WO2013189108A1

WO2013189108A1 - Tunable fabry-pérot filter

Info

Publication number: WO2013189108A1
Application number: PCT/CN2012/078336
Authority: WO
Inventors: 高培良
Original assignee: 天津奇谱光电技术有限公司
Priority date: 2012-06-18
Filing date: 2012-07-09
Publication date: 2013-12-27
Also published as: CN102955279A

Abstract

A tunable Fabry-Pérot filter, comprising a first reflector (10), a liquid crystal material (18), a second reflector (20) and a drive circuit (14), the liquid crystal material (18) being arranged inside a Fabry-Pérot cavity formed by the first reflector (10) and the second reflector (20), and the drive circuit (14) tuning the filter by controlling the effective refractive index of the liquid crystal material (18) inside the Fabry-Pérot cavity. In the filter, the liquid crystal is disposed inside the Fabry-Pérot standard cavity so as to achieve continuous, rapid, and precision tuning of the frequency of linearly polarized light passing through the Fabry-Pérot filter, thus allowing the filter to utilize non-mechanical moving parts and to be stable, reliable, low in cost, small in size, easy to install and produce, and so on. The filter meets requirements for reliable operation in small and extreme working environments, and can be broadly applied in lasers, optical testing, optical fiber communications, biology, medical instruments, optical fiber sensor networks, and other such fields.

Description

A tunable Fabry-Perot filter

The invention belongs to the field of optoelectronic technology, in particular to a tunable Fabry-Perot filter.

Background technique

The traditional optical Fabry-Perot etalon is a filter element fabricated using the principle of multi-beam interference. There are two main types: one is air-spaced and the other is optical glass-spaced. The multi-wavelength interference effect of the Fabry-Perot cavity formed by the high reflectivity of the multilayer dielectric film on the two light-passing surfaces enables multi-wavelength narrow-band filtering output over a wide spectral range, and has stable performance. It has wide optical aperture, high optical power destruction threshold, simple structure and low cost. Therefore, it is widely used in various types of lasers, optical measuring instruments and optical fiber communication devices.

The tuning function of the transmitted optical frequency can be achieved using a conventional optical Fabry-Perot etalon. For air-spaced Fabry-Perot etalons, tuning can be done by changing the angle of incidence of the light, but the tuning range of this method is small; it is also possible to change the Fabry by mechanical means (such as stepper motors). The cavity length of the Perot etalon is tuned. This method can achieve a large tuning range, but the tuning accuracy is low, and the precision of the mechanical components is high and the stability is not good. In addition, the PZT piezoelectric ceramic (lead zirconate titanate) technology can improve the tuning accuracy and speed by changing the cavity length of the Fabry-Perot etalon, but it is not easy to miniaturize and the drive circuit is complicated. Changing the temperature of the etalon can also achieve a wider range of tuning, but the disadvantage of this method is that it is slow.

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to overcome the deficiencies of the prior art and to provide a tunable Fabry-Perot filter with high stability, high tuning accuracy, fast speed and small volume.

The present invention solves the prior art problem by adopting the following technical solutions:

A tunable Fabry-Perot filter comprising a first mirror, a liquid crystal material, a second mirror and a driving circuit, wherein a high-reflectivity multilayer dielectric film is disposed outside the light-passing surface of the first mirror, An optical antireflection film is disposed on a first layer inside the light-passing surface of the first mirror, and a transparent electrode is disposed on the optical anti-reflection film; a high-reflectivity multilayer dielectric film is disposed outside the second mirror, and the second mirror is disposed An optical antireflection film is disposed on the inner first layer, a transparent electrode is disposed on the optical antireflection film, and a non-conductive material film having a thickness of several micrometers to ten micrometers is disposed on the transparent electrode to cover a portion other than the clear aperture And a channel extending to the edge of the mirror by a width of about one millimeter, and forming a cavity having a thickness of several micrometers to ten micrometers from the inner side of the first mirror, wherein the liquid crystal material is placed in the cavity; the driving circuit Connected to the two transparent electrodes, the outer side of the light-passing surface of the first mirror and the outer side of the light-passing surface of the second mirror are kept parallel and constitute a Fabry-Perot multi-beam interference cavity. Moreover, the liquid crystal material is a nematic liquid crystal.

Moreover, the first mirror and the second mirror are both optically transparent materials and have the same refractive index of light. Moreover, the driving circuit is a square wave pulse circuit having a frequency of several hundred hertz to several kilohertz, and the pulse voltage amplitude can be adjusted from 0 volts to 5 volts.

