Kunihiko Asama

Compact optical isolator for fibers using birefringent wedges

A new type of optical isolator for fibers is proposed in this paper. A birefringent wedge used to separate and combine the polarized light is developed, giving the isolator low forward loss and high isolation. The antire-flection process at the fiber endface reduces the forward loss and reflected return. A forward loss of 0.8 dB, a backward loss of 35 dB, and a reflected return of -32 dB were obtained. These characteristics were measured from fiber to fiber using multimode fibers with 50-/microm core diam at a wavelength of 1.3 microm. Details of the design, fabrication, and characteristics of this isolator are presented.

Crystalline and magnetic properties of an ion‐implanted layer in bubble garnet films

Crystalline properties of Ne+‐implanted garnet films with varying implantation energies and dosages have been studied by means of the double‐crystal x‐ray‐diffraction method, and it was found that when implantation‐induced damage was low, Pendellosung interference was observed which is directly related to crystal perfection, and a layer with large microscopic strain was found to become amorphous. The damage profiles were determined by measuring changes in x‐ray rocking curves after etching the implanted layers. Based on these experimental results, an implanted layer model was derived. The influences of the crystalline properties on the magnetic properties were also investigated from the viewpoints of the flux keeper and hard‐bubble‐suppression effects. For high implantation dosage the amorphous layer becomes magnetically inactive. This phenomenon is ascribed to randomly oriented micro‐magnetic‐domains with zero net magnetization caused by large microscopic strain in the amorphous layer. The effect of anne...

Effect of Deposition Conditions on Intrinsic Stress in a-Si:H Films

Intrinsic stress in the a-Si: H film, which reflects the internal microstructure of the film under deposition and thus gives the information about the construction of amorphous network, has been evaluated by the Baser interferometric method. The intrinsic stress induced in the a-Si: H film is compressive and increases with the deposition temperature. As the intrinsic compressive stress is increased, decreases are observed in the deposition rate, the total hydrogen concentration, and the ratio of hydrogen concentration with the configuration SiH2, SiH3, and (SiH2)n to that with SiH. These results on the temperature dependence of a-Si: H film growth indicate that the contribution of excited species in the plasma to the growth of the a-Si: H is restricted by the intrinsic compressive stress induced in the a-Si: H through differences in molecular dimensions of the excited species.

Nonmechanical optical switch for single-mode fibers

This paper introduces a bistable nonmechanical optical switch for single-mode optical fibers. A l-input/2-output device for the l-microm wavelength range, the optical losses of the switch are independent of the polarization state in the input fiber. The insertion losses for the optical signal from the input fiber to the output fiber are 1.4 dB and the crosstalks are -28 dB at 1.3-microm wavelength. Switching is performed by a 20-microsec one-shot pulse with a maximum current of 500 mA. The voltage to switch the optical path is 5 V.

Magnetooptical 2×2 switch for single-mode fibers

An optical switch for single-mode fibers is presented in this paper. A novel polarizing prism is introduced to make the 2 input, 2 output optical switch insertion loss low and independent of the polarization state of the input fiber. This switch operates by one electric pulse with a voltage of only 2.5 V and a current of 35 mA. The insertion loss was 1.2 dB, its fluctuation for different input polarizations was within 0.03 dB, and the far-end crosstalk was −26 dB at a wavelength of 1.3 μm. The shock resistance of the switch was confirmed during an acceleration of 100 g.

Contact-Type Linear Sensor Using Amorphous Si Diode Array

A contact-type linear sensor using amorphous Si diodes as photodetectors has been developed. The sensor structure can largely reduce the number of electrodes to be connected to the switching FETs and hence has an advantage of realizing a facsimile reader which is compact and easy to construct. The linear sensor developed is constructed with 256 pairs of In2O3/a-Si photodiodes and Pt/a-Si blocking diodes and this combination of two types of diodes has been found to yield high output signal. In this sensor structure, incident light is introduced to the photodiodes through a glass substrate in order to protect the photodetectors from contamination and scratching.

