JPH04299203A - Absolute length measurer - Google Patents

Abstract

PURPOSE:To realize an absolute length measure being small-sized and inexpensive and having long lifetime. CONSTITUTION:An absolute length measurer measures an absolute distance by making a plurality of lights different in wavelength enter an interferometer section 6 for length measurement and by utilizing a phase difference between interference phase signals obtained from this interferemeter section 6 for length measurement. The measurer has a construction wherein an integrated multi- wavelength LD light source 1 constructed by integrating a plurality of LDs 11 to 13 including at least one variable-wavelength LD 13 and a beam combiner 16 formed of fibers 15a to 15c or optical waveguides for combining emission lights of these LDs in a plurality is employed for a light source emitting a plurality of lights being different in wavelength.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an absolute length measuring device that measures the absolute distance to an object using optical interference, and in particular, a multi-wavelength laser diode (
By using a light source (hereinafter simply referred to as LD), a compact and highly reliable device is realized.

0002

2. Description of the Related Art Various reports have been made regarding absolute length measuring devices, but none have been put to practical use yet. The reason for this is that the configuration of the light source required to perform absolute length measurement becomes extremely complicated. The currently reported absolute length measuring device with an accuracy of 1 x 10-7 or higher uses a CO2 (carbon dioxide) laser as a light source, and has multiple measuring devices with different wavelengths in the length measuring interferometer. This is a length measuring device that uses the fractional method to sequentially select and inject light and determine the absolute distance from the difference in interference phase obtained.

[0003] However, the CO2 laser is not a gas laser.
As a result, the equipment is large, has a short lifespan, and is expensive.
The point is that a length measuring device has not yet been commercialized.

0004

[Problems to be Solved by the Invention] The present invention has been made based on the above-mentioned problems of the prior art, and it integrates a plurality of LDs with different wavelengths in the light source section of an absolute length measuring device, and outputs them. The purpose of this invention is to provide a compact, inexpensive, and long-life device by using a multi-wavelength LD light source that combines and emits light.

[0005]

[Means for Solving the Problems] The structure of the present invention for solving the above problems is such that a plurality of lights having different wavelengths are incident on a length measurement interferometer section, and the interference obtained from the length measurement interferometer section is In an absolute length measuring device that measures absolute distance using the phase difference of phase signals, at least one wavelength tunable laser diode is used as a light source that emits a plurality of lights with different wavelengths.
An integrated multi-wavelength laser diode that integrates a plurality of laser diodes including a laser diode and a multiplexer using a fiber or optical waveguide for multiplexing the light emitted from the plurality of laser diodes. It is characterized by a configuration that uses a light source.

[0006]

[Operation] According to the present invention, the light source includes a plurality of L having different wavelengths.
A multi-wavelength LD that integrates D and combines its output with a fiber.
A light source is used. Therefore, it is possible to realize a compact, inexpensive, and long-life absolute length measuring device.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. FIG. 1 is a block diagram showing an embodiment of the absolute length measuring device of the present invention. In FIG. 1, 1 is an integrated multi-wavelength LD light source, and this integrated multi-wavelength LD light source 1 consists of two wavelength-stabilized LDs 11 and 12, an active region 13a, a phase adjustment region 13b, and a wavelength variable region 13c. A 3-electrode wavelength tunable LD13 is integrated, and a wavelength stabilized LD11,1
Fiber input microlenses 14a to converge the light emitted from the 2- and 3-electrode wavelength tunable LDs 13, respectively.
Fibers 15a to 15 that guide the light focused by 14c
c, and a fiber multiplexer 16 that multiplexes light guided by fibers 15a to 15c. 2 is an LD driving current source that controls the wavelength and output of the wavelength stabilized LDs 11, 12 and the three-electrode wavelength variable LD 13; 3 is a collimating source that collimates the light emitted from the integrated multi-wavelength LD light source 1; A microlens, 4 is a half mirror, and 5 is light for monitoring the wavelength difference of the light into which one of the lights branched by the half mirror 4 is incident, multiplexed and output from the integrated multi-wavelength LD light source 1. It is a wavelength meter. Reference numeral 6 denotes a phase difference type length measurement interferometer section consisting of a Michelson interferometer with a 1/8 wavelength plate on one optical path and a polarizing beam splitter. The other light branched by the half mirror 4 is incident on the half mirror 61 which is further branched into two, a 1/8 wavelength plate 62 installed on the optical path on the reference side, and a reference corner. - It consists of a Michelson interferometer consisting of a cube 63 and a corner cube 64 for length measurement installed on the optical path on the length measurement side, and the interference light is converted into s-polarized light by a polarization beam splitter 65. component and p-polarized component,
They are detected by photodetectors 66 and 67, respectively, and the interference phase is measured by an interference phase measuring circuit 68.

