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Abstract
Broadband multifunction optical devices can play an important role in the field of integrated photonics but achieving high tunability and versatility on a fabricated device by implementing external control or structural modification is still challenging. In this article, what we believe to be a new dual-function optical device based on photonic crystal fiber, having an ultra-broad bandwidth that partially covers near-infrared (IR) to mid-IR regions, is proposed and analyzed. This device is designed on a fabrication friendly geometry such a way that it can be used as a polarization filter as well as refractive index sensor without any external tuning or structural modification. In this case, plasmonic material plays a crucial role for achieving simultaneous operation of the device both in communication and sensing applications. Our proposed device, with a fiber length of 100 µm, can effectively suppress the y-polarized light within the wavelength range of 1.29 µm to 1.60 µm, while the x-polarized light is maintained properly in the core, and vice-versa for the region of 1.69 µm to 4.39 µm. The maximum confinement losses of 840.8 dB/cm, 1013.2 dB/cm, 659.65 dB/cm, and 792.68 dB/cm are obtained at wavelengths of 1.37 µm, 1.56 µm, 1.72 µm, and 2.65 µm, respectively. By maintaining a crosstalk level of better than 20 dB, this device achieves broad bandwidths of 310 nm over the 1.29 µm to 1.60 µm wavelength range and 2700 nm over the 1.69 µm to 4.39 µm wavelength range. In addition to the filtering performance, our device possesses sensing capabilities, which is also well discussed as an example of refractive index sensor. Considering the analyte refractive index of 1.10-1.40, this device shows an average wavelength sensitivity of 1000 nm/RIU. Therefore, the above exceptional characteristics of our proposed device make it suitable for both optical communication and sensing systems.
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1. Introduction
In the modern world, optical fibers have become an integral part of communication and information systems. In the recent years, a new class of fiber, known as photonic crystal fibers (PCFs), has emerged. It is also acquainted as microstructured optical fibers due to the cross-sectional arrangement of air holes in a regular pattern [1–2]. PCFs are capable of controlling light in many ways that were not imaginable in the past, and they have exceptional properties such as high birefringence [3], endless single mode transmission [4], anomalous dispersion [5], and higher nonlinearity [6], etc. It is more advantageous than standard solid core fiber specially in terms of the design flexibility, which is useful for adjusting fiber performance parameters [7]. This freedom on PCF design has opened up new possibilities for various PCF based optical devices such as polarization filters [8,9], sensors [10], polarizer [11], splitters [12], rotators [13], and so on. In order to make these optical devices, the air holes of the PCFs can be filled with semiconductors [14], fluids [15], and metals [16]. For example, Tyagi and colleagues [14] filled air holes of a PCF by pure germanium to modify the fiber properties for applications in nonlinear optical devices. Among the various possibilities, plasmonics or plasmonic materials have contributed significantly in enhancing device performance. This plasmonic effect in PCF is generally achieved by adding a thin layer of gold in PCF structures or by completely filling specific air holes using various fabrication processes [9,16]. When photons are incident on metal surface, the surface plasmon polaritons (SPPs) [9] are incited along the metal periphery. The effect of surface plasmon resonance (SPR) arises when the resonance condition is met between SPPs on metal periphery and incident photons [8,16–18]. As a result, energy gets transferred from the PCF core to SPP mode, leading to abrupt energy drop of PCF core mode. This feature can be used to design PCF based compact (few hundred microns) optical devices such as polarization filter [8], splitter [12], etc. Among those devices, compact polarization filters are very important not only in many polarizations sensitive research purposes but also in communication and sensing.
