Beam splitter with adjustable power ratio

Abstract

The invention discloses a beam splitter with an adjustable power ratio, which comprises a beam splitter, a first reflector and a second reflector are respectively arranged on a transmission light path and a reflection light path of the beam splitter, and an input light beam is transmitted and reflected into a first light beam and a second light beam through the beam splitter, the first light beam is reflected to a first position of the beam splitter through a first reflector, the second light beam is reflected to a second position of the beam splitter through a second reflector, and the first position and the second position coincide and interfere to form first output light and second output light; and the power ratio of the first output light to the second output light is adjusted by adjusting the optical path difference between the first light beam and the second light beam. The beam splitter is low in manufacturing cost, and the power ratio of the beam splitter is continuously adjustable.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical beam splitters, and particularly relates to a power ratio adjustable beam splitter. BACKGROUND

[0002] 1x2 power beam splitter is a commonly used component in optical network. According to the application, the power ratio can be changed from 1 / 99 to 50 / 50. The power ratio of the traditional splitter is fixed and cannot be adjusted. However, for some applications, for example, for a splitter, the splitting ratio is from 100 / 0 to 0 / 100, and the light completely enters another output from one output, and the splitter with adjustable power ratio can make the optical network more flexible. SUMMARY

[0003] To solve the above technical problems, the application provides a power ratio adjustable beam splitter, and provides a low-cost power ratio continuously adjustable beam splitter to solve the problems existing in the prior art.

[0004] To achieve the above object, the application provides a power ratio adjustable beam splitter, which comprises:

[0005] The beam splitter is provided with a first mirror and a second mirror on a transmission light path and a reflection light path respectively, the input light beam is transmitted and reflected into a first light beam and a second light beam through the beam splitter, the first light beam is reflected to a first position of the beam splitter through the first mirror, the second light beam is reflected to a second position of the beam splitter through the second mirror, and the first position and the second position coincide and interfere to form a first output light and a second output light; and the power ratio of the first output light and the second output light is adjusted by adjusting the optical path difference between the first light beam and the second light beam.

[0006] Optionally, the beam splitter is a non-polarized beam splitter.

[0007] Optionally, the power ratio of the first output light and the second output light is P L / P B ;

[0008] The power P B of the second output light is:

[0009]

[0010] The power P L of the first output light is:

[0011]

[0012] Wherein, ∈ represents the phase difference generated by the interface of the beam splitter, τ represents the optical path difference between the first light beam and the second light beam, and λ represents the optical wavelength of the input light beam, is the phase difference between the first light beam and the second light beam, and the power of the first output light and the second output light is only related to the phase difference between the first light beam and the second light beam.

[0013] Optionally, an optical path difference adjuster is arranged on the optical path between the beam splitter and the first mirror, an optical path difference thermal compensator is arranged on the optical path between the beam splitter and the second mirror, the optical path difference adjuster and the optical path difference thermal compensator adopt the same heat-sensitive material, a heater is arranged in the optical path difference adjuster, the positions of the first mirror and the second mirror are fixed, the optical path of the first light beam is adjusted by heating the optical path difference adjuster through the heater, and the optical path difference is adjusted by adjusting the temperature difference between the optical path difference adjuster and the optical path difference thermal compensator.

[0014] Optionally, the relationship between the temperature difference and the optical path difference is:

[0015]

[0016] Wherein, τ(T1) represents the optical path difference when the temperature of the optical path difference adjuster is T1, D is the thickness of the optical path difference adjuster, T1 is the temperature of the optical path difference adjuster, T2 is the temperature of the environment, that is, the temperature of the optical path difference compensator, n represents the refractive index of the optical path difference compensator, and σ is the thermal expansion coefficient.

[0017] Optionally, the first mirror adopts a PZT-driven mirror.

[0018] Optionally, an anti-reflection film is arranged on the optical path between the beam splitter and the first mirror and the second mirror through a transparent material.

