image: (a) Schematic diagram and (b) photo of the fabricated gas-filled hollow-core fiber phase modulator. (c) Measured loss spectrum and (d) transient response of the phase modulator. view more
Credit: OEA
A new publication from Opto-Electronic Advances, 10.29026/oea.2023.220085 discuss broadband low-loss all-optical phase modulator using gas-filled hollow-core fiber.
Optical phase modulators are key components in optical communication, sensing, and signal processing systems. All-optical modulators, which modulate the phase or intensity of a light signal by a control light beam, have attracted much research interest. The phase of signal beam is controlled by the control light beam rather than an electronical signal, which avoids electro-optical conversion in the optical link and makes it possible to breakthrough the “electronic bottleneck” in principle.
The reported all-optical phase modulators are mainly based on 2D-material-coated optical waveguides. The signal light beam is modulated by the control beam through the interaction between the waveguide evanescent field and the 2D materials, including Kerr nonlinear effect and photo-thermal effect. Kerr effect enables fast modulation but the attainable phase modulation is small limited by the optical power density of evanescent field and the nonlinear coefficient of 2D material. Longer interaction length contributes to a higher phase modulation, but also leads to increased loss. Photo-thermal effect enables larger phase modulation over π. However, these phase modulators typically have high insertion loss and narrow wavelength band, limited by the absorption and imperfect deposition of low-dimensional materials, and long response time of several milliseconds due to heat conduction process. Although a lot of low-dimensional materials have been studied, there is still a big gap from practical usage. Developing novel all-optical phase modulators with low loss, broad wavelength band, fast response is essential to promote the development of all-optical technology.
The authors of this article discuss a broadband all-fiber optical phase modulator based on the light-gas interaction in a hollow-core fiber (HCF). In the HCF, most of the optical mode power propagates in the hollow core, which is free from absorption of the solid fiber materials. This enables extremely broadband low-loss transmission, from the ultraviolet to the mid-infrared, apart from a few narrow resonant loss bands. The HCF can confine gas phase material, a high intensity control beam and a signal beam simultaneously in the hollow core, providing an ideal platform for strong light-gas interaction over a long interaction length.
An all-optical phase modulator with insertion loss about 0.6 dB within C+L band and half-wave power about 289 mW at 100 kHz is fabricated. It has response time at μs scale, which is 2-3 orders better than the 2D-material-coated microfiber-based all-optical modulators. Due to the intrinsic limitation of the thermal conduction process, it is quite challenging to achieve modulation bandwidth over 1 MHz using this method. It may have promising applications in fiber optic interferometer-based phase demodulation systems in particular for harsh environment and remote applications, as well as for all-fiber actively Q-switched lasers, which do not require very high modulation bandwidth. The broad transmission bands of the state-of-the-art HCFs in combination with the many available gas species would also allow the development of all-optical modulators from ultraviolet to mid-infrared, which are quite challenging to realize with solid state materials.
Keywords: optical modulators / photo-thermal effects / hollow-core fibers
# # # # # #
The team of Prof. Wei Jin from the Photonics Research Center at the Shenzhen Research Institute of the Hong Kong Polytechnic University focus on the research of optical fiber sensing and devices. They have contributed to the theory of micro-structured optical fibers, fiber-enhanced gas sensing, and fiber grating sensing, and so on. Their research result on trace gas detection was rated as “China’s Top 10 Optical Breakthroughs in Optics in 2020”.
Prof. Wei Jin currently holds the position of Chair Professor of Photonic Instrumentation in Department of Electrical Engineering at the Hong Kong Polytechnic University. He is also Chiang Jiang Chair Professor award from Ministry of Education of China and a fellow of OSA. He has undertaken over 10 projects in the past few years, including National Major Scientific Instruments and Equipments Development Project of China, National Key Research and Development Program of China, General Research Fund of Hong Kong, and Innovation and Technology fund of Hong Kong. He edited 4 books/proceedings, authored/co-authored 8 book chapters, >300 Journal papers, and >10 patents in the area of fiber optic devices and sensors. He delivered >90 plenary/keynote/invited speeches at international/national conferences.
# # # # # #
Opto-Electronic Advances (OEA) is a high-impact, open access, peer reviewed monthly SCI journal with an impact factor of 8.933 (Journal Citation Reports for IF2021). Since its launch in March 2018, OEA has been indexed in SCI, EI, DOAJ, Scopus, CA and ICI databases over the time and expanded its Editorial Board to 36 members from 17 countries and regions (average h-index 49).
The journal is published by The Institute of Optics and Electronics, Chinese Academy of Sciences, aiming at providing a platform for researchers, academicians, professionals, practitioners, and students to impart and share knowledge in the form of high quality empirical and theoretical research papers covering the topics of optics, photonics and optoelectronics.
# # # # # #
More information: http://www.oejournal.org/oea
Editorial Board: http://www.oejournal.org/oea/editorialboard/list
All issues available in the online archive (http://www.oejournal.org/oea/archive).
Submissions to OEA may be made using ScholarOne (https://mc03.manuscriptcentral.com/oea).
ISSN: 2096-4579
CN: 51-1781/TN
Contact Us: oea@ioe.ac.cn
Twitter: @OptoElectronAdv (https://twitter.com/OptoElectronAdv?lang=en)
WeChat: OE_Journal
# # # # # #
Article reference: Jiang SL, Chen FF, Zhao Y, Gao SF, Wang YY et al. Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber. Opto-Electron Adv 6, 220085 (2023). doi: 10.29026/oea.2023.220085