JP2005233646A - Method for measuring group delay time difference, and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group delay time difference measuring method and a device, capable of measuring the group delay time difference in one sitting, relative to a wide wavelength region. <P>SOLUTION: In a light source 11, the plane of the polarization of the laser light generated from a laser 111 is adjusted in the optional direction by a polarized light control element 112, and the laser light is allowed to enter an object of measurement. Outgoing light, emitted from the object to be measured 19 by incidence of the laser light, is transmitted relative to an optional plane of polarization by an analyzer 15, and the intensity to the wavelength of light transmitted through a photodetector 17 is measured relative to each arbitrary wavelength. As light source, one can be used that has a short-pulse laser for generating short pulsed laser light and a medium, having a nonlinear optical effect and outputs the short pulse laser light generated from the short pulse laser, after widening its band by the nonlinear optical effect of the medium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a group delay time difference measuring method and apparatus for measuring a group delay time difference of an object to be measured such as an optical fiber and an optical component.

  For example, in the optical fiber, the ovalization and eccentricity of the core, non-axial symmetry would cause birefringence occurs. This causes the birefringence axis (slow axis and the fast axis), the propagation constant is different for each birefringent axes. Therefore, a group delay time difference is generated in the optical pulse moving along the birefringence axis. Polarization mode dispersion obtained from the group delay time difference is the amount quantitatively representing the spread of the pulse, a significant effect on the transmission characteristics. Therefore, it is necessary to measure the group delay time difference with high accuracy to obtain the polarization dispersion.

  In conventional group delay time difference measuring method, the light source output light on which a linear polarization state by the polarizer, equal angles with respect to the two axes, for example, a predetermined 45 degree in the case of the birefringent axes are orthogonal It is incident on the light entrance (one end of the optical fiber) of the measurement object at an angle. Light emitted from the light exit (the other end of the optical fiber) of the measurement object is transmitted through an arbitrary polarization plane by an analyzer, and the intensity of the transmitted light with respect to the wavelength is measured by a photodetector for each arbitrary wavelength. As a light source, a broadband light source such as EDFA (Er (erbium) doped fiber amplifier), LED, or a semiconductor laser is used. (See Patent Document 1.)

  In this type of measurement method, the measurement points obtained by one measurement is determined by the optical spectral bandwidth of the light source. Therefore, when the above-described broadband light source that generates light having a wide optical spectrum width is used, it is possible to measure at a large number of measurement points by one measurement, but since the output level of the light source is small, the measurement accuracy of the wavelength dependence of the polarization mode dispersion can not help but become lower when the fiber length is greater.

  On the other hand, when using a narrow-band light source that generates light with a high output level but a narrow optical spectrum width, prepare a light source for each wavelength to be measured and measure intermittently with respect to the wavelength. since is performed, light sources having different wavelength bands is more necessary when an attempt is made to measure the relative wide wavelength region. For this reason, there is a problem that measurement conditions differ for each wavelength. In addition, the number of measurements increases in proportion to the number of light sources.

Therefore, with respect to a wide wavelength region, a method and apparatus capable of measuring a group delay time difference it is sought at once.
JP-A-6-34446

  Therefore, in view of the present situation described above, the present invention has an object to provide a group delay time difference measuring method and apparatus capable of measuring a group delay time difference at a time for a wide wavelength region.

  The present invention also provides a group delay time difference measuring method and apparatus capable of measuring a group delay time difference at a time over a wide wavelength region by using a light source having high output, wide bandwidth, and excellent wavelength flatness. It is an issue.

  In order to solve the first problem, the invention according to claim 1 is that a laser beam whose polarization plane is adjusted in an arbitrary direction is incident on a measurement object, and the measurement object is separated from the measurement object by the incidence of the laser beam. A group that transmits outgoing outgoing light with respect to an arbitrary polarization plane, obtains an interval between adjacent extreme values of intensity with respect to the wavelength of the transmitted light, and measures a group delay time difference of a measurement object based on the obtained interval In the delay time difference measuring method, a short pulse laser beam is used as the laser beam, and broadband light generated in the measurement object by the incidence of the short pulse laser due to the nonlinear optical effect of the measurement object is the emitted light. it has to be emitted lies in the group delay time difference measuring method comprising the.

