JP2894829B2 - Polyimide waveguide as optical sensor - Google Patents

Description

The invention is used for the quantitative detection of liquids in the vapor phase, in particular polar liquids in the vapor phase, and for the detection of NH ₃ , “NH ₄ OH”, NO ₂ and N ₂ O _5. The present invention relates to a polyimide waveguide as an optical sensor.

Polyimides are used as waveguide materials and as coatings and fillers for electronic embedding materials in optoelectronics. This utility of the polyimide arises from its sensitivity to "humidity" due to the interaction of the vapor phase of the liquid components near the surface of the polyimide. Humidity measurements are usually obtained in two ways. For example, in the hair hygrometer method, the dependence of the length of the hair or textile fibers on the humidity is measured, in particular with specially prepared hair and textile fibers. In another method, a capacitive treatment is performed using a polymer film, and the "humidity" is measured by a change in capacitance (a humidity and temperature indicating device, Driesen + Cologne Company, Tangstet). See the product description for the HMI32 model).

Further, a single-layer polyimide waveguide is known as a sensor using an uncured polyimide film for qualitative measurement of water (Applied Physical Letters (Ap.
pl.Phys. Lett.), 52, page 10, 1988). However, these devices do not allow for the quantitative detection of water and other liquids.

Therefore, "humidity", ie the moisture content in the air, and
The content of a particular molecule in the vapor phase of the liquid containing the molecule is
It is necessary to provide a measurement plan for quantitative measurement.

Surprisingly, liquid molecules in the vapor phase, especially polar molecules in the vapor phase, are involved in the optically anisotropic interaction with the polyimide surface, and the interaction can be optically detected and quantitatively measured. Have been found. The optical sensor of the present invention can be used repeatedly.

This objective has been achieved by producing a polyimide waveguide that functions as an optical sensor and has several advantages over known measurement methods.

The measuring method has the following features: a) the detection and measurement are performed optically; b) the detected signal can be digitally displayed; c) the method compares and measures the phase difference of the two polarized light. Independent of the variation of the absolute value, thus allowing an accurate measurement of the phase difference; d) the sensor can function in vacuum as well as under various pressure conditions; e) the method can be applied to the vapor phase Works for some liquids, especially polar liquids; and f) The method can distinguish water and other liquids separately.

The present invention relates to a polyimide waveguide containing at least two layers of polyamide-imide or perfluorinated polyimide, and a method for detecting humidity using the waveguide.

It is an object of the present invention to use a polyimide waveguide as an optical sensor for detecting liquid in a vapor phase.

Another object of the present invention is to provide a polyimide waveguide with NH ₃ , “NH ₄ O
H ", is to use as an optical sensor for detecting the NO ₂ and N ₂ O _5.

Still another object of the present invention is to provide a structured polyimide waveguide in the form of a strip waveguide, an interferometer structure or a directional coupler structure as an optical sensor for detecting a liquid in a vapor phase. To use.

Polyimide waveguide, for example, HFDA-ODA, HFDA-HFDAM
-33, HFDA-HFDAM-44 or HFDA-HFDAM-33 and HFD
Polyamide-imides and perfluorinated polyimides such as the combination of A-HFDAM-44 ("polyimide (s)")
). The meanings of these abbreviations are shown below: HFDA: hexafluoro-iso-propylidene-2,2'-di (phthalic anhydride) ODA: oxydianine HFDAM-33: hexafluoro-iso-propylidene-2,
2'-di (3-aminobenzene) and HFDAM-44: hexafluoro-isopropylidene-2,
2'-di (4-aminobenzene).

The polyimides used according to the invention have the following structural formula: Where n is 50,000 to 100,000 for HFDA-ODA
Of HFDA-HFDAM-33, and an integer of 50,000 to 100,000 for HFDA-HFDAM-44.

Particularly preferred waveguides are HFDA-ODA or HFDA-HFD
Includes combinations of AM-33 and HFDA-HFDAM-44.

