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(a) Effective index of the even and odd modes versus frequency for the air-doped coupler (Λ = 682.5 µm, d/Λ = 0.52, Λc = 102.375 µm, dc/Λc = 0.25) and un-doped solid-core coupler (Λ = 682.5 µm, d/Λ = 0.52). Solid red curve is the calculated FSM. Green short vertical solid line represent the cross point between the odd mode and cladding mode of the air-doped coupler, corresponding to the fundamental-mode cut-off frequency. (b) Coupling lengths of the air-doped (black dashed line) and un-doped solid-core (black solid line) coupler versus frequency. Blue solid curve represents the frequency dependent total loss of the air-doped coupler.
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We present a thorough practical design optimization of broadband low loss, terahertz (THz) photonic crystal fiber directional couplers in which the two cores are mechanically down-doped with a triangular array of air holes. A figure of merit taking both the 3-dB bandwidth and loss of the coupler into account, is used for optimization of the structu...
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The development of SPP-based terahertz waveguides has demonstrated being of great potential to achieve an appropriate trade-off between losses and dispersion, particularly for sensing and imaging operations at that spectral band. In this work, we implement a microstructured fiber comprising an air core surrounded by an array of silver rods and air...
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Citations
... Further, PCF sensors (Elhelw et al. 2023;Hameed et al. 2017;Rabee et al. 2019) have high sensitivity, compact size, and flexibility compared to other optical sensors. Nowadays, terahertz (THz) PCFs with hollow core or porous core have been suggested in different applications such as absorbers (Shi et al. 2016), polarization rotator , and directional couplers (Bao et al. 2014). Further, terahertz sensors gained great importance because most of the molecular absorption spectra lie in the terahertz range (Saadeldin et al. 2019). ...
In this work, THz photonic crystal fiber (PCF) is used to detect the creatinine level in the blood with high sensitivity. The sensing technique depends on increasing the light interaction with the analyte infiltrated into the air holes in the fiber core region. In this regard, most of the light power should be confined through the analyte region. This will increase the relative sensitivity coefficient that is proportional to the analyte power fraction. The operation of the suggested sensor is based on studying the light–analyte interaction at different creatinine concentrations by detecting the change of the analyte power fraction against the change of the creatinine level in the blood at the THz range 0.5–1.5 THz. The effective mode index (neff), effective material loss (EML), effective modal area (Aeff), and relative sensor sensitivity are calculated using the full vectorial finite element method. Additionally, the different geometrical parameters are studied to maximize the sensor’s sensitivity. The proposed THz-PCF has a 93% and 95% relative sensitivity for x- and y-polarized modes, respectively. Therefore, the suggested THz-PCF biosensor gives a promising usage in measuring the creatinine level in the blood.
... To sample a small amount of power out of the fiber for measurement and connect fibers of different configurations or sizes, various sorts of directional couplers and mode couplers have been developed, respectively. In the THz regime, directional couplers have been investigated experimentally and numerically [31][32][33][34]. Besides, long period gratings have been applied to achieve core-cladding mode coupling and progress has been made in the visible and infrared regime [35,36]. ...
With the rapid development of optoelectronic fibers of multi-materials and structures, coupling between the optoelectronic fibers and the conventional optical fibers with high transmission is desirable. In this article, we propose a mode coupler to facilitate the transmission of electromagnetic wave from a dielectric fiber to a simple metal-core optoelectronic fiber in the terahertz regime. The coupler mainly consists of an air cone along its symmetric axis. The transmission characteristics of the terahertz wave of the frequency ranging from 2 to 8 THz for five hybrid modes are investigated using finite difference time domain method. We show the dependence of the transmission on the height of the air cone for the selected frequencies.
... Although great progresses have been made in the field of THz fiber research, compared with optical fiber devices [8,9], the development of THz fiber devices has been slow so far, the advancement of THz field is constrained. In order to promote the rapid development of THz technology, THz fiber devices have become a research hotspot, such as THz fiber directional coupler [10,11] and THz fiber filters [12,13]. ...
