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Coupler

A coupler is a device or mechanism used to join or connect two components, allowing the transfer of energy, signals, or motion between them. The term is applied across various fields of engineering and science, with specific types tailored to different applications. In mechanical engineering, couplers include shaft couplings for transmitting torque between rotating components, railway couplers for linking rail vehicles, and pipe couplings for joining tubing systems. Electrical and electronics engineering employs couplers such as directional couplers for signal sampling in waveguides, optocouplers for electrical isolation, and acoustic couplers for modem connections. In optics and photonics, output couplers and fiber optic couplers manage light transmission in lasers and optical networks. Other uses include organ couplers in musical instruments to combine ranks of pipes, and diazo couplers in photographic and chemical processes for color development. Detailed descriptions of these types are provided in the following sections.

Mechanical Engineering

Shaft Couplings

Shaft couplings are mechanical components designed to join two rotating shafts end-to-end, transmitting torque and power from a driving shaft to a driven shaft while potentially accommodating minor misalignments or vibrations.^[1] These devices ensure efficient power transfer in machinery such as motors, pumps, and compressors, maintaining alignment to prevent excessive wear or failure.^[1] Shaft couplings are categorized into rigid, flexible, and fluid types based on their ability to handle misalignment and shock. Rigid couplings, including sleeve, clamp, and flange variants, provide a solid connection with no flexibility, suitable for applications requiring precise shaft alignment and high torque transmission without any offset.^[1] Flexible couplings, such as jaw (using elastomeric inserts), gear, and elastomeric designs, allow for angular, parallel, or axial misalignment up to 1°-4° and absorb vibrations or shocks through elastic elements.^[2] Fluid couplings, like hydraulic torque converters, use a fluid medium to transmit torque smoothly, offering shock absorption by slipping under overload conditions to protect connected equipment.^[1] Key design considerations for shaft couplings include maximum torque capacity, allowable misalignment, speed limits, and backlash prevention to ensure reliable operation. Torque capacity varies by type; for instance, gear couplings can handle over 1 million in-lbs (113,000 Nm), often limited by the shaft itself rather than the coupling.^[2] Misalignment tolerances encompass angular (up to 1.5° per flex plane in gear types), parallel (0.010"-0.165"), and axial (up to 0.020") displacements, with flexible designs compensating to reduce stress on bearings.^[2] Speed limits depend on the coupling's balance and material; beam types support up to 10,000 RPM, while high-speed applications above 3,000 RPM require dynamic balancing per ISO 1940 standards to avoid vibration.^[2] Backlash prevention is critical for precision motion control, achieved in zero-backlash designs like beam or disc couplings through tight tolerances, though some gear types retain minimal clearance for lubrication.^[2] The torque transmitted by a shaft coupling can be calculated using the relation between power, torque, and rotational speed:

T = \frac{P \times 60}{2 \pi n}

where T is torque in Nm, P is power in kW, and n is rotational speed in rpm; this equation derives from the fundamental power transmission formula P = T \omega, with \omega = 2 \pi n / 60 in rad/s.^[3] Shaft couplings originated in the 19th century with the rise of steam engines during the Industrial Revolution, where they connected engines to line shafts for distributing power in factories via belts and pulleys.^[4] Over time, designs evolved from cast iron rigid types to incorporate advanced materials like composites in modern high-speed applications, enabling lighter weight, electrical insulation, and operation beyond 10,000 RPM in turbines and renewable energy systems.^[5] Installation of shaft couplings requires precise alignment to minimize loads, using techniques such as rim-and-face dial indicators or laser alignment tools.^[6] Maintenance involves periodic inspection for wear, with flexible couplings like gear types needing relubrication every 6-12 months using high-viscosity grease with extreme pressure additives to prevent fretting and ensure smooth operation.^[6] Elastomeric elements in jaw couplings should be replaced if thickness reduces by 25%, and all types benefit from vibration monitoring to detect early misalignment.^[2]

Railway Couplers

Railway couplers serve the primary function of connecting adjacent rail vehicles to form trains, transmitting tensile (draft) and compressive (buff) forces during movement while accommodating track irregularities and dynamic loads.^[7] These devices ensure the structural integrity of the train consist, allowing efficient power transfer from locomotives to haul heavy loads, such as 11,000-ton coal trains.^[7] Major types of railway couplers include the Janney knuckle coupler, which has been the standard in North America since its adoption as the Type D in 1916, featuring a swinging knuckle for automatic coupling.^[8] The SA3 semi-automatic coupler, developed for Eastern European standards, is used in regional and intercity trains, incorporating a pivot anchor for crash energy absorption.^[9] The Scharfenberg coupler, a fully automatic design, is prevalent in metros and light rail, with variants like Type 10 providing high-strength connections up to 1,500 kN compression for freight applications.^[10] In contrast, the buffers-and-chain system remains common for European freight, using screw links with buffers to absorb impacts manually.^[11] Safety features in railway couplers include uncoupling levers that allow remote release without personnel entering the coupling area, reducing injury risks during operations.^[12] Anti-climbing provisions, such as interlocking faces on coupler ends, engage under high buff loads to prevent vehicles from overriding each other and causing derailments.^[13] Energy-absorbing elements, like deformation units in knuckles, act as mechanical fuses by failing controllably to dissipate forces, with tensile strength enhancements from 120 ksi to 125 ksi extending fatigue life by nearly 400%.^[14] Historically, Eli Janney patented the knuckle coupler in 1873, with improvements in 1879 and 1882, enabling automatic coupling that halved accidents between 1890 and 1909 by eliminating the need for workers to step between moving cars.^[8] This innovation addressed severe safety issues, including 300 deaths and 6,700 injuries in 1888 from manual link-and-pin methods, and led to its endorsement by the Master Car Builders Association in 1888.^[8] In the US, the Association of American Railroads (AAR) adopted standards for these couplers, promoting interchangeability and ongoing technological updates through committees like the Standard Coupler Manufacturers Committee.^[15] Compatibility issues arise from regional differences, such as the incompatibility between North American Janney and European buffers-and-chain systems, necessitating adapters like those used in Finland's SA3-to-screw coupling conversions for mixed traffic.^[11] These variations hinder seamless international freight operations, requiring hybrid couplers or manual interventions that increase time and costs, as seen in Europe's ongoing shift toward standardized automatic systems under UIC guidelines.^[11] Modern advancements include electronic couplers with integrated sensors for real-time monitoring of forces and structural integrity, such as Voith's Digital Automatic Coupler (DAC), which automates air, data, and power connections while detecting wagon positions to support predictive maintenance.^[16] Deployed since 2019 on over 200 SBB Cargo wagons, these systems enable automatic brake tests and reduce pre-departure checks, enhancing operational efficiency and safety in freight networks. As of 2025, DAC trials continue across Europe, with Germany planning commercial deployment on test trains in late 2025 to further standardize the technology for improved rail freight interoperability.^[16]^[17]