As a result, researchers are currently very interested in SPR based polarization filters in PCF platform. In 2017, Li et al. reported two gold nanowires filling PCF based filter where confinement loss reaches 330.75 dB/cm at 1.31 µm resonance wavelength [19], but air hole diameter tuning is required to operate the filter in multiple windows. Another single window operated V shaped polarizer was investigated by Qu and co-authors, where y and x polarization core mode losses are 689 dB/cm and 8.58 dB/cm, respectively, at 1.55 µm [20]. Moreover, some double windows polarization filters were also reported by other authors [21–23]. For example, a tunable filter was reported by Yang and colleagues with undesired mode loss of 53.10 dB/cm at 1.31 µm and 305.1 dB/cm at 1.55 µm [21], and the proposed device also requires parameters tuning (liquid filling, silver layer variation) for operating in two well-known communication windows. Again, in another literature [23], Wang and his co-workers reported a filter capable of working in dual windows, but liquid infiltration is compulsory for that design. Moreover, researchers [24,25] achieved a high loss ratio on complex structures having different diameters of air holes, but these devices are unable to work simultaneously on two popular communication windows of 1.31 µm and 1.55 µm. For example, a tunable D-shaped polarization filter having complex structure was proposed in 2022, where the structural modification is required for operating the device in dual optical windows [25]. To summarize the research gaps, it is noticed from the literature that most of the filters work at single communication window (i.e., limited bandwidth). Moreover, few works have been reported on filters for operation in dual communication windows, but those reported filters require additional modifications such as liquid filling, changes in air holes diameter, modification in metal structures etc. Moreover, some designs proposed by the researchers are also difficult to fabricate [24,25,26]. Up to date, to the best of our knowledge, there is no report of a PCF based filter that covers the bandwidth partially from near-IR to mid-IR wavelength regions, provides dual functionalities, and does not require any post fabrication modifications or external control.
Being motivated from the aforementioned research gaps, we propose a fabrication friendly PCF based dual-function plasmonic optical device, which has been modeled and analyzed numerically in this work. Notably, the proposed device can be used not only in communication region but also for sensing applications due to its wideband (near IR to mid-IR ranges) filtering characteristics without the requirement of any external control or post processing to our fiber geometry. Our analysis shows that y-polarized light is lossier than the x-polarized one from the wavelength range of 1.29 µm to 1.60 µm and vice-versa for 1.69 µm to 4.39 µm of wavelengths. Therefore, the device achieves the best bandwidths performance up to date, as far as we know, which are 310 nm (1.29 to 1.60 µm) for near-IR and 2700 nm (1.69 to 4.39 µm) for about mid-IR regions, respectively. This is achieved with a fiber length of 100 µm fiber and crosstalk exceeding 20 dB. To demonstrate the sensing capabilities of our proposed device, we considered one way of analyte filling in our device and obtained an average wavelength sensitivity of 1000 nm/RIU. This sensitivity is limited, and further improvements can be achieved by exploring alternative methods of analyte infiltration or creating better analyte channels.
2. Device design with theory
Figure 1 exhibits the cross section of the proposed polarization filter geometry. The structure has three air holes rings (equivalently considered as layers in this case) and each air hole is circular in shape. One air hole is removed from the center to create the core of the fiber. The separation between two air holes in a ring is referred as the lattice constant and is denoted by $\varLambda$. In the 1st layer (closest air holes ring to the core), the diameter of the smaller air holes along the horizontal direction is marked by d1 and the diameter of the other four air holes (arranged along vertical directions) is d2. In the 2nd layer (middle ring), two air holes are larger whose diameter is marked by d3 (without gold coating) and chosen to implement gold coating layer with a thickness of th = 27 nm. The remaining air holes of 2nd layer are uniform and their diameter is presented as d. Similarly, the air holes diameter of third layer (the outer most air holes ring) is uniform with the same diameter as d. Finally, the optimized structural dimensions are summarized as $\varLambda$ = 1.59 µm, d1 = 0.25 µm, d2 = 0.89 µm, d3 = 1.64 µm, d = 1.28 µm, and th = 27 nm. The horizontal and vertical directions are denoted by x and y as shown in Fig. 1. The outer layer is used to fix the computational area of our device and is marked as the perfectly matched layer (PML). The material for PML region is same as background material (silica). Moreover, the silica, air, gold, and PML regions are represented by gray, white, red and purple colors, respectively (Fig. 1).
Fig. 1. 2D view of the suggested PCF based filter with optimized designed dimensions of $\varLambda$ = 1.59 µm, d = 1.28 µm, d1 = 0.25 µm, d2 = 0.89 µm, d3 = 1.64 µm, and th = 27 nm. Silica, air, gold, and perfectly matched layer (PML) regions are marked as gray, white, dark red, and purple colors, respectively.
The basic background material for the proposed fiber is selected as silica and can be effectively modeled using the Sellmeier’s equation [8,27] as follows
3. Results and discussions
The mode coupling characteristics were observed using finite element method (FEM) in COMSOL Multiphysics software. By choosing the proper geometric dimensions and material properties, the proposed structure was optimized. The unwanted signals in the computational area were eliminated by using proper PML. To facilitate the design process, a COMSOL 2D model was used, and a mode analysis was performed. For optimizing mesh element size and thickness of boundary layer, a convergence test was performed on the device model, following the literatures [27,29], and the results are shown in Figs. 2(a) and 2(b), respectively.