[0019] Optionally, a gasket is arranged between the two sides of the first mirror and the beam splitter, and the gasket is used to fix the relative positions of the first mirror and the beam splitter.

[0020] Optionally, a gasket is arranged between the two sides of the second mirror and the beam splitter, and the gasket is used to fix the relative positions of the second mirror and the beam splitter.

[0021] Compared with the prior art, the present application has the following advantages and technical effects:

[0022] In the present application, a power ratio adjustable beam splitter is proposed. This is achieved by slightly adjusting the optical path length difference between the two side (top and right) mirrors of a Michelson interferometer. By slightly adjusting the optical path length difference between the two side mirrors, the power distribution can be adjusted to any desired ratio. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application and are incorporated herein for a purpose of explanations. The present application illustratively shown in the drawings is intended to explain the present application and is not intended to limit the present application. In the drawings:

[0024] Figure 1 A power ratio adjustable beam splitter is an embodiment of the present application; reference signs are: 6, a power ratio continuously adjustable beam splitter;

[0025] Figure 2 A Michelson interferometer structure diagram is an embodiment of the present application; reference signs are: 1, a first mirror; 2, a second mirror; 3, a beam splitter; 11, a first light beam; 21, a second light beam; 211, a first interference light beam; 212, a second interference light beam; 111, a third interference light beam; 112, a fourth interference light beam; 14, an incident light beam; 151, a first output light; 152, a second output light;

[0026] Figure 3 A bandwidth coefficient and a splitting power ratio relationship diagram is an embodiment of the present application;

[0027] Figure 4 A thermally driven power ratio adjustable beam splitter is an embodiment of the present application; reference signs are: 1, a first mirror; 2, a second mirror; 3, a beam splitter; 14, an incident light beam; 151, a first output light; 152, a second output light; 431, a first anti-reflection film; 432, a second anti-reflection film; 441, an optical path difference thermal compensator; 442, an optical path difference adjuster; 443, a heater;

[0028] Figure 5 A PZT driven power ratio adjustable beam splitter is an embodiment of the present application; reference signs are: 1, a first mirror; 2, a second mirror; 3, a beam splitter; 14, an incident light beam; 151, a first output light; 152, a second output light; 431, a first anti-reflection film; 432, a second anti-reflection film; 51, a PZT. DETAILED DESCRIPTION

[0029] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] It is noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0031] In the present application, a low manufacturing cost power ratio continuously tunable beam splitter is proposed. As shown in Figure 1 The input power P0 of the power ratio continuously tunable beam splitter 6 is divided into two paths, αP0 and (1-α)P0, where 0≤α≤1. The ratio α is tunable.

[0032] Michelson interferometer:

[0033] Based on the structure of the Michelson interferometer, the present application provides a low manufacturing cost power ratio continuously tunable beam splitter.

[0034] As shown in Figure 2 The principle diagram of the Michelson interferometer is shown. The Michelson interferometer includes a beam splitter 3 and two mirrors (a first mirror 1 and a second mirror 2). The beam splitter 3 divides the incident light beam 14 into two parts at point P, where P is the splitting point of the beam splitter 3, a first light beam 11 and a second light beam 21. After being reflected by the first mirror 1 and the second mirror 2 respectively, the first light beam 11 and the second light beam 21 are incident to the beam splitter 3 for the second time at point Q, where Q is the converging point of the beam splitter 3. The second light beam 21 reflected from the top is divided into two beams, a first interference light beam 211 on the left side of the beam splitter 3 and a second interference light beam 212 on the bottom of the beam splitter 3; the first light beam 11 reflected from the right is divided into two beams, a third interference light beam 111 on the left side of the beam splitter 3 and a fourth interference light beam 112 on the bottom of the beam splitter 3. The two beams on the left side of the beam splitter 3, the first interference light beam 211 and the third interference light beam 111, interfere with each other to form a first output light 151; the two beams on the bottom of the beam splitter 3, the second interference light beam 212 and the fourth interference light beam 112, interfere with each other to form a second output light 152. The beam splitter 3 uses a non-polarized beam splitter.