Pipe Couplings

A pipe coupling is a short section of pipe or tube, typically a few inches long, featuring sockets or female threads at one or both ends to connect two pipes of the same diameter, ensuring alignment and a sealed joint for fluid, gas, or material flow without the need for welding in many cases.^[18] These fittings maintain continuity in piping systems by bridging gaps or repairing sections, and they are essential in applications where disassembly is required.^[19] Common types of pipe couplings include threaded couplings, suitable for low-pressure systems where pipes are joined by screwing into matching male threads; compression couplings, which use a gasket and nut to seal plastic or copper pipes without threading; flanged couplings, designed for high-pressure environments by bolting two flanged ends together; and mechanical couplings, such as clamp or grooved styles, ideal for quick repairs or joining dissimilar materials.^[20] Threaded variants are often used in smaller diameters for water or gas lines, while flanged types handle elevated pressures up to several thousand psi in industrial settings.^[21] Compression and mechanical types provide flexibility for non-welded installations, particularly in plastic piping.^[22] Materials for pipe couplings are selected based on the conveyed medium, environmental conditions, and pressure requirements, with common options including brass for potable water systems due to its corrosion resistance, PVC for lightweight plastic applications handling non-aggressive fluids, and stainless steel for chemical or high-corrosion scenarios.^[23] For instance, Schedule 40 PVC couplings are rated up to approximately 300 psi at ambient temperatures for typical sizes, while stainless steel variants can exceed 6000 psi depending on the class.^[24] Standards govern these specifications, such as ASME B16.11, which defines dimensions, tolerances, pressure ratings, and marking for forged socket-welding and threaded fittings in classes from 2000 to 9000.^[21] Additionally, ISO 49 establishes requirements for malleable cast iron threaded fittings, including tolerances for threads per ISO 7-1 to ensure interchangeability. Pipe couplings find applications in residential plumbing for water supply lines, oil and gas pipelines for secure media transport, and HVAC systems for ductless refrigerant routing.^[25] Installation methods vary by type: threaded couplings require precise pipe cutting and thread sealing with tape or compound, compression types involve sliding a ferrule and nut over the pipe ends for tightening, flanged installations use gaskets and bolts for alignment, and plastic couplings like PVC often employ solvent welding with primer and cement for a permanent bond.^[26] Compared to welding, couplings offer advantages such as easier disassembly for maintenance, reduced costs for temporary or repair setups, and compatibility with field adjustments in diverse piping materials.^[27]

