A review of some properties of chalcogenide glasses and the current status of their applications is given. Techniques to characterize the linear and non-linear properties of these glasses are introduced and used to measure the optical constants of chalcogenide glasses in the form of bulk, thin film and fiber. Different techniques for the fabrication of gratings and waveguides in these glasses are described. Achievable efficiencies of gratings, as well as propagation losses of fabricated waveguides, are presented. The possibilities of fabricating active devices, such as fiber amplifiers and lasers, are presented. Finally, a novel application of chalcogenide glasses, namely all-optical switching for the fabrication of efficient femtosecond switches, is introduced.

Optical properties and applications of chalcogenide glasses: a review

High-bandwidth (2 GHz/spl middot/km) graded-index polymer optical fiber (GI POF) was successfully obtained by the new interfacial-gel polymerization technique in which the unreactive component was used in order to obtain the quadratic refractive-index distribution. This high-bandwidth GI POF makes it possible to transmit high-speed optical signals in the short range network which was not covered by the step-index type POF commercially available. The high bandwidth GI POF will open the way for great advantages in the high-speed multimedia network. >

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High-bandwidth graded-index polymer optical fiber

A method is presented for synthesizing a coherent two-port lattice-form optical delay-line circuit that is composed of optical delay lines, directional couplers, and phase shifters. The two bases of the method are the use of a unimodulus para-unitary matrix as a transfer matrix and the division of the transfer matrix into basic component transfer matrices. We succeeded in obtaining a set of recurrent equations with which to calculate circuit parameters to use for designing an optical delay-line circuit with a desired cross-port (through-port) transfer function. In the developed method, it is shown that two-port optical delay-line circuits can have the same transmission characteristics as finite impulse response digital filters with complex expansion coefficients. Three synthesis examples for optical frequency filters are described: a linear-phase Chebyshev filter, a multi-channel selector, and a group-delay dispersion equalizer. It is confirmed that transmission characteristics with a maximum transmittance of 100% can be always synthesized. The allowable parameter error for the synthesized linear-phase Chebyshev filter is also discussed. >

Synthesis of coherent two-port lattice-form optical delay-line circuit

Silica-based integrated optical waveguide technology is reviewed. Low loss and manufacturable waveguides are made by chemical vapour, flame hydrolysis and electron beam deposition. Fibre to fibre insertion loss is as low as 0.3 dB for a 6 cm long waveguide. Bragg reflective add-drop filters are made with gratings formed by ultraviolet irradiation. The waveguide grating router has found important application as a multiplexer in dense wavelength multiplexed communications systems. Multiplexers with wide pass bands and stop bands are made with Fourier filters: these filters consist of a chain of alternating couplers and delaying arms. The good performance of waveguide grating routers and Fourier filters is due to the high degree of path delay and coupler control achievable by and processing in this technology.

Silica-based optical integrated circuits

The number of services providing large-volume information content, such as high-definition movies, continues to increase rapidly. Single-mode glass optical fiber (SM GOF), which has been widely deployed in data trunk lines and pipelines connecting large cities and nations, has already become indispensable as an information transmission medium. However, SM GOF is mechanically weak and lacks sufficient bending ability. Moreover, as the core diameter is very small, just 10 μm, extremely precise techniques and expensive devices are required to connect fibers to signal receiving devices. It is therefore difficult to lay SM GOF for very short reach networks, such as local area networks in buildings. These difficulties are recognized as the problem of the ‘last hundred meters’ for optical fiber infrastructure. Plastic optical fiber (POF) has a relatively large-diameter core and is flexible enough to be laid down for network infrastructure in the last hundred meters. However, POF has two important weaknesses: it has significantly lower bandwidth than GOF, and its attenuation is far higher. Recent developments conquering both of these issues now mean that POF is regarded as the strongest candidate at present for optical data transmission over the last hundred meters. Here we review the status of POF development and research, particularly with respect to the application of ‘photonics polymer’.

