Kokusai Denshin Denwa Kabushiki Kaisha

Other

Itsuro Morita

Masatoshi Suzuki

Noboru Edagawa

Shu Yamamoto

Shigeyuki Akiba

Hidenori Taga

Takashi Mizuochi

Katsuhiro Shimizu

Tadayoshi Kitayama

Kiwami Matsushita

Takeshi Komiya

Tadakatsu Shimada

Kazuo Koya

The soliton pulse compression optical fiber comprises a core and a clad that surrounds the core for compressing the injected light pulse in width. The maximum relative index difference between the core and the clad is between about 1.2% and 2.5%. The core diameter of the soliton pulse compression optical fiber varies along the length of the soliton pulse compression optical fiber and the core has a step-like refractive index distribution. The optical fiber perform of the soliton pulse compression optical fiber comprises a core preform, which is to be a core of the soliton pulse compression optical fiber, and a clad preform that surrounds the core preform. The maximum relative index difference between the core perform and the clad preform is also between about 1.2% and 2.5%.

Soliton pulse compression optical fiber and method for making soliton pulse compression optical fiber

Detection of an optical pulse position uses an optical pulse string with a determined repetitive ratio and an electric clock signal with a same frequency as the repetitive ratio of the optical pulse string. A phase of the electric clock signal oscillator is shifted and supplied to an optical modulator. The optical modulator modulates the optical pulse string based on the electric clock signal and outputs a modulated optical signal. A photo detector converts the modulated optical signal output from the optical modulator to an electric signal. The phase shift amount of the electric clock signal is controlled to maximize an output from the photo detector. Additionally, a dither signal may be used in the control of the phase shift, more than the optical modulator may be employed, and/or more than color light source may be employed. The use of at least one of feed forward and feedback control provided by maximizing an output of the photo detector allows an optical pulse having a short width to be realized.

Optical pulse position detecting circuit and an optical pulse generating apparatus and their methods

An optical transmission device using return-to-zero optical pulses as transmission optical pulses, which is capable of enhancing a transmission distance as well as a wavelength range with satisfactory transmission characteristics and enabling an easy realization of the wavelength division multiplexing optical transmission. The optical transmission device is formed by an optical transmitter for transmitting transmission optical pulses by superposing digital data signals onto return-to-zero optical pulses, and a modulator for applying one of a phase modulation and a frequency modulation in synchronization with a transmission rate of the transmission optical pulses, to the transmission optical pulses transmitted by the optical transmitter. This optical transmission device can be utilized in forming a wavelength division multiplexing optical transmission apparatus and an optical transmission system.

Optical transmission device, WDM optical transmission apparatus, and

An optical pulse generator, capable of generating ultrashort optical pulses suitable for optical soliton transmission, includes a DFB laser 10 for continuous laser oscillation, an electroabsorbtion modulator 12 for creating a sequence of optical pulses of the pulse width 14.6 ps from optical output of the laser 10. Output from an optical modulator 12 enters into a dispersion decreasing fiber 16 via an optical isolator 14. The dispersion decreasing fiber 16 has chromatic dispersion that decreases from 13.7 ps/nm/km to 2.3 ps/nm/km with distance, and its fiber length is 15 km. Pump laser beams from pump lasers 20, 24 are introduced to the dispersion decreasing fiber 16 by optical couplers 18, 22, and the fiber 16 functions as a Raman amplifier. When the Raman gain is 2.4 dB, the pulse width is compressed from 14.6 ps to 5.8 ps, approximately, even when the power of input pulses to the dispersion decreasing fiber 16 complies with the soliton condition.

Optical pulse generator

Incident light 1 is inputted to an electro-absorption-type optical modulator 4 via an optical circulator 2 and a lens 3, and subjected to intensity modulation that corresponds to a modulation signal 8. The optical signal outputted by the electro-absorption-type optical modulator 4 is inputted to a Faraday rotator 6 via a lens 5, and the plane of polarization is rotated 45.degree.. The optical signal transmitted by the Faraday rotator 6 is totally reflected by a totally reflecting mirror 7, inputted for the second time to the Faraday rotator 6, then passed through the lens 5 after the plane of polarization has been rotated 45.degree. by this Faraday rotator 6, and readmitted by the electro-absorption-type optical modulator 4. The output of the electro-absorption-type optical modulator 4 is emitted via the lens 3 and the optical circulator 2. The polarization dependence of insertion loss can be eliminated because the plane of polarization is rotated 90.degree., and the incident light 1 readmitted to the electro-absorption-type optical modulator 4 at any plane of polarization. In view of this, the polarization dependent loss of an electro-absorption-type optical modulator can be eliminated by employing such optical modulators and creating a high-performance optical short pulse generating device, optical waveform shaping device, and optical demultiplexer.