Electrical and Electronics Engineering

Directional Couplers

Directional couplers are passive devices used in radio frequency (RF) and microwave engineering to sample a portion of the signal power traveling in one direction along a transmission line, while allowing the majority of the power to pass through with minimal reflection. These four-port networks operate on the principle of electromagnetic coupling between transmission lines or waveguides, where energy is transferred directionally to a coupled port without significantly affecting the input signal's propagation. The device ensures that power incident from the input port couples preferentially to one output port (the coupled port) and is isolated from the opposite port (the isolated port), enabling precise measurement of forward or reflected waves.^[28] The basic structure of a directional coupler consists of four ports: an input port for the incident signal, a through port for the primary transmission path, a coupled port that extracts a fraction of the input power, and an isolated port that receives negligible power when the device is properly matched. The coupling factor C, which quantifies the power sampled, is defined as C = -10 \log_{10} \left( \frac{P_{\text{coupled}}}{P_{\text{input}}} \right) in decibels (dB), a positive value indicating the attenuation from input to coupled port. For ideal performance, the coupler exhibits high directivity, defined as D = 10 \log_{10} \left( \frac{P_{\text{coupled}}}{P_{\text{isolated}}} \right) dB, which measures the device's ability to distinguish between forward and reverse power directions. These parameters ensure low insertion loss in the through path and high isolation between the input and isolated ports.^[29] Several types of directional couplers are employed based on the transmission medium and frequency range. Branch-line couplers, also known as 90-degree hybrids, utilize quarter-wavelength transmission line sections arranged in a parallel configuration to achieve quadrature phase shift and equal power splitting at specific frequencies, making them suitable for narrowband applications. Coupled-line couplers employ two parallel striplines or microstrips in close proximity, where the even- and odd-mode velocities create backward-wave coupling over a broader bandwidth, often up to an octave. Waveguide couplers, such as the Bethe-hole type, involve apertures in waveguide walls to couple power between adjacent guides, offering high power handling for high-frequency radar systems. The coupling coefficient k, a key design parameter for coupled-line structures, is given by k = \sqrt{ \frac{10^{C/10} - 1}{10^{C/10} + 1} }, relating the physical geometry to the desired coupling level.^[30]^[31]^[29] In practical applications, directional couplers facilitate power monitoring in RF amplifiers by sampling output signals to prevent overdrive conditions, with typical coupling values of 20–40 dB to avoid loading the main path. They are essential for signal sampling in radar systems, where the coupled port extracts echoes for processing while the through port maintains transmitter output integrity. Additionally, dual-directional couplers measure voltage standing wave ratio (VSWR) by simultaneously detecting forward and reflected power, enabling mismatch detection in antenna feeds with directivities exceeding 30 dB for accurate results. These uses highlight the device's role in ensuring system reliability and performance in high-power environments.^[32]^[33]^[34] The development of directional couplers originated in the 1940s at the MIT Radiation Laboratory during World War II, where they were invented to support radar systems by enabling efficient power sampling and measurement in waveguides. Key innovations included the Bethe-hole coupler, theorized by Hans A. Bethe in his seminal 1944 paper on small-hole diffraction, which provided a foundational model for aperture-based coupling in microwaves. These wartime advancements laid the groundwork for modern RF components, with subsequent refinements in stripline and microstrip forms emerging in the 1950s.^[29]

Optocouplers

Optocouplers, also known as optoisolators, are electronic components that transfer electrical signals between two electrically isolated circuits using light as the intermediary, thereby preventing direct electrical connection and minimizing noise interference. The basic operation involves an input side with a light-emitting diode (LED), typically made from gallium arsenide phosphide (GaAsP) or similar materials, which emits light when forward-biased by an electrical signal, and an output side featuring a photodetector such as a phototransistor or photodiode that converts the received light back into an electrical signal. These elements are encased in a light-tight package, often with an insulating material like epoxy or silicone, ensuring no physical conduction path exists between input and output.^[35]^[36]^[37] Optocouplers are classified into several types based on their output configuration and intended use. Transistor-output optocouplers, the most common variant, employ a phototransistor for digital switching applications, providing high current transfer ratios (typically 20% to 100%) suitable for on/off signal isolation. Analog optocouplers use matched photodiodes paired with amplifiers to enable linear signal transfer, preserving voltage or current proportionality across the isolation barrier. High-speed optocouplers, often incorporating aluminum gallium arsenide (AlGaAs) LEDs and integrated signal processing circuits, support data rates up to 10 Mbps, making them ideal for communication interfaces. Isolation capabilities are standardized, with typical working voltages of 2.5 kV to 5 kV and creepage distances exceeding 8 mm to comply with safety norms like IEC 60950-1 for information technology equipment, which defines minimum paths over surfaces to prevent arcing.^[38]^[39]^[40] In applications, optocouplers are widely used in power supplies for feedback loops to isolate control circuits from high-voltage sections, ensuring stable regulation without ground loops. In industrial controls, they provide isolation for programmable logic controllers (PLCs), protecting sensitive electronics from harsh environments and voltage spikes. Medical devices, such as patient monitors and defibrillators, leverage optocouplers for patient safety by maintaining galvanic isolation compliant with IEC 60601-1 standards, preventing leakage currents that could harm users. Advantages include robust galvanic isolation and immunity to electromagnetic interference, outperforming direct wiring in noisy settings, though limitations arise from bandwidth constraints—typically below magnetic or capacitive couplers—and LED degradation over time, which can reduce current transfer efficiency.^[41]^[42]^[43] The evolution of optocouplers traces back to their invention in 1963 at IBM, initially using incandescent lamps or early LEDs for basic isolation, with commercial development accelerating in the 1960s through companies like Monsanto, which introduced LED-based models such as the MCT2 in 1973. By the 1970s, adoption grew in computing and telecommunications, but early silicon-based designs limited speeds to below 1 Mbps due to phototransistor response times. Modern advancements feature GaAs and AlGaAs emitters for faster switching and higher efficiency, enabling high-speed variants that support up to 25 Mbps in some cases while maintaining reliability over extended lifetimes, as verified through accelerated aging tests.^[44]^[45]^[46]

