CN101398541A - Wide spectrum narrowband adjustable optical filter based on LCD electric-controlled birefraction - Google Patents

Abstract

The invention discloses a wide spectrum narrowband adjustable filter system based on liquid crystal electric-control dual-refraction and a design method thereof; a first polarizer, a first liquid crystal box, a second polarizer, a second liquid crystal box, a third polarizer, a first wave plate, a third liquid crystal box, a fourth polarizer, a second wave plate, a fourth liquid crystal box, a fifth polarizer, a third wave plate, a fifth liquid crystal box, a sixth polarizer, a fourth wave plate, a sixth liquid crystal box and a seventh polarizer are sequentially arranged on the same optical passage; each step of adjustable filter is formed by the polarizer, the liquid crystal boxes and the wave plates. The invention is the combination of liquid crystal boxes and the dual-refraction crystal and polarizer, utilizes the maximum adjustment capability of the liquid crystal by the optimum design of the adjusting quantity of the liquid crystal box and the delay quantity of the filter, achieves continuous adjustable narrowband filter light in the wide spectrum range, has the advantages of large light aperture, simple assembly, convenient manufacture, wide filter spectrum and high spectrum resolution, and can be applied to the fields such as biomedicine, astronomical observation and the like.

Description

Based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter

Technical field

The present invention relates to a kind ofly, can be applicable to fields such as biomedicine, astronomical sight based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system.

Background technology

Tunable filter system comprises acousto-optic tunable, electro-optical tuning, mechanical tuning filter system.

Wherein the acousto-optic adjusting mainly is the tunable filter system that utilizes the unusual Bragg diffraction effect of aeolotropic crystal under acoustic optic interaction to make, thereby can carry out the monochromatic light that diffraction obtains specific wavelength to the incident polychromatic light according to the difference of the radio frequency signal frequency that imposes on it.The acousto-optic tunable filter system has compact conformation, the advantage that tuning response speed is fast, but costing an arm and a leg, assembly precision requires high, the defective that clear aperture is little.

Mechanical adjustment is mainly used among interference filter system and the polarization interference filter system, by physical parameter such as thickness, the angle etc. of device in the change system, reaches the purpose of tuning filter system spectral characteristic.The tuning response speed of mechanical adjustment filter system is slow, complex structure.

It then mainly is to utilize the electro-optic birefringent effect of the electrooptical effect of crystal and liquid crystal and the purpose that reaches tuning filter that electric light is regulated.The electrooptical effect of crystal requires to apply high voltage, uses less; Along with the improvement of liquid crystal material technology, technology of preparing, utilize the electro-optic birefringent effect of liquid crystal, change the polarization interference filter system into tunable filter system, it is fast to have response speed, and the advantage that clear aperture is big is present widely used method.

Tradition Lyot type optical filter is a kind of polarization birefringence filter system, is made up of N birefringence device and N-1 polarizer usually.Wherein the optical axis of polarizer is parallel to each other, clips a phase delay device between per two polarizers, and the fast axle of phase delay device is at 45 with the optical axis of polarizer, and the retardation that each grade phase delay device produces is the twice of upper level retardation.According to the polarization interference theory, the transmitance T that can obtain single-stage Lyot optical filter is the function of phase differential δ:

$T={\cos }^2\left(\frac{\mathrm{\δ}}{2}\right)---\left(1\right)$

In order to obtain narrower passband width, by above-mentioned single-unit Lyot type optical filter by certain phase delay than the more piece Lyot type optical filter that is formed by stacking.

Summary of the invention:

The purpose of this invention is to provide that a kind of spectral range is wide, spectral resolution is high, clear aperture is big, assembling is easily based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system and method for designing thereof.

