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Polarization Control
Published in Kenichi Iga, Yasuo Kokubun, Encyclopedic Handbook of Integrated Optics, 2018
It is essential in many applications that the polarization controller generates the desired polarization transformation continuously and without any interruptions or significant degradations of the transmitted optical signal. It is often further required that the controller automatically searches for the desired transformation using just a single electrical feedback signal, which typically is proportional to the optical amplitude or power of the output light in the desired SOP. This feedback signal is generated by an optical receiver downstream the optical path, as shown in Figure 1, and the polarization controller is the part of an automatic feedback loop that generates its error signals by dithering the various adjustable parameters of the controller slightly about their current values. Then an electronic circuit monitors the effects of these dither variations on the feedback signal and readjusts the control parameters for maximal signal level.
Optical Fiber Sensing Solutions
Published in Krzysztof Iniewski, Ginu Rajan, Krzysztof Iniewski, Optical Fiber Sensors, 2017
Yuliya Semenova, Gerald Farrell
Fiber-optic Sagnac interferometers (SIs) were developed in the 1970s based on the well-known principle of Sagnac interference. In a fiber-optic SI, input light is split into two parts propagating in the opposite directions by a 3 dB fiber coupler and these two counterpropagating beams are combined again at the same coupler as shown in Figure 2.8 [41]. The fabrication of such an interferometer can be simply achieved by connecting the ends of a conventional 3 dB coupler. Highly birefringent fibers or polarization-maintaining fibers (PMFs) are typically utilized as sensing fibers since such fibers maximize the polarization dependence of the signal within the SIs. In order to control the input light polarization, a polarization controller is connected to the sensing fiber.
Passive Optical Components
Published in Jerry D. Gibson, The Communications Handbook, 2018
The polarization controller is a fiber device for producing a desired state of polarization. Although most fiber systems operate independently of the state of polarization of the optical beam, coherent systems and certain sensors are very much dependent on the state of polarization of the optical signal.
Intra-cavity fibre dislocation structure assisted all-fibre ring laser sensor
Published in Journal of Modern Optics, 2021
The experimental schematics of the proposed strain sensing based on few-mode interference is presented in Figure 3. The pump light is provided by a laser. It is coupled into the cavity by a wavelength division multiplexer (WDM). The gain medium is Er-doped fibre (EDF). An optical isolation (ISO) at is utilized to maintain the ring laser unidirectional operation. A polarization controller (PC) is used to control the polarization states in the cavity, balance the gain and loss, and control the number of wavelength peaks in the laser-output spectrum. A 5/95 optical coupler is inserted into the cavity with a 95% power feedback into the cavity and 5% power coupled out. The output power is coupled into an OSA.
Liquid crystal technology for vergence-accommodation conflicts in augmented reality and virtual reality systems: a review
Published in Liquid Crystals Reviews, 2021
where nave is the average refractive index (∼ (ne + no) / 2), and in Equation (8) is the angle of the incident light with respect to the helical axis of the cholesteric LC (Figure 16(a)). Ne and no are the extraordinary and ordinary refractive index, respectively. Two LC reflective polarizers using cholesteric LCs are placed in the AR optical system as mirrors, as shown in Figure 16(b). The polarization controller changes the polarization of light between the right-handed circular polarization and left-handed circular polarization. Then, the right-handed and left-handed circularly polarized light is reflected by the reflective polarizer of the same handedness. The reflected light returns to the beam splitter and is then redirected into the eyes. The distance between the two reflective polarizers results in two different virtual image planes. Hence, by switching the polarization controller on and off, the virtual image plane can be adjusted. The drawbacks of the LC reflective polarizer are the narrow reflective bandwidth ( ∼ 150 nm) of cholesteric LC, low oblique light tolerance (small FOV), and existence of only two image planes. The reflection bandwidth can be broaden by engineering the pitch of LCs as mentioned [57,91], and the FOV can be enlarged with compensation films.