# US 7,612,936 B2 · Optical amplifying apparatus for wavelength division multiplexed signals > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,612,936 B2 - Document ID: US7612936B2 - Status: Granted - Kind: B2 - Application number: 10/639,467 - Filed: 2003-08-13 - Published: 2004-03-25 - Granted: 2009-11-03 - Earliest claimed: 2002-09-10 - Assignees: Fujitsu Limited - Inventors: Kaoru Usui; Yoshio Shimano; Hiroshi Iizuka; Hiroyuki Itou - Web page: https://patentgrep.com/patent/US7612936B2 ## CPC - H04B 10/296: Transient power control, e.g. due to channel add/drop or rapid fluctuations in the input power - H01S 3/06758: {Tandem amplifiers} - H01S 3/1301: {in optical amplifiers} - H01S 3/13013: {by controlling the optical pumping} - H04J 14/02216: {by gain equalization} - H01S 3/10015: {by monitoring or controlling, e.g. attenuating, the input signal} - H01S 2301/04: Gain spectral shaping, flattening - H04B: TRANSMISSION - 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 - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) ## Abstract A photo amplifying apparatus for amplifying wavelength division multiplexed signals includes a specific wavelength measuring unit for measuring a specific wavelength at a measuring point, a total power measuring unit for measuring all wavelengths at the measuring point, and an output control unit for controlling the output of the photo amplifying apparatus based on the light power measured by the specific wavelength measuring unit and the total power measuring unit. Since the photo amplifying apparatus measures both the specific wavelength and all wavelengths, the photo amplifying apparatus can determine change in the number of multiplexed wavelengths and the gain gradient of the photo signals, and can properly control its output level. ## Claims ### Claim 1 An optical amplifying apparatus for amplifying wavelength division multiplexed signals, comprising: an optical amplifying unit amplifying an input light; an input branching unit branching the input light; an optical filter passing a specific wavelength of the branched light; a specific wavelength measuring unit measuring a power of filtered light; a total power measuring unit measuring a total light power of the branched light; and a control unit controlling the optical amplifying unit based on the power of the filtered light and the total light power measured by the specific wavelength measuring unit and the total power measuring unit, respectively, wherein the control unit determines whether a change of the output light is caused by a loss of transmission path or a change in wavelength number by comparing a first change of the power of the filtered light with a second change of the total light power. ### Claim 2 (depends on 1) The optical amplifying apparatus as claimed in claim 1, wherein said specific wavelength measuring unit further comprises a variable-wavelength optical filter. ### Claim 3 (depends on 1) The optical amplifying apparatus as claimed in claim 1, wherein said control unit, when the light power measured by said specific wavelength measuring unit does not change and the total light power measured by said total power measuring unit changes, determines the number of multiplexed wavelengths of said optical signals based on the light power measured by said specific wavelength measuring unit and the total light power measured by said total power measuring unit. ### Claim 4 (depends on 1) The optical amplifying apparatus as claimed in claim 1, wherein said control unit, when change in the light power measured by said specific wavelength measuring unit is equal to change in the total light power measured by said total power measuring unit, controls the input of said amplifying apparatus based on the light power measured by said specific wavelength measuring unit and the total light power measured by said total power measuring unit so as to compensate for the loss of optical transmission path. ### Claim 5 (depends on 1) The optical amplifying apparatus as claimed in claim 1, wherein said measuring point is positioned at an output stage; and said control unit controls the input of said optical amplifying apparatus based on the number of multiplexed wavelengths, the light power measured by said specific wavelength measuring unit, and the total light power measured by said total power measuring unit so as to compensate a gain gradient of input optical signals. ### Claim 6 An optical amplifying apparatus for amplifying wavelength division multiplexed signals, comprising: an optical amplifying unit amplifying an output light; an output branching unit branching the output light; an optical filter passing a specific wavelength of the branched light; a specific wavelength measuring unit measuring a power of filtered light; a total power measuring unit measuring a total light power of the branched light; and a control unit controlling the optical amplifying unit based on the power of the filtered light and the total light power measured by the specific wavelength measuring unit and the total power measuring unit, respectively, wherein the control unit determines whether a change in output light is caused by a loss of transmission path or a change in wavelength number by comparing a first change of the power of the filtered light with a second change of the total light power. ### Claim 7 (depends on 6) The optical amplifying apparatus as claimed in claim 6, wherein said specific wavelength measuring unit further comprises a variable-wavelength optical filter. ### Claim 8 (depends on 6) The optical amplifying apparatus as claimed in claim 6, wherein said control unit, when the light power measured by said