JP4129596B2 - Optical device - Google Patents

Description

The present invention relates to an optical apparatus that includes a diffraction grating element that diffracts light having different wavelengths and transmits / receives light having different wavelengths.

  In optical communication, light having different wavelengths is bidirectionally transmitted using an optical transmission member such as an optical fiber. An optical device used for transmission / reception in such optical communication, that is, a signal is carried in light and transmitted to the light transmission member, and light is received from the light transmission member and the signal carried in the light is detected. In an optical device, it is necessary to arrange a transmitting unit for transmitting light and a light receiving unit for receiving light at different positions while sharing the same optical transmission medium for the transmitted light and the received light. Therefore, a separating and coupling member that separates and couples the light flux is disposed on the extension of the optical transmission member, and the optical path from the sending unit to the separating and coupling member and the optical path from the separating and coupling member to the light receiving unit are separated, and the separating and coupling member The optical paths of both light fluxes from the optical transmission member to the optical transmission member are coupled (matched).

  In order to increase the amount of communication, the light transmitted in the same direction by the optical transmission member is also included with light having different wavelengths. In such an optical device for optical communication, in addition to providing a plurality of transmission units or light receiving units, a plurality of separation coupling members are provided, or a function of separating light having different wavelengths from the optical transmission member is a single function. It will also be attached to the separating and coupling member.

  As the separating and coupling member, a multilayer filter that reflects or transmits incident light according to its wavelength is used. However, the multilayer filter has a problem that the production process is complicated and time is required for production, and the cost is high.

In an optical recording / reproducing apparatus that records information on a recording medium using light and reads information from the recording medium, it is necessary to separate and combine light beams as in the optical apparatus for optical communication. Japanese Patent Laid-Open No. 2000-163791 proposes to use a diffraction grating that diffracts incident light at different angles according to the wavelength as an optical coupling head of an optical recording / reproducing apparatus that uses light of different wavelengths. Has been.
JP 2000-163791 A

  Since the diffraction grating is formed by arranging irregularities periodically, it can be formed by resin molding. Therefore, the diffraction grating element provided with the diffraction grating has an advantage that it is suitable for mass production and low cost.

  In order to spatially separate a plurality of light beams having different wavelengths by utilizing the wavelength dependence of the diffraction angle by the diffraction grating, it is necessary to reduce the period of the unevenness of the diffraction grating. In addition, since the wavelength of the light to be diffracted has a certain width, the diffracted light beam spreads even if a parallel light beam is incident on the diffraction grating. The spread of the light beam after diffraction increases as the wavelength band of incident light increases, and increases as the period of the diffraction grating decreases.

  In the optical communication device, when the diffracted light beam spreads, a part of the transmitted light does not enter the light transmission member, or a part of the light from the light transmission member does not enter the light receiving unit, As a result, the accuracy of the transmitted and received signals is reduced. In order to prevent this, a condensing optical member must be disposed between the optical transmission member and the separation / coupling member, or between the separation / coupling member and the light receiving unit, which leads to an increase in the size of the apparatus. .

  In the optical recording / reproducing apparatus, when the light beam after diffraction spreads, the light cannot be converged to a minute range on the recording medium, the recording density is lowered, or a part of the light from the recording medium is received in the light receiving unit. Incident light is lost and reading accuracy decreases. In order to prevent this, the movable objective lens disposed between the separation coupling member and the recording medium has to be enlarged, which increases the size of the apparatus and reduces the response speed of the objective lens. The performance of the apparatus is reduced in terms of processing speed.

  Further, the diffraction efficiency of the diffraction grating tends to decrease as the period of the unevenness decreases. As a method of maintaining high diffraction efficiency while reducing the period of the unevenness, a Littrow arrangement is known in which the diffracted light beam is closer to the incident light beam than the normal line of the diffraction grating at the incident position. However, when the Littrow arrangement is adopted in the optical device for optical communication, the optical transmission member and the light receiving unit are spatially close to each other, so that it is not easy to dispose both of them.

  Furthermore, when the period of the concave and convex portions of the diffraction grating is reduced, the difference in diffraction efficiency between the polarization component that becomes p-polarized light and the polarization component that becomes s-polarized light increases. In optical communications, linearly polarized light is generally used as the transmitted light. Therefore, unless the polarization direction of the light with respect to the diffraction grating is taken into account, the intensity of the transmitted / received light is reduced, and the accuracy of the transmitted / received signal is reduced. Result.

The present invention aims to solve the above-described problems in diffraction grating elements that diffract light of different wavelengths, and in particular, is a diffraction grating element that separates or combines light beams and suppresses the spread of the light beams. It is an object of the present invention to provide an optical device that can easily separate light beams having different wavelengths and that can easily suppress loss of light.

In order to achieve the above object, in the present invention, a first light flux having a first wavelength and a second light flux having a longer wavelength than the first wavelength are incident from different directions, and the first light flux is made to be a second light flux. An optical apparatus having a diffraction grating element that emits light in the direction of the incident source of
n2 ≧ n1 ・ sinθ
Λ / λL ≤ 1 / (n1 + n1 · sinθ)
And Λ / λ S> 1 / (n 1 + n 1 · sin θ) −0.04
Satisfy the relationship. Here, n1 and n2 are the refractive indices of the first medium located on the incident side of the first light beam and the second medium located on the opposite side of the medium sandwiching the diffraction grating, and Λ is the unevenness of the diffraction grating. Λs and λL are the wavelengths of the first and second light beams, respectively, and θ is the incident angle of the first light beam to the diffraction grating.

The diffraction grating element transmits the first light flux having the wavelength λS while generating diffraction, and transmits the second light flux having the wavelength λL without causing diffraction. Therefore, the second light flux does not spread. In addition, due to the feature of the diffraction grating element that suppresses the spread of the light beam, the light beam can be guided to a narrow range, and the light loss can be suppressed.

In order to achieve the above object, according to the present invention, the first light flux having the first wavelength and the second light flux having a longer wavelength than the first wavelength are incident from different directions, and the first light flux is changed to the first light flux. An optical apparatus having a diffraction grating element that emits light in the direction of the incident source of the two light beams
n2 ≧ n1 ・ sinθ
Λ / λL ≤ 1 / (n2 + n1 · sinθ)
And 1 / (n2 + n1 · sinθ) −0.04 <Λ / λS <1 / (n2 + n1 · sinθ) +0.02.
Satisfy the relationship. Here, n1 and n2 are the refractive indices of the first medium located on the incident side of the first light beam and the second medium located on the opposite side of the medium sandwiching the diffraction grating, and Λ is the unevenness of the diffraction grating. Λs and λL are the wavelengths of the first and second light beams, respectively, and θ is the incident angle of the first light beam to the diffraction grating.

The diffraction grating element transmits the second light flux having the wavelength λL without causing diffraction, and reflects the first light flux having the wavelength λS without causing diffraction. Therefore, neither the first light beam nor the second light beam is spread. In addition, due to the feature of the diffraction grating element that suppresses the spread of the light beam, the light beam can be guided to a narrow range, and the light loss can be suppressed.

Each of the above diffraction grating elements can be configured to have a surface having a light collecting function in addition to the surface on which the diffraction grating is provided. In this way, the spread of the light beam is further suppressed, and a convergent light beam can be obtained.

  A configuration in which the diffraction grating is provided on a curved surface may be employed. In this way, the optical power due to refraction can be given to the diffraction grating, so that the spread of the light beam after diffraction can be further suppressed or a converged light beam can be obtained.

  In that case, when the diffraction grating is projected onto the tangent plane at an arbitrary position on the curved surface where the diffraction grating is provided, the period of the irregularities of the diffraction grating on the plane is Λ, and the incident angle with respect to the plane is θ. It is preferable to satisfy the relationship.

  It is preferable that the cross section of each concavo-convex parallel to the direction of the period of the concavo-convex of the diffraction grating is a substantially rectangular structure. The design of the diffraction grating is facilitated, and the manufacture of the element by resin molding is facilitated.

  Here, a mechanism for changing the incident angle of the light beam with respect to the diffraction grating may be provided. Even when the wavelength of light fluctuates depending on the temperature or the like, the traveling direction of the diffracted light beam can be made constant by changing the incident angle.

An optical component that receives the light beam having the first wavelength emitted from the diffraction grating and having the light beam having the second wavelength incident on the diffraction grating can be provided. With such a configuration, to lead the light of the first wavelength receives the light of the second wavelength from the outside to the outside, a device that may perform through the same optical components. An example of such an optical component is an optical fiber.

You may make it provide the optical component which condenses the light beam which injects into a diffraction grating, or the light beam radiate | emitted from the diffraction grating. In this way, the light beam incident on the diffraction grating can be brought close to a parallel light beam, and the spread of the light beam emitted from the diffraction grating can be further suppressed, so that the device can further suppress the loss of light .

The optical device according to the present invention can separate or combine a plurality of light beams having different wavelengths, but can guide the light beam from the diffraction grating to a narrow range and suppress light loss.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
The configuration of the optical device 1 of the first embodiment is schematically shown in FIG. The optical device 1 is a device for transmission and reception in optical communication, and includes a light emitting unit 21, a light emission control unit 22, an optical fiber 31, a light receiving unit 41, a signal detection unit 42, and a diffraction grating element 51.

