# US 5,706,116 A · Drive circuit optical modulator and optical transmitter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,706,116 A - Document ID: US5706116A - Status: Granted - Kind: A - Application number: 08/710,556 - Filed: 1996-09-19 - Granted: 1998-01-06 - Earliest claimed: 1995-12-26 - Assignees: Fujitsu Limited - Inventors: Akihiko Sugata - Web page: https://patentgrep.com/patent/US5706116A ## CPC - H04B 10/50593: {to control the modulating signal amplitude including amplitude distortion} - G02F 1/0121: {Operation of devices; Circuit arrangements, not otherwise provided for in this subclass} - H04B 10/50575: {to control the modulator DC bias} - H04B 10/564: Power control - H04B 10/588: in external modulation systems - H04B: TRANSMISSION - 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 ## Abstract A drive circuit for an optical modulator having first and second electrodes for receiving a drive voltage. The optical modulator modulates carrier light from a light source according to the drive voltage to output modulated signal light. A terminating resistor for generating the drive voltage is connected between the first and second electrodes. A first end of a transmission line is connected to one of the first and second electrodes. A circuit for generating a drive signal is connected to a second end of the transmission line. A reflection rejecter (e.g., attenuator) for suppressing a reflected wave generating in the transmission line is provided on the transmission line. This drive circuit improves the waveform of the modulated signal light in case that the carrier light has large power. ## Claims ### Claim 1 A drive circuit for an optical modulator having first and second electrodes for receiving a drive voltage, said optical modulator receiving carrier light from a light source and modulating said carrier light according to said drive voltage to output modulated signal light, said drive circuit comprising: a terminating resistor connected between said first and second electrodes, for generating said drive voltage; a transmission line having a first end and a second end, said first end being connected to one of said first and second electrodes; a drive signal circuit connected to said second end of said transmission line, for generating a drive signal corresponding to said drive voltage according to a data signal received; and a reflection rejecter provided on said transmission line, for suppressing a reflected wave generating in said transmission line. ### Claim 2 (depends on 1) A drive circuit for an optical modulator according to claim 1, wherein said reflection rejecter comprises an attenuator. ### Claim 3 (depends on 1) A drive circuit for an optical modulator according to claim 1, wherein said reflection rejecter comprises an isolator. ### Claim 4 (depends on 1) A drive circuit for an optical modulator according to claim 1, wherein said reflection rejecter comprises a buffer circuit having a transistor. ### Claim 5 (depends on 1) A drive circuit for an optical modulator according to claim 1, wherein said reflection rejecter comprises an attenuator having a variable attenuation factor, said drive circuit further comprising: a first means for monitoring power of said carrier light; a second means for changing an amplitude of said drive signal; and a third means for controlling said attenuation factor and said ampltude according to said power monitored by said first means. ### Claim 6 (depends on 5) A drive circuit for an optical modulator according to claim 5, wherein said third means increases said attenuation factor and said amplitude with an increase in said monitored power. ### Claim 7 (depends on 5) A drive circuit for an optical modulator according to claim 5, wherein said first means comprises means for branching said carrier light into first branch light and second branch light, and a photodetector for receiving said first branch light and outputting a signal corresponding to power of said first branch light; said second branch light being supplied to said optical modulator. ### Claim 8 (depends on 5) A drive circuit for an optical modulator according to claim 5, wherein said light source comprises a laser diode supplied with a bias current, and said first means comprises a means for detecting said bias current. ### Claim 9 (depends on 1) A drive circuit for an optical modulator according to claim 1, wherein said optical modulator comprises an electro-absorption type of optical modulator for outputting intensity-modulated signal light by absorbing said carrier light according to said drive voltage. ### Claim 10 An optical transmitter comprising: a light source supplied with a bias current and outputting carrier light having power corresponding to said bias current; an optical modulator having first and second electrodes for receiving a drive voltage, said optical modulator receiving said carrier light and modulating said carrier light according to said drive voltage to output modulated signal light; a terminating resistor connected between said first and second electrodes, for generating said drive voltage; a transmission line having a first end and a second end, said first end being connected to one of said first and second electrodes; a drive signal circuit connected to said second end of said transmission line, for generating a drive signal corresponding to said drive voltage according to a data signal received; and a reflection rejecter provided on said transmission line, for suppressing a reflected wave generating in said transmission line. ### Claim 11 (depends on 10) An optical transmitter according to claim 10, wherein: said light source comprises a laser diode having an active layer for generating said carrier light; and said optical modulator comprises an electro-absorption type of optical modulator having an absorbing layer for absorbing said carrier light according to said drive voltage; said absorbing layer being monolithically connected to said active layer. ### Claim 12 (depends on 11) An optical transmitter according to claim 11, wherein: said reflection rejecter comprises an attenuator having a variable attenuation factor, said optical transmitter further comprising: a means for detecting said bias current to thereby monitor the power of said carrier light; and a means for controlling said attenuation factor and an amplitude of said drive signal so that said attenuation factor and said amplitude increase with an increase in the power of said carrier light monitored.