Fig. 2. Convergence test of proposed design for (a) maximum element size of mesh, and (b) the thickness of perfectly matched layer (PML).
From Fig. 2(a), it is observed that the confinement loss curve becomes stable for maximum mesh element size less than 4.07 µm because larger mesh element size indicates weak meshing; hence, for better computational accuracy, we took maximum mesh element size of 0.13 µm for our computational design model. Similarly, it is evident from Fig. 2(b) that the characteristic curve stabilizes when the thickness of PML layer is above 0.3 µm, but 1 µm thick PML layer was used in our simulation for better computational accuracy. In addition, some recent and related structures [24,28] were simulated and the results were compared for the justification of our numerical accuracy and good agreement was observed. Fiber parameters such as confinement loss, refractive index, and crosstalk were computed with the help of COMSOL Multiphysics and MATLAB softwares.
We have included effective refractive index and confinement loss spectra in Fig. 3 where core and plasmonic (SPP) modes of our presented filter are taken into consideration. The core modes of both x- and y-polarized lights are shown by blue and red colors, respectively, while the SPP modes are represented by different colors and corresponding different symbols. From the Fig. 3(a), it is evident that the 1st and 2nd order SPP modes (y-pol.) undergo strong coupling showing distinct filter characteristics in the communication wavelength region. To be specific, the y-polarized core mode is coupled with the 1st and 2nd order SPP (y-pol.) modes at the wavelengths of 1.37 µm and 1.56 µm respectively, resulting in two loss peaks as indicated in Fig. 3(b). In contrast, 1st and 2nd order SPP (x-pol.) modes dominate the filter performance in the mid-IR region. Here, the x-polarized core mode is coupled with the 2nd and 1st order SPP (x-pol.) modes at the wavelengths of 1.72 µm and 2.65 µm, respectively. Notably, the coupling strength between 2nd order SPP and core mode is much higher at 1.56 µm than other coupling points (Fig. 3(b)). The confinement losses at this point are 1013.2 dB/cm and 166.29 dB/cm for y- and x-polarized, respectively. At the wavelength of 1.37 µm, the confinement losses are 840.8 dB/cm and 81.57 dB/cm for y- and x-polarized light, respectively. Moving further in the mid-IR region, the confinement losses are found as 659.65 dB/cm and 792.68 dB/cm for x-polarized light and 174.43 dB/cm and 66.59 dB/cm for y-polarized light at resonance wavelengths of 1.72 µm and 2.65 µm, respectively.
Fig. 3. (a) The characteristics of effective refractive index (ERI) with the wavelength while two (x, y) polarized core and SPP modes are considered, and (b) the confinement loss scenario of both polarized (x, y) core modes with the variation of wavelength, for our proposed optimized design. Red and blue peaks indicate the maximum loss in near IR and a portion of mid-IR wavelength regions, respectively.
The electric field distribution profile with the direction of x- and y-polarized light for our proposed filter are inset in Fig. 3(b) at the resonance wavelength of 1560 nm. At this wavelength, it is noticed that the core mode of y-polarized light is coupled with the 2nd SPP mode when phase matching condition is satisfied and therefore, maximum energy from the core mode is transferred to the SPP mode. For this reason, maximum confinement loss is found at this wavelength for y-polarized light. In the same way, maximum loss peaks can be found at the wavelengths of 1370, 1720, and 2650 nm with corresponding loss ratios of 10.3, 3.8, and 11.90, respectively.
To operate the proposed filter in our desired bands, proper structural parameters optimization is required. For this reason, we initially varied the lattice constant ($\varLambda$) by keeping remaining parameters unaltered and Fig. 4(a) reveals the effect of changing $\varLambda$ on the polarization filtering response. It is found that as the value of $\varLambda$ increases, the resonance wavelength shifts to longer wavelengths. This is owing to the change of coupling effect between the ERI of core mode and SPP modes [8]. Now, when the value of $\varLambda$ is selected as 1.59 µm, the maximum loss is found as 1013.2 dB/cm at the wavelength of 1560 nm. Further increment of the lattice constant to 1.61 µm results the loss peaks shifting towards longer wavelengths. In contrast, the loss peaks are shifted towards shorter wavelengths along with the reduced loss strength due to the reduction of lattice constant to 1.57 µm. So, lattice constant, $\varLambda$ = 1.59 µm is chosen as optimized value for this structure due to the improved performance observed at around 1.55 µm of wavelength.