Acoustic Couplers

An acoustic coupler is a device that enables data transmission between a computer or terminal and a telephone line without direct electrical connection, instead using sound waves to interface with the telephone handset. The mechanism involves converting digital signals into audible tones via a modem's speaker, which are then acoustically coupled to the telephone handset's microphone for transmission over the phone network; conversely, incoming tones from the receiver's handset speaker are captured by the coupler's microphone and converted back to electrical signals for the modem. This acoustic-to-electrical and electrical-to-acoustic transduction allows binary data to be modulated onto audio frequencies within the standard voice band.^[47] Acoustic couplers were first developed in the 1950s by Bell Laboratories under AT&T to facilitate secure data links, particularly for military applications during the Cold War, where electrical isolation was critical to prevent interception or tampering. Prior to the 1968 Carterfone decision by the FCC, which prohibited AT&T from banning non-harmful attachments to its network, acoustic couplers were the primary method for connecting customer-owned equipment to telephone lines due to regulatory restrictions on direct electrical connections. Their peak usage occurred in the 1970s and 1980s, supporting baud rates up to 300 bps, before direct-plug modems became widespread following regulatory changes.^[48]^[49]^[50] In design, acoustic couplers typically feature two rubber cups or cradles to securely align the telephone handset, positioning the mouthpiece over the coupler's microphone and the earpiece over its speaker to minimize acoustic leakage and ensure efficient signal transfer. The frequency response is optimized for the telephone voice band of 300-3400 Hz, accommodating the tones generated by frequency shift keying (FSK) modulation, where binary data is represented by shifts between two distinct audio frequencies—for example, in the Bell 103 standard, originate mode uses 1070 Hz for mark (1) and 1270 Hz for space (0), while answer mode uses 2025 Hz and 2225 Hz to enable full-duplex operation. The Bell 103, introduced by AT&T in 1962, became a foundational standard for these devices, supporting asynchronous data at 300 bps using FSK.^[51]^[52]^[53] The primary advantages of acoustic couplers include electrical isolation, which provides security by avoiding direct network contact, and portability, as they require no wiring modifications and can be used with any standard telephone handset. However, they suffer from disadvantages such as susceptibility to background noise and interference, which can corrupt signals, and inherently low data speeds limited by acoustic transmission inefficiencies and the voice channel bandwidth. Today, acoustic couplers persist in niche applications, such as secure environments in government or military settings where electrical connections are prohibited, and in legacy systems compatible with standards like Bell 103.^[54]^[55]

Optics and Photonics

Output Couplers

In laser cavities, output couplers serve as partially reflective mirrors that enable a controlled fraction of the circulating light to exit the resonator while reflecting the majority back to maintain optical feedback and amplification. Typically, a laser resonator consists of one highly reflective mirror (reflectivity approaching 100%) and an output coupler with reflectivity between 50% and 99%, allowing precise control over the output power by adjusting the transmission level.^[56]^[57] Output couplers are primarily constructed using dielectric coatings, which consist of multiple thin layers of materials deposited on a substrate to achieve the desired reflectivity at specific wavelengths, ensuring minimal absorption and high durability. For applications requiring polarization control, Brewster-angle configurations are employed, where the coupler is oriented at the Brewster angle to minimize reflection losses for p-polarized light and enhance beam polarization. Common substrate materials include fused silica, valued for its low thermal expansion, high transparency across ultraviolet to near-infrared wavelengths, and resistance to laser-induced damage.^[56]^[58]^[59] Key performance metrics for output couplers include reflectivity R, transmission T, and negligible absorption A, governed by the relation T = 1 - R - A, where absorption is typically less than 0.1% in high-quality designs. The output power is then given by P_{\text{out}} = P_{\text{circ}} \times T, with P_{\text{circ}} representing the intracavity circulating power, allowing engineers to optimize extraction efficiency without excessive resonator losses.^[56]^[60] These components find essential applications in various laser systems, such as helium-neon (HeNe) gas lasers, where low-reflectivity output couplers (around 99%) extract stable, low-power beams for precision alignment and interferometry. In solid-state lasers like neodymium-doped yttrium aluminum garnet (Nd:YAG), output couplers with 80-95% reflectivity enable high-power operation at 1064 nm for industrial tasks, including beam extraction in holography setups that demand coherent, monochromatic light and in laser cutting processes where focused outputs achieve clean material ablation.^[61]^[58]^[62] Design considerations emphasize wavelength dependence, as dielectric coatings must be tailored to the lasing wavelength (e.g., 632.8 nm for HeNe or 1064 nm for Nd:YAG) to maintain consistent R and T across the operational spectrum. Additionally, the laser-induced damage threshold is critical, particularly for pulsed systems, where couplers must withstand intensities exceeding 1 GW/cm² without degradation, achieved through optimized coating stacks and substrate polishing to reduce scattering sites.^[56]^[63]^[64] The concept of output couplers was integral to the foundational theoretical development of lasers in the 1960s, as proposed by Arthur L. Schawlow and Charles H. Townes in their seminal 1958 paper, which outlined optical resonators using partially transmitting mirrors to couple out coherent light while sustaining amplification.^[65]

Fiber Optic Couplers

Fiber optic couplers are passive optical devices used to split or combine light signals in fiber optic networks, enabling the distribution of optical power from one or multiple input fibers to one or more output fibers through evanescent field coupling.^[66] These devices are essential for signal routing in telecommunications and sensing applications, operating primarily in the near-infrared spectrum. Unlike active components, they rely on the physical interaction of light modes without amplification or modulation.^[67] The most common construction method for fiber optic couplers involves fusion-based techniques, where two or more optical fibers are aligned parallel, twisted together, and heated—typically using a flame or CO2 laser—to soften the glass, allowing them to be elongated and fused into a biconical taper structure.^[68] This process creates an interaction region where the evanescent fields of the guided modes overlap, enabling controlled power transfer between fibers based on the taper length and geometry.^[69] Fused biconic taper (FBT) couplers, produced via this method, support various splitting ratios such as 50:50 for equal power division or 90:10 for unequal distribution, determined by the degree of twisting and pulling during fabrication.^[70] Other types include planar lightwave circuit (PLC) couplers, fabricated using photolithographic techniques on silica-on-silicon substrates to create waveguide arrays for precise splitting, often achieving higher port counts like 1x32 without cascading losses.^[71] Polarization-maintaining (PM) couplers, designed for single-mode fibers, incorporate stress rods or elliptical claddings to preserve light polarization, making them suitable for applications requiring stable birefringence, such as coherent detection systems.^[72] These types are selected based on network requirements, with FBT favored for simplicity and cost in low-port counts, while PLC excels in compact, high-density designs.^[73] Key performance parameters include insertion loss, typically less than 0.2 dB for high-quality 2x2 couplers at specified wavelengths, representing the total power reduction from input to output ports.^[67] Excess loss accounts for inefficiencies beyond the ideal split, often below 0.1 dB in optimized devices, while directivity exceeds 50 dB to minimize crosstalk from reverse propagation.^[74] Operating wavelength ranges commonly cover 1310 nm and 1550 nm for telecommunications, with bandwidths up to 100 nm for standard couplers.^[66] The power splitting ratio in decibels (dB) relates the outputs via the equation:

