WO2021063013A1

WO2021063013A1 - Tunable optical filter

Info

Publication number: WO2021063013A1
Application number: PCT/CN2020/094170
Authority: WO
Inventors: 刘哲; 李昱; 苏炎; 于光龙
Original assignee: 福州高意光学有限公司
Priority date: 2019-09-30
Filing date: 2020-06-03
Publication date: 2021-04-08
Also published as: CN112578494A

Abstract

A tunable optical filter (101). The tunable optical filter is a multi-cavity interference optical filter, has a transmission band within a wavelength range of 1200 nm to 1800 nm, and comprises a substrate (102) and an optical filter film layer plated on the surface of the substrate (102); the optical filter film layer comprises multiple cavity layers (104, 108) and reflective film stacks (103, 105, 107, 109) disposed on two end surfaces of the cavity layers (104, 108), and each reflective film stack (103, 105, 107, 109) comprises multiple high refractive index layers (103-2) and multiple low refractive index layers (103-1) alternately stacked, wherein the material for making the high refractive index layer (103-2) at least contains Si:H; the number of cavity layers of the optical filter (101) is greater than or equal to 3; the pass band of the optical filter (101) has a center wavelength, and when the working temperature range of the optical filter (101) partially overlaps a temperature range of 20 degrees Celsius to 85 degrees Celsius, the temperature drift coefficient of the center wavelength is greater than 70 pm/degrees Celsius and less than 300 pm/degrees Celsius. The optical filter can be obtained by one vacuum plating, avoiding the cumbersome processes of polishing silicon wafers and plating reflective films of two surfaces separately; a Si:H cavity layer having three cavities or more is easily implemented, and the optical filter has high rectangular degree.

Description

Tunable filter

Technical field

The invention relates to the field of lasers and optical communication application devices, in particular to the technical field of optical filters, in particular to tunable optical filters.

Background technique

The tunable filter is an important part of the optical system. For example, in narrow-pulse, broad-spectrum laser applications, a tunable filter is required to select a specific output wavelength; through a tunable etalon in the laser cavity, the functions of laser mode selection and wavelength locking can be realized. In the field of optical communications, tunable filters are widely used for wavelength management and control of devices, such as wavelength switching, wavelength division multiplexing, and dispersion compensation.

The key performance requirements of the tunable filter used in the field of optical communication are low insertion loss, better rectangular spectrum shape, high reflection isolation, and controllable dispersion. There are various ways to achieve wavelength tuning, such as micro-electromechanical systems (MEMS), fiber Bragg gratings, liquid crystal devices, and so on. With traditional optical interference filters, wavelength tuning can also be achieved by rotating the filter to adjust the angle of incidence of light. However, these methods or working principles are complicated, or rely on mechanical structures, and it is difficult to achieve miniaturization and high reliability of the device.

The temperature tuning filter used in optical communication generally uses a Fabry-Perot structure, and the cavity layer material uses Si material. Compared with conventional oxide materials, the temperature index of refraction coefficient of Si materials is about an order of magnitude higher, and the properties are sensitive to temperature and can provide a wider range of temperature tuning. The general solution is to polish the Si substrate on both sides to a good optical surface, and plate a reflective film on both sides to form a single cavity etalon structure. Since the insertion loss of the filter requires high parallelism and scattering of the upper and lower surfaces of the cavity layer, the polishing method requires strict control of the cavity layer thickness, surface flatness, and smoothness. In production, the process of polishing a silicon wafer, coating a reflective film on one surface, and coating a reflective film on the other surface requires a long process cycle and high cost. Limited by the single cavity structure, the rectangularity of the filter is not good.

The document "Tunable and Switchable Multiple-Cavity Thin Film Filters (Journal of Lightwave Technology, Vol.22, No.1, 2004)" reports a multiple-cavity film filter based on Si:H Cavity thin film filter, one cavity layer of the filter uses Si:H, and the other cavity layer uses conventional oxide materials such as SiO ₂ and Ta ₂ O _5. Through temperature adjustment, the wavelength switching function can be realized, but it cannot The center wavelength of the transmission band is tunable.