On same light path, be placed with first polaroid successively, first liquid crystal cell, second polaroid, second liquid crystal cell, the 3rd polaroid, first wave plate, the 3rd liquid crystal cell, the 4th polaroid, second wave plate, the 4th liquid crystal cell, the 5th polaroid, the 3rd wave plate, the 5th liquid crystal cell, the 6th polaroid, the 4th wave plate, the 6th liquid crystal cell, the 7th polaroid, first polaroid wherein, first liquid crystal cell, second polaroid is the first segment optical filter, second polaroid, second liquid crystal cell, the 3rd polaroid is the second joint optical filter, the 3rd polaroid, first wave plate, the 3rd liquid crystal cell, the 4th polaroid is the 3rd joint optical filter, the 4th polaroid, second wave plate, the 4th liquid crystal cell, the 5th polaroid is the 4th joint optical filter, the 5th polaroid, the 3rd wave plate, the 5th liquid crystal cell, the 6th polaroid is the 5th joint optical filter, the 6th polaroid, the 4th wave plate, the 6th liquid crystal cell, the 7th polaroid is the 6th joint optical filter, the polaroid optical axis is parallel to each other, and the optical axis of wave plate and liquid crystal cell and polaroid angle are 45 °.

In described first wave plate is positive crystal, and its retardation is: 1400nm＜D_WP1＜1550nm.

Second wave plate is a positive crystal, and its retardation is: 3000nm＜D_WP2＜3150nm.

The 3rd wave plate is a positive crystal, and its retardation is: 6250nm＜D_WP3＜6350nm.

The 4th wave plate is a positive crystal, and its retardation is: 12600nm＜D_WP4＜12750nm.

First liquid crystal cell, second liquid crystal cell, the 3rd liquid crystal cell, the 4th liquid crystal cell, the 5th liquid crystal cell, the 6th liquid crystal cell are twisted nematic liquid crystals, thickness of liquid crystal layer is 5～15 microns, applying frequency range is the adjustable amplitude value alternating voltage of 100Hz＜f＜10KHz, and the amplitude range of adjustment is 10V to 0V.

Method for designing based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system comprises the steps:

1) filter system Component Design:

(1) wave plate retardation design:

The initial wavelength of uniting of setting up departments is WL1, and the retardation when liquid crystal cell adds 10V voltage is D_lc_min, and the wave plate retardation of N joint optical filter is: D_WP=2 ^N-1* WL1-D_lc_min;

(2) liquid crystal cell control lag amount design:

If the additional delay amount that the tuning back of liquid crystal cell produces is D_lc, its maximum additional delay amount is D_lc_max, and the retardation that wave plate produces is D_WP, and target wavelength is WL2, and then the control lag amount computing method of liquid crystal cell are in the N joint optical filter:

(a) work as D_lc_max+D_WP〉2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝2 ^N-1*WL2-D_WP；

(b) when D_lc_max+D_WP＜2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝[(D_lc_max+D_WP)/WL2]*WL2-D_WP；

Wherein [] symbolic representation rounds downwards.

2) filter system component mounting method:

(1) each joint single-unit filter system is followed successively by from front to back along light path: preceding polaroid, adjustable phase retarder, rear polarizer, wherein optical axis is parallel to each other between the polaroid, adjustable phase retarder comprises the combination of liquid crystal cell or liquid crystal cell and wave plate, liquid crystal cell is parallel with the optical axis of wave plate, be the optical axis of adjustable phase retarder, 45 ° of the optical axis of adjustable phase retarder and polaroid angles;

(2) the single-unit filter system is joined at the enterprising luggage of same light path, the rear polarizer of each joint single-unit filter system is the preceding polaroid of next joint single-unit filter system, the preceding polaroid of first segment single-unit filter system is the light input window of total system, and the rear polarizer of final section single-unit filter system is the light output window of total system.

The present invention is the combination of liquid crystal cell and birefringece crystal and polaroid; Realized continuously adjustable narrow-band-filter in the wide spectral range, have that clear aperture is big, assembling is simple and easy, easily manufactured, optical filtering spectrum is wide, spectral resolution is high, tuned speed is fast, passband is located accurate characteristics, can be applicable to fields such as biomedicine, astronomical sight.

Description of drawings:

Fig. 1 is based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter structural representation;

Fig. 2 (a) is six grades of filter system original state optical filter spectral transmittance at different levels synoptic diagram;

Fig. 2 (b) is that six grades of filter system original states are finally exported synoptic diagram;

Fig. 3 (a) is that six grades of filter systems are regulated back optical filter spectral transmittance synoptic diagram at different levels;

Fig. 3 (b) is that six grades of filter systems are regulated the final output in back synoptic diagram;

Among the figure: first polaroid 1, first liquid crystal cell 2, second polaroid 3, second liquid crystal cell 4, the 3rd polaroid 5, first wave plate 6, the 3rd liquid crystal cell 7, the 4th polaroid 8, second wave plate 9, the 4th liquid crystal cell 10, the 5th polaroid 11, the 3rd wave plate 12, the 5th liquid crystal cell 13, the 6th polaroid 14, the 4th wave plate 15, the 6th liquid crystal cell 16, the 7th polaroid 17.

