Wavelength controlling circuit for laser signal

Claim 2

A wavelength controlling circuit for a laser signal which includes a laser diode having a semiconductor laser diode, a temperature detection element , a temperature adjustment element, monitoring means having an element which branches part of a laser signal output from the semiconductor laser diode, a wavelength discrimination element for monitoring the wavelength of the laser signal, and first adjustment means for generating a signal for finely adjusting the wavelength of the laser signal in response to an output from the monitoring means, characterized in that there is provided second adjustment means for generating a signal for roughly adjusting the wavelength of the laser signal in response to the result of the monitoring of the temperature which is monitored by the temperature detection element of the laser diode module switching means for discriminating, in response to the result of the temperature monitoring of the laser diode module, that a predetermined wavelength is reached, and for performing switching from the second adjustment means to the first adjustment means, and driving means for driving the temperature adjustment element of the laser diode module with the adjustment signals of the first and second adjustment means.

Claim 3

A wavelength controlling circuit for a laser signal as claimed in claim 1, in which the wavelength controlling means for controlling the wavelength within the range of fine adjustment includes monitoring means having an element which branches part of a laser signal output from the semiconductor laser diode, a wavelength discrimination element for monitoring the wavelength of the laser signal, and first adjustment means for generating a signal for finely adjusting the wavelength of the laser signal in response to an output from the monitoring means.

Claim 4

A wavelength controlling circuit for a laser signal as claimed in either claim 2 or claim 3 in which the monitoring means for monitoring the wavelength of the laser signal includes an element for branching a part of the laser signal output from the semiconductor laser diode, and a wavelength monitoring circuit having a beam splitter for splitting the branched laser signal into two laser signals, an optical band-pass filter having a particular transmission factor of an optical wavelength for receiving one of the split laser signals, a first optical detector for receiving the laser signal after transmission through the optical band-pass filter, and a second optical detector for receiving the other of the split laser signals.

Claim 5

A wavelength controlling circuit for a laser signal as claimed in claim 4, in which the first adjustment means for generating a signal for finely adjusting the wavelength of the laser signal in response to an output from the monitoring means is a first controlling circuit having a divider for dividing an output from the first optical detector by an output from the second optical detector, and a first amplifier for amplifying a difference voltage between an output signal from the divider and a first reference voltage.

Claim 6

A wavelength controlling circuit for a laser signal as claimed in claim 2, in which the second adjustment means for generating a signal for roughly adjusting the wavelength of the laser signal in response to a result of the monitoring is a second controlling circuit having a temperature monitoring circuit connected to a thermistor of the laser diode module for detecting a voltage signal proportional to the temperature, and a second amplifier for amplifying a difference between an output voltage from the temperature monitoring circuit and a second reference voltage.

Claim 7

A wavelength controlling circuit for a laser signal as claimed in claim 2, in which the switching means for performing switching from the second adjustment means to the first adjustment means is a switching circuit having a comparison circuit for receiving a voltage proportional to the result of monitoring the temperature and generating an activation signal with a predetermined voltage, and a switch which operates in response to the activation signal of the comparison circuit.

Claim 8

A wavelength controlling circuit for a laser signal as claimed in claim 7, in which the comparison circuit is a function generator of a variable rising input voltage having a hysteresis characteristic.

Claim 9

A wavelength controlling circuit for a laser signal which includes a laser diode module having a semiconductor laser diode, a temperature detection element and a temperature adjustment element, an element for branching part of a laser signal output from the semiconductor laser diode, a wavelength monitoring circuit including a beam splitter for splitting the branched laser signal into two laser signals, an optical band-pass filter having a particular transmission factor of an optical wavelength for receiving one of the split laser signals, a first optical detector for receiving the laser signal after transmission through the optical band-pass filter, and a second optical detector for receiving the other of the split laser signals, the wavelength monitoring circuit monitoring a range within which the wavelength of the laser signal can be discriminated by the optical band-pass filter, a first controlling circuit for generating a signal for finely adjusting the wavelength of the laser signal, the first controlling circuit including a divider for dividing an output from the second optical detector of the wavelength monitoring circuit by an output from the first optical detector and a first amplifier for amplifying a difference voltage between an output signal from the divider and a first reference voltage, and a driving circuit for driving the temperature adjustment element of the laser diode module with the fine adjustment signal of the first controlling circuit, characterized in that there is provided a second controlling circuit for generating a signal for roughly adjusting the wavelength of the laser signal so that the wavelength of the laser signal may come within a discrimination allowing range, the second controlling circuit having a temperature monitoring circuit connected to a thermistor of the laser diode module for detecting a voltage signal proportional to the temperature after an operation has started and a second amplifier for amplifying a difference between an output from the temperature monitoring circuit and a second reference voltage, and a switching circuit for performing switching from the second controlling circuit which roughly adjusts the wavelength of the laser signal to the first controlling circuit which finely adjusts the wavelength of the laser signal, the switching circuit having a comparison circuit for receiving the voltage proportional to the temperature by the rough adjustment of the wavelength of the laser signal, and for generating an activation signal with a predetermined voltage, and a switch which operates in response to the activation signal of the comparison circuit.