Wide-angle phase difference depolarization reflector with silicon as substrate

Abstract

The invention discloses a wide-angle phase difference depolarization reflector with silicon as a substrate. According to the reflector, the metal nickel-chromium film layer and the metal silver film layer are combined, so that the binding force between the silicon substrate and the metal film layer is improved; high reflectivity and low polarization sensitivity of a signal channel are realized by utilizing the characteristics of the metal film layer; the metal film layer is prevented from being oxidized by using the protective layer, so that the reflecting mirror has relatively high environmental adaptability; and phase difference depolarization in a wide angle range of a signal channel is realized by utilizing a plurality of dielectric phase suppression film layers. The wide-angle phase difference depolarization reflector with the silicon substrate has the advantages that the number of film layers is small, the technology is easy to implement, and reliability is good.

Description

Technical Field

[0001] The present invention relates to an optical reflector, specifically an optical reflector which utilizes a combination of a metal reflective film and a multilayer dielectric phase suppression film layer, utilizes the characteristics of the metal thin film material to achieve high reflectivity and low polarization sensitivity, and utilizes the phase difference suppression film layer to achieve signal channel phase difference control. Background Art

[0002] Reflectors play a pivotal role in optical systems. In infrared high-energy laser systems, single-crystal silicon reflectors are favored because they can maintain high precision and high stability of beam transmission under long-term irradiation of high-power density lasers, and can meet the high standards of component precision and laser load capacity. The present invention cleverly combines a metal reflective film with a multi-layer dielectric phase suppression film layer to make the reflector have optical properties of high reflectivity, low polarization sensitivity, and small phase difference in the signal channel, and can be applied to laser radar, optical communications, spectral analysis and other fields.

[0003] When light is incident at an angle, S light and P light will inevitably separate, and the optical element will show polarization characteristics. Polarization sensitivity (LPS) is usually used to quantitatively describe the polarization characteristics of optical elements. Polarization sensitivity describes the sensitivity of the optical element of the instrument to the polarization state of the incident light. Polarization sensitivity can be expressed as the following formula (1):

[0004] LPS=(Rs-Rp) / (Rs+Rp)×100% (1)

[0005] Where Rs and Rp are the reflectivity of the S light component and the reflectivity of the P light component respectively. Summary of the invention

[0006] The present invention provides a wide-angle phase difference depolarization reflector based on silicon, which can achieve high reflectivity, low polarization sensitivity and phase difference depolarization of a signal channel.

[0007] The structure of the reflector described in the present invention includes an optical substrate, an adhesive layer, a metal film layer, a protective layer and a multi-layer dielectric phase suppression film layer, wherein the metal film layer realizes the high reflectivity of the reflector; the protective layer can ensure that the metal film layer is free from oxidation and has a high environmental adaptability; and the multi-layer dielectric phase suppression film layer realizes the phase difference control of the signal channel. The reflector structure described above not only ensures high reflectivity and low polarization sensitivity, but also realizes the phase difference depolarization of the signal channel.

[0008] The technical solution of the present invention is as follows:

[0009] 1) The optical substrate is a silicon substrate;

[0010] 2) coating a 10-15 nm thick metal nickel-chromium composite material or metal chromium material on a silicon substrate as an adhesive layer;

[0011] 3) Plating 120-150nm thick silver as the metal film layer can ensure that the reflector has sufficiently high reflectivity and low polarization sensitivity;

[0012] 4) Plating 30-50nm thick aluminum oxide as a protective layer can protect the metal silver film from oxidation and improve the environmental adaptability of the product;

[0013] 5) Coating a multi-layer dielectric phase suppression film. The film system structure is:

[0014] a1L b1H a2L b2H……a n L n H

[0015] Where n is the number of periods, ranging from 2 to 5; H represents a high refractive index thin film layer, whose material is Ta2O5, Nb2O5, TiO2 or ZnS; L represents a low refractive index thin film layer, whose material is SiO2, YbF3 or MgF2; a1, b1…a n 、b n is the thickness of each thin film layer, unit: nm; the thickness parameter is determined according to the phase difference requirement of the reflector.

[0016] Furthermore, the wide-angle phase difference depolarization reflector based on silicon is characterized in that when the reflector is used at an angle within the range of 15-45 degrees, n takes a value of 1 to 3; when the reflector is used at an angle within the range of 45-60 degrees, n takes a value of 3 to 5.

