Single-mode optical fiber

In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, obtained by combining Maxwell's equations and the boundary conditions; these modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves have different frequencies; this is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is called transverse mode since its electromagnetic oscillations occur perpendicular to the length of the fiber; the 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber; the standard G.652 defines the most used form of single-mode optical fiber.

In 1961, Elias Snitzer while working at American Optical published a comprehensive theoretical description of single mode fibers in the Journal of the Optical Society of America. At the Corning Glass Works, Robert Maurer, Donald Keck and Peter Schultz started with fused silica, a material that can be made pure, but has a high melting point and a low refractive index, they made cylindrical preforms by depositing purified materials from the vapor phase, adding controlled levels of dopants to make the refractive index of the core higher than that of the cladding, without raising attenuation dramatically. In September 1970, they announced they had made single-mode fibers with attenuation at the 633-nanometer helium-neon line below 20 dB/km. Like multi-mode optical fibers, single-mode fibers do exhibit modal dispersion resulting from multiple spatial modes but with narrower modal dispersion. Single-mode fibers are therefore better at retaining the fidelity of each light pulse over longer distances than multi-mode fibers.

For these reasons, single-mode fibers can have a higher bandwidth than multi-mode fibers. Equipment for single-mode fiber is more expensive than equipment for multi-mode optical fiber, but the single-mode fiber itself is cheaper in bulk. A typical single-mode optical fiber has a core diameter between 8 and 10.5 µm and a cladding diameter of 125 µm. There are a number of special types of single-mode optical fiber which have been chemically or physically altered to give special properties, such as dispersion-shifted fiber and nonzero dispersion-shifted fiber. Data rates are limited by chromatic dispersion; as of 2005, data rates of up to 10 gigabits per second were possible at distances of over 80 km with commercially available transceivers. By using optical amplifiers and dispersion-compensating devices, state-of-the-art DWDM optical systems can span thousands of kilometers at 10 Gbit/s, several hundred kilometers at 40 Gbit/s; the lowest-order bounds mode is ascertained for the wavelength of interest by solving Maxwell's equations for the boundary conditions imposed by the fiber, which are determined by the core diameter and the refractive indices of the core and cladding.

The solution of Maxwell's equations for the lowest order bound mode will permit a pair of orthogonally polarized fields in the fiber, this is the usual case in a communication fiber. In step-index guides, single-mode operation occurs when the normalized frequency, V, is less than or equal to 2.405. For power-law profiles, single-mode operation occurs for a normalized frequency, V, less than 2.405 g + 2 g,where g is the profile parameter. In practice, the orthogonal polarizations may not be associated with degenerate modes. OS1 and OS2 are standard single-mode optical fiber used with wavelengths 1310 nm and 1550 nm with a maximum attenuation of 1 dB/km and 0.4 dB/km. OS1 is defined in ISO/IEC 11801, OS2 is defined in ISO/IEC 24702. Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required; the basic connector unit is a connector assembly. A connector assembly consists of two connector plugs. Due to the sophisticated polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are assembled onto optical fiber in a supplier’s manufacturing facility.

However, the assembly and polishing operations involved can be performed in the field, for example to make cross-connect jumpers to size. Optical fiber connectors are used in telephone company central offices, at installations on customer premises, in outside plant applications, their uses include: Making the connection between equipment and the telephone plant in the central office Connecting fibers to remote and outside plant electronics such as Optical Network Units and Digital Loop Carrier systems Optical cross connects in the central office Patching panels in the outside plant to provide architectural flexibility and to interconnect fibers belonging to different service providers Connecting couplers and Wavelength Division Multiplexers to optical fibers Connecting optical test equipment to fibers for testing and maintenance. Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles.

The closures that enclose them may be hermetic, or may be “free-breathing.” Hermetic closures will prevent the connectors within being subjected to temperature swings unless th

2020 TCU Horned Frogs football team

The 2020 TCU Horned Frogs football team will represent Texas Christian University during the 2020 NCAA Division I FBS football season. The Horned Frogs will compete as a member of the Big 12 Conference and will play their home games at Amon G. Carter Stadium on campus in Fort Worth, Texas, they will be led by 20th-year head coach Gary Patterson. The Horned Frogs finished the 2019 season with a 5–7 record, 3–6 in Big 12 play, failing to earn bowl eligibility. In December 2019, co-offensive coordinator and running backs coach Curtis Luper was hired as the offensive coordinator at Missouri; the other co-offensive coordinator, Sonny Cumbie, was promoted to offensive coordinator. Brian Applewhite was hired to fill his role as running backs coach; the Big 12 media days will be held on July 21 -- 2020 in Frisco, Texas. The Horned Frogs will hold spring practices in March and April 2020; the TCU football spring game will take place in Fort Worth, TX on March 28, 2020. TCU released its 2020 schedule on October 22, 2019.