We present a new scheme of dual-core THz fiber for tunable polarization splitter based on the mode coupling theory. Each elliptical polymer core is modified with two elliptical air holes, which is helpful for high modal birefringence and low transmission loss. Due to different coupling lengths for x and y polarizations, the two orthogonal polarizations can be easily separated in an appropriate transmission length. Characteristics of the proposed fiber are discussed numerically in detail, including modal birefringence, effective material absorption loss, coupling and splitting length, transmission loss, extinction ratio, tunability. For the THz polarization splitters, 0.865 cm splitting length is numerically demonstrated at the operation frequency of 1 THz. An efficient tuning method is provided that the operation frequency can be tuned by the applied pressure. This tuning method extends the operation frequency bandwidth from 0.9 to 1 THz in the fixed splitting length. This proposed pressure-tuning THz fiber polarization splitter has potential applications in the field of on-chip integrated THz polarization devices and in-fiber integrated optical devices.
... Among these waveguides, porous fiber with slotted cladding and core has made a remarkable achievement for low loss of 0.01 cm − 1 (0.043 dB/cm) [16]. Apart from the transmission of light, THz systems incur a high desire of optical components, which include fiber filters [17], fiber switches [18], polarization-maintaining fibers [19,20] and fiber couplers [21,22]. The incorporation of some optical components into the optical fiber would be beneficial for an integrated "all-fiber" network. ...
We propose a terahertz polarization splitter based on suspended dual-core fiber. Each core of the fiber is formed with two adherent subwavelength polymer tubes, which is helpful for a high modal birefringence. Due to the difference of coupling length between x and y polarizations, the proposed splitter can completely separate two orthogonal polarization modes at a specific splitting length. A 1.184 cm long splitter can be obtained at a center frequency of 1 THz. Meanwhile, the low insertion loss of 0.6 dB, the bandwidth of 0.05 THz and the extinction ratio better than −10 dB can be supplied. Moreover, an efficient design rule for the proposed splitter is demonstrated aiming to high extinction ratio at any desired operation frequency. The proposed terahertz polarization splitter has some potential applications in all-optical networks in THz systems.
... Due to the inherent design flexibility and robustness of dual-core PCFs, couplers based on dual-core PCFs have been extensively studied and reported. They are used in several applications, such as Gaussian and tunable bandpass and bandstop filters [2], biosensing and refractive index sensing using wavelength shift [3,4] and intensity shift [5], and also in terahertz directional couplers which are mechanically downdoped to achieve broadband functionality [6,7]. These couplers play an important role in realizing power exchange between two parallel waveguides along their lengths. ...
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... The purpose of these designs is to guide the THz radiation through the air (which is a transparent medium for THz) while keeping the wave well confined within the fiber core. Possibility of low-loss waveguide in the THz range facilitates efficient applications of this band in communication [6], sensing [7], imaging [8], spectroscopy [9], biotechnology [10], non-invasive screening [11], medical diagnosis [12], directional coupling [13], and many more. ...
A suspended core microstructured fiber with extremely high birefringence has been proposed for terahertz (THz) wave propagation. An elliptical-shaped core has been formed with slotted rectangular airholes to disrupt the vertical symmetry of the refractive index of the designed fiber. Different design parameters such as the core diameter, ellipticity, porosity, and suspended strut width have been checked to achieve optimum performance from the fiber. The resultant birefringence of the proposed fiber is unprecedented, of the order of 10 − 1 ( 1.057 × 10 − 1 to be precise) with a low effective material loss of 0.047 cm − 1 and confinement loss of 9.4 × 10 − 3 cm − 1 at 1 THz. The dispersion of the designed fiber is below 1 ps/THz/cm extended over a band of 500 GHz (1–1.5 THz) with almost flat profile. It is expected that this fiber could be useful in interferometry, filtering, and sensing applications in the THz range where polarized lights are favorably essential.