The polyimide waveguide is configured to couple TM and TE mode polarized light in phase in the polyimide layer (s). TM means transverse magnetic polarization, and TE means transverse electric polarization. TM polarization is such that the electric field "E" vector of the electromagnetic wave oscillates perpendicular to the polyimide film surface. The TE polarization is such that the electric field "E" vector of the electromagnetic wave oscillates parallel to the polyimide film surface. The air on the surface of the polyimide layer optically interacts with the in-phase TM and TE modes to cause phase disturbance (birefringence change), which is measured optically to measure the molecules of the liquid vapor in the air. Can be identified and quantified.

Polyimide waveguides manufactured for "humidity" measurements may be arranged using a minimum of four layers as follows: For a four-layer waveguide, the coating layer / polyimide layer / polyimide layer / Support.

Preferably, a four-layer waveguide is used. An additional polyimide layer may be added to form a waveguide with an auxiliary layer.

In both the four and more layers arrangement of the polyimide waveguide, the "air" containing the vapor phase acts as a coating layer and the support is preferably glass. However, the support may be any support that is transparent and has a refractive index lower than the refractive index of the polyimide layer.

The waveguide having four layers preferably includes any of the layers HFDA-HFDAM-33 and HFDA-HFDAM-44.

HFDA-HFDAM-33 and HFDA-HFDAM-44 can be completely cured and used for good and stable waveguides.

By using the two layers including HFDA-HFDAM-33 and HFDA-HFDAM-44 as the waveguide, the measurement sensitivity can be increased up to 10 times.

One example of a four-layer waveguide includes the following arrangements of layers: cladding layer / upper layer consisting of HFDA-HFDAM-33 (called "33") / lower layer consisting of HFDA-HFDAM-44 ("44"). ) /
Support. The index of refraction “n” will have the following parameters: n _TE (upper) is approximately or approximately equal to n _TE (lower); and n _TM (upper) is greater than n _TM (lower) .

In this case, n _TE (33) = 1.543, n _TE (44) = 1.541, n _TM
(33) = 1.538 and n _TM (44) = 1.516; where n _TE is the refractive index for TE polarized light and n _TM is the refractive index for TM polarized light. The layers (33 and 44) used to form the waveguide are the lower layers (44) for TM polarization.
_Are distinguishable in that they do not transmit TM mode because of low nTM. Conversely, the TM mode is transmitted only to the upper layer (33). However, the TE mode is transmitted to both polyimide layers because n _{TE of} both layers is almost equal. Since the TM mode travels a short distance limited to the upper layer, the intensity of the TM mode light at the polyimide surface is increased, thereby traveling a longer distance in both layers and correspondingly interacting with air. Increases the anisotropic interaction with the air,
Amplify the phase shift. In this way, the phase disturbance to the TM polarization at the surface increases, increasing the sensitivity of the device (see FIG. 7).

Using the optical sensor of the present invention, a liquid in a vapor phase,
For example, water, C ₁ -C ₃ alcohol, gasoline, light heating fuel oil and C ₁ -C ₃ carboxylic acids, it is possible to detect and measure. Furthermore, it is possible to detect and measure NH ₃ , NH ₄ OH, NO ₂ and N ₂ O ₅ . The optical sensor is
It is preferable to use it for detecting C ₁ -C ₃ alcohols or a mixture thereof. It is also preferred to use the sensor for detecting a single type of molecule or a mixture of two types of molecules.

Polyimide waveguides can also be used as optical sensors for liquid detection, taking the form of strip waveguides, interferometer structures or directional coupler structures.

The optical sensor may be used to detect other physical properties that affect the equilibrium between the polyimide surface and moist air, such as local pressure, temperature and electric field. An example of this is observed when, for a given humidity, the adsorption / desorption equilibrium changes when infrared or microwave is absorbed by the polyimide film. This radiation absorption raises the local temperature, resulting in a different local relative humidity on the surface. Changes in relative humidity at the polyimide surface can be detected and measured by the present invention.

