An optical source emits a source optical signal having a source optical signal power and a wavelength. A splitter or other similar device splits the source optical signal into a first optical signal having a first optical signal power and into a second optical signal having a second optical signal power such that the source optical signal power is split between the first optical signal power and the second optical signal power. This split is dependent upon the wavelength of the source optical signal. A first detector detects the first optical signal power and a second detector detects the second optical signal power. A controller responds to the first and second detectors in order to control the wavelength of the source optical signal.
Even when manufacturing of a waveguide is fluctuated and an optical parameter is fluctuated or a wavelength of emitted light is fluctuated, a phase difference between two intrinsic modes can be compensated (positive integral multiple of .pi.). Thus, it is possible to prevent a reproduced signal from being deteriorated by elliptically polarized light. A magneto-optical reproducing pickup includes an optical waveguide (4) for guiding light reflected on a magneto-optical recording medium to a differential photo-detecting unit (9) side and phase compensating circuitry for compensating a phase difference between light components of a TE mode an a TM mode included in reflected light. In this case, the phase compensating circuitry comprises the optical waveguide (4) composed of a substrate formed of an electrooptic crystal and a thin film having a light refractive index higher than that of the substrate formed on the substrate, phase control electrodes (21a and 22b) for applying an electric field to the optical waveguide (4) in the direction along the TM mode and a feedback circuit (11).
Even when manufacturing of a waveguide is fluctuated and an optical parameter is fluctuated or a wavelength of emitted light is fluctuated, a phase difference between two intrinsic modes can be compensated (positive integral multiple of .pi.). Thus, it is possible to prevent a reproduced signal from being deteriorated by elliptically polarized light. A magneto-optical reproducing pickup includes an optical waveguide (4) for guiding light reflected on a magneto-optical recording medium to a differential photo-detecting unit (9) side and phase compensating circuitry for compensating a phase difference between light components of a TE mode an a TM mode included in reflected light. In this case, the phase compensating circuitry comprises the optical waveguide (4) composed of a substrate formed of an electrooptic crystal and a thin film having a light refractive index higher than that of the substrate formed on the substrate, phase control electrodes (21a and 21b) for applying an electric field to the optical waveguide (4) in the direction along the TM mode and a feedback circuit (11).
A fiber optic wavelength measuring apparatus using the wavelength dependent nature of a fused fiber coupler to measure the wavelength of light propagating in an optical fiber. The input light is coupled, using a fused fiber coupler, of the type commonly used as wavelength division mutiplexers, into two fibers and the light in these two fibers is then measured using a pair of fiber coupled photodiodes. The ratio of the optical power of light in the two fibers corresponds to the wavelength of the input light. Hence it is possible to perform precise real-time measurement of the wavelength of light in a fiber with a compact, inexpensive, and field rugged apparatus.
A method for monitoring the power of a laser beam in real time is disclosed. At least one optical fiber is placed through the laser beam, where a portion of light from the laser beam is coupled into the optical fiber. The optical fiber may be maintained in a stationary position or moved periodically over a cross section of the laser beam to couple light from each area traversed. Light reaching both fiber ends is monitored according to frequency and processed to determine the power of the laser beam.
A laser source with an extremely stable output is provided. A laser diode has an output intensity centered at a peak wavelength which is responsive to a control signal. First and second fiber Bragg gratings are coupled to the laser diode. The first fiber Bragg grating having a reflectivity centered about a first wavelength and the second fiber Bragg grating having a reflectivity centered about a second wavelength different from the first wavelength. Each of the first and second fiber Bragg gratings generates a feedback signal responsive to the reflectivity of the fiber Bragg grating and the output intensity of the laser diode. A controller connected to the laser diode generates the control signal responsive to the feedback signals from the first and second fiber Bragg gratings so that the peak wavelength of the laser diode is maintained at a fixed wavelength between the first and second wavelengths.
