According to Huang , the simplest model for the coupled waveguide system is a directionalcoupler which consists of two uniform, parallel waveguides placed in close proximity. However, exact analytical solutions for practical directionalcoupler are difficult to find. Coupled mode theory gives simple analytical solutions that provide insight into the mode coupling process in directionalcoupler. When two guided modes are brought into close proximity, the modes will couple to each other as the results of evanescent fields.
The beam propagation method is one of the commonly used numerical method used to determine the field’s propagation inside the waveguide . It decomposes the wave into superposition of plane waves, each travelling in different direction. These individual plane waves are propagated through a finite predetermined distance through the waveguide until the point where the field needs to be determined has arrived. At this point, all the individual plane waves are numerically added in order to get back the spatial mode.
A directionalcoupler (DC) is a basic component in integrated photonics that couples light propagating in a waveguide to another parallelwaveguide placed in close proximity. The operation principle of the DC can be explained by the coupled mode theory. It has been widely used in optical switches , multiplexers/de-multiplexers  and polarization beam splitters  etc. On the other hand, tunable silicon photonic devices are based primarily on the thermo-optic (TO) effect or the free carrier dispersion effect (FCD). They are both volatile and require constant power to maintain tuning. The power consumption can be reduced considerably, if the refractive index change can be maintained using a non-volatile tuning method.
It was also declared that in case of 3-rows, the resonance in upper band will happen. The reason is, where the electric vector is in parallel to broad wall, the even mode is excited and coupler acts as side wall coupler. Such case is not happened for 2-rows couplers. By reduc‐ ing the height of “b” it is possible to put the resonance frequency of even modes out of oper‐ ating frequency band. Only a slight reduction in “b” is needed since the resonance is occurred when the coupling region has length of λ g / 2 and it is near cut-off for even modes.
The coupling factor represents the primary property of a directionalcoupler. Coupling is not constant, but varies with frequency. While different designs may reduce the variance, a perfectly flat coupler theoretically cannot be built. Directional couplers are specified in terms of the coupling accuracy at the frequency band center. For example, a 10 dB coupling +/- 0.5 dB means that the directionalcoupler can have 9.5 dB to 10.5 dB coupling at the frequency band center. The accuracy is due to dimensional tolerances that can be held for the spacing of the two coupled lines. Another coupling specification is frequency sensitivity. A larger frequency sensitivity will allow a larger frequency band of operation. Multiple quarter-wavelength coupling sections are used to obtain wide frequency bandwidth directional couplers. Typically this type of directionalcoupler is designed to a frequency bandwidth ratio and a maximum coupling ripple within the frequency band. For example a typical 2:1 frequency bandwidth coupler design that produces a 10 dB coupling with a +/- 0.1 dB ripple would, using the previous
The diﬀerent types of conventional microwave coupled line couplers have a trade oﬀ between bandwidth, coupling level, and structure implementation constraints. The novel properties of the LH TL can lead to novel performance of LH coupled line coupler . Unlike to the conventional quarter wave coupled line coupler, the LH coupler can provide arbitrary high coupling level, even 0 dB, with relatively wide lines separation over a broad bandwidth. Also, it has high forward coupling at lower frequency without the need to increase the physical length which is the case in conventional one. The left handed coupled line couplers were introduced in microstrip conﬁguration [12, 13] and using CPW conﬁguration .
Abstract - DirectionalCoupler is a four port passive device, used in the field of radio technology. It couples a defined amount of the electromagnetic power from the primary transmission line to the secondary transmission line depending on value of coupling factor. Its performance is evaluated based on certain parameters like coupling, directivity, isolation, insertion loss. This paper focuses on designing two line microstrip directionalcoupler for IRNSS application at S band (2.5 GHz centre frequency) by using ADS software. By using multisection coupler, the performance of the coupler can be improved. The directionalcoupler is fabricated by using FR4 substrate.
Abstract: Coupling light from an optical fibre to small optical waveguides is particularly problematic in semiconductors, since the refractive index of the silica fibre is very different from that of a semiconductor waveguide. There have been several published methods of achieving such coupling, but none are sufficiently efficient whilst being robust enough for commercial applications. In this paper experimental results of our approach called a Dual-Grating Assisted DirectionalCoupler, are presented. The principle of coupling by this novel method has been successfully demonstrated, and a coupling efficiency of 55% measured.
The POF coupler presented here is a potential optical device for the next generation ‘do-it yourself’ optical component. This device eliminates the used of sophisticated production equipment and technically skilled manpower for device fabrication and assembling. The device which is based on low cost acrylic material has been designed with a high index contrast waveguide taper. Modeling of the device has been performed both at the device level using an optical simulator tool and at the CAD/CAM level prior to machining. Optimization of the design has been performed at the CAD/CAM stage to allow an improvement to the fiber-waveguide taper coupling. The manufacturing of the component has been done using EGX400 desktop engraver system. The first prototype device showed an insertion loss of 7.5 dB and coupling ratio of 50 : 50 whereas the second prototype device with additional slot for the jacketed fibers showed the insertion loss dropped to 5.9 dB and maintaining the coupling ratio at 50 : 50. The reduction of the insertion loss makes this device comparable to that of the previous develop devices based on metal hollow waveguide taper structure which sees the loss at 5.8 dB. These acrylic-based devices can be easily manufactured using low cost plastic injection molding tool.