specific wavelength measuring unit does not change and the total light power measured by said total power measuring unit changes, determines the number of multiplexed wavelengths of said optical signals based on the light power measured by said specific wavelength measuring unit and the total light power measured by said total power measuring unit. ### Claim 9 (depends on 6) The optical amplifying apparatus as claimed in claim 6, wherein said control unit, when change in the light power measured by said specific wavelength measuring unit is equal to change in the total light power measured by said total power measuring unit, controls the output of said amplifying apparatus based on the light power measured by said specific wavelength measuring unit and the total light power measured by said total power measuring unit so as to compensate for the loss of optical transmission path. ### Claim 10 (depends on 6) The optical amplifying apparatus as claimed in claim 6, wherein said measuring point is positioned at an output stage; and said control unit controls the output of said optical amplifying apparatus based on the number of multiplexed wavelengths, the light power measured by said specific wavelength measuring unit, and the total light power measured by said total power measuring unit so as to compensate a gain gradient of output optical signals. ### Claim 11 An optical amplifying apparatus for amplifying wavelength division multiplexed signals, comprising: a first optical amplifying unit amplifying an input light; a second optical amplifying unit amplifying light outputted by the first optical amplifying unit; a first input branching unit branching the input light; a second output branching unit branching an output light of the second optical amplifying unit; a first optical filter passing a specific wavelength of the branched input light; a second optical filter passing a specific wavelength of the branched output light; a first specific wavelength measuring unit measuring a power of filtered input light; a second specific wavelength measuring unit measuring a power of filtered output light; a first total power measuring unit measuring a total input light power of the branched input light; a second total power measuring unit measuring a total output light power of the branched output light; and a control unit controlling the optical amplifying units based on the power of filtered input light, the power of filtered output light, the total light power of the branched input light, and a total light power of the branched output light measured by the first and second specific wavelength measuring units and the first and second total power measuring units, wherein the control unit determines whether a change of the output light is caused by a loss of transmission path or a change in wavelength number in the first or the second amplifier, by comparing a first change of the power of the filtered input light with a second change of the total input light power, and a third change of the power of the filtered output light with a fourth change of the total output power. ### Claim 12 (depends on 11) The optical amplifying apparatus as claimed in claim 11, wherein said specific wavelength measuring units further comprises variable-wavelength optical filters. ### Claim 13 (depends on 11) The optical amplifying apparatus as claimed in claim 11, wherein said control unit, when the light power measured by said specific wavelength measuring units does not change and the total light power measured by said total power measuring unit changes, determines the number of multiplexed wavelengths of said optical signals based on the light power measured by said specific wavelength measuring units and the total light power measured by said total power measuring unit. ### Claim 14 (depends on 11) The optical amplifying apparatus as claimed in claim 11, wherein said control unit, when change in the light power measured by said specific wavelength measuring unit is equal to change in the total light power measured by said total power measuring unit, controls the input and output of said amplifying apparatuses based on the light power measured by said specific wavelength measuring units and the total light power measured by said total power measuring unit so as to compensate for the toss of optical transmission path. ### Claim 15 (depends on 11) The optical amplifying apparatus as claimed in claim 11, wherein said measuring point is positioned at an output stage; and said control unit controls the output of said optical amplifying apparatus based on the number of multiplexed wavelengths, the light power measured by said specific wavelength measuring units, and the total light power measured by said total power measuring unit so as to compensate a gain gradient of output optical signals and input optical signals. ### Claim 16 An optical amplifying apparatus for amplifying wavelength division multiplexed signals, comprising: a power measuring unit measuring a total light power of branched light which is branched from the wavelength division multiplexed signals, and light power of the branched light corresponding to a predefined wavelength range; and a control unit controlling an optical amplifying unit based on the light power of branched light corresponding to the predefined wavelength range, and the total light power of the branched light, wherein the control unit determines whether a change of output light is caused by a loss of transmission path or a change in wavelength number by comparing a first change of the light power of branched light corresponding to the predefined wavelength range with a second change of the total light power.