U.S. patent application number 12/109739 was filed with the patent office on 2008-10-02 for magnetic field measuring apparatus capable of measuring at high spatial resolution.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Shigeki HOSHINO, Mizuki IWANAMI, Masato KISHI, Masahiro TSUCHIYA.
Application Number | 20080238419 12/109739 |
Document ID | / |
Family ID | 34879672 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080238419 |
Kind Code |
A1 |
IWANAMI; Mizuki ; et
al. |
October 2, 2008 |
MAGNETIC FIELD MEASURING APPARATUS CAPABLE OF MEASURING AT HIGH
SPATIAL RESOLUTION
Abstract
A condenser lens is incorporated into the end portion of a
magnetic field measuring apparatus including a magneto-optical
crystal. Alternatively, the end portion of the magnetic field
measuring device includes an optical fiber having a core diameter
smaller than that of a normal single-mode optical fiber.
Inventors: |
IWANAMI; Mizuki; (Tokyo,
JP) ; HOSHINO; Shigeki; (Tokyo, JP) ;
TSUCHIYA; Masahiro; (Tokyo, JP) ; KISHI; Masato;
(Tokyo, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
34879672 |
Appl. No.: |
12/109739 |
Filed: |
April 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10927376 |
Aug 27, 2004 |
7385393 |
|
|
12109739 |
|
|
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Current U.S.
Class: |
324/244.1 |
Current CPC
Class: |
G01R 33/0322 20130101;
G01R 31/002 20130101 |
Class at
Publication: |
324/244.1 |
International
Class: |
G01R 33/032 20060101
G01R033/032 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
JP |
52859/2004 |
Claims
1. A magnetic field measuring apparatus comprising: a
magneto-optical crystal as a magnetic field detecting element; a
measuring system comprised of a plurality optical devices; and an
optical fiber connecting between the magneto-optical crystal and
the measuring system; wherein the optical fiber has a core diameter
smaller than that of a single-mode optical fiber.
2. The magnetic field measuring apparatus according to claim 1,
wherein the optical fiber having the core diameter smaller than
that of the single-mode optical fiber is a high-numerical-aperture
fiber or a photonic crystal fiber.
Description
[0001] This application claims priority to prior application JP
2004-52859, the disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for measuring
a magnetic field closely above an integrated circuit or a
large-scale-integration device (hereinafter referred to as IC/LSI),
an IC/LSI package, and a printed circuit board.
[0004] 2. Description of the Related Art
[0005] FIG. 1A is a schematic view showing an example of a
conventional magnetic field measuring apparatus using optical
technology. This magnetic field measuring apparatus includes a
magneto-optical crystal (hereinafter referred to as MO crystal) as
a magnetic field detecting element, optical fibers, and optical
devices. Such a magnetic field measuring apparatus is disclosed in,
for example, Tsuchiya, Yamazaki, Wakana, and Kishi, "Hikari faiba
tan jiki kogaku (FEMO) purobu ni yoru bisho ryoiki maikuro ha tai
jikai bumpu sokutei (Microscopic Distribution Measurements of
Microwave Frequency Magnetic Fields by Fiber-Edge Magneto-Optic
(FEMO) Probing)", Nihon Oyo Jiki Gakkaishi (Journal of the
Magnetics Society of Japan), Vol. 26, No. 3, pp. 128-134 (2002)
(hereinafter referred to as Document 1).
[0006] FIG. 1B is an enlarged view of the end portion of this
magnetic field measuring apparatus. The end portion includes an
optical fiber 3, an MO crystal 12 attached to the end of the
optical fiber 3, and a dielectric film 13 formed onto the bottom of
the MO crystal 12. The dielectric film 13 is for reflecting light
incident on the MO crystal 12.
[0007] The principle of magnetic field detection in this magnetic
field measuring apparatus will be described schematically below.
The light emitted from a continuous-wave-generating semiconductor
laser light source 2 is amplified by a fiber amplifier (light
amplifier) 4-1. The amplified light passes through a polarization
controller 5 and an optical circulator 6, and becomes
perpendicularly incident on the MO crystal 12 from the end of the
optical fiber 3. The incident light is reflected by the dielectric
film 13 formed onto the bottom of the MO crystal 12, and returns to
the optical fiber 3. Between incidence on the MO crystal 12 and
return to the optical fiber 3, the light is polarization-modulated
due to the Faraday effect according to the intensity of an external
magnetic field.
[0008] The polarization-modulated light passes through the optical
circulator 6 again, and is then intensity-modulated by an analyzer
7. The intensity-modulated light is amplified by another fiber
amplifier 4-2 and then converted photoelectrically by a
photodetector 8. The photocurrent from the photodetector 8 is input
into a spectrum analyzer 10 through a coaxial cable 9. The spectrum
analyzer 10 detects the peak of the photocurrent as a signal caused
by the external magnetic field.