[0035] In the present application, it is assumed that the power of the incident light beam 14 is 1 unit, and the beam splitter 3 has a 50 / 50 power splitting ratio for two orthogonal polarization states. In this case, the power of each of the four light beams (the first interference light beam 211, the second interference light beam 212, the third interference light beam 111 and the fourth interference light beam 112) is 1 / 4. After interference, the two light beams formed (the first output light 151 and the second output light 152), the output power P L of the first output light 151 on the left side is 1 / 2, and the output power P BThe size of the interference depends on the phase difference between the beams. Due to energy conservation, P B and P L sum to 1.

[0036] To better describe the phase difference between the interference beams, the following parameters are defined:

[0037] φ r : the phase produced by the upward reflection of the left input light of beamsplitter 3.

[0038] φ r' : the phase produced by the downward reflection of the right input light of beamsplitter 3.

[0039] φ t : the phase produced by the transmission of beamsplitter 3.

[0040] ∈: the phase difference between the transmitted and reflected beams of beamsplitter 3, ∈ = (φ t - φ r )

[0041] L1: the optical path length from point P to first mirror 1 to point Q.

[0042] L2: the optical path length from point P to second mirror 2 to point Q.

[0043] τ: the difference in optical path length between the right and top paths, τ = (L1 - L2).

[0044] For a non-absorbing material used for the beamsplitting surface in beamsplitter 3, the phases produced by the reflection and transmission of the beamsplitting surface of beamsplitter 3 must satisfy the following equation:

[0045] φ r + φ r' = 2φ t + π (1)

[0046] At the bottom end of beamsplitter 3, the phases ψ tr' and ψ rt of the second and fourth interference beams 212 and 112, respectively, and their difference Δψ B at the output end are:

[0047]

[0048] where v represents the frequency of the incident light beam 14 and C represents the speed of light.

[0049] At the left end of beamsplitter 3, the phases ψ tt and ψ rr of the first and third interference beams 211 and 111, respectively, and their difference Δψ L at the output end are:

[0050]

[0051] Based on equation (1), (φ r' -φ r ) = 2(φ t -φ r ) + π = 2∈ + π

[0052] For a symmetric coated beamsplitter 3, φ r = φ r' , thus

[0053] Based on (2) and (3), the output powers P B and P L of the second output light 152 and the first output light 151 are:

[0054]

[0055] Equation (4) shows that the sum of the output powers P L and P B of the first output light 151 and the second output light 152 is always equal to 1. As mentioned before, ∈ is a result of the coating and the Fresnel coefficients of the beamsplitter 3. The following derivation assumes that ∈ is independent of wavelength.

[0056] For a given design wavelength λ0of the beamsplitter 3, the power split ratio can be adjusted by changing the optical path difference. To adjust P T from 0 to 1, one needs:

[0057]

[0058] Equation (4) states that the optical path length difference needs to be changed by only to adjust the power of one of the outputs from 0 to 100%.

[0059] It is important to note that in equation (4), the power ratio is a function of the operating wavelength λ of the input light. When the operating wavelength is close to the design wavelength λ0, the beamsplitter 3 will split the light close to the designed split ratio. The following analysis considers how far the split ratio will deviate from the designed value when the wavelength deviates from λ0. The following calculations consider the case where the coating on the beamsplitter 3 is symmetric, meaning that the coating structure from left to right is the same as from right to left, i.e., the phase If the designed power ratio is the power ratio of the output power P L of the first output light 151 and the output power P B of the second output light 152 is α / (1-α), and the beamsplitter is designed to have λ0as the center wavelength. When the operating wavelength of the input beam is λ0, the power of the first output light 151, α0, is:

[0060]

[0061] When the operating wavelength λ deviates from λ0, the output light power α(λ) is:

[0062] α(λ)=sin 2 (2πτ / λ) (7)

[0063] If the deviation of the operating wavelength from λ0 is much smaller than λ0, the corresponding change in Δα will be...