  The light emitting unit 21 emits a light beam LT to be transmitted, and the light emission control unit 22 controls light emission of the light emitting unit 21 to carry a signal to be transmitted to the light beam LT emitted from the light emitting unit 21. Although not shown, the light emitting unit 21 includes a laser diode and a condenser lens, and emits light emitted from the laser diode as a parallel light beam by the condenser lens.

  The optical fiber 31 transmits the light beam LT from the light emitting unit 11 carrying the transmission signal to the outside, and transmits the light beam LR carrying the signal to be received from the outside.

  The light receiving unit 41 receives the light beam LR transmitted through the optical fiber 31 and outputs a signal indicating the amount of received light. The signal detection unit 41 receives a signal carried by the light beam LR from the output signal of the light receiving unit 41. To detect. The wavelength band of the light beam LT and the wavelength band of the light beam LR are different and separated from each other. The wavelength of the light beam LT is shorter than the wavelength of the light beam LR.

  The diffraction grating element 51 includes a diffraction grating 52 (see FIG. 2) on the surface thereof, and guides the light beam LT from the light emitting unit 21 to the optical fiber 31 and guides the light beam LR from the optical fiber 31 to the light receiving unit 41.

  The setting of the diffraction grating 52 will be described. Here, the period of the unevenness of the diffraction grating 52 is Λ, the height difference of the unevenness of the diffraction grating 52 is h, and of the two media sandwiching the diffraction grating 52, the refractive index of the one located on the incident side of the light beam LT is n1, The other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the exit angle of the light beam from the diffraction grating 52 is θ2, the center wavelength of the shorter wavelength light beam LT is λs, and the longer wavelength light beam LR Let the center wavelength be λL.

The diffraction grating 52 satisfies the relationships of formulas (A1) to (A3).
n2 ≧ n1 · sinθ1 Expression (A1)
Λ / λL ≦ 1 / (n1 + n1 · sinθ1) Equation (A2)
Λ / λ S> 1 / (n 1 + n 1 · sin θ 1) −0.04 Expression (A3)

  By satisfying these relationships, the diffraction grating 52 diffracts and transmits the light beam LT having a shorter wavelength in the −1st order and diffracts and transmits the light beam LR having a longer wavelength in the 0th order.

  Setting example in which the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelength of the received light beam LR is 1490 nm, and the light beam LT is incident on the diffraction grating 52 from the inner side of the diffraction grating element 51 and the light beam LR from the air side. The optical path is schematically shown in FIG. 2 and various parameters are shown in Table 1. The incident surfaces of the principal rays of the light beams LT and LR are parallel to the direction of the period of the diffraction grating 52.

[Table 1]
Diffraction grating 52
Cross-sectional shape: Rectangle Concavity and convexity Λ: 0.69 μm
Uneven height difference h: 1.39 μm
Convex width: 0.35 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.53
Incident angle θ1: 60 ° Output angle θ2: -42.6 ° s-polarized light transmission diffraction efficiency: 0.72
Luminous flux LR
Wavelength (λL): 1490 nm
Period / wavelength (Λ / λL): 0.46
Incident angle θ1: 60 ° Output angle θ2: 35.3 ° p-polarized light transmittance: 0.87
s-polarized light transmittance: 0.73
Average transmittance: 0.8

  In Table 1, the convex portion width of the diffraction grating 52 is the width of the portion that is convex toward the incident side of the light beam LT (inside the diffraction grating element 51). Further, here, contrary to the usage pattern in the optical apparatus 1, values are shown in the case where the light beam LT is incident from the same direction as the light beam LR and the light beams LT and LR are separated. That is, in the usage pattern in the optical device 1, the incident angle θ1 and the outgoing angle θ2 of the light beam LT are opposite to the values in Table 1.

  In the above setting example (n1 = 1, θ1 = 60 °), the figure shows how the diffraction efficiency changes when the value of 1 / (n1 + n1 · sinθ1) included in equations (A2) and (A3) changes. 3 shows. The value of 1 / (1 + 1 · sin 60 °) is 0.536. As can be seen from FIG. 3, the light beam LR to be transmitted as the 0th-order transmitted light has a higher transmittance by setting the center wavelength λL within the range of the formula (A2), and the light beam to be converted into the −1st-order transmitted light. The LT has a high transmittance by setting its center wavelength λ S within the range of the formula (A3).

  Since the spread of the light beam after diffraction is proportional to the width of the wavelength band, the diffraction grating 52 allows the light beam LR having a longer wavelength to pass through without being diffracted like the diffraction grating element 51 in the optical device 1 of the present embodiment. It is effective to prevent the light beam LR from spreading. With this setting, the entire light beam LR can be guided to the light receiving unit 41 without increasing the size of the light receiving unit 41.

<Second Embodiment>
The optical device 2 of this embodiment is also for optical communication and has the same configuration as that of the optical device 1 shown in FIG. 1, and includes a light emitting unit 21, a light emission control unit 22, an optical fiber 31, a light receiving unit 41, and a signal detection unit. 42, and a diffraction grating element 51.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 2 will be described. Here, as in the first embodiment, the period of the unevenness of the diffraction grating 52 is Λ, the height difference of the unevenness of the diffraction grating 52 is h, and the two media sandwiching the diffraction grating 52 are on the incident side of the light beam LT. The refractive index of the one located is n1, the other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, and the center wavelength of the light beam LT having a shorter wavelength is Let λS be the center wavelength of the longer wavelength light beam LR, λL.

The diffraction grating 52 satisfies the relationships of formulas (B1) to (B3).
n2 <n1 · sinθ1 Equation (B1)
Λ / λL ≦ 1 / (n1 + n1 · sinθ1) Equation (B2)
1 / (n1 + n1 · sinθ1) ≤ Λ / λS ≤ 1 / (n2 + n1 · sinθ1) Equation (B3)

  By satisfying these relationships, the diffraction grating 52 diffracts and reflects the shorter wavelength light beam LT in the −1st order and diffracts and reflects (regular reflection) the longer wavelength light beam LR in the 0th order.

  FIG. 4 shows an optical path in a setting example in which the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelength of the received light beam LR is 1490 nm, and the light beams LT and LR are incident on the diffraction grating 52 from the inside of the diffraction grating element 51. It shows schematically and various parameters are shown in Table 2. The incident surfaces of the principal rays of the light beams LT and LR are parallel to the direction of the period of the diffraction grating 52.

[Table 2]
Diffraction grating 52
Cross-sectional shape: Rectangle Unevenness period Λ: 0.585 μm
Uneven height difference h: 0.42 μm
Convex width: 0.293 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.45
Incident angle θ1: 45 ° Output angle θ2: −51.8 ° s-polarized reflection diffraction efficiency: 0.85
Luminous flux LR
Wavelength (λL): 1490 nm
Period / wavelength (Λ / λL): 0.39
Incident angle θ1: 45 ° Output angle θ2: 45 ° p-polarized reflectance: 0.89
s-polarized reflectance: 0.86
Average reflectance: 0.875

  In Table 2, the convex portion width of the diffraction grating 52 is the width of the portion that is convex toward the incident side of the light beams LT and LR (inside the diffraction grating element 51). Further, here, the values in the case of separating the light beams LT and LR by entering the light beam LT from the same direction as the light beam LR are listed, contrary to the usage pattern in the optical device 2. That is, in the usage form in the optical device 2, the incident angle θ1 and the outgoing angle θ2 of the light beam LT are opposite to the values in Table 2.

  The light beam LR as the 0th-order reflected light has a higher reflectance by setting its center wavelength λL within the range of the formula (B2), and the light beam LT as the −1st-order reflected light has its center wavelength λS. By making the value in the range of the formula (B3), the reflectance is increased. The value of 1 / (1.5 + 1.5 · sin45 °) is 0.391, and the value of 1 / (1 + 1.5 · sin45 °) is 0.485.

  Since the spread of the light beam after diffraction is proportional to the width of the wavelength band, the diffraction grating 52 reflects the longer wavelength light beam LR without diffracting it, like the diffraction grating element 51 in the optical device 2 of the present embodiment. It is effective to prevent the light beam LR from spreading. With this setting, the entire light beam LR can be guided to the light receiving unit 41 without increasing the size of the light receiving unit 41.

<Third Embodiment>
The optical device 3 of the present embodiment is also for optical communication and has the same configuration as that of the optical device 1 shown in FIG. 1, and includes a light emitting unit 21, a light emission control unit 22, an optical fiber 31, a light receiving unit 41, and a signal detection unit. 42, and a diffraction grating element 51.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 3 will be described. Here, as in the first embodiment, the period of the unevenness of the diffraction grating 52 is Λ, the height difference of the unevenness of the diffraction grating 52 is h, and the two media sandwiching the diffraction grating 52 are on the incident side of the light beam LT. The refractive index of the one located is n1, the other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, and the center wavelength of the light beam LT having a shorter wavelength is Let λS be the center wavelength of the longer wavelength light beam LR, λL.

The diffraction grating 52 satisfies the relationships of formulas (C1) to (C3).
n2 <n1 · sinθ1 Equation (C1)
1 / (n1 + n1 · sinθ1) ≤ Λ / λL ≤ 1 / (n2 + n1 · sinθ1) Equation (C2)
1 / (n2 + n1 · sinθ1) ≤ Λ / λS ≤ 2 / (n1 + n1 · sinθ1) (C3)

  By satisfying these relationships, the diffraction grating 52 diffracts and reflects the longer wavelength light beam LR in the −1st order and diffracts and reflects the shorter wavelength light beam LT in the 0th order (regular reflection).