Embodiment

As shown in Figure 1, be on same light path, to be placed with successively first polaroid 1 based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system, first liquid crystal cell 2, second polaroid 3, second liquid crystal cell 4, the 3rd polaroid 5, first wave plate 6, the 3rd liquid crystal cell 7, the 4th polaroid 8, second wave plate 9, the 4th liquid crystal cell 10, the 5th polaroid 11, the 3rd wave plate 12, the 5th liquid crystal cell 13, the 6th polaroid 14, the 4th wave plate 15, the 6th liquid crystal cell 16, the 7th polaroid 17, first polaroid 1 wherein, first liquid crystal cell 2, second polaroid 3 is the first segment optical filter, second polaroid 3, second liquid crystal cell 4, the 3rd polaroid 5 is the second joint optical filter, the 3rd polaroid 5, first wave plate 6, the 3rd liquid crystal cell 7, the 4th polaroid 8 is the 3rd joint optical filter, the 4th polaroid 8, second wave plate 9, the 4th liquid crystal cell 10, the 5th polaroid 11 is the 4th joint optical filter, the 5th polaroid 11, the 3rd wave plate 12, the 5th liquid crystal cell 13, the 6th polaroid 14 is the 5th joint optical filter, the 6th polaroid 14, the 4th wave plate 15, the 6th liquid crystal cell 16, the 7th polaroid 17 is the 6th joint optical filter, the polaroid optical axis is parallel to each other, and the optical axis of wave plate and liquid crystal cell and polaroid angle are 45 °.

Described first wave plate 6 is a positive crystal, and its retardation is: 1400nm＜D_WP1＜1550nm.Second wave plate 9 is a positive crystal, and its retardation is: 3000nm＜D_WP2＜3150nm.The 3rd wave plate 12 is a positive crystal, and its retardation is: 6250nm＜D_WP3＜6350nm.The 4th wave plate 15 is a positive crystal, and its retardation is: 12600nm＜D_WP4＜12750nm.First liquid crystal cell 2, second liquid crystal cell 4, the 3rd liquid crystal cell 7, the 4th liquid crystal cell 10, the 5th liquid crystal cell 13, the 6th liquid crystal cell 16 are twisted nematic liquid crystals, thickness of liquid crystal layer is 5～15 microns, applying frequency range is the adjustable amplitude value alternating voltage of 100Hz＜f＜10KHz, and the amplitude range of adjustment is 10V to 0V.

Method for designing based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system comprises the steps:

1) filter system Component Design:

(1) wave plate retardation design:

The initial wavelength of uniting of setting up departments is WL1, and the retardation when liquid crystal cell adds 10V voltage is D lc_min, and the wave plate retardation of N joint optical filter is: D_WP=2 ^N-1* WL1-D_lc_min;

(2) liquid crystal cell control lag amount design:

If the additional delay amount that the tuning back of liquid crystal cell produces is D_lc, its maximum additional delay amount is D_lc_max, and the retardation that wave plate produces is D_WP, and target wavelength is WL2, and then the control lag amount computing method of liquid crystal cell are in the N joint optical filter:

(a) work as D_lc_max+D_WP〉2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝2 ^N-1*WL2-D_WP；

(b) when D_lc_max+D_WP＜2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝[(D_lc_max+D_WP)/WL2]*WL2-D_WP；

Wherein [] symbolic representation is divided by and is rounded downwards.