The 2020 schedule consists of 6 home games and 6 away games in the regular season. The Horned Frogs will host 1 non-conference game against Prairie View A&M and will travel to non-conference games at California and SMU. TCU will host Oklahoma State, Kansas State, Iowa State, Texas Tech and travel to West Virginia, Baylor and Kansas in regular season conference play. Schedule Source

Rennie v. Klein

Rennie v. Klein, 462 F. Supp. 1131, was a case heard in the United States District Court for the District of New Jersey in 1978 to decide whether an involuntarily committed mental patient has a constitutional right to refuse psychiatric medication. It was the first case to establish that such a patient has the right to refuse medication in the United States. John Rennie, age 38, was a former pilot and flight instructor, a patient at Ancora Psychiatric Hospital in Winslow Township, New Jersey, his case was brought in December 1977. Rennie's psychiatric history indicates that he did not show signs of mental illness until he was 31, he was first hospitalized in 1973, subsequently he was discharged and re-admitted many times as trial judge Stanley Brotman noted, because of "his failure to continue taking medications after he has left the hospital's custody." He had been given various diagnoses over time including paranoid schizophrenia and manic-depressive psychosis. Rennie had suicidal ideation, his eighth hospitalization was initiated.

On subsequent hospitalizations he became abusive and assaultive. In December 1977, during his twelfth hospitalization that began on August 10, 1976, doctors had unsuccessfully tried various psychiatric medications. Rennie sued in federal district court to prevent the hospital from administering psychotropic medications to him without a clear emergency, his counsel was the Office of the Public Advocate. As Judge Brotman describes in his decision, the precipitating factors occurred earlier in the month when Rennie had become homicidal. Hospital staff felt, they believed. Following initiation of the prolixin regime, Rennie's condition did improve markedly. Judge Brotman responded to Rennie's appeal for an injunction by issuing a compromise ruling. Rather than enjoining the hospital from giving him any medication, he insisted that the prolixin be lowered to a minimum maintenance dosage, which staff psychiatrists considered too low, he conducted fourteen days of hearings between January 13 and April 28, 1978.

Several months after issuing his initial ruling that asserted a right to refuse treatment grounded in a constitutional right to privacy, Judge Brotman made the case into a class action that included all involuntarily committed patients at the five mental health facilities operated by the state of New Jersey, held an additional seventeen days of hearings. An involuntarily committed patient who has not been found incompetent, barring an emergency, has a qualified right to refuse psychotropic medication when forced treatment violates his First Amendment rights to freedom of speech or to practice his religion, or his Eighth Amendment rights to be free of cruel and unusual punishment. New Jersey's administrative policies, which provide for a second psychiatric opinion in the case of refusing patients, must give adequate scope for the exercise of that right to satisfy constitutional requirements. Additionally, due process must be followed in order to forcibly medicate an individual against his will.

Judge Brotman's order that the least restrictive alternative concept applied to choice of medications was upheld upon appeal. Before this case, although attention had been focused on involuntary commitment standards, it was assumed that once the patient was hospitalized, hospitals could administer psychoactive medication without consulting either the patient or the family; this was the first case in which the focus shifted from standards of commitment to standards of treatment once hospitalized. This was the first of a series of cases that acknowledged patient rights to refuse treatment and right to least restrictive treatment by way of a variety of First Amendment rights including freedom of religion and thought as well as the ultimate right to privacy, control over one's own body. However, as this case illustrates, applying the least restrictive principles and working with a patient on medication choices brings up difficult empirical issues in ranking treatment options in accord with constitutional rights.

O'Connor v. Donaldson United States v. Binion Washington v. Harper Jackson v. Indiana Perry v. Louisiana Rogers v. Okin Youngberg v. Romeo Text of Rennie v. Klein, 462 F. Supp. 1131 is available from: CourtListener Google Scholar Justia