Fig. 4. Confinement loss scenario of both polarized (x, y) core modes with the variation of wavelength for different (a) lattice constant ($\varLambda$), and (b) diameter d, of our proposed filter. Legend colors and markers are correlated with the corresponding line curves. The other structural parameters of the proposed filter are set as d1 = 0.25 µm, d2 = 0.89 µm, d3 = 1.64 µm, and th = 27 nm.
Next, the diameter, d is tuned by keeping other parameters fixed as stated before. When the value of d is 1.28 µm, the loss peaks are found at the wavelengths of 1.37 µm and 1.56 µm with corresponding loss values of 840.8 dB/cm and 1013.2 dB/cm, respectively in the communication region. Now if we decrease d from 1.28 µm to 1.26 µm, then loss peaks are shifted right (to longer wavelengths) which is noticeable from Fig. 4(b). Again, if d is raised from 1.28 µm to 1.30 µm, the curve is left shifted (to shorter wavelengths). But in both cases, 1st loss peak almost remains fixed and this is due to the rapid variation of the ERI of 1st order SPP mode compared to higher order SPP modes. As the ERI of 1st order SPP varies rapidly than other higher order SPP modes, the coupling between 1st order SPP and core mode is stronger than upper order SPP and core modes. The same phenomenon can also be observed from the reported literature [9]. Observing the better performance at 1.28 µm (Fig. 4(b)), d = 1.28 µm is selected as our optimum value.
Now we will examine the effect of change in d1 (= 0.25 µm) on the polarization characteristics of the suggested filter from Fig. 5(a). If the value of d1 is changed from 0.25 µm to 0.27 µm or 0.23 µm, then the confinement loss peaks remain almost in same wavelength. With the increase of d1, most of the energy will be contained at the fiber core, preventing it from reaching the metal surface. This significantly reduces the SPR effect and therefore, the required confinement loss also gets reduced [28]. As maximum loss is observed for 0.25 µm, so d1 = 0.25 µm is taken as optimum value. Figure 5(b) indicates the effect of d2 alteration on our PCF based polarization filter and negligible change is observed. But for getting maximum confinement loss ratio at our desired wavelength, careful consideration for the dimension of d2 is necessary. In this case, when d2 is set as 0.89 µm, the maximum confinement loss is found at our expected wavelengths of 1.37 µm and 1.56 µm with the corresponding loss values of 840.8 dB/cm and 1013.2 dB/cm, respectively, in the communication wavelength region. The reason behind this is the coupling between core mode and SPP modes to a great extent at this value of d2; hence, d2 = 0.89 µm is chosen as the optimum value.
Fig. 5. Confinement loss behavior of both polarized (x, y) core modes with the variation of wavelength for different (a) d1, and (b) d2. Legend colors and markers are correlated with the corresponding line curves.
Figure 6(a) shows the result of the variation of d3 on the nature of confinement loss, and it is observed that with the rise of d3, the ERI of SPP modes decrease while core mode remains almost same. As a result, the phase matching point between core and SPP modes is shifted left to the shorter wavelengths [24]. Again, with the increment of air hole diameter d3, the core mode faces difficulties to leak light in the cladding area, hence, the strength of coupling between core and SPP modes gets weaker [24]. For this reason, if the value of d3 is increased, the confinement losses are also decreased. Now, if the value of d3 is selected as 1.64 µm, then the maximum confinement losses are found at 1.37 µm and 1.56 µm in the communication region. As expected, if the value of d3 is increased from 1.64 µm to 1.66 µm, the peaks of the loss curves are shifted to shorter wavelengths with decreased confinement losses and opposite results are found for decreasing d3. So, d3 = 1.64 µm is the optimum value for this structure.
Fig. 6. The nature of loss of both polarized (x, y) core modes with the variation of wavelength for different (a) d3, and (b) gold coating thickness (th) of our proposed filter. Legend colors and markers are correlated with the corresponding line curves.