[0009] In the principle of this measuring system, since the
intensity of the signal detected by the spectrum analyzer 10 varies
according to the intensity of the external magnetic field, the
magnetic field distribution can be measured by changing the
position of the MO crystal 12 above a measured object 11.
[0010] When the external magnetic field is measured by using the
conventional magnetic field measuring apparatus shown in FIGS. 1A
and 1B, the spatial resolution is determined by the volume of the
probe light propagating in the MO crystal 12. The smaller the
volume of the probe light, the higher the spatial resolution.
[0011] As shown in FIG. 2, the volume of a probe light 15 in the MO
crystal 12 is approximately defined as the volume of the following
cylinder. That is to say, the volume of the probe light in the
crystal is equal to the volume of the cylinder having a diameter
equal to the diameter of a core 14 of the optical fiber 3 and a
height equal to the thickness of the MO crystal 12. This is
disclosed in, for example, Wakana, Yamazaki, Iwanami, Hoshino,
Kishi, and Tsuchiya, "Study of the Crystal Size Effect on Spatial
Resolution in Three-Dimensional Measurement of Fine Electromagnetic
Field Distribution by Optical Probing", Jpn. J. Appl. Phys. Vol. 42
(2003), pp. 6637-6640 (hereinafter referred to as Document 2).
[0012] The hitherto known magnetic field measuring apparatus has an
end portion including an optical fiber with core diameter about 10
.mu.m and an MO crystal with thickness 11 .mu.m. It is reported
that this magnetic field measuring apparatus has a spatial
resolution capable of distinguishing the magnetic field generated
from parallel conductors spaced at a distance of 10 .mu.m and
constituting a zigzag wiring. This is disclosed in, for example,
Iwanami, Hoshino, Kishi, and Tsuchiya, "Magnetic Near-Field
Distribution Measurements over Fine Meander Circuit Patterns by
Fiber-Optic Magneto-Optic Probe", Proc. 2003 IEEE Symp. on
Electromagnetic Compatibility, pp. 347-352, August 18-22 (2003)
(hereinafter referred to as Document 3). That is to say, the
conventional magnetic field measuring apparatus using optical
technology has achieved a 10-.mu.m-level spatial resolution.
[0013] As described above, a magnetic field measuring apparatus
having a 10-.mu.m-level spatial resolution has been achieved.
However, the 10-.mu.m-level spatial resolution is inadequate for
searching the source of electromagnetic interference (hereinafter
referred to as EMI) in electronic devices or electronic circuits.
An IC/LSI is a typical object searched for EMI sources. When a
recent LSI chip or a compact LSI package having microscopic wiring
is measured, a magnetic field measuring apparatus with higher
spatial resolution is desired.
[0014] As described above, in the case of the magnetic field
measuring apparatus including an MO crystal and optical devices,
the spatial resolution is determined by the volume of the probe
light propagating in the MO crystal. Therefore, in order to achieve
a magnetic field measuring apparatus with a spatial resolution
higher than that of the conventional magnetic field measuring
apparatus including an MO crystal and optical devices, it is
necessary to reduce the volume of the probe light in the MO
crystal.
SUMMARY OF THE INVENTION
[0015] An object of the present invention is to provide a magnetic
field measuring apparatus for measuring the high-frequency magnetic
field generated from an IC/LSI, an IC/LSI package, and a printed
circuit board as the objects searched for EMI sources at high
spatial resolution.
[0016] The present invention attains this object by incorporating a
condenser lens into the end portion of the magnetic field measuring
apparatus. The object is attained by, for example, interposing the
condenser lens between an optical fiber and an MO crystal in the
end portion of the magnetic field measuring apparatus.
Alternatively, the object is also attained by using a
high-numerical-aperture fiber or a photonic crystal fiber having a
core diameter smaller than that of a normal single-mode optical
fiber for the optical fiber in the end portion of the magnetic
field measuring apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a schematic view showing an example of a
conventional magnetic field measuring apparatus using optical
technology;
[0018] FIG. 1B is an enlarged view of the end portion of the
magnetic field measuring apparatus shown in FIG. 1A;
[0019] FIG. 2 is a schematic view of the probe light in the MO
crystal in the end portion of the conventional magnetic field
measuring apparatus shown in FIG. 1A;
[0020] FIGS. 3A and 3B are schematic views showing the end portion
of the conventional magnetic field measuring apparatus and that of
the magnetic field measuring apparatus according to the present
invention, respectively, for comparison;
[0021] FIG. 4 is a schematic view showing the end portion of the
magnetic field measuring apparatus according to a first embodiment
of the present invention;
[0022] FIG. 5 is a schematic view showing an exemplary end portion
of the magnetic field measuring apparatus according to the present
invention;
[0023] FIG. 6 shows the magnetic field distribution measured by the
conventional magnetic field measuring apparatus and that measured
by the magnetic field measuring apparatus according to the present
invention for comparison; and
[0024] FIG. 7 is a schematic view showing the end portion of the
magnetic field measuring apparatus according to a second embodiment
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] First, the principle of the present invention will be
described with reference to FIGS. 3A and 3B. FIGS. 3A and 3B are
schematic views showing the end portion of the magnetic field
measuring apparatus including an MO crystal and optical devices.