  The optical path in the setting example in which the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelength of the received light beam LR is 1490 nm, and the light beams LT and LR are incident on the diffraction grating 52 from the inside of the diffraction grating element 51 is shown in FIG. It shows schematically and various parameters are shown in Table 3-1. The incident surfaces of the principal rays of the light beams LT and LR are parallel to the direction of the period of the diffraction grating 52.

[Table 3-1]
Diffraction grating 52
Cross-sectional shape: Rectangle Concavity and convexity Λ: 0.6 μm
Uneven height difference h: 0.645 μm
Convex width: 0.3 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.46
Incident angle θ1: 60 ° Output angle θ2: 60 ° Reflectance: 0.81 (−1.83 dB)
Luminous flux LR
Wavelength (λL): 1490 nm
Period / wavelength (Λ / λL): 0.40
Incident angle θ1: 60 ° Output angle θ2: −52.1 ° p-polarized reflection diffraction efficiency: 0.83 (−1.63 dB)
s-polarized reflection diffraction efficiency: 0.87 (−1.20 dB)
Average reflection diffraction efficiency: 0.85 (−1.41 dB)

  In Table 3-1, the convex width of the diffraction grating is the width of the convex portion toward the incident side of the light beams LT and LR (inside the diffraction grating element 51). Table 3-1 also shows dB conversion values of reflectance and reflection efficiency.

  The LR first-order reflected light beam LR has a higher reflectance by setting its center wavelength λL within the range of the equation (C2), and the 0-order reflected light beam LT has a center wavelength λS. By making the value in the range of the formula (C3), the reflectance is increased. The value of 1 / (1.5 + 1.5 · sin 60 °) is 0.357, and the value of 1 / (1 + 1.5 · sin 60 °) is 0.434, 2 / (1.5 + 1.5 · sin 60 °). The value of is 0.715.

  When the width of the wavelength band is the same, the short wavelength light beam LT is less spread after diffraction than the light beam LR. However, if the width of the wavelength band is widened, the spread after diffraction becomes large even for the light beam LT having a shorter wavelength. In such a case, it becomes difficult to make all the light beam LT enter the optical fiber 31. However, in the diffraction grating element 51 of the optical device 3 of the present embodiment, the diffraction grating 52 causes zero-order diffraction to the light beam LT, that is, does not cause diffraction. It is easy to cause all the light beam LT to enter the optical fiber 31 having a diameter as small as μm.

  Tables 3-2 and 3-3 show parameters relating to the light beam LT when the wavelength band of the light beam LT has a width of ± 50 nm centered on the wavelength λ S. The wavelength band of the light beam LR is ± 10 nm centered on the wavelength λ L. Tables 3-4 and 3-5 show parameters related to the luminous flux LR when having a width. Other parameters are the same as in Table 3-1.

[Table 3-2]
Luminous flux LT
Shortest wavelength (λS-50): 1260nm
Period / wavelength (Λ / (λS-50)): 0.48
Incident angle θ1: 60 ° Output angle θ2: 60 ° Reflectance: 0.85 (−1.43 dB)
[Table 3-3]
Luminous flux LT
Longest wavelength (λS + 50): 1360 nm
Period / wavelength (Λ / (λS + 50)): 0.44
Incident angle θ1: 60 ° Output angle θ2: 60 ° Reflectance: 0.78 (−2.11 dB)

[Table 3-4]
Luminous flux LR
Shortest wavelength (λL-10): 1480 nm
Period / wavelength (Λ / (λL−10)): 0.41
Incident angle θ1: 60 ° Output angle θ2: −51.1 ° p-polarization reflection diffraction efficiency: 0.82 (−1.76 dB)
s-polarized reflection diffraction efficiency: 0.81 (-1.80 dB)
Average reflection diffraction efficiency: 0.81 (−1.78 dB)
[Table 3-5]
Luminous flux LR
Maximum wavelength (λL + 10): 1500 nm
Period / wavelength (Λ / (λL + 10)): 0.40
Incident angle θ1: 60 ° Output angle θ2: −53.2 ° p-polarization reflection diffraction efficiency: 0.83 (−1.62 dB)
s-polarized reflection diffraction efficiency: 0.91 (−0.79 dB)
Average reflection diffraction efficiency: 0.87 (−1.20 dB)

  Since the diffraction grating 52 does not cause diffraction in the light beam LT, there is no change in the reflection angle even at the shortest wavelength and the longest wavelength in the wavelength band, and as is clear from Tables 3-2 and 3-3, the shortest wavelength and High reflectance even at the longest wavelength.

<Fourth Embodiment>
The configuration of the optical device 4 according to the fourth embodiment is schematically shown in FIG. The optical device 4 is a transmission / reception device similar to the optical devices 1 to 3 of the first to third embodiments, but receives two light beams LR1 and LR2 having different wavelength bands via the optical fiber 31. Therefore, in addition to the light emitting unit 21, the light emission control unit 22, the optical fiber 31, the light receiving unit 41, the signal detecting unit 42, and the diffraction grating element 51, the light receiving unit 43 and the signal detecting unit 44 are provided. The element 51 uses a total of three light beams, that is, a transmitted light beam LT and received light beams LR1 and LR2 as objects of diffraction. The light beam LT has the shortest wavelength, the light beam LR2 has the longest wavelength, and the light beam LR1 has the intermediate wavelength.

The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 4 will be described.
The period of the unevenness of the diffraction grating 52 is Λ, the height difference of the unevenness of the diffraction grating 52 is h, and the refractive index of the two media sandwiching the diffraction grating 52 that is located on the incident side of the light beam LT is n1, and the other refraction. The rate is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, the central wavelength of the shortest light beam LT is λs, and the central wavelength of the longest light beam LR2 is Let λL be the center wavelength of the light beam LR1 having an intermediate wavelength.

The diffraction grating 52 satisfies the relations (D1) to (D3).
n2 <n1 · sinθ1 Equation (D1)
1 / (n1 + n1 · sinθ1) ≤ Λ / λL ≤ 1 / (n2 + n1 · sinθ1) Equation (D2)
1 / (n1 + n1 · sinθ1) ≤ Λ / λM ≤ 1 / (n2 + n1 · sinθ1) Expression (D2 ')
1 / (n2 + n1 · sinθ1) ≤ Λ / λS ≤ 2 / (n1 + n1 · sinθ1) Equation (D3)

  By satisfying these relationships, the diffraction grating 52 diffracts and reflects the light beam LR2 having the longest wavelength and the light beam LR1 having the intermediate wavelength in the −1st order and diffracted and reflects the light beam LT having the shortest wavelength in the 0th order (regular reflection). ).

  Setting that the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelengths of the received light beams LR1 and LR2 are 1490 nm and 1555 nm, respectively, and the light beams LT, LR1 and LR2 are incident on the diffraction grating 52 from the inside of the diffraction grating element 51. The optical path in the example is schematically shown in FIG. 7, and various parameters are shown in Table 4-1. The principal ray incident surfaces of the light beams LT, LR1 and LR2 are parallel to the direction of the period of the diffraction grating 52.

[Table 4-1]
Diffraction grating 52
Cross-sectional shape: Rectangle Concavity and convexity Λ: 0.629 μm
Uneven height difference h: 0.645 μm
Convex width: 0.239 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.76 (−2.41 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Incident angle θ1: 51 ° Output angle θ2: −53.3 ° p-polarization reflection diffraction efficiency: 0.95 (−0.44 dB)
s-polarized reflection diffraction efficiency: 0.85 (−1.45 dB)
Average reflection diffraction efficiency: 0.90 (−0.93 dB)
Luminous flux LR2
Wavelength (λM): 1555 nm
Incident angle θ1: 51 ° Output angle θ2: −60.6 ° p-polarized reflection diffraction efficiency: 0.76 (−2.34 dB)
s-polarized reflection diffraction efficiency: 0.75 (−2.45 dB)
Average reflection diffraction efficiency: 0.76 (-2.39 dB)

  In Table 4-1, the convex width of the diffraction grating is the width of the convex portion toward the incident side (inside the diffraction grating element 51) of the light beams LT, LR1, and LR2.

  The light beams LR1 and LR2 used as the −1st order reflected light have a higher reflectance by setting the center wavelengths λM and λL within the ranges of the expressions (D2 ′) and (D2), and thus are used as the 0th order reflected light. The reflectance of the light beam LT is increased by setting the center wavelength λ S within the range of the equation (D3). The value of 1 / (1.5 + 1.5 · sin 51 °) is 0.375, and the value of 1 / (1 + 1.5 · sin 51 °) is 0.462, 2 / (1.5 + 1.5 · sin 51 °). The value of is 0.750.

  Also in the present embodiment, as in the third embodiment, the diffraction grating 52 causes zero-order diffraction with respect to the light beam LT, that is, does not cause diffraction, so that the spread of the light beam LT is increased. Without inviting, it is easy to make all the light beam LT enter the thin optical fiber 31.

