Nippon Telegraph and Telephone Corporation

Kotaro Takeda

Yusuke Nasu

Kiyofumi Kikuchi

Hiroshi Fukuda

Ken Tsuzuki

Shin Kamei

Yuichiro Ikuma

Yoshiho Maeda

Yuriko Kawamura

Makoto Jizodo

Tatsuro Hiraki

Kentaro Honda

Toshihiro Ito

A photodetector having a sufficient ESD withstand voltage is provided. An embodiment of a photodetector includes a plurality of photodiodes including germanium or a germanium compound in a light absorption layer, and a plurality of heaters configured to apply heat to the light absorption layer of each of the plurality of photodiodes, in which the plurality of heaters are connected in series, the plurality of heaters are connected in parallel, or a plurality of sets of the plurality of heaters serially connected are connected in parallel.

Photodetector

An optical circuit of the present disclosure shares at least a part of an electrical path including phase variable means between neighboring optical interference circuits, or configures an electrical path so as to straddle neighboring optical interference circuits, thereby performing electrical or thermal feedback. The optical circuit includes a mechanism using the electrical or thermal feedback for cancelling components of thermal crosstalk from one optical interference circuit to another neighboring optical interference circuit. The optical circuit of the present disclosure has a resistor element that shares electrical paths including respective phase variable means between the neighboring optical interference circuits. The optical circuit changes the phase change amount by the phase variable means in the neighboring optical interference circuit, in such a way as to cancel the thermal crosstalk components by the resistor element.

Optical circuit with common ground configuration for resistors and thermo-optic phase shifters

A problem to be solved is to make plural Ge PDs uniform in sensitivity by heating based on the Ge PDs with heaters photocurrent measurements taken by a current monitor, and thereby curb deterioration in a common-mode rejection ratio. A photodetector according to the present invention is a germanium photodetector (Ge PD) that uses germanium or a germanium compound in a light absorption layer, the photodetector including two or more Ge PDs placed to receive an input differential signal; a current monitor adapted to measure photocurrents of the two or more Ge PDs; resistors adapted to heat the respective Ge PDs; voltage sources connected to the respective resistors and capable of controlling voltage values independently of each other, wherein the voltage sources are connected with the current monitor, and the voltage sources manipulate voltages applied to the heaters such that current values output by the two or more Ge PDs will match each other.

Photodector including germanium layer and doped region

Provided is a photodetector which can be manufactured in a standard process of a mass-produced CMOS foundry. The photodetector includes a silicon (Si) substrate; a lower clad layer; a core layer including a waveguide layer configured to guide signal light, and including a first Si slab doped with first conductive impurity ions and a second Si slab doped with second conductive impurity ions; a germanium (Ge) layer configured to absorb light and including a Ge region doped with the first conductive impurity ions; an upper clad layer; and electrodes respectively connected to the first and second Si slabs and the Ge region. A region of the core layer sandwiched between the first Si slab and the second Si slab operates as an amplification layer.

A photodetector is realized which does not need an additional circuit for an inspection and may perform a characteristic evaluation inspection of optical input and electrical output such as optical sensitivity and OE characteristics of a photodetector alone with respect to wavelength and temperature dependent characteristics. A photodetector is provided in which light absorption layers are formed on a semiconductor substrate, the photodetector detects signal light incident on the light absorption layers from a direction in a substrate surface of the semiconductor substrate, and the light absorption layers have a portion not covered by an electrode for photocurrent detection connected with the light absorption layers in a case where the substrate surface of the semiconductor substrate is seen from a direction from an outside of the substrate surface.

A problem to be solved is to prevent deterioration of a signal-to-noise ratio. A photodetector according to the present invention is a germanium photodetector (Ge PD) that uses germanium or a germanium compound in a light absorption layer, the photodetector including a resistor connected in series with a cathode or an anode of the Ge PD; and a capacitor connected at one end to a connection point between the resistor and a cathode or anode of the Ge PD and grounded at another end, another connection point of the resistor being connected to a bias power supply, wherein to withstand maximum operating optical input power, the value of the resistor is determined such that electric power applied to the Ge PD will be lower than a breakdown threshold.