  According to the second aspect of the present invention, a laser beam whose polarization plane is adjusted in an arbitrary direction is made incident on a measurement object, and outgoing light emitted from the measurement object is incident on the arbitrary polarization plane by the incidence of the laser light. In a group delay time difference measuring method for transmitting, obtaining an interval between adjacent extreme values of the intensity with respect to the wavelength of the transmitted light, and measuring a group delay time difference of a measurement object based on the obtained interval, has a nonlinear optical effect A short pulse laser beam is incident on the medium so that the spectrum spread due to the nonlinear optical effect of the medium is maximized, and a short pulse laser beam is incident, and the broadband light emitted from the medium by the incidence of the short pulse laser beam is It consists in the group delay time difference measuring method which comprises causing incident on the measurement object as a laser beam.

  The invention described in claim 3 includes a laser that generates laser light and a polarization control element that adjusts a polarization plane of the laser light generated by the laser, and the polarization plane is adjusted in an arbitrary direction by the polarization control element. A light source that outputs the laser beam to be incident on the measurement object, an analyzer that transmits the outgoing light emitted from the measurement object by the incidence of the laser beam with respect to an arbitrary polarization plane, and the analyzer that has passed through the analyzer In a group delay time difference measuring apparatus comprising a photodetector for measuring the intensity with respect to the wavelength of light for each arbitrary wavelength, the laser of the light source is a short pulse laser that generates a short pulse laser beam, Broadband light generated in the measurement object by the nonlinear optical effect of the measurement object by the incidence of the short pulse laser light is emitted as the emitted light. It consists in the group delay time difference measuring device for.

  According to a fourth aspect of the present invention, there is provided a light source that outputs a laser beam whose polarization plane is adjusted in an arbitrary direction and is incident on a measurement object, and an arbitrary light emitted from the measurement object by the incidence of the laser light. A group delay time difference measuring apparatus comprising: an analyzer that transmits the plane of polarization of the light; and a photodetector that measures the intensity with respect to the wavelength of the light transmitted through the analyzer for each arbitrary wavelength. a short pulse laser for generating a first polarization control element for adjusting the polarization plane of the pulse laser light from the short-pulse laser, is adjusted polarization in any direction by the polarization control element of the first A medium having a nonlinear optical effect on which a short pulse laser beam is incident, and a second polarization that adjusts a polarization plane of broadband light generated by the nonlinear optical effect of the medium by the incidence of the short pulse laser beam A group delay time difference measurement, characterized in that the broadband light whose polarization plane is adjusted in an arbitrary direction by the second polarization control element is output as the laser light and incident on a measurement object. Exists in the device.

  According to the method of claim 1, a short pulse laser beam is used as the laser beam, and broadband light generated in the measurement object by the incidence of the short pulse laser is used as the outgoing light due to the nonlinear optical effect of the measurement object. The emitted light emitted from the measurement object is transmitted with respect to an arbitrary polarization plane, the interval between adjacent extreme values of the intensity with respect to the wavelength of the transmitted light is obtained, and the measurement object is measured based on the obtained interval. since measuring the group delay time difference, when the measurement object is one having a nonlinear optical effect, using a laser for generating a laser beam having a narrow spectral width light source for generating laser light incident on the measurement object also, it is possible to perform highly accurate measurement of the group delay time over the wide wavelength range in a single measurement.

  According to the method of claim 2, a short pulse laser beam is incident on a medium having a nonlinear optical effect by adjusting a polarization plane so that a spectrum spread due to the nonlinear optical effect of the medium is maximized. Broadband light emitted from the medium by the incidence of pulsed laser light is incident on the measurement object with the polarization plane adjusted in an arbitrary direction, and the emitted light emitted from the measurement object by the incidence of the laser light is deflected arbitrarily. The wavefront is transmitted, the interval between adjacent extreme values of the intensity with respect to the wavelength of the transmitted light is obtained, and the group delay time difference of the measurement object is measured based on the obtained interval, so that it enters the measurement object. Even when a laser that generates laser light having a narrow spectral width is used as a light source that generates laser light, high-accuracy group delay time can be measured over a wide wavelength region by a single measurement. .