  Tables 4-2 and 4-3 show parameters related to the light beam LT when the wavelength band of the light beam LT has a width of ± 50 nm centered on the wavelength λs, and the wavelength band of the light beam LR1 is ± 10 nm centered on the wavelength λM. Tables 4-4 and 4-5 show parameters related to the light beam LR1 having a width. Tables 4-6 show parameters related to the light beam LR2 when the wavelength band of the light beam LR2 has a width of ± 5 nm centered on the wavelength λL. And shown in Table 4-7. Other parameters are the same as in Table 4-1.

[Table 4-2]
Luminous flux LT
Shortest wavelength (λS-50): 1260nm
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.87 (−1.26 dB)
[Table 4-3]
Luminous flux LT
Longest wavelength (λS + 50): 1360 nm
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.74 (−2.64 dB)

[Table 4-4]
Luminous flux LR1
Shortest wavelength (λM-10): 1480 nm
Incident angle θ1: 51 ° Output angle θ2: −52.3 ° p-polarization reflection diffraction efficiency: 0.96 (−0.33 dB)
s-polarized reflection diffraction efficiency: 0.84 (-1.52 dB)
Average reflection diffraction efficiency: 0.90 (-0.90 dB)
[Table 4-5]
Luminous flux LR1
Maximum wavelength (λM + 10): 1500 nm
Incident angle θ1: 51 ° Output angle θ2: −54.4 ° p-polarization reflection diffraction efficiency: 0.93 (−0.60 dB)
s-polarized reflection diffraction efficiency: 0.85 (−1.45 dB)
Average reflection diffraction efficiency: 0.89 (−1.02 dB)

[Table 4-6]
Luminous flux LR2
Shortest wavelength (λL-5): 1550 nm
Incident angle θ1: 51 ° Output angle θ2: −60 ° p-polarization reflection diffraction efficiency: 0.78 (−2.12 dB)
s-polarized reflection diffraction efficiency: 0.77 (-2.30 dB)
Average reflection diffraction efficiency: 0.78 (−2.21 dB)
[Table 4-7]
Luminous flux LR2
Longest wavelength (λL + 5): 1560 nm
Incident angle θ1: 51 ° Output angle θ2: −61.2 ° p-polarization reflection diffraction efficiency: 0.74 (−2.56 dB)
s-polarized reflection diffraction efficiency: 0.74 (−2.62 dB)
Average reflection diffraction efficiency: 0.74 (−2.59 dB)

  Since the diffraction grating 52 does not cause diffraction in the light beam LT, the reflection angle does not change even at the shortest wavelength and the longest wavelength in the wavelength band, and as is clear from Tables 4-2 and 4-3, the shortest wavelength and High reflectance even at the longest wavelength.

<Fifth Embodiment>
The optical device 5 of the present embodiment is also for optical communication and has the same configuration as that of the optical device 1 shown in FIG. 1, and includes a light emitting unit 21, a light emission control unit 22, an optical fiber 31, a light receiving unit 41, and a signal detection unit. 42, and a diffraction grating element 51.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 5 will be described. Here, as in the first embodiment, the period of the unevenness of the diffraction grating 52 is Λ, the height difference of the unevenness of the diffraction grating 52 is h, and the two media sandwiching the diffraction grating 52 are on the incident side of the light beam LT. The refractive index of the one located is n1, the other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, and the center wavelength of the light beam LT having a shorter wavelength is Let λS be the center wavelength of the longer wavelength light beam LR, λL.

The diffraction grating 52 satisfies the relations (E1) to (E3).
n2 ≧ n1 · sinθ1 Expression (E1)
Λ / λL ≦ 1 / (n2 + n1 · sinθ1) ... Formula (E2)
1 / (n2 + n1 · sinθ1) −0.04 <Λ / λS <1 / (n2 + n1 · sinθ1) +0.02
... Equation (E3)

  By satisfying these relationships, the diffraction grating 52 diffracts and transmits the longer wavelength light beam LR in the 0th order and diffracts and reflects (regular reflection) the shorter wavelength light beam LT in the 0th order.

  The optical path in a setting example in which the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelength of the received light beam LR is 1490 nm, and the light beams LT and LR are incident on the diffraction grating 52 from the inside of the diffraction grating element 51 is shown in FIG. It shows schematically and various parameters are shown in Table 5-1. The incident surfaces of the principal rays of the light beams LT and LR are parallel to the direction of the period of the diffraction grating 52.

[Table 5-1]
Diffraction grating 52
Cross-sectional shape: rectangle Uneven period Λ: 0.667 μm
Uneven height difference h: 1.167 μm
Convex width: 0.267 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.509
Incident angle θ1: 36 ° Output angle θ2: 36 ° Reflectance: 0.71 (-2.93 dB)
Luminous flux LR
Wavelength (λL): 1490 nm
Period / wavelength (Λ / λL): 0.448
Incident angle θ1: 36 ° Output angle θ2: 61.8 ° p-polarized light transmittance: 0.91 (−0.86 dB)
s-polarized light transmittance: 0.76 (-2.34 dB)
Average transmittance: 0.83 (−1.57 dB)

  In Table 5-1, the convex width of the diffraction grating is the width of the convex portion toward the incident side of the light beams LT and LR (inside the diffraction grating element 51).

  In the above setting example (n1 = 1.5, n2 = 1, θ1 = 36 °), the diffraction efficiency when the value of 1 / (n2 + n1 · sinθ1) included in the equations (E2) and (E3) changes The state of the change is shown in FIG. The value of 1 / (1 + 1.5 · sin 36 °) is 0.531. As can be seen from FIG. 9, the luminous flux LR to be transmitted as the 0th-order transmitted light is increased in transmittance by setting the center wavelength λL within the range of the formula (E2), and the luminous flux LT to be converted into the 0th-order reflected light. The reflectance is increased by setting the center wavelength λ S within the range of the equation (E3).

  In the optical device 5, the diffraction grating 52 causes zero-order diffraction to both the light beams LT and LR, that is, does not cause diffraction, so that the light beams LT and LR are spread. It is easy to make all the light beam LT enter the thin optical fiber 31 and to make all the light beam LR enter the small light receiving portion 41.

  Table 5-2 and Table 5-3 show parameters related to the light beam LT when the wavelength band of the light beam LT has a width of ± 50 nm centered on the wavelength λ S. The wavelength band of the light beam LR is ± 10 nm centered on the wavelength λ L. Tables 5-4 and 5-5 show parameters related to the light flux LR when having a width. Other parameters are the same as in Table 5-1.

[Table 5-2]
Luminous flux LT
Shortest wavelength (λS-50): 1260nm
Period / wavelength (Λ / (λS-50)): 0.529
Incident angle θ1: 36 ° Output angle θ2: 36 ° Reflectance: 0.85 (−1.39 dB)
[Table 5-3]
Luminous flux LT
Longest wavelength (λS + 50): 1360 nm
Period / wavelength (Λ / (λS + 50)): 0.490
Incident angle θ1: 36 ° Output angle θ2: 36 ° Reflectance: 0.59 (−4.65 dB)

[Table 5-4]
Luminous flux LR
Shortest wavelength (λL-10): 1480 nm
Period / wavelength (Λ / (λL−10)): 0.451
Incident angle θ1: 36 ° Output angle θ2: 61.8 ° p-polarized light transmittance: 0.90 (−0.92 dB)
s-polarized light transmittance: 0.76 (−2.44 dB)
Average transmittance: 0.83 (−1.64 dB)
[Table 5-5]
Luminous flux LR
Maximum wavelength (λL + 10): 1500 nm
Period / wavelength (Λ / (λL + 10)): 0.445
Incident angle θ1: 36 ° Output angle θ2: 61.8 ° p-polarized light transmittance: 0.91 (−0.80 dB)
s-polarized light transmittance: 0.77 (-2.25 dB)
Average transmittance: 0.84 (−1.50 dB)

  Since the diffraction grating 52 does not cause diffraction in the light beams LT and LR, there is no change in the emission angle even at the shortest wavelength and the longest wavelength of those wavelength bands, and high reflectivity and transmittance at each shortest wavelength and longest wavelength. It becomes.

<Sixth Embodiment>
FIG. 10 schematically shows the configuration of the optical device 6 according to the sixth embodiment. The optical device 6 is a transmission / reception device similar to the optical device 5 of the fifth embodiment, but sends out two light beams LT1 and LT2 having different wavelength bands via the optical fiber 31. Therefore, in addition to the light emitting unit 21, the light emission control unit 22, the optical fiber 31, the light receiving unit 41, the signal detection unit 42, and the diffraction grating element 51, the light emitting unit 23 and the light emission control unit 24 are provided. The element 51 uses a total of three light fluxes, that is, the light fluxes LT1 and LT2 to be transmitted and the light flux LR to be received, as a diffraction target. The light beam LT1 has the shortest wavelength, the light beam LR has the longest wavelength, and the light beam LT2 has an intermediate wavelength.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 6 will be described. Here, the period of the concave and convex portions of the diffraction grating 52 is Λ, the height difference of the concave and convex portions of the diffraction grating 52 is h, and the refractive index of the two media sandwiching the diffraction grating 52 that is located on the incident side of the light beam LT1 is n1. Is the refractive index of n2, the incident angle of the light beam on the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, the center wavelength of the shortest light beam LT1 is λs, and the center of the longest light beam LR Let λL be the wavelength, and λM be the center wavelength of the light beam LT2 having an intermediate wavelength.

