Patents by Inventor Kazutaka Nara

Kazutaka Nara has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 8422118
    Abstract: A PLC-type delay demodulation circuit includes a planar lightwave circuit that is provided on one PLC chip and demodulates a DQPSK signal. The planar lightwave circuit includes a Y-branch waveguide that branches a DQPSK-modulated optical signal into two optical signals and first and second MZIs that delay the branched optical signals by one bit. The length of a short arm waveguide of the first MZI is different from the length of a short arm waveguide of the second MZI, and the length of an optical path from the Y-branch waveguide to output ports of the first MZI through the short arm waveguide of the first MZI is equal to that of an optical path from the Y-branch waveguide to output ports of the second MZI through the short arm waveguide of the second MZI.
    Type: Grant
    Filed: December 21, 2011
    Date of Patent: April 16, 2013
    Assignee: Furukawa Electric Co., Ltd.
    Inventors: Hiroshi Kawashima, Kazutaka Nara
  • Patent number: 8401351
    Abstract: The present invention provides a 90-degree hybrid capable of miniaturization and also capable of a stable operation in a wide band. According to an embodiment of the present invention, a PLC-type 90-degree hybrid comprises: a PLC chip having a planar lightwave circuit formed therein; and a 90-degree hybrid circuit formed in the planar lightwave circuit, mixing a modulated signal light and an LO light to separate the signal light into quadrature components I and Q, and outputting the same. The 90-degree hybrid circuit includes: two Y-branch couplers each branching the signal light and the LO light; and two wavelength-independent directional couplers which cause LO lights passing through two paths and signal lights passing through two paths to interfere with each other, respectively. The above-described paths include waveguides having mutually inverted shapes and waveguides having an identical shape, and have a shape substantially symmetrical with respect to the signal light.
    Type: Grant
    Filed: March 1, 2012
    Date of Patent: March 19, 2013
    Assignee: Furukawa Electric Co., Ltd.
    Inventors: Takashi Inoue, Kazutaka Nara
  • Patent number: 8380023
    Abstract: A waveguide-type optical circuit comprises an optical coupler being an optical branch coupler constructed from waveguide cores which are closely arranged to each other, and dummy patterns that lay along sides of the waveguide cores in the optical coupler for preventing optical major axes of the waveguide cores from inclining.
    Type: Grant
    Filed: July 14, 2010
    Date of Patent: February 19, 2013
    Assignee: Furukawa Electric Co., Ltd.
    Inventors: Noritaka Matsubara, Kazutaka Nara
  • Publication number: 20130010350
    Abstract: Disclosed are a PLC-type delay demodulation circuit and a PLC-type optical interferometer capable of reducing the size of a PLC chip with respect to the arrangement of various kinds of light output waveguides. In a PLC-type delay demodulation circuit, arm waveguides of a first MZI and arm waveguides of a second MZI are formed so as to overlap each other in the same region of a planar lightwave circuit. The optical paths of the MZIs are arranged such that the propagation directions of two DQPSK signals branched by a Y-branch waveguide are opposite to each other.
    Type: Application
    Filed: September 13, 2012
    Publication date: January 10, 2013
    Applicants: FUJITSU OPTICAL COMPONENTS LIMITED, FURUKAWA ELECTRIC CO., LTD.
    Inventors: Hiroshi KAWASHIMA, Kazutaka Nara, Kohei Shibata
  • Publication number: 20120251047
    Abstract: The present invention provides a Mach-Zehnder interferometer-arrayed waveguide grating (MZI-AWG) and a planar light-wave circuit chip in which a certain number of chips can be secured without degradation of MZI-AWG characteristics. An MZI-AWG (10) includes a Mach-Zehnder interferometer (MZI) (20) and an arrayed waveguide grating (AWG) (30) using the MZI for an input waveguide. The FSR of the MZI and the channel spacing of the AWG coincide with each other. An input side coupler (21) and an output side coupler (22) of the MZI are disposed on a straight line connecting a center part (a0) in one end surface (31a) of an input slab waveguide (31) and a center part (b0) in the other end surface (31b) which is a circular-arc shaped end surface having a radius of a focal length (Lf) from the center part (a0).
