chanelink logo
CHANELINK
English

The scientific research team has proposed a modeless Raman fiber laser using a traditional resonant cavity structure

393
2023-08-15 15:00:52
See translation
The pump source, gain material, and resonant cavity are the three elements that make up a laser. Due to the selective effect of the resonant cavity on the lasing frequency, multi longitudinal mode operation is one of the characteristics of fiber lasers based on traditional resonant cavity structures, manifested as periodic beat peaks in the radio frequency (RF) spectrum and periodic fluctuations in the intensity sequence in the time domain, and the frequency interval of the laser longitudinal mode is determined by the length of the resonant cavity.
 
However, the discrete multi longitudinal mode structure also poses challenges for some laser based applications. For example, in laser based optical sensing systems, the single frequency signal peak obtained through sensing elements such as phase-shifting gratings can only jump between discrete longitudinal modes and cannot achieve continuous frequency shift when it shifts with sensing parameters such as temperature and strain.

Therefore, the discrete longitudinal mode limits the maximum resolution of such optical sensors. In addition, in secure communication based on hardware encryption technology, the periodic fluctuations of the optical signal introduced by the resonant cavity feedback in the time domain can leak the length information of the laser cavity, reducing the security of secure optical communication.
 
In the generation of ultra fast random bit sequences based on laser intensity fluctuations, time period fluctuations can lead to signal repetition, thereby weakening the randomness of the generated sequence. Meanwhile, it seems impossible for multi longitudinal mode fiber lasers to achieve extremely low relative intensity noise similar to single frequency lasers.

Recently, Professor Shu Xuewen's team from the Wuhan National Center for Optoelectronics at Huazhong University of Science and Technology proposed a modeless Raman fiber laser (RFL). The laser adopts a traditional resonant cavity structure, but the output cavity mirror uses a fiber Bragg grating (FBG) with ultra-low reflectivity. Due to modulation instability, as the Stokes wave power inside the cavity increases, the longitudinal modes inside the cavity gradually widen, ultimately covering the longitudinal mode spacing, resulting in adjacent longitudinal modes overlapping each other and presenting a state of modeless operation. The relevant research results are titled "Modeless Raman fiber laser" and published in Optica, Vol. 10, Issue 8, 2023.

The structure of patternless RFL is shown in Figure 1. In order to avoid the transfer of relative intensity noise from the pump source to the Raman laser, the pump source uses an ASE light source built in the laboratory, with a central wavelength of 1540nm and a maximum output power of 10.3 W. The output grating adopts an ultra-low reflection FBG with a reflectivity of -27 dB.

The longitudinal mode of the laser can be reflected through the RF spectrum. Figure 2 (a) shows the RF spectra of Raman lasers experimentally measured at different laser output powers. At low power levels, there are significant characteristic peaks on the RF spectrum. But as the Stokes wave power increases, the periodic beat frequency peak related to the cavity length gradually widens and the height of the peak decreases. When the laser output power reaches 5.71 W, there are no longer distinguishable periodic beat peaks on the RF spectrum. This means that the discrete multiple longitudinal modes of the laser will gradually broaden with the increase of power, gradually covering the longitudinal mode spacing, and ultimately the longitudinal modes will completely overlap. In this case, RFL no longer has a discrete longitudinal mode structure like traditional lasers, but generates quasi continuous spectra similar to ASE light sources.

The research team used the generalized nonlinear Schr ö dinger equation to simulate the evolution of the optical field in Raman fiber lasers with laser output power, and obtained the RF spectrum of RFL as shown in Figure 2 (b). The simulation results show that the periodic beat frequency peak gradually disappears with the increase of power, which is basically consistent with the experimental measurement results.

Due to the generation of quasi continuous spectra by modeless Raman fiber lasers, their use in laser sensing systems can achieve continuous frequency modulation, significantly improving the resolution of optical sensors. At the same time, the disappearance of beat frequency peaks in the RF spectrum means that laser radiation no longer has temporal periodicity corresponding to the length of the resonant cavity, which has enormous application potential in secure communication, random sequence generation, and time-domain ghost imaging. Meanwhile, compared with traditional lasers, the modeless Raman fiber laser constructed has extremely low relative intensity noise. This research work has been supported by the National Key R&D Program (2018YFE0117400), the National Natural Science Foundation of China (62275093), and the EU H2020 MSCA RISE project.

Article link: https://doi.org/10.1364/OPTICA.488920


Figure 1. Schematic diagram of patternless RFL structure

Source: China Optical Journal Network
Related Recommendations

  • AWOL Vision will showcase cutting-edge laser projectors and award-winning innovations at CEDIA 2023

    AWOL Vision has announced that it will be showcasing the latest innovations in home entertainment at this year's CEDIA Expo in Denver, Colorado from September 7-9.At the show, AWOL Vision will debut the new LVV-3000 Pro and LVV-3500 Pro laser projectors with Dolby Vision and Control4 integration, and will showcase the latest Vanish TV, The TV recently received the prestigious "IFA 2023 Best of the...

    2023-09-08
    See translation

  • The most advanced gas sensing laser technology will be exhibited at the upcoming CEM 2023 exhibition in Barcelona

    Nanoplus Nanosystems and Technologies GmbH is an ISO 9001:14001 certified supplier and one of the world's most famous laser manufacturers for gas sensing applications. The cornerstone of nanoplus's success is its unique patented method of manufacturing DFB laser sources. Nanoplus celebrates its 25th anniversary this year and separated from the University of Vilzburg in 1998.Among the outstanding i...

    2023-09-14
    See translation

  • Researchers propose NeuFlow: an efficient optical flow architecture that can solve high-precision and computational cost issues

    Real time and high-precision optical flow estimation is crucial for analyzing dynamic scenes in computer vision. Although traditional methods are fundamental, they often encounter issues with computation and accuracy, especially when executed on edge devices. The emergence of deep learning has driven the development of this field, providing higher accuracy, but at the cost of sacrificing computati...

    2024-03-23
    See translation

  • Measuring invisible light through an electro-optic cavity

    Researchers have developed a new experimental platform that can measure the light wave electric field captured between two mirrors with sub periodic accuracy. This electro-optical Fabry Perot resonant cavity will achieve precise control and observation of the interaction between light and matter, especially in the terahertz (THz) spectral range. The research results were published in the journal "...

    02-19
    See translation

  • 330 million US dollars! This laser ophthalmic treatment developer has been acquired

    Recently, according to a report submitted by BioLight to the Tel Aviv Stock Exchange, Swiss American pharmaceutical and medical device giant Alcon Pharmaceuticals is acquiring Israeli medical technology company Belkin Vision.It is reported that BioLight will sell its 4% stake in Belkin Vision, which may be worth up to $330 million based on the milestones established in the transaction.Belkin Visio...

    2024-05-06
    See translation