The diffraction grating 52 satisfies the relationships of formulas (F1) to (F4).
n2 ≧ n1 · sinθ1 Formula (F1)
Λ / λL ≦ 1 / (n2 + n1 · sinθ1) Equation (F2)
1 / (n2 + n1 · sin θ1) −0.04 <Λ / λM <1 / (n2 + n1 · sin θ1) +0.02
... Formula (F3)
Λ / λS ≧ 1 / (n2 + n1 · sinθ1) Expression (F4)

  In this way, the diffraction grating 52 diffracts and transmits the longest wavelength light beam LR and the shortest wavelength light beam LT1 in the 0th order, and diffracts and reflects (regular reflection) the intermediate wavelength light beam LT2 in the 0th order. Become.

<Seventh Embodiment>
The optical device 7 of the present embodiment is a modification of the optical device 4 of the fourth embodiment that receives two light beams LR1 and LR2 having different wavelength bands via an optical fiber 31. The optical path of the diffraction grating element 51 and the light beams LR1 and LR2 in the optical device 7 is shown in FIG. Of the surface of the diffraction grating element 51 where the diffraction grating 52 is not provided, a portion 53 through which the diffracted light beams LR1 and LR2 pass is a cylindrical shape centering on an axis perpendicular to the direction of the period of the diffraction grating 52. It is a curved surface and acts as a convex lens for the light beams LR1 and LR2.

Since the light beams LR1 and LR2 are diffracted light, the light beams LR1 and LR2 expand according to the width of the wavelength band. By providing the condensing function to the portion 53 through which the light beams LR1 and LR2 pass in this way, the light beams LR1 and LR2 are brought close to a parallel light beam or converged. Or a light beam. Therefore, all the light beams LR1 and LR3 can be incident on the light receiving units 41 and 43 without increasing the size of the light receiving units 41 and 43. In addition, the aberration can be suppressed by the curved shape of the portion 53.

  If the radius of curvature of the portion 53 that is a curved surface is made equal to the distance from the incident point of the light beam to the diffraction grating 52 to the portion 53, the portion 53 does not have a condensing function. However, it is possible to prevent the light beams LR1 and LR2 from further spreading due to refraction as in the case where the portion 53 is flat.

  In the present embodiment, the center wavelength λM of the light beam LR1 is 1480 nm, and the center wavelength λL of the light beam LR2 is 1500 nm. The incident angle θ1 of the light beams LR1 and LR2 is 51 °, the reflection angle θ2 of the light beam LR1 is 52.3 °, and the reflection angle θ2 of the light beam LR2 is 54.3 °. Although not shown, the transmitted light beam LT is incident at an incident angle of 55.49 ° when the center wavelength LS is 1260 nm, at an incident angle of 51.8 ° when the center wavelength LS is 1310 nm, and incident when the center wavelength LS is 1360 nm. The angle is 48.39 °.

<Eighth Embodiment>
The optical device 8 of this embodiment is a modification of the optical device 2 of the second embodiment that diffracts and reflects the transmitted light beam LT in the −1st order. The optical path of the diffraction grating element 51 and the light beam LT in the optical device 8 is shown in FIG. Of the surface of the diffraction grating element 51 where the diffraction grating 52 is not provided, a portion 54 through which the light beam LT before incidence passes is a cylindrical curved surface centered on an axis perpendicular to the direction of the period of the diffraction grating 52. It acts as a convex lens for the light beam LT. Even when the light beam LT from the light emitting unit 21 is diverging light, the light beam LT incident on the diffraction grating 52 can be made close to a parallel light beam by providing the condensing function to the portion 54 in this way.

  The optical device 8 includes an arc-shaped rail 25 that is located on a plane perpendicular to the diffraction grating 51 and parallel to the direction of the period, centered on the incident position of the light beam LT on the diffraction grating 52. The light emitting unit 21 is set to be movable along the rail 25, and the incident angle of the light beam LT with respect to the diffraction grating 52 varies depending on the position of the light emitting unit 21. A temperature sensor 26 is attached to the light emitting unit 21, and the position of the light emitting unit 21 is controlled according to the temperature detected by the temperature sensor 26.

  The characteristics of the laser diode of the light emitting unit 21 that emits the light beam LT vary depending on the temperature. Therefore, the wavelength of the light beam LT also varies depending on the temperature. When the wavelength fluctuates, the diffraction angle of the light beam LT by the diffraction grating 52 also fluctuates, and a part of the diffracted light beam LT may not enter the optical fiber 31 in some cases. However, by changing the incident angle of the light beam LT with respect to the diffraction grating 52 in accordance with the temperature as described above, the entire light beam LT can be reliably incident on the optical fiber 31.

  Instead of providing the temperature sensor 26, a plurality of optical sensors 35 are provided near the end of the optical fiber 31, and the position of the light emitting unit 21 is controlled according to which optical sensor 35 the light beam LT is incident on. You may do it. In that case, by setting the position of the light emitting unit 21 so that the light beam LT does not enter any of the optical sensors 35, all of the light beam LT can be incident on the optical fiber 31.

  The wavelengths of the light beams LT and LR, the setting of the diffraction grating 52, and the like are the same as in the second embodiment.

<Ninth Embodiment>
A diffraction grating element 11 of the optical device 9 of this embodiment is shown in FIG. In FIG. 13, (a) is a side view and (b) is a plan view. In the present embodiment, the surface of the diffraction grating element 11 is a convex curved surface, and the diffraction grating 52 is provided on the curved surface. By providing the diffraction grating 52 on the curved surface, the diffraction grating 52 has optical power due to refraction, and the spread of the emitted light beam can be suppressed. Therefore, it is not necessary to separately provide means for suppressing the spread of the luminous flux after emission.

  In the case where the light beam incident on the diffraction grating 52 is not a parallel light beam, the distance between the concave and convex portions of the diffraction grating 52 is changed without being constant, or the individual convex portions 52a and concave portions 52b are not made straight. By using a curved shape, it is possible to suppress aberrations that cause the light beam to spread.

  When the diffraction grating 52 is provided on the curved surface as in the present embodiment, the diffraction grating 52 is projected onto the tangent plane P at an arbitrary position on the diffraction grating 52, the incident angle with respect to the tangential plane P is θ1, and the tangential plane. The period on P is set as Λ, so that the conditions of each group from the above-described equations (A1) to (A3) to equations (F1) to (F4) are satisfied. Thus, the effects described in the above embodiments can be obtained.

<Tenth Embodiment>
The configuration of the optical device 10 according to the tenth embodiment is schematically shown in FIG. The optical device 10 is an optical recording / reproducing device that records information on a recording medium using light and reads information from the recording medium. The optical device 10 includes three light emitting units 27, 28, 29, two diffraction grating elements 55, 57, and an objective. A lens 61 is provided. The diffraction grating elements 55 and 57 are both prism-shaped, and the diffraction gratings 56 and 58 (see FIG. 15) are provided on one surface, respectively.

  The light emitting units 27, 28, and 29 emit light beams LT1, LT2, and LT3 having different wavelength bands for irradiating the recording medium M, respectively. Although not shown, the light emitting units 27 to 29 include a laser diode and a condensing lens, and emit light emitted from the laser diode as a parallel light beam by the condensing lens.

  The diffraction grating element 55 combines the light beam LT1 from the light emitting unit 27 and the light beam LT2 from the light emitting unit 28. The diffraction grating element 57 combines the light beams LT1 and LT2 combined by the diffraction grating element 55 and the light beam LT3 from the light emitting unit 29.

  The objective lens 61 converges the light beams LT1, LT2, and LT3 combined by the diffraction grating element 55 on the recording medium M.

  The setting of the diffraction gratings 56 and 58 of the diffraction grating elements 55 and 57 will be described. Here, the period of the concave and convex portions of the diffraction gratings 56 and 58 is Λ, the height difference of the concave and convex portions of the diffraction gratings 56 and 58 is h, and one of the two media sandwiching the diffraction gratings 56 and 58 is located on the incident side of the light flux. The refractive index is n1, the other refractive index is n2, the incident angle of the light beam on the diffraction gratings 56 and 58 is θ1, the emission angle of the light beam from the diffraction gratings 56 and 58 is θ2, and the light beams LT1, LT2, and LT3 are in the wavelength band. The center wavelength of the shortest wavelength is λS, the center wavelength of the longest wavelength is λL, and the center wavelength of the intermediate wavelength is λM. Here, although each parameter of the diffraction grating 56 and the diffraction grating 58 is represented by the same symbol, each parameter (for example, the period Λ) is different between the diffraction grating 56 and the diffraction grating 58.

The diffraction gratings 56 and 58 satisfy the relationships of the expressions (G1) to (G4).
n2 ≧ n1 · sinθ1 Expression (G1)
Λ / λL ≦ 1 / (n2 + n1 · sinθ1) Equation (G2)
Λ / λM ≒ 1 / (n2 + n1 ・ sinθ1) Equation (G3)
Λ / λS ≥ 1 / (n2 + n1 · sinθ1) Equation (G4)

  By satisfying these relationships, the diffraction gratings 56 and 58 transmit or reflect the zero-order diffraction with respect to any of the light beams LT1, LT2, and LT3, that is, without generating diffraction. It becomes.

