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Passive Fibre Optic Devices
Published in Abdul Al-Azzawi, Photonics, 2017
Optical circulators are used in a wide variety of applications within fibre communication systems. In advanced optical communication systems, optical circulators are used for bi-directional transmissions, wavelength division multiplexing (WDM) networks, fibre amplifier systems, optical time domain reflectrometers (OTDR), etc. Optical circulators are nonreciprocal devices that redirect a signal from port to port sequentially, in only one direction. The operation of an optical circulator is similar to that of an optical isolator; however, its construction is more complex. Figure 27.13(a) shows a three-port optical circulator. An input signal (λ1) at Port 1 exits at Port 2, an input signal (λ2) at Port 2 exits at Port 3, and an input signal (λ2) at Port 3 exits at Port 1. Similarly, in a four-port optical circulator, as shown in Figure 27.13(b), one could ideally have four inputs and four outputs. In practise, many applications do not need four inputs and four outputs. Therefore, in a four-port circulator, it is common to have three input ports and three output ports. This is done by making Port 1 an input-only port, Ports 2 and 3 input and output ports, and Port 4 an output-only port. A typical application of the isolators is demonstrated in Figure 21.13. Input signals of different wavelengths are circulated to the next port in a clockwise direction.
Passive Fibre Optic Devices
Published in Abdul Al-Azzawi, Fibre Optics, 2017
Optical circulators are used in a wide variety of applications within fibre communication systems. In advanced optical communication systems, optical circulators are used for bi-directional transmissions, wavelength division multiplexing (WDM) networks, fibre amplifier systems, optical time domain reflectrometers (OTDR), etc. Optical circulators are nonreciprocal devices that redirect a signal from port to port sequentially, in only one direction. The operation of an optical circulator is similar to that of an optical isolator; however, its construction is more complex. Figure 6.13(a) shows a three-port optical circulator. An input signal (λ1) at Port 1 exits at Port 2, an input signal (λ2) at Port 2 exits at Port 3, and an input signal (λ2) at Port 3 exits at Port 1. Similarly, in a four-port optical circulator, as shown in Figure 6.13(b), one could ideally have four inputs and four outputs. In practise, many applications do not need four inputs and four outputs. Therefore, in a four-port circulator, it is common to have three input ports and three output ports. This is done by making Port 1 an input-only port, Ports 2 and 3 input and output ports, and Port 4 an output-only port. A typical application of the isolators is demonstrated in Figure 21.13. Input signals of different wavelengths are circulated to the next port in a clockwise direction.
Passive Fibre-Optic Devices
Published in Abdul Al-Azzawi, Fibre Optics, 2017
Optical circulators are used in a wide variety of applications within fibre communication systems. In advanced optical communication systems, optical circulators are used for bi-directional transmissions, wavelength division multiplexing (WDM) networks, fibre amplifier systems, optical time domain reflectrometers (OTDR) and so on. Optical circulators are non-reciprocal devices that redirect a signal from port to port sequentially, in only one direction. The operation of an optical circulator is similar to that of an optical isolator; however, its construction is more complex. Figure 6.13a shows a three-port optical circulator. An input signal (λ1) at Port 1 exits at Port 2, an input signal (λ2) at Port 2 exits at Port 3 and an input signal (λ2) at Port 3 exits at Port 1. Similarly, in a four-port optical circulator, as shown in Figure 6.13b, one could ideally have four inputs and four outputs. In practice, many applications do not need four inputs and four outputs. Therefore, in a four-port circulator, it is common to have three input ports and three output ports. This is done by making Port 1 an input-only port, Ports 2 and 3 input and output ports and Port 4 an output-only port. A typical application of the isolators is demonstrated in Figure 6.13. Input signals of different wavelengths are circulated to the next port in a clockwise direction.
Bidirectional coherent optical communication system combining unidirectional optical signal amplification
Published in Journal of Modern Optics, 2020
Shiwen Jin, Shuqiang Chen, Miao Yan, Yuanyuan Jiang
In our recent study, a single-fiber bidirectional coherent optical communication system based on unidirectional optical signal amplification is proposed, as showed in Figure 1. The carrier emitted by the laser from the receiving end goes through the coupler into the transmission fiber, via the polarization controller and optical circulator into the modulator. After completing the signal modulation, the output modulated signal goes along the original optical path back to the homodyne coherent demodulation, and the carrier reflected back by port 3 acts as a coherently received LO. Finally, the transmission compensation is completed by DSP. Since the carrier and LO are the same laser, it greatly decreases the phase shift caused by the frequency offset between the carrier and local oscillator as well as the laser linewidth, which simplify the phase shift compensation algorithm of the DSP, and avoid the usage of OPLL. In addition, this new type of bidirectional coherent optical communication system can be used as a new technology for secure communication. Once the transmission fiber is cut, the signal cannot be modulated due to the carrier source being interrupted, and of course the signal cannot be intercepted.
Fibre axial strain sensor based on a microwave photonic filter with dual-passband
Published in Journal of Modern Optics, 2018
Jianghai Wo, Jin Zhang, Anle Wang, Pengfei Du, Yalan Wang, Wenshan Cong, Xiong Luo, Xin Xu, Lan Yu
The schematic of the proposed MPF-based sensing system is shown in Figure 1. The dual-passband MPF, including two tunable laser sources, a phase modulator (PM), two cascaded FBG-FPs and a photodetector (PD) are employed as the sensing system. Light emitted from two lasers is combined by an optical coupler and sent to a PM via and a polarization controller (PC). The PM is driven by a sinusoidal microwave signal generated by a vector network analyzer (VNA). Then the signals are sent to the cascaded FBG-FPs through an optical circulator (OC) to achieve the phase-modulation to intensity-modulation (PM-IM) conversion. After detection by a PD, the electrical signal is amplified by a low noise amplifier (LNA) and finally sent back to the VNA to obtain the frequency response.
Wide-band flat-gain optical amplifier using Hafnia and zirconia erbium co-doped fibres in double-pass parallel configuration
Published in Journal of Modern Optics, 2019
Alabbas A. Al-Azzawi, Aya A. Almukhtar, P. H. Reddy, D. Dutta, S. Das, A. Dhar, M. C. Paul, H. Ahmad, S. W. Harun
At the input of the amplifier, we employ an optical circulator to forward the input signal from a tunable laser source (TLS) into the C/L-band coupler, and to allow the twice amplified signal to be routed into the optical spectrum analyzer (OSA). We employ a C/L-band coupler to separate/combine both C- and L-band signals into/from first and second stage. At the end of each stage, an optical circulator is used as a reflector so that the test signal is allowed to propagate twice in the active fibre. The amplified signal is allowed to reflect into the active fibre by joining port 3 with port 1 for the circulator. This allows the light from port 2 is routed back into the same port.