  According to the apparatus of claim 3, the short-pulse laser beam generated by the short-pulse laser included in the light source is incident on the measurement object with its polarization plane adjusted in an arbitrary direction by the polarization control element, Broadband light generated and emitted in the measurement object due to the nonlinear optical effect of the measurement object due to incidence of the short pulse laser beam is transmitted through an arbitrary polarization plane by the analyzer, and the intensity with respect to the wavelength of the transmitted light is increased. Since the measurement is performed at an arbitrary wavelength by the photodetector, when the measurement object has a nonlinear optical effect, the broadband light generated in the measurement object by the nonlinear optical effect and propagated through the measurement object The distance between adjacent extreme values of the intensity with respect to the measured wavelength of light is obtained, and the group delay time difference of the measurement object can be measured based on the obtained distance. Therefore, even when a laser that generates laser light with a narrow spectral width is used as a light source that generates laser light incident on a measurement object, high-accuracy group delay time can be measured over a wide wavelength region with a single measurement. Can do.

  According to the apparatus of claim 4, the short-pulse laser light generated by the short-pulse laser is incident on the medium having a nonlinear optical effect by adjusting the plane of polarization of the short-pulse laser light by the first polarization control element. The polarization plane of the broadband light generated by the effect is adjusted in an arbitrary direction by the second polarization control element and a light source incident on the measurement object is used, and the light emitted from the measurement object by the incidence of the broadband light is detected. Since an arbitrary polarization plane is transmitted by a photon and the intensity with respect to the wavelength of the transmitted light is measured for each arbitrary wavelength by a photodetector, the adjacent extreme values of the intensity with respect to the wavelength of the light measured for broadband light are measured. The interval can be obtained, and the group delay time difference of the measurement object can be measured based on the obtained interval, and the light source that generates the laser light incident on the measurement object is narrowly narrowed. Even using a laser for generating a laser beam of vector width, it is possible to perform highly accurate measurement of the group delay time over the wide wavelength range in a single measurement.

  As described above, according to the invention described in claim 1 or 3, since the broadband light generated in the measurement object by the incidence of the short pulse laser beam is used, the group delay time difference with respect to the wide wavelength region is used. it is possible to provide a group delay time difference measurement method and device capable of measuring at once.

  According to the invention described in claim 2 or 4, by using a light source that generates broadband light having high output, broadband and excellent wavelength flatness by making short pulse laser light incident on the medium, Te, it is possible to provide a group delay time difference measuring method and apparatus capable of measuring a group delay time difference at once.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 shows an embodiment of a differential group delay measurement apparatus for carrying out the group delay time difference measurement method of the first invention.

  In FIG. 1, the group delay time difference measuring apparatus includes a light source 11 having a short pulse laser 111 that generates a short pulse laser beam and a polarization control element 112 that controls a polarization plane after being in a linear polarization state, and an analyzer 15. And an optical spectrum analyzer 17 as a photodetector. Measurement object apparatus is to be measured 19 is a photonic crystal fiber is an optical fiber having a nonlinear optical effect. The photonic crystal fiber has two orthogonal polarization axes (x, y), and is mounted between the light source 11 and the analyzer 15 so that the polarization plane can be aligned with these optical axes and is detachable. .

  As the polarization control element 112 included in the light source 11, a configuration in which a polarizer, a wave plate, or a combination of both are combined is used depending on the type of the short pulse laser 111. When the short pulse laser 111 generates linearly polarized laser light, the polarization plane may be adjusted in an arbitrary direction by an analyzer composed of a half-wave plate, but the short pulse laser may be incident. If the laser beam 111 generates an elliptically polarized laser beam, the polarization plane is adjusted to an arbitrary direction by an analyzer composed of a half-wave plate after entering a linearly polarized state with a polarizer. It is necessary to do.

  Analyzer 15, the outgoing light emitted from the object to be measured to transmit for any polarization. The optical spectrum analyzer 17 includes a spectroscope that transmits only light of an arbitrary wavelength, and a photodetector that receives the light transmitted through the spectroscope and converts it into an electrical signal. The optical spectrum analyzer 17 corresponds to the wavelength of the light transmitted through the analyzer 15. The intensity can be measured for each arbitrary wavelength and displayed on the display screen.

