Showing papers on "Birefringence published in 1988"

Fiber loop reflectors

Abstract: The theory and application of fiber loop reflectors, fabricated by forming a fiber loop between the output ports of a directional coupler, is described. The reflectivity of the loop is shown to depend upon the coupling characteristics of the coupler and on the degree of birefringence in the fiber loop. Measured loop reflectivities, in terms of wavelength response, coupling ratio, and loop birefringence are shown to agree very well with theory. Two applications of the fiber reflector are briefly discussed; an all fiber laser and a duplex optical communications link using a single light source. >

Vector solitons in birefringent nonlinear dispersive media

Abstract: It is shown that a novel class of optical solitons is possible in nonlinear dispersive media with birefringence.

Growth and Optical Properties of Li13Nd(GeO4)4 Single Crystal

Abstract: In this paper, single crystals of Li13Nd(GeO4)4 are grown by the Czochralski method. The unit cell dimensions and the crystal system are determined by an X-ray diffraction method. The principal refractive indices, na, nb and nc and the temperature dependence of birefringences, nc-nb, nc-na and na-nb, over the temperature range from room temperature to 500degC are measured. A fluorescence spectrum at around 1.06 µm is observed, and strong fluorescence is detected.

Poled electro‐optic waveguide formation in thin‐film organic media

Abstract: We describe a novel technique for the fabrication of electro‐optic (EO) waveguides in integrated optic device structures employing organic EO materials. The technique combines the poling and waveguide formation steps by utilizing patterned poling electrodes and the induced birefringence associated with the poling process. Several prototype waveguide devices fabricated using this procedure are reported.

Endless polarization control systems for coherent optics

Abstract: In coherent optical systems or sensors, polarization matching between the superposed beams must be assured. The tracking range of automatic polarization control systems should be endless, i.e. any resets of finite range retarders, which transform the polarization, should cause no significant intensity losses. A variety of experimental systems including a computer as feedback controller are described. They include the minimum configuration of three fixed eigenmode retarders, i.e. the orientation of birefringence cannot be changed. These retarders are realized by fiber squeezers. Error-tolerant systems which contain more than the minimum number of elements, however, are better suited to cope with time variant retarder transfer functions, etc. A fourth fiber squeezer allows the losses of a nonideal systems to be kept to only 0.07 dB. Finally, for the first time, a closed loop system with two integrated optical retarders is described. These retarders have variable eigenmodes, i.e. adjustable birefringence orientation. An optimization procedure helps to idealize the device behavior. The system has less than 0.15 dB intensity losses, coupling and attenuation not included. >

Bound solitary waves in a birefringent optical fiber.

Abstract: We present the first mixed-type solutions to the coupled nonlinear Schr\"odinger equations which govern optical pulse propagation in a birefringent fiber. These represent polarization-modulated pulses which, apart from the absolute phase, propagate unchanged in form. It is shown they are bound states of two solitary waves which separately have constant and uniform orthogonal linear polarizations. Furthermore, there exists a minimum-energy threshold for the formation of these bound states.

Stability of birefringent linear retarders (waveplates).

Abstract: The effects of changes in temperature, wavelength, and direction of propagation (angle of incidence) on the retardance of zero-order, multiple-order, compound zero-order, and temperature-compensated waveplates are described in detail. A disagreement in the literature regarding the properties of a compound zero-order waveplate is resolved by showing that with respect to temperature and wavelength it behaves like a true zero-order waveplate, but with respect to angle of incidence it behaves like a multiple-order waveplate. A previously proposed temperature-compensated design is shown to suffer from the same directional limitations. A new design for a retarder consisting of one element of a positive uniaxial crystal and one element of a negative uniaxial crystal is proposed. The retardance of such a waveplate would be much less sensitive to the direction of propagation, but somewhat more sensitive to temperature, than a typical compound zero-order waveplate.

