A wavelength estimation device including a light detector to receive light emitted from a light source and an estimation unit. The estimation unit estimates a wavelength of the light based on an amount of light received by the light detector.

An optical network using an optical amplifier in a gain saturation region includes an optical transmission apparatus. The optical transmission apparatus includes an optical transmitter configured to output an optical signal, a semiconductor optical amplifier (SOA) configured to amplify the optical signal outputted through the optical transmitter, and a controller configured to control the SOA to operate in a gain saturation region or a linear gain region depending on whether a forward error correction (FEC) function is used in the optical network.

In the method for controlling a tunable wavelength laser, information designating an oscillation wavelength is inputted. A driving condition for causing laser oscillation at a first wavelength is acquired from a memory. A control value of wavelength characteristics of the etalon and a difference between the first wavelength and a second wavelength are referred to, and a control value of wavelength characteristics of the etalon for causing laser oscillation at the second wavelength is calculated. The control value of wavelength characteristics of the etalon are assigned to the tunable wavelength laser, and a wavelength is controlled so that a wavelength sensing result becomes a first target value. Information indicating a wavelength shift amount from the designated oscillation wavelength is inputted. The wavelength sensing result is calculated as a second target value. The wavelength is controlled so that the wavelength sensing result becomes the second target value.

A method of calibrating a tunable laser includes shifting a filter output peak defined by a tunable optical feedback filter of the tunable laser in an optical spectral domain to align with a target etalon output peak of a plurality of spaced etalon output peaks defined by an etalon of the tunable laser. The method also includes shifting a cavity frequency grid defined by cavity modes of the tunable laser to align a target cavity mode of the cavity frequency grid with the filter output peak and shifting the spaced output peaks defined by the etalon to align a target etalon output peak with a target wavelength of an output wavelength grid. The method includes modifying a bias current and a modulation current of a gain section of the tunable laser to achieve a defined output modulation amplitude and a defined extinction ratio.

A method of operating a laser includes generating a first signal having a first frequency, and generating a second signal having a second frequency. The first frequency varies in accord with an amplitude of a drive current provided to a laser. The method further includes incrementing or decrementing a count responsive to a relationship between the first frequency and the second frequency; determining the count satisfies a threshold count; and modifying operation of the laser when the count satisfies the threshold count.

A method of controlling a wavelength tunable laser to control an oscillation wavelength based on a difference between a detection result of a wavelength by a wavelength detecting unit and a target value, the method includes: acquiring a first drive condition of the wavelength tunable laser to make the wavelength tunable laser oscillate at a first wavelength from a memory; calculating a second drive condition to drive the wavelength tunable laser at a second wavelength by referring to the first drive condition and a wavelength difference between the first wavelength and the second wavelength, the second wavelength differing from the first wavelength; and driving the wavelength tunable laser based on the second drive condition calculated at the calculating of the second drive condition.

A driving condition for causing the tunable wavelength laser to conduct laser oscillation at a first wavelength is acquired. a driving condition for causing the tunable wavelength laser to conduct laser oscillation at the second wavelength is calculated. The tunable wavelength laser is driven based on the driving condition of the second wavelength, feedback control that changes the driving condition of the tunable wavelength laser based on a difference between an output of the wavelength sensing unit and the target value is performed, and the tunable wavelength laser is caused to oscillate at the second wavelength. The driving condition of the tunable wavelength laser obtained by the feedback control when oscillation has occurred at the second wavelength is stored in the memory. Thereafter, the tunable wavelength laser is driven with reference to the stored driving condition of the tunable wavelength laser.

A laser diode driving method that reliably maintains average optical power and extinction ratio is disclosed. The present invention for laser driving uses a preloaded laser diode characteristic curve/table and/or mathematical equations to create a programmable bias and modulation current range. This ensures stable closed-loop operation and prevents system failure if the feedback signal is impaired by confining the operation of the laser diode to a normal operating range.

A tunable laser wavelength measurement system includes an interferometric wavelength tracking system that uses a combination of interferometric and wavelength reference measurements to directly measure the laser output wavelength, The measurement exhibits the following desirable error signal characteristics: directional information, continuity, low latency, absolute information, high accuracy, high precision, and little or no drift, A tunable laser wavelength control system additionally incorporates electronics to compare the measured laser wavelength to a desired wavelength or wavelength function, and to generate a feedback control signal to control the wavelength of the laser output based on the comparison. In one non-limiting example implementation, the desired wavelength function is repetitive. The difference between the desired wavelength function and the interferometrically-measured wavelength function is taken, and a successive approximation technique is employed to calculate and adjust a repetitive controlling signal to obtain the desired wavelength function.

An illumination apparatus includes at least one laser diode, an illumination section, and a light control circuit. The illumination section uses light emitted from the laser diode as illumination light. The light control circuit controls light intensity of the laser diode by pulse-modulating a drive current supplied to the laser diode. The light control circuit controls the light intensity of the laser diode in combination with a duty ratio and a peak current of the pulse-modulated pulse drive current in combination in a multi-oscillation mode region in which a wavelength spectrum width of the light emitted from the laser diode is equal to or larger than a threshold wavelength width.