  The center wavelengths of the respective wavelength bands of the light beams LT1, LT2, and LT3 are set to 650 nm, 780 nm, and 405 nm, respectively. The light beam LT1 is incident on the diffraction grating 56 of the diffraction grating element 55 from the inside of the element 55, and the light beam LT2 is input from the air side. FIG. 15 schematically shows an optical path in a setting example in which the light beams LT1 and LT2 are incident on the diffraction grating 58 of the diffraction grating element 57 from the air side and the light beam LT3 is incident on the inner side of the element 57. Various parameters are shown in Tables 6-1 and 6-2. In this example, the center wavelength of the light beam LT3 is the shortest wavelength λS, the center wavelength of the light beam LT2 is the longest wavelength λL, and the center wavelength of the light beam LT1 is the intermediate wavelength λM.

  For the diffraction gratings 56 and 58, the light beam LT1 is s-polarized light, the light beam LT2 is p-polarized light, and the light beam LT3 is s-polarized light. Note that double-headed arrows in FIG. 15 indicate that the plane of polarization is parallel to the plane of the paper, and double circles indicate that the plane of polarization is perpendicular to the plane of the paper.

[Table 6-1]
Diffraction grating 56
Cross-sectional shape: Rectangle Concavity and convexity Λ: 326 nm
Uneven height difference h: 571 nm
Convex width: 163 nm
Medium refractive index: 1.5
Luminous flux LT1
Wavelength (λM): 650 nm
Period / wavelength (Λ / λM): 0.502
Incident angle θ1: 38 ° Output angle θ2: 38 ° s Polarized reflectance: 0.962
Luminous flux LT2
Wavelength (λL): 780 nm
Period / wavelength (Λ / λL): 0.418
Incident angle θ1: 67.4 ° Output angle θ2: 38 ° p-polarized light transmittance: 0.952

[Table 6-2]
Diffraction grating 58
Cross-sectional shape: Rectangle Concavity and convexity Λ: 203 nm
Uneven height difference h: 571 nm
Convex width: 163 nm
Medium refractive index: 1.5
Luminous flux LT1
Wavelength (λM): 650 nm
Period / wavelength (Λ / λM): 0.312
Incident angle θ1: 67.4 ° Output angle θ2: 38 ° s Polarized light transmittance: 0.74
Luminous flux LT2
Wavelength (λL): 780 nm
Period / wavelength (Λ / λL): 0.260
Incident angle θ1: 67.4 ° Output angle θ2: 38 ° p-polarized light transmittance: 0.944
Luminous flux LT3
Wavelength (λS): 405 nm
Period / wavelength (Λ / λS): 0.501
Incident angle θ1: 38 ° Output angle θ2: 38 ° s Polarized reflectance: 0.962

  In Tables 6-1 and 6-2, the convex width of the diffraction grating is the width of the portion that is convex toward the inside of the diffraction grating elements 55 and 57. The incident angles of the light beams LT1, LT2, and LT3 with respect to the surfaces of the diffraction grating elements 55 and 57 other than the diffraction gratings 56 and 58 are 90 °. Assuming that the transmittance on the surface other than the diffraction gratings 56 and 58 is 1, the light quantity of each of the light beams LT1, LT2, and LT3 after passing through the diffraction grating elements 55 and 57 is 0.712, compared to the light quantity before passing through. 0.899 and 0.962 times. The value of 1 / (1.5 + sin 38 °) is 0.520.

<Eleventh embodiment>
The optical device 11 of the eleventh embodiment is a device for transmission / reception in optical communication, and sends out a light beam LT via an optical fiber 31 as in the optical device 4 of the fourth embodiment shown in FIG. At the same time, the two light beams LR1 and LR2 are received via the optical fiber 31. The wavelength bands of the light beams LT, LR1, and LR2 are different.

In addition, the diffraction grating 52 of the diffraction grating element 51 has an uneven period in the first direction and the second direction perpendicular to each other. FIG. 16 schematically shows the diffraction grating 52. Period of the unevenness is different in the first direction and the second direction, towards the cycle of the first direction is short. Hereinafter, the period in the first direction is referred to as a main period, and the period in the second direction is referred to as a sub period. Further, the main period is Λx, the subperiod is Λy, the distance between the convex parts 52a in the main period direction is Wx, and the distance between the convex parts 52a in the subperiod direction is Wy.

  The relationship between the diffraction grating 52 and the angle of the light beam is shown in FIG. An angle φ formed by a plane perpendicular to the diffraction grating 52 and parallel to the direction of the main period and the incident surface of the light beam incident on the diffraction grating 52 is referred to as an azimuth angle. The incident angle θ1 is an angle formed between the principal ray of the incident light beam and the normal line of the diffraction grating 52, and is an angle within the incident plane.

  In the optical device 11, the light beams LT, LR1, and LR2 are incident on the diffraction grating 52 such that their incident surfaces are slightly inclined with respect to the direction of the main period. Accordingly, the azimuth angle φ of the light beams LT, LR1, and LR2 is not zero.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 11 will be described. Here, the main period (Λx) of the concave and convex portions of the diffraction grating 52 is Λ, the height difference of the concave and convex portions of the diffraction grating 52 is h, and the refractive index of the two media sandwiching the diffraction grating 52 is located on the incident side of the light beam. Is n1, the other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, and the shortest wavelength among the wavelength bands of the light beams LT, LR1, and LR2 The shortest wavelength and the longest wavelength of the band are λ1L and λ1U, respectively. The shortest wavelength and the longest wavelength of the longest wavelength band are λ3L and λ31U, respectively. The shortest wavelength and the longest wavelength of the intermediate band are λ2L and λ2U, respectively.

The diffraction grating 52 satisfies the relations (H1) to (H5).
λ1L <λ1U <λ2L <λ2U <λ3L <λ3U (H1)
n2 <n1 · sinθ1 Formula (H2)
φ ≠ 0 ... Formula (H3)
1 / [n1 · (1-sin ² θ1 · sin ² φ) ^1/2 + n1 · sinθ1 · cosφ] ≤ Λ / λ3U <Λ / λ2L ≤ 1 / [(n2 ² −n1 ² · sin ² θ1 · sin ² φ) ^1/2 + n1 ・ sinθ1 ・ cosφ] ... Formula (H4)
1 / [(n2 ² −n1 ² · sin ² θ1 · sin ² φ) ^1/2 + n1 · sinθ1 · cosφ] ≤ Λ / λ1U <Λ / λ1L ≤ 2 / [n1 · (1-sin ² θ1 · sin ² φ) ^1/2 + n1 ・ sinθ1 ・ cosφ] Formula (H5)

  By satisfying these relationships, the diffraction grating 52 diffracts and reflects (regular reflection) the transmitted light LT in the 0th order, and diffracts and reflects the two received light beams LR1 and LR2 in the −1st order. The diffraction grating 52 and the light beams LR1 and LR2 have a relationship close to a Littrow arrangement.

  Setting that the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelengths of the received light beams LR1 and LR2 are 1490 nm and 1555 nm, respectively, and the light beams LT, LR1 and LR2 are incident on the diffraction grating 52 from the inside of the diffraction grating element 51. The optical path in the example is schematically shown in FIG. 18, and parameters are shown in Table 7-1. The azimuth angle φ of the light beams LT, LR1, and LR2 is 10 °.

[Table 7-1]
Diffraction grating 52
Cross-sectional shape: rectangle Uneven main period Λx (Λ): 0.649 μm
Uneven sub-period Λy: 1.298 μm
Uneven height difference h: 0.649 μm
Convex main period direction width Wx: 0.389 μm
Protrusion sub-cycle direction width Wy: 0.13 μm
Medium refractive index: 1.48
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λx / λS): 0.495
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.77 (−1.14 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λx / λM): 0.436
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: −49.3 ° p-polarization reflection diffraction efficiency: 0.92 (−0.35 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.22 dB)
Average reflection diffraction efficiency: 0.94 (−0.28 dB)
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λx / λL): 0.417
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: -55.7 ° p-polarized reflection diffraction efficiency: 0.82 (−0.85 dB)
s-polarized reflection diffraction efficiency: 0.90 (−0.45 dB)
Average reflection diffraction efficiency: 0.86 (−0.64 dB)

  In Table 7-1, the width of the convex portion of the diffraction grating is the width of the portion that is convex toward the incident side of the light beams LT, LR1, and LR2 (inside the diffraction grating element 51).

  Parameters relating to the shortest wavelength (λ1L) and longest wavelength (λ1U) of the light beam LT when the wavelength band width is 100 nm are shown in Tables 7-2 and 7-3, and the shortest light beam LR1 when the wavelength band width is 20 nm. Parameters relating to the wavelength (λ2L) and the longest wavelength (λ2U) are shown in Tables 7-4 and 7-5, and the parameters relating to the shortest wavelength (λ3L) and the longest wavelength (λ3U) of the light beam LR2 when the wavelength band width is 10 nm. Tables 7-6 and 7-7 show.