2) filter system component mounting method:

(1) each joint single-unit filter system is followed successively by from front to back along light path: preceding polaroid, adjustable phase retarder, rear polarizer, wherein optical axis is parallel to each other between the polaroid, adjustable phase retarder comprises the combination of liquid crystal cell or liquid crystal cell and wave plate, liquid crystal cell is parallel with the optical axis of wave plate, be the optical axis of adjustable phase retarder, 45 ° of the optical axis of adjustable phase retarder and polaroid angles;

(2) the single-unit filter system is joined at the enterprising luggage of same light path, the rear polarizer of each joint single-unit filter system is the preceding polaroid of next joint single-unit filter system, the preceding polaroid of first segment single-unit filter system is the light input window of total system, and the rear polarizer of final section single-unit filter system is the light output window of total system.

First liquid crystal cell 2, second liquid crystal cell 4, the 3rd liquid crystal cell 7, the 4th liquid crystal cell 10, the 5th liquid crystal cell 13, the 6th liquid crystal cell 16 are twisted nematic liquid crystals in the system, thickness of liquid crystal layer is 10 microns, applying frequency is the adjustable amplitude value alternating voltage of 5KHz, and the amplitude range of adjustment is 10V to 0V.

The D_lc_min of liquid crystal cell is 50nm when adding 10V voltage, and then the retardation of first wave plate 6 is 1550nm, and the retardation of second wave plate 9 is 3150nm, and the retardation of the 3rd wave plate 12 is 6350nm, and the retardation of the 4th wave plate 15 is 12750nm.When liquid crystal cell all applied 10V voltage, system was an original state, and each saves the optical filter spectral transmittance shown in Fig. 2 (a), and the integral body of system is exported shown in Fig. 2 (b).Filter range is whole visible range, and the passband halfwidth is 5nm.

If the range of adjustment of liquid crystal cell is: 50nm～1500nm will be adjusted to target wavelength WL2=700nm with the 3rd joint filter system.The retardation that this joint wave plate produces is for being D_WP=1550nm, and the retardation that needs after the adjusting to produce is 2 ²* WL2=2800nm, and D_lc_max+D_WP=1500+1550=3050nm, the retardation that produces greater than needs, so the liquid crystal cell retardation should be:

D_LC=2 ^3-1* WL2-D_WP=2800-1550=1250nm needs only regulation voltage, and the retardation that liquid crystal cell is produced is adjusted to 1250nm.

If the 4th joint filter system will be adjusted to target wavelength WL2=700nm, the retardation that this grade wave plate produces is D_WP=3150nm, and the retardation that needs after the adjusting to produce is 2 ^4-1* WL2=5600nm, and D_lc_max+D_WP=1500+3150=4650nm, the retardation that produces less than needs, so liquid crystal cell retardation:

D_LC＝D_LC＝[D_lc_max+D_WP/WL2]*WL2-D_WP

=[4650/700] * 700-3150=6*700-3150=1050nm promptly needs regulation voltage, and the retardation that liquid crystal cell is produced is adjusted to 1050nm, produces the 6th grade of subwave peak value on 700nm.

According to this method, calculate six joint filter systems, when being adjusted to target wavelength 700nm, each saves the regulated quantity that liquid crystal cell needs:

The N joint:	1	2	3	4	5	6
							Wave plate retardation: D_WP	0	0	1550	3150	6350	12750
The maximum-delay amount that can produce: D_lc_max+D_WP	1500	1500	3050	4650	7850	14250
							The total delay amount that needs generation: 2 N-1*700nm	700	1400	2800	5600	11200	22400
Whether liquid crystal cell can meet the demands: D_lc_max+D_WP〉2 N-1*700	Be	Be	Be	Not	Not	Not
							Liquid crystal cell is regulated and is produced retardation:	700	1400	1250	1050	1350	1250
It is inferior to save the optical filtering chip level after the adjusting	1	2	4	7	11	20

After the adjusting, optical filter spectral transmittances at different levels are shown in Fig. 3 (a), and the integral body of system is exported shown in Fig. 3 (b).Filter range is whole visible range, and the passband halfwidth is 15nm.

