Distributed Bragg Reflector Fiber Laser Research Articles

Single-frequency DBR Nd-doped fiber laser at 1120 nm with a narrow linewidth and low threshold.

We report a narrow linewidth and low threshold single-frequency distributed Bragg reflector (DBR) fiber laser at 1120 nm based on a short 1.5 cm long Nd-doped silica fiber which, to the best of our knowledge, is the first demonstration of a Nd-doped fiber-based single-frequency fiber laser with a wavelength greater than 1100 nm. A stable single-longitudinal-mode laser operation with a signal-to-noise ratio greater than 67 dB was verified by a scanning Fabry-Perot interferometer. The laser threshold is as low as 10 mW. The DBR fiber laser has a maximum output power of 15 mW and optical-to-optical efficiency for the launched pump power reaches more than 8%. The narrow linewidth of 71.5 kHz is obtained in such a single-frequency fiber laser (SFFL). Our result is expected to offer an exciting new opportunity to realize high-performance SFFLs above 1100 nm.

Ultra-high-temperature resistant distributed Bragg reflector fiber laser based on type II-IR fiber Bragg gratings.

We demonstrate a distributed Bragg reflector fiber laser that is capable of long-term operation at ultra-high temperatures. To form the laser cavity, a piece of Er-doped fiber is fusion spliced to a pair of type II-IR gratings, which are written using a femtosecond laser with a phase mask. Saturated gratings with different reflectivities are fabricated by varying the position of the grating region relative to the fiber core center. An eccentric grating with a relatively low reflectivity is chosen as the laser output coupler, while a regular grating with a higher reflectivity is used as the laser's high-reflection reflector. After an annealing process, the laser performance is tested at high temperatures. The results show that the laser can operate with a stable output wavelength and no output power degradation at high temperatures up to 1000°C.

Optimal feedback-interferometric fiber laser microphones

Design and experimental verification are presented in this Letter for a feedback-interferometric fiber laser microphone (FLM) based on the distributed Bragg reflector fiber laser (DBR-FLM) and the distributed feedback reflector fiber laser (DFB-FLM), optimized for power efficiency, response sensitivity, and linearity. First-principle self-consistent simulation has been performed to design the optimal DBR-FLM and DFB-FLM. The self-consistent simulation takes care of the laser power coupled Er/Yb rate equations and makes full use of the encompassing coupled mode theory for fast computation. The experimental results agreed well with the simulation results. A comparison between the DBR-FLM and the DFB-FLM is made and explained in terms of lasing power and noise performance.

Ultra-short DBR fiber laser with high-temperature resistance using tilted fiber Bragg grating output coupler.

We demonstrate a high-temperature resistant distributed Bragg reflector (DBR) fiber laser that is highly compact with an entire cavity length of 12 mm. A partial-reflection tilted fiber Bragg grating (PR-TFBG) is used as the laser output coupler whose reflectivity can be adjusted by changing the TFBG tilt angle. The laser cavity consists of two strong gratings including the PR-TFBG and a high-reflection fiber Bragg grating (HR-FBG), which is directly fabricated in an Er-doped fiber using a femtosecond laser and a phase mask. The thermal stability of the PR-TFBG and HR-FBG is experimentally investigated. After an annealing process, their remained gratings are stable at high temperatures and strong enough for laser oscillation. The laser is also annealed before its stability is tested. The results show that the laser can stably operate in single longitudinal mode with a signal-to-noise ratio better than 65 dB over the temperature range from room temperature to 550°C.

Distributed Bragg reflector fiber laser directly written in a composite fiber manufactured by melting phosphate glass in a silica tube.

We demonstrate a single-frequency distributed Bragg reflector (DBR) fiber laser based on the novel erbium-doped composite fiber fabricated by melting phosphate glass in a silica tube. The fabricated composite fiber was single-mode at the wavelength of 1.55μm; the measured cutoff wavelength was 1.4μm. The composite fiber was photosensitive to irradiation at the wavelength of 193nm. Using the phase mask method, the DBR fiber laser cavity with the total length of 21mm was inscribed directly into the erbium-doped composite fiber. A stable single-frequency regime of the fabricated DBR laser at the wavelength of 1565nm is demonstrated.

