OPTICAL REDISTRIBUTION LAYERS FOR HIGH-CHANNEL-COUNT PHOTONICS
High-channel-count optical transceivers can be implemented in photonic integrated circuits (PICs) with shared lasers, splitting the light of each laser between multiple lanes prior to modulation. To reduce waveguide crossings in such PICs, transmitter and self-test functionality may be distributed between separate device layers. Various beneficial transmitter circuitry layouts are disclosed.
1 . A photonic integrated circuit (PIC) comprising:
a device layer; and
formed in the device layer, optical transmitter circuitry comprising:
at least four lasers configured to output laser light at at least four respective wavelengths;
optical splitters configured to split the output laser light of each of the at least four laser between multiple lanes associated with the respective wavelength;
optical modulators configured to modulate the output laser light in each of the lanes to generate a modulated optical signal associated with the respective lane;
a first multiplexing stage comprising first multiplexers configured to multiplex the modulated optical signals across a first subset of the at least four wavelengths into first multiplexed optical signals and second multiplexers configured to multiplex the modulated optical signals across a second subset of the at least four wavelengths into second multiplexed optical signals; and
a second multiplexing stage configured to multiplex the first multiplexed signals and the second multiplexed optical signals into the optical transmitter output signals.
2 . The PIC of claim 1 , wherein the second multiplexing stage is implemented by optical output couplers of the optical transmitter circuitry.
3 . The PIC of claim 1 , wherein the optical modulators are arranged along a first column, grouped by wavelength, the optical transmitter circuitry further comprising waveguides coupling the first and second multiplexers of the first multiplexing stage to the optical modulators and waveguides coupling the first and second multiplexers of the first multiplexing stage to the second multiplexing stage.
4 . The PIC of claim 3 , wherein the first and second optical multiplexers are arranged in a second column, and wherein the waveguides cross only between the first and second columns.
5 . The PIC of claim 4 , wherein the first and second optical multiplexers alternate along the second column.
6 . The PIC of claim 4 , wherein the multiple wavelengths consist of N λ wavelengths and the lanes consist of M lanes, and wherein, for each of the lanes, a number of waveguide crossings associated with the lane does not exceed
M
-
M
N
λ
-
(
N
λ
-
1
)
.
7 . The PIC of claim 3 , wherein the first and second optical multiplexers are arranged in a second column, each grouped together along the second column.
8 . The PIC of claim 7 , wherein the multiple wavelengths consist of N λ wavelengths and the lanes consist of M lanes, and wherein, for each of the lanes, a number of waveguide crossings associated with the lane does not exceed
2
(
M
N
λ
-
1
)
.
9 . The PIC of claim 3 , wherein the first multiplexers are arranged in a first row and the second multiplexers are arranged in a second row.
10 . The PIC of claim 9 , wherein the waveguides coupling the first and second multiplexers of the first multiplexing stage to the optical modulators form nested sets of waveguides about the first and second rows, respectively.
11 . The PIC of claim 10 , wherein the waveguides coupling the first and second multiplexers of the first multiplexing stage to the second multiplexing stage are configured symmetrically about an axis between the rows and parallel to the rows.
12 . The PIC of claim 11 , wherein the multiple wavelengths consist of N λ wavelengths and the lanes consist of M lanes, and wherein, for each of the lanes, a number of waveguide crossings associated with the lane does not exceed
2
(
M
N
λ
-
1
)
.
13 . The PIC of claim 10 , wherein the waveguides coupling the first and second multiplexers of the first multiplexing stage to the second multiplexing stage are configured asymmetrically about an axis between the rows and parallel to the rows.
14 . The PIC of claim 13 , wherein the multiple wavelengths consist of N λ wavelengths and the lanes consist of M lanes, and wherein, for each of the lanes, a number of waveguide crossings associated with the lane does not exceed
M
N
λ
.
15 . The PIC of claim 3 , wherein the device layer comprises a silicon layer, the waveguides being formed in the silicon layer.
16 . The PIC of claim 15 , wherein the device layer is a hybrid layer further comprising III-V semiconductor structures formed on top of the silicon layer.
17 . The PIC of claim 1 , wherein passive device structures of the optical transmitter circuitry are formed in a first waveguide layer within the device layer, the PIC further comprising a second waveguide layer disposed below and separated from the first waveguide layer by a dielectric layer, and formed in the second waveguide layer, optical loopback circuitry optically coupled to the optical transmitter circuitry and configured to selectively couple the modulated optical signals associated with each lane to a photodiode associated with the lane.
18 . A method of manufacturing a photonic integrated circuit (PIC), the method comprising:
patterning a waveguide layer of a substrate to form therein passive device structures of optical transmitter circuitry; and
bonding compound semiconductor material to the patterned waveguide layer and patterning the bonded compound semiconductor material to form active device structures of the optical transmitter circuitry, the waveguide layer of the substrate and the bonded compound semiconductor material collectively forming a hybrid device layer,
wherein the optical transmitter circuitry comprises:
at least four lasers configured to output laser light at at least four respective wavelengths;
optical splitters configured to split the output laser light of each of the at least four laser between multiple lanes associated with the respective wavelength;
optical modulators configured to modulate the output laser light in each of the lanes to generate a modulated optical signal associated with the respective lane;
a first multiplexing stage comprising first multiplexers configured to multiplex the modulated optical signals across a first subset of the at least four wavelengths into first multiplexed optical signals and second multiplexers configured to multiplex the modulated optical signals across a second subset of the at least four wavelengths into second multiplexed optical signals; and
a second multiplexing stage configured to multiplex the first multiplexed signals and the second multiplexed optical signals into the optical transmitter output signals.
19 . The method of claim 18 , wherein the waveguide layer is a silicon layer of a silicon-on-insulator substrate.
20 . The method of claim 18 , wherein the compound semiconductor material comprises III-V material.