Fiber couplers are usually directional couplers, which means that essentially no optical power sent into some input port can go back into one of the input ports. Directional coupler is a 4port waveguide junction consisting of a primary main waveguide and a secondary auxiliary waveguide. Directional couplers typically have strong wavelength dependence due to high modal dispersion and the natural dependence of the interference phenomenon on wavelength. Directional coupler is one of the very important devices which can be used for various applications like, optical amplitude modulator, power tapping, power divider. Microwave engineering directional couplers tutorialspoint. Internal view of a typical coaxial coupler figure 3. Dwdm applications and integrated polarization diversity schemes. A directional optical coupler is shown and described, which includes an optical cell that is made of a first transparent conductor, a second transparent conductor and an electro optical member interposed between the two transparent conductors, the electro optical member having an index of refraction which can be varied only along one crystal axis by application of an electric field. Alloptical switching and coupling characteristics of. Four sbend waveguides formed out of the asi traces are used to create the odc. Part of the forward or reflected power is decoupled with a fixed coupling factor and fed. Optical directional couplers and their applications foundations for.
Brian zinda ee558 optical fiber communication systems prof. Directional couplers an overview sciencedirect topics. The device allows the transmission of light waves through multiple paths. Unrestricted parameters of a directional coupler 01. Energy transfer of two wavelengths in a fused coupler. The linearization of the response function of the optical directional coupler modulator uses variable coupling along the length of the device, and the coupling function can be synthesized for a desired response function.
Introduction qualitative description of the operation of directional couplers marcatilis improved. In order to efficiently route optical signals onchip, precise control over the interaction and polarization of evanescently coupled waveguide modes is required. The wavelength dependence of waveguidetype directional couplers is investigated with respect to waveguide pattern symmetry in the coupling region. Bidirectional lasing characteristics of rectangular ring.
Channel optical waveguide directional couplers aip publishing. Dts0042 directional fiber optic power monitors tapsphotodiodes author. Integrated optics directional couplers for optical coherence. Osa optical gears in a nanophotonic directional coupler. To match the sops between the input optical signal and the lo, a polarization controller is used. The optical directional coupler, analogous to the microwave element1of the same name, consists of parallel channel optical waveguides sufficiently closely. Pdf channel optical waveguides and directional couplers in. Pdf optical bistability in a nonlinear directional. This paper reports on the designing details of an optical directional coupler for extensive use. To read the fulltext of this research, you can request a copy directly from the author. There is often a specification of return loss, which indicates how much weaker the backreflected light is, compared with the input. Figure 1 a shows the schematic top view of our traveling wave directional coupler modulator. Broadband directional couplers fabricated in bulk glass.
Schematics of the studied device configuration static coupling length ls is define as the required. Optical directional couplers odcs consist of two or more closelylocated optical waveguides, whose modes can couple evanescently and thereby exchange their powers, realizing, under certain. For the twoguide case, a new critical power formula and two exact identities are derived. Intensity modulators based on directional couplers. Optical directional coupler, an important component for most optical communication systems, is the fundamental building block in a great variety of photonic components such as switches, power. All optical switches using nonlinear 2x2 directional couplers fabricated by means of many different kinds of technologies have already been demonstrated. This is an example of a wavelength division multiplexer. A directional coupler is an essential photonic device on photonic chips it splits an input optical signal with a specified ratio into two output optical signals for. In a dc, two optical waveguides are brought so close to each other that light starts coupling evanescently. A covering, or cladding, generally covers each optical fiber in order to prevent light from being emitted through. Tsironis, irection al couplers with linear and nonlinear elements, appl. This synthesis gives rise to coupling functions which have negative coupling regions realized by placing a phase shift.