The fiber can be operated as an optical amplifier, an optical switch, wavelength converter, soliton in a source, a compressor noise, a filter, and optical memory. The fiber optics directional couplers are widely used in modern optical communications systems. Nonlinear effects in directional couplers were studied starting in 1982. Fiber couplers, also known as directional couplers, constitute an essential component of light wave technology. They are used routinely for a multitude of fiber-optic devices that require splitting of an optical field into two coherent but physically separated parts. Although most applications of fiber couplers only use their linear characteristics, nonlinear effects have been studied since 1982 and can lead to all-optical switching among other applications . The transfer of optical power between the modes of the two cores of the coupler is explained as evanescent field coupling between the modes of the individual cores of the coupler. The mechanism is described by a parameter known as the coupling coefficient, where it determined the coupling ratio between both fibers. It arises from the coupling of the propagating fields inside the two cores. In this study, we use the normal coupling ratio of 50% or coupling coefficient, =0.5.
Light which is guided in this manner can be classified according to its symmetry, particu- larily its frequency ω and propagation constant k of the mode in the waveguide. The frequency describes temporal symmetry, or how far in time we must travel until we see the same wave. Similarily, the propagation constant is associated with spatial symmetry, or how far in space we must travel until see the same wave. Due to the in-plane symmetry of the dielectric slab, the direction of propagating light is arbitrary and the propagation constant may be represented as a scalar k quantity. The mode H(r) which represents the vector amplitude of the field, or its ”shape”, indicates where the field is mostly concentrated and the direction it points in. Regard- ing light in terms of its symmetry is crucial to understanding photonic crystals and interpreting how light propagates inside them. It is helpful to examine the dispersion diagram of the slab, as seen in Fig. 2.2, to see the relationship between these concepts. Due to continuous 2D sym- metry, k can be projected on to any arbitrary in-plane direction e ff ectively making it scalar k.
Abstract—The design of a terahertz short-slot coupler with curved waveguide is proposed. A traditional short-slot coupler uses a step-like structure in order to suppress higher order modes and improve bandwidth. It becomes diﬃcult to control the fabrication of tiny steps with the incensement of frequency especially in terahertz band. The designed coupler is composed of two curved waveguides overlapping in the middle to realize a speciﬁc coupling coeﬃcient. Then the step-like structure can be replaced with a curved structure which is much easier to fabricate. The coupling coeﬃcient of the coupler is 3 dB, and the variation is less than 1 dB around the center frequency. The phase diﬀerence between two output ports is 90 ◦ . The isolation is greater than 10 dB in the whole working band. Measured results show high agreement with simulation predictions. The designed coupler can be widely used as feed networks of horn antenna array.
In the RF power amplifier circuit, power detection is of great significance. In terms of measurement, accurate power detection allows the user to understand the current state of operation of the device; in terms of control, power detection in the power control process, especially the protection of amplifiers and other ancillary equipment is not a long time overload work play a very important role The Which on the power detection accuracy made a very high demand. In this paper, the theoretical analysis and simulation analysis of the power detection accuracy of the directionalcoupler in different positions are carried out to determine the optimal position of the directionalcoupler. Which provides theoretical guidance for the location of the directionalcoupler in the design of the actual power detection circuit.
At this moment in time, rectangular waveguide components are used in communication and microwave system, radar with outstanding features such as increase power capability and small insertion loss . However, it is in bulky size that strict and limits the accuracy and precision in manufacturing. Unfortunately, Printed Circuit Board (PCB) is sensitive toward about radiation by others active and passive devices in the same dielectric substrate  .
Diﬀerent axial periodic corrugation proﬁles such as sinusoidal, trapezoidal, and rectangular can be used. The rectangular corrugation proﬁle is shown in Fig. 1. It includes two circular waveguide sections with radii a and b in one period. This proﬁle has a simple structure making it easy to fabricate [16, 17]. In addition, it can be quickly and accurately analyzed by mode matching techniques. Because of these advantages, the rectangular corrugation proﬁle is studied in this paper.
Abstract—In this paper, a novel ultra-wideband switched-beam antenna system based on 4 × 4 two-layer Butler matrix is presented and implemented to be used in hostile environment, such as underground mines. This matrix is based on the combination of a broadband two- layer slot-coupled directionalcoupler and a multilayer slot-coupled microstrip transition. With this conﬁguration, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices. Moreover, this new structure is compact and oﬀers an ultra-wide bandwidth of 6 GHz. To examine the performance of the proposed matrix, experimental prototypes of the multilayer microstrip transition and the Butler matrix were fabricated and measured. Furthermore, a three 4-antenna arrays were also designed, fabricated and then connected to the matrix to form a beamforming antenna system at 3, 5.8 and 6 GHz. As a result, four orthogonal beams are produced in the band 3–9 GHz. This matrix is suitable for ultra- wideband communication systems in conﬁned areas.
The MultiFlex is a state-of-the-art, bi-directional amplifier offered as an indoor (UL, CUL & CE listed) mains powered (90 - 240 VAC) or an outdoor cable powered (40 - 90 VAC) amplifier. It can be ordered with forward bandwidths of 750, 870, or 900 MHz. Available operational gains are 37 dB @ 750 MHz, 37 or 40 dB @ 870 or 900 MHz.
(Here, the tolerances of amplitude and phase mismatches are 1 dB and 5 ◦ , respectively). The amplitude imbalance and phase imbalance are caused by several reasons such as fabrication tolerance, junction loss and variance of substrate parameters. The performance of this work and state-of-the-art dual-band 180 ◦ directional couplers is listed in Table 3. In comparison, the proposed design can provide a superior frequency ratio with large design ﬂexibility. Moreover, the dual-band couplers implemented in [26, 27] are based on the conventional rat-race coupler structure. The dual-band coupler presented in this work is implemented based on a generalized rat-race coupler structure, which leads to a more compact size.