An optical transmitter comprises a first unit for generating an optical signal having a bandwidth given by a main signal, a second unit modulating the optical signal according to a control signal to extend the bandwidth of the optical signal, a third unit extracting backward light including SBS(stimulated Brillouin scattering) light generated in an optical fiber transmission line, and a fourth unit performing feedback control so that the power of the SBS light becomes substantially constant. Through the structure of the optical transmitter good transmission characteristics of a main signal are obtained and the suppression of the SBS is allowed.

Optical transmitter, optical communication system and optical communication method

A method and apparatus to enable the use of low cost high RIN optical sources for microwave photonic links by combining the wide-gain bandwidth and low cost of an EDFA, with the narrow gain bandwidth of a Brillouin amplifier. The hybrid Brillouin/EDFA (“hybrid amplifier”) apparatus of the present invention includes at least two couplers, a phase modulator, an Erbium-doped fiber, a laser source to pump the Erbium fiber, an optical circulator, and a length of fiber used for Brillouin amplification. Optical signals from the laser source are split into two optical paths by a polarization maintaining coupler. Optical signals passing through a first path are amplified by the Erbium doped fiber, and the amplified signals are passed through the optical circulator before sending the optical signals into one end of a spool of fiber in order to pump the Brillouin acoustic wave. Optical signals that follow a second path are phase modulated in a phase modulator at the Brillouin frequency and injected into an opposite end of the fiber spool in order to seed the Brillouin amplifier and improve its low frequency stability. The output of the Brillouin section of the hybrid amplifier is directed through the optical circulator, and the output may be used as an optical source for a photonic link.

Hybrid brillouin/erbium doped fiber amplifier apparatus and method

An apparatus and a method for generating an optical carrier is disclosed. The apparatus includes: a light source generating a pump light; a SBS generator for stimulated Brillouin scattering the pump light to generate a stokes light from the light source; an attenuator for controlling an amplitude of the pump light from the light source to generate an amplitude controlled pump light; and a detector for heterodyne beating the stokes light and the amplitude controlled pump light to generate an optical carrier.

Apparatus and method for generating optical carrier for microwave and millimeterwave photonics system

PROBLEM TO BE SOLVED: To provide a method of compensating the dispersion on an optical communication line that a dynamic control is made and a system thereof which reduces the received data reproduction delay time for compensating the dispersion between ends (End-to-End) of the optical communication line that the dynamic control is made. SOLUTION: The method of compensating the dispersion on an optical communication line that a dynamic control is made, having a data transmission network and a network control network cooperating with the data transmission network, comprises a step of showing a dispersion value of the communication line from a specified transmit end of the data transmission network to a receive end, to be generated according to a dynamic control request of the communication line in the network control network; and a step of starting a variable dispersion compensator to compensate the dispersion on the communication line, based on the dispersion value shown in the dispersion value showing step, before establishing the communication line from the specified transmit end to the receive end of the data transmission network to be generated according to the control request. The compensator is provided at least on one of the specified transmit end and the receive end of the communication line. COPYRIGHT: (C)2004,JPO&NCIPI

Dispersion compensation method and system for optical communication line for dynamic control

PROBLEM TO BE SOLVED: To provide an optical amplification device where degradation of complex distortion characteristics is effectively reduced, and to provide an optical transmission system using the same. SOLUTION: An optical amplification device which amplifies a light signal generated by direct modulation of semiconductor laser by a frequency multiplication image signal modulated by a predetermined modulation mode, comprises an optical input portion which receives the light signal, an excitation light source which generates an excitation light, a double cladding type optical amplification fiber where an optical amplification substance is added to a core portion, the light signal and the excited light are received, and the light signal is amplified by induction and release and a light output portion for outputting the amplified light signal. The optical amplification fiber is designed so that an absorption and length product expressed as a product of fiber length of the optical amplification fiber and a peak value at a predetermined wavelength band of absorption coefficient will be smaller than a folding point where a rate of reduction of composite distortion characteristics to a reduction in an absorption and length product drastically increases, in a curve showing the relation between the absorption and length product, and the composite distortion characteristics of the amplified light signal. COPYRIGHT: (C)2009,JPO&INPIT