[0064]

[0065] The key parameter of beam splitter 3 is the percentage error β of the splitting power variation, i.e., β = Δα / α0.

[0066]

[0067] In equation (9), Ω is called the bandwidth factor; the smaller the better. For example, if Ω = 1, when the wavelength deviates from the design wavelength... At that time, the splitting power ratio will deviate by 5%. Figure 3 The relationship between Ω and the percentage error in output power is shown.

[0068] It can be seen that the error is larger when the normalized power is low. If the design wavelength is 1550nm and the operating wavelength is 1600nm, the percentage error at low power will be significantly higher. The error is negligible at the high power end. For example, if such a power-adjustable beam splitter is used with two output powers set to 1% / 99%, the ratio is 1 / 99 at the designed wavelength. However, at a distance of 50 nm from the designed wavelength, the splitting ratio becomes (1-0.065) / (99+0.065). In other words, the error on the low power side is 6.5%. For a 1 / / 99 beam splitter, an error of less than 10% on the 1% output side is quite good. In this invention, the error on the 1% output side is 6.5% of 1%.

[0069] Thermally driven tuned power ratio adjustable beam splitter:

[0070] Figure 4This describes a heat-driven and temperature-tunable beam splitter. It features a symmetrical structure where a first reflector 1 and a second reflector 2 are connected to a beam splitter 3 via two pairs of gaskets. The first reflector 1, second reflector 2, gaskets, and beam splitter 3 form two cavities. A first antireflection coating 431 and a second antireflection coating 432 are respectively disposed between the first reflector 1, second reflector 2, and beam splitter 3. The right-side cavity has an optical path difference (OPD) adjuster 442 for setting the desired split ratio; the top cavity has an optical path difference thermal compensator 441 to ensure that the optical path difference τ does not change with ambient temperature. The optical path difference adjuster 442 and the optical path difference thermal compensator 441 use the same thermistor material, and their thicknesses are close to or the same. A heater 443, typically a thermistor, is disposed on the optical path difference adjuster 442 in the right-side cavity to change the temperature of the optical path difference adjuster 442. By setting an appropriate temperature difference between the optical path difference adjuster 442 and the optical path difference thermal compensator 441, the optical path difference required to achieve the target spectral ratio can be generated.

[0071] For example, taking a silicon wafer as the thermally sensitive material, if the physical length of the cavity is L0 and the silicon wafer with thickness D is inside the cavity, and if the temperatures of the optical path difference adjuster 442 and the optical path difference thermal compensator 441 are T1 and T2, respectively, where T2 is the ambient temperature and T1 is equal to or greater than T1, the temperature-related optical path length difference is:

[0072]

[0073] In equation (10), σ is the coefficient of thermal expansion, and n represents the refractive index of the optical path difference thermal compensator 441. Taking silicon as an example, the second term... It is much larger than the first term (n-1)σ. For D = 1 mm, When the temperature difference is 1 degree, the optical path difference τ changes by 0.2 micrometers. If the designed wavelength is 1.6 μm, a path length change of 0.4 μm is required to change the normalized power in an output port from 0 to 1. In this specific case, changing the silicon wafer temperature by 2 degrees is sufficient.

[0074] All existing shunts have a fixed shunt ratio. To achieve an adjustable power ratio, it requires many shunts with different ratios, using an optical switch to select the desired one. Therefore, it is quite expensive and large in size. Thermally tuned beam splitters are the most cost-effective method. If faster adjustment is required for certain applications, the fixed first reflector 1 can be replaced with a first reflector 1 driven by a PZT51 (piezoelectric ceramic).

