Reflection means (24) such as a mirror are provided on the output end of an optical fiber (23), and the input signal light and control light are returned to the optical fiber (23). Although the zero-dispersion wavelength of the optical fiber (23) fluctuates in the longitudinal direction, if the length is relatively short, it is possible to manufacture a high yield optical fiber, which monotonically changes the zero-dispersion wavelength. Therefore, a relatively short optical fiber with a monotonic zero-dispersion change can be used. Since the zero-dispersion change is monotonic and the optical fiber is short, the amount of change in the zero-dispersion wavelength is small and the bandwidth becomes broader when the control light is set at the position of the, average zero-dispersion wavelength. Additionally, although the length of the optical fiber is short, the operating length is twice as long and thus the generation efficiency does not degrade.

A polarization controlling apparatus is disclosed wherein the degree of freedom in apparatus design can be enhanced while increase of the power dissipation and increase of the apparatus scale are suppressed and a high-speed operation can be achieved. The polarization controlling apparatus includes a permanent magnet (2) itself or a permanent magnet to which a part capable of being magnetized is applied, an electromagnet (3) capable of changing the magnitude of a magnetic field to be generated thereby, and a Faraday rotation effect element (4), disposed at a position at which an interaction magnetic field produced by an interaction between a magnetic field generated by the permanent magnet (2) and a magnetic field generated by the electromagnet (3) acts, for producing a Faraday rotation effect on inputted light by means of the interaction magnetic field. The magnitude of the interaction magnetic field in the Faraday rotation effect element (4) is varied by a magnetic field component generated by the electromagnet (3) to vary the amount of the Faraday rotation effect to be had on the inputted light.

A technique for handling an optical pulse signal, wherein the handling includes one or more operations out of: pulse shaping, treatment of nonlinearity and monitoring; the technique uses a device capable of performing a cascaded second harmonic generation (SHG) with respect to a particular fundamental harmonic (FH), and comprises:

• selecting in the device a particular optical path length suitable for performing at least one of the above operations with respect to an incoming optical pulse signal carried by a wavelength defined by the particular fundamental harmonic (FH),
• conveying the incoming optical pulse signal carried by the defined wavelength along the selected optical path in the device,
• obtaining from the device an output optical pulse signal at the fundamental harmonic (FH), wherein the treatment of nonlinearity and/or the pulse shaping are performed, and/or obtaining an output optical pulse signal at the second harmonic (SH) for further monitoring it and judging about the input optical pulse signal.

A spectroscopic apparatus which is compact in size and performs high-precision light-splitting with a large angular dispersion. An optical input-processing section outputs a filtered transmitted light, using a bandpass filter that transmits only wavelength bands at one period of an input light, and collects the filtered transmitted light to generate a collected beam. An optic includes a first reflection surface and a second reflection surface which are high but asymmetric in reflectivity, and causes the collected beam incident thereon to undergo multiple reflections within an inner region between the first reflection surface and the second reflection surface, to thereby cause split beams to be emitted via the second reflection surface,. A received light-processing section performs received light processing of the beams emitted from the optic. A control section variably controls at least one of a filter characteristic of the bandpass filter and an optical length through the optic.

According to an embodiment of the invention, improved multipass second harmonic generation (SHG) is provided by the use of an inverting, self-imaging telescope. This embodiment ensures parallelism of all passes of all beams within the nonlinear medium. According to another embodiment of the invention, improved multipass SHG is provided by the use of a wedged phasor. This arrangement provides a simple adjustment of the relative phase of the pump beam and second harmonic beam between passes. According to a further embodiment of the invention, improved multipass SHG is provided by the use of an inverting self-imaging telescope in combination with a wedged phasor. This arrangement provides a simple adjustment of the relative phase of the pump beam and second harmonic beam between passes, and ensures parallelism of all passes of all beams within the nonlinear medium. This arrangement also allows corresponding passes of the pump beam and second harmonic beam to be made collinear within the nonlinear medium by design.

An optical wavelength division multiplexing (WDM) device comprising optical components that are integrated together to provide an optical WDM that does not require circulators, that has simplified alignment and that is relatively low in cost. The WDM device comprises an integrated port separator (251), a dispersive element (28) and a reflector (30). The integrated port separator comprises various optical components that spatially separate the polarization components of a light beam input (I1,I2) through an input port of the integrated port separator. The spatially separated polarization components are output from the integrated port separator and impinge on the dispersive element, which spatially separates the wavelengths associated with the polarization components impinging thereon. The spatially separated wavelengths then impinge on the reflective element and are reflected with angles of polarization that depend on the state of the reflective element. The reflected polarization components maintain their respective wavelengths when they are reflected. However, when they are reflected, they are directed along a path through the integrated port separator that depends on the angles of polarization of the reflected polarization components, which depends on the state of the reflective element being rotated or not rotated.