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The future of plastic optical fiber

Low loss plastic optical fibers (POF’s) have been prepared employing a poly(methylmethacrylate‐d8) core and fluorinated alkyl methacrylate copolymer cladding with attenuation losses of 20, 25, and 50 dB/km at wavelengths of 660, 780, and 850 nm, respectively. These values were attained using the POF fabrication method which incorporates a closed polymerization and fiber drawing procedure. The POF can allow optical signal transmission over about 1300 m at −34 dBm at a rate up to 10 MHz using a display grade GaAlAs light‐emitting diode whose emission power at 660 nm and 20 mA of forward input current is 1 mW. The loss limit of this poly(methylmethacrylate‐d8) core POF is estimated to be 10 dB/km at 680 nm.

Low loss poly(methylmethacrylate‐d8) core optical fibers

An integrated optical device comprising a substrate (1); a single-mode optical waveguide having a cladding layer (12) disposed on the substrate (1) and a core portion (4, 5) embedded in the cladding layer (12) and for transmitting light therethrough; and a stress applying film (31) disposed on a desired portion of the cladding layer (12) and for adjusting stress-induced birefringence of the single-mode optical waveguide by irreversibly changing a stress exerted on the core portion (4) by trimming technique. The integrated optical device can be manufactured by the steps of forming a cladding layer (12) on a substrate (1); forming a single-mode optical waveguide having a core portion (4, 5) embedded in the cladding layer (12) and for transmitting light therethrough; and forming, on the cladding layer (12), a stress applying film (31) for exerting a stress on the single-mode optical waveguide to irreversibly change the stress by trimming the film (31). The device exhibits a precisely adjusted birefringence and a desired polarization dependence or independence and is effective for constructing an integrated optical device for optical communication, for optical sensor or for optical signal processing, in which the polarization characteristics play an important role.

Integrated optical device and method for manufacturing thereof

In a single mode optical waveguide having a substrate, a cladding layer formed on the substrate, a core portion embedded in the cladding layer, and an elongated member for applying a stress to the core portion or a stress relief groove for relieving a stress from the core portion in the cladding layer along the core portion. The position, shape and material of the elongated member or the groove are determined in such a way that stress-induced birefringence produced in the core portion in accordance with a difference in thermal expansion coefficient between the substrate and the single mode optical waveguide is a desired value.

Single mode channel optical waveguide with a stress-induced birefringence control region

Bridge-Suspended Silica-Waveguide Thermo-Optic Phase Shifter and Its Application to Mach-Zehnder Type Optical Switch

A guided-wave optical branching component composed of Mach-Zehnder interferometer having two or more directional couplers (34, 35, 43, 44, 50, 51, 52, 75, 76, 85, 86). A slight difference ΔL in the optical-path length is given to the two or more optical waveguides (32, 33, 41, 42, 82, 83, 84) connecting the two or more directional couplers (34, 35, 43, 44, 50, 51, 52, 75, 76, 85, 86). The difference of the optical-path length is determined less than the shortest wavelength in the operational wavelength region of the guided-wave optical branching component, and a coupling ratio of each of the two directional couplers (34, 35, 43, 44, 50, 51, 52, 75, 76, 85, 86) is determined to monotonically increase according to the wavelength in the operational wavelength region. By using the optical branching components thus constructed (i.e., Mach-Zehnder interferometer type 3-dB optical coupler (101,102)) in conjunction with a phase shifter, Mach-Zehnder interferometer type optical switch can be achieved.

Kaname Jinguji

Papers

Low loss poly(methylmethacrylate‐d8) core optical fibers

Integrated optical device and method for manufacturing thereof

Single mode channel optical waveguide with a stress-induced birefringence control region

Bridge-Suspended Silica-Waveguide Thermo-Optic Phase Shifter and Its Application to Mach-Zehnder Type Optical Switch

Guided-wave optical branching components and optical switches