    Type: Application
    Filed: April 17, 2012
    Publication date: October 4, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventor: Kazutaka NARA
  • Publication number: 20120251046
    Abstract: The present invention provides an optical waveguide circuit which includes: a waveguide made of a material whose temperature coefficient of refractive index has a second-order component; a groove formed in a part of the waveguide; and a compensation material having a temperature coefficient of refractive index different from the temperature coefficient of refractive index of the waveguide, and in which a normal line of an interface between the groove and the waveguide, and an optical axis of light propagating through the waveguide intersect at a predetermined intersection angle, and the predetermined intersection angle is determined so as to reduce a second-order component of optical path length change of the waveguide due to the second-order component of temperature coefficient of the refractive index of the waveguide.
    Type: Application
    Filed: April 12, 2012
    Publication date: October 4, 2012
    Applicant: Furukawa Electric Co., Ltd.
    Inventors: Hiroshi Kawashima, Kazutaka Nara
  • Publication number: 20120224812
    Abstract: The present invention provides a 90-degree hybrid capable of miniaturization and also capable of a stable operation in a wide band. According to an embodiment of the present invention, a PLC-type 90-degree hybrid comprises: a PLC chip having a planar lightwave circuit formed therein; and a 90-degree hybrid circuit formed in the planar lightwave circuit, mixing a modulated signal light and an LO light to separate the signal light into quadrature components I and Q, and outputting the same. The 90-degree hybrid circuit includes: two Y-branch couplers each branching the signal light and the LO light; and two wavelength-independent directional couplers which cause LO lights passing through two paths and signal lights passing through two paths to interfere with each other, respectively. The above-described paths include waveguides having mutually inverted shapes and waveguides having an identical shape, and have a shape substantially symmetrical with respect to the signal light.
    Type: Application
    Filed: March 1, 2012
    Publication date: September 6, 2012
    Applicant: Furukawa Electric Co., Ltd.
    Inventors: Takashi INOUE, Kazutaka Nara
  • Publication number: 20120207474
    Abstract: The invention provides a PLC-type DP-QPSK demodulator that reduces connection loss between a polarization beam splitter and a 90-degree hybrid circuit and aims at reducing the manufacturing cost and an optical transmission system using the same. In an embodiment of the invention, a PLC-type DP-QPSK demodulator that receives a DP-QPSK signal includes one PLC chip having a planar lightwave circuit. Input ports and output ports of signal light are provided at an input end and at an output end of the PLC chip, respectively. Within the planar lightwave circuit, there are integrated a polarization beam splitter that splits the DP-QPSK signal into an X-polarization QPSK signal and a Y-polarization QPSK signal, and two 90-degree hybrid circuits that mix the X-polarization QPSK signal and local oscillation light and the Y-polarization QPSK signal and local oscillation light, respectively, split each QPSK signal into orthogonal components I, Q and output them.
    Type: Application
    Filed: March 1, 2012
    Publication date: August 16, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Takashi INOUE, Kazutaka Nara
  • Publication number: 20120195552
    Abstract: An arrayed waveguide grating type optical multiplexer and demultiplexer which achieves a low crosstalk even when temperature changes is provided, comprising, on a substrate, a waveguide chip in which an arrayed waveguide grating is formed that has a first waveguide, a first slab waveguide, an arrayed waveguide, a second slab waveguide, and a second waveguide, the waveguide chip being divided into two by any of the first and second slab waveguide, and includes a first glass plate to which one side of the arrayed waveguide grating divided into two in the waveguide chip is fixed, a second glass plate to which the other side thereof is fixed, and a compensation member compensating a temperature dependent shift of a light transmission center wavelength of the arrayed waveguide grating, wherein a part for the arrayed waveguide is not fixed to any of the first and second glass plates.
    Type: Application
    Filed: January 30, 2012
    Publication date: August 2, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Junichi Hasegawa, Kazutaka Nara
  • Publication number: 20120195553
    Abstract: An arrayed waveguide grating type optical multiplexer and demultiplexer which reduces a package size although plural arrayed waveguide gratings are included, is provided, comprising plural arrayed waveguide gratings which are provided in parallel to one another on a substrate and each of which has a first waveguide, a first slab waveguide, an arrayed waveguide, a second slab waveguide, and a second waveguide, and also includes a waveguide chip divided into a first and second separated waveguide chip in the first or second slab waveguide in each of the arrayed waveguide gratings and a compensation member compensating a temperature dependent shift of a light transmission center wavelength in the arrayed waveguide grating by relatively moving the first and second waveguide chip when expanded or contracted according to a temperature change. The waveguide chip has a shape bending along a bending direction of the arrayed waveguide.
