Optical Transmitter
In an optical transmitter in which an optical modulator and a driver IC thereof are integrally packaged, a new configuration for improving temperature dependency of an optical modulation output characteristic and a mounting form adapted to each configuration are disclosed. An optical transmitter includes an optical modulator chip, a driver IC that operates the optical modulator chip, and a Peltier element, in which the driver IC is placed on the Peltier element, and only the driver IC is temperature-controlled.
1 . An optical transmitter, comprising:
an optical modulator chip;
a driver IC that operates the optical modulator chip; and
a Peltier element, wherein
the driver IC is placed on the Peltier element, and only the driver IC is temperature-controlled.
2 . The optical transmitter according to claim 1 , wherein the optical modulator chip and the driver IC are mounted on a carrier and the Peltier element, respectively, in a face-up manner, a pad of the optical modulator chip and a pad of the driver IC are connected by a bonding wire, and a difference in height between upper surfaces of the driver IC and the optical modulator chip is equal to or less than 100 μm.
3 . The optical transmitter according to claim 2 , wherein the optical modulator chip and the driver IC are arranged in such a manner that a distance between the optical modulator chip and the driver IC is equal to or less than 50 μm, and the pad of the optical modulator chip and the pad of the driver IC are arranged within 50 μm from a chip end.
4 . The optical transmitter according to claim 1 , wherein the optical modulator chip are mounted on a carrier and the driver IC are mounted on the Peltier element, respectively, in a face-up manner and electrically connected by a wiring board that is flip-chip mounted using a pillar or a bump between the optical modulator chip and the driver IC in a face-down manner, a difference in height between upper surfaces of the driver IC and the optical modulator chip is equal to or less than 100 μm, an inclination in a height direction of a main surface of the wiring board with respect to main surfaces of the optical modulator chip and the driver IC is within ±3°, and a distance between the optical modulator chip and the driver IC is equal to or more than 300 μm and equal to or less than 2 mm.
5 . The optical transmitter according to claim 1 , wherein
the optical modulator chip and the driver IC are flip-chip mounted face down on a subcarrier using a pillar or a bump, and
the driver IC is mounted on the Peltier element via the subcarrier, the optical modulator chip is mounted on a carrier via the subcarrier, and the driver IC and the optical modulator chip are electrically connected by the subcarrier.
6 . The optical transmitter according to claim 5 , wherein the subcarrier includes an aluminum nitride (AIN) substrate, flatness of an outermost surface of the subcarrier is 0.05 mm or less, and a distance between the optical modulator chip and the driver IC is 300 μm or more and 2 mm or less.
7 . The optical transmitter according to claim 5 , wherein
an optical component is mounted on a side different from a side of the optical modulator chip facing the driver IC, an underfill material having a thermal conductivity of 3 W/mK or more is embedded in a gap between the subcarrier and the driver IC, and a space between the subcarrier and the optical modulator chip is embedded with a material that is identical to or different from the underfill material, and
a groove is formed on a surface of the subcarrier near one side of the optical modulator chip on a side of the optical component.
8 . The optical transmitter according to claim 5 , wherein
an optical component is mounted on the carrier on a side of the optical modulator chip opposite to the driver IC, and a region of the carrier where the optical component is mounted has a thickness smaller than a thickness of a region of the carrier where the optical modulator chip is mounted.
9 . The optical transmitter according to claim 1 , wherein the Peltier element is controlled to be constant at any temperature in a range of 25° C. to 50° C. regardless of an outside air temperature, and the driver IC is fixed on the Peltier element by paste or solder having a thermal conductivity of 30 W/mK or more.