Side-Polished DBR Fiber Laser with Enhanced Sensitivity for Axial Force and Refractive Index Measurement

A highly sensitive optical fiber sensor for the measurement of axial force and refractive index (RI) is presented. The optical sensor consists of a distributed Bragg reflector (DBR) based fiber laser, the laser cavity of the DBR is polished to D-shape by the wheel fiber polishing system. Birefringence has been introduced with side polishing of the fiber, and then, it is utilized for sensing applications. The working principle of the device is based on the principle of the change in beat frequency of the two orthogonal polarization modes of the DBR fiber laser with external perturbations. In this work, it has been shown that the dual polarization beat frequency can be used for RI-based measurement applications along with the measurement of the axial force. The sensitivity of the DBR fiber laser sensor with change in axial force is enhanced significantly with side polishing. Such a device is robust, simple in fabrication and most importantly low-cost interrogation techniques can be used for the detection purpose. A resolution of 5.6014 × 10–8 N has been achieved in case of recognition of axial force and 1.9259 × 10–5 RIU is the observable detection limit for the RI based measurement.

Realization of Sub-Nano-Strain Static Resolution With Injection-Locking Between Two Fiber Laser Sensors

Fiber Bragg grating (FBG) based sensors have achieved great performance in dynamic strain sensing, while static strain measurement is still very challenging because it requires extra reference for temperature compensation. In this paper, a high-resolution FBG laser sensor system is presented, which is capable of both static and dynamic strain measurements. In the proposed sensor, a distributed feedback fiber laser (DFB-FL) works as the strain sensing element, and a distributed Bragg reflector fiber laser (DBR-FL) works as the reference. The DFB-FL is injection-locked to the DBR-FL with closed loop control using Pound–Drever–Hall (PDH) technique and an acousto-optic frequency shifter. No independent narrow-linewidth probe laser source is required. In experiments, a frequency fluctuation range of 31.6 kHz in 1000 s between the DFB-FL and the DBR-FL is obtained, corresponding to a static strain resolution of 248 pico-strain. Meanwhile, a dynamic resolution of 580 femto-strain at l kHz is achieved. The limitation on strain resolution and dynamic range of the sensor is also discussed. Due to the high strain resolution and moderate cost, the proposed sensor system provides a powerful tool for various applications of strain measurement.

DBR Fiber Laser Based High-Resolution Accelerometer Network

In this paper, we report a high-resolution and precision acceleration sensor network with potential large sensing capacity, which is based on distributed Bragg reflector fiber lasers. To start with, a transducer based on a T-shaped cantilever beam and an adjustable bearing is theoretically designed and experimentally employed to achieve high sensitivity and wideband frequency response. Second, the beat frequency interrogation system that utilizes super-heterodyne receiver and digital orthogonal phase identifying technology is developed to improve the resolution of the sensors. In addition, assisted with the wavelength/time division multiplexing technology, hundreds of sensing units could be potentially multiplexed in the prototype system. A proof-of-concept sensing network with three acceleration sensor units is established for experimental validation. The sensor network demonstrates a sensitivity of 1.16064 GHz/g with a flat frequency response region from 20 to 200 Hz, corresponding to a noise equivalent acceleration of 17.99 ng/√Hz at 90 Hz. In particular, the measurement precision of the prototype system has been calibrated as high as 1.305 μg. The proposed acceleration sensor network could benefit potential applications in smart unmanned platforms and seismic monitoring.

Dual-color distributed Bragg reflector fiber laser with simultaneous emission at 1.06 μm and 1.55 μm wavebands.

A dual-wavelength fiber laser is proposed by the use of Er/Yb co-doped active fiber and a pair of novel Bragg-grating reflectors. The Bragg grating presents strong reflections of both third and second harmonics in accordance with the gain of ytterbium and erbium ion, respectively, enabling the laser emitted at 1.06μm and 1.55μm wavebands simultaneously with a short linear cavity structure. Adjusting reflectivity of the harmonics in the grating can influence the intensity contrast of the two lasing signals. Optimization on the compactness and brightness of the laser is achieved by adapting the harmonic wavelengths with the optimal gain windows of the ytterbium and erbium ions.

Pressure characteristics of a self-Q-switched distributed Bragg reflector fiber laser.