Summary of the invention

In view of the existing technology, the purpose of the present invention is to provide a temperature-tunable filter with a simple structure and an optical communication waveband.

In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

The tunable filter is a multi-cavity interference filter with a transmission band in the wavelength range of 1200nm to 1800nm, which includes a substrate and a filter film layer plated on the surface of the substrate;

The filter film layer includes a plurality of cavity layers and reflective film stacks arranged on both ends of the cavity layer,

The reflective film stack includes a plurality of high refractive index layers and a plurality of low refractive index layers alternately superimposed, wherein the material of the high refractive index layer includes at least Si:H;

The number of cavity layers of the filter is greater than or equal to 3;

The pass band of the filter has a center wavelength. When the working temperature range of the filter partially overlaps the temperature range of 20 degrees Celsius to 85 degrees Celsius, the temperature drift coefficient of the center wavelength is greater than 70 pm/degree Celsius and less than 300 pm/degree Celsius.

Further, the cavity layer material of the filter film layer is all made of Si:H material.

Further, the cavity layer material of the filter film layer is obtained by a physical vapor deposition method, preferably, obtained by a magnetron sputtering method.

Further, the material of the low refractive index layer includes at least one or more of _{SiO 2} , Si ₃ N ₄ , Ta ₂ O ₅ , and Nb ₂ O _5.

Further, the filter includes a heating layer that can conduct electricity, and the heating layer is disposed between the substrate and the filter film layer.

Further, a coupling layer is also provided between the adjacent reflective film stacks.

Further, the refractive index of the Si:H material in the range of 1200 nm to 1800 nm is greater than 3.2.

Further, the extinction coefficient of the Si:H material in the range of 1200nm to 1800nm is less than 5×10 ^-5 .

Further, the substrate of the filter is made of fused silica or silicon material.

Further, the -15dB bandwidth of the transmission band of the filter is not greater than 1.2nm.

Further, the filter has multiple transmission peaks in the wavelength range of 1200 nm to 1800 nm, the transmission peaks are arranged at equal intervals in frequency, and the distance between adjacent transmission peaks is not greater than 50 nm.

By adopting the above technical solution, compared with the prior art, the present invention has the beneficial effect that: the filter of the present invention can be obtained by vacuum coating at one time, avoiding the polishing of silicon wafer and the two-surface reflective film coating. A tedious process; easy to realize a Si:H cavity layer with 3 cavities or more, and the filter has a higher rectangular degree.

Description of the drawings

The solution of the present invention will be further described below in conjunction with the drawings and specific implementations:

Figure 1 is a schematic structural diagram of the scheme of the present invention;

Figure 2 is a schematic diagram of the absorption characteristics of Si:H materials, where the abscissa is the wavelength (nm) and the ordinate is the extinction coefficient (dimensionless).

Figure 3 is a schematic diagram of the refractive index characteristics of Si:H materials, where the abscissa is the wavelength (nm) and the ordinate is the refractive index (dimensionless).

4 is a diagram of the relationship between transmittance and wavelength in Example 1 of the present invention at 25 degrees Celsius, where the abscissa is the wavelength (nm), and the ordinate is the transmittance (dB).

5 is a diagram of the relationship between transmittance and wavelength at 25 degrees Celsius and 100 degrees Celsius in Example 1 of the present invention, where the abscissa is wavelength (nm), and the ordinate is transmittance (dB).

6 is a diagram of the relationship between transmittance and wavelength in Example 2 of the present invention at 25 degrees Celsius, where the abscissa is the wavelength (nm), and the ordinate is the transmittance (dB).