[Table 7-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λx / λ1L): 0.515
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Outgoing angle θ2: 52.5 ° Reflectivity: 0.82 (−0.86 dB)
[Table 7-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λx / λ1U): 0.477
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.72 (−1.46 dB)

[Table 7-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λx / λ2L): 0.438
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: -48.4 ° p-polarization reflection diffraction efficiency: 0.91 (-0.40 dB)
s-polarized reflection diffraction efficiency: 0.92 (−0.35 dB)
Average reflection diffraction efficiency: 0.92 (−0.37 dB)
[Table 7-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λx / λ2U): 0.433
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Outgoing angle θ2: −50.2 ° p-polarized reflection diffraction efficiency: 0.93 (−0.34 dB)
s-polarized reflection diffraction efficiency: 0.96 (−0.16 dB)
Average reflection diffraction efficiency: 0.95 (−0.25 dB)

[Table 7-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λx / λ3L): 0.419
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: -55.1 ° p-polarization reflection diffraction efficiency: 0.84 (-0.77 dB)
s-polarized reflection diffraction efficiency: 0.92 (−0.38 dB)
Average reflection diffraction efficiency: 0.88 (−0.57 dB)
[Table 7-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λx / λ3U): 0.416
Azimuth angle φ: 10 ° Incident angle θ1: 52.5 ° Output angle θ2: -56.2 ° p-polarization reflection diffraction efficiency: 0.81 (-0.94 dB)
s-polarized reflection diffraction efficiency: 0.89 (−0.52 dB)
Average reflection diffraction efficiency: 0.85 (−0.72 dB)

The lower limit value and upper limit value of the formula (H4), that is, the values of the following two formulas are 0.381 and 0.468, respectively, and the period / wavelength values of the light beams LR1 and LR2 satisfy the formula (H4). .
1 / [n1 ・ (1-sin ² θ1 ・ sin ² φ) ^1/2 + n1 ・ sinθ1 ・ cosφ]
1 / [(n2 ² −n1 ² · sin ² θ1 · sin ² φ) ^1/2 + n1 · sinθ1 · cosφ]

Further, the lower limit value and upper limit value of the formula (H5), that is, the values of the following two formulas are 0.468 and 0.763, respectively, and the period / wavelength value of the light beam LT satisfies the formula (H5).
1 / [(n2 ² −n1 ²・ sin ² θ1 ・ sin ² φ) ^1/2 + n1 ・ sinθ1 ・ cosφ]
2 / [n1 ・ (1-sin ² θ1 ・ sin ² φ) ^1/2 + n1 ・ sinθ1 ・ cosφ]

  By satisfying the formula (H4), it is possible to increase the diffraction efficiency of the light beams LR1 and LR2 having a relatively long wavelength as the −1st order diffraction reflected light. Further, by satisfying the formula (H5), it is possible to increase the reflectance of the light beam LT having a relatively short wavelength that is regularly reflected without being diffracted.

  In the optical device according to the present embodiment, the diffraction grating 52 and the light beams LR1 and LR2 are in a relationship close to the Littrow arrangement, but the azimuth angle φ is not 0, so that the optical fiber 31 and the light receiving units 41 and 43 (FIG. 6) interfere with each other. The overall design of the apparatus is easy. However, when the azimuth angle φ is in the range of 0 to 0.5 °, the optical fiber 31 and the light receiving portions 41 and 43 easily interfere with each other. Further, when the azimuth angle φ exceeds 15 °, unnecessary orders of diffracted light increase. Therefore, the azimuth angle φ is preferably 0.5 ° or more and 15 ° or less.

  For comparison, Tables 8-1 to 8-7 show parameters when the azimuth angle φ of the light beams LT, LR1, and LR2 is 0 °.

[Table 8-1]
Diffraction grating Cross-sectional shape: Rectangle Uneven main period Λx (Λ): 0.649 μm
Uneven sub-period Λy: 1.298 μm
Uneven height difference h: 0.649 μm
Convex main period direction width Wx: 0.389 μm
Protrusion sub-cycle direction width Wy: 0.13 μm
Medium refractive index: 1.48
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λx / λS): 0.495
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.81 (−0.90 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λx / λM): 0.436
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -49.3 ° p-polarization reflection diffraction efficiency: 0.88 (-0.55 dB)
s-polarized reflection diffraction efficiency: 0.85 (−0.71 dB)
Average reflection diffraction efficiency: 0.86 (−0.63 dB)
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λx / λL): 0.417
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -55.7 ° p-polarization reflection diffraction efficiency: 0.87 (−0.59 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.23 dB)
Average reflection diffraction efficiency: 0.91 (−0.41 dB)

[Table 8-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λx / λ1L): 0.515
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.88 (−0.57 dB)
[Table 8-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λx / λ1U): 0.477
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.76 (−1.21 dB)

[Table 8-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λx / λ2L): 0.438
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -48.4 ° p-polarization reflection diffraction efficiency: 0.85 (−0.70 dB)
s-polarized reflection diffraction efficiency: 0.79 (-1.00 dB)
Average reflection diffraction efficiency: 0.82 (−0.85 dB)
[Table 8-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λx / λ2U): 0.433
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -50.2 ° p-polarization reflection diffraction efficiency: 0.90 (-0.45 dB)
s-polarized reflection diffraction efficiency: 0.89 (−0.50 dB)
Average reflection diffraction efficiency: 0.90 (−0.48 dB)

[Table 8-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λx / λ3L): 0.419
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -55.1 ° p-polarization reflection diffraction efficiency: 0.88 (-0.53 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.21 dB)
Average reflection diffraction efficiency: 0.92 (−0.37 dB)
[Table 8-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λx / λ3U): 0.416
Azimuth angle φ: 0 ° Incident angle θ1: 52.5 ° Output angle θ2: -56.2 ° p-polarization reflection diffraction efficiency: 0.86 (-0.64 dB)
s-polarized reflection diffraction efficiency: 0.94 (−0.26 dB)
Average reflection diffraction efficiency: 0.90 (−0.45 dB)

  From the comparison between Tables 7-1 to 7-7 and Tables 8-1 to 8-7, even when the azimuth angle φ is 10 °, a good diffraction efficiency comparable to that when the azimuth angle φ is 0 ° is obtained. I understand.

The angle between the diffracted light beam and the main period direction will be described. When the angle formed by the principal ray of the diffracted light beam projected onto the diffraction grating 52 and the direction of the principal period is α and the wavelength is λ, it is necessary to satisfy the relations of the expressions (J1) and (J2). Further, when close to the Littrow arrangement as in the present embodiment, Expression (J3) is established.
{N1 · sinθ1− (λ / Λ) · cosφ} ² + {(λ / Λ) · sinφ} ² = (n1 · sinθ2) ²
... Formula (J1)
sinα = λ · sinφ / (n1 · Λ · sinθ2) Equation (J2)
λ / Λ = 2 ・ n1 ・ sinθ1 Formula (J3)

The formula (J4) is obtained from the formulas (J1) to (J3). Equation (J4) indicates that the diffracted light beam is separated from the direction of the main period at an angle twice the azimuth angle φ.
sinα ≒ 2 ・ sinφ ... Formula (J4)

  It is also possible to provide the diffraction grating 52 on a curved surface. In that case, as described in the ninth embodiment, the diffraction grating 52 is projected onto the tangent plane P at an arbitrary position on the diffraction grating 52, the incident angle with respect to the tangential plane P is θ1, and the period on the tangent plane P is As Λ, the conditions of the expressions (H1) to (H5) are satisfied.

  Moreover, although the diffraction grating of this embodiment receives two light beams R1 and R2, it is also possible to receive three or more light beams having different wavelength bands. In this case, the longest wavelength band of the received light flux is λ3U, the shortest wavelength of the second longest wavelength band is λ2L, and the equation (H4) may be satisfied.

<Twelfth Embodiment>
The optical device 12 of the twelfth embodiment is also a device for transmission / reception in optical communication, and sends out the light beam LT via the optical fiber 31 as in the optical device 4 of the fourth embodiment shown in FIG. At the same time, the two light beams LR1 and LR2 are received via the optical fiber 31. The wavelength bands of the light beams LT, LR1, and LR2 are different.

  The setting of the diffraction grating 52 of the diffraction grating element 51 in the optical device 12 will be described. Here, the main period of the concave and convex portions of the diffraction grating 52 is Λ, the difference in height of the concave and convex portions of the diffraction grating 52 is h, and the refractive index of the two media sandwiching the diffraction grating 52 that is located on the incident side of the light beam is n1. The other refractive index is n2, the incident angle of the light beam to the diffraction grating 52 is θ1, the emission angle of the light beam from the diffraction grating 52 is θ2, and the shortest of the shortest wavelength bands among the wavelength bands of the light beams LT, LR1, and LR2. The wavelength and the longest wavelength are λ1L and λ1U, respectively, the shortest wavelength in the longest wavelength band, the longest wavelength is λ3L and λ31U, respectively, and the shortest wavelength and the longest wavelength in the intermediate band are λ2L and λ2U, respectively.

The diffraction grating 52 satisfies the relationships of equations (K1) to (K5).
λ1L <λ1U <λ2L <λ2U <λ3L <λ3U Equation (K1)
n2 <n1 · sinθ1 Equation (K2)
1 / (n1 + n1 · sinθ1) ≤ Λ / λ3U <Λ / λ2L ≤ 1 / (n2 + n1 · sinθ1)
... Formula (K3)
1 / (n2 + n1 · sinθ1) ≦ Λ / λ1U <Λ / λ1L ≦ 2 / (n1 + n1 · sinθ1)
... Formula (K4)
Λ / λ3L <1 / (2 · n1 · sinθ1) <Λ / λ2U Equation (K5)

By satisfying these relationships, the diffraction grating 52 diffracts and reflects (regular reflection) the transmitted light beam LT in the 0th order, and diffracts and reflects the received two light beams LR1 and LR2 in the −1st order .

