Patents by Inventor Junichi Fujikata

Junichi Fujikata 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: 11054675
    Abstract: Provided is an optical modulator which is small in optical loss, is small in a size, and is low in required voltage and is operable to perform high-speed operation. The optical phase modulator 100 comprises a rib-type waveguide structure 110 including: a PN junction 106 which is formed of Si and is formed in a lateral direction on a substrate; and an Si1-xGex layer 108 which is constituted of at least one layer and is doped with an impurity to a p-type and is superposed on the PN junction 106 so as to be electrically connected to the PN junction 106. The rib-type waveguide structure 110 has a substantially uniform structure along a light propagation direction, and in a direction parallel with the substrate and perpendicular to the light propagation direction, a position of a junction interface 106a of the PN junction 106 is offset from a center of the Si1-xGex layer 108.
    Type: Grant
    Filed: August 24, 2018
    Date of Patent: July 6, 2021
    Assignees: PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION, THE UNIVERSITY OF TOKYO
    Inventors: Junichi Fujikata, Shigeki Takahashi, Mitsuru Takenaka
  • Patent number: 11009726
    Abstract: An electro-absorption optical modulator capable of realizing optical coupling with a Si waveguide with high efficiency, improving modulation efficiency, reducing light absorption by an electrode layer and achieving low optical loss includes a substrate; a first silicon layer doped to exhibit a first type of conductivity and a second silicon layer doped to exhibit a second type of conductivity that are disposed parallel to the substrate; and a Ge1?xSix (0<x<1)/Si stack in which a Ge1?xSix layer and a Si layer are stacked on the first and second silicon layers in this order.
    Type: Grant
    Filed: March 15, 2019
    Date of Patent: May 18, 2021
    Assignees: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATE
    Inventor: Junichi Fujikata
  • Patent number: 10996539
    Abstract: Provided is a SIS-type electro-optic modulator capable of realizing highly efficient optical coupling with a rib-type Si waveguide, improving modulation efficiency, realizing reduction of electric capacity and lead-out resistance in stacked semiconductor layers. The modulator includes a SIS junction constituted by first and second semiconductor layers having different type of conductivity and a dielectric layer interposed therebetween, wherein an electrical signal from electrodes coupled to the first and second semiconductor layers causes free carriers accumulate, deplete or invert on both sides of the dielectric layer, thereby modulating a free carrier concentration felt by an optical signal electric filed, light having a polarization component orthogonal to the width direction of the SIS junction is incident on the dielectric layer, and the width of the SIS junction is ?/neff or less (? is the wavelength of the incident light and neff is an effective refractive index of the modulator to the incident light).
    Type: Grant
    Filed: June 13, 2019
    Date of Patent: May 4, 2021
    Assignees: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Shigeki Takahashi, Junichi Fujikata
  • Publication number: 20200313021
    Abstract: A photodetector which can perform high-speed operation and make the manufacturing process thereof easy is provided. A photodetector 400 comprises an Si layer including a lateral pin junction structure, and a light absorbing layer stacked on the lateral pin junction structure. At least part of an upper part of the light absorbing layer is doped to exhibit a first conductivity type. At least part of a side wall of the light absorbing layer is doped to exhibit the first conductivity type, for making the at least part of the upper part of the light absorbing layer to be electrically connected to a region of the first conductivity type in the lateral pin junction structure.
    Type: Application
    Filed: March 12, 2020
    Publication date: October 1, 2020
    Inventor: Junichi Fujikata
  • Publication number: 20200301177
    Abstract: Provided is an optical modulator which is small in optical loss, is small in a size, and is low in required voltage and is operable to perform high-speed operation. The optical phase modulator 100 comprises a rib-type waveguide structure 110 including: a PN junction 106 which is formed of Si and is formed in a lateral direction on a substrate; and an Si1-xGex layer 108 which is constituted of at least one layer and is doped with an impurity to a p-type and is superposed on the PN junction 106 so as to be electrically connected to the PN junction 106. The rib-type waveguide structure 110 has a substantially uniform structure along a light propagation direction, and in a direction parallel with the substrate and perpendicular to the light propagation direction, a position of a junction interface 106a of the PN junction 106 is offset from a center of the Si1-xGex layer 108.