Gold layer thickness (th) plays a significant role on the polarization filtering [8,24,28]. To get proper filtering performance at desired wavelengths, it is important to carefully choose the gold layer thickness because with the increment of gold layer thickness, the electric field faces difficulties to penetrate through the gold layer [8,24]. As a result, confinement loss reduces with thicker gold layer as shown in the Fig. 6(b). Again, with the rise of th, the ERI of SPP mode reduces while the core mode has negligible changes [24]. Hence, the intersection point between SPP and core modes (i.e., loss peaks) are shifted towards left (i.e., shorter wavelengths) due to the increase in th. When the value of th is chosen as 27 nm, the maximum confinement losses are observed in the communication region (at 1.37 µm and 1.56 µm) with the corresponding loss values of 840.8 dB/cm and 1013.2 dB/cm, respectively. If the value of th is increased from 27 nm to 29 nm, then the loss curves are shifted towards shorter wavelengths with a decrease in loss strength and vice versa (for decreasing th). Therefore, th = 27 nm is the optimum value for our designed structure.
The structure should be kept as simple as possible for fabrication, and fabrication tolerance of our proposed device is investigated by modifying the structural parameters within ±2%. It is noted that the PCF design parameters can be regulated within ±1% tolerance during the fabrication process as argued in the literatures [8,12,30] and specially by Reeves and his colleagues (Russell’s group) [30]. Figures 7(a) and 7(b) indicate the variation of loss spectrum for $\varLambda$ and d, respectively, with the manufacturing tolerance of ±2%. From the curve, it is observed that though the loss peaks show slight changes with the variations in $\varLambda$ and d (the reason has already been discussed in the optimization section in Figs. 4(a) and 4(b)) but the overall bandwidth remains almost same. Similarly, Figs. 8(a) and 8(b) indicate the effect of the variation in d1 and d2, respectively, considering ±2% manufacturing tolerance, and Figs. 9(a) and 9(b) show the impact of variations in d3 and gold thickness (th). From these figures (Figs. 8 and 9), it is noticed that these variations in the parameters have less effect on the confinement loss spectra, and the overall bandwidth is weekly influenced by structural parameters (d1, d2, d3, and th). Therefore, our proposed design can also be fabricated commercially even if the PCF parameters are changed by ±2% due to manufacturing tolerance, without losing our desired filter output.
Fig. 7. Confinement loss scenario of both polarized (x, y) core modes with the variation of wavelength having ±2% alteration of (a) pitch ($\varLambda$), and (b) d. The corresponding line curves correlate with the legend colors and markers. Other structural parameters are kept at their optimized values.
Fig. 8. Confinement loss spectra with ±2% variation of (a) d1, and (b) d2 for the core modes for both polarized (x, y) lights in our discussed filter. Legend colors and markers are matched with line curves.
Fig. 9. Effect of ±2% variation of (a) d3, and (b) gold thickness (th) on the confinement loss scenario for different wavelengths for both polarized core modes (x, y) of our proposed filter is considered. Same colors and markers are used for legend and line curves.
Crosstalk (CT) has similar meaning with the extinction ratio in our case and is another important term to characterize a filter by which the influence of unwanted polarized mode can easily be understood. It is well known that the CT level of more than 20 dB or less than -20 dB indicates the well segregation of two polarized modes (x, y) [20,25], and is determined [20,25,31,32] as
Table 1 shows the comparative summary of the achievements between our proposed work and several recent studies [19–25,28,33]. Analyzing the reported works [19–25,28,33], it becomes evident that most of the designs work within a single window. For achieving dual window operation, either parameter tuning, or liquid infiltration is required which presents major drawbacks for these reported PCF filters [19,21–23,25]. For instance, Li et al. [19] proposed a polarizer for single communication window that requires air hole diameter tuning to operate the filter in dual windows. In another work, Qu and colleagues [20] reported a V shaped filter which operates only in single window. In addition, some researchers tried to design filters with complex structures having different diameters of air holes for dual windows but these filters lack the coverage of popular communication windows [24,33]. Furthermore, most of the reported works in the literature are unable to cover all the communication bands (O, E, S, C, L). In contrast, our designed filter overcomes these limitations and offers broad bandwidth which covers most of the optical communication bands to the mid-IR region (approximately) without the need of structural modifications. Moreover, our device offers dual functionality as it can also be used as a refractive index sensor. This versatility distinguishes our proposed device as a new and innovative solution compared to the previously reported works as shown in Table 1.
Fig. 10. The crosstalk (dB) of the suggested filter with various optical fiber lengths (L) at optimized condition where 20 dB crosstalk is chosen as reference. Legend colors and markers are correlated with the corresponding line curves.
