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 having a light absorption layer. The depletion layer capacitance generated in the light absorption layer is canceled by an inductor 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;
an optical modulator optically connected to the laser light source and having an optical waveguide structure, the optical waveguide structure having a first type semiconductor base layer, a light absorption layer and a second type semiconductor layer arranged in this order;
an electrode pad receiving a modulation signal;
a modulation electrode formed on the second type semiconductor layer; and
a high frequency line connecting the electrode pad and the modulation electrode and providing inductance in series with respect to a depletion layer capacitance of the optical waveguide structure;
wherein a portion under the high frequency line and the electrode pad is composed of a material having a dielectric constant lower than a dielectric constant of the semiconductor base layer,
the material is configured such that the electrode pad is higher than the modulation electrode, and
the high frequency line is a meander wiring.
2. The optical semiconductor chip according to claim 1 ,
wherein a line width of the high frequency line 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 high frequency line is 0.17 nH or less.
4. The optical semiconductor chip according to claim 1 ,
wherein the laser light source is a distributed feedback (DFB) laser.
5. An optical modulator assembly, comprising:
an optical semiconductor chip, comprising:
a laser light source;
an optical modulator optically connected to the laser light source and having an optical waveguide structure, the optical waveguide structure having a first type semiconductor base layer, a light absorption layer and a second type semiconductor layer arranged in this order;
an electrode pad receiving a modulation signal;
a modulation electrode formed on the second type semiconductor layer; and
a high frequency line connecting the electrode pad and the modulation electrode and providing inductance in series with respect to a depletion layer capacitance of the optical waveguide structure;
a chip in which terminators are integrated; and
a wiring board for leading the modulation signal.