Ando Electric Company

Nippon Telegraph and Telephone Corporation

Other

Haruyoshi Uchiyama

Tsuneo Horiguchi

Nobunari Takeuchi

Kaoru Shimizu

Tekken Lee

Toshio Kurashima

Yasushi Sato

Kazuo Aida

Yahei Koyamada

Zhixien Li

Zhixien Lee

Takashi Iwasaki

Yoshiyuki Sakairi

Yoshiaki Sato

Yasushi Satoh

Optical fiber characteristic measuring device comprising a coherent light supply device, a light pulse generating device, a wave mixing device, a opto-electrical converting device, and a processing device, is provided such that parts have the frequency characteristic for corresponding to low frequency component for an opto-electrical converting device and a processing section so as to reduce the cost of the circuits.

Optical fiber characteristic measuring device

The present invention provides an optical fiber distortion measuring apparatus and optical fiber distortion measuring method which make it possible to measure the amount of distortion of an optical fiber efficiently and in a short period of time. The time change waveform when a light pulse having a frequency of &ngr;1 is applied is compared with initial data (the time change waveform obtained in a case in which there is no distortion). Then, the light intensity L at a position Dx at which the light intensities do not agree is obtained. Next, the time change waveform is measured when a light pulse having a frequency of &ngr;2 is applied, and the light intensity L at position Dx is obtained. After this, the loss (resulting from distortion) in light intensities L and L is corrected, and light intensities LC and LC are obtained. Curve calculating unit obtains a second-order curve which is a curve resulting from the parallel movement of a curve approximating the spectrum waveform of the initial data, and which contains the (&ngr;1, LC ) and (&ngr;2, LC ) described above. The peak frequency detecting unit obtains the light frequency exhibiting a maximum value in the light intensity in the second-order curve. The distortion amount calculating unit calculates the amount of distortion based on this light frequency.

Optical fiber distortion measuring apparatus and optical fiber distortion measuring method

The present invention relates to an optical-fiber characteristics measuring apparatus that does not require frequency conversion of pulse light which enters an optical fiber to be measured, and does not restrict the cycle period of the pulse light, thereby ensuring fast measuring of the characteristics of the optical fiber. This apparatus comprises an optical directional coupler, an optical pulse generator, a balanced-light reception circuit, a signal generation section and a mixer. The optical directional coupler branches coherent light into first and second coherent lights. The optical pulse generator converts the first coherent light into pulse light which in turn enters an optical fiber to be measured. Returned light whose frequency is shifted from that of the first coherent light by a predetermined frequency through reflection and scattering in the optical fiber to be measured enters the balanced-light reception circuit. The balanced-light reception circuit carries out balanced-light reception of the second coherent light and the returned light and converts the resultant light into an electric signal. The signal generation section generates an RF signal whose frequency is equal to the predetermined frequency. The mixer mixes the electric signal and the RF signal to thereby detect the shifted frequency.

Optical-fiber characteristics measuring apparatus

There is provided an apparatus for measuring the characteristics of an optical fiber in which a frequency difference between first and second coherent light respectively generated by first and second light sources can be accurately set and wherein preferable coherent detection can be carried out in accordance with frequency components of returned light. First coherent light at a frequency f1 is converted into a pulse light which is output to the optical fiber to be measured. The characteristics of the optical fiber are measured by multiplexing returned light from the optical fiber to be measured and second coherent light at a frequency f2 and by detecting the multiplexed light. A component .vertline.f1-f2.vertline. is detected from an optical signal obtained by the multiplexed light and is mixed with a signal at a frequency fr to decrease the frequency. An electric signal at a voltage level corresponding to a differential frequency .vertline.f1-f2.vertline.-fr included in the mixed signal is generated, and a predetermined voltage level is generated which corresponds to a set value for an optical frequency difference between the first and second coherent light. The second light source is driven based on the difference between the two voltage levels to correct the frequency of the second coherent light.

