CN102053396A - Method and device for measuring thickness of liquid crystal box - Google Patents

Abstract

The invention belongs to the field of preparation of electro-optical functional materials, and relates to a method and a device for measuring the thickness of a liquid crystal box. In the method, the thickness of the liquid crystal box can be determined without wavelength values corresponding to a maximum value and a minimum value of a transmission spectrum, so that the uncertainty of searching the maximum value and the minimum value of the transmission spectrum is avoided; a convergent beam is adopted to facilitate improving signal-to-noise ratio; and the section of a light cone on the liquid crystal box can be small so as to facilitate measuring the surface distribution of the thickness of the box. The thickness of the liquid crystal box is measured by a measuring device which comprises a light source, a condensing lens, the liquid crystal box to be measured, an optical fiber coupling head and a spectrum measuring instrument. The adopted white light emitting diode (LED) has a flat emission spectrum in the visible light range of 500 to 550nm so as to facilitate simplifying a measuring system; meanwhile, the thickness is convenient to calculate.

Description

A kind of liquid crystal cell method for measuring thickness and device

Technical field

The invention belongs to electric light functional material preparation field, be specifically related to a kind of liquid crystal cell method for measuring thickness and device.

Background technology

Usually liquid crystal cell is to be bonded by two (conduction) glass substrates, has sept (spacer) to be used to control its gap length therebetween.The thick two substrates thickness at interval that just is meant of liquid crystal cell is generally several microns to tens microns.Liquid crystal cell is thick to be an important parameter of liquid crystal device, and after two base plate glass were bonded together, the thickness in its gap (box is thick) had certain difference with the diameter at used interval (spacer), and this difference also can be very big sometimes.Therefore, accurately measuring box is thick, and is significant to the accurate grasp of liquid crystal device (LCD, photomodulator) performance.

In the prior art, measuring the thick method of liquid crystal cell has: with its equivalence is a Fabry-Perot chamber, utilize the multiple-beam interference principle, adjacent very big (or minimum) according to transmitted spectrum is worth pairing wavelength, obtain the thick d of liquid crystal cell, its principle can be expressed as the function that transmissivity is angle of incidence of light θ, wavelength X, surface strength reflectivity and the thick d of box:

$T(\mathrm{\θ},\mathrm{\λ})=\frac{1}{1+\frac{4R}{{(1-R)}^2}\·{\sin }^2\frac{\mathrm{\δ}(\mathrm{\θ},\mathrm{\λ},d)}{2}}---(e.1)$

In the formula $\mathrm{\δ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}2d\·\cos \mathrm{\θ}$

By measuring the adjacent greatly pairing wavelength value λ of (or minimum) value of transmitted spectrum _p, λ _P+1(λ _v, λ _V+1), can determine the thick d of liquid crystal cell:

$d=\frac{1}{2(\frac{1}{{\mathrm{\λ}}_{p\left(v\right)}}-\frac{1}{{\mathrm{\λ}}_{p+1(v+1)}})}---(e.2)$

The application of above-mentioned principle needs the parallel incident of polychromatic light.But because the existence of aberration, this requirement also is not easy to reach.In addition, in order to obtain the thick face distribution situation of box, the diameter of light beam can not be too big, thereby luminous flux is restricted, and like this, the measurement signal to noise ratio (S/N ratio) of transmitted spectrum seriously descended, thus give very big (or minimum) peak position determine to bring serious error.

Summary of the invention

The objective of the invention is provides a kind of liquid crystal cell method for measuring thickness and device for overcoming the above-mentioned difficulties that prior art exists.

Particularly, the present invention proposes a kind of converging beam measuring method, promptly adopts focused beam rather than parallel beam as measuring incident light, with effective raising luminous flux, signal to noise ratio (S/N ratio) is significantly improved, and the spot size of may command transflective liquid crystal box, the face resolution of measuring improved.

The inventive method does not need to determine thickness of liquid crystal box by the very big and minimum pairing wavelength value of transmitted spectrum, thereby has removed the very big and minimizing uncertainty of searching transmitted spectrum from.Owing to adopted converging beam, helped improving signal to noise ratio (S/N ratio).The cross section of light cone on liquid crystal cell can be very little, helps the thick face of measuring box and distribute.The white light LEDs that is adopted has more smooth luminous spectrum in visible light 500-550nm scope, thereby helps the simplified measurement system, calculates also very convenient simultaneously.

