Nec Corporation

Yoshiyasu Ueno

Kazuhito Tajima

Shigeru Nakamura

Hiroaki Fujii

Hiroyuki Sawano

Akiko Gomyo

Hiroaki Chida

A system for all-optical signal regeneration is provided, which makes it possible to exhibit desired intensity noise suppressing function with respect to pulsed input signal light without increasing the injection current of semiconductor optical amplifiers even if the magnitude of nonlinear phase shift of the input signal light is less than &#x3c0;. The output light of the first delay interference unit is subjected to phase shift in the first nonlinear semiconductor waveguide and then, applied to the second delay interference unit along with the clock light. In the second delay interference unit, the first interfered light is generated from the output light while the second interfered light is generated from the clock light having an opposite logic to the input light. The second interfered light is subjected to phase shift by the first interfered light in the second nonlinear semiconductor waveguide and then, applied to the third delay interference unit. The third interfered light having an opposite logic to the input light is generated from the second interfered light in the third delay interference unit. The third interfered light is the output light of the system.

Method and system for all-optical signal regeneration

A wavelength converter which has simple configuration and can be easily controlled and operated with stability, and used for a long-distance mass optical communication, comprises a waveguide for causing a change of a nonlinear refractive index. The converter includes a delay interference circuit having two optical paths and of different optical path lengths. A CW light source is input into the waveguide. A coherent length determined by a spectral line width of CW light output from the CW light source is longer than an optical path difference between the two optical paths in the delay interference circuit.

Wavelength converter

An all-optical switch for outputting output light by transmitting/interrupting second input light with a second wavelength synchronizing with first input light with a first wavelength. The all-optical switch has: an optical interferometer to which the first and second input lights are input and which is composed of a non-linear semiconductor waveguide; a supervisory laser light source which supplies supervisory light with a third wavelength to the optical interferometer; and a controller to which supervisory light output from the optical interferometer is input as output supervisory light and which controls the phase bias of the interferometer according to the output supervisory light.

All-optical switch and wavelength converter

To a first nonlinear waveguide and a second nonlinear waveguide each having a refractive index which varies in response to the input of an optical signal, input optical signal pulses are inputted together with continuous light of a predetermined wave length said input optical signal pulses being caused to have a time delay corresponding to 0.6&tilde;1.2 times the pulse width of said input optical signal pulses. Then, the phase of an optical signal outputted from the second nonlinear waveguide is adjusted to a predetermined amount with respect to the phase of an optical signal outputted from the first nonlinear waveguide, and the optical signal outputted from the first nonlinear waveguide and an output signal outputted from the second nonlinear waveguide are coupled, whereafter a wavelength component of the input optical signal pulse is removed from the coupled optical signal. Consequently, an output optical signal pulse of a wavelength different from that of the input optical signal pulse can be obtained while little wavelength chirping is generated.

Wavelength converter and wavelength conversion method

A semiconductor laser capable of producing a high optical output has a coating film applied to an exit end. The coating film has a refractive index (n,) which is large compared with the refractive index (n,) of a semiconductor waveguide. The refractive index (n,) and the refractive index (n,) satisfy the relationship: n,>n,.

Semiconductor laser

Disclosed is a wavelength converter that is appropriate for long-distance large-capacity optical communication, a wavelength converter according to the present invention includes: waveguides,and,for producing nonlinear changes in refractive indices; light interaction circuits,and,; and light delay circuits,and,. When an input signal pulse interval is denoted by T,and a speed at which signal pulse light proceeds through a delay circuit is denoted by v,, a difference &Dgr;L,for optical paths in the light delay circuits satisfies a relation &Dgr;L,&equals;v,T,/2. As a result, when there is an interaction involving two sequential light beams, the phases of which are demodulated by the input signal pulse, the wavelength chirping affecting the light beams is canceled out.

In a semiconductor laser device comprising a plurality of semiconductor layers laminated in a vertical direction on a substrate to form a laser resonator, the laser resonator comprises a saturable absorbing region. A spot size of a light waveguide profile in the vertical direction is greater than 0.4 .mu.m. The laser resonator further comprises first and second reflecting films to provide a reflectivity greater than 50(%).

Semiconductor laser device operable with low noise even in high ambient

Disclosed is a novel combination of a particular class of semiconductors with a particular waveguide structure, realizing a practically efficient optical semiconductor device. The class of material used is ordered semiconductors, examples of which are GaInP and AlGaInP in which atomic-layer superlattices are formed. These superlattices are demonstrated to be useful with respect to a particular nonlinear mechanism, by combining with a particular waveguide structure known as a quasi-phase matching structure. The device disclosed is particularly useful for being utilized as a light switch and a light-wavelength converter used for ultrafast optical communication.

Ordered semiconductor having periodical disorder and devices made

A semiconductor laser with a semiconductor multilayer has at least one double heterostructure. There area pair of cladding layers and an active layer and, where a bandgap energy of the cladding layers is E.sub.1 and that of the active layer is E.sub.2, these bandgap energies satisfy a relation substantially E.sub.1 .gtoreq.2.times.E.sub.2. The semiconductor laser produces green SHG (second harmonic generation) light and the efficiency of producing such light is high because the cladding layers absorb substantially no SHG light.

Semiconductor laser for use as light source in data processing device

In a semiconductor laser, an active layer includes a semiconductor layer having the ordered structure along the [-1,1,1] direction or along the [1,-1,1] direction. By the action of the ordered structure, the electric vector of the recombination light generated in the active layer is concentrated in the (-1,1,1) plane or the (1,-1,1) plane. Alternatively, the semiconductor layer has not only the ordered structure along the [-1,1,1] direction or along the [1,-1,1] direction, but also the compressive strain in the (0,0,1) plane. By the action of the ordered structure and the compressive strain, the recombination light generated in the active layer is emitted in the (1,1,0) plane. As a result, the recombination light effectively gives a gain to the oscillation mode. Thus, the oscillation threshold current of the semiconductor laser is reduced, and the laser characteristics is improved.

A semiconductor laser has a super-lattice active layer to which a high density impurity as equal to or over 1.times.10.sup.17 cm.sup.-3 is selectively diffused in the vicinity of a facet of the semiconductor laser, so that a high power output is realized. The active layer in the impurity diffusion region is formed in a three-layer structure comprising first, second and third semiconductor layers. The second semiconductor layer has an opposite type of conductivity as the first and third semiconductor layer, and is sandwiched thereby. In such a structure, a depletion layer is generated around the active layer, so that injection of current into the active layer is prevented. The blocking layer also protects the active layer from the strain stress during a process of attaching the semiconductor laser to a heatsink. In the fabricating process, a dielectric is temporarily formed to be used as a mask in a selective diffusion and in a selective growth, so that it is not necessary to align a selective growth mask and an impurity diffusion region. An impurity selective diffusion into the multi-layer epitaxial layers having GaAs layer or AlGaAs layer as a surface layer is carried out using As compound as an impurity source, so that the crystal quality of the surface layer is hard to decrease.

Growing community of inventors

Tokyo, Japan

Yoshiyasu Ueno