Research Status of Photonic Crystal Fiber Gratings

The photonic crystal fiber grating has its historical inevitability. It is said that the production of photonic crystal fiber gratings has historical inevitability, because science and technology are in the process of continuous development. When new substances are discovered, there will be new breakthroughs in related substances that surround this substance, that is, when photonic crystals New and new materials have been discovered and produced. The fiber grating that surrounds the photonic crystals will produce new materials - photonic crystal fiber gratings.

Since Hill 1978 produced the first fiber grating, fiber gratings quickly entered all walks of life, especially optical fiber communication and fiber optic sensing, and its application brought a qualitative leap to fiber sensing. The FBG is formed by changing the refractive index written at a part of the position of the core of the optical fiber in a certain function, so that the core and the cladding produce different coupling efficiencies between different modes (reflected on the transmission line and the reflection line). The characteristics. He can be widely used in the detection and monitoring of the sensor system, such as real-time monitoring of the pressure on the bridge to ensure the safety of the bridge, which is mainly used at different pressures, the fiber grating will produce a slight change in refractive index, The small refractive index change will make the central wavelength of the transmission spectrum (or reflection spectrum) of the fiber grating move by several nm, and then know the bridge to bear the pressure in real time. In addition to the safety inspection of public facilities such as bridges, it can also be applied in many industries such as alarm, biosensing, and medical devices. The extensive application of fiber Bragg gratings has promoted the further maturation and development of its theory and laid a solid theoretical foundation for photonic crystal fiber gratings.

By 1987 Yablonovith proposed photonic crystals, which immediately attracted the attention of many scientific workers. They deeply realized that this would cause changes in industrial products. The arrangement of the periodical dielectric constant of the photonic crystal will cause the photon to be similar to the electron in the crystal to generate the energy band and generate the photonic bandgap, so that the era of electricity is well into the era of light. With the people's yearning for the light age, the theoretical analysis and production methods of photonic crystals are rapidly developing. Soon, photonic crystal fibers were proposed in 1992, and in 1996 Knight and others produced the first photonic crystal. Fiber optics have revolutionized traditional fiber optics. It solves the problem that has always caused headaches in traditional optical fiber. For example, the bending loss problem, the traditional optical fiber is the use of light in the transmission to the boundary between the cladding and the outside world to generate total reflection to transmit optical signals, if the fiber is bent for some reason, this will make the light in the The interface does not satisfy the total reflection condition and is mostly transmitted to the outside world, thereby losing the signal. Photonic crystal fibers are different. Photonic crystal fiber band gap theory points out that if the transmitted light falls exactly on the band gap of the photonic crystal, the light cannot propagate in the photonic crystal regardless of whether the fiber is bent or bent. Large losses may occur. For example, the controllable dispersion characteristics of photonic crystal fibers can relax the requirements of optical fiber transmission light sources. Widespread use of photonic crystal fibers also predicts the generation of photonic crystal fiber gratings.

Soon, in 1999, Eggleton et al. produced the first photonic crystal fiber grating in the laboratory and investigated and measured its characteristics. Its successful production opened the door to the subject of photonic crystal fiber gratings. Subsequently, almost every year, different scientists created different photonic crystal fiber gratings. Looking at the overall situation, the photonic crystal fiber grating is actually an inevitable scientific and technological achievement of the premise technology. This collection of various technologies (fiber grating, photonic crystal, photonic crystal fiber) and integrated photonic crystal fiber grating, it has the advantages of various technologies, it will also meet the needs of society.

Research Status of Photonic Crystal Fiber Gratings in China

For photonic crystal fiber gratings, China has also done a lot of research on it, and has achieved very good research results. In the early days, the Institute of Modern Optics at Nankai University realized the fabrication of a Bragg fiber grating using a phase mask method in a photonic crystal fiber treated with high-pressure hydrogen sensitization. In 2004, Zhi et al. showed that the long-period fiber grating-based long-period fiber grating simulation analysis showed that the resonant wavelength of the long-period fiber grating has a non-monotonic change to the grating period, and for a certain grating period, there may be multiple Resonant wavelength. In 2005, Fu et al. used an ultraviolet femtosecond laser to write a fiber Bragg grating on a pure silicon photonic crystal fiber, and the method of writing a grating with a transmission loss of 10 dB and an average refractive index change greater than 4×10-4. Wang et al. used CO2 laser pulses to write long-period fiber gratings with high-strain sensitivity (-7.6pm/με) and low-temperature sensitivity (3.91pm/oC) on photonic crystal fibers. Sensors made with such long-period fiber gratings can effectively reduce the cross-sensitivity between stress and temperature, and the temperature-induced strain measurement error is only 0.5 με/oC without the use of compensation techniques. In 2007, Li Yan et al. used the beam propagation method to study the mode cutoff characteristics of solid-doped photonic crystal fiber Bragg gratings. The three conditions that the excited high-order response mode is satisfied in the photonic crystal fiber Bragg grating are given: the phase matching condition, the electric field overlap in the grating region and the corresponding response mode to be excited (ie satisfy the inequality relationship: Vpcf>π). In 2008, Wang et al. successfully fabricated long-period gratings on hollow-core photonic bandgap fibers using high-frequency short-cycle CO2 pulsed lasers. Analysis of its characteristics shows that this LPG also has high strain sensitivity and insensitivity to temperature, bending, and refractive index. It can be used to make strain sensors without the cross-sensitivity problems of temperature, curvature and refractive index. Li Zhiquan et al. proposed the concept and analysis method of photonic crystal to study the sampling fiber grating. The characteristics of the reflection spectrum of the sampling fiber grating were studied from the perspective of the photonic crystal and compared with the results obtained by the sampling fiber grating transmission matrix method. The characteristics of the theoretical analysis using photonic crystals and the analysis using the traditional model-coupling theory were obtained. Jin et al. used a 193 nm ArF excimer laser to write Bragg gratings in high-doped erbium-doped PCFs, which greatly improved the gate grating efficiency, and the entire exposure time lasted less than 180 seconds. In 2009, Zhang et al. used beam propagation to study the effect of interstitial pores on a erbium-doped photonic crystal fiber Bragg grating. The analysis shows that the interstitial pores can cause the Bragg resonance wavelength to shift to a short wavelength, increasing the difference between the Bragg center wavelength value λB and the wavelength value λ1 of the nearest neighbor side lobe (ie, λB−λ1), and can also affect the coupling coefficient. Now photonic crystal fiber grating has become a hot topic in the world. More and more scientists in China have invested in it, making outstanding contributions to China's science and technology.