Detailed ways

As shown in FIG. 1, it shows the filter 101 of the present invention, which includes a substrate 102 and a filter film layer; the material of the substrate 102 is generally fused silica or silicon. The filter film layer in this solution is a multi-cavity band-pass filter, which includes a plurality of

cavity layers

104, 108 and

reflective film stacks

103, 105, 107, and 109 provided on both sides of the

cavity layers

104, 108.

Among them, the material of the

cavity layers

104 and 108 is made of Si:H, and its optical thickness is generally an even multiple of 1/4λ of the working center wavelength. The reflective film stacks 103, 105, 107, 109 are formed by alternately superimposing the low refractive index material layer 103-1 and the high refractive index material layer 103-2. The optical thickness of each layer is generally an odd number of the thickness of 1/4λ of the working center wavelength. Times.

In addition, between the reflective film stacks of two adjacent cavities, there is a coupling layer 106 composed of a low refractive index material, the optical thickness of which is generally an odd multiple of the thickness of 1/4λ of the working center wavelength. For illustration, Figure 1 only illustrates the partial implementation structure of the multi-cavity filter, which mainly includes two cavity layers, four reflective film stacks, and each reflective film stack contains 4 film layers, but it can actually be carried out according to needs. Adjust to achieve the purpose of the application.

In the tunable filter of the present invention, the number of

cavity layers

104, 108 made of Si:H material is greater than or equal to 3, and the material of the low refractive index layer 103-1 of the filter film layer is preferably SiO ₂ , Si ₃ N ₄ , Ta ₂ O ₅ , Nb ₂ O ₅ one or more of them. Optionally, a heating layer 110 may be plated between the substrate 102 and the filter film layer, the material of which is conductive and transparent to the working wavelength, generally a ZnO or polysilicon heating layer. By controlling the current of the heating layer 110, the working temperature of the filter can be controlled.

Figure 2 is a schematic diagram of the absorption characteristics of Si:H materials, where the abscissa is the wavelength (nm) and the ordinate is the extinction coefficient (dimensionless). The Si film material obtained by physical vapor deposition in the conventional process has a large absorption in the 1200nm-1800nm waveband (the extinction coefficient is greater than 1×10 ^-4 ), resulting in excessively high insertion loss and cannot be used. The extinction coefficient of Si:H material from 1200nm to 1800nm is less than 5×10 ^-5 , which better solves the absorption problem of deposited Si material. Figure 3 is a schematic diagram of the refractive index characteristics of Si:H materials, where the abscissa is the wavelength (nm) and the ordinate is the refractive index (dimensionless). The refractive index of Si:H material in the wavelength range of 1200nm to 1800nm is greater than 3.2, which is slightly lower than that of bulk silicon material.

Example 1

In this embodiment, the working center wavelength of the filter is 1550.3 nm, and it contains 3 cavity layers made of Si:H material. The refractive index at 1500 nm is 3.40 and the extinction coefficient is 2.54×10 ^-6 . The film structure is as follows:

HLHLHLHL 4H LHLHLHLHL

HLHLHLHL 4H LHLHLHL3.12H 1.39L

Among them, H represents a Si:H material film layer with an optical thickness of 1/4λ (λ is 1550.3 nm), and L represents a SiO ₂ material film layer with an optical thickness of 1/4λ (λ is 1550.3 nm).

Figure 4 is a diagram showing the relationship between transmittance and wavelength of the embodiment at 25 degrees Celsius. The -0.5dB bandwidth of the filter of this embodiment is greater than 0.3nm, the -15dB bandwidth is less than 1.2nm, and the transmission insertion loss is less than 0.35dB. The advantage of this embodiment is that benefiting from the increase in the number of cavities, the jitter and rectangularity of the filter are better than those of current tunable filter products.

Fig. 5 is a diagram showing the relationship between transmittance and wavelength at 25 degrees Celsius and 100 degrees Celsius in Example 1 of the present invention. At 25 degrees Celsius, the central wavelength of the transmission band of this embodiment is 1550.3 nm; at 100 degrees Celsius, the central wavelength of the transmission band of this embodiment is 1559.2 nm. In the range of 25 to 100 degrees Celsius, the thermal tuning coefficient of the center wavelength is dλ/dT=119pm/°C.

