JPH0117081B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wavelength-controlled laser-applied optical sensor that can perform optical measurement with ease and high precision.

Recently, attempts have been made to optically detect physical changes such as temperature and pressure.
This type of optical sensing system has many advantages, such as excellent explosion-proof safety. Naturally, with conventional systems, it is difficult to achieve sufficiently high measurement accuracy, and the system configuration becomes considerably complex, making it difficult to realize an all-optical sensing system. Moreover, there are still some problems in effectively demodulating the laser light information modulated by the optical sensing element.

The present invention was made in consideration of these circumstances, and its purpose is to provide a highly practical wavelength-controlled laser applied optical system that can perform all-optical, simple, and highly accurate optical measurement. The goal is to realize and provide sensors.

That is, in the present invention, for example, when the wavelength interval is 10 Å or more,
Using a 10-channel wavelength-controlled laser with a wavelength of 0.7 to 1.5 μm, an optical sensing element detects the 10-channel laser light information modulated by an external force, making it possible to perform optical measurement with an accuracy of, for example, ^2.10 . This effectively achieves the above objectives.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an optical sensor system according to the present invention. The wavelength swept laser light source 1 is
For example, it generates laser light whose wavelength is controlled by changing the effective resonator optical path length of the laser active layer. Sweeping and outputting. Note that the output laser light may be a combination of a plurality of wavelength components. The output laser beam is transmitted through the optical fiber 2 and guided to the integrated optical sensor 3 provided at the site to be examined. This integrated optical sensor 3
As will be explained in detail later, this device is equipped with an optical sensing element that changes the light propagation characteristics in response to external forces such as pressure, temperature, and humidity, and this modulates the laser beam according to the external force. It is being said. The laser light modulated by this optical sensor 3 is guided to an integrated optical demodulator 5 via an optical fiber 4, where it is demodulated and detected for each wavelength component. This demodulated detection output is led to a display 6 to display the measurement results.

Now, the optical sensor 3 is configured as shown in FIG. 2, for example. The wavelength-controlled laser beam transmitted through the optical fiber 2 is converted into a parallel beam by an optical coupler 11 via a lens 12 and guided to a demultiplexer 13 . The demultiplexer 13 is made of, for example, a grating lens, and wavelength-selectively demultiplexes the laser beam to a focal position specific to each wavelength. An optical sensing element 14 is provided at the focal position of the laser beam of a specific wavelength that is wavelength-selectively demultiplexed by the demultiplexer 13 to change the optical propagation characteristics, such as the transmitted wavelength and transmittance, as a whole in response to an external force. It is being
The optical sensing element 14 can detect, for example, temperature, pressure,
It consists of other members that expand and contract in response to physical external forces, and thereby the wavelength-selectively demultiplexed laser light is selectively transmitted and propagated in accordance with the external forces. As a simple example, the optical sensing element ₁₄ is constituted by a cell equipped with a spot hole corresponding to the number of channels _{of wavelength} -controlled laser light. After 10 channels of laser wavelength only wavelengths λ ₁ and λ ₂ are transmitted and propagated, and at another temperature T ₂ wavelengths λ ₂ , λ ₅ , λ ₉
The three channels are adapted for transmission propagation. That is, each of the ten channels of laser light is selectively transmitted and propagated in response to temperature, which is an external force. In other words, the laser light is wavelength-selectively modulated. However, the laser light that has been modulated according to this external force is
The light is input from the focal position corresponding to each wavelength component to a multiplexer 15 consisting of a second grating lens, and is unified by wavelength multiplexing or the like. The light is then focused through a lens 16 and introduced into the optical fiber 4 through an optical coupler 17.

By the way, the laser light propagated through the optical fiber 4 after being modulated by an external force is input to an integrated optical demodulator 5 having the configuration shown in FIG. 3, for example. The demodulator 5 includes an optical coupler 18 that inputs the laser light propagated through the optical fiber 4, a lens 19 that converts the output of the optical coupler 18 into a parallel beam, and a lens 19 that converts the output of the optical coupler 18 into a parallel beam, and converts the collimated laser beam into a parallel beam for each wavelength component. It consists of a grating lens 20 for demultiplexing, and a plurality of light receivers 21a, 21b, . still,
In the figure, 22 is an electrical lead wire bundle for deriving the photoelectric conversion output. The display device 6 is electrically connected via this electrical lead wire bundle 22.

