Abstract: A flame rod (1) including: a rod portion (11) made of a metal material containing aluminum; and a protective cover layer (21) containing a cover material having high conductivity and high heat resistance, wherein the protective cover layer (21) covers a surface of an insertion portion (11A) of the flame rod (11), and the protective cover layer (11) has a thickness of 0.002 mm or more and less than 0.1 mm.

Abstract: A flame rod (1) including: a rod portion (11) made of a metal material containing aluminum; and a protective cover layer (21) containing a cover material having high conductivity and high heat resistance, wherein the protective cover layer (21) covers a surface of an insertion portion (11A) of the flame rod (11), and the protective cover layer (11) has a thickness of 0.002 mm or more and less than 0.1 mm.

Abstract: An optical fiber includes a core, a first cladding, a second cladding, and a third cladding. The core has a refractive index n.sub.0. The first cladding is formed around the core and has a refractive index n.sub.1. The second cladding is formed around the first cladding and has a refractive index n.sub.2. The third cladding is formed around the second cladding and has a refractive index n.sub.3. The refractive indices have relationships n.sub.1 >n.sub.2 >n.sub.3 and n.sub.1 >n.sub.0.

Abstract: The optical connector according to the present invention comprises, at least, an optical filter with a waveguide structure having a grating with a predetermined reflection wavelength and a plug attached to a tip of the optical filter. The grating is disposed at a tip portion of the optical filter and accommodated in the plug attached to the tip portion of the optical filter. Further, the optical connector has various light-blocking structures for preventing unnecessary light from traveling a filter region of the optical filter including the grating.

Abstract: Lead-containing fluoride glass comprises 50-70 mol % of ZrF.sub.4, 3-5 mol % of LaF.sub.3, 0.1-3 mol % of YF.sub.3, and 2-15 mol % of NaF and/or LiF and/or CsF, where LaF.sub.3 +YF.sub.3 =4.5-6 mol %, and further comprises lead. An optical fiber comprises a core made of the lead-containing fluoride glass and a cladding surrounding the core. A process for producing an optical fiber comprises forming a base material for a core of the lead-containing fluoride glass, forming a base material for a cladding of fluoride glass containing 30-60 mol % of HfF.sub.4, and drawing the base materials into an optical fiber at a drawing temperature of 315-340 .degree. C.

Abstract: Lead-containing fluoride glass comprises 50-70 mol % of ZrF.sub.4, 3-5 mol % of LaF.sub.3, 0.1-3 mol % of YF.sub.3, and 2-15 mol % of NaF and/or LiF and/or CsF, where LaF.sub.3 +YF.sub.3 =4.5-6 mol %, and further comprises lead. An optical fiber comprises a core made of the lead-containing fluoride glass and a cladding surrounding the core. A process for producing an optical fiber comprises forming a base material for a core of the lead-containing fluoride glass, forming a base material for a cladding of fluoride glass containing 30-60 mol % of HfF.sub.4, and drawing the base materials into an optical fiber at a drawing temperature of 315.degree.-340.degree. C.

Abstract: An optical functioning glass for enabling optical amplification at 1.3-.mu.m wavelength band or increasing efficiency of the amplification is disclosed. The optical functioning glass contains Nd.sup.3+ as an active material and uranium, both of which are doped in a multi-component function glass serving as a host glass. Since uranium is doped in the optical functioning glass, light emission of Nd.sup.3+ in the 1.06-.mu.m wavelength band can be absorbed by uranium. A decrease in efficiency of induced emission in a 1.3-.mu.m wavelength band can be prevented, and an optical functioning glass suitable for optical amplification in the 1.3-.mu.m wavelength band can be obtained. When a fiber is formed using the optical functioning glass as a core, a low-threshold, high-gain fiber amplifier, fiber laser, and the like can be obtained.

Abstract: An optically active device comprising an optical fiber, a light source and a coupler is disclosed. The optical fiber has a core made of a silicate glass containing Rb and/or Cs oxide. The core is doped with Nd.sup.3+ as an active ion and transmits light at 1.3 .mu.m band. The light source generates excitation light at 0.8 .mu.m. The coupler directs the excitation light from the light source into the core of the optical fiber. A signal light or a spontaneous light at 1.3 .mu.m band which is transmitted in the core stimulates Nd.sup.3+ to emit light at 1.3 .mu.m band. As a result an optical function such as optical amplification can be effected at 1.3 .mu.m band.

Abstract: The present invention relates to an optical functioning glass containing Nd.sup.+3 as an active ion which amplifies an input light, and at least one other optical active ion different from Nd.sup.+3 which absorbs light at and near 1 .mu.m. The present invention also relates to an optical functioning glass containing Nd.sup.+3 as an active ion which amplifies the input light, and at least one other optical active ion different from Nd.sup.+3 functioning as a promoter. An efficiency of the stimulated emission of Nd.sup.3+ caused by signal light propagated through the optical functioning glass is enhanced and a gain of the light amplification at 1.3 .mu.m is increased.

Abstract: An optical functioning glass for enabling optical amplification at 1.3-.mu.m wavelength band or increasing efficiency of the amplification is disclosed. The optical functioning glass contains Nd.sup.3+ as an active material and uranium, both of which are doped in a multi-component function glass serving as a host glass. Since uranium is doped in the optical functioning glass, light emission of Nd.sup.3+ in the 1.06-.mu.m wavelength band can be absorbed by uranium. A decrease in efficiency of induced emission in a 1.3-.mu.m wavelength band can be prevented, and an optical functioning glass suitable for optical amplification in the 1.3-.mu.m wavelength band can be obtained. When a fiber is formed using the optical functioning glass as a core, a low-threshold, high-gain fiber amplifier, fiber laser, and the like can be obtained.