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We proposed a silver-coated 45 radiated tilted fiber grating (45 RTFG) based interferometer, in which the 45 RTFG is working as a beam splitter and a coupler, and the light transmitting in the fiber core is radiated out and resonant in the cladding radial cavity formed by the fully coated silver film, which forms multiple beam interference. We have theoretically and experimentally investigated the proposed fiber interferometer in terms of polarization-dependent transmission spectra, the free spectral range (FSR), spectral visibility and sensing characteristics. Due to the single polarization radiation feature of 45 RTFG, only S-polarized light could form the multiple beam interference and P-polarized light would pass through the grating with low loss. And the FSR of the proposed fiber interferometer is around 6.8 nm, which is determined by the 125 m cladding diameter. The theoretical results show that the spectral visibility of interference is proportional to the coupling efficient of 45 RTFG and when the coupling efficient reaches 0.92, the spectral visibility is the maximum. In the experiment, the fiber interferometer formed by the 45 RTFG with 11 dB polarization extinction ratio has the spectral visibility of 26 dB. Moreover, we have also investigated the temperature, strain and twist characteristics of the proposed interferometer. The experimental results show that the transmission peak has a red shift with increasing temperature, with a sensitivity of 10 0.1 pm/C; The strain causes a blue shift for the transmission peak with -0.42 0.01 pm/ sensitivity, and the twist sensitivity reaches 22.408 0.2 dB/rad. The proposed silver-coated 45 RTFG based interferometer has an in-fiber and compact structure, which can be potentially used for optical fiber sensing.

We have experimentally demonstrated an all-fiber mode-locked laser by using a 45°-tilted fiber grating (45°-TFG) based in-fiber polarization beam splitter (PBS). Based on the nonlinear polarization rotation (NPR), the slanted refractive index modulation structure of the 45° TFG is able to tap the pluses out from the side face of the fiber. The central wavelength of the laser is 1559.9 nm and the period of pulse train is 156 ns, corresponding to the fundamental repetition rate of 6.79 MHz, the pulse energy of 0.26 nJ and the pulse duration of 1.06ps. Additionally, the laser shows a high degree of polarization (DOP) output of 99.8%. This mode-locked fiber laser with single polarization mode output is reliable during long-term operation and thus promising for many practical applications. As a proof of principle, the demonstrated laser can provide neat solution in designing compact mode-locked fiber laser.

A multi-switchable generation between dissipative solitons (DSs) and noise-like pulses (NLPs) in a fiber laser is demonstrated. A 45° tilted fiber grating is applied as an effective in-line all-fiber polarizer to realize the nonlinear polarization rotation (NPR) mechanism. With the fixed orientations of polarization controllers, the operation regimes of the fiber laser can be alternatively switched between DS and NLP by monotonically increasing pump power only. We observed five switching stages between DS/NLP regimes with the pump power elevating from 200 to 660 mW. Remarkably, the whole procedure could be precisely controlled forwardly and backwardly. This multi-shuttle behavior between the two distinct types of output pulse can be attributed to the transmission of NPR mechanism together with the gain filtering effect. To the best of our knowledge, this is the first report on the multi-shuttle behavior between DS and NLP in a fiber laser under monotonic change of pump power. Our findings may contribute to in-depth understanding of nonlinear dynamics and laser physics.

We review the wavelength selective switch (WSS) for ultra-broadband transmission and spatial division multiplexing. We also discuss and present experimental results of WSS components with high spectral resolution and compactness.

We report the observation of second order Bragg resonance (2nd-OBG) produced by tilted fiber gratings (TFGs) fabricated using phase mask UV inscription. The theoretical analysis has revealed that the generation of high order Bragg resonance of gratings is induced by a square-shape refractive index profile, which is caused by over-saturated UV exposure. In the experiment, we have studied the TFGs with different tilt angles under over-saturated UV exposure, in which all gratings have showed the 2nd-OBR, and the larger tilt angle of the grating has the stronger 2nd-OBR. When the tilt angle of the grating is ∼45°, the Bragg resonance exhibits very strong polarization dependence, because the 2nd-OBR wavelength is located within the polarizing bandwidth of 45° TFG. Finally, we have demonstrated an erbium-doped fiber laser with >99.9% degree of polarization, and, by applying mechanical stretching on the grating, a wavelength tunable laser output has been achieved. The output laser shows ∼0.2 dB amplitude variation within 1 h continuous monitoring of the laser.

In this paper, we report a Surface Plasmon Resonance (SPR) Surrounding Refractive Index (SRI) sensing system based on a hybrid grating structure comprising of a 45o tilted fiber grating (TFG) and a silver coated small angle tilted fiber Bragg grating (TFBG) that have been inscribed into a single mode fiber in series. In this structure, the 45o-TFG is used as a polarizer (replacing a Polarizer Controller) to filter out the S-Polarization mode of the light, and enable the TFBG operating at the P-Polarization mode for SRI sensing. The experiment results show that the sensor covers a range between 1.33 and 1.40 refractive index units (RIU) with a sensitivity of 509.32 nm/RIU.

We demonstrate a pump-controlled wavelength switchable Yb-doped fiber laser (YDFL) by nonlinear polarization rotation (NPR) for the first time. The polarizer replaced by a 45° tilted fiber grating (45°-TFG) combines with a section of polarization maintaining fiber (PMF) to form a fiber-based birefringent filter. Stable dissipative soliton (DS) with center wavelength of 1068.39 nm is generated under the mode-locked threshold of 277 mW. The operating wavelength switching between 1046.51 nm and 1067.90 nm can be realized via increasing the pump power simply while keeping the polarization controllers (PCs) in a fixed state. The laser maintains stable mode-locking operation at each wavelength, which can be regarded as a type of multi-wavelength ultrafast light source with precise control and integration potential.

We experimentally demonstrate a harmonic-order controllable L-band Er-doped passively mode-locked fiber laser based on nonlinear polarization rotation (NPR). Distinct from all previous reports, we find that the intracavity birefringence is able to control the harmonic order of a passively mode-locked fiber laser. Experimentally, under a constant pump power of 704 mW, the harmonic order can be tuned from 113th to 39th monotonically by adjusting the polarization controller orientation only. The corresponding repetition rate changes from 2.21 to 0.77 GHz simultaneously. Remarkably, the super-mode suppression ratio of each harmonic order we observed is higher than 29 dB with a maximum of 36.5 dB. Simulated transmission spectra of NPR prove that the changed transmission plays an important role in controlling the harmonic order.

We proposed a hybrid tilted fiber gratings (polarizing grating and tilted fiber Bragg grating)-based surface plasmon resonance (SPR) sensor. The hybrid tilted fiber grating, consisting of a polarizing grating and tilted fiber Bragg grating (TFBG), is fabricated in a single-mode fiber in series by using a UV-inscription technique, in which the TFBG could generate a dense cladding mode resonance to excite SPR and the polarizing grating could filter out the S-polarization cladding mode of the TFBG. Such proposed hybrid tilted fiber gratings could greatly simplify the interrogation system of the TFBG-based SPR sensor. The experiment results showed that the hybrid tilted fiber gratings-based SPR sensor has the refractive index sensitivity of 522.8 nm/RIU. Finally, by using the proposed sensor, we have achieved the hemoglobin concentration detection within a sensing range from 0.1 mg/mL to 1.0 mg/mL and the sensitivity of 8.144 nm/(mg/mL).