    Type: Application
    Filed: February 2, 2012
    Publication date: August 2, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Junichi HASEGAWA, Kazutaka Nara
  • Publication number: 20120162746
    Abstract: The PLC-type delay demodulation circuit includes a planar lightwave circuit that is provided on one PLC chip and demodulates a DQPSK signal. The planar lightwave circuit includes a Y-branch waveguide that branches a DQPSK-modulated optical signal into two optical signals and first and second MZIs that delay the branched optical signals by one bit. A wave plate is provided in central portions of first and second arm waveguides of the first MZI and first and second arm waveguides of the second MZI in such a manner that the wave plate intersects all of the four arm waveguides, the four arm waveguides being close to one another in a portion where the wave plate is provided.
    Type: Application
    Filed: December 23, 2011
    Publication date: June 28, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Hiroshi KAWASHIMA, Kazutaka NARA
  • Publication number: 20120154901
    Abstract: A PLC-type delay demodulation circuit includes a planar lightwave circuit that is provided on one PLC chip and demodulates a DQPSK signal. The planar lightwave circuit includes a Y-branch waveguide that branches a DQPSK-modulated optical signal into two optical signals and first and second MZIs that delay the branched optical signals by one bit. The length of a short arm waveguide of the first MZI is different from the length of a short arm waveguide of the second MZI, and the length of an optical path from the Y-branch waveguide to output ports of the first MZI through the short arm waveguide of the first MZI is equal to that of an optical path from the Y-branch waveguide to output ports of the second MZI through the short arm waveguide of the second MZI.
    Type: Application
    Filed: December 21, 2011
    Publication date: June 21, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Hiroshi KAWASHIMA, Kazutaka Nara
  • Publication number: 20120014636
    Abstract: A waveguide-type optical circuit comprises an optical coupler being an optical branch coupler constructed from waveguide cores which are closely arranged each other, and dummy patterns that lay along sides of the waveguide cores in the optical coupler for preventing optical major axes of the waveguide cores from inclining.
    Type: Application
    Filed: July 14, 2010
    Publication date: January 19, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Noritaka Matsubara, Kazutaka Nara
  • Publication number: 20120002918
    Abstract: The present invention provides a wavelength multiplexer/demultiplexer comprising a Mach-Zehnder interferometer and an arrayed waveguide diffraction grating, the wavelength multiplexer/demultiplexer having a simple configuration and being capable of reducing the degradation in the temperature compensation characteristics of a temperature compensation material provided in the Mach-Zehnder interferometer or the peeling-off of the temperature compensation material, and a method of manufacturing the same. A wavelength multiplexer/demultiplexer comprises an AWG including two separated slab waveguides and an MZI including two arm waveguides.
    Type: Application
    Filed: June 23, 2011
    Publication date: January 5, 2012
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Hiroshi KAWASHIMA, Kazutaka NARA, Junichi HASEGAWA
  • Publication number: 20110305253
    Abstract: A semiconductor laser module includes a semiconductor laser section, a light selecting section, and an optical converting section. The semiconductor laser section includes a semiconductor laser substrate, a plurality of semiconductor laser elements mounted on the semiconductor laser substrate, and a first temperature adjusting element for adjusting temperature of the semiconductor laser elements. The light selecting section includes a light selecting element substrate and a light selecting element mounted on the light selecting element substrate and optically connected to the semiconductor laser elements, which selects laser light output from at least one of the semiconductor laser elements.
    Type: Application
    Filed: June 8, 2011
    Publication date: December 15, 2011
    Applicant: FURUKAWA ELECTRIC CO., LTD.
    Inventors: Go KOBAYASHI, Tatsuya KIMOTO, Toshio KIMURA, Takeshi AKUTSU, Kazutaka NARA
  • Patent number: 8068736
    Abstract: The tunable dispersion compensator 10 of the present invention comprises: the Mach-Zehnder interferometers (MZIs) 21 to 25 cascaded on a planar lightwave circuit; and the tunable couplers 31 to 34 connected to between each corresponding pair of the MZIs respectively. The Y-branch waveguide 15 and 16 are used for connecting to between the MZIs 21, 25 as both end sides and the input/output optical waveguides 13, 14 respectively. The waveguide loop mirror 40 is connected to the final stage MZI 25 among the MZIs 21 to 25 which an incident light is propagated last therethrough. The half-wave plate 50 is inserted to the loop waveguide 41 of the waveguide loop mirror 40. And it becomes able to enhance (double) the amount of tunable dispersion because an input light signal is passed twice through the similar path by the waveguide loop mirror 40.