The present invention measures liquid crystal cell thick (Fig. 1) by adopting measurement mechanism.Described measurement mechanism comprises: light source (1), lens (2), liquid crystal cell to be measured (3), optical fiber coupling head (4), optical spectrum instrumentation (5).Wherein, light source adopts the very little white light LEDs (1) of light-emitting area, make it to be similar to pointolite, the white light that led light source (1) is sent by an achromatism compound lens (2) converges and forms light cone, and is focused into a picture, light cone transmission liquid crystal cell to be measured (3), place optical fiber coupling head (4) at the picture point place, import light into optical spectrum instrumentation (5), liquid crystal cell to be measured (3) can be tried one's best near optical fiber head, thereby reduces the cross section of light cone at the liquid crystal cell face.During measurement, in certain wavelength coverage, measure the spectrum I that liquid crystal cell is put into the light path front and back respectively ₀(λ) and I _t(λ), its spectrum ratio T (λ)=I _t(λ)/I ₀(λ), comprise the thickness information of liquid crystal cell,, adopt the light cone method of average to calculate, the light beam transmissivity of respective wavelength is asked in the light cone scope on average, and the spectrum ratio of measurement of comparison just can obtain the thick data of liquid crystal cell according to the Fabry-Perot principle.

Among the present invention, described collector lens (2) is an achromat.

Among the present invention, the optical fiber coupling head of described optical fiber (4) is a multimode optical fiber.

Among the present invention, described optical spectrum instrumentation (5) is the visible light wave range optical spectrum instrumentation.

Among the present invention, described computing method are the light cone method of average. promptly calculate the mean value of the light intensity transmitance of all light beams in the light cone.

Among the present invention, for obtaining the thick data of liquid crystal cell, the incident light element of a cone is a main systematic parameter to the subtended angle θ c of normal, among the present invention, can measure from the diameter and the image distance of light cone.If the intensity of certain wavelength coverage spectrum all equates in the light cone, be I ₀(λ), its incident angle to liquid crystal cell is θ, and its position angle to the liquid crystal cell face is φ, and according to F-P chamber principle, this light beam can be represented by (1) formula the transmitance of liquid crystal cell.Visible its position angle with light beam has nothing to do in the formula.

If the area element in the light cone is ds, ds=sin θ d θ d φ, then when no liquid crystal cell, the light intensity of the spectrometer that optical fiber is coupled to is

And the transmitted light intensity that optical fiber receives when having liquid crystal cell in light path is Average transmittance can be expressed as $\stackrel{\‾}{T}\left(\mathrm{\λ}\right)=\frac{\underset{\mathrm{conic}}{\text{\∫}}{I}_t(\mathrm{\θ},\mathrm{\λ})\·\mathrm{ds}}{\underset{\mathrm{conic}}{\∫}{I}_0(\mathrm{\θ},\mathrm{\λ})\·\mathrm{ds}}=\frac{\underset{\mathrm{conic}}{\∫}\frac{I_t(\mathrm{\θ},\mathrm{\λ})}{I_0(\mathrm{\θ},\mathrm{\λ})}\·\mathrm{ds}}{\underset{\mathrm{conic}}{\∫}\mathrm{ds}}=\frac{\underset{\mathrm{conic}}{\∫}T(\mathrm{\θ},\mathrm{\λ})\·\mathrm{ds}}{\underset{\mathrm{conic}}{\∫}\mathrm{ds}}$

Further arrangement, final average transmittance can be expressed as:

$\stackrel{\‾}{T}\left(\mathrm{\λ}\right)=\mathrm{\γ}\·\frac{{\∫}_{x_c}^{1}T(x,\mathrm{\λ},d)\·\mathrm{dx}}{1-\cos {\mathrm{\θ}}_c}---(e.3)$

X in the formula _c=cos θ _c. γ=0.92 is a correction factor, with four surfaces of reflecting liquid crystal box glass substrate to the reflection of light loss.