Based on the study of self-Q-switching of a short cavity erbium-doped distributed Bragg reflector (DBR) fiber laser in time domain, the influence of pressure disturbance on the self-Q-switched output is analyzed. In the experiment, the erbium-doped DBR fiber laser (EDFL) was encapsulated with epoxy resin and curing agent to protect and sensitize the fiber. The EDFL sends out self-Q-switched laser pulses when the pump power of the 980nm laser source is more than 110mW. The external pressure is exerted on the DBR fiber and increased gradually from 0g (0N) to 120g (1.176N) in 10g unit with the pump power fixed at 360mW, and the following approximately linear changes of self-Q-switched laser pulses outputs are observed by the oscilloscope: the peak voltage of output pulses reduces from 12.59mV to 1.883mV; the pulse repetition rate reduces from 125.0kHz to 66.67kHz; and the pulse width increases from 0.4083μs to 1.28μs.

A contact vibration measurement sensor based on a distributed Bragg reflector fiber laser

A new contact method to measure vibrations with a frequency range of about 30–110 Hz by a distributed Bragg reflector (DBR) fiber laser sensor, based on a beat frequency modulation, has been proposed. In order to demonstrate the plausibility for a DBR fiber sensor to detect vibrations lower than 110 Hz without any complex structures, it is encapsulated in a rectangular slice composed of an epoxy resin glue, with a Young’s modulus of about 2.9 GPa. In experiments, the packaged DBR fiber sensor is placed on a vibration platform to sense the vibration, with a commercial magnet-electrical vibration velocity transducer as a reference. Experimental results indicate that the single DBR fiber laser is able to measure the low-frequency vibration with a few tens of Hertz and several microns of amplitude, offering potential for a low-frequency vibration measurement.

Efficient 16 μm linearly-polarized single-frequency phosphate glass fiber laser

Based on the heavily Er3+/Yb3+ co-doped phosphate glass fiber (EYPF) with a larger emission cross-section, an efficient linearly-polarized single-frequency distributed Bragg reflector fiber laser at 1603 nm is demonstrated. By balancing the cavity length against the longitudinal mode spacing, a stable single-longitudinal-mode laser with more than 20 mW is generated from a 16-mm-long EYPF. The measured relative intensity noise of the fiber laser is less than –140 dB/Hz at frequencies of over 5 MHz. The signal-to-noise ratio is greater than 62 dB and the linewidth is less than 1.9 kHz, while the obtained polarization extinction ratio is higher than 25 dB. The L-band operating combined with the narrow linewidth and low noise characteristic makes this laser an ideal candidate for high-resolution molecular spectroscopy and coherent lidar applications.

A 1030 nm single-frequency distributed Bragg reflector Yb-doped silica fiber laser

We demonstrate a single-frequency fiber distributed Bragg reflector (DBR) laser operating at 1030 nm by using a 1.1 cm long commercially available highly Yb-doped silica fiber. The DBR fiber laser has a threshold pump power of 5 mW, and the maximum output power is over 160 mW with a slope efficiency of 27% relative to the launched pump power. The linewidth of the laser at 1030 nm is 6 kHz. With the aid of only a 5 cm long amplifier stage, the output power is scaled up to 306 mW with a slope efficiency of 51.5%.

Performance of dual-frequency ultrasound measurement based on DBR fiber laser hydrophone

The ability of distributed Bragg reflector (DBR) fiber laser sensor in dual-frequency ultrasound (DFUS) measurement has been demonstrated. The influences of DFUS pressure on fiber grating laser sensor were theoretically analyzed, considering the effects of relative distance of the ultrasound field and the amplitude of the DFUS on the degrees of birefringence modulation. In experiment, the birefringence in sensing fiber was modulated by ultrasound signals at 3MHz and 5MHz, and the test distance and driving voltage were set respectively according to the ultrasound frequency. Agreement between theoretical and experimental results was obtained for ultrasound wave propagating from different distances (40mm to 10mm) and different DFUS driving voltage (5V to 20V). The results demonstrate that the DBR fiber grating laser acoustic sensor has a multi-frequency ultrasound recognizable ability, offering a potential for ultrasound medicine and biology

Wide bandwidth dual-frequency ultrasound measurements based on fiber laser sensing technology.