    Type: Application
    Filed: August 24, 2018
    Publication date: September 24, 2020
    Inventors: Junichi Fujikata, Shigeki Takahashi, Mitsuru Takenaka
  • Publication number: 20190384135
    Abstract: Provided is a SIS-type electro-optic modulator capable of realizing highly efficient optical coupling with a rib-type Si waveguide, improving modulation efficiency, realizing reduction of electric capacity and lead-out resistance in stacked semiconductor layers. The modulator includes a SIS junction constituted by first and second semiconductor layers having different type of conductivity and a dielectric layer interposed therebetween, wherein an electrical signal from electrodes coupled to the first and second semiconductor layers causes free carriers accumulate, deplete or invert on both sides of the dielectric layer, thereby modulating a free carrier concentration felt by an optical signal electric filed, light having a polarization component orthogonal to the width direction of the SIS junction is incident on the dielectric layer, and the width of the SIS junction is ?/neff or less (? is the wavelength of the incident light and neff is an effective refractive index of the modulator to the incident light).
    Type: Application
    Filed: June 13, 2019
    Publication date: December 19, 2019
    Applicants: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Shigeki TAKAHASHI, Junichi FUJIKATA
  • Publication number: 20190285916
    Abstract: An electro-absorption optical modulator capable of realizing optical coupling with a Si waveguide with high efficiency, improving modulation efficiency, reducing light absorption by an electrode layer and achieving low optical loss includes a substrate; a first silicon layer doped to exhibit a first type of conductivity and a second silicon layer doped to exhibit a second type of conductivity that are disposed parallel to the substrate; and a Ge1?xSix (0<x<1)/Si stack in which a Ge1?xSix layer and a Si layer are stacked on the first and second silicon layers in this order.
    Type: Application
    Filed: March 15, 2019
    Publication date: September 19, 2019
    Applicants: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventor: Junichi FUJIKATA
  • Patent number: 10340399
    Abstract: Provided is an optical device in which an Si cap layer is provided on a Ge layer, and which is capable of effectively reducing dark current, while having a good effect on prevention of production line contamination by Ge. One embodiment of the optical device according to the present invention is provided with: a semiconductor layer which contains Ge and has a (001) surface and a facet surface between the (001) surface and a (110) surface; and a cap layer which is formed from Si, and which is formed on the (001) surface and the facet surface of the semiconductor layer. The ratio of the film thickness of the cap layer on the facet surface to the film thickness of the cap layer on the (001) surface is 0.4 or more; and the film thickness of the cap layer on the (001) surface is from 9 nm to 30 nm (inclusive).
    Type: Grant
    Filed: July 28, 2016
    Date of Patent: July 2, 2019
    Assignee: PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Shigekazu Okumura, Tohru Mogami, Keizo Kinoshita, Tsuyoshi Horikawa, Junichi Fujikata
  • Patent number: 10274757
    Abstract: An electro-optic device includes a first semiconductor layer including the rib-type waveguide, which includes a rib part and a first slab part, which extends in a first direction from the rib part; a dielectric layer, which is formed on the rib part; a second semiconductor layer, which extends in a second direction, which is opposite to the first direction, from an upper surface of the dielectric layer; a first high-concentration impurity region, which is formed in the first semiconductor layer to be in contact with the first slab part on the first direction side; and a second high-concentration impurity region, which is formed in a region of the second semiconductor layer on the second direction side. The second high-concentration impurity region is formed in a region other than a region overlapping the first semiconductor layer in a lamination direction.
    Type: Grant
    Filed: February 17, 2016
    Date of Patent: April 30, 2019
    Assignees: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Junichi Fujikata, Shigeki Takahashi
  • Publication number: 20190006532
    Abstract: Provided is an optical device in which an Si cap layer is provided on a Ge layer, and which is capable of effectively reducing dark current, while having a good effect on prevention of production line contamination by Ge. One embodiment of the optical device according to the present invention is provided with: a semiconductor layer which contains Ge and has a (001) surface and a facet surface between the (001) surface and a (110) surface; and a cap layer which is formed from Si, and which is formed on the (001) surface and the facet surface of the semiconductor layer. The ratio of the film thickness of the cap layer on the facet surface to the film thickness of the cap layer on the (001) surface is 0.4 or more; and the film thickness of the cap layer on the (001) surface is from 9 nm to 30 nm (inclusive).
