# US 8,772,725 B2 · Photo detector and optical device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,772,725 B2 - Document ID: US8772725B2 - Status: Granted - Kind: B2 - Application number: 13/840,956 - Filed: 2013-03-15 - Published: 2013-11-14 - Granted: 2014-07-08 - Earliest claimed: 2012-05-14 - Assignees: Electronics and Telecommunications Research Institute - Applicants: Electronics and Telecommunications Research Institute - Inventors: Jeong Woo Park; Kyung Hyun Park; Han-Cheol Ryu; Dong-Hun Lee; Sang-Pil Han; Hyunsung Ko; Namje Kim - Web page: https://patentgrep.com/patent/US8772725B2 ## CPC - H10F 77/00: Constructional details of devices covered by this subclass (constructional details of integrated devices, or assemblies of multiple devices, comprising at least one element in which radiation controls the flow of current H10F39/00) - G02F 1/3534: {Three-wave interaction, e.g. sum-difference frequency generation (G02F1/3532 takes precedence)} - H01S 5/4087: {emitting more than one wavelength} - H10F 30/223: the potential barrier being a PIN barrier - H10F 77/40: Optical elements or arrangements (surface textures H10F77/70) - H10F 77/413: {directly associated or integrated with the devices, e.g. back reflectors (directly associated or integrated with photovoltaic cells H10F77/42)} - G02F 2203/13: involving THZ radiation - H01S 5/005: {Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping (H01S5/026, H01S5/18388 take precedence)} - H01S 5/0092: {for nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity} - H01S 5/4012: {Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms} - H03B 2200/0084: dedicated to Terahertz frequencies - H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL - H03B: GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS (generators adapted for electrophonic musical instruments G10H; masers or lasers H01S; generation of oscillations in plasma H05H) ## Abstract An optical device may include first and second lasers generating first and second laser beams; and a photo detector detecting the first and second laser beams. The optical detector comprises a substrate, a first impurity layer on the substrate, an absorption layer on the first impurity layer and a second impurity layer on the absorption layer. The absorption layer generates a terahertz by a beating of the first and second laser beams and has a thickness of less than 0.2 μm. ## Claims ### Claim 1 An optical device comprising: a laser generating first and second laser beams; and a photo detector detecting the first and second laser beams, wherein the optical detector comprises a substrate, a first impurity layer on the substrate, an absorption layer on the first impurity layer and a second impurity layer on the absorption layer, and wherein the absorption layer generates a terahertz by a beating of the first and second laser beams and has a thickness of less than 0.2 μm. ### Claim 2 (depends on 1) The optical device of claim 1, wherein the absorption layer has a thickness of 0.005 μm or more. ### Claim 3 (depends on 2) The optical device of claim 2, wherein the first impurity layer, the absorption layer and the second impurity layer are a ridge waveguide extending in a specific direction. ### Claim 4 (depends on 3) The optical device of claim 3, wherein the photo detector further comprises a first electrode formed on the first impurity layer of both sides of the absorption layer and a second electrode formed on the second impurity. ### Claim 5 (depends on 3) The optical device of claim 3, further comprising an optical waveguide between the laser and the photo detector. ### Claim 6 (depends on 5) The optical device of claim 5, wherein the optical waveguide comprises a lensed optical fiber. ### Claim 7 (depends on 6) The optical device of claim 6, wherein the ridge waveguide has a beam width of more than 0.5 times that of the lensed optical fiber and absorbs the first and second laser beams. ### Claim 8 (depends on 1) The optical device of claim 1, wherein the absorption layer comprises intrinsic indium gallium arsenic. ### Claim 9 (depends on 1) The optical device of claim 1, wherein the laser comprises a first laser and a second laser generating the first and second beams etch other. ### Claim 10 (depends on 1) The optical device of claim 1, wherein the optical waveguide comprises a joint waveguide connected to the photo detector, a first branch waveguide connected between the joint waveguide and the first laser and a second branch waveguide connected between the joint waveguide and the second laser. ### Claim 11 (depends on 1) The optical device of claim 1, further comprising an output circuit receiving a terahertz wave being output by a beating of the first and second laser beams from the optical detector. ### Claim 12 (depends on 11) The optical device of claim 11, wherein the photo detector is a travelling-wave type photo detector matching impedance of the output circuit to characteristic impedance of photo detector. ### Claim 13 (depends on 12) The optical device of claim 12, wherein the photo detector is a travelling-wave type photo detector with an input resistor of which impedance match to a characteristic impedance of the travelling-wave type photo detector. ### Claim 14 (depends on 1) The optical device of claim 1, wherein the photo detector is a travelling-wave type photo detector with an input resistor of which impedance match to a characteristic impedance of a travelling-wave type photo detector. ### Claim 15 A photo detector comprising: a substrate; a first impurity layer on the substrate; an absorption layer on the first impurity layer; and a second impurity layer on the absorption layer, wherein the absorption layer has a thickness of less than 0.2 μm. ### Claim 16 (depends on 15) The photo detector of claim 15, wherein the absorption layer has a thickness of 0.005 μm or more.