A tunable Fabry-Perot filter comprising a first mirror, a first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet, and a second mirror; the first mirror is permeable to light A high-reflectivity multilayer dielectric film is disposed on the outer side of the surface, and the inner side of the light-passing surface of the first mirror is an optically polished surface; the first optically transparent glass sheet is disposed inside the first mirror, and the outer side of the light-transmitting surface of the first optically transparent glass sheet An optically polished surface, an optical antireflection film is disposed on a first inner side of the light-transmitting surface of the first optically transparent glass sheet, and a transparent electrode is disposed on the optical anti-reflection film; and a high reflection is disposed outside the light-transmitting surface of the second mirror a multi-layer dielectric film, the inner side of the light-passing surface of the second mirror is an optically polished surface; the second optically transparent glass sheet is disposed inside the second mirror, and the outer side of the light-transmitting surface of the second optically transparent glass sheet is an optically polished surface. An inner first layer of the second optically transparent glass sheet is provided with an optical antireflection film, and a transparent electrode is disposed on the optical antireflection film, and a non-conductive layer having a thickness of several micrometers to ten micrometers is disposed on the transparent electrode a film of material covering a portion other than the light-passing aperture and forming a cavity having a thickness of several micrometers to ten micrometers from the inner side of the first optical glass sheet, in which the liquid crystal material is placed; the driving circuit is connected to the first optical On the transparent electrodes of the transparent glass sheet and the second optically transparent glass sheet, the outer side of the light-passing surface of the first mirror and the outer side of the light-transmitting surface of the second mirror are kept parallel and constitute a Fabry-Perot multi-beam interference cavity.

Moreover, the liquid crystal material is a nematic liquid crystal.

Moreover, the inner side of the first mirror and the outer side of the first optically transparent glass sheet are bonded together by an optically transparent index matching glue; the inner side of the second mirror and the outer side of the second optically transparent glass sheet are optically The transparent index matching glue is bonded together.

Moreover, the first mirror, the second mirror, the first optically transparent glass sheet, and the second optically transparent glass sheet are all optically transparent materials and have the same refractive index of light.

Moreover, the refractive index of the optically transparent index matching glue is the same as the refractive index of the optically transparent material.

Moreover, the driving circuit is a square wave pulse circuit having a frequency of several hundred hertz to several kilohertz, and the pulse voltage amplitude can be adjusted from 0 volts to 5 volts.

The advantages and positive effects of the present invention are:

The invention has reasonable design, and the liquid crystal is placed in the cavity of the Fabry-Perot etalon and utilizes the electronically controlled birefringence effect of the liquid crystal and the optical phase modulation of the linearly polarized light incident on a specific polarization direction to realize the transparent Continuous, fast and precise tuning of the linearly polarized light frequency through the Fabry-Perot filter, as well as fast and precise tuning of the optical frequency over a wide spectral range. Since the thickness of the liquid crystal material is very thin, a wideband tunable Fabry-Perot filter having a small size and a large free spectral range can be fabricated. The filter has no mechanical moving parts, stable and reliable performance, low cost, small size and easy Features such as installation and production for reliable operation in demanding small size and extreme operating environments, and are widely used in lasers, optical testing, fiber optic communications, biological, medical devices and fiber optic sensor networks.

DRAWINGS

Figure 1 is a schematic view of a conventional Fabry-Perot etalon;

Figure 2 is a schematic structural view of the present invention;

Figure 3 is a graph showing the phase of light transmitted through the liquid crystal material as a function of an applied electric field;

Figure 4 is a schematic view showing another structure of the present invention;

Figure 5 is a schematic diagram of the transmission spectrum of a common Fabry-Perot etalon;

Figure 6 is a schematic diagram of the transmission spectrum of the present invention.

Specific real Ife^

The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

A schematic of a conventional Fabry-Perot light etalon 100 is shown in FIG. The material of the Fabry-Perot etalon 100 is generally optical glass such as fused silica or BK7 in the near-infrared and visible-light bands, assuming that the material has a refractive index n and both light-passing surfaces 2 and 4 are plated high. The reflective film has a reflectance R and a thickness h. When the light is incident at an incident angle close to zero, the free spectral range FSR1 of the optical etalon 100 can be expressed as: Δλ^λ2/(2η1), or expressed by frequency: Av =c/(2nh), where c is the speed of light. The peak frequency of transmitted light can be expressed as: v = mc / (2nh), where m is the interference order, and the frequency broadband of the transmitted light can be expressed as: Δν ( FWHM ) = c(lR) / (2nhRl / 2), where c is the speed of light.