The three-electrode wavelength variable LD 13 can continuously vary the frequency of light up to about 0.2% (TYP) by adjusting the current flowing through the phase adjustment region 13b and the wavelength variable region 13c. Therefore, for example, a three-electrode wavelength-tunable LD 13 and a wavelength-stabilized LD with a 1% wavelength difference.
By integrating the wavelength stabilizing LD11 in the 12 and 1.3 μm bands, the combined wavelength Λ1 = 1.5 mm (variable by 0.1% with the 3-electrode wavelength variable LD 13), and the combined wavelength Λ2 = 150 μm.
m (3-electrode wavelength tunable LD13 and wavelength stabilized LD12),
The combined wavelength Λ3 can be set to 15 μm (3-electrode wavelength variable LD 13 and wavelength stabilized LD 11). Furthermore, since the three-electrode wavelength variable LD 13 can be continuously variable, it is possible to respond to changes in span with the same light source.

In such a configuration, the integrated multi-wavelength L
Emitted from D light source 1, collimating microlens 3
The parallel light is split into two by the half mirror 4. One of the lights is reflected by the half mirror 4 and enters the optical wavelength meter, and the wavelength difference is monitored. The other light is
The light passes through the Humira 4 and enters the length measurement interferometer section 6. In the length measuring interferometer section 6, the beam is further branched into two by a half mirror 61. One of the lights (reference light) is reflected by a half mirror 61, passes through a 1/8 wavelength plate 62, is reflected at a reference corner cube 63, and passes through a 1/8 wavelength plate 62 again. and enters the half mirror 61. This reference light is 1/8
By passing through the wave plate 62 twice, the s-polarized light component and the p-polarized light component are separated.
A phase difference of 90° occurs between the polarized light components. The other light (measuring light) passes through the half mirror 61, is reflected by the length measuring corner cube 64, and returns to the half mirror 61.
is incident on the This measurement light has no phase difference between the s-polarized component and the p-polarized component. Both incident lights interfere with each other at a half mirror 61 and enter a polarizing beam splitter 65. The interference light is separated into an s-polarized component and a p-polarized component by a polarizing beam splitter 65, and is incident on photodetectors 66 and 67. The signals detected by the photodetectors 66 and 67 are given a 90° phase difference between the p-wave and the s-wave, so the sin signal and c
The two detected signals are electrically processed by the interference phase measurement circuit 68 to determine the absolute distance.

The absolute length measuring device of the present invention uses a fraction method in which a plurality of lights of different wavelengths are incident on the length measuring interferometer section 6 and the absolute distance is determined from the difference in the obtained interference phases. What is important in the fraction method is how each wavelength value is given, which is determined from the span distance and required measurement accuracy. How to give this wavelength value is the synthetic wavelength ΛN given from the wavelength difference =
To explain using λ1 λN /(λ1 - λN), first, a wavelength difference such that the measurement span Ls≦Λ1 is emitted, and a rough absolute value is specified. At this time, the measurement accuracy determined by the interference phase measurement circuit 68 is assumed to be Λ1/M. Next, emit the next wavelength where Λ1 /M≧Λ2,
Increase the specific measurement accuracy of the absolute value to Λ2/M. By increasing the wavelength accuracy in order of Λ3, Λ4, .

[0011]

Effects of the Invention As described above in detail with the embodiments, according to the present invention, a plurality of LDs with different wavelengths are integrated as a light source of an absolute length measuring device, and their outputs are combined using a fiber. By using a waved multi-wavelength LD light source,
It is possible to realize a compact, inexpensive, and long-life absolute length measuring device, and by using at least one variable wavelength LD for the LD of the multi-wavelength LD light source, it is possible to respond to span changes with the same light source, Furthermore, by integrating a plurality of LDs, it is possible to realize an absolute length measuring device that has the effect of realizing a wide variable width that cannot be achieved with a single wavelength variable LD.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of an absolute length measuring device of the present invention.

[Explanation of symbols]

1 Integrated multi-wavelength LD light source 2 LD driving current source 5 Optical wavelength meter 6 Length measurement interferometer section 11, 12 Wavelength stabilizing LD 13 3-electrode wavelength tunable LD 14a to 14c Microlens for fiber injection 15
a~15c Fiber 16 Fiber multiplexer

Claims (1)

[Claims] [Claim 1] An absolute method in which a plurality of lights with different wavelengths are incident on a length measurement interferometer section, and an absolute distance is measured using the phase difference of interference phase signals obtained from the length measurement interferometer section. In the length measuring device, the light source that emits a plurality of lights with different wavelengths includes a plurality of laser diodes including at least one wavelength tunable laser diode, and the light emitted from the plurality of laser diodes is combined. 1. An absolute length measuring device characterized in that it uses an integrated multi-wavelength laser diode light source that integrates a multiplexer using a fiber or optical waveguide for transmitting waves.