The polyimide waveguide can be used as an optical sensor due to the interaction of molecules with polar imide groups in the polyimide skeleton. Each type of molecule in the vapor phase is associated with a time constant at which each molecule is adsorbed and desorbed by the polyimide waveguide at various time intervals, so that it can be identified in the vapor phase mixture. The intensity of the resulting anisotropy (birefringence change) corresponds to the concentration of that particular molecule in the vapor phase air.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an instrument used to measure polar molecules in the vapor phase of a liquid according to the present invention.

FIG. 2 shows that the mode matching the TE and TM polarizations is HFDA-ODA.
To determine at what film thickness
5 is a graph of film thickness (μm) versus effective refractive index (N _eff ).

FIG. 3 is a graph of intensity versus coupling angle (τ) depicting the TE / TM intersection determined from the graph of FIG.

FIG. 4 is a calibration curve showing a change in birefringence (ΔN _eff · 10 ⁻³ ) and a corresponding humidity in the air when HFDA-ODA is used for a polyimide waveguide material.

FIG. 5 is a graph of the time dependence of the birefringence change, ΔN _eff , measured for water on an HFDA-ODA waveguide.

FIG. 6 is a graph of the anisotropic reaction of the three-layered waveguide of HFDA-HFDAM-33 and the change in birefringence ΔN _eff · 10 ⁻⁵ vs. time [s] when the mixture of water and methanol is concentrated It is.

FIG. 7 illustrates that high sensitivity is obtained with certain matching modes, HFDA-HFDAM-33 / HFDA-HFDAM on glass.
Birefringence change ΔN _eff
10 is a graph of 10 ^-5 versus various exponential matching modes, m _TE / m _TM .

FIG. 8 is a graph of intensity versus time depicting the sensitivity of the polyimide waveguide optical sensor to the presence of petroleum gasoline in the vapor phase.

FIG. 9 depicts the structural arrangement in both three-layer and four-layer polyimide optical waveguides.

One embodiment that may be used to measure "humidity" is the instrument shown in FIG. He-Ne laser light (1) passes through a half-wave plate (2), which deflects the laser light to 45 ° (so that the TE and TM modes are equal), And TM polarization mode at a specific angle of incidence, τ,
Spin on a polyimide waveguide containing a support (4) coated with a polyimide film (3). Light is reflected into the polyimide because the support is a material having a lower refractive index than the polyimide. Glass is a suitable support. A 90 ° prism (5) made of heavy flint glass is used to adjust the angle of incidence of the laser beam,
The TE mode was used to couple into and out of the waveguide. The polyimide film (3)
The TM and TE modes coupled into it may generally be several centimeters, preferably about 2 cm long,
The light is reflected off the surface (S) of the film, where it comes into contact with the liquid vapor, causing an optically anisotropic interaction, which shifts the phase of the TM and TE modes. The TM and TE modes are coupled out of the film by heavy flint glass prisms (5 ') and pass through an analyzer (6) that detects changes in the TM and TE modes. The analyzer (6) may be set at an angle of 90 ° with respect to the polarization direction so as to be able to detect phase disturbances in the TM and TE modes. The detector (7) receives the disturbance signal from the analyzer (6), measures the absolute intensity of a phase change called a birefringence change, and converts the optical signal into an electric signal that can be displayed by any well-known means.

The instrument may be sealed with a glass bell (8) containing silica gel (9) to reduce the humidity in the instrument due to the humidity in the air and reveal the sensitivity of the device to changes in humidity.

To obtain the desired result, the humidity sensor (Figure 1)
_May simultaneously transmit a particular TE mode (eg, TE ₅ ) and a matched TM mode (eg, TM ₆ ) polarization. Specific polarization modes, for example, TE ₅ and TM _6, may be selected to transmit in the waveguide by adjusting the incident angle tau.

