In this paper, we describe the spectral characteristics that can be achieved in fiber reflection (Bragg) and transmission gratings. Both principles for understanding and tools for designing fiber gratings are emphasized. Examples are given to illustrate the wide variety of optical properties that are possible in fiber gratings. The types of gratings considered include uniform, apodized, chirped, discrete phase-shifted, and superstructure gratings; short-period and long-period gratings; symmetric and tilted gratings; and cladding-mode and radiation-mode coupling gratings.

Fiber grating spectra

The historical beginnings of photosensitivity and fiber Bragg grating (FBG) technology are recounted. The basic techniques for fiber grating fabrication, their characteristics, and the fundamental properties of fiber gratings are described. The many applications of fiber grating technology are tabulated, and some selected applications are briefly described.

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Fiber Bragg grating technology fundamentals and overview

Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed.

Fiber Bragg gratings

We report the experimental demonstration of an electrically driven, single-mode, low threshold current (∼260 μA) photonic band gap laser operating at room temperature. The electrical current pulse is injected through a sub-micrometer-sized semiconductor wire at the center of the mode with minimal degradation of the quality factor. The actual mode of interest operates in a nondegenerate monopole mode, as evidenced through the comparison of the measurement with the computation based on the actual fabricated structural parameters. As a small step toward a thresholdless laser or a single photon source, this wavelength-size photonic crystal laser may be of interest to photonic crystals, cavity quantum electrodynamics, and quantum information communities.

http://science.sciencemag.org/content/sci/305/5689/1444.full.pdf

Electrically Driven Single-Cell Photonic Crystal Laser

Studies of optical microresonators with dimensions between 0.1 and 10 microns are now under way in a wide variety of condensed matter systems. Ideally, one can isolate a single mode of the optical field in a cube a halfwavelength on a side with perfectly reflecting walls. Liquid droplets, polymer spheres and semiconductor Fabry‐Perot microcavities with dielectric mirrors are examples of microresonators with which one can approach this ideal limit and nearly isolate a few modes of the electromagnetic field from the continuum of surrounding free‐space modes.

Optical Processes in Microcavities

Electrically pumped whispering-gallery mode microdisc lasers with singlemode operation and submilliamp threshold current at room temperature are demonstrated.

Room temperature operation of microdisc lasers with submilliamp threshold current

The authors report a mode-locked pulse source with extremely wide operating frequency range and very stable operation, through the use of a long, linearly chirped Bragg reflector as the output coupler integrated in a fiber external cavity. A 1.55 mu m strained MQW laser diode is used, with one facet high reflectivity (HR) coated for improved cavity Q, and the other antireflection (AR) coated to allow coupling to the external cavity and suppress Fabry-Perot modes. Near-transform-limited pulses are obtained over a frequency range of 700 MHz around a system operating frequency of 2.488 GHz, with pulsewidths of 50 ps, as required for a practical soliton transmission system. >

Mode-locked hybrid soliton pulse source with extremely wide operating frequency range

The authors describe a new technique for extracting the intrinsic laser-diode dynamic properties accurately. This simple technique eliminates the need for accurate microwave calibration of the test equipment and problems of microwave reflections, nonideal frequency response of laser mount, and detector. The effect of the parasitic components of the laser diode are also eliminated from the results so that measurements of important dynamic properties of the laser can be found up to high frequencies (10-20 GHz) on standard laser diodes. The techinque being used to measure variations of resonance peak and damping factor at different bias levels for a standard bulk active region 1.3 mu m laser diode is shown. >

Frequency response subtraction for simple measurement of intrinsic laser dynamic properties

We investigate the high temperature performance of conventional separate confinement and lattice matched and compressively strained multi‐quantum‐well InGaAsP lasers emitting at 1.3 μm. Low threshold buried heterostructure lasers operate reproducibly at temperatures as high as 130 °C. The rate of threshold change with temperature is described by T0∼45°–55° for both conventional and quantum well lasers. The rate of change is not influenced by any modifications in the active layer structure. In contrast, excellent correlation is observed between the active layer structure, parametrized as the threshold gain, and the peak cw operating temperature.

High temperature characteristics of InGaAsP/InP laser structures

A novel and accurate technique for measuring the internal losses of semiconductor lasers is demonstrated. The technique is based on two measurements: the injection current required for reaching material transparency and the corresponding ripple in the spontaneous emission spectrum. This method, which is independent of the internal quantum efficiency, allows the measurement of individual laser chips rather than an ensemble of chips, and can also be used to determine the loss dependence on wavelength and temperature.

D.L. Coblentz

Papers

Room temperature operation of microdisc lasers with submilliamp threshold current

Mode-locked hybrid soliton pulse source with extremely wide operating frequency range

Frequency response subtraction for simple measurement of intrinsic laser dynamic properties

High temperature characteristics of InGaAsP/InP laser structures

Novel technique for determining internal loss of individual semiconductor lasers