Apparatus for measuring characteristics of optical fiber

An optical fiber distortion measurement system (i.e., device and method) measures an optical fiber, which is constructed by alternately connecting two kinds of optical fibers whose Brillouin frequency shifts are different from each other. The system sequentially supplies optical pulses to the measured optical fiber while changing their light frequencies, so that Brillouin backscattering beams are output from the measured optical fiber. At first, the system supplies an optical pulse having a prescribed light frequency to the measured optical fiber of a non-distortion state, so that the device produces initial data representing time-related variations of light intensity of Brillouin backscattering light output from the measured optical fiber. Then, the system measures a time-related variation waveform representing light intensity of Brillouin backscattering light, which is output from the measured optical fiber supplied with the optical pulse of the prescribed light frequency. By comparing the measured time-related variation waveform with the initial data, the system determines occurrence of distortion in the measured optical fiber. Thereafter, the system discriminates a kind of the distortion, which corresponds to expansion or contraction, on the basis of a relationship between Brillouin frequency shifts, which are respectively calculated with respect to a detection point and its adjacent point on the measured time-related variation waveform. The Brillouin frequency shift is calculated in accordance with a quadratic approximation formula, which is created on the basis of the initial data.

Optical fiber distortion measurement device and method thereof

An object of the present invention is to provide an optical fiber strain measuring apparatus which can perform precise measurement without causing any fluctuation in signal level. To achieve the above object the present invention comprises: a polarization plane rotation device 105 which rotates a plane of polarization of an optical pulse; a photo-directional coupler 106 which projects an optical pulse projected from the polarization plane rotation device 105 into an optical fiber 107 to be measured, and projects out backscattering light produced in the optical fiber 107 to be measured; a polarization plane rotation device 160 which rotates a plane of polarization of a reference light; a light mixing device 109 for mixing the backscattering light projected out from the photo-directional coupler 106 and the reference light projected from the polarization plane rotation device 160; and a signal processing section 111 which detects the mixed light projected from the light mixing device 109, converts the detected light into an electrical signal and subjects the electrical signal to a predetermined operational processing to obtain a measurement waveform.

Optical fiber strain measuring apparatus

The objective of the present invention is to offer an optical fiber strain-measuring apparatus, which allows the detecting of the amount of strain at an arbitrary distance within a test optical fiber as well as the distance strain distribution, and facilitates the detecting of the back scattered light. In order to achieve the above objective, the present invention comprises an acousto-optic switch 108 which outputs a measuring pulse light, an optical circulator 112 which forwards the measuring pulse light to an optical ring circuit possessing a test optical fiber 124, while allowing the natural Brillouin back scattered light generated from the test optical fiber 124 to travel through the optical ring circuit, a frequency conversion section 132 to successively convert the reference light outputted from an optical directional coupler 102 into a reference pulse train which has its frequency change into a step form, and an acousto-optic switch 134 to output the reference pulse train as a sampling pulse, and the sampling pulse and the natural Brillouin back scattered light outputted from the optical ring circuit are converted into electrical signals by the opto-electric conversion section 138, and the signal processing section 146 measures the strain of the test optical fiber 124 based on these electrical signals.

Optical fiber strain-measuring apparatus

The objective of the present invention is to offer an optical fiber strain-measuring apparatus, which allows the measurement of the strain at an arbitrary position within an optical fiber. An optical frequency conversion section 3 shifts, in a step-wise manner for prescribed frequencies, the frequencies of a continuous light emitted from a light source 1. A sound-light switch 4 coverts into pulses the continuous light forwarded from the optical frequency conversion section 3. When those light pulses are entered into a test optical fiber, back-scattered light is generated. An optical directional coupler 11 branches and forwards to an optical ring circuit and to an optical directional coupler 13 the back-scattered light. A photo-electric converter 14 receives employing heterodyne detection and converts into electric signals the synthesized light signals of the back-scattered light forwarded from the optical directional coupler 11 and the continuous light forwarded from the optical directional coupler 2. A signal processing section 18 reads at an arbitrary timing the electric signals, performs necessary processes, and obtains the amount of strain of the test optical fiber 7.

An optical pulse signal produced by modulating a continuous laser light by means of a first pulse having a period sufficiently shorter than the atomic lifetime in the upper energy state of a rare earth doped fiber is input to an optical amplifier to be measured, while an output signal from the optical amplifier is modulated by a second pulse synchronized with the first pulse and having a phase difference relative to the first pulse which can be optionally set so that rapid phase adjustment relative to the first pulse is possible based on the phase at the time of minimum optical power. The noise figure of the optical amplifier is then measured based on, the maximum photoelectric power (P.sub.AMP +P.sub.ASE) and the minimum photoelectric power P.sub.ASE of the resultant optical signal.