As can be seen from the above two equations, the free spectral range FSR1 of the optical etalon 100 is inversely proportional to the thickness h. Assuming that the material has a refractive index of n = 1.5, it is necessary to achieve FSRl = 100 GHz and a thickness of h - 1 mm. The free spectral range FSR1 is larger, the smaller its thickness. After the material and thickness of the etalon are determined, the frequency broadband of the transmitted light is mainly related to the reflectance R. The higher the reflectance, the smaller the frequency bandwidth or the sharpness. The Fabry-Perot optical etalon's transmission spectrum is characterized by a very narrow bandwidth for each transmission spectrum, a uniform frequency spacing of the transmission spectrum and a very wide optical bandwidth, typically covering an optical spectrum of 100 nm. Belt, as shown in Figure 5.

Since a liquid crystal material generally used as a photovoltaic device has a high electrical resistivity, it can be considered as an ideal dielectric material. The liquid crystal has anisotropic dielectric properties and uniaxial symmetry due to the ordered orientation of the molecules and the stretched morphology. Like a uniaxial crystal, the direction of the optical axis coincides with the alignment of the molecules. When the liquid crystal molecules act under the external electric field, an electric dipole is formed. Under the action of the moment formed by the electric dipole, the orientation of the liquid crystal molecules is turned to the direction of the electric field, and the direction of the optical axis of the liquid crystal can be changed by changing the strength of the electric field. Therefore, this characteristic of the liquid crystal can be utilized to fabricate an optical phase modulator, a tunable filter or other optoelectronic device such as an optical switch and a light emphasizer. The thickness of the liquid crystal film layer generally used as a photovoltaic device is from several micrometers to ten micrometers. Formal utilization liquid of the invention The crystal is designed to change the refractive index of linearly polarized light under the action of an electric field.

As shown in FIG. 2, a tunable Fabry-Perot filter 200 includes a first mirror 10, a liquid crystal material 18, a second mirror 20, and a driving circuit 14, a first mirror 10 and a second mirror. 20 are optically transparent materials and are coated with a high-reflectivity multilayer dielectric film on the outer surfaces 8 and 22 of the light-passing surface to form Fabry-Perot between two high-reflectivity multilayer dielectric films. a cavity; an optical anti-reflection film 12 and a transparent electrode film layer 16 are disposed in order from the outside to the inside of the light-passing surface of the first mirror 10; and the inside of the light-passing surface of the second mirror 20 is sequentially arranged from the outside to the inside. An optical antireflection film 24, a transparent electrode 26 and a film 19 of non-conductive material, the optical anti-reflection film 12 and the optical anti-reflection film 24 are respectively plated on the inner surface of the light-passing surface of the first mirror 10 and the second mirror 20 The inner surface of the light-passing surface. The non-conductive material film 19 has a thickness of several micrometers to ten micrometers, covers other portions except the light-passing aperture, and a channel extending to the edge of the mirror by a width of about one millimeter, in order to provide a liquid crystal for injecting excess liquid in the cavity. Export channel. The non-conductive material film and the inner side of the first transparent optical material form a cavity having a thickness of several micrometers and a few micrometers for arranging the liquid crystal material 18, and the liquid crystal material 18 is a nematic liquid crystal. The thickness of the liquid crystal material is from about several micrometers to ten micrometers. Since the thickness of the liquid crystal is small (several micrometers to ten micrometers), tunable Fabry-Perot can be made in the intrinsic free spectral range (ie, the free spectral range of the tunable filter without an applied electric field) filter. Two transparent electrodes are connected to the driving circuit 14, and a driving signal generated by the driving circuit forms a driving electric field between the two transparent electrode film layers; the Fabri is adjusted by changing the effective refractive index n of the liquid crystal in the Fabry-Perot cavity by the electric field. The optical frequency V and the free spectral range (FSR) of the transmitted light of the Perot filter. A typical driving electric field is a square wave signal having a voltage of several volts and a frequency of several hertz to several kilohertz.