  When birefringence axes having different propagation constants exist in the measurement object, extreme values (peaks and valleys) are generated in the light intensity with respect to the wavelength of light of a specific polarization plane transmitted through the analyzer 15. This wavelength interval between adjacent peaks and peaks or valleys and valleys corresponds to the difference in group delay time caused by the difference in propagation constant. by obtaining from the display screen of the optical spectrum analyzer to display, it is possible to measure the group delay time difference.

  In the present embodiment, the short pulse laser 111 included in the light source 11 is configured by, for example, a titanium sapphire laser capable of generating a high-output short pulse laser beam. The short pulse laser beam from the short pulse laser 111 is linearly polarized by the polarization controller 112 and the plane of polarization is adjusted in an arbitrary direction. This adjustment, by adjusting the direction of polarization with respect to the birefringence axis of the object to be measured, the difference between the extreme values is performed so as to maximize. Specifically, the adjustment is performed while observing the display screen of the optical spectrum analyzer 17 so that the difference between the displayed extreme values is maximized. Thus, the plane of polarization can be adjusted in an arbitrary direction, and the short pulse laser beam can be incident at a predetermined angle with respect to the birefringence axis of the measurement object 19. As described above, as a result of the polarization plane being adjusted after the short pulse laser light is linearly polarized by the polarizer, the direction of the polarization plane relative to the birefringence axis is such that the polarization plane component is that of the photonic crystal fiber. The angles are equally incident on the two birefringence axes. Incidentally, when the birefringence axes are orthogonal, the angle is 45 degrees.

  By making the short pulse laser light incident on the measurement object 19 made of a photonic crystal fiber, the short pulse laser light is broadened by the nonlinear optical effect of the photonic crystal fiber and propagates through the measurement object 19. Broadband light is emitted from the output end. The emitted light is incident on an analyzer 15 that transmits an arbitrary plane of polarization. The extreme value of the light intensity with respect to the wavelength of the light transmitted through the analyzer 15 is equal to or orthogonal to the direction of the polarization plane of the analyzer 15 that is the same as the polarization plane adjusted by the polarization controller 112 described above. As a result, when the relationship of the polarization plane of the analyzer 15 with respect to the birefringence axis also becomes a predetermined angle, the difference between the extreme values is maximized. Therefore, adjustment of the polarization plane of the analyzer 15 is also performed while viewing the display screen of the optical spectrum analyzer 17.

Broadband light emitted from the photonic crystal fiber, by the birefringence caused by the non-axial symmetry of the photonic crystal fiber, polarization mode for the two birefringent axes (slow axis and the fast axis) different propagation constants, the group delay time difference between the optical pulses traveling along two birefringent axes occurs. When there is a difference in group delay time, the interval between the extreme value and the extreme value of the periodic function with respect to the wavelength (peaks of light intensity peaks and peaks or valleys and valleys) is determined based on the measurement result by the optical spectrum analyzer 17 (see FIG. By setting the interval: Δλ) to the phase difference 2π, the polarization dispersion value τ _p of the measurement object can be obtained by the following equation (1).

τ _p = −λ ² / cLΔλ (1)
Wherein, tau _p deviation dispersion, lambda is the wavelength, c is the speed of light, L is the fiber length. The formation of equation (1) will be described below.

Now, .beta.x the propagation constant of the x-axis direction of the optical fiber, [beta] y the propagation constant in the y-axis direction, the wavelength lambda, when the fiber length is L, the propagation constant difference [Delta] [beta] is Δβ = βx-βy = kB
It is expressed. Where k is the wave number,
k = 2π / λ
Where B is birefringence,
B = (βx−βy) / k
It is expressed.

Then, the phase φ (λ) is φ (λ) = kB (λ) L ··· (2)
From equation (1), the phase difference [Delta] [phi is Δφ = φ (λ + Δλ) -φ (λ)
= [2π · B (λ + Δλ) / (λ + Δλ)] - 2πL · B (λ)
^{= - (Δλ / λ 2)} · 2πL · [B (λ) -λ (dB / dλ)] ··· (3)
It is expressed.