Table 1. Comparative Results of Our Proposed Polarization Filter with Some Other Related Reported Filters
To demonstrate the sensing capabilities of the proposed device, the four air holes with the diameter d2, around the core of our device, were filled with analyte having refractive index (n) of 1.00, 1.10, 1.20, 1.30 and 1.40 as shown in Fig. 11(a). Then the sensing performance of our device was analyzed under each condition. The confinement loss curves of y- and x-pol. core modes with different analytes in the aforementioned configuration are depicted in Figs. 11(a) and 11(b), respectively. From the Fig. 11, it is evident that the loss peaks exhibit a blue shift corresponding to the change in refractive index of the analyte. This observation confirms the sensing capability of the presented device and the corresponding wavelength sensitivity (S) is evaluated by [34]
where ∂λ is resonance wavelength gap between two loss peaks for any two consecutive analyte RI, and ∂n is distinction of those two RI. In accordance with Eq. (5), the calculated wavelength sensitivity is presented in Fig. 12, where the average wavelength sensitivity is determined to be 1000 nm/RIU. Furthermore, sensitivity enhancement for this device can be achieved by filling different air holes with specific analytes or by creating new analyte channels in future designs.Fig. 11. The confinement loss spectra while four air holes of 1st layer is filled with the analyte having different refractive index (n) of 1.00, 1.10, 1.20, 1.30, and 1.40 for (a) y- polarized, and (b) x-polarized core modes of our proposed filter. Loss peaks change due to the refractive index change of analyte although the optimized structural parameters are kept unchanged.
Fig. 12. The change of resonance wavelength with the variation of analyte refractive index. Refractive indices are chosen arbitrarily to show the sensing possibility of the presented fiber over a wide spectral region. Interestingly, only x-polarized light is useful for sensing within around communication windows and y-polarized light able to work on around mid-IR region.
Due to the advancement of nanotechnology, there are different available methods [1,2,35–38] for fabricating PCF or fiber based optical devices [39]. Hence, for the practical realization of our proposed work, the device can be fabricated using very well-known fabrication technologies such as stack-and-draw method [1,35], liquid phase deposition [36], and chemical vapor deposition [37] techniques. Firstly, using the conventional stack-and-draw technique, silica capillaries and rods can be assembled together to make desired preform stack so that it will be very similar to the cross section of our proposed fiber structure. The stackable units that would be used to produce preform stack should be in appropriate size and shape. Then, the preform stack must be kept in glass tube and fused together. Finally, it would be pulled down by fiber drawing tower through furnace having high temperature (about 1800 ° C to 2000 ° C) and the proper fiber size can be achieved [1,35]. The size of the air holes and their regularity can be controlled by adjusting the different parameters during fabrication such as furnace temperature, fiber drawing speed, preform feed rate, etc. Finally, gold layer can be accumulated on the inner parapet of desired air holes of our proposed filter by chemical vapor deposition or liquid phase deposition method as presented in [36,37]. Formerly, Bise and his colleagues fabricated a circular lattice PCF [38] which conveyed the evidence of such type of PCF in reality. Again, gold or silver coated PCF was also fabricated as indicated in the existing literatures [2,11]. Therefore, it is hoped that modern fabrication technologies should be able to fabricate our proposed device having circular type air holes with gold coating layers.
4. Conclusion
In summary, a polarization filter on a fabrication friendly PCF geometry is designed for communication as well as sensing purposes in the range of about near-IR to mid-IR regions (without any liquid filling or dimension variation) by combining the benefits of x- and y- polarized lights. The proposed design is analyzed using FEM and the effect of the change in structural parameters, fabrication tolerance, and sensing mechanism are well discussed. It is found that the device has broad bandwidths which are 310 nm (1.29 to 1.60 µm) for communication wavelength region (which covers O-band partially, E- to C-band fully and L-band partially) and 2700 nm (1.69 to 4.39 µm) for mid-IR region when 20 dB of crosstalk (i.e., extinction ratio) is taken as reference with the short fiber length of 100 µm. Our findings highlight the robust performance and versatility of the proposed device, making it a promising candidate for optical communication and sensing applications.
Acknowledgments
This research work was supported by the Department of Electrical & Electronic Engineering, Rajshahi University of Engineering & Technology (RUET), Bangladesh. In addition, Abdul Khaleque specially thanks the university grant commission of Bangladesh through Research & Extension of RUET (DRE/7/RUET/574(58)/PRO/2022-23/18).
Disclosures
The authors declare no conflicts of interest.
Data Availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
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