According to the contrast of (e.3) formula and measure spectrum transmissivity, promptly can calculate the thick data of corresponding box very delicately, and not need to determine concrete very big or minimum wavelength.

For the ease of understanding, below will describe in detail of the present invention by concrete drawings and Examples.It needs to be noted, instantiation and accompanying drawing only are in order to illustrate, obviously those of ordinary skill in the art can illustrate according to this paper, within the scope of the invention the present invention is made various corrections and change, and these corrections and change are also included in the scope of the present invention.

Description of drawings

Fig. 1 is a measurement mechanism synoptic diagram of the present invention, wherein, the 1st, white light source, the 2nd, collector lens, the 3rd, survey liquid crystal cell, the 4th, optical fiber coupling head, the 5th, optical spectrum instrumentation.

Fig. 2 is the transmitance spectrum of measurements and calculations in the embodiment

Embodiment

Embodiment 1

The device that proposes according to the present invention, set up a cover measuring system, described measuring system device comprises: white light source (1), collector lens (2), liquid crystal cell to be measured (3). optical fiber coupling head (4), optical spectrum instrumentation (5). wherein, light source adopts the very little white light LEDs (1) of light-emitting area, making it to be similar to pointolite. the white light that led light source (1) is sent by a collector lens (2) converges and forms light cone, and is focused into a picture, light cone transmission liquid crystal cell to be measured (3), place optical fiber coupling head (4) at the picture point place, import light into optical spectrum instrumentation (5), liquid crystal cell to be measured (3) can be tried one's best near optical fiber head, thus reduce light cone the liquid crystal cell face the cross section.During measurement, in certain wavelength coverage, measure the spectrum I that liquid crystal cell is put into the light path front and back respectively ₀(λ) and I _t(λ), its spectrum ratio T (λ)=I _t(λ)/I ₀(λ), comprise the thickness information of liquid crystal cell,, the light beam transmissivity of respective wavelength is asked in the light cone scope on average, and the spectrum ratio of measurement of comparison just can obtain the thick data of liquid crystal cell according to the Fabry-Perot principle.

The subtended angle θ c of the bus of light cone is about 11.8 ° in the present embodiment, and measurement result as shown in Figure 2.Fig. 2 has shown the transmissivity spectrum of the inventive method measurements and calculations, and the result shows that what meet is fairly good, and the thick data of the liquid crystal cell that is simulated are 32.5 μ m.

Claims (8)

1. liquid crystal cell method for measuring thickness, it is characterized in that, do not need to determine thickness of liquid crystal box by the very big and minimum pairing wavelength value of transmitted spectrum, adopt focused beam as measuring incident light, improve luminous flux and signal to noise ratio (S/N ratio), the spot size of control transflective liquid crystal box, it is thick to adopt the light cone method of average to calculate the measurement liquid crystal cell.

2. liquid crystal cell method for measuring thickness according to claim 1 is characterized in that, described computing method are the light cone method of average, in the described method, calculates the mean value of the light intensity transmitance of all light beams in the light cone.

3. liquid crystal cell thickness measuring device, it is characterized in that, described measurement mechanism comprises: light source (1), collector lens (2), liquid crystal cell to be measured (3), optical fiber coupling head (4), optical spectrum instrumentation (5), the light that light source (1) sends pools light cone through collector lens (2), and light cone is injected liquid crystal cell (3), liquid crystal cell (3) is near optical fiber coupling head (4), and optical fiber coupling head (4) imports light into optical spectrum instrumentation (5).

4. liquid crystal cell thickness measuring device according to claim 2 is characterized in that, described light source (1) is a white light LEDs.

5. liquid crystal cell thickness measuring device according to claim 4 is characterized in that, described white light LEDs is in visible light 500-550nm scope.

6. liquid crystal cell thickness measuring device according to claim 2 is characterized in that, described collector lens (2) is an achromat.

7. liquid crystal cell thickness measuring device according to claim 2 is characterized in that, described optical fiber coupling head (4) is a multimode optical fiber.

8. liquid crystal cell thickness measuring device according to claim 2 is characterized in that, described optical spectrum instrumentation (5) is the visible light wave range optical spectrum instrumentation.

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