The humidity sensor is constructed by utilizing a theoretical curve (FIG. 2) calculated from actual refractive index parameters for TE and TM. Here, FIG. 2 shows HFDA-OD
These curves are drawn for A.

The curves shown in FIG. 2 graph the film thickness [μm] of the waveguide against the effective refractive index N _eff for the appropriate TE and TM modes. These curves for the TE and TM polarizations represent resonances arising from the transverse resonance (TRC) of a planar waveguide. In order for the TE and TM modes to pass through the polyimide film (3) so that they are in phase, the TE and TM modes must be matched to a particular film thickness. Desirable properties for matching modes exist at the intersection of TM and TE curves. For example, the intersection shown in FIG. 2 corresponds to the alignment mode of the TE ₅ and TM ₆ in the thickness of the film of 6.1μm by HFDA-ODA. The TE and
As the TM mode passes through the polyimide film, the birefringence change caused by the anisotropic interaction between the waveguide and molecules in the liquid vapor phase of the waveguide surface (S) (or
To measure phase shift), it has a matching mode,
Thereby, it is desirable to transmit the TE mode and the TM mode in the same phase.

FIG. 3 shows the modes TM ₅ and TE ₆ for the coupling angle τ and TM ₆ from the mode spectrum (FIG. 2) extracted from the anisotropic polyimide film HFDA-ODA with a layer thickness of 6.1 μm. and it depicts the optical signal intensity of the TE _7. The believed TM ₅ and TE ₆ modes are matched is in the thickness of the film as shown in FIG. The representation can be coupled at the same angle of incidence
The TE ₆ mode (10) and the TM ₅ mode (11) are shown. The two modes overlap in a range where the matched modes overlap sufficiently after the anisotropic interaction shifts them out of phase. Therefore, the intensity is as strong as possible. The figure also shows that for 6.1 μm thick HFDA polyimide, the TE ₇ and TM ₆ modes are out of phase and therefore are not matched. The time depicted in FIG. 3 is the initial state (in the vapor phase) before the birefringence change is measured.

The overlap of the TE and TM modes shown in FIG.
Is experimentally guaranteed by manufacturing a waveguide of selected thickness from the intersection of. The thickness of the film is obtained by selecting a spin at a particular centrifugal speed in the photoresist centrifuge used to make the film from the polyimide solution.

EXAMPLES Example 1 Preparation of Calibration Curve for Material HFDA-ODA: FIG. 4 shows a calibration curve representing the birefringence changes ΔN _eff · 10 ⁻³ and ΔN _eff = N _TE6 −N _{TM5 at} equilibrium for the material HFDA-ODA. , Relative humidity RH [%] to humidity in the air.
The anisotropy measurements were obtained in the entire range of 0 to 100%. This calibration curve depends on which polyimide waveguide and polar molecule is used.

Example 2 Vent and Ventilation of Vessel with Wet Air: Various intensity fluctuations were observed during the evacuation of the test vessel. By assessing these variations, the directly related optical birefringence change ΔN _eff could be expressed as a function of time [s]. FIG. 5 shows that water on the HFDA-ODA waveguide is adsorbed during the first period (12) (before equilibrium) and desorbed during the second period (13) (after equilibrium). The fluctuation is shown. Equilibrium is the state where adsorption and desorption are at or equal to equilibrium. Here, ΔN _eff is an index difference obtained from the phase difference or birefringence change of the transmitted TE and TM polarization modes. In each case, the reaction constant, meaning the adsorption speed, could be related to the valley bottom curve.

Example 3 Sensitivity Measurement of an Alcohol / Water Mixture: A mixture of methanol and water was enriched in air around a four-layer waveguide containing a HFDA-HFDAM-33 / HFDA-HFDAM-44 bilayer. The sensor first responded to water with a specific rate constant and then to the alcohol.