In FIG. 2, the light beam 6 incident on the filter 200 is a beam traveling in the z direction, and the polarization axis is linearly polarized light in the X direction, assuming that the refractive index of the optically transparent material is n, and both of the light passing surfaces 8 and 22 are The highly reflective film is plated. Assuming a reflectance of R and a thickness of D, the free spectral range FSR2 and transmitted light of the filter 200 are: Δλ^λ2/(2ηϋ+Γ), or expressed by frequency: Av=c/ (2nD+r), where c is the speed of light, and Γ represents the optical path produced by the liquid crystal under the action of an applied electric field to change the incident light. The peak frequency of transmitted light can be expressed as: _V = m _C / (2nD + r), where m is the order of interference, and the frequency broadband of transmitted light can be expressed as: Δν (FWHM) = c(lR) / ((2nD+ r) Rl/2), where c is the speed of light.

Figure 3 shows the relationship between the phase change of a light-wavelength phase of a nematic liquid crystal with a thickness of 10 μm and a wavelength of 1550 nm. A maximum optical phase delay of about 6π can be achieved. According to the above formula, the tunable Fabry-Perot filter 200 can obtain a tuning range of the transmitted optical frequency of about 100 GHz for linearly polarized light incident at near zero degrees. In comparison, according to the above formula, the change of the free spectral range Δν and the frequency band of the transmitted light is much smaller. A schematic diagram of the transmission spectrum of the tunable Fabry-Perot filter is shown in Fig. 6.

It can be seen that the tunable Fabry-Perot filter 200 can achieve a larger range under the action of an applied electric field. The tuning of the transmitted light peak frequency does not substantially change the frequency broadband and free spectral range of the transmitted light. This feature is important for many applications in tunable Fabry-Perot filter 200, such as lasers and spectrum instruments.

Since the tunable Fabry-Perot filter 200 is fabricated, the surfaces of the light-transmitting surface outer surfaces 8 and 22 of the two optically transparent materials are required to be strictly parallel, which is an assembly of the tuned Fabry-Perot filter 200. It brings certain difficulties. To this end, we have designed another tunable Fabry-Perot filter 300, as shown in Figure 4. The tunable Fabry-Perot filter 300 includes a first mirror 32, a first optical glass sheet 36, a liquid crystal material 41, a second optical glass sheet 50, a second mirror 46, and a drive circuit 56. The difference between the filter 300 and the filter 200 is that, in the filter 300, the liquid crystal material 41 is first placed between two optically transparent glass sheets 36 and 50, and the light passing through the two optically transparent glass sheets 36 and 50 The inner side of the face is respectively coated with optical anti-reflection layers 38 and 52, transparent electrodes 40 and 54, and a film layer 41 of non-conductive material is disposed on the optically transparent glass piece 50 and the inner side of the first optically transparent glass piece 36 is formed. A cavity having a thickness of a few micrometers and a few micrometers is used to place the liquid crystal material. The other light-passing surfaces of the above two optically transparent glass sheets 36 and 50 are not coated, and the optically transparent glass sheets 36 and 50 and the liquid crystal material 42 constitute a liquid crystal cell. When the above liquid crystal cell is assembled, it is not necessary to keep the faces of the optically transparent glass sheets 36 and 50 strictly parallel, which makes it easier to handle during assembly. The light-passing surface 30 of the first mirror 32 is plated with a high-reflectance film, and the other light-passing surface is not coated. First, the first mirror 32 and the optically transparent glass sheet 36 are bonded together by an index matching adhesive 34. The light-passing surface 44 of the second mirror 46 is plated with a high-reflectance film, and the other light-passing surface is not coated. The second mirror 46 is then bonded to the optically clear glass sheet 50 by the index matching glue 48. In this process, the two highly reflective film faces of the two optically transparent glass sheets 32 and 46 are required. The 30 and 44 adjustments are strictly parallel to achieve the effect of multi-beam interference of the Fabry-Perot etalon. In general, the index matching adhesive 48 and the refractive index matching adhesive 34 are also the same due to the same optically transparent material employed. This technical solution is more convenient to assemble than the first design.

It is to be understood that the foregoing description is not intended to Many modifications and variations of the present invention are possible in the light of the above description. The specific implementation chosen is merely to better explain the principles of the invention and the application in practice. This description enables those skilled in the art to make better use of the present invention, designing different specific implementations and making corresponding changes as needed.