    Type: Grant
    Filed: March 5, 2008
    Date of Patent: November 29, 2011
    Assignee: The Furukawa Electric Co., Ltd.
    Inventors: Hiroshi Kawashima, Kazutaka Nara
  • Patent number: 8036505
    Abstract: An athermal AWG module 10 comprises: an AWG 11 having waveguides partially divided to separate a chip, separated chips being connected by a compensation plate 33 to achieve temperature-independence; an athermal AWG chip 12 having a substrate and the AWG 11 formed on the substrate; a package 13 having an opening 14 and accommodating the athermal AWG chip 12; and a cover for blocking the opening 14. The athermal AWG chip 12 is fully covered with a gelled refractive index matching agent 16 that is matched in refractive index to the waveguides of the AWG 11. As the gelled refractive index matching agent 16 is excellent in water resistance and hardly passes water, the adhesive agent for fixing the compensation plate 33 to the surfaces of the separated two chips is prevented from being deteriorated due to ingress of water, thereby enhancing the reliability.
    Type: Grant
    Filed: December 23, 2009
    Date of Patent: October 11, 2011
    Assignee: Furukawa Electric Co., Ltd.
    Inventors: Junichi Hasegawa, Kazutaka Nara
  • Patent number: 8023781
    Abstract: Two Mach-Zehnder optical interferometer circuits are accurately point-symmetrically connected to each other to form a first point-symmetrically connected optical interferometer circuit constituting a light input side circuit. Optical signals having a plurality of wavelengths are input to a light input terminal. A second point-symmetrically connected optical interferometer circuit having the same functional structure as the first point-symmetrically connected optical interferometer circuit is connected to a through port, which is an output terminal of the light input side circuit, as a first light output side circuit. A cross port, which is the other output terminal of the light input side circuit, is connected to a second light output side circuit having at least one of Mach-Zehnder optical interferometer circuits whose transmittance characteristics are different from those of the Mach-Zehnder optical interferometer circuits.
    Type: Grant
    Filed: January 3, 2011
    Date of Patent: September 20, 2011
    Assignee: The Furukawa Electric Co., Ltd.
    Inventors: Kazutaka Nara, Haruki Urabe, Tsunetoshi Saitoh, Masahito Morimoto
  • Patent number: 7978401
    Abstract: The delay demodulation device 1 comprises: an input waveguide 2 which receives DQPSK signals; a Y-branch waveguide 3 which splits the input waveguide 2; a first Mach-Zehnder interferometer 4; and a second Mach-Zehnder interferometer 5. Both end of two arm-waveguides 8, 9 of the first Mach-Zehnder interferometer 4 and both ends of two arm-waveguides 12, 13 of the second Mach-Zehnder interferometer 5 are angled toward the center portion of a planar lightwave circuit (PLC) 1A. Because of the angle, the length of the two arm-waveguides 8, 9 of the first Mach-Zehnder interferometer 4 and the length of the two arm-waveguides 12, 13 of the second Mach-Zehnder interferometer 5 in Z-direction can be shortened, and input couplers 6,10 and output couplers 7,11 of each Mach-Zehnder interferometers in Z-direction can be shortened as well. The area occupied by each Mach-Zehnder interferometers 4, 5 are also reduced.
    Type: Grant
    Filed: March 31, 2009
    Date of Patent: July 12, 2011
    Assignee: The Furukawa Electric Co., Ltd.
    Inventors: Junichi Hasegawa, Kazutaka Nara
  • Patent number: 7961991
    Abstract: The delay demodulation device 1 comprises an input waveguide 2 which receives DQPSK signals; a Y-branch waveguide 3 which splits the light waveguide 2; a first Mach-Zehnder interferometer (MZI) 4; and a second Mach-Zehnder interferometer 5. Both ends of the arm-waveguides 8, 9 of the MZI 4 and the both ends of the arm-waveguides 12, 13 of the MZI 5 are bent toward the center portion of the planar lightwave circuit (PLC) 1A. Thereby, the length of the arm-waveguides 8, 9 of the MZI 4 and the length of the arm-waveguides of the MZI 5 are shortened in the Z-direction. And, the length of the input couplers 6, 10 and the output couplers 7, 11 of the MZIs 4, 5 are shortened in the Z-direction. Therefore, the area covered by the MZIs 4, 5 can be made smaller.
    Type: Grant
    Filed: March 27, 2009
    Date of Patent: June 14, 2011
    Assignee: The Furukawa Electric Co., Ltd.
    Inventors: Junichi Hasegawa, Kazutaka Nara