However, large coupling regions and high optical powers are needed to achieve switching when using these technologies. Optical directional couplers with variable spacing osa publishing. Twochannel imbedded directional couplers were fabricated with proton implantation, yielding complete light transfer in 2 mm. Optical directional coupler based on siwire waveguides. We calculate the mode properties of the soi based nanowires and numerically study the light propagation for optical mode exchange by three dimensional finite difference time domain 3d fdtd simulations. A fiber optical coupler is a device with one or more input fibers to distribute or. A crossbar switch has two different states it can be in, the bar state and the cross state. The coupler provided for this purpose is a directional star coupler which is constructed so as to eliminate any need for the employment of a mixing chamber. Variation of the coupling coefficients with wavelength have been done, and found that, out of all four coupling. These taps and monitors provide a way to easily measure the signal intensity through an optical fiber in a simple, miniature package, and are. Usually a simple directional fiber coupler consists of two fibers coupled having two output ports with typical coupling ratio 2. Aug 20, 2006 a new design of ytype endfused singlemode fiber directional couplers has been suggested and its optimum parameters to obtain losses of 0,51 db have been determined. Optical directional coupler design an odc is a twoinputtwooutput optical device with isolated input and outputs ports.
The theoretical results show that slight changes in the ratio of input powers or a mismatch in the linear coupler slight changes in the input power in the nonlinear coupler can lead to a phase shift of this characteristic of the coupler may lead to electro optical switching with an ultralow. The symmetric waveguide structure of the mmifed directional coupler is intrinsically biasfree. A directional coupler is typically used to make nonintrusive measurements of the output power of an amplifier system andor the reflected power of a sink load impedance, antenna or other dut fig. Matrix coupled mode theory model of stronglycoupled. They couple a defined amount of the electromagnetic power in a transmission line to a port enabling the signal to be used in another circuit. Burns, naval research laboratory, in which a three. So far, many all optical switches using directional couplers including the phc ones have been designed and demonstrated 15. Our work illustrates the potential of aln circuits for coupled waveguide optics. Summary the potential applications of nonlinear directional couplers nldcs in all optical processing have attracted extensive interests since they were firstly introduced by jensen in 1982. A technique has been developed for fabricating such couplers by electric arc fusion of singlemode fibers with thin claddings. The result of characterizing the directional coupler using osa is shown in table 1 with the input value of 69. Here, we consider a slot waveguide coupler as shown in fig.
Optical outputs from the parallel and cross ports of an 800umlong device changed reciprocally with a 2. Wavelength characteristics of 22 optical channeltype. Interrelation between the overlap integral and nonlinear crosscoefficients is demonstrated. In asia communications and photonics conference acp, optical society of america, paper ath3a. The cross state is when input 1 is routed to output 2 and input 2 is routed to output 2. In a dc, two optical waveguides are brought so close. The directional coupler is used as a basic 2x2 crossbar switch. The following figure shows the image of a directional coupler. In fact, an optical switch based on phc directional couplers comprising two parallel waveguides adjacent to each other is the most appropriate one. Their ultrafast all optical switching operation was demonstrated at 1. The optical directional coupler, analogous to the micro wave element2 of the same name, consists of parallel channel optical waveguides sufficiently closely. The path length difference between the two arms is l, thus the transfer matrix of the delay path in between the two couplers is exp 0 i 01 jl t. In particular, this abrupt phase shift occurs when light coupling in a directional coupler consisting of two photonic waveguides wgs.
Extracting coupling coefficients of directional couplers. Simulated characteristics of a nonlinear directional. Tipabi, extended m atix method for the analysis bistability. Compact integrated optical directional couplers with symmetrically and asymmetrically etched sbend waveguides on soi platform have been designed, fabricated and characterized. Numerical simulation of nonlinear pulses propagation in a. Fused couplers are used to split optical signals between two fibers, or to combine optical signals from two fibers into one fiber.
Coaxial directional couplers are offered for use at frequencies from 100 khz to 50 ghz, and can be obtained with any of the standard or precision miniature coaxial figure 1. Two embedded optical waveguides in close proximity form a directional coupler. Broadband directional coupling in aluminum nitride. Pdf alloptical switching structure based on a photonic. The power measurements include incident power, reflected power, vswr values, etc. Although this would seem to be a particularly mundane and simple task, these devices are both very important in microwave systems, and very. Closed form solutions to the coupledmode equations with variable coupling. Fiber directional coupler an overview sciencedirect topics. The output spectra of directional couplers are measured and the wavelength dependence of the. Power dividers also power splitters and, when used in reverse, power combiners and directional couplers are passive devices used mostly in the field of radio technology. Paper open access design and fabrication of optical. Channel optical waveguides and directional couplers in gaaslmbedded and ridged. Onchip optical mode exchange using tapered directional coupler. Abstractthis paper presents a nonlinear directional coupler for optical power switching.