Small angle relaxation of highly deformed nematic liquid crystals

Abstract: Transient phase response associated with a small angle relaxation from highly deformed nematic liquid crystal (LC) directors is analyzed experimentally and numerically. Qualitative agreement between computer simulations and experimental results is obtained. Based on these results, decay time of a fast LC modulator employing the transient nematic effect is derived. This decay time is found to be fast (with potential to achieve ∼50 μs), insensitive to LC thickness, but proportional to (λ/Δn0)2, λ being the wavelength and Δn0 the corresponding birefringence.

A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission

Abstract: A four-channel optical waveguide multi/demultiplexer for 5-GHz spaced optical FDM transmission is developed. The multi/demultiplexing principle is first presented, followed by the extinction ratio dependence on the power transfer ratio of the directional couplers, transmission loss of the waveguide, and birefringence of the waveguide. Experimental results are described for waveguides of high-silica glass fabricated on the silicon substrate by combination of flame hydrolysis and reactive ion etching. Their measured characteristics, such as frequency transmittance, loss, extinction ratio, and dependence of polarization and temperature are reported and evaluated. >

Wavelength-tunable electrooptic polarization conversion in birefringent waveguides

Abstract: Wavelength-tunable, electrooptic polarization conversion in a birefringent waveguide accomplished with a multiple cascade of alternating TE from to TM mode converter and TE/TM phase shifter sections is analyzed. Such polarization converters have been demonstrated in LiNbO/sub 3/ and have been used as electrooptically tunable narrowband ( Delta lambda >

Ultrafast all-optical switching utilizing the optical Kerr effect in polarization-maintaining single-mode fibers

Abstract: An ultrafast all-optical switching scheme utilizing the optical Kerr effect in two birefringent fibers concatenated with each fast axis crossed is proposed Stable optical Kerr modulation and all-optical demultiplexing of an ultrashort (30 ps) optical pulse train at 197 GHz from a gain-switched distributed-feedback laser diode (DFB LD) have been sufficiently demonstrated using CW mode-locking Nd:YAG laser pulses as a pump Switching speed and required pump powers are studied in terms of fiber bandwidth due to fiber birefringence, and combined effects of chromatic and polarization dispersions on Kerr modulation profiles By utilizing the optical Kerr modulation properties in the presence of dispersions, the nondiagonal yx component of the nonlinear refractive index is also determined to be 034 relative to the diagonal component xx The intrinsic stability and ultimate switching capabilities are discussed >

Integrated optical device and method for manufacturing thereof

Abstract: 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.

Film with partial pre-alignment of polymer dispersed liquid crystals for electro-optical devices, and method of forming the same

Abstract: A polymer dispersed liquid crystal (PDLC) film, along with various fabrication methods that enable partial prealignment of the film's LC bubbles, are described. The film is formed with a matrix of liquid crystal bubbles. Individual liquid crystals within the bubbles are partially, but substantially less than fully, aligned in a given direction. Partial alignment is attained by the controlled application of an electric or magnetic field, or a mechanical flow, during photopolymerization. The resulting films retain the positive qualities of prior PDLCs, and in addition exhibit generally lower threshold and operating voltages, and can be used as tunable birefringent films in the infrared region.

Stabilised current sensor using Sagnac interferometer

Abstract: A current sensor based on a stabilised fibre-optic Sagnac interferometer has been constructed and preliminary tests have been carried out Measurements made with this system are independent of variations in the following parameters: laser intensity, light intensity injected into the optical fibre and birefringence within the fibre The stabilised output is obtained by electronically combining the output signal from the interferometer with samples of the signal which have traversed the optical fibre in opposite directions The mathematical basis for the stabilisation technique and construction details for the instrument are given

Thin‐film garnet materials with zero linear birefringence for magneto‐optic waveguide devices (invited)

