Optical semiconductor chip
An optical semiconductor chip of the present disclosure includes a high frequency line between an electrode pad receiving a modulation signal and a modulation electrode on the optical waveguide constituting a laser. The depletion layer capacitance generated in an active layer of the optical waveguide is cancelled by an inductance component of the high frequency line. When a portion directly below the high frequency line is embedded with a low-dielectric-constant material or is made hollow, the parasitic capacitance is further reduced. The high frequency line may have a zigzag shape as well as a linear shape. The electrode pad on the optical semiconductor chip can be connected to other substrates including RF lines for modulation signal input by bumps or wire bonding.
1 . An optical semiconductor chip, comprising:
a laser light source having an optical waveguide structure, the structure having a first type semiconductor base layer, an active layer and a second type semiconductor layer arranged in this order;
an electrode pad receiving a modulation signal;
a modulation electrode being formed on the second type semiconductor layer; and
a meander wiring connecting the electrode pad and the modulation electrode and providing inductance in series with respect to a depletion layer capacitance of the optical waveguide,
wherein a portion under the meander wiring and the electrode pad is composed of a material having a dielectric constant lower than a dielectric constant of the semiconductor base layer; and
a thickness of the material is set such that a height of the meander wiring and the electrode pad is higher than a top surface of the optical waveguide.
2 . The optical semiconductor chip according to claim 1 ,
wherein a line width of the meander wiring is narrower than a width of the electrode pad.
3 . The optical semiconductor chip according to claim 1 ,
wherein the amount of inductance of the meander wiring is 0.18 nH or less.
4 . The optical semiconductor chip according to claim 1 ,
wherein the laser light source is a direct modulation laser.
5 . An optical modulator assembly, comprising:
the optical semiconductor chip according to claim 1 ;
a chip in which terminators are integrated; and
a wiring board for leading the modulation signal.