Optical waveguides – Polarization without modulation
Reexamination Certificate
1998-10-30
2001-05-15
Lee, John D. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S003000, C385S008000
Reexamination Certificate
active
06233370
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an interference measurement apparatus and a probe used for an interference measurement apparatus, more particularly, to an interference measurement apparatus and a probe used for an interference measurement apparatus which utilize a phase modulation method.
FIG. 11
shows a constitutional view of a conventional interference measurement apparatus (see the Publication of Unexamined Japanese Patent Application No. 64-88202).
This interference measurement apparatus comprises a light source instrument
111
, a half mirror
113
, a movement corner cube
114
, a reference corner cube
115
, a polarization beam splitter
116
, detectors
117
and
118
, and a signal processing circuit.
In such interference measurement apparatus, a luminous flux P emitted from the light source instrument
111
is divided into the measurement luminous fluxes P
1
and P
2
by the half mirror
113
as the beam splitter. The measurement luminous flux P
1
is reflected by the movement corner cube
114
serving as a reflection means disposed at a measurement position on the measurement optical path. The reference light P
2
is reflected by the reference corner cube
115
disposed on the reference optical path. The interference light P
3
of both luminous fluxes is guided to the polarization beam splitter
116
and is separated into the P and S components by the polarization beam splitter
116
. The interference light of the P component is guided to the detector
117
, and the interference light of the S component is guided to the detector
118
. In accordance with the interference state based on the movement of the movement corner cube
114
, the interference signals Q
1
and Q
2
shifted by 90° from each other are inputted to the signal processing circuit from the detectors
117
and
118
, and subjected to a predetermined signal processing by the signal processing circuit, so that the distance to the movement corner cube
114
is measured.
Next, a second background known art will be described.
FIG. 12
shows a conventional bulk type phase modulation interference measurement apparatus (see the Publication of Unexamined Japanese Patent Application No. 64-12205).
In this apparatus, the coherent light P emitted from a laser light source
121
is split into a reference light P
1
and a measurement light P
2
, and the reference light P
1
is reflected by a reference prism
123
. The measurement light P
2
is reflected by a measurement prism
124
, and the returned reference light P
1
and the returned measurement light P
2
are allowed to interfere with each other and the interfered light is guided to a photodetector
125
. Here, a measurement prism
124
is moved to the arrow direction or to opposite direction to the arrow, and the reference prism
123
is vibrated with a predetermined period as shown by the arrow. The difference of the optical distance of the reference light P
1
from that of the measurement light P
2
is relatively changed with the predetermined period, and the interference signal based on the interference light which changes in response to the change of that difference is obtained by the photodetector
125
. In the manner described above, the direction of the phase change of the measurement light (movement direction of the measurement prism
124
) can be obtained, the movement amount of the measurement prism
124
can be obtained without an influence of the DC bias component based on the light amount or the like.
However, in the first conventional background art, the structure of the optical system is complicated. In the second conventional background art, a driving section for mechanically driving the reference prism is necessary, so, the structure of the control system is complicated. Moreover, in the first and second conventional background arts, since the prism is used as the reflection mirror, the range of use is limited by the size of the prism itself and an axial shift may occur, and it is hard to handle it.
SUMMARY OF THE INVENTION
From the viewpoint of the above described circumstances, the object of the present invention is, by adopting a phase modulating method, to make an optical system simplified and to perform signal processing for a direction discrimination function and a high resolving detection function by one light receiving section.
The present invention achieves a phase modulation system having no mechanical driving section by adopting phase modulation method in a waveguide device type. Moreover, the object of the present invention is to simplify a waveguide pattern so as to fit to mass production, by forming two signals having different phases only with one waveguide.
Another object of the present invention is, by adopting a push-pull type phase modulation method, to reduce an applied voltage to approximately half and to make a voltage amplitude at the time of modulation small, thereby achieving a low power consumption type apparatus. Moreover, the object of the present invention is to provide an apparatus in which a detection precision of the displacement is not influenced by a manufacturing error of a wave plate.
In a first embodiment of the present invention, the object of the present invention is to make it easy to handle an apparatus by adopting a plane mirror as a reflection mirror and to lessen an axis shift. Moreover, the object of the present invention is to provide an interference measurement apparatus which can be easily applied to a bi-axial displacement positioning sensing system by a L-character mirror.
According to the present invention, provided is an interference measurement apparatus comprising:
a light source section for supplying a linearly polarized light;
an optical waveguide section having a phase modulation section provided therein, which gives different phases to TM and TE modes of a incidence luminous flux by a predetermined modulation frequency, the optical waveguide section receiving a luminous flux from the light source section and emitting a phase modulation luminous flux;
a beam splitter section which separates the phase modulation luminous flux subjected to the phase modulation by the optical waveguide section into a measurement luminous flux and a reference luminous flux depending on each polarization direction, and allows the measurement luminous flux to travel to a measurement optical path where a measurement objective is arranged as well as the reference luminous flux to travel to a reference optical path where reference reflection section is arranged;
a light receiving section which receives an interference luminous flux obtained by interfering the reference luminous flux and the measurement luminous flux, the reference luminous flux returning from the reference optical path via the beam splitter section and the measurement luminous flux returning from the measurement optical path via the beam splitter section; and
a displacement measurement section which extracts a frequency component, phases of which are shifted by 90° each other, from the light receiving section, and measures a displacement of the objective based on the extracted signal.
According to the present invention, provided is a probe used for an interference measurement apparatus comprising an optical waveguide module, the optical waveguide module including:
an incidence terminal for receiving a linearly polarized light;
a phase modulation section which gives different phases to TM and TE modes of the linearly polarized light by a predetermined modulation frequency;
an emission terminal which emits a phase modulation luminous flux; and
an optical waveguide having the incidence terminal and the emission terminal,
wherein the optical waveguide module is formed of a substrate exhibiting an electro-optic effect, which receives a linearly polarized light so that a polarization direction thereof is approximately 45° relative to a surface of the substrate, and a signal for a predetermined frequency is applied to the phase modulation section of the optical waveguide module, thereby allowing the TM and TE modes of the li
Fujino Makoto
Hori Nobuo
Nagano Shigenori
Foley & Lardner
Kabushiki Kaisha Topcon
Lee John D.
Song Sarah N
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