FIG. 3A shows the case where probe light 16 is directly incident on
an MO crystal 12. On the other hand, FIG. 3B shows the case where
the probe light 16 is incident on the MO crystal 12 via a condenser
lens 17. By these figures, the volumes of the probe light 15 in the
MO crystal 12 in both cases can be compared easily.
[0026] In the case where the probe light 16 is directly incident on
the MO crystal 12, as explained with FIG. 2, the volume of the
probe light 15 in the MO crystal 12 is approximately equal to the
volume of the cylinder having a diameter equal to the diameter of
the probe light 16 and a height equal to the thickness of the MO
crystal 12.
[0027] On the other hand, in the case where the probe light 16 is
incident on the MO crystal 12 via the condenser lens 17, the light
is converged by the condenser lens 17. Consequently, as shown in
FIG. 3B, the volume of the probe light 15 is obviously smaller than
that in the case of FIG. 3A. As described above, incorporating a
condenser lens 17 into the end portion of the magnetic field
measuring apparatus reduces the volume of the probe light in the MO
crystal 12 as compared with the conventional magnetic field
measuring apparatus. Consequently, the magnetic field measuring
apparatus according to the present invention can measure the
magnetic field at a higher spatial resolution.
[0028] Alternatively, using an optical fiber having a core diameter
smaller than that of a normal single-mode optical fiber for the
optical fiber in the end portion of the magnetic field measuring
apparatus reduces the diameter of the probe light incident on the
MO crystal 12. Consequently, the magnetic field measuring apparatus
according to the present invention can measure the magnetic field
at a spatial resolution higher than that of the conventional
magnetic field measuring apparatus.
[0029] Next, embodiments of the present invention will be
described. The magnetic field measuring apparatus according to a
first embodiment of the present invention has the end portion shown
in FIG. 4. In FIG. 4, the end portion is composed of a single-mode
optical fiber 18, a condenser lens 17, and an MO crystal 12. The
condenser lens 17 is disposed between the single-mode optical fiber
18 and the MO crystal 12. Specifically, the condenser lens 17 is
disposed so as to be in contact with the surface of the MO crystal
12 on which the probe light is incident. Of course, a dielectric
film (not shown) is formed onto the bottom of the MO crystal 12, as
shown in FIG. 1B. This magnetic field measuring apparatus is
composed of the end portion shown in FIG. 4 and the measuring
system shown in FIG. 1. The components of the end portion are
joined with, for example, epoxy resin adhesive.
[0030] As described in conjunction with FIG. 1A, the measuring
system comprises a plurality of the optical devices which are
connected with optical fibers. In FIG. 4, the optical fiber is also
included in the end portion of the magnetic field measuring
apparatus. The optical propagation means in the magnetic field
measuring apparatus are not limited to the optical fibers. Laser
light propagating in the space may be used as probe light. In this
case, the condenser lens is also disposed on the surface of the MO
crystal on which the probe light is incident. The magnetic field
measuring apparatus of the present invention needs a laser light
source. The laser light source may be a continuous wave light
source and a pulsed light source.
[0031] In the magnetic field measuring apparatus composed of the
end portion shown in FIG. 4 and the measuring system shown in FIG.
1, the principle of magnetic field detection or magnetic field
distribution measurement is the same as that in the conventional
magnetic field measuring apparatus described above.
[0032] As described above, the magnetic field measuring apparatus
including an MO crystal and optical devices uses the polarization
modulation due to the Faraday effect of light propagating in the MO
crystal for detecting the magnetic field. Its spatial resolution is
determined by the volume of the probe light in the MO crystal
12.
[0033] For example, incorporating the condenser lens 17 into the
end portion of the magnetic field measuring apparatus as shown FIG.
4 reduces the volume of the probe light in the MO crystal 12 as
compared with the conventional magnetic field measuring apparatus.
Consequently, the magnetic field measuring apparatus according to
the present invention can measure the magnetic field at a spatial
resolution higher than that of the conventional magnetic field
measuring apparatus.
