Light transmitter
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorShinji Shibao
Life of this patent
Estimating the term…
Abstract
A light transmitter for preventing the degradation of the extinction ratio and the occurrence of pulse width distortion in the light output in spite of the variation of current to light conversion efficiency A of the laser diode. The transmitter uses the characteristics such that the light pulse width becomes narrower than the modulation current pulse width if the laser diode is modulated by a bias current smaller than the threshold level. The light transmitter includes mismatch detection circuit (14) which detects the decrease of the light pulse width. By the detected mismatch signal, the modulation current control circuit (15) limits to increase the modulation current. The modulation current control circuit (15) operates together with the control circuit which controls automatically the light output peak value to be constant.
Claims16
A light transmitter having a modulator which applies a binary modulation current to a light generation element, and in response to binary transmitted data, a light receiving element which receives a part of the light from the light generation element means for applying a current to the light generation element in proportion to the current difference between a reference current generated in the reference current source and a current flowing in the light receiving element, the transmitter comprising:
- a first current to voltage conversion circuit for converting the signal current flowing in the light receiving element to a voltage signal;
- a second current to voltage conversion circuit for converting the modulation current outputted from the modulator to a voltage signal;
- a mismatch detection circuit for receiving, and determining the mismatch between, the voltage outputted from the first current to voltage conversion circuit and the voltage outputted from the second current to voltage conversion circuit and for providing an output;
- and
- a modulation current control circuit for controlling the modulation current of the modulator in response to the output from the mismatch detection circuit.
A light transmitter having a modulator which applies a binary modulation current to a light generation element in response to binary transmitted data, a light receiving element which receives a part of the light from the light generation element, and means for applying a current to the light generation element in proportion to the current difference between a reference current generated in the reference current source and a current flowing in the light receiving element, the transmitter comprising:
- a first current to voltage conversion and averaging circuit for converting the signal current flowing in the light receiving element to a voltage signal;
- a second current to voltage conversion and averaging circuit for converting the modulation current outputted from the modulator to a voltage signal;
- a comparison circuit for comparing the output voltage from the first current to voltage conversion and averaging circuit and the voltage from the second current to voltage conversion and averaging circuit;
- and
- a modulation current control circuit for controlling the modulation current of the modulator by the output of the comparison circuit.
A light transmitter comprising:
- a light generating element;
- a modulator for applying a modulation current to the light generation element;
- a light receiving element which receives part of the light from the light generation element;
- a circuit for detecting and comparing the current flowing in the light receiving element and the modulation current and for providing a comparison signal;
- and
- a modulation current control circuit for controlling the modulation current of the modulator in response to the comparison signal.
A method for maintaining constant extinction ratio and pulse width in a light transmitter comprising a light generating element, a light receiving element which receives part of the light from the light generation element, and a modulator for providing a modulation current to the light generation element, when the current to light conversion efficiency of the light generating element varies, the method comprising the steps of:
- detecting the current flowing through the light receiving element;
- detecting the modulation circuit;
- comparing the detected currents;
- providing a comparison signal based on the comparing step and
- changing the modulation current in response to the comparison signal.
Dependencies are inferred from the claim text.