... However, for fluid sensing with porous fibers, (i) terahertz components are easier to manufacture compared to those in the optical regime, and (ii) molecular resonances tend to be in the terahertz range, making it an ideal candidate for chemical sensing. As an advancement of terahertz technology, different types of terahertz functional devices such as terahertz absorbers [17][18][19] and terahertz directional couplers [20] have been developed. Moreover, dielectric tube [21] and PCF-based waveguides [22,23] have also been introduced for terahertz wave transmission. ...
Ethanol is widely used in chemical industrial processes as well as in the food and beverage industry. Therefore, methods of detecting alcohol must be accurate, precise, and reliable. In this content, a novel Zeonex-based photonic crystal fiber (PCF) has been modeled and analyzed for ethanol detection in terahertz frequency range. A finite-element-method-based simulation of the PCF sensor shows a high relative sensitivity of 68.87% with negligible confinement loss of 7.79 × 10 − 12 cm − 1 at 1 THz frequency and x -polarization mode. Moreover, the core power fraction, birefringence, effective material loss, dispersion, and numerical aperture are also determined in the terahertz frequency range. Owing to the simple fiber structure, existing fabrication methods are feasible. With the outstanding waveguiding properties, the proposed sensor can potentially be used in ethanol detection, as well as polarization-preserving applications of terahertz waves.
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A novel waveguide consisting of oligo-porous core photonic crystal fiber (PCF) with a kagome lattice cladding has been designed for highly birefringent and near zero dispersion flattened applications of terahertz waves. The wave guiding properties of the designed PCF including birefringence, dispersion, effective material loss (EML), core power fraction, confinement loss, and modal effective area are investigated using a full vector Finite Element Method (FEM) with Perfectly Matched Layer (PML) absorbing boundary condition. Simulation results demonstrate that an ultra-high birefringence of 0.079, low EML of 0.05 cm−1, higher core power fraction of 44% and negligible confinement loss of 7.24×10−77.24×10−7 cm−1 can be achieved at 1 THz. Furthermore, for the y-polarization mode a near zero flattened dispersion of 0.49±0.050.49±0.05 ps/THz/cm is achieved within a broad frequency range of 0.8–1.7 THz. The fabrication of the proposed fiber is feasible using the existing fabrication technology. Due to favorable wave-guiding properties, the proposed fiber has potential for terahertz imaging, sensing and polarization maintaining applications in the terahertz frequency range.
... The effective approach is to design a waveguide that confines most of the guide mode power in the dry air and propagate a small portion to material [4]. Then various forms of plastic or polymer fibers have been proposed, which include hollow-core fibers [5], anti-resonant tubes [6], Bragg fibers [7], flexible tube lattice fibers [8], and porous fibers [9,10], etc. Recently, intense attention has been paid to porouscore photonic crystal fibers (PCFs), which offer relatively low effective material loss and low confinement loss, and are relatively convenient to manufacture [11,12]. ...
We propose a kind of square porous-core photonic crystal fiber (PCF) for polarization-maintaining terahertz (THz) wave guidance. An asymmetry is introduced by implementing rectangular array air holes in the porous core of the PCF, and ultrahigh birefringence and low effective material loss (EML) can be achieved simultaneously. The properties of THz wave propagation are analyzed numerically in detail. The numerical results indicate that the proposed fiber offers a high birefringence of 0.063 and a low EML of 0.081 cm − 1 at 1 THz. Moreover, a very low flattened dispersion profile is observed over a wide frequency domain of 0.85–1.9 THz. The zero flattened dispersion can be controlled. It is predicted that this PCF would be used potentially in polarization maintaining and dispersion management of THz waves.
... Wireless communication with terahertz (THz) carrier waves is a rapidly developing field [1,2], with considerable effort being devoted to demonstrations of high-data rate links [3][4][5] as well as devices for transporting [6,7] and manipulating [8][9][10][11] THz signals. Dielectric waveguides represent one important platform for both signal transport and signal processing. ...