Method and apparatus for measuring the noise figure of an optical

An OTDR measurement device employs optical heterodyne wave detection to perform measurement on optical fibers. Optical pulses are incident on a measuring optical fiber, which in turn outputs backward scattering light. The device performs heterodyne wave detection on the backward scattering light as well as probe light whose frequency is set in proximity to a frequency of the backward scattering light, thus producing a detection voltage. The device provides a differential amplifier which performs amplification on a difference between the detection voltage and a reference voltage to produce a difference signal. An A/D converter converts the difference signal to a digital signal. Square addition is performed on the digital signal to produce a mean square signal representing property of the measuring optical fiber. Herein, calculations are performed on the mean square signal to produce a reference signal, which is then converted to the reference voltage. Herein, the reference signal is produced based on a reference value which is determined in advance such that the difference signal corresponds to an intermediate value of a voltage conversion range of the A/D converter under a state where only the probe light is incident on the device. Moreover, the reference signal is automatically changed to correct a shift of the reference voltage due to disturbance factors such as variations of temperature.

OTDR measurement device

The present invention provides light frequency control apparatus comprising a light pulse signal generating mechanism for generating a light pulse signal of a standard frequency; a light frequency shifting mechanism for circulating this light pulse signal a predetermined number of times, delaying this light pulse signal at each cycle thereby sequentially shifting and outputting the aforementioned light pulse signal; an extracting mechanism for extracting a light pulse signal in the second half of a cycle from the output of the light frequency shifting mechanism; and a polarization control mechanism inserted into the light frequency shifting mechanism for controlling the angle of polarization of the light pulse signal circulating in the light frequency shifting mechanism based on the amount of attenuation of the light pulse signal outputted by the extracting mechanism.

Light frequency control apparatus

A simple, quick and precise method for determining a noise factor of an optical amplifier system is presented and demonstrated with an apparatus based on rare-earth doped optical fibers. The method is based on rapid adjustments of the phase differentials between the input optical signals into and the output optical signals from the optical amplifier to compensate for system variables including the optical fiber lengths within the apparatus as well as in the ancillary devices. A cw laser source is modulated with a first pulse having a significantly shorter cycle than a lifetime of excited atoms within the doped fiber, and the modulated pulses are continually applied to the noise determining apparatus. The optical output signal from the apparatus is synchronized with the first pulse and the optical output signal is further modulated with a series of second pulses having increasing phase differentials in relation to the first pulse. The electrical output power from the noise determining apparatus undergoes a maximum and a minimum values, and the noise factor of the apparatus is calculated by using the values of the respective maximum and the minimum electrical output power.

Method and apparatus for determining noise factor of optical amplifier

The present invention provides light frequency control apparatus comprising a light pulse signal generating mechanism for converting continuous light into a light pulse signal, and outputting this light pulse signal; a light signal generating mechanism for repeatedly generating at predetermined cycles, a light signal, in which a light frequency component therein is shifted to form a staircase shape based on the number of cycles of a loop within which the light pulse signal circulates; and a dummy light generating mechanism for generating dummy light at a timing such that the level of the light signal becomes zero, and supplying this dummy light to the light amplifying mechanism. The aforementioned loop is formed from a light amplifying mechanism for amplifying the light pulse signal outputted from the light pulse signal generating mechanism, light delay mechanism for delaying the light pulse signal a fixed amount; and frequency shifting mechanism for shifting the frequency of the light pulse signal.

A reference light generating mechanism generates reference light, a light frequency component of which varies in a stepped manner at fixed intervals, repeatedly at pre-specified cycles, and generates a timing signal in accordance with this variance. A detecting mechanism detects a frequency difference between a reference light frequency freely selected from among the light frequency component and a feedback light frequency of feedback light fed back so as to conform to the reference light frequency, and synchronizes this with a timing signal, and an output light generating mechanism generates output light, the light frequency of which is controlled in accordance with the frequency difference, and conducts the feedback of this output light to the detecting mechanism as feedback light.

Light frequency synthesizer

A light frequency shifter repeatedly generates, at predetermined cycles, an optical signal, an optical frequency component of which varies in a stepped manner at fixed intervals, and timing generating circuit generates timing signals corresponding to this variation. Detecting mechanisms synchronize, with the timing signal, a frequency difference between a reference light frequency freely selected from the light frequency component and a feedback light frequency of feedback light fed back so as to conform to this reference light frequency, and detect this. Light frequency-regulated light source extracts an output optical signal circulating within a closed loop circuit controlling the light frequency in accordance with the frequency difference described above, and supplies this to a light output terminal, and feeds back a portion of the output optical signal to the detecting mechanism as the feedback light described above.

Growing community of inventors

Tokyo, Japan

Haruyoshi Uchiyama