Further, in a three-layer waveguide using HFDA-HFDAM-33, the birefringence change ΔN _eff · 10 ^{−5 with} respect to time [s]
FIG. It was observed that the curve adopted a different curve for water (14) when compared to methanol (15). The sensor has a unique sensitivity (ΔN _eff / t) different from its sensitivity to water
At the same time, so that water can be distinguished from methanol. Time is shown in seconds.

The curve for water (14) and the curve for methanol (15) Where C is a constant relating to the concentration of the molecule, d is the diffusion coefficient for each molecule type, and t is the time. It is believed that the curves are unique for each different molecule and allow the identification of various molecules.

The concentration of a molecule is determined by the change in equilibrium birefringence for the molecule in the mixture (such as that shown in FIG. 6) and the corresponding birefringence change in the calibration curve for that molecule (such as that shown in FIG. 4).
It can be obtained by comparing with. The concentration of that molecule in the sample to be analyzed can be read from the calibration curve.

By providing the memory (7) containing data for generating a calibration curve for the specific molecule to be analyzed and the ability to generate birefringence change data over time, the detector (7) of FIG. The change in birefringence at the equilibrium point can be determined, and the identification and concentration determination of the molecule can be automatically performed by comparison with a calibration curve.

Example 4 The figure shows a HFDA-HFDAM-33 / HFDA-HFDAM-44 four-layer waveguide, 42% relative air humidity (16) and exhaust conditions (17).
Is the matching mode for TE and TM modes
The birefringence change ΔN _eff · 10 ^-5 with respect to m _TE / m _TM is shown. The symbol "m" represents "mode order" for TE and TM.

Therefore, FIG. 7 shows the sensitivity of the sensor when using different mode matching. The measurement was performed for three types of mode matching with different TE and TM polarizations. The displayed ΔN _eff value is
All three cases correspond to an air humidity (humidity) of 42%. Using 4/1 mode matching is clearly evident from the increase in measurement sensitivity when compared to the higher mode combinations 6/4 and 8/7. 4/1 is m _TE = 4 and m _TM = 1
Represents the phase matching. In this matching example, the TM mode,
That is, m _TE = 1 was used as being transmitted only through the upper HFDA-HFDAM-33 layer. The last-mentioned mode can be referred to as "surface mode".

The expression “surface mode” means that the mode exhibits a particularly high intensity at the surface, thereby resulting in a high dissipation field
It is intended that _TM ≦ 2. These surface modes, m
_TE = 0,1, or 2, generally appears to be transmitted into the top layer of the two polyimide layers, which means that the sensitivity of the waveguide can be increased. On the other hand, "spatial mode" indicates a high strength in the interior of the film, show only very weak dissipation field on the surface is m _TM> 2. Spatial modes, m _TE = 2,3,4, etc., generally appear to exhibit high intensity at the surface and therefore do not appear to be as sensitive as in a four-layer waveguide. The spatial mode is transmitted through both polyimide layers.

Example 5 Measurement of Ethanol Vapor: The four-layer polyimide sensor described in Example 3 was enclosed in a sealed container. After that, the enclosed air volume (20 ℃, 65%
RH) with ethanol vapor. In this case, 3 μl /
C ₂ H ₅ OH less than m ³ could be detected.