This demodulator 5 wavelength-selectively demultiplexes the wavelength-controlled and swept laser light and is modulated according to an external force, and this is performed by a grating lens 20. The light receivers 21a, 21b, . . . , 21n are arranged at focal positions of the grating lens 20 for each wavelength. Therefore, each light receiver 21
a, 21b, . By the way, these receivers 2
1a, 21b, . . . , 21n are photodiodes having an array structure made of InGaAsP and arranged on an InP substrate. Further, the grating lens 20 is composed of interference fringes or the like formed on the waveguide.

According to the optical sensor configured in this manner, the wavelength-controlled laser light consisting of, for example, ₁₀ channels of wavelength components λ ₁ , λ ₂ , . . . It will be modulated accordingly. Moreover, since the optical sensor 3 is totally sensitive to the external force, all wavelength components are selectively modulated by the external force, that is, transmission and modulation in this case. Therefore, if the optical modulator 4 separates and detects the modulated laser beam for each wavelength component, the modulation information can be obtained, and the external force can be measured from this modulation information.

Further, the modulated laser light includes the following information. In other words, each wavelength component of the laser beam has selective modulation information depending on the external force, so if 10 channels of laser beam are used, 2 ¹⁰ (=
1024) information will exist. This is an extremely large amount of information, in this case more than 10 times that of conventional optical sensors, which exhibit selective wavelength selection characteristics. For example, if the cell's spot hole pitch is set according to the expansion/contraction rate of the cell material, which changes in response to external force, light of each wavelength component can have selective light transmission characteristics at several different external force values. It will be shown. Therefore, from the perspective of external force, each external force value gives the optical sensor 3 a corresponding unique wavelength selectivity, so if each wavelength component is detected here, the above unique external force value can be measured from the combination. It becomes possible to do so. Therefore, the wavelengths of the 10 channels λ ₁ , λ ₂ , ~, λ ₁₀
When using , it is now possible to detect external force with a quantization accuracy of up to 1024 levels, whereas conventionally it was not possible to detect external force with a quantization accuracy of up to 1024 levels.
Further, as is clear from the system configuration described above, the configuration of the optical sensor according to the present invention is extremely simple. In particular, the laser light source 1, the optical sensor 3, the optical demodulator 5, etc. can be individually and simultaneously integrated on the same substrate. For example, on an InP substrate
An optical waveguide is formed by forming an InGaAsP layer, and various lenses, optical sensing elements, etc. can be formed on this optical waveguide, so the structure is very simple and manufacturing is easy. In addition, since it is easy to control and handle, it is highly practical.

By the way, in the above embodiment, the integrated optical sensor 3
Although the laser beam was wavelength-selectively demultiplexed in the above, it may be simply demultiplexed into a plurality of optical paths without regard to the wavelength. In this case, the optical sensing elements interposed in each of the plurality of optical paths should be constructed of filters with mutually different characteristics (wavelength selectivity) such as Liot filters or nonuniformly spaced diffraction gratings. Bye. That is, for example, as shown in FIG.
The split light waves are filtered through filters 24a and 24 having mutually different characteristics (wavelength selectivity).
The optical sensor 3 is configured so as to lead to the multiplexer 25 via lines b, to, and 24n. The filter 24a,
24b, . By making them different, we make their characteristics different from each other. It goes without saying that the above-mentioned Rio filter may be used in place of these non-uniformly spaced diffraction gratings. Furthermore, the grating pitches of the filters 24a, 24b, . Acts as a narrowband filter. In other words, under standard external force conditions _, the filters _24a , 24b _, . Then, in response to an external force, the substantial optical path length (refractive index) is changed to (λ _x + Δλ) and 2 (λ _x + Δλ).
,
3(λ _x +Δλ)... This results in a wavelength selectivity of 3(λ x +Δλ).

Such filters 24a, 24b, ~, 24
If the optical sensor 3 configured with n is used,
The wavelength component of the wavelength-controlled laser beam is selectively transmitted in response to external force, so if that wavelength component is detected, it is possible to measure the external force as in the previous example. . Moreover, even in this case, as in the previous embodiment, several wavelength components each satisfy the transmission condition for a certain external force value,
Since the state of the combination corresponds to the external force value, highly accurate measurement with a large maximum quantization number is possible. Also, at this time, the wavelength of the wavelength control laser is continuously swept, and the filter 24
It is convenient to increase the number of a, 24b, . Furthermore, the system configuration is simple and no special control is required, making it easy to handle. For example, if you set an optical path of 10 channels,
It produces effects that cannot be expected from conventional optical sensors, such as being able to measure a temperature range of 100°C in 0.1°C steps.