In a photodetector using GePDs, a photodetector having small change in light sensitivity due to temperature is provided. A photodetector includes a plurality of photodiodes formed on a silicon substrate and having germanium or a germanium compound in a light absorption layer, and two chips of integrated circuits arranged parallel to two sides connected to one corner of the silicon substrate, respectively, the two integrated circuits are connected to photodiodes formed on the silicon substrate, two or more of the photodiodes are arranged equidistantly from the integrated circuit that is parallel to one side connected to the one corner, and the numbers of equidistantly arranged photodiodes are equal, when viewed from the integrated circuits.

The present invention is to provide a GePD, the optical sensitivity of which is independent from a temperature, and to achieve a photodetector in which heat applied from heaters is constant even when a plurality of GePDs are provided and in which a temperature and sensitivity of each of the GePDs are the same. The photodetector includes germanium photoreceivers including a silicon substrate, a lower clad layer, a silicon core layer, a silicon waveguide layer, a germanium layer, an upper clad layer, and electrodes. In the photodetector, two or more germanium photoreceivers are arranged adjacent to each other on the silicon substrate, and the photodetector includes resistors embedded in the upper clad layer to cover or surround respective germanium layers of the two or more germanium photoreceivers arranged adjacent to each other, the resistors being made of a metal or a metal compound.

A GePD having uniform sensitivity in C and L bands is provided and a photodetector in which deterioration of a common-mode rejection ratio is curbed is provided. A photodetector according to an embodiment includes one or a plurality of sets of two photodiodes to which a differential signal is input, a monitor connected to each of the two photodiodes and configured to measure a photocurrent, and a voltage supply configured to control a voltage applied to each of the two photodiodes, and the voltage supply controls the voltage applied to each of the two photodiodes so that the photocurrent measured by the monitor connected to one of the two photodiodes is equal to the photocurrent measured by the monitor connected to another one of the two photodiodes.

To provide a photodetector that is capable of preventing breakdown caused by electrostatic discharge and with which the breakdown voltage can be expected to enhanced by at least 100 V. In the photodetector of the present invention, a Zener diode made of a germanium and a silicon is connected to a germanium photodiode (GePD). In the photodetector, a silicon substrate, a lower cladding layer, a silicon core layer, and an upper cladding layer provided in the photodiode and the Zener diode are shared by the photodiode and the Zener diode.

There is provided an optical communication device capable of minimum suppressing inter-signal interference of inductors mounted to enable a transmission signal to be transmitted and received with a high frequency. The optical communication device comprises a sub-package as a subassembly in each of a plurality of signal channels. The sub-package includes a substrate on which an optical semiconductor and an IC are flip-chip connected. The optical semiconductor includes a pair of photodiodes receiving a differential optical signal and outputting a differential current signal. The IC includes a transimpedance amplifier converting the differential current signal from the optical semiconductor to a voltage signal. The optical semiconductor has a pair of inductors formed for each of the pair of photodiodes and a ground wiring formed so as to surround the formed pair of inductors.

Optical communication apparatus

The visual detection of a silicon optical circuit in a conventional technique depends on sensory decision by a human who visually conducts checking, and there has been limitation in completely detecting small flaws. The optical circuit of the present invention includes, in addition to an optical circuit that implements desired functions, an optical waveguide for flaw detection which surrounds the entire optical circuit and which is sufficiently proximate to the optical waveguide of the optical circuit and grating couplers connected to the optical waveguide for detection. Based on the transmission characteristic measurement of the optical waveguide for detection using the grating couplers, a flaw within each chip can be efficiently discovered in the state of a wafer before being cut into chips. A flaw can also be discovered hierarchically by providing individual optical waveguides for detection for respective chips and by further forming one common optical waveguide for detection over the plurality of chips.

Growing community of inventors

Musashino, Japan

Kotaro Takeda