\frac{P_{\text{out1}}}{P_{\text{out2}}} = 10^{\frac{\text{ratio}}{10}}

where total loss incorporates coupling efficiency and excess factors.^[67] In applications, fiber optic couplers facilitate passive optical networks (PON) for broadband distribution, fiber optic sensors for environmental monitoring via interferometric splitting, and wavelength division multiplexing (WDM) systems for combining channels.^[66] They adhere to standards such as IEC 61300, which specify testing for attenuation, return loss, and environmental reliability in passive components. Advancements since the 1990s include wideband couplers optimized for WDM, leveraging erbium-doped fiber amplifiers to extend operational bandwidths across C- and L-bands, enabling terabit-scale data transmission over single fibers.^[75]

Other Applications

Organ Couplers in Music

Organ couplers are mechanical or electrical mechanisms in pipe organs that connect one manual (keyboard) or division to another, allowing the stops (sets of pipes) selected on one to be activated by playing keys on the other. This enables the organist to play pipes from multiple divisions simultaneously from a single manual, such as the swell to great coupler, which transfers swell division sounds to the great manual.^[76]^[77] Couplers are classified into manual and pedal types, with manual couplers further divided by pitch: unison couplers operate at the normal pitch (denoted as 8'), sub-octave couplers sound one octave lower (16'), and super-octave couplers sound one octave higher (4'). Pedal couplers link manual divisions to the pedalboard, facilitating bass lines with upper voices. These are implemented through mechanical trackers in traditional organs, where wooden rods and wires physically link keys; electropneumatic systems, using air pressure and solenoids for remote control; or MIDI interfaces in contemporary setups for digital signaling.^[76]^[78]^[79] The origins of organ couplers trace to the 17th-century Baroque era, when builders like Arp Schnitger incorporated them into North German organs to support complex polyphony in works by composers such as Johann Sebastian Bach. Schnitger's 1693 organ at St. Jacobi Church in Hamburg featured intermanual couplers, such as Oberwerk to Hauptwerk, allowing seamless integration of divisions for richer textures essential to Baroque repertoire.^[80] Acoustically, couplers enhance volume by activating additional pipes and blend timbres across divisions, creating fuller, more unified sounds that expand the organ's expressive range. In musical notation, unison couplers are indicated by "8'" to specify pitch, guiding performers on registration choices.^[81]^[76] In modern digital organs, software-based couplers simulate these effects through virtual pipe modeling and MIDI protocols, replicating mechanical actions without physical linkages. For instance, Hauptwerk software emulates coupler behaviors in virtual pipe organs, enabling precise control over interdivisional coupling.^[82] A prominent example is the Wanamaker Grand Court Organ in Philadelphia, installed in 1911, which includes a full complement of inter- and intra-manual couplers across its six manuals, supporting multiple coupler levels for symphonic-scale performances.^[83]

Diazo Couplers in Chemistry

Diazo couplers are electron-rich aromatic compounds, such as phenols and anilines, that react with diazonium salts to form azo dyes through a coupling reaction.^[84] This process, pivotal in synthetic dye chemistry, was first observed in 1861–1862 by Johann Peter Griess, who coupled diazonium compounds with phenols to produce colored azo derivatives.^[85] Griess's discovery built on his earlier invention of diazotization in 1858, laying the foundation for the azo dye industry, which became central to 20th-century colorants.^[86] The reaction mechanism involves electrophilic aromatic substitution, where the diazonium ion (ArN₂⁺) acts as an electrophile attacking the activated aromatic ring of the coupler (Ar'H), typically at the para position.^[87] The process proceeds via addition of the electrophile to form a sigma complex, followed by deprotonation to yield the azo compound.^[84] The general equation is:

\text{ArN}_2^+ + \text{Ar'H} \rightarrow \text{Ar-N=N-Ar'} + \text{H}^+

This reaction requires specific pH control; alkaline conditions (pH > 7.5) are used for phenolic couplers to generate the more nucleophilic phenoxide ion, while acidic conditions (pH < 6) suit aniline-based couplers.^[84] The resulting azo dyes are stable and exhibit vibrant colors due to the extended conjugation in the Ar-N=N-Ar' structure.^[88] Common types of diazo couplers include phenolic compounds, which produce red dyes upon coupling, naphtholic derivatives valued for their acid stability in producing scarlet to blue hues, and heterocyclic couplers such as pyrazolones or pyridones that enable specific shades like yellows and greens for specialized applications.^[87]^[89] Phenolic couplers, exemplified by phenol itself, react readily under basic conditions to form ortho or para-substituted azo products.^[90] Naphtholic couplers, like 2-naphthol, enhance color fastness in acidic media, making them suitable for textile dyes.^[91] Heterocyclic variants introduce varied electron densities, allowing fine-tuning of absorption wavelengths for precise color control.^[92] Diazo couplers find broad applications in dye synthesis, particularly for textile dyeing where azo compounds account for over 70% of commercial dyes due to their versatility and cost-effectiveness.^[89] Diazo compounds are also used in diazotype printing processes to produce direct positive images via coupling reactions upon light exposure.^[93] Additionally, they serve as analytical reagents; for instance, in the Griess test, sulfanilic acid-derived diazonium salts couple with α-naphthylamine to detect nitrite ions via a red azo dye, enabling quantification in environmental and biological samples.^[94] Despite their utility, azo compounds pose safety concerns as some can degrade into carcinogenic aromatic amines, such as benzidine, linked to bladder cancer.^[95] Under the EU's REACH regulation (Annex XVII, entry 43), certain azo dyes are restricted in consumer products like textiles and leather if they release more than 30 mg/kg of specified amines, requiring manufacturers to test and certify compliance to mitigate health risks.^[96]