By the way, in the above-mentioned example, the filters 24a, 24b, .
It is also possible to realize b, .about.24n, respectively, for example by Fabry-Perot etalons.

As shown in FIG. 6, this Fabry-Perot etalon has a structure in which etalons 27 and 28 are placed parallel to each other on both sides of a sensing material 26 that changes its physical length, that is, the resonant optical path length and its refractive index, depending on external force. has. According to a filter using such a Fabry-Perot etalon, the wavelength selectivity occurs at equal intervals at a predetermined wavelength pitch P as shown in FIG. 7, so that the same effects as in the previous embodiment can be expected. Furthermore, the wavelength pitch P is determined as P=c/ηl, where c is the speed of light, η is the refractive index of the sensing material 26, and l is the physical length of the sensing material 26, so optical design is very easy. be. Furthermore, although this filter is excellent in practicality because it is easy to integrate, it also has drawbacks such as a large size.
The selection of item 6 is important.

As described above with reference to the embodiments, according to the present invention, it is possible to measure external force in an all-optical manner, in a simple manner, and with high accuracy. In addition, since functions can be integrated individually, manufacturing and system configuration are simple and highly practical, producing tremendous effects that could not be expected in the past.

Note that the present invention is not limited to the above embodiments. For example, a wavelength-controlled laser may be one in which multiple laser beams set to different wavelengths are synthesized and wavelength-multiplexed, one in which the wavelength of the output laser beam is changed in a time-divisional manner, or one in which the wavelength of the output laser beam is changed in a time-sharing manner, or one in which the wavelength of the output laser beam is changed in a time-division manner, or one in which the wavelength of the output laser beam is changed in a continuous manner. The wavelength may be swept. Further, the wavelength range of the laser beam, the number of channels, the characteristics of the filter constituting the optical sensor, etc. may be determined according to the specifications. Furthermore, as an external force to be measured,
The target is not limited to pressure, temperature, and humidity, but can also be targeted to gas concentration, etc. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, and FIG. 1 is a system configuration diagram, FIG. 2 is a schematic configuration diagram of an integrated optical sensor, FIG. 3 is a schematic configuration diagram of an integrated optical demodulator, and FIG. FIG. 4 is a block diagram showing another example of an integrated optical sensor, FIGS. 5 a to f are diagrams showing filter characteristics, FIG. 6 is a block diagram of a filter using a Fabry-Perot etalon, and FIG. FIG. 3 is a diagram showing characteristics. DESCRIPTION OF SYMBOLS 1... Wavelength swept laser light source, 2, 4... Optical filter, 3... Integrated optical sensor, 5... Integrated optical demodulator, 6... Display, 11, 17, 18... Optical coupler, 12, 16, 19...lens, 13, 2
3... Demultiplexer, 14... Optical sensing element, 1
5, 25... Multiplexer, 20... Grating lens (branching filter), 21a, 21b, ~, 21n...
...Receiver, 22...Electric lead wire bundle, 24a, 2
4b, ~, 24n... Filter, 26... Sensing substance, 27, 28... Fabric Perot etalon.

Claims (1)

[Scope of Claims] 1. A demultiplexer that demultiplexes a wavelength-controlled laser beam into a plurality of optical paths, and a demultiplexer that is interposed in each of the plurality of optical paths to adjust the propagation characteristics of the demultiplexed laser beam as a whole according to an external force. A variable optical sensing element, a multiplexer for combining the demultiplexed laser beams that have passed through each of the optical paths, and a means for detecting the wavelength component of the laser beam combined by the multiplexer to measure the external force. A wavelength-controlled laser-applied optical sensor characterized by comprising: 2. The optical sensing element consists of a plurality of filters consisting of Fabry-Perot etalons provided corresponding to the number of wavelengths of laser light, and simultaneously changes the product of the physical length between the mirrors of each etalon and the refractive index in response to an external force. The wavelength-controlled laser-applied optical sensor according to claim 1, which is variable.