[0017] The reflector of the present invention has the following advantages:

[0018] 1) The metal film layer ensures that the reflector has high reflectivity in the near-infrared band, meeting the energy transmission requirements of the optical system;

[0019] 2) The multi-layer dielectric phase suppression film layer realizes the phase difference depolarization of the signal channel of the reflector in a wide angle range;

[0020] 3) The reflector has low polarization sensitivity in the near-infrared band;

[0021] 4) The reflector film system designed by the present invention has a simple structure, is easy to implement in process, and has high reliability of the film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Reflector structure diagram

[0023] Figure 2 Mirror reflectivity curve

[0024] Figure 3 Reflector phase difference curve

[0025] Figure 4 Reflector Polarization Sensitivity Curve DETAILED DESCRIPTION

[0026] The specific implementation modes of the present invention are described below based on examples.

[0027] The reflector works at 1550nm in the near-infrared band, with an incident angle of 51±8.5°, a reflectivity of >98%, LPS<1%, and a phase difference of <±3°. NiCr is selected as the bonding layer material, Ag as the metal film layer material, Al2O3 as the protective layer material, Nb2O5 as the high refractive index material, and SiO2 as the low refractive index material.

[0028] With the help of FilmWizard optical thin film design software, the multi-layer dielectric phase suppression film a1L b1H a2Lb2H……a n L n H, n is the number of cycles (2≤n≤5) for optimization. According to the incident angle of the reflector of 51±8.5°, n is selected as 3. Setting a reasonable optimization target during the optimization process is the key step in the optimization process. The final film structure is: 77.74L216.62H 211.16L 185.58H 165.79L 45.67H (unit: nm).

[0029] In the actual design process, the optimization target can also be adjusted according to the range of use angles, but the thickness of a single film layer should fully consider the firmness and stress matching between the film layers. The film system design using the design ideas of this patent belongs to the protection scope of this patent.

[0030] The specific implementation of the present invention is further described in detail in conjunction with the accompanying drawings: φ50×5mm silicon is used as a substrate, NiCr composite material is selected as the bonding layer 2, Ag is used as the metal film layer 3, Al2O3 is used as the protective layer material, SiO2 and Nb2O5 are used as low refractive index L and high refractive index H materials respectively, and the reflector structure is shown in the schematic diagram Figure 1 As shown. The working angle of the reflector is 51±8.5°, and the signal channel is 1550nm. The thickness of the NiCr layer is designed to be 10nm. The thickness of the metal silver film layer is designed to be 150nm. The thickness of Al2O3 is designed to be 50nm. The multilayer dielectric phase suppression film layer 5 is plated, and the film system is: 77.74L 216.62H 211.16L185.58H 165.79L 45.67H (unit: nm).

[0031] The process of implementing the reflector is as follows: 1) The silicon substrate is cleaned with a mixture of alcohol and ether, then placed on the workpiece holder in the vacuum chamber, and the vacuum chamber is evacuated to 1.5×10 -3Pa; 2) NiCr film layer and Ag film layer were grown in sequence by resistance thermal evaporation, and their deposition rates were 1nm / s and 0.8nm / s respectively; 3) Al2O3 film layer was deposited by electron beam evaporation; 4) When depositing the multi-layer dielectric phase suppression film layer, the ion source was turned on and O2 gas was filled into the vacuum chamber to make the vacuum chamber pressure between 4 and 5×10 -2 Pa range, electron beam evaporation is used to deposit SiO2 and Nb2O5 film layers, and the deposition rates are 0.8nm / s and 0.15nm / s respectively; 5) After completing the preparation of each film layer, the vacuum is maintained for 120 minutes, then the vacuum chamber is opened to take out the reflector, and finally the preparation of the reflector is completed.

Claims

1. A wide-angle phase difference depolarization reflector based on silicon, comprising an optical substrate (1), an adhesive layer (2), a metal film layer (3), a protective layer (4) and a multi-layer dielectric phase suppression film layer (5), characterized in that: The optical substrate (1) is made of silicon; The bonding layer (2) is a nickel-chromium metal composite film or a metal chromium film; The metal film layer (3) is a metal silver film with high reflectivity; The protective layer (4) is aluminum oxide; The multi-layer phase difference suppression film layer (5) is formed by overlapping two high and low refractive index materials with different thickness coefficients. a1L b1H a2L b2H……a n L n H in, n is the number of periods, ranging from 2 to 5; H represents a high-refractive-index thin film layer, whose material is Ta2O5, Nb2O5, TiO2 or ZnS; L represents a low-refractive-index thin film layer, whose material is SiO2, YbF3 or MgF2; a1, b1…a n , b n is the thickness of each thin film layer, unit: nm; the thickness parameter is determined according to the phase difference requirement of the reflector.

2. A wide-angle phase difference depolarization reflector based on silicon as claimed in claim 1, characterized in that: When the reflector is used at an angle within the range of 15-45 degrees, n takes a value of 1 to 3; when the reflector is used at an angle within the range of 45-60 degrees, n takes a value of 3 to 5.

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