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In stock 21-day returnsThis Standard covers ratings, dimensions, tolerances, marking and material requirements for socket-welding and threaded forged fittings.
[23]
Mechanical Piping Connectors Explored - Unified Alloys
Compression couplers work similarly to grooved end coupling designs–however, they require no grooves! This means you can securely join two pipes without ...
[24]
Understanding Different Types and Applications for Pipe Fittings
Sep 3, 2020 · Couplings are typically used to connect and join straight lengths of pipe together. Fittings are available in standard shapes and styles and ...<|control11|><|separator|>
[25]
Pressure Ratings of Pipes and Fittings - The Engineering ToolBox
Pressure ratings of pipes and tubes and their fittings - carbon steel , stainless steel, plastic, copper and more.
[26]
How Couplings Are Used for Water & Sewer Line Pipe Repair
Aug 6, 2020 · Connecting pipe sections of different materials: pipe couplings are generally made from similar or identical materials as that of the tube or ...Missing: definition | Show results with:definition
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Complete Guide to Pipe Fittings | Oatey
Pipe fittings ensure smooth plumbing operations. Choosing the right types, materials, and installation method is key to a successful DIY or professional job.2. Elbow Fittings · Additional Pipe Fittings To... · Threaded Vs. Welded Pipe...
[28]
Coupling Pipe Fitting Techniques for Beginners - Sealexcel
Dec 7, 2023 · Coupling pipe fittings join two pipes. Key steps include measuring, aligning, sliding pipes, and tightening the coupling.
[29]
Microwaves101 | Directional Couplers - Microwave Encyclopedia
Directional couplers are four-port circuits where one port is isolated from the input port. Directional couplers are passive reciprocal networks.
[30]
Microwaves101 | Coupler Fundamentals - Microwave Encyclopedia
Microwave couplers are devices which divert a fraction of the signal on one transmission line to another transmission line.
[31]
Microwaves101 | Coupled Line Couplers - Microwave Encyclopedia
Coupled lines occur when two transmission lines are close enough in proximity so that energy from one line passes to the other.
[32]
Microwaves101 | Quadrature couplers - Microwave Encyclopedia
A quadrature coupler is one in which the input is split into two signals (usually with a goal of equal magnitudes) that are 90 degrees apart in phase.
[33]
Log amps and directional couplers enable VSWR detection
Jan 1, 2007 · A directional coupler and a dual detector were used to detect the reflection coefficient. When the VSWR is more than the safe limit, the ...
[34]
How to Measure VSWR Using a Directional Coupler
A directional coupler can be used to sample some power in a standing wave, which can be used for a voltage standing wave ratio measurement. measure VSWR ...
[35]
What is a Directional Coupler? | Directional Coupler Primer - KRYTAR
Directional couplers are used in many different testing applications where power or frequency needs to be monitored, leveled, alarmed or controlled.
[36]
Optocoupler Tutorial and Optocoupler Application
This insulating material creates the electrical isolation (often rated for 2.5kV to 5kV or more between the input and output sides. A semiconductor photo- ...Missing: standards | Show results with:standards
[37]
Optocouplers in Electrical Isolation and Signal Transmission
Dec 6, 2024 · Optocouplers, also called optoisolators, use light to transfer electrical signals between isolated circuits, providing electrical isolation.
[38]
Introduction to Optocouplers - Circuit Digest
May 13, 2025 · An optocoupler, also known as an opto-isolator, is an electronic component that transfers electrical signals between two isolated circuits using light.Missing: standards | Show results with:standards
[39]
Optocoupler Circuits | Nuts & Volts Magazine
Typical isolating optocoupler applications include low-voltage to high-voltage (or vice versa) signal coupling, interfacing of a computer's output signals ...
[40]
Types of Optocouplers - PCB HERO
Jun 16, 2025 · The most common type, featuring an LED as the input and a phototransistor as the output. They are suitable for general-purpose signal isolation.
[41]
The Ultimate Optocouplers Guide: Isolation, Types, and Applications
Sep 22, 2025 · Optocouplers are categorized based on the type of photosensor used on the output side. This choice dictates the device's speed, output current ...
[42]
A Look at High-Voltage Optocoupler Characteristics
Sep 24, 2024 · Common applications include industrial automation, where optocouplers provide reliable signal isolation between control systems and high ...
[43]
https://www.icdrex.com/how-optocouplers-work-and-their-applications/
[44]
How Optocouplers Work and Their Applications - DRex Electronics
Mar 31, 2025 · They provide electrical insulation and protection for circuits. They can be used in power supplies, motor control and communication systems.
[45]
The Development History Of Optocoupler - News
May 28, 2024 · Early development: Optocoupler technology first originated in the 1960s. The original optical coupler used fluorescent materials as the signal ...
[46]
Monsanto: Bringers of the Light | The CPU Shack Museum
Dec 20, 2014 · Monsanto MCT2 – LED Based Opto-coupler. This little chip, dated from 1973, is part of the history of what we are surrounded by, LEDs. ... Monsanto ...Missing: invention | Show results with:invention
[47]
https://www.computerhistory.org/revolution/networking/19/371
[48]