Further, deviation dispersion .tau.p is τp = (1 / c) · [d (βx-βy) / dk]
= (1 / c) · [d (kB) / dk]
= (1 / c) · [B-λ · (dB / dλ)] ··· (4)
From the above formulas (3) and (4),
Δφ = 2πcL · (Δλ / λ ² ) · τ _p
Is obtained. In summary adjusted to be [Delta] [phi = 2 [pi, the relationship of the above formula (1) is obtained.

  When a titanium sapphire laser is used as a short pulse laser and a photonic crystal fiber is used as an object to be measured as in the embodiment of FIG. 1, the nonlinear optical phenomenon in the optical fiber causes an incident of 850 nm laser light. spectrum of the fiber output light, as shown in FIG. 2, is shown a 6 times more spread. In the figure, the horizontal axis represents wavelength and the ordinate indicates the normalized light intensity peaks of both the 1.

  FIG. 3 shows that the light emitted from the fiber having the waveform shown in FIG. 2 is transmitted through an analyzer 15 whose polarization plane is adjusted so as to be at an arbitrary angle with respect to the birefringence axis of the fiber. the shows a waveform of displaying by measuring the intensity to the wavelength of light for each desired wavelength by the optical spectrum analyzer 17. The horizontal axis indicates the wavelength, and the vertical axis indicates the received light intensity. From this display result, a waveform in which extreme values (peaks and valleys) are periodically generated in the light intensity of the transmitted light is observed, and the wavelength interval (Δλ) between the valleys and valleys or the peaks and peaks of the periodic function can be calculated.

  FIG. 4 shows the polarization dispersion value obtained from the above equation (1) using Δλ obtained from the result of FIG. 3 and plotted against the wavelength. From the figure, the polarization dispersion value (round point) between wavelengths (approximately 820 nm to 860 nm) corresponding to the optical spectrum width spread by the optical nonlinear effect is obtained. In the figure, the polarization dispersion value measured by conventional techniques using an interferometer (corner points) are also plotted together. From the figure, it can be seen that the value of polarization mode dispersion obtained in two measurement methods are in good agreement.

  In the embodiment described above, a titanium sapphire laser is used as the short pulse laser, and a photonic crystal fiber is used as the measurement object 19. However, as the short pulse laser, a high output short pulse laser beam with a steep rise is used. Other than a titanium sapphire laser, for example, a combination of a mode-locked fiber laser and an EDFA (Erbium-doped fiber amplifier) can be used. Other than photonic crystal fiber, for example, dispersion flat / decreasing fiber, etc., as long as it has a nonlinear optical effect that generates a broadband light when a short pulse laser beam with a steep rise and a high output is incident be able to.

  When the photonic crystal fiber is the measurement object 19 as in the above-described embodiment, when the fiber output light is measured with an optical spectrum analyzer, it is shown as broadband light in FIG. As is clear from comparison with the measurement results of the output light of a white light source such as a halogen lamp and an LED light source such as a super luminescence diode (SLD) shown for comparison in FIG. fiber output is the largest in the case of the embodiment, it has a wide band also wavelength region than in the SLD. Also, as can be seen from the comparison with the wavelength region used for optical transmission shown together in the figure, in order to measure the group delay time difference, the SLD must use a plurality of light sources having different wavelengths. hand, it is possible to measure the one used wavelength region once in this embodiment. It should be noted that the measurement of the target wavelength region can be performed only once in the same manner as described above by using a short-wave pulse laser having a different center wavelength for the measurement of the other used wavelength region.

  In the above-described embodiment, it is possible to measure the group delay time difference for a wide wavelength region at a time by generating broadband light using the nonlinear optical effect of the measurement object. Is a group delay that implements the group delay time difference measurement method of the second invention that enables a group delay time difference to be measured at once in a wide wavelength region by using a light source having high output, wide bandwidth, and excellent wavelength flatness. 1 shows an embodiment of a time difference measuring device. In the figure, a detailed description thereof will be omitted given the same reference numerals in the apparatus equivalent to the portion shown in FIG.