Abstract: The many advantages of thin‐film waveguide magneto‐optic devices have been difficult to realize because of the linear birefringence of these films, which makes it very difficult to achieve the required Faraday rotation. In epitaxial garnet films, this linear birefringence (the difference between the refractive indices of the TE and TM modes) can be reduced to small values by (1) growing single‐mode multilayer films to minimize the shape effect, (2) growing the films in compression to control the photoelastic effect, and (3) annealing at high temperatures to eliminate the growth‐induced effect. The remaining birefringence can be reduced to zero by growing the top active layer too thick so that the shape effect is smaller in magnitude than the stress effect, and then thinning it by chemical etching until the effects exactly cancel each other at a particular wavelength. An alternative method is to grow the top layer too thin and then to deposit a dielectric layer such as silicon nitride of the proper thickness to reduce the shape effect so that it exactly cancels the stress effect. Theoretical results on multilayer magneto‐optic waveguides and successful etch‐tuning experiments at 1.32 and 1.51 μm are presented. These tuning procedures can produce polarization‐independent waveguide devices such as isolators or polarization rotators which may replace bulk or thick‐film devices.

Linear birefringence effects on fiber-optic current sensors.

Abstract: The occurrence of linear birefringence is inevitable when dealing with fiber optics. Intrinsic birefringence can be minimized, but deploying the fiber on an experiment will introduce stress birefringence due to bending and pressure. We have studied the effects of this extraneous linear birefringence on the measurement of current-induced circular birefringence in a fiber which also has a strong twist circular birefringence bias. Orienting the analyzing polarizer by a proscribed procedure gives minimum error. Quantitative error limits on the current for given fiber coil radii and winding tensile stress are calculated. Additional restrictions on the fiber lead-in and lead-out sections are discussed.

Relaxation of Stress and Birefringence in Polymers of High Molecular Weight

Abstract: Stress relaxation behavior of concentrated solutions of high molecular weight polystyrene following a step shear strain is studied using both mechanical and optical birefringence techniques. Using the stress‐optic law, which we find to be valid for our solutions, we obtain time‐dependent shear stress and first normal stress difference values from birefringence measurement that are free of transducer compliance effects. Similar to the previously reported experimental observations of Fukuda, Osaki and Kurata, we obtain unusually low values for nonlinear shear moduli, much lower than the predictions of Doi‐Edwards model, for the sample with more than about 60 entanglements per molecule. Moreover, the shear stress and first normal stress difference data measured on this sample do not conform to the Lodge‐Meissner relationship, especially at long times, suggesting the formation of regions in which the imposed strain is not homogeneously distributed.

Optically-controlled Photo-induced Birefringence in Photo-anisotropic Materials

Abstract: A theoretical and experimental investigation is made of the possibility of controlling the photo-induced birefringence in photo-anisotropic materials by means of irradiation with a suitably chosen additional light. The applicability of the method is estimated by a consideration of the parameters of the optically and thermally activated processes taking place in the materials. The experimental results obtained in layers of rigid solutions of azo-dyes confirm the practical feasibility of such optical control.

Birefringent channel waveguides defined by impurity‐induced superlattice disordering

Abstract: The waveguiding characteristics of GaAs/AlGaAs channel waveguides defined by silicon‐induced superlattice disordering were investigated at 1.15 μm wavelength. These waveguides guide laterally only TE‐polarized light. Because of the birefringence of the superlattice core of the waveguide, only the TE mode experiences a positive refractive index step between the unmixed and disordered superlattices. The TM mode, on the other hand, experiences a negative refractive index step resulting in antiguiding. The operation of these waveguides as efficient waveguide polarizers is demonstrated.

Analysis of the birefringence of the smooth muscle anococcygeus of the rat, at rest and in contraction. I.

Abstract: The birefringence of the rat anococcygeus muscle was measured at rest and in contraction. A large increase (+30%) of the optical retardation was observed in muscles fully stimulated by Noradrenaline, in isometric conditions. This was associated with a reduction of the muscle thickness (-12%), so that the birefringence increased by 48%. These changes were reversed upon relaxation. The relationship between the birefringence increase and the mechanical response was investigated as a function of time and of Noradrenaline concentration. Possible origins for the birefringence increase are considered: an increased density of birefringent material, mainly filaments, seems the most likely explanation of the results.