Connecting Over Phone Lines - CHM Revolution
Some early modems used an “acoustic coupler” for the telephone handset, eliminating the need to wire them directly to phone lines.Missing: first | Show results with:first
[49]
In the 1950s, Bell Laboratories under AT&T enhanced the original ...
Aug 20, 2019 · In the 1950s, Bell Laboratories under AT&T enhanced the original device created during the Cold War for transmitting radar signals, modulating digital data ...
[50]
[PDF] Carterfone: My Story - Santa Clara Law Digital Commons
The Carterfone was an acoustic device connecting a phone to a radio. AT&T prohibited it, leading to a lawsuit and the FCC's landmark decision.
[51]
Modems: 60 Years of Hooking Up | PCWorld
Jan 31, 2011 · In 1962, AT&T introduced the Bell 103 Data Phone (seen here), which set the standard for 300-baud (approximately 300-bps) full-duplex modems.
[52]
US3553374A - Acoustic coupler - Google Patents
An acoustic coupler for coupling a telephone handset to a source of shift frequency signals representing binary information comprising an enclosure adapted ...
[53]
Acoustically Coupled Modems - Columbia University
IBM PC/AT with Hayes Smartmodem Ven-Tel and Anderson-Jacobson acoustically coupled Bell 103 modems, 1970s (we also used to have some A-J wooden models but ...Missing: mechanism design FSK
[54]
Modem Overview
Bell 103 Modem ... This modem supports asynchronous rates up to 300 baud using Frequency Shift Keying (FSK) modulation. Different carrier frequencies are used at ...Missing: history acoustic<|control11|><|separator|>
[55]
From Baud to Awed: The History of the Modem | Auvik
May 24, 2022 · The majority of modems during this time were acoustic couplers – the user required a regular phone to dial the remote computer, then the ...
[56]
75 Years of Innovation: Acoustic Modem - SRI International
Mar 3, 2021 · Weitbrecht invented an acoustic coupler that was inserted between the teletypewriter (TTY) and a telephone handset. This acoustic coupler was an ...Missing: Bell 103 FSK
[57]
Output Couplers – mirrors - RP Photonics
An output coupler is usually a semi-transparent dielectric mirror used in a laser resonator. Its function is to transmit part of the circulating intracavity ...
[58]
Laser Cavity - an overview | ScienceDirect Topics
An additional important detail is that one of the cavity elements (typically a mirror) functions as an output coupler that transmits a fraction of the incident ...
[59]
https://www.altechna.com/products/dieletric-coated-optics/laser-output-coupler/
[60]
Laser Output Coupler | Dielectric coated optics - Altechna
A laser output coupler is a semi-transparent dielectric mirror used in a laser cavity. It has the function of transmitting part of the circulating intracavity ...Missing: types Brewster fused
[61]
Output Couplers - OPTOMAN
IBS-coated output couplers are designed to transmit a controlled portion of the laser beam while reflecting the rest back into the resonator.Missing: metrics formula
[62]
Lasers: Understanding the Basics - Photonics Spectra
Applications such as holography, which demand excellent coherence, benefit from using a single-longitudinal-mode laser. For some laser types with a narrow gain ...
[63]
Nd:YAG Laser Applications Across Various Industries
Mar 12, 2025 · Manufacturers use this technology to drill, cut, weld, and engrave metals, ceramics, polymers, and even transparent materials like acrylic glass ...
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Wavelength dependence of femtosecond laser-induced damage ...
Jun 10, 2015 · An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented.
[65]
Optimize design and manufacture of high-laser-damage-threshold ...
Jun 1, 2024 · Optimizing the laser damage threshold (LDT) of these coatings usually requires a compromise of the selected coating materials and the electric ...
[66]
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[67]
Fiber Couplers – optical fiber - RP Photonics
Fiber couplers are fiber devices for coupling light from one or several input fibers to one or several output fibers, or from free space into a fiber.
[68]
Fiber Coupler Tutorials - Thorlabs
Coupling Ratio. Insertion loss (in dB) is the ratio of the input power to the output power from each leg of the coupler as a function of wavelength. It ...
[69]
F-CPL-S14150 Optical Fiber Coupler - Newport
In stock Free deliveryFused Biconical Taper Construction. A fused coupler consists of two, parallel optical fibers that have been twisted, stretched and fused together so that ...
[70]
[PDF] Reproducible Method for Fabricating Fused Biconical Tapered ...
We describe two prototype manufacturing process that produces low-loss fibre tapers and fused FBT coupler devices using CO2 lasers as the heat source instead of ...
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https://www.m2optics.com/blog/bid/64174/fiber-optic-splitters-common-types
[72]
Fiber Optic Splitters - Common Types
Sep 28, 2011 · Information about commonly used fiber optic splitters, including Fused Biconic and PLC types.
[73]
530 nm 2x2 Polarization-Maintaining Fiber Optic Couplers / Taps
The bandwidth of these couplers enables operation at 520 nm and 532 nm, popular wavelengths for medical and imaging applications. 2x2 couplers are bidirectional ...
[74]
Fiber Optical Coupler: Design, Working, and Its Types - DK Photonics
Jul 31, 2019 · Optical Fused Coupler. Also called fused fiber optical coupler, it is formed on the basis of fused biconical taper (FBT) technology.
[75]
Definitions | OEM Optical Communication Solutions - Corning
