High-speed optical transmitter with a silicon substrate and multiple multiplexers

Abstract

A 400 Gb/s transmitter is integrated on a silicon substrate. The transmitter uses four gain chips, sixteen lasers, four modulators to modulate the sixteen lasers at 25 Gb/s, and four multiplexers to produce four optical outputs. Each optical output can transmit at 100 Gb/s to produce a 400 Gb/s transmitter. Other variations are also described.

1 . An optical transmitter comprising:
 a substrate;   a first gain chip integrated on the substrate;   a second gain chip integrated on the substrate;   a first multiplexer integrated on the substrate, wherein the first multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip; and   a second multiplexer integrated on the substrate, wherein the second multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip.   
     
     
         2 . The optical transmitter of  claim 1 , further comprising:
 a third multiplexer integrated on the substrate, wherein the third multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip; and   a fourth multiplexer integrated on the substrate, wherein the fourth multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip.   
     
     
         3 . The optical transmitter of  claim 2 , further comprising a plurality of waveguides integrated on the substrate, configured to guide light to the first multiplexer, the second multiplexer, the third multiplexer, and the fourth multiplexer. 
     
     
         4 . The optical transmitter of  claim 1 , further comprising a plurality of reflectors, wherein the plurality of reflectors are configured to form a plurality of lasers with the first gain chip and the second gain chip. 
     
     
         5 . The optical transmitter of  claim 4 , wherein the plurality of lasers operate on optical channels that are spaced using a 20 nm channel spacing plus or minus 30%. 
     
     
         6 . The optical transmitter of  claim 4 , wherein the plurality of lasers operate on optical channels that are spaced using a channel spacing between 3.5 nm and 13 nm. 
     
     
         7 . The optical transmitter of  claim 1 , wherein the first gain chip has a different bandgap than the second gain chip. 
     
     
         8 . The optical transmitter of  claim 1 , further comprising a modulator chip, wherein:
 the modulator chip is optically between the first gain chip and the first multiplexer; and   the modulator chip is optically between the first gain chip and the second multiplexer.   
     
     
         9 . The optical transmitter of  claim 1 , wherein:
 the first gain chip comprises III-V material;   the second gain chip comprises III-V material;   the substrate is part of a silicon-on-insulator (SOI) wafer;   the SOI wafer comprises a device layer of crystalline silicon;   the first multiplexer is formed in the device layer of the SOI wafer; and   the second multiplexer is formed in the device layer of the SOI wafer.   
     
     
         10 . A method of operating an optical transmitter, the method comprising:
 generating light using a first gain chip integrated on a substrate, wherein generating light comprises applying electrical power to the first gain chip;   generating light using a second gain chip integrated on the substrate, wherein generating light using the second gain chip comprises applying electrical power to the second gain chip;   guiding light generated by the first gain chip to a first multiplexer, wherein the first multiplexer is integrated on the substrate;   guiding light generated by the second gain chip to the first multiplexer;   combining, using the first multiplexer, light generated by the first gain chip and light generated by the second gain chip into a first output;   guiding light generated by the first gain chip to a second multiplexer, wherein the second multiplexer is integrated on the substrate;   guiding light generated by the second gain chip to the second multiplexer; and   combining, using the second multiplexer, light generated by the first gain chip and light generated by the second gain chip into a second output.   
     
     
         11 . The method of  claim 10 , further comprising modulating light generated by the first gain chip before guiding light generated by the first gain chip to the first multiplexer and to the second multiplexer. 
     
     
         12 . The method of  claim 10 , wherein modulating light generated by the first gain chip comprises using a pulse-amplitude modulation (PAM) technique having more than two levels. 
     
     
         13 . The method of  claim 11 , wherein:
 modulating light generated by the first gain chip comprises modulating light generated by the first gain chip to transmit at 25 Gb/s plus or minus 20%.   
     
     
         14 . The method of  claim 10 , wherein the first gain chip and the second gain chip are each configured to generate four laser beams. 
     
     
         15 . The optical transmitter of  claim 1 , wherein:
 the first gain chip and the second gain chip are part of a plurality of gain chips integrated on the substrate;   the optical transmitter comprises a plurality of modulator chips integrated on the substrate;   the plurality of modulator chips are configured to modulate light from the plurality of gain chips; and   there are more modulator chips than gain chips integrated on the substrate.   
     
     
         16 . The optical transmitter of  claim 9 , wherein the device layer has a thickness equal to or greater than 1 micron and equal to or less than 2.5 microns. 
     
     
         17 . An optical transmitter comprising:
 a substrate;   a gain chip integrated on the substrate, wherein the gain chip is configured to generate light;   a modulator chip integrated on the substrate, wherein the modulator chip is configured to module light generated by the gain chip;   a first multiplexer integrated on the substrate, wherein the first multiplexer is configured to receive an optical input from the gain chip; and   a second multiplexer integrated on the substrate, wherein the second multiplexer is configured to receive an optical input from the gain chip.   
     
     
         18 . The optical transmitter of  claim 17 , wherein:
 the gain chip is configured to support only one laser; and   the modulator chip is configured to support two modulators.   
     
     
         19 . The optical transmitter of  claim 17 , wherein the gain chip is configured to support four lasers. 
     
     
         20 . The optical transmitter of  claim 17 , wherein:
 the gain chip is a first gain chip;   the optical transmitter comprises a second gain chip;   the first multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip; and   the second multiplexer is configured to receive an optical input from the first gain chip and an optical input from the second gain chip.