    Type: Application
    Filed: July 28, 2016
    Publication date: January 3, 2019
    Applicant: PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Shigekazu Okumura, Tohru Mogami, Keizo Kinoshita, Tsuyoshi Horikawa, Junichi Fujikata
  • Publication number: 20180373067
    Abstract: An electroabsorption optical modulator capable of realizing optical coupling with a Si waveguide with high efficiency, improving modulation efficiency, reducing light absorption by an electrode layer and achieving low optical loss includes first Si layer 34 of a first conductive type and second Si layer 35 of a second conductive type disposed parallel to substrate 31 and GeSi layer 51 stacked on the first and second Si layers.
    Type: Application
    Filed: June 25, 2018
    Publication date: December 27, 2018
    Applicants: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventor: Junichi FUJIKATA
  • Patent number: 10146070
    Abstract: An optical phase modulator 100 according to an embodiment of this disclosure comprises a rib-type waveguide structure 110 comprising: a PN junction 106 comprising Si and formed in a lateral direction on a substrate; and a Si1-xGex layer 108 that is doped with a p-type impurity and comprises at least one layer laminated on the PN junction 106, so as to be electrically connected to the PN junction 106.
    Type: Grant
    Filed: February 2, 2016
    Date of Patent: December 4, 2018
    Assignee: PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Junichi Fujikata, Shigeki Takahashi, Mitsuru Takenaka, Younghyun Kim
  • Publication number: 20180284559
    Abstract: Provided is a silicon-based electro-optic modulator that exhibits an improved carrier plasma effect which is capable of realizing a low current density, low power consumption, a high modulation rate, low-voltage driving and high-speed modulation in a sub-micron region. The electro-optic modulator includes a waveguide structure including an Si or SiGe crystal. The electric field direction of light that propagates inside the waveguide structure is set to be approximately parallel with the <110> direction of the Si or SiGe crystal.
    Type: Application
    Filed: March 29, 2018
    Publication date: October 4, 2018
    Applicants: NEC CORPORATION, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIAT ION
    Inventors: Junichi FUJIKATA, Tohru MOGAMI, Takahiro NAKAMURA, Tsuyoshi HORIKAWA
  • Patent number: 10025159
    Abstract: An output monitoring method for an optical modulator includes: branching light into first and second lights; modulating a phase of the first light within a first waveguide; modulating a phase of the second light within a second waveguide; multiplexing the first and second lights to generate interference light, and outputting the interference light from first and second output ports; detecting a difference or ratio between a portion of the interference light from the first output port and a portion of the interference light from the second output port; and setting an operating point of light based on the detected difference or ratio; and controlling phase modulation of follow-on light that propagates through the first and second waveguides so as to keep the operating point constant.
    Type: Grant
    Filed: March 23, 2015
    Date of Patent: July 17, 2018
    Assignee: NEC CORPORATION
    Inventor: Junichi Fujikata
  • Publication number: 20180074349
    Abstract: An electro-optic device includes a first semiconductor layer including the rib-type waveguide, which includes a rib part and a first slab part, which extends in a first direction from the rib part; a dielectric layer, which is formed on the rib part; a second semiconductor layer, which extends in a second direction, which is opposite to the first direction, from an upper surface of the dielectric layer; a first high-concentration impurity region, which is formed in the first semiconductor layer to be in contact with the first slab part on the first direction side; and a second high-concentration impurity region, which is formed in a region of the second semiconductor layer on the second direction side. The second high-concentration impurity region is formed in a region other than a region overlapping the first semiconductor layer in a lamination direction.