A dual-frequency ultrasound measurement system based on a distributed Bragg reflector (DBR) fiber laser sensor in a liquid medium was presented. To compare the dual-frequency measurement performance of a DBR fiber laser acoustic sensor with that of a piezoelectric (PZT) ultrasound sensor, two experiments were performed. First, we fixed the driving frequencies of two ultrasound signals at 3 and 5 MHz, and decreased the driving voltage from 15 to 3 V. The outputs of the DBR acoustic sensor show flat-balanced response to dual-frequencies, compared with the PZT acoustic sensor whose response to one of the dual-frequency signals (5 MHz in this paper) has been covered by noise at low acoustic pressure. Then we increased the acoustic pressure by fixing the driving voltage at 20 V, and changed the frequency spacing between the two ultrasound signals. By analyzing the frequency response, sensitivity, signal-to-noise ratio, and noise equivalent pressure of two acoustic sensors under different frequencies, we found that the response of the DBR sensor to wideband dual-frequency is stable, while the response of the PZT sensor deteriorates sharply with increasing frequency spacing. The results demonstrate that the DBR fiber laser sensor performs better for wide bandwidth dual-frequency ultrasound measurements.

Thermally triggered fiber lasers based on secondary-type-In Bragg gratings.

The secondary-type-In grating formed in a small-core photosensitivity active fiber is discovered and investigated. Due to the different grating types, the transmission dip of a secondary grating structure chases and integrates with the type-In grating structure as the temperature increases, which strengthens the reflectivity of the grating. By use of these secondary-type-In gratings as Bragg reflectors, a thermally activated distributed Bragg reflector (DBR) fiber laser is proposed, which can be potentially used in high-temperature alarms and sensors.

Type IIa Bragg grating based ultra-short DBR fiber laser with high temperature resistance.

We report on the fabrication of a thermally resistant ultra-short distributed Bragg reflector (DBR) fiber laser based on the photo inscription of two wavelength-matched type IIa gratings in a thin-core Er-doped fiber. With continuous UV exposure, each Bragg reflector initially grows as a type I grating, followed by decay in strength, and then re-grows as a type IIa grating with enhanced thermal resistance. The DBR laser, with an entire length of 13 mm, can stably operate at 600°C with single longitude mode, which provides potential applications in high temperature environments.

High-power, high signal-to-noise ratio single-frequency 1 μm Brillouin all-fiber laser.

We demonstrate a high-power, high signal-to-noise ratio single-frequency Brillouin all-fiber laser with high slope efficiency at 1 μm wavelength. The laser is pumped by an amplified single-longitudinal-mode distributed Bragg reflector fiber laser with a linewidth of 33 kHz. By optimizing the length of the Brillouin ring cavity to 10 m, stable single-frequency Brillouin fiber laser is obtained with 3 kHz linewidth owing to the linewidth narrowing effect. At the launched pump power of 2.15 W, the Brillouin fiber laser generates maximum output power of 1.4 W with a slope efficiency of 79% and the optical signal-to-noise ratio of 77 dB.

Design Evaluation of DBR Fiber Laser Sensor for Directional Lateral Force Monitoring

This letter reports an analysis of the potential of distributed Bragg reflector (DBR) fiber laser sensor designed to monitor the force orientation information, and with the birefringence characteristics of optical fiber, enabling the measurement of a directional lateral force applied to the fiber. In system design, to interrogate birefringence variation of the sensor according to the change of applied force angles, a reference lasing signal was employed following the results of an analysis using heterodyning theory. Agreement between theoretical and experimental results was obtained for a constant lateral force loading from different directions corresponding to the variation of sensitivity in beat signals. The design created in this letter is based on fundamental principles and generic, thus suitable for use with any DBR fiber laser structure for vector sensor applications.

Magnetic field sensor based on the Ampere’s force using dual-polarization DBR fiber laser

A novel magnetic field sensor using distributed Bragg reflector (DBR) fiber laser by Ampere’s force effect is proposed and experimentally demonstrated. The key sensing element, that is the dual-polarization DBR fiber laser, is fixed on the middle part of two copper plates which carry the current. Ampere’s force is applied onto the coppers due to an external magnetic field generated by a DC solenoid. Thus, the lateral force from the coppers is converted to a corresponding beat frequency signal shift produced by the DBR laser. The electric current sensing is also realized by the same configuration and same principle simultaneously in an intuitive manner. Good agreement between the theory calculation and the experimental results is obtained, which shows a good linearity. This sensor’s sensitivity to the magnetic field and to the electric current finally reaches ~258.92 kHz/mT and ~1.08727 MHz/A, respectively.