Multimode interferometer mmi or directional coupler dc are commonly used as a 3db coupler in a mzi. However, the optical power couplers in the mzi switch are required to maintain a 50% splitting ratio over a broad wavelength range in order to reach a broadband operation of the switch. Optical couplers basics, types and working youtube. A rough approximation of the dependence is determined based on simplified transfer matrix multiplications, followed by a more detailed computer calculation using the beam propagation method bpm. Compact integrated optical directional coupler with large. These taps and monitors provide a way to easily measure the signal intensity through an optical fiber in a simple, miniature package, and are ideal for real time monitoring and feedback for optical amplifiers or wdm. Directional coupler is used to couple the microwave power which may be unidirectional or bi directional. An essential feature of directional couplers is that they only couple power. A new singleline matrix equation is derived for the multiwaveguide case. Improved performance of travel ing wave directional coupler. Diagram of a typical coaxial directional coupler figure 2.
Then, the scattering matrix of the coupler can be written as cos sin sin cos ii i ii j c j. Pdf channel optical waveguides and directional couplers. The theoretical study has been done to study the coupling characteristics of the nonlinear directional coupler. Already a number of integrated optics devices have been realized based on directional couplers, such as optical filters, 3db splitters. Us4240694a single optical fiber directional coupler. The cladding material is gaas and the core material is ionimplanted gaas.
The first fibre consists solely of a core 10 and cladding 11 while the second has a core a primary cladding 14 whose crosssectional area is larger than that of the core, and a secondary cladding 15. Therefore, it is of much practical significance to study the am behavior in a directional coupler. In integrated optics, directional couplers dcs perform an equivalent function as. Various reports on optical directional couplers have been presented. Waveguide parameters for the isolated slot waveguide are as follows. Thg29 design of photonic crystal directional couplers for. Directional couplers with uniform cross section and constant spacing.
Lens coupler to break out of fiber for a short distance, to insert some optical element use lenses to make collimated beam between fibers typical gradient index grin lens rwv page 754 less than 1db loss. The directional couplers are circuits that are essential in many optical communications systems and microwave bands. In this paper, we present an optical exchange function in the mode domain based on tapered directional couplers on soi platform. An optical fibre directional coupler has first and second optical fibres clamped together by a piece of low index heatshrunk tubing 12. Directional coupler is a basic function in an integrated photonic circuit, in which energy of the optical signal is coupled between adjacent optical waveguides. A new phasetuning method for an optical directional coupler fabricated in a cplate linb03 by ti02. Ridged channel guides were fabricated by ionmicromachining epitaxial layers, and a method of directional coupling was demonstrated. Here, two wavelengths are launched into fiber 1 and each exit separately at the other end the green line indicates the far end of the coupler. Onchip optical mode multicasting using tapered directional coupler. The mn9604c is used in combination with stabilized light source and optical power meter to measure optical return loss of optical connectors at approx.
A polarizationindependent optical directional coupler based on slot waveguides is proposed and analyzed by using rigorous fullvectorial analysis methods. Pdf optical bistability in a nonlinear directional coupler. Concept of directional couplers directional coupler structure. Polarizationindependent optical directional coupler based. Optical directional couplers with variable separation are introduced and analyzed. For this coupling to take place cumulatively over a substantial length, the light must propagate with the same phase velocity in each. Normal mode theory of directional couplers with three or more waveguides. The coupler is compact and easy to handle, since it is.
A broadband optical switch based on adiabatic couplers. In the center is a coupling region that allows the transfer of power between the branches as a function of coupling length l. The switching ability of nldc depends on input coupled power and coupling between the two waveguides of the directional coupler. For this coupling to take place cumulatively over a substantial length, the light must propagate with the same phase velocity in each channel. For example, a directional coupler is a crucial ingredient for the manipulation of angular momentum am of light in nanophotonic waveguides when two orthogonal polarized modes are involved. We have found that the directional couplers with asymmetrically etched waveguide structures can increase the device compactness to about 4 to 5 times that of the.
