Optical Transmitter
Disclosed is a new configuration for improving temperature dependency of optical modulation output characteristics, and an implementation form adapted to each configuration in an optical transmitter in which an optical modulator and a driver IC thereof are integrally packaged. The optical transmitter includes: an optical modulator; a driver IC for supplying a modulation electrical signal for the optical modulator; a first Peltier device for controlling a temperature of the optical modulator; a second Peltier device for controlling a temperature of the driver IC; and a subcarrier including an electrical wiring between the optical modulator and the driver IC and being mounted on the first Peltier device and the second Peltier device. The chip of the optical modulator and the driver IC are flip-chip mounted face down, and the temperature of the second Peltier device is set to be lower than the temperature of the first Peltier device.
1 . An optical transmitter comprising:
an optical modulator;
a driver integrated circuit (driver IC) for supplying a modulation electrical signal for the optical modulator;
a first Peltier device for controlling a temperature of the optical modulator;
a second Peltier device for controlling a temperature of the driver IC; and
a subcarrier that including an electrical wiring between the optical modulator and the driver IC and being mounted on the first Peltier device and the second Peltier device,
wherein a chip of the optical modulator and the driver IC are flip-chip mounted face down, and
the temperature of the second Peltier device is set to be lower than the temperature of the first Peltier device.
2 . The optical transmitter according to claim 1 , wherein a distance between the driver IC and the chip of the optical modulator is 500 μm or more and 5 mm or less, and the electrical wiring on the subcarrier has a differential signal interface and is linearly formed.
3 . The optical transmitter according to claim 1 , wherein the temperature of the first Peltier device is set to 45±10° C., and
the temperature of the second Peltier device is set to 30±10° C.
4 . The optical transmitter according to claim 1 , wherein the optical modulator is made of InP,
at least one of an upper surface of the first Peltier device or an upper surface of the second Peltier device is made of aluminum nitride (AlN),
a gap between the subcarrier and the driver IC and the chip of the optical modulator generated by flip-chip mounting of the subcarrier, and the driver IC and the chip of the optical modulator is filled with an underfill material having thermal conductivity of 3 W/mK or more, and
the subcarrier has an outermost surface with flatness of 0.05 mm or less, the subcarrier including one or more layers of AlN.
5 . The optical transmitter according to claim 1 , wherein a spatial optical component is mounted above the first Peltier device on a side of the chip of the optical modulator opposite to the driver IC, and
a region of the subcarrier on which the spatial optical component is mounted has a thickness smaller than a thickness of a region of the subcarrier on which the optical modulator and the driver IC are mounted, or
a second subcarrier having a thickness smaller than the thickness of the subcarrier is further provided in the region in which the spatial optical component is mounted.
6 . The optical transmitter according to claim 1 , wherein a spatial optical component is mounted above the first Peltier device on a side different from a side of the chip of the optical modulator facing the driver IC, and
a groove is formed on a surface of the subcarrier in a vicinity of one side of the chip of the optical modulator on a side of the spatial optical component.
7 . The optical transmitter according to claim 1 , wherein a thermal separation groove is provided on an upper surface of the subcarrier in a vicinity of at least one of facing sides of the driver IC and the chip of the optical modulator or on at least one of an upper surface or a lower surface of the subcarrier between the driver IC and the chip of the optical modulator.
8 . The optical transmitter according to claim 1 , wherein the chip of the optical modulator and the driver IC are mounted in a package of a high-speed driver integrated optical modulator (HB-CDM),
a high frequency electrical wiring using a differential signal interface from an input unit of the package and an electrode pad for the modulation electrical signal are formed on an upper surface of the subcarrier, and
a difference in height between an upper surface of an RF terrace on which a radio frequency (RF) electrode pad of the input unit is formed and the upper surface of the subcarrier is 100 μm or less,
a gap between the RF terrace and the subcarrier in a circuit plane is 100 μm or less, and
the RF electrode pad of the RF terrace and the electrode pad of the subcarrier are connected by a wire.
9 . The optical transmitter according to claim 1 , wherein a spatial optical component is mounted above the first Peltier device on a side of the chip of the optical modulator opposite to the driver IC,
the first Peltier device and the second Peltier device respectively include an n-type semiconductor element and a p-type semiconductor element, and
in-plane densities of the n-type semiconductor element and the p-type semiconductor element are set such that the in-plane density of the second Peltier device, the in-plane density of a mounting region of the chip of the optical modulator on the first Peltier device, and the in-plane density of a mounting region of the spatial optical component on the first Peltier device are in descent order.