Polarization-maintaining Fiber Sagnac Loop Research Articles

High-Sensitivity Temperature Sensor Based on Polarization Maintaining Fiber Sagnac Loop

A high-sensitivity all-fiber temperature sensor based on a Sagnac interferometer is demonstrated by splicing a section of polarization maintaining fiber (PMF) between two sections of standard single mode fibers (SMFs). In this sensor, the SMF-PMF-SMF structure in the Sagnac loop is bent into a circle to enhance the sensitivity. The length and curvature of the PMF in the loop are investigated and can be optimized to further increase the temperature sensitivity of the sensor. Results show that the radius of the circle has an important effect upon temperature sensitivity due to the bend-induced birefringence variation of the PMF. The SMF-PMF-SMF structure bent into a circle with a radius of 30 mm exhibits a high-sensitivity temperature of 1.73 nm/°C. The sensor is provided with the advantages of easy fabrication, low-insertion loss, and high sensitivity, which may find potential applications in the field of high precision temperature measurement.

Multiwavelength thulium-doped silica fiber laser incorporating an all-fiber phase modulator

A novel multiwavelength thulium-doped silica fiber laser incorporating an all-fiber phase modulator is first presented in 2μm band. In the laser cavity, a phase modulator with a modulation frequency is efficient and beneficial to overcome the mode competitions. A polarization maintaining fiber Sagnac loop mirror is used as the filter. Large number of lasing wavelengths can easily and conveniently obtained at a proper modulation frequency under room temperature. The fiber laser can achieve ten output channels within a 15dB bandwidth from 1982nm to 1998nm.

A multiwavelength thulium-doped silica fiber laser incorporating a highly nonlinear fiber

A multiwavelength Tm3+-doped silica fiber laser incorporating a highly nonlinear fiber is presented. In the laser cavity, a nonlinear polarization rotation (NPR) based fiber loop mirror is used to overcome the mode competition and a polarization-maintaining fiber Sagnac loop mirror is used as the filter. The 150 m highly nonlinear fiber can improve the NPR effect in the laser cavity, which can increase the number of output channels. By adjusting the polarization state of the polarization controllers properly, stable multiwavelength operation at the 2 μm spectrum can be obtained at room temperature. It can achieve 15 output channels within a 10 dB bandwidth from 1990 to 2007.5 nm. The channel spacing of the multiwavelength Tm3+-doped silica fiber laser is 1.22 nm. Moreover, the performance of the laser is investigated for different pump powers and fibers.

Tunable and switchable six-wavelength erbium-doped fiber ring laser

A tunable and switchable six-wavelength erbium-doped fiber ring laser based on a fiber Bragg grating based FP filter (FBG-FPF) and a polarization-maintaining fiber Sagnac loop (PMFSL) is proposed and demonstrated experimentally at room temperature. The FBG-FPF with low insertion loss is used to generate dense multiwavelength output. The PMFSL acts as a comb filter and frequency stabilizer. Through adjusting the squeezed fiber polarization controllers, six kinds of single-wavelength with the tunable range of 11 nm, eleven kinds of dual-wavelength, three kinds of triple-wavelength and one kind of six-wavelength can be obtained and switched with one another. All lasing lines with 3 dB linewidth of less than 0.29 nm and optical signal-to-noise ratio of more than 22 dB locate in the range of C- and L-bands of the optical communication waveband.

A linearly-polarized tunable Yb-doped fiber laser using a polarization dependent fiber loop mirror

A Ytterbium-doped linearly-polarized fiber laser is constructed with a polarization maintaining fiber Sagnac loop mirror. The fiber loop mirror made of polarization maintaining fiber coupler has a polarization dependent reflectivity, which provides the necessary polarization discrimination between the slow and fast axes. With a fiber Bragg grating written in normal polarization maintaining fiber as an output coupler, laser output of up to 5.6W at 1070nm is generated with a polarization extinction ratio of >20dB and an overall efficiency of 55%. The broadband polarization dependent reflection of the fiber loop mirror offers advantages of easy spectral tuning and simple linearly-polarized laser generation.