  In FIG. 6, the group delay time difference measuring apparatus uses a light source 21 that generates broadband light whose optical spectrum is flatly distributed over a wide wavelength region, and a measurement object 19 to be measured by the apparatus is nonlinear. All optical fibers are not limited to optical fibers having an optical effect, and are positioned between the polarizer 13 and the analyzer 15 so as to be able to align with these optical axes and to be detachable. In short, the difference between the apparatus of Figure 1 is in the light source and the object to be measured, the other portions are substantially the same.

  The light source 21 includes a short pulse laser 211 made of, for example, a titanium sapphire laser that generates short pulse laser light, and a first polarization controller that adjusts the polarization state and the polarization plane of the short pulse laser light generated by the short pulse laser 211. 212, a medium 213 having a nonlinear optical effect, and a second polarization control element 214 that adjusts the polarization state and polarization plane of the broadband light from the medium 213. With this configuration, the short pulse laser beam generated by the short pulse laser is linearly polarized by the first polarization controller 212 and the polarization plane is adjusted in an arbitrary direction and incident on the medium 213. 213 is emitted by generating a broadband light optical spectrum is flat distributed over a wide wavelength region by the nonlinear optical effect. The broadband light emitted from the medium 213 is output from the light source 21 with the polarization state and plane of polarization adjusted by the second polarization control element 214. The broadband light output from the light source 21 is generated based on the high-power laser beam, so although the bandwidth is widened, the output level is configured using the LED mentioned as the conventional example. Larger than the light source.

  The light source 21 that generates broadband light is configured using the phenomenon that when a high-power short pulse laser beam is incident on a medium 213 having an optical nonlinear effect, the optical spectrum of the laser beam emitted from the medium is broadened. For example, when a photonic crystal fiber is used as the medium 213 and a short pulse laser beam (wavelength 790 nm) generated by a titanium sapphire laser is incident on the medium 213, the emitted light from the medium has an optical spectrum as shown in FIG. Is broadened (450 nm to 1550 nm) due to the spread of. This phenomenon is caused by the fact that when high-intensity light is confined in a narrow core region of about 10 μm in the optical fiber, the intensity density is effectively increased and a nonlinear optical phenomenon called self-phase modulation occurs.

Self-phase modulation occurs when a short pulse laser beam with high output and short pulse (steep rise / fall characteristics) is incident on an optical medium, etc., and is caused by a refractive index change (light power-effect) proportional to the electric field strength. This is a phenomenon in which phase modulation occurs in the short-pulse laser beam. In addition, the generation of broadband light occurs due to the combined effect of self-phase modulation, cross-phase modulation, and four-light mixing generated in the optical fiber. Generating broadband light is also confirmed short fibers of a few tens of cm in these methods.

  Note that a laser beam having a wide band due to the nonlinear optical effect of the medium 213 may cause a group delay time difference in the process of propagating through the medium 213. In the case of the broadband light in which such a group delay time difference has occurred, if the polarizer is simply transmitted through any polarization plane, a valley occurs in the light intensity depending on the wavelength. Therefore, the second polarization control element 214 is provided with an analyzer that extracts only the linearly polarized wave of the slow axis or the fast axis. In this way, broadband light having a flat light intensity over a wide band can be obtained. The light transmitted through the polarization plane of one of the linearly polarized waves by the polarizer of the polarization control element 214 is adjusted in an arbitrary direction by the analyzer composed of the half-wave plate of the polarization control element 214 and measured. 19 enters.

  The adjustment of the polarization plane by the analyzer of the polarization control element 214 described above is performed by adjusting the direction of the polarization plane that passes through the analyzer with respect to the birefringence axis of the optical fiber that is the measurement object. By this adjustment, when the polarization plane component is at an angle that is uniformly incident on the two birefringence axes of the optical fiber that is the object to be measured, the extreme values of the peaks and valleys of the light intensity generated by the group delay time difference are obtained. Since the difference is maximized, the adjustment is performed while viewing the display screen of the optical spectrum analyzer 17 that is a photodetector, as in the embodiment described with reference to FIG.

  When the medium length is short and the polarization dispersion value is small, and as a result, the group delay time difference does not occur or is extremely small, the second polarization control element 214 has a slow axis or a fast axis. It is not necessary to have an analyzer that extracts only one of the linearly polarized waves.