Optical amplification device and optical transmission system

PURPOSE: To provide an optical transmission equipment capable of suppressing the generation of clipping distortion by simple constitution and reducing the limitation of a transmission band CONSTITUTION: An AM signal line 110 multiplexes the frequency of plural AM signals and outputs the frequency-multiplex AM signal A soft clipper 130 constituted of an amplifier or the like non-linearly and moderately limits the large amplitude part (a part to be impulsively changed) of the frequency-multiplexed AM signal Then an attenuator 140 adjusts the level of the frequency-multiplexed AM signal so as to set up the signal to a prescribed degree of optical modulation On the other hand, a 16QAM signal source 120 multiplexes the frequency of plural 16QAM signals having respectively different carrier frequencies and outputs the frequency-multiplexed signal A frequency multiplexing part 150 multiplexes the frequency of the AM multiplex signal and the 16Q AM multiplex signal An optical transmitter 160 modulates the intensity of laser output light by a frequency multiplex signal outputted from the multiplexing part 150 and transmits the intensity-modulated signal At this time, no clipping distortion is generated An optical signal from the transmitter 160 is transmitted to a receiving system through an optical fiber 170 and demodulated

Optical transmission equipment

PURPOSE:To provide an external modulated light signal transmitter capable of surely assuring always stable transmission performance regardless of the optical fibers to be used and the characteristics of a light source. CONSTITUTION:The level of the beat light of a laser beam and the SBS light induced by this laser beam of the light signal transmitter is detected by a beat detecting section 6 and the line width (wavelength fluctuation width) of the laser beam is feedback controlled by a phase modulator 2 according to the level of the beat light detected by this section. Only the SBS which is a fault to high power light transmission is detected in such a manner and the suppression thereof is automatically executed and, therefore, the transmission performance stable over a long period of time is realized.

External modulated light signal transmitter

PROBLEM TO BE SOLVED: To provide a high-frequency modulated signal generating device which can be constituted easily at low cost and can generate a modulated signal of a high frequency having a stable center frequency. SOLUTION: Output light from a light source 102 is branched by an optical branching part 103 into a 1st light wave and a 2nd light wave. The 1st light wave is inputted to an optical coupling part 105 through a 1st optical waveguide part 107. The 2nd light wave is inputted to an SBS generation part 104 through a 2nd optical waveguide part 108. At this SBS generation part 104, induced Brillouin scattering is caused to perform conversion to a 3rd light wave (Stokes light) whose frequency becomes lower than that of the 2nd light wave (Stokes shift frequency), and the light wave is inputted to the optical coupling part 105 through a 3rd optical waveguide part 109. The optical coupling part 105 couples the 1st light wave and 3rd light wave with each other and outputs resulting light to an optical detection part 106. The optical detection part 106 performs heterodyne detection to generate a beat component of the Stokes shift frequency (about 10 GHz).

High-frequency modulated signal generating device

PURPOSE:To miniaturize a hub, to make a subscriber terminal more inexpensive and to make possible the video service of multiple channels by dividing a signal into a channel block and performing batch frequency multiplexing with the hub. CONSTITUTION:At a CATV center, (n) pieces of digital video signals are respectively orthogonally modulated by a 16-QAM modulator group 1 and outputted to a frequency multiplexing part 2. At the hub, an optical signal is converted into an electric signal by an optical reception part 5 and distributed later to 12 pieces of block converters 1-12. The respective block converters 1-12 convert the frequencies of the prescribed channel blocks to the band of a tuner 11 installed at a subscriber's house. Then, the frequency-converted signal is transmitted to a distributing switch part 7 and connected to transmitters 1-i for transmitting it to the relevant subscriber's house. Concerning (m) channel multiplex signals received by a reception part 10 installed at the subscriber's house, a desired channel is turned by the turning part 11 corresponding to a select signal from a tuning keyboard 13, and the signal is demodulated by a 16-QAM demodulator 12, decoded by a compressed digital decoding part and transmitted to a monitor TV.

Catv transmission system

PURPOSE:To obtain a simple distortion measurement method, for a hybrid optical transmitter sending an optical through plural individual channels altogether each having different optical modulation and to realize the optical transmitter with an excellent characteristic by using the method so as to decide arrangement of optical modulation optimum to each channel CONSTITUTION:The distortion measurement equipment is made up of a measurement section 111 measuring power at a prescribed frequency being an output of an optical reception section and signal generators (2XL sets) 101a, 101b, 102a, 102b provided two for each channel in place of L-sets of multi-channel signal sources corresponding to the hybrid optical transmitter sending a signal through L (L is a natural number being two or over) sets of channels not overlapped with each other When an overall modulation is selected to be sufficiently high to cause the overmodulation state in this measurement equipment, the optical modulation at the prescribed channel is set so that a secondary (ternary) intermodulation distortion IM2 (IM3) produced by two signals in a predetermined channel is less than a required secondary (ternary) intermodulation distortion IM2s (IM3s) for a prescribed channel of an optical transmitter

Kudo Yoshiharu

Papers

Optical transmission equipment

External modulated light signal transmitter

High-frequency modulated signal generating device

Catv transmission system

Distortion measurement method