Optical modulator, optical short pulse generating device, optical

An optical frequency shifter which has no insertion loss polarization dependency and no polarization mode dispersion is formed by: at least one ultrasonic wave generator for generating ultrasonic waves; at least one electric acousto-optic element forming at least one diffraction grating therein upon being applied with the ultrasonic waves generated by the ultrasonic wave generator; at least one polarization rotator for rotating a polarization plane of a first primary diffracted light produced by the diffraction grating, by 90.degree.; and a light path through which an input light is entered into the electric acousto-optic element at a Bragg angle of the diffraction grating in a prescribed direction side, the prescribed direction being defined as either identical or opposite to a propagation direction of the ultrasonic waves, so that the first primary diffracted light is produced by the diffraction grating from the input light, a polarization plane rotated light produced by the polarization rotator is entered into the electric acousto-optic element at a Bragg angle of the diffraction grating in the prescribed direction side, and a second primary diffracted light produced by the diffraction grating from the polarization plane rotated light is outputted as an output light. An optical soliton-like return-to-zero pulse transmission system using a combination of this optical frequency shifter and a fixed optical filter in an optical amplifier repeater is also disclosed.

Optical frequency shifter and optical soliton-like return-to-zero pulse

An optically amplifying transmission system available for wider signal bands includes an optical transmission line 42 divided into two sections 42a and 42b, optically amplifying repeaters 48a having 7 m-long erbium-doped optical fibers to repeat transmission optical fibers 46a in the section 42a, and optically amplifying repeaters 48b having 10.8 m-long erbium-doped optical fibers to repeat transmission optical fibers 46b in the section 42b. The transmission optical fibers 46a an 46b are optical fibers absolutely identical in construction and length.

Optically amplifying transmission system

An optical transmission system which permits long-distance, ultrafast, high-capacity optical soliton transmission by suppressing timing jitter with simple means. In an optical transmission system which uses a transmission line composed of an optical fiber for transmitting therethrough a lightwave signal having digital information added to a return-to-zero lightwave pulse and a plurality of optical amplifying repeaters for compensating for losses by the optical fiber and in which the pulse compression effect by the nonlinear optical effect on the optical pulse and the pulse expansion effect by the dispersion effect are compensated, at least one optical band limited element which has a flat group delay characteristic near the center frequency is disposed in the transmission line at intervals of a period Z equal to the soliton period Z.sub.sol and the product, aB.sub.sol.spsb.2, of the curvature a of the product of the intensity transfer funtions of the optical band limited elements in the vicinity of the center frequency in the soliton period and the square of the full width at half maximum, B.sub.sol, of the spectrum of the lightwave pulse to be transmitted is set to a value in the range of 2.1.times.10.sup.-2 to 8.3.times.10.sup.-2.

Optical transmission system

An optical amplifying-repeating transmission system is disclosed which is composed of an optical fiber for transmitting a lightwave signal with digital information added to return-to-zero lightwave pulses and a plurality of optical amplifying repeaters inserted in the optical fiber for transmission use. The mean value of wavelengths at which the wavelength dispersion of the optical fiber is zero is smaller than the wavelength of the lightwave signal which is transmitted over the system. The accumulated wavelength dispersion value of the optical fiber tends to increase with the distance of transmission, from a macroscopic viewpoint. The optical fiber for transmission is divided into a plurality of sections. In accordance with the accumulated wavelength dispersion value of the optical fiber in each section except at least the last one, a wavelength dispersion medium, which locally changes the wavelength dispersion in a manner to cancel the accumulated wavelength dispersion in the section at the wavelength of the lightwave signal, is inserted in the section to eliminate the accumulation of the timing jitter.

Optical amplifying-repeating transmission system

An optical amplifying transmission system is disclosed in which a large quantity of optical fiber whose zero dispersion wavelength is longer than the wavelength of the lightwave signal is introduced to provide an RZ lightwave signal transmission system. In this system, the average zero dispersion wavelength by the optical fiber is shorter than the wavelength of the lightwave signal, the zero dispersion wavelength by the optical fiber whose length is in the range of one-thirds to two-thirds of the entire length of the optical fiber is longer than the wavelength of the lightwave signal, and the absolute value of the wavelength dispersion is larger than one-half the absolute value of the average wavelength dispersion value over the entire length of the optical fiber.

Growing community of inventors

Tokyo, Japan

Itsuro Morita