It illustrates an embodiment of a differential group delay measurements implementing the apparatus of the first invention. Wavelength for explaining a short pulse broadening phenomena caused by nonlinear optical effects of the fiber - is a graph showing the light intensity. It is a graph which shows the optical spectrum analyzer observation waveform in the apparatus of FIG. Is a graph illustrating the consistency of a dispersion obtained by dispersing the prior art obtained by the apparatus of FIG. The results of measuring the photonic crystal fiber output light in the optical spectrum analyzer is a graph comparing a conventional light source of the output light. It illustrates an embodiment of a differential group delay measurements implementing the apparatus of the second invention. It is a graph of the wavelength-light intensity which shows the typical example of an optical nonlinear effect.

Explanation of symbols

11, 21 Light sources 111, 211 Short pulse laser 112 Polarization control element 15 Analyzer 17 Photo detector 19 Measurement object 212 First polarization control element 213 Medium 214 Second polarization control element

Claims (4)

A laser beam whose polarization plane is adjusted in an arbitrary direction is incident on the measurement object, and the outgoing light emitted from the measurement object by the incidence of the laser beam is transmitted through the arbitrary polarization plane. In a group delay time difference measurement method for obtaining an interval between adjacent extreme values of intensity with respect to a wavelength and measuring a group delay time difference of a measurement object based on the obtained interval,
Using the short-pulse laser beam as the laser beam by the nonlinear optical effect in which the measurement object has, and the broadband light generated within the object to be measured by the incidence of the short pulse laser to emit as the outgoing light A method for measuring a group delay time difference. A laser beam whose polarization plane is adjusted in an arbitrary direction is incident on the measurement object, and the outgoing light emitted from the measurement object by the incidence of the laser beam is transmitted through the arbitrary polarization plane. In a group delay time difference measurement method for obtaining an interval between adjacent extreme values of intensity with respect to a wavelength and measuring a group delay time difference of a measurement object based on the obtained interval,
For a medium having a nonlinear optical effect, a short pulse laser beam is incident after adjusting the plane of polarization so that the spectrum spread due to the nonlinear optical effect of the medium is maximized, and is emitted from the medium by the incidence of the short pulse laser beam. group delay time difference measuring method which comprises causing incident on the measurement object broadband light as the laser beam. It has a laser that generates laser light and a polarization control element that adjusts the polarization plane of the laser light generated by the laser, and outputs and measures laser light whose polarization plane is adjusted in an arbitrary direction by the polarization control element A light source that is incident on the object, an analyzer that transmits the outgoing light emitted from the measurement object by the incidence of the laser beam with respect to an arbitrary polarization plane, and an intensity with respect to the wavelength of the light that has passed through the analyzer In a group delay time difference measuring apparatus comprising a photodetector for measuring each wavelength,
The laser of the light source is a short pulse laser that generates short pulse laser light,
Group delay time difference measuring device, characterized in that to emit broadband light generated within the measuring object by a nonlinear optical effect having said measured object by the incidence of the short pulse laser light to the measurement target as the emitted light . A light source that outputs a laser beam whose polarization plane is adjusted in an arbitrary direction and enters the measurement object, and an analyzer that transmits the outgoing light emitted from the measurement object by the incidence of the laser beam with respect to the arbitrary polarization plane And a group delay time difference measuring apparatus comprising a photodetector that measures the intensity with respect to the wavelength of the light transmitted through the analyzer for each arbitrary wavelength,
The light source is
A short pulse laser that generates short pulse laser light;
A first polarization control element for adjusting the polarization plane of the pulse laser light from the short-pulse laser,
A medium having a nonlinear optical effect on which a short pulse laser beam whose polarization plane is adjusted in an arbitrary direction by the first polarization control element is incident;
A second polarization control element that adjusts a polarization plane of broadband light generated by the nonlinear optical effect of the medium by incidence of the short pulse laser beam,
The group delay time difference measuring apparatus characterized in that the broadband light whose polarization plane is adjusted in an arbitrary direction by the second polarization control element is output as the laser light and incident on a measurement object.

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