    Type: Application
    Filed: February 17, 2016
    Publication date: March 15, 2018
    Applicants: NEC Corporation, Photonics Electronics Technology Research Association
    Inventors: Junichi FUJIKATA, Shigeki TAKAHASHI
  • Patent number: 9897752
    Abstract: An optical end coupling type silicon optical integrated circuit is provided using an SOI substrate. This optical integrated circuit is constituted so as to connect with an external optical circuit at an end coupling part and have signal light incident to an optical circuit that includes a curved part. In the plane of the optical integrated circuit, the position of one end coupling part selected from among any thereof and the position of any multimode optical waveguide element to which a respective optical waveguide is connected via a respective curved part satisfy a positional relationship defined on the basis of a beam divergence angle [theta] of stray light.
    Type: Grant
    Filed: March 20, 2014
    Date of Patent: February 20, 2018
    Assignee: PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Shigeki Takahashi, Junichi Fujikata
  • Publication number: 20180024410
    Abstract: An optical phase modulator 100 according to an embodiment of this disclosure comprises a rib-type waveguide structure 110 comprising: a PN junction 106 comprising Si and formed in a lateral direction on a substrate; and a Si1-xGex layer 108 that is doped with a p-type impurity and comprises at least one layer laminated on the PN junction 106, so as to be electrically connected to the PN junction 106.
    Type: Application
    Filed: February 2, 2016
    Publication date: January 25, 2018
    Inventors: Junichi FUJIKATA, Shigeki TAKAHASHI, Mitsuru TAKENAKA, Younghyun KIM
  • Patent number: 9829726
    Abstract: An electro-optical modulator includes a substrate 201; an optical waveguide formed of a silicon-containing i-type amorphous semiconductor 204 on the substrate; and a silicon-containing p-type semiconductor layer 203 and a silicon-containing n-type semiconductor layer 205 arranged apart from each other with the silicon-containing optical waveguide formed of an i-type amorphous semiconductor 204 interposed therebetween and constituting optical waveguides together with the silicon-containing optical waveguide formed of an i-type amorphous semiconductor. The silicon-containing p-type semiconductor layer 203 and/or silicon-containing n-type semiconductor layer 205 area crystalline semiconductor layer.
    Type: Grant
    Filed: February 20, 2014
    Date of Patent: November 28, 2017
    Assignees: NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY, PHOTONICS ELECTRONICS TECHNOLOGY RESEARCH ASSOCIATION
    Inventors: Toshihiro Kamei, Ryohei Takei, Masahiko Mori, Youichi Sakakibara, Junichi Fujikata
  • Patent number: 9703125
    Abstract: Provided is a silicon-based electro-optic modulator which is small in size and capable of high speed operation. A first silicon semiconductor layer (120) doped to exhibit a first type of conductivity and a second semiconductor layer (160) doped to exhibit a second type of conductivity are at least partly stacked together, and a relatively thin dielectric (150) is formed at the interface between the stacked first and second silicon semiconductor layers (120, 160). The first silicon semiconductor layer (120) has a rib waveguide shape (130) comprising a rib portion (131) and slab portions (132). A first heavily doped region (140) formed by a high concentration doping process is arranged at a location, in the first silicon semiconductor layer (120), neighboring to each of the slab portions (132). The first heavily doped region (140) has almost the same height as that of the rib portion (131) of the rib waveguide (130).
    Type: Grant
    Filed: November 28, 2013
    Date of Patent: July 11, 2017
    Assignee: NEC CORPORATION
    Inventors: Junichi Fujikata, Shigeki Takahashi
  • Patent number: 9621279
    Abstract: An optical receiver circuit has a function of converting a differential optical signal into a differential current signal. The optical receiver circuit has a pair of light-receiving elements including first and second light-receiving elements operable to convert an optical signal into a current signal and a pair of signal lines. An anode of the first light-receiving element and a cathode of the second light-receiving element are connected to a first signal line of the pair of signal lines via first and second AC coupling capacitors, respectively. A cathode of the first light-receiving element and an anode of the second light-receiving element are connected to a second signal line of the pair of signal lines via third and fourth AC coupling capacitors, respectively. Differential signal currents are generated in the first and second signal lines in response to reception of differential optical signals inputted into the first and second light-receiving elements.
    Type: Grant
    Filed: February 4, 2014
    Date of Patent: April 11, 2017
    Assignees: NEC CORPORATION, FUJITSU LIMITED
    Inventors: Daisuke Okamoto, Junichi Fujikata, Tatsuya Usuki