Kazuo Fujiura

Fabrication of praseodymium‐doped arsenic sulfide chalcogenide fiber for 1.3‐μm fiber amplifiers

Pr3+‐doped As‐S chalcogenide fiber is fabricated using a double‐crucible method. The thermal and spectroscopic properties of Pr3+‐doped As‐S glasses are clarified. Pr3+‐doped As‐S fiber is shown to be a promising candidate that will lead to efficient Pr3+‐doped fiber amplifiers.

High-density near-field readout using solid immersion lens made of KTaO3 monocrystal

We developed solid immersion lenses made of a KTaO3 monocrystal. The refractive index of KTaO3 is 2.382 at a wavelength of 405 nm. Using KTaO3 as the raw material of a solid immersion lens, we could design an effective numerical aperture of 2.20. We observed an eye pattern of a 150 GB capacity with a 130 nm track pitch and a 47.6 nm bit length. The areal density is 104.3 Gbit/in.2.

Improvement of coherence length in a 200-kHz swept light source equipped with a KTN deflector

We are developing a new light source for swept-source OCT, namely, an external-cavity LD equipped with a KTN electro-optic deflector. Being free from mechanical resonance, our 1.3-μm laser exhibits scanning range of almost 100 nm up to 200-kHz under a ±300 V deflector driving voltage. Using a semi-empirically derived equation, we find that KTNs convex lens power degrades the coherence length, and this can be compensated with a cylindrical concave lens. Such compensation was experimentally confirmed by observing reduction of elliptical beam divergence. OCT images of a human fingernail are obtained using the swept source.

Organometallic Chemical Vapor Deposition of ZrF4-Based Fluoride Glasses

By organometallic chemical vapor deposition (OMCVD), fluoride glasses in a ZrF4-BaF2 binary system are successfully synthesized. β-Diketone chelates of Zr and Ba as starting materials can be volatilized and completely fluorinated with HF gas into ZrF4-BaF2 compounds. 65 mol%ZrF4-35 mol%BaF2 powder synthesized by OMCVD is identified as homogeneous glass by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). By this method, ZrF4 is also obtained in an amorphous state. The OMCVD is available for preparation of fluoride glass, which is promising for optical fiber.

Reliability of fluoride fiber module for optical amplifier use

We report reliability test results for a fluoride fiber module. We developed a sealed fluoride fiber module for practical optical fiber amplifier use. Trouble-free damp heat storage and low-temperature storage for 5000 h and trouble-free temperature cycling and temperature-humidity cycling tests revealed that our fluoride fiber module has long-term stability under practical environmental conditions.

Fabrication of low‐loss and high‐Δn single‐mode fluoride fiber for 1.3 μm praseodymium‐doped fiber amplifiers

The crystallization properties of ZrF4‐based fluoride glasses containing PbF2 are clarified and single‐mode fibers for an optical amplifier operating at 1.3 μm are fabricated. The crystallization tendency increases as the PbF2 content of the glasses increases and the optimum PbF2 content ranges from 11 to 12.5 mol % in terms of glass stability and refractive indices. The 4%‐Δn single‐mode fiber with a transmission loss of 44 dB/km at 1.2 μm was prepared as the amplifier host fiber. ZrF4‐based glass with a PbF2 content of 11 mol % was used as a core glass and HfF4‐based glass was used as a cladding glass.

KTN optical waveguide devices with an extremely large electro-optic effect

KTa1-xNbxO3 crystal exhibits an extremely large quadratic electro-optic effect, which is 20 times greater than that of LiNbO3. This property makes this crystal attractive for optical signal processing applications. We have successfully prepared a 2-inch KTN crystal that exhibits the largest quadratic electro-optic coefficient ever reported. We have also fabricated a buried optical waveguide with a low transmission loss and demonstrated an optical switch with a driving voltage of 2.6 V and a 92 nsec rise time. This paper reviews the crystal growth, material properties, electro-optic effect, waveguide fabrication, and optical switch operation of KTN crystal.

Preparation and properties of ZrF4-based fluoride glass films by plasma-enhanced chemical vapor deposition

ZrF4-based binary glass films are for the first time synthesized by plasma-enhanced chemical vapor deposition (PCVD) and their optical transmission spectrum is measured from the UV to near IR region. The films are pore-free and transparent. No absorption band caused by OH or other impurities can be observed in the near IR region. Weak absorption bands attributed to defect centers, which are induced by plasma bombardment, are observed in the UV to visible region.

Reliability of rare-earth-doped fluoride fibers for optical fiber amplifier application

We have clarified the strength and estimated lifetime of fluoride fibers for optical amplifier use. We fabricated a UV-curable epoxy-acrylate coated fluoride fiber with a strength of 542 MPa. We estimated the lifetime of the fluoride fiber to be longer than 25 years at 80/spl deg/C and 50% RH.

A Mechanical-free 150-kHz Repetition Swept Light Source Incorporated a KTN Electro-optic Deflector

We present a new light source for the swept-source OCT, that is, an external-cavity LD incorporating an electro-optic deflector. We use a KTN deflector that is unique in being very fast and simultaneously providing an appreciable deflection caused by injected carriers. Particularly, high-speed and nearly linear to the applied voltage operation is attained when KTN crystal is pre-charged. Our 1.3-μm Littman-Metcalf external-cavity laser exhibits static linewidth < 0.1 nm, and a 110-nm scanning range up to 150-kHz under a ±200 V sinusoidal driving voltage to the deflector. Being free of mechanical resonance, the laser would hopefully realize a faster (in a separate study, deflector itself worked up to 400 kHz) and wavenumber-linear scan that is ideal for the swept-source OCT by designing the waveform of driving voltage. And as for the resolving power of deflector, while our KTN deflector has only 35 spatial resolvable points, the number of wavelength points for the swept source clearly exceeds to this limit, which we attribute to line narrowing effect accompanied by the laser operation. Preliminary OCT images taken using the swept source are also presented.