Claims

claims

1. A tunable Fabry-Perot filter, characterized in that: it includes a first reflector, a liquid crystal material, a second reflector and a drive circuit, and a high reflectivity is provided outside the light-passing surface of the first reflector. A high-reflectivity multi-layer dielectric film, an optical anti-reflection film is set on the first layer inside the light-passing surface of the first reflector, and a transparent electrode is set on the optical anti-reflection film; a high-reflectivity multi-layer dielectric is set on the outside of the second reflector. film, an optical anti-reflection film is set on the first layer inside the second reflector, a transparent electrode is set on the optical anti-reflection film, and a non-conductive material film with a thickness of several microns to more than ten microns is set on the transparent electrode, covering the The part outside the clear aperture and a channel about one millimeter wide leading to the edge of the reflector form a cavity with a thickness of several microns to more than ten microns together with the inside of the first reflector, and the liquid crystal material is placed in the cavity; The driving circuit is connected to two transparent electrodes. The outside of the light-passing surface of the first reflector and the outside of the light-passing surface of the second reflector are kept parallel and form a Fabry-Perot multi-beam interference cavity.

2. A tunable Fabry-Perot filter according to claim 1, characterized in that: the liquid crystal material adopts nematic liquid crystal.

3. A tunable Fabry-Perot filter according to claim 1, characterized in that: both the first reflector and the second reflector are optically transparent materials and have the same light refractive index. .

4. A tunable Fabry-Perot filter according to any one of claims 1 to 3, characterized in that: the driving circuit is a method with a frequency of several hundred hertz to several thousand hertz. Wave pulse circuit, the pulse voltage amplitude is adjustable from 0 volts to 5 volts.

5. A tunable Fabry-Perot filter, characterized by: including a first reflective mirror, a first optically transparent glass sheet, a liquid crystal material, a second optically transparent glass sheet and a second reflective mirror; the second reflective mirror A high-reflectivity multi-layer dielectric film is provided on the outside of the light-passing surface of the first reflector, and an optically polished surface is provided on the inside of the light-passing surface of the first reflector; a first optically transparent glass piece is disposed on the inner side of the first reflector, and the first optically transparent glass The outside of the light-passing surface of the first optically transparent glass sheet is an optically polished surface, the first layer inside the light-passing surface of the first optically transparent glass sheet is provided with an optical anti-reflection film, and a transparent electrode is provided on the optical anti-reflection film; A high-reflectivity multilayer dielectric film is provided on the outside of the light surface, and the inside of the light-passing surface of the second reflector is an optically polished surface; the second optically transparent glass sheet is disposed on the inside of the second reflector, and the light-passing surface of the second optically transparent glass sheet is The outer side is an optically polished surface, the inner first layer of the second optically transparent glass sheet is provided with an optical anti-reflection film, a transparent electrode is provided on the optical anti-reflection film, and a non-conductive layer with a thickness of several microns to more than ten microns is provided on the transparent electrode A thin film of conductive material covers the part except the clear aperture and forms a cavity with a thickness of several microns to more than ten microns with the inside of the first optical glass sheet. The liquid crystal material is placed in the cavity; the driving circuit is connected to the first optical glass sheet. On the transparent electrodes of the optically transparent glass sheet and the second optically transparent glass sheet, the outside of the light-passing surface of the first reflector and the outside of the light-passing surface of the second reflector remain parallel and form a Fabry-Perot multi-beam interference cavity.

6. A tunable Fabry-Perot filter according to claim 5, characterized in that: the liquid crystal material is nematic liquid crystal.

7. A tunable Fabry-Perot filter according to claim 5, characterized in that: the inside of the first reflector and the outside of the first optically transparent glass sheet are made of optically transparent refractive index matching glue. Bonded together; The inner side of the second reflector and the outer side of the second optically transparent glass sheet are bonded together using optically transparent refractive index matching glue.

8. A tunable Fabry-Perot filter according to claim 7, characterized in that: the first reflecting mirror, the second reflecting mirror, the first optically transparent glass sheet and the second optically transparent The glass sheets are all optically transparent materials and have the same light refractive index.

9. A tunable Fabry-Perot filter according to claim 8, characterized in that: the refractive index of the optically transparent refractive index matching glue is the same as the refractive index of the optically transparent material.

10. A tunable Fabry-Perot filter according to any one of claims 5 to 9, characterized in that: the driving circuit is a method with a frequency of several hundred hertz to several thousand hertz. Wave pulse circuit, the pulse voltage amplitude is adjustable from 0 volts to 5 volts.