A vibration detection system based on two-stage polarization maintaining fiber Sagnac loop fiber laser

A novel fiber grating sensing technique utilized for vibration detection is proposed and experimentally demonstrated. A single wavelength laser is formed by polarization controllers and polarization maintaining fiber (PMF) to construct the high birefringence (Hi-Bi) Sagnac loop, PMF combined with erbium-doped fiber, single mode fiber and polarizer. The cantilever glued to an FBG is used as a sensor probe, and the linear edge of Sagnac ring laser are used to demodulate fiber optic seismic vibration signal. Sagnac ring theory and its edge effects are described in detail, and numerical simulation and experiment show that the vibration signal detection system is adjusted periodically in a range from L1 to L1 + L2, sensitivity goes up to 38.2 W/nm of discrimination, the linearity is 0.9996, and the dynamic range is 4070 dB, these meeting the requirements for vibration detection technical parameters.

Switchable dual-wavelength erbium-doped fiber laser based on polarization-maintaining fiber Sagnac loop mirror and fiber Bragg gratings

A switchable dual-wavelength erbium-doped fiber laser is proposed and experimentally demonstrated, which is constructed by a polarization-maintaining fiber Sagnac loop mirror (PMF-SLM) and two FBGs with different wavelengths. Wavelength switching operation is achieved by properly adjusting the polarization controller (PC) in the PMF-SLM. Stable single- or dual-wavelength lasing output can be realized. The maximum amplitude variation for every lasing wavelength is less than 1 dB, and the signal-to-amplified spontaneous emission (ASE) ratio is about 35 dB.

Switchable and tunable multiple-channel erbium-doped fiber laser using graphene-polymer nanocomposite and asymmetric two-stage fiber Sagnac loop filter

A high-performance multiple-channel erbium-doped fiber laser (EDFL) is proposed and experimentally demonstrated, using graphene-polymer nanocomposite as a multiwavelength equalizer and an asymmetric two-stage polarization-maintaining fiber (PMF) Sagnac loop as a flexible comb filter. At first, the filtering characteristics of the PMF Sagnac loop filter (SLF) are investigated. Both theoretical and experimental results show that it can provide a flexibly switchable and tunable comblike filtering. Then, the two-stage PMF SLF is inserted into a graphene-assisted EDFL cavity for generating multiwavelength oscillation. The extreme-high third-order optical nonlinearity of graphene is exploited to suppress the mode competition of the EDFL, and a stable multiple-channel lasing is observed. By carefully adjusting the polarization controllers in the two-stage PMF SLF, not only can the lasing-line number per channel be switchable between single and multiple wavelengths, but also the wavelength spacing in the triple-wavelength condition can be tunable. In the case of triple wavelengths per channel, up to 12 wavelengths with four channels stable oscillations can be achieved. The multiple-channel EDFL can keep a high extinction ratio of >40 dB and a narrow linewidth of <0.01 nm.

Graphene-Assisted Multiwavelength Erbium-Doped Fiber Ring Laser

We propose and experimentally demonstrate a stable multiwavelength erbium-doped fiber (EDF) ring laser based on four-wave-mixing of atomic few-layer graphene. The compact laser cavity consists of 3-m EDF, an optically deposited ultrathin graphene device, and a polarization-maintaining fiber Sagnac loop filter. The comparison between the ring laser cavity without and with the graphene device shows that the highly nonlinear graphene can be helpful to mitigate the mode competition of EDF laser and stabilize the multiwavelength oscillation. Under the assistance of the graphene device, power-equalized eleven-channel simultaneous lasing with a wavelength-spacing of 0.54 nm is achieved at room temperature. This laser has a very high extinction ratio up to 57 dB and a narrow linewidth per channel of less than 0.01 nm.

Multi-point interrogation of FBG sensors using cascaded flexible wavelength-division Sagnac loop filters

A simple optical signal demodulation technique is demonstrated for multi-point interrogation of fiber Bragg grating sensors. The wavelength-division responses of polarization-maintaining fiber Sagnac loop filters are flexibly controlled to interrogate the simultaneous optical intensity changes from the independent wavelength shifts of multiple fiber Bragg grating sensors. Experimental performance is also demonstrated to show the simultaneous detection of the separated FBG sensing signals by individual photo detectors.

Ultrafast all-optical logic operations in a nonlinear Sagnac interferometer with two control beams

Ultrafast highly stable all-optical logic operations, including inversion, AND, XOR, and XOR, in a two-wavelength nonlinear Sagnac interferometer with two control beams have been reported. The interferometer consists of a dichroic polarization-maintaining fiber coupler and a 200-m-long dispersion-shifted polarization-maintaining fiber Sagnac loop. The logic operations were successfully demonstrated at multigigabit operation per second, and the required signal power was 1.8 W for a 200-m fiber.