Example 2

In this embodiment, the working wavelength of the filter is 1500nm to 1600nm, and it is designed to have multiple transmission peaks in this wavelength range, including three Si:H cavity layers. Its refractive index at 1500nm is 3.40 and the extinction coefficient is 2.54× 10 ^-6 . The film structure is as follows: HL 160H LHL HLHL160H LHLHLHL 160H LH

Wherein, H represents a Si:H material film layer with an optical thickness of 1/4λ (λ is 1550 nm), and L represents a SiO ₂ material film layer with an optical thickness of 1/4λ (λ is 1550 nm). Fig. 6 is a diagram showing the relationship between transmittance and wavelength of the embodiment at 25 degrees Celsius. In the wavelength range of 1500nm to 1600nm, the filter has multiple transmission peaks, the transmission bands are arranged at equal intervals in frequency, the distance between adjacent transmission peaks is 18.3nm, and the full width at half maximum (FWHM) of each transmission peak is about 0.51 nm. The advantage of this embodiment is that the effect of the silicon etalon is realized by a vacuum coating method at one time, and the tedious process of polishing the silicon wafer and plating two reflective films separately is avoided, and it is convenient for mass production.

The above are the embodiments of the present invention. For those of ordinary skill in the art, according to the teachings of the present invention, all the equivalent changes made according to the scope of the patent application of the present invention without departing from the principle and spirit of the present invention, Modifications, substitutions and variations should all fall within the scope of the present invention.

Claims

The tunable filter, which is a multi-cavity interference filter, is characterized in that it has a transmission band in the wavelength range of 1200nm to 1800nm, and includes a substrate and a filter film layer plated on the surface of the substrate;

The filter film layer includes a plurality of cavity layers and reflective film stacks arranged on both ends of the cavity layer,

The reflective film stack includes a plurality of high refractive index layers and a plurality of low refractive index layers alternately superimposed, wherein the material of the high refractive index layer includes at least Si:H;

The number of cavity layers of the filter is greater than or equal to 3;

The pass band of the filter has a center wavelength. When the working temperature range of the filter partially overlaps the temperature range of 20 degrees Celsius to 85 degrees Celsius, the temperature drift coefficient of the center wavelength is greater than 70 pm/degree Celsius and less than 300 pm/degree Celsius.
The tunable filter according to claim 1, wherein the cavity layer material of the filter film layer is all made of Si:H material.
The tunable filter according to claim 1, wherein the cavity layer material of the filter film layer is obtained by a physical vapor deposition method.
The tunable filter according to claim 1, wherein the material of the low refractive index layer includes at least one or more of SiO 2 , Si 3 N 4 , Ta 2 O 5 , and Nb 2 O 5 Kind.
The tunable filter according to claim 1, wherein the filter comprises a heating layer that can conduct electricity, and the heating layer is arranged between the substrate and the filter film layer.
The tunable filter according to claim 1, wherein the refractive index of the Si:H material in the range of 1200nm to 1800nm is greater than 3.2; the Si:H material has a refractive index in the range of 1200nm to 1800nm. The extinction coefficient is less than 5×10 -5 .
The tunable filter according to claim 1, wherein a coupling layer is further provided between the adjacent reflective film stacks.
The tunable filter according to claim 1, wherein the substrate of the filter is made of fused silica or silicon material.
The tunable filter according to claim 1, wherein the -15dB bandwidth of the transmission band of the filter is not greater than 1.2 nm.
The tunable filter according to claim 1, wherein the filter has multiple transmission peaks in the wavelength range of 1200nm to 1800nm, the transmission peaks are arranged at equal intervals in frequency, and the distance between adjacent transmission peaks Not more than 50nm.