Claims (7)

1. one kind based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system, it is characterized in that on same light path, being placed with successively first polaroid (1), first liquid crystal cell (2), second polaroid (3), second liquid crystal cell (4), the 3rd polaroid (5), first wave plate (6), the 3rd liquid crystal cell (7), the 4th polaroid (8), second wave plate (9), the 4th liquid crystal cell (10), the 5th polaroid (11), the 3rd wave plate (12), the 5th liquid crystal cell (13), the 6th polaroid (14), the 4th wave plate (15), the 6th liquid crystal cell (16), the 7th polaroid (17), first polaroid (1) wherein, first liquid crystal cell (2), second polaroid (3) is the first segment optical filter, second polaroid (3), second liquid crystal cell (4), the 3rd polaroid (5) is the second joint optical filter, the 3rd polaroid (5), first wave plate (6), the 3rd liquid crystal cell (7), the 4th polaroid (8) is the 3rd joint optical filter, the 4th polaroid (8), second wave plate (9), the 4th liquid crystal cell (10), the 5th polaroid (11) is the 4th joint optical filter, the 5th polaroid (11), the 3rd wave plate (12), the 5th liquid crystal cell (13), the 6th polaroid (14) is the 5th joint optical filter, the 6th polaroid (14), the 4th wave plate (15), the 6th liquid crystal cell (16), the 7th polaroid (17) is the 6th joint optical filter, the polaroid optical axis is parallel to each other, and the optical axis of wave plate and liquid crystal cell and polaroid angle are 45 °.

2. according to claim 1ly it is characterized in that based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system described first wave plate (6) is a positive crystal, its retardation is: 1400nm＜D_WP1＜1550nm.

3. according to claim 1ly it is characterized in that based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system described second wave plate (9) is a positive crystal, its retardation is: 3000nm＜D_WP2＜3150nm.

4. according to claim 1ly it is characterized in that based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system described the 3rd wave plate (12) is a positive crystal, its retardation is: 6250nm＜D_WP3＜6350nm.

5. according to claim 1ly it is characterized in that based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system described the 4th wave plate (15) is a positive crystal, its retardation is: 12600nm＜D_WP4＜12750nm.

6. according to claim 1 based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system, it is characterized in that described first liquid crystal cell (2), second liquid crystal cell (4), the 3rd liquid crystal cell (7), the 4th liquid crystal cell (10), the 5th liquid crystal cell (13), the 6th liquid crystal cell (16) are twisted nematic liquid crystals, thickness of liquid crystal layer is 5～15 microns, applying frequency range is the adjustable amplitude value alternating voltage of 100Hz＜f＜10KHz, and the amplitude range of adjustment is 10V to 0V.

7. the method for designing based on LCD electric-controlled birefringent wide spectrum narrowband adjustable optical filter system is characterized in that comprising the steps:

1) filter system Component Design:

(1) wave plate retardation design:

The initial wavelength of uniting of setting up departments is WL1, and the retardation when liquid crystal cell adds 10V voltage is D_1c_min, and the wave plate retardation of N joint optical filter is: D_WP=2 ^N-1* WL1-D_1c_min;

(2) liquid crystal cell control lag amount design:

If the additional delay amount that the tuning back of liquid crystal cell produces is D_1c, its maximum additional delay amount is D_1c_max, and the retardation that wave plate produces is D_WP, and target wavelength is WL2, and then the control lag amount computing method of liquid crystal cell are in the N joint optical filter:

(a) work as D_1c_max+D_WP〉2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝2 ^N-1*WL2-D_WP；

(b) when D_1c_max+D_WP＜2 ^N-1* during WL2, the control lag amount calculating formula of liquid crystal cell is:

D_LC＝[(D_1c_max+D_WP)/WL2]*WL2-D_WP；

Wherein mod represents to round downwards.

2) filter system component mounting method:

(1) each joint single-unit filter system is followed successively by from front to back along light path: preceding polaroid, adjustable phase retarder, rear polarizer, wherein optical axis is parallel to each other between the polaroid, adjustable phase retarder comprises the combination of liquid crystal cell or liquid crystal cell and wave plate, liquid crystal cell is parallel with the optical axis of wave plate, be the optical axis of adjustable phase retarder, 45 ° of the optical axis of adjustable phase retarder and polaroid angles;

(2) the single-unit filter system is joined at the enterprising luggage of same light path, the rear polarizer of each joint single-unit filter system is the preceding polaroid of next joint single-unit filter system, the preceding polaroid of first segment single-unit filter system is the light input window of total system, and the rear polarizer of final section single-unit filter system is the light output window of total system.

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