Effect of in‐plane magnetic field on bubble collapse field in ion‐implanted garnet films

Bubble collapse fields in several kinds of garnet films ion implanted for hard‐bubble suppression were measured in the presence of an in‐plane magnetic field and were found to vary according to the direction of the in‐plane field. That is, bubble collapse fields exhibit a threefold symmetry in response to the threefold symmetry of crystallographic axes. The appearance of this threefold symmetry was explained by the response of closure domains associated with bubbles to in‐plane fields. This phenomenon is shown to be dependent on the properties of garnet films and implantation conditions, i.e., dose, energy, and ion species used: H, Ne, and Ar.

Temperature stability of bubble domain wall states

It is well known that bubbles with revolution numbers S=1 and S=0 can exist in a capped garnet film. The stability of these two types of bubbles is considered to be a very important problem, especially when they are used for binary coding of bubble lattice devices. This paper describes the temperature stability of these two types of bubbles. The sample used was (YGdYb)3(FeGa)5 O12 with a bubble diameter of 3 μm. An S=1 bubble was stable up to about 100°C, although the deflection angle ϑ increased linearly from 40° at room temperature to 70° at 100°C. An S=0 bubble was generated by applying an in‐plane magnetic field Hp=100 Oe and after reducing Hp to a certain value, temperature dependences of the deflection angle ϑ and the bubble velocity V were measured at a constant drive field ∇Hz=3.5×103 Oe/cm. When Hp=40 Oe, ϑ remained 0° up to 80°C, indicating that the S=0 state was stable up to 80°C. When Hp=20 Oe, on the other hand, ϑ changed discretely from 0° to 27° at about 55°C, thereafter increasing with tem...

Effect of B2O3 concentration on magnetic defects and properties of garnet films grown in PbO‐B2O3 solvents

For the purpose of eliminating magnetic defects on garnet films, various molar concentrations of R=B2O3/(PbO+B2O3) have been extensively studied. It was found that the density of magnetic defects was reduced remarkably in films grown in B2O3 rich solvent. Experiments were carried out on YSmLuCaGeIG films within the 4πMs range of 200 to 300 gauss, and defects were evaluated using an interference contrast microscope having a magnification of 1000×. Observed defects were broadly classified into four types of pitting: circular, triangular, hexagonal and elliptical. For the film thickness range of 2.5 to 4.0 μm grown in a solution, where R=6.0 mol%, the average pit densities of circular, triangular and hexagonal pits were 8.0, 6.4 and 2.1 cm−2, respectively. Each of these pit densities were reduced to 0.7, 0.2 and 0.0 for R=11.4 mol%. The effect of R on growth conditions was also investigated to obtain films suitable for 3 μm diameter bubbles with 4πMs=280 gauss and l=0.33 μm. The appropriate growth temperatur...

FMR study of an ion‐implanted layer on bubble garnet films

Properties of magnetic anisotropy of an ion‐implanted layer on [111]‐oriented bubble garnet films have been studied in relation to implantation dosages by ferromagnetic resonance techniques. As has been reported, subpeaks generated in the implanted layer were observed in addition to the main peak related to the garnet film itself. The resonant field of these subpeaks showed a strong dependence on the orientation in the (110) plane, whereas dependence was weak in the (111) plane. Data was analyzed under the assumption that signals from the implanted region of specimens are of uniform mode, and it was found that implanted layers of a Y1.33Eu0.2Yb0.57Ca0.9Ge0.9Fe4.1O1 2 film implanted with neon at an energy of 100 keV with dosages ranging from 1.1×1014 to 2.0×1014/cm3 were magnetically uniaxial, the easy axis being the (111) plane and the hard axis, the [111] axis. A precisely defined method for determining implantation‐induced anisotropy was developed, and results showed that its magnitude is several 104 e...