[0075] PZT-driven tuned power ratio adjustable beam splitter:

[0076] like Figure 5As shown, the top of the beam splitter 3 is fixed to the second reflector 2 by a shim, and the first reflector 1 driven by PZT51 is set on the right side. By adjusting the physical length of PZT51, the optical path difference between the first reflector 1 and the second reflector 2 is adjusted, thereby adjusting the output power ratio.

[0077] This invention proposes a beam splitter with adjustable power ratio. This is achieved by adjusting the optical path length difference between the two (top and right) mirrors of a Michelson interferometer. By slightly adjusting the path length difference between the two mirrors, the power distribution can be adjusted to any desired ratio.

[0078] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power ratio adjustable beam splitter, characterized in that, include: A beam splitter has a first reflecting mirror and a second reflecting mirror respectively disposed on its transmission and reflection optical paths. The beam splitter transmits and reflects an input light beam into a first beam and a second beam. The first reflecting mirror reflects the first beam to a first position of the beam splitter, and the second reflecting mirror reflects the second beam to a second position of the beam splitter. The first position and the second position coincide and interfere to form a first output beam and a second output beam. The power ratio of the first output beam and the second output beam can be adjusted by adjusting the optical path difference between the first beam and the second beam.

2. The power ratio adjustable beam splitter according to claim 1, characterized in that, The beam splitter is a non-polarized beam splitter.

3. The power ratio adjustable beam splitter according to claim 1, characterized in that, The power ratio of the first output light to the second output light is P. L / P B ; The power P of the second output light B for: The power P of the first output light L for: Where ∈ represents the phase difference generated at the interface of the beam splitter when the first beam passes through it and the second beam is reflected by it; τ represents the optical path difference between the first and second beams; and λ represents the optical wavelength of the input beam. It is the phase difference between the first beam and the second beam, and the power of the first output light and the second output light is only related to the phase difference between the first beam and the second beam.

4. The power ratio adjustable beam splitter according to claim 1, characterized in that, An optical path difference adjuster is provided on the optical path between the beam splitter and the first reflector, and an optical path difference thermal compensator is provided on the optical path between the beam splitter and the second reflector. The optical path difference adjuster and the optical path difference thermal compensator use the same thermosensitive material. A heater is provided in the optical path difference adjuster. The positions of the first reflector and the second reflector are fixed. The optical path difference adjuster is heated by the heater to adjust the optical path of the first beam. The optical path difference is adjusted by adjusting the temperature difference between the optical path difference adjuster and the optical path difference thermal compensator.

5. The power ratio adjustable beam splitter according to claim 4, characterized in that, The relationship between the temperature difference and the optical path difference is as follows: Where τ(T1) represents the optical path difference when the optical path difference adjuster is at temperature T1, D is the thickness of the optical path difference adjuster, T1 is the temperature of the optical path difference adjuster, T2 is the ambient temperature, i.e. the temperature of the optical path difference compensator, n represents the refractive index of the optical path difference compensator, and σ is the coefficient of thermal expansion.

6. The power ratio adjustable beam splitter according to claim 1, characterized in that, The first reflector is a PZT driven reflector. The position of the first reflector is fixed, and the optical path difference is adjusted by driving the distance between the first reflector and the beam splitter through PZT.

7. The power ratio adjustable beam splitter according to claim 1, characterized in that, The beam splitter is fixed with an anti-reflection film on the optical path between the first and second reflectors by a transparent material.

8. The power ratio adjustable beam splitter according to claim 1, characterized in that, Gaskets are provided between the two sides of the first reflector and the beam splitter, and the gaskets are used to fix the relative position between the first reflector and the beam splitter.

9. The power ratio adjustable beam splitter according to claim 4, characterized in that, Gaskets are provided between the two sides of the second reflector and the beam splitter, and the gaskets are used to fix the relative position between the second reflector and the beam splitter.

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