Example 6 Sensitivity to propanol was determined using the arrangement described in connection with Example 5. In this case, the sensitivity limit was at the level of 1 ml / m ³ C ₃ H ₇ OH.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-32151 (JP, A) JP-A-2-210308 (JP, A) JP-A-1-84205 (JP, A) JP-A 63-321 311306 (JP, A) JP-A-63-40105 (JP, A) JP-A-62-204209 (JP, A) JP-A-62-187705 (JP, A) (58) Fields investigated (Int. ^6, DB name) G01N 21/00 - 21/01 G01N 21/17 - 21/74 G02B 6/02 EPAT WPI / L

Claims (13)

(57) [Claims] 1. A polyimide waveguide as an optical sensor for measuring a liquid in a vapor phase, wherein said polyimide waveguide has at least two layers of polyamide-imide or perfluorinated coating on a support (4). made of polyimide (3), the waveguide polyamide - imide or surface of the perfluorinated polyimide characterized in that is adapted to contact the coating layer of the liquid vapor, n _TM of the polyimide waveguide The upper layer is larger than the _nTM lower layer, and the _nTE upper layer is substantially equal to the _nTE lower layer. 2. The arrangement of layers is as follows: coating layer / HFDA-HFDAM-33 / HFDA
HFDAM-44 / support, where HFDA-HFDAM-33 means hexafluoro-iso-propylidene-2,2'-di (3-aminobenzene) and HFDA-HFDAM-44 means hexafluoro-iso- 2. Optical according to claim 1, characterized in that it means propylidene-2,2'-di (4-aminobenzene), the coating layer means gas space and the support means glass. Polyimide waveguide as sensor. 3. The method according to claim 1, which is used for measuring water, C ₁ -C ₃ alcohols, gasoline, lightly heated fuel oil and C ₁ -C ₃ carboxylic acids in a vapor phase. A polyimide waveguide as the optical sensor described in the above. 4. The polyimide waveguide as an optical sensor according to claim 1, wherein the polyimide waveguide is used for measuring NH ₃ , “NH ₄ OH”, NO ₂ and N ₂ O ₅ . 5. The optical sensor according to claim 1, wherein the optical sensor is in the form of a strip waveguide, an interferometer structure or a directional composite structure for measuring a liquid in a vapor phase. Polyimide waveguide. 6. The method according to claim 3, which is used for adjusting or measuring the effect of pressure fluctuation, electric field and microwave on the equilibrium on the polyimide surface and the measurement space. Polyimide waveguide. 7. The method according to claim 7, wherein said support is glass, and said polyamide-
Imide or perfluorinated polyimide is HFDA-OD
A, HFDAM-33, HFDA-HFDAM-44 or HFDA-HFDAM-
The polyimide waveguide according to claim 1, wherein the polyimide waveguide is a combination of 33 and HFDA-HFDAM-44. 8. An apparatus for detecting the presence of molecules in a vapor and measuring the relative amounts thereof, said polyimide comprising at least two layers of polyamide-imide or perfluorinated polyimide coated on a support. a waveguide n _TM layer of the polyimide waveguide n _TM greater than the lower layer, and those n _TE layer is substantially equal to n _TE lower; directs polarized light into the polyimide waveguide on, polarizing Means for coupling to a polyamide-imide or perfluorinated polyimide layer; an area adjacent to the polyimide waveguide for receiving a liquid vapor and contacting the vapor with the polyamide-imide or perfluorinated polyimide layer; Means for coupling out of the polyimide waveguide; and means for measuring the intensity of the phase shift of the polarized light. Mukoto those characterized by. 9. Apparatus according to claim 8, wherein the means for directing polarization comprises means for directing the TM and TE modes of the polarization. 10. The apparatus of claim 8, wherein the means for directing the polarized light includes means for directing the TM and TE modes of the polarized light at an angle of about 45 °. 11. The device according to claim 10, wherein the support has a refractive index lower than that of polyamide-imide or perfluorinated polyimide. 12. The polyamide-imide or perfluorinated polyimide is HFDA-ODA, HFDA-HFDAM-33, HFDA
-HFDAM-44 or HFDA-HFDAM-33 and HFDA-HFDAM
12. The device according to claim 11, wherein the device is selected from the group consisting of -44 combinations. 13. n _TM upper layer of the polyimide waveguide is greater than n _TM layer, and n _TE upper layer is equal to or approximately equal to n _TE underlying Apparatus according to claim 11.