[0034] FIG. 5 shows an exemplary end portion of the magnetic field
measuring apparatus according to the present invention. The end
portion of the magnetic field measuring apparatus is composed of a
cylindrical glass tube 20, a single-mode optical fiber 18, a glass
sleeve 19 for holding the fiber, a cylindrical condenser lens 17,
and an MO crystal 12. A dielectric film (not shown) is formed onto
the bottom of the MO crystal 12. The MO crystal 12 has the shape of
a rectangular solid and is attached to the end of the condenser
lens 17. The condenser lens 17 is held in one end of the glass tube
20. The MO crystal 12 is attached to the exit surface side of the
condenser lens 17 projecting from the glass tube 20. The single
mode optical fiber 18 is held in the other end of the glass tube 20
with the glass sleeve 19. The fiber 18 emits probe light toward the
condenser lens 17. The cylindrical glass tube 20 has a length of
15.8 mm and an outside diameter of 2.8 mm. The cylindrical
condenser lens 17 has a length of 4.4 mm and a diameter of 1.8
mm.
[0035] FIG. 5 is a schematic view in which the glass tube 20 is
partly removed for showing the inside. In FIG. 5, a gap 21 is
provided between the glass sleeve 19 and the condenser lens 17 in
order to reduce the diameter of the probe light in the MO crystal
12. The MO crystal 12 has a plane size of 289 .mu.m by 289 .mu.m
and a thickness of 16.5 .mu.m.
[0036] The exemplary end portion shown in FIG. 5 is connected with
the measuring system composed of a plurality of optical devices
shown in FIG. 1A. For example, an optical connector is used for
connecting the end portion and the measuring system.
[0037] When the magnetic field measuring apparatus composed of the
end portion shown in FIG. 5 and the measuring system shown in FIG.
1 is operated, the volume of the probe light in the MO crystal is
approximately as follows. That is to say, the volume of the probe
light in the MO crystal is equal to the volume of the cylinder
having a diameter of about 5 .mu.m (the diameter of light) and a
height of 16.5 .mu.m (the thickness of the MO crystal). This volume
is less than half the volume of the probe light in the MO crystal
in the above-described conventional magnetic field measuring
apparatus having a 10-.mu.m-level spatial resolution. Therefore,
the magnetic field measuring apparatus according to the present
invention is capable of magnetic field measurement at a spatial
resolution higher than that of the conventional magnetic field
measuring apparatus.
[0038] FIG. 6 shows the magnetic field distribution measured by the
conventional magnetic field measuring apparatus and that measured
by the magnetic field measuring apparatus according to the present
invention for comparison. The measured object is a zigzag wiring
consisting of three parallel conductors spaced at a distance of 5
.mu.m.
[0039] FIG. 6 shows the results obtained when the end portion of
the magnetic field measuring apparatus scans in the direction
crossing the wiring. The conventional magnetic field measuring
apparatus can hardly distinguish the magnetic fields from the
conductors. On the other hand, the magnetic field measuring
apparatus according to the present invention can distinguish the
magnetic fields from the conductors. These results show that the
magnetic field measuring apparatus according to the present
invention has a spatial resolution higher than that of the
conventional magnetic field measuring apparatus.
[0040] Next, a second embodiment of the present invention will be
described. The second embodiment is the magnetic field measuring
apparatus shown in FIG. 1A, wherein the optical fiber in the end
portion has a core diameter smaller than that of a single-mode
optical fiber. Such optical fibers include a
high-numerical-aperture fiber and a photonic crystal fiber. In
either case, this embodiment needs no condenser lens in the first
embodiment.
[0041] Referring to FIG. 7, assume that a magnetic field measuring
apparatus composed of the end portion composed of a
high-numerical-aperture fiber 31 with a core diameter of 5 .mu.m
and an MO crystal 12 with a thickness of 16.5 .mu.m and the
measuring system shown in FIG. 1A is used. In this case, the volume
of the probe light in the MO crystal 12 is approximately equal to
the volume of the cylinder having a diameter of about 5 .mu.m and a
height of 16.5 .mu.m. The comparison between the magnetic field
distribution measured by the conventional magnetic field measuring
apparatus and that measured by the magnetic field measuring
apparatus according to the present embodiment is also as shown in
FIG. 6. Therefore, the magnetic field measuring apparatus according
to the second embodiment of the present invention can also measure
the magnetic field at a spatial resolution higher than that of the
conventional magnetic field measuring apparatus.
[0042] The magnetic field measuring apparatus according to the
present invention has the following advantageous effects.
[0043] First, it can search electronic circuits, particularly
recent LSIs having microscopic wiring, for EMI sources in detail
and precisely.
[0044] Second, since it can measure the current distribution with a
high degree of accuracy by measuring the magnetic field at high
spatial resolution, it can perform an operation check or a fault
diagnosis/analysis of complicated electronic circuits.
* * * * *