL) sensor array, a power equalization method based on array structure optimization is proposed. By analyzing the influencing factors of the output power flatness of the array, an output power prediction model of a DFB FL wavelength division multiplexing (WDM) array is established, and the standard deviation coefficient of the output power is proposed as the main evaluating indicator for assessing the output power flatness. An array structure optimization scheme based on the simulated annealing algorithm is designed, and the optimized array structure of the 64-element DFB FL sensor array is achieved. The results show that the power fluctuation of the optimized array is significantly reduced from universal 5-10 dB to smaller than 2.6 dB, while the performance of the DFB FL sensor array is improved with better noise floor and increased multiplexing capacity, as well as improved array design efficiency.

Distributed Feedback Fiber Laser Strain Sensor Technology

Distributed feedback fiber laser (DFB FL) sensors have been the subject of considerable research interest over the past decade, due primarily to their remarkable inherent strain sensitivity. Recent research has led to significant advances in both fundamental understanding of DFB FL devices and in practical performance outcomes in demanding real-world applications. Here, we provide an overview of the basic operating principles of wavelength division multiplexed DFB FL sensor systems and review the underlying theory of DFB FL.

Effects of Intensity Noise in Digital Demodulation for Fiber Laser Sensor

Hydrophone array-based distributed feedback fiber laser (DFB FL) has a small size and large sensitivity; however, it also suffers from intensity noise completely. In this letter, a transfer function for intensity noise propagation through the use of a DFB FL sensor interrogation system is derived, basing on which a symmetric algorithm using $3\times 3$ coupler is improved. Both experimental and simulation data are provided to validate the model. A noise reduction of 20 dB is achieved.

Study of Rayleigh-backscattering induced coherence collapse in an asymmetric DFB FL sensor

Abstract Rayleigh-back scattering induced coherence collapse of an asymmetric distributed feedback fiber laser (DFB FL) sensor is investigated using a composite cavity model. The coherence collapse threshold condition of the asymmetric DFB FL sensor is measured. The DFB FL sensor shows different dynamic behaviors in different pump configurations. According to the asymmetric behavior to the external optical feedback, a novel method to find the actual phase shift position of the asymmetric DFB FL sensor is presented.

Measurement of Acoustic Noise Induced Linewidth Broadening of Unpackaged Distributed Feedback Fiber Laser

The acoustic noise induced linewidth broadening phenomenon of distributed feedback fiber laser (DFB FL) is experimentally studied in this paper. Using the delayed self-homodyne method, we performed linewidth measurements on one unpackaged short cavity asymmetrical DFB FLs under increasing acoustic noise influence. The experiment results show the linewidth of tested laser increased from 5.8 KHz at 50 dB sound level to 32.5KHz at 80 dB sound level. This proves acoustic noise can drastically change the linewidth performance of unpackaged DFB FL. In addition, we performed another experiment on the same DFB FL to measure its linewidth with increasing tensile loads at fiber ends; the result shows a linewidth increase from 5.8 KHz at 0g tensile force to 51.2 KHz at 50g tensile force.

Experimental evidence for the thermal origin of1/ffrequency noise in erbium-doped fiber lasers

We present experimental evidence in support of the recent theoretical proposal that intrinsic $1/f$ frequency noise in short cavity erbium-doped fiber lasers is of thermal origin. We demonstrate that the power spectral density of frequency noise in distributed-feedback fiber lasers (DFB FL) exhibits predicted ${T}^{2}$ temperature dependence across all frequencies over a temperature range of almost 200 K. This temperature dependence is observed both in direct interferometric measurements of frequency noise in a single mode DFB FL and noninterferometric measurements of polarization-beat-frequency noise in a dual frequency DFB FL. It is also shown that frequency noise of orthogonal polarization modes in the dual frequency DFB FL is substantially correlated providing a strong indication of a common origin.

Fundamental Thermal Noise in Distributed Feedback Fiber Lasers

A detailed analysis of fundamental thermal frequency noise in distributed feedback fiber lasers (DFB FL) is presented. An expression relating the laser frequency noise spectrum to the spectrum of thermal (temperature) fluctuations in the fiber, accounting for the nontrivial DFB FL mode shape, is derived. A new expression for the thermal fluctuation spectrum of single-mode optical fiber is derived which predicts high-frequency thermal noise 3 dB higher than previously published results. Theoretical predictions are compared against experimental measurements for a well characterized DFB FL. Anomalous 1/f noise at low frequency is discussed

Performance limitations of high-power DFB fiber lasers

In this letter, we experimentally study several different configurations of high-power single-frequency sources based on distributed-feedback fiber laser (DFB FL). In particular, we have compared two schemes in terms of pumping efficiency, relative intensity noise (RIN) and optical signal-to-noise ratio (OSNR): directly pumped DFB FLs pumped by a high-power fiber-based pump source (stand-alone DFB FL) and a combination of a DFB FL and a power amplifier (amplified DFB FL). At the output powers below 40 mW, a stand-alone DFB FL has the highest OSNR (> 63 dB) and the lowest RIN (< -165 dB/Hz). The net efficiency of a stand-alone DFB FL can be doubled by using an amplified DFB FL at the expense of degraded OSNR and RIN. It is also shown that RIN below -160 dB/Hz and OSNR > 60 dB can be achieved by an amplified DFB with output power greater than 1 W.