Insertion loss is the ratio of the optical power launched at the input port of the coupler to the optical power from any single output port, expressed in dB.
[76]
Fiber-optic transmission and networking: the previous 20 and the ...
In the early 1990s, practical gain flattening filter technology was unavailable, thus limiting the transmission distance of wide-band WDM systems. A simple ...
[77]
OrganTutor :: Couplers : Page 1 of 10 - BYU Organ
In General. A coupler "couples" or copies a combination of stops from its division (such as the Swell) or pitch range of origin, to another location (such ...
[78]
OrganTutor :: Couplers : Page 2 of 10 - BYU Organ
They are the UNISON COUPLERS; that is, they couple all stops at their actual or unison pitch. OCTAVE COUPLERS couple one octave higher or lower. TRY IT ...Missing: pipe types super-
[79]
OrganTutor :: Couplers : Page 5 of 10 - BYU Organ
A 16' indication on a coupler means “AN OCTAVE LOWER,” not 16-foot pitch. TRY IT: Try each of the combinations to the right. If there are no subcouplers on your ...
[80]
The Elderly Novice Virtual Organist - The Pipe Organ in a Nutshell
These are inter-division couplers that operate at unison pitch. Many organs also have octave couplers that couple an octave higher or lower, rather than at ...
[81]
Hamburg: Jacobikirche - The Organ Historical Society
The organ in the St. Jacobikirche in Hamburg is one of Arp Schnitger's most well-known instruments. It has survived all the vagaries of time.
[82]
[PDF] the use of couplers - Organists Online
Couplers are mechanical devices that allow different organ units to be played from other manuals, increasing sonority and creating varied tones.
[83]
About Hauptwerk - MIDI Works
Hauptwerk is a software that allows the user to play a pipe organ from the comfort of their own space. To put it simply, it is a modern day sampler that uses ...
[84]
Wanamaker Grand Court Organ - AGO Philadelphia Local Instruments
The console is prepared for a Piano II, a Harp I and a Harp II. COUPLERS AND ACCESSORIES Full compliment of inter- and intra-manual couplers. Independent, full ...
[85]
Electrophilic Substitution with Arenediazonium Salts: Diazo Coupling
Jul 19, 2015 · The most important application of diazo coupling reactions is electrophilic aromatic substitution of activated benzene derivatives by diazonium ...Study Notes · Diazonium Salts: The... · Diazonium Coupling Reactions · Exercises
[86]
NATURE
The diazo-reaction itself was discovered in 1858, and Griess obtained the first azo-colour in the years 1861--62. This dye was first manufactured in 1865 by ...
[87]
Johann Peter Griess FRS (1829–88): Victorian brewer and synthetic ...
Dec 16, 2015 · The German organic chemist Johann Peter Griess (1829–88), who first developed the diazotization of aryl amines (the key reaction in the synthesis of the azo ...
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Kodachrome | Timeline of Historical Colors in Photography and Film
Kodachrome ; Year. 1935 ; Principle. Subtractive 3 color: chromogenic monopack, reversal, 8 and 16 mm, still photography and film ; Invented by. Leopold D. Mannes ...
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Azo Coupling - Organic Chemistry Portal
Aromatic diazonium ions acts as electrophiles in coupling reactions with activated aromatics such as anilines or phenols.
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Azo Coupling - an overview | ScienceDirect Topics
Azo coupling is defined as a chemical reaction in which aromatic diazonium ions react with other compounds to form 6-arylazo derivatives. AI generated ...<|control11|><|separator|>
[91]
Classifications, properties, recent synthesis and applications of azo ...
These dyes are synthesized from a simple method of diazotization and coupling. Different routes and modifications are made to obtain the desired color ...
[92]
Making an Azo Dye from Phenol - Chemistry LibreTexts
Jan 22, 2023 · This page looks at some typical reactions of diazonium ions, including examples of both substitution reactions and coupling reactions.
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Synthesis and Spectroscopic Study of Naphtholic and Phenolic Azo ...
A series of naphtholic azo dyes 1-9 were synthesized via diazotization of substituted aniline derivatives followed by azo coupling with 2-naphthol.<|control11|><|separator|>
[94]
Synthesis and pharmacological activities of azo dye derivatives ...
Sep 13, 2022 · ... diazo coupling nucleophile components such as phenol, naphthol, or amine. ... heterocyclic dispersed azo dyes coupling with 5-methyl-2-(6 ...
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A short history of colour photography
Jul 7, 2020 · In 1912, Rudolph Fischer had patented a proposal to use what later became known as 'colour couplers'—substances that react with chemicals ...
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Griess Test - an overview | ScienceDirect Topics
The Griess test is defined as a chemical reaction that detects nitrite by reacting it with sulfanilic acid under acidic conditions, resulting in the ...
[97]
Azo Dye Regulations in the European Union: An Overview
Sep 22, 2020 · EU regulations restrict some azo dyes due to potential carcinogens, especially those producing aromatic amines, under REACH, Toy Safety ...Which products and materials... · Azo Dyes Product Regulations
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Substances restricted under REACH - ECHA - European Union
The list of substances restricted under REACH will be available in our new chemicals database, ECHA CHEM, since 16 September 2025.