Optical and electro‐optic properties of cyanotolanes and cyanostilbenes: Potential infrared liquid crystals

Abstract: Optical and electro‐optic properties of some highly conjugated nematic liquid crystals (LCs): 4‐cyano‐4’‐n‐alkyltolanes (n‐CDP) and 4‐cyano‐4’‐n‐alkylstilbene (n‐CS) were studied at elevated temperature. Results are compared with 4‐cyano‐4’‐n‐pentylbiphenyl (5CB). These LCs exhibit large birefringence, small viscoelastic coefficient, and low threshold voltage. Their potential application for modulating visible and infrared radiation is addressed.

Electric current sensor using the faraday effect

Abstract: An electric current detector has a light source for generating light having substantially linear polarization and a predetermined polarization direction, a material substantially transparent to the light, the material having at least one characteristic direction, and the material exhibiting the Faraday effect in response to a magnetic field generated by the electric current. Also the light is launched into the material, and a predetermined angle established between the polarization direction and the characteristic direction, the predetermined angle chosen to permit separation of a rotation of the polarization of the light by the Faraday effect from polarization effects on the light by a birefringence of the material. A value of 22.5° for the magnitude of the predetermined angle permits a separation of the rotation of the polarization due to the Faraday effect from polarization effects due to a birefringence of the material.

Transient effects during dynamic hologram formation in BSO crystals: theory and experiment

Abstract: A model is presented for the time dependence of energy transfer between two incident beams and the concomitant grating formation in photorefractive materials. The theory includes the effects of birefringence, optical activity, and absorption of light. The predictions of the model are compared in detail with sets of experimental measurements performed with bismuth silicon oxide (BSO) crystals. Good agreement of the measured values and theory was found. >

Picosecond nonlinear polarization switching with a fiber filter

Abstract: We report ultrafast all‐optical switching between two orthogonal linear polarizations in a periodically twisted, birefringent fiber filter.

Low-loss short-wavelength optical waveguides using ZnSe-ZnS strained-layer superlattices

Abstract: Low‐loss short‐wavelength optical ridge waveguides using ZnSe‐ZnS strained‐layer superlattices (SLS’s) were successfully fabricated on GaAs substrates by low‐pressure metalorganic vapor phase epitaxy. A propagation loss α as low as 0.71 cm−1 was obtained for the SLS waveguide composed of 80 periods of ZnSe(50 A)‐ZnS(50 A) at the 0.633‐μm wavelength TE fundamental mode. Therefore, this waveguide may be suited for optoelectronic integrated circuits composed of II‐VI and III‐V compound semiconductor devices. Furthermore, these waveguides exhibited a large difference in the propagation loss between TE and TM polarizations which may be related to the birefringence for TE and TM polarizations due to the slight anisotropy of the refractive index in the ZnSe‐ZnS superlattice structure. This birefringence effect will be very useful for a polarizing optical device.

Temperature dependence of bend- and twist-induced birefringence in a low-birefringence fiber.

Abstract: The temperature dependence of the bend- and twist-induced birefringence in LB600 low-birefringence fiber has been measured at λ = 0.633 μm. The relative temperature dependence B = (1/β)dβ/dT of the bend-induced birefringence β was found to be (5.7 ± 0.2) × 10−4 K−1 over a temperature range from −5 to 70°C. The relative temperature dependence A = (1/g)dg/dT of the twist-induced birefringence g was found to be (4.95 ± 0.25) × 10−4 K−1 (between 22 and 150°C). The measured values of A and B are in accordance with a relative temperature dependence (1/C)dC/dT of the stress-optic coefficient C equal to (4.2 ± 0.2) × 10−4 K−1.