Optical directional couplers and their applications researchgate. A directional coupler is a device that samples a small amount of microwave power for measurement purposes. A directional couples is a device capable of extracting a part of a signal that travels over a transmission line or waveguide, leaving the rest of power not coupled direct route at the exit. When the mn9604c is combined with the total reflection optical fiber sold separately and the ms9710b optical spectrum analyzer or the ms9720a wdm network tester, the return loss can be measured. Uvadare digital academic repository integratedoptics. The study of propagation in a directional coupler the directional coupler is a device consisting of two parallel single mode optical fiber which are passive components used in modern optical communication systems. Design of electro optical wavelength switch electro optical wavelength switch has been further designed with a hole radius in directional coupler central row ra of 0. For such designs, the properties of the output coupler also change as the current applied to the device changes. This paper discusses an improved coupled mode theory model for the nonlinear directional coupler in the strongcoupling range.
Onchip optical mode exchange using tapered directional. To study the switching properties of nldc, coupled mode theory has been used. The directional coupler dc is a fourport reciprocal passive optical device frequently used for splitting and combining of optical power in ring resonators, machzehnder interferometers mzi and optical. The am of photons has great potential in nanophotonics. All optical switching and coupling characteristics of femtosecond pulses in a nonlinear fiber directional coupler 103 a b fig. The optical coupler can be made by a partial reflection mirror in free space, or more conveniently made by a fiber directional coupler in guided wave optics. Integratedoptics directional couplers for optical coherence tomography we simulated, fabricated, and characterized symmetric 2x2 directional couplers in silicon oxynitride for sweptsource optical coherence tomography ssoct. Oz optics offers a series of inline optical power monitors and tap couplers based on a revolutionary, patented technology. Simulated characteristics of a nonlinear directional coupler. Dut total reflection optical fiber for reference mn9604c optical directional coupler builtin sld or. Polarizationindependent optical directional coupler based on. Results of directional coupler fabrication at 40 mm interaction length one of the observations of optical signal input and output on the directional coupler is shown in figure 6. Dts0042 directional fiber optic power monitors taps.
Normal mode theory of directional couplers with two waveguides. Broadband directional couplers fabricated in bulk glass with. The bar state is when input 1 is routed to output 1 and input 2 is routed to output 2. On the other hand, reconfigurable phase shifters are circuit actuators that introduce a local phase shift of the optical signal when a control signal. In this video, i have covered optical couplers with following outlines. Introduction to fiber optic couplers tutorials of fiber. The phase jumps in a linear coupler and a nonlinear coherent coupler are demonstrated analytically. Broadband directional coupling in aluminum nitride nanophotonic. Channel optical waveguides and directional couplers. Jun 28, 20 types of fiber optic couplers include optical splitters, optical combiners, x couplers, star couplers, and tree couplers. While such dispersion may be attractive for coarse optical filtering such as fibertothehome. Energy transfer is bi directional in a fused coupler. Impact of various parameters on the performance of optical.
Optical directional couplers are potential devices in. Pdf polarizationindependent optical directional coupler based on. Fusedbiconical coupler or directional coupler they get fused together over length w. A coupler for transferring signals from a first group of single optical fibers to a second group of single optical fibers. Rp photonics encyclopedia fiber couplers, optical fiber.
Hunsperger, journalapplied optics, year1974, volume 2, pages 327. A robust method for characterization of optical waveguides. Optical fibre directional coupler the optical bre directional coupler is the guided w a v e equiv alen t of bulk optic b eam splitter and is one of the most imp ortan t inline bre comp onen ts. The optical directional coupler, analogous to the microwave element 1 of the same name, consists of parallel channel optical waveguides sufficiently closely spaced that energy is transferred from one to another. An optical directional coupler is one of the most important devices for an optical fiber communication system, such as catv and datalink, and for optical fiber measurement.
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