A GePD having uniform sensitivity in C and L bands is provided and a photodetector in which deterioration of a common-mode rejection ratio is curbed is provided. A photodetector according to an embodiment includes one or a plurality of sets of two photodiodes to which a differential signal is input, a monitor connected to each of the two photodiodes and configured to measure a photocurrent, and a voltage supply configured to control a voltage applied to each of the two photodiodes, and the voltage supply controls the voltage applied to each of the two photodiodes so that the photocurrent measured by the monitor connected to one of the two photodiodes is equal to the photocurrent measured by the monitor connected to another one of the two photodiodes.
1. A photodetector comprising:
one or a plurality of sets of two photodiodes to which a differential signal is input;
a first monitor connected to a first one of the two photodiodes and a second monitor connected to a second one of the two photodiodes, the first and second monitors configured to measure a photocurrent of the photodiode connected to the respective first and second monitor, the first and second monitors being connected to each other so as to exchange detected photocurrent values with each other; and
a first voltage supply configured to control a voltage applied to the first one of the two photodiodes and a second voltage supply configured to control a voltage applied to the second one of the two photodiodes,
wherein the first and second voltage supplies control the voltage applied to the two photodiodes based on the detected photocurrent values exchanged by the first and second monitors so that the photocurrent value measured by the first monitor connected to the first on of the two photodiodes is equal to the photocurrent values measured by the second monitor connected to the second one of the two photodiodes.
2. The photodetector according to claim 1 , wherein
the photodiode includes
a silicon substrate;
a lower clad layer formed on the silicon substrate;
a core layer formed on the lower clad layer and including a silicon slab doped with impurity ions having a first conductivity type, an electrode portion doped with the impurity ions having the first conductivity type at a high concentration, and a waveguide layer connected to the silicon slab;
a germanium layer formed on the core layer and including a germanium region doped with impurities having a second conductivity type;
an upper clad layer formed on the core layer and the germanium layer; and
electrodes connected to the electrode portion and the germanium region, respectively.
3. The photodetector according to claim 1 , wherein
the photodiode includes
a silicon substrate;
a lower clad layer formed on the silicon substrate;
a core layer formed on the lower clad layer and including a silicon slab doped with impurity ions having a first conductivity type, and a waveguide layer connected to the silicon slab;
a germanium layer formed on the core layer and including a first germanium region doped with the impurity ions having the first conductivity type and a second germanium region doped with impurity ions having a second conductivity type;
an upper clad layer formed on the core layer and the germanium layer; and
electrodes connected to the first germanium region and the second germanium region, respectively.
4. The photodetector according to claim 1 , wherein
the photodiode includes
a silicon substrate;
a lower clad layer formed on the silicon substrate;
a core layer formed on the lower clad layer and including a silicon slab, the silicon slab including a first silicon region doped with impurity ions having a first conductivity type, a first electrode portion doped with the impurity ions having the first conductivity type, a second silicon region doped with impurity ions having a second conductivity type, and a second electrode portion doped with the impurity ions having the second conductivity type, and a waveguide layer connected to the silicon slab;
a germanium layer formed on the core layer;
an upper clad layer formed on the core layer and the germanium layer; and
electrodes connected to the first electrode portion and the second electrode portion.
5. The photodetector according to claim 1 , wherein the first and second monitors are an ammeter connected to an anode or a cathode of each of the two photodiodes.
6. The photodetector according to claim 1 , wherein the first and second monitors are a transimpedance amplifier connected to an anode or a cathode of each of the two photodiodes.
7. The photodetector according to claim 6 , wherein the first and second monitors are a digital signal processor connected to the transimpedance amplifier.