  Setting that the center wavelength of the transmitted light beam LT is 1310 nm, the center wavelengths of the received light beams LR1 and LR2 are 1490 nm and 1555 nm, respectively, and the light beams LT, LR1 and LR2 are incident on the diffraction grating 52 from the inside of the diffraction grating element 51. The optical path in the example is schematically shown in FIG. 19, and various parameters are shown in Table 9-1.

[Table 9-1]
Diffraction grating 52
Cross-sectional shape: Rectangle Unevenness period Λ: 0.645 μm
Uneven height difference h: 0.709 μm
Convex width: 0.451 μm
Medium refractive index: 1.48
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.492
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 0.96 (−0.18 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λ / λM): 0.433
Incident angle θ1: 53 ° Output angle θ2: −49.7 ° p-polarization reflection diffraction efficiency: 0.81 (−0.92 dB)
s-polarized reflection diffraction efficiency: 0.83 (−0.79 dB)
Average reflection diffraction efficiency: 0.82 (−0.85 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.13 dB
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λ / λL): 0.415
Incident angle θ1: 53 ° Output angle θ2: −56.2 ° p-polarization reflection diffraction efficiency: 0.88 (−0.56 dB)
s-polarized reflection diffraction efficiency: 0.90 (−0.45 dB)
Average reflection diffraction efficiency: 0.89 (−0.51 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.11 dB

  In Table 9-1, the width of the convex portion of the diffraction grating is the width of the portion that is convex toward the incident side (inside the diffraction grating element 51) of the light beams LT, LR1, and LR2.

  Parameters relating to the shortest wavelength (λ1L) and longest wavelength (λ1U) of the light beam LT when the wavelength band width is 100 nm are shown in Tables 9-2 and 9-3, and the shortest light beam LR1 when the wavelength band width is 20 nm. The parameters relating to the wavelength (λ2L) and the longest wavelength (λ2U) are shown in Tables 9-4 and 9-5, and the parameters relating to the shortest wavelength (λ3L) and the longest wavelength (λ3U) of the light beam LR2 when the wavelength band width is 10 nm. Tables 9-6 and 9-7 show.

[Table 9-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λ / λ1L): 0.512
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 1.00 (−0.01 dB)
[Table 9-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λ / λ1U): 0.474
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 0.89 (−0.49 dB)

[Table 9-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λ / λ2L): 0.436
Incident angle θ1: 53 ° Output angle θ2: −48.8 ° p-polarization reflection diffraction efficiency: 0.76 (−1.19 dB)
s-polarized reflection diffraction efficiency: 0.78 (−1.09 dB)
Average reflection diffraction efficiency: 0.77 (−1.14 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.10 dB
[Table 9-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λ / λ2U): 0.430
Incident angle θ1: 53 ° Output angle θ2: −50.7 ° p-polarization reflection diffraction efficiency: 0.85 (−0.73 dB)
s-polarized reflection diffraction efficiency: 0.88 (−0.58 dB)
Average reflection diffraction efficiency: 0.86 (−0.65 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.15 dB

[Table 9-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λ / λ3L): 0.416
Incident angle θ1: 53 ° Output angle θ2: −55.7 ° p-polarization reflection diffraction efficiency: 0.89 (−0.52 dB)
s-polarized reflection diffraction efficiency: 0.91 (−0.41 dB)
Average reflection diffraction efficiency: 0.90 (−0.47 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.11 dB
[Table 9-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λ / λ3U): 0.413
Incident angle θ1: 53 ° Output angle θ2: −56.8 ° p-polarization reflection diffraction efficiency: 0.87 (−0.60 dB)
s-polarized reflection diffraction efficiency: 0.89 (−0.50 dB)
Average reflection diffraction efficiency: 0.88 (−0.55 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.10 dB

The lower limit value and upper limit value of the equation (K3), that is, the values of the following two equations are 0.376 and 0.458, respectively, and the period / wavelength values of the light beams LR1 and LR2 satisfy the equation (K3). .
1 / (n1 + n1 · sinθ1)
1 / (n2 + n1 ・ sinθ1)

Further, the lower limit value and the upper limit value of the formula (K4), that is, the values of the following two formulas are 0.458 and 0.751, respectively, and the period / wavelength value of the light beam LT satisfies the formula (K4).
1 / (n2 + n1 ・ sinθ1)
2 / (n1 + n1 · sinθ1)

Further, the value of the following equation is 0.423, and the period / wavelength values of the light beams LR1 and LR2 satisfy the equation (K5).
1 / (2 ・ n1 ・ sinθ1)

  By satisfying the expression (K3), it is possible to increase the diffraction efficiency of the light beams LR1 and LR2 having a relatively long wavelength as the −1st order diffraction reflected light. Further, by satisfying the equation (K4), the reflectance of the light beam LT having a relatively short wavelength that is regularly reflected without being diffracted can be increased. Furthermore, by satisfying the equation (K5), the difference in diffraction efficiency between the p-polarized light and the s-polarized light of the light beams LR1 and LR2 having relatively long wavelengths can be reduced. In the above setting, the difference in diffraction efficiency between the p-polarized light and the s-polarized light is 0.10 to 0.15 dB for the light beam LR1 and 0.10 to 0.11 dB for the light beam LR2.

  For comparison, Tables 10-1 to 10-7 show parameters with settings that satisfy Expressions (K1) to (K4) but do not satisfy Expression (K5).

[Table 10-1]
Diffraction grating Cross-sectional shape: Rectangle Unevenness period Λ: 0.629 μm
Uneven height difference h: 0.645 μm
Convex width: 0.239 μm
Medium refractive index: 1.5
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λ / λS): 0.480
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.76 (−1.21 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λ / λM): 0.422
Incident angle θ1: 51 ° Output angle θ2: −53.3 ° p-polarization reflection diffraction efficiency: 0.95 (−0.22 dB)
s-polarized reflection diffraction efficiency: 0.85 (−0.72 dB)
Average reflection diffraction efficiency: 0.90 (−0.46 dB)
p-polarization, s-polarization diffraction efficiency difference: 0.51 dB
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λ / λL): 0.405
Incident angle θ1: 51 ° Output angle θ2: −60.6 ° p-polarized reflection diffraction efficiency: 0.76 (−1.17 dB)
s-polarized reflection diffraction efficiency: 0.75 (−1.23 dB)
Average reflection diffraction efficiency: 0.76 (−1.20 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.06 dB

[Table 10-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λ / λ1L): 0.499
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.87 (−0.63 dB)
[Table 10-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λ / λ1U): 0.463
Incident angle θ1: 51 ° Output angle θ2: 51 ° Reflectance: 0.74 (−1.32 dB)

[Table 10-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λ / λ2L): 0.425
Incident angle θ1: 51 ° Output angle θ2: −52.3 ° p-polarization reflection diffraction efficiency: 0.96 (−0.17 dB)
s-polarized reflection diffraction efficiency: 0.84 (−0.76 dB)
Average reflection diffraction efficiency: 0.90 (−0.45 dB)
p-polarization, s-polarization diffraction efficiency difference: 0.59 dB
[Table 10-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λ / λ2U): 0.419
Incident angle θ1: 51 ° Output angle θ2: −54.4 ° p-polarization reflection diffraction efficiency: 0.93 (−0.30 dB)
s-polarized reflection diffraction efficiency: 0.85 (−0.73 dB)
Average reflection diffraction efficiency: 0.89 (−0.51 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.43 dB

[Table 10-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λ / λ3L): 0.406
Incident angle θ1: 51 ° Output angle θ2: −60.0 ° p-polarization reflection diffraction efficiency: 0.78 (−1.06 dB)
s-polarized reflection diffraction efficiency: 0.77 (−1.15 dB)
Average reflection diffraction efficiency: 0.78 (−1.11 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.09 dB
[Table 10-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λ / λ3U): 0.403
Incident angle θ1: 51 ° Output angle θ2: −61.2 ° p-polarization reflection diffraction efficiency: 0.74 (−1.28 dB)
s-polarized reflection diffraction efficiency: 0.74 (−1.31 dB)
Average reflection diffraction efficiency: 0.74 (−1.30 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.03 dB

  In this setting, the lower limit value and the upper limit value of the formula (K3) are 0.375 and 0.462, respectively, and the lower limit value and the upper limit value of the formula (K4) are 0.462 and 0.750, respectively. (K4) is met. However, the value of 1 / (2 · n1 · sinθ) is 0.429, which does not satisfy the equation (K5).

  The difference in diffraction efficiency between the p-polarized light and the s-polarized light is as small as 0.03 to 0.09 for the light beam LR2, but as large as 0.43 to 0.59 for the light beam LR3. For this reason, the amount of light received by the light receiving unit 43 (see FIG. 6) that receives the light beam LR2 greatly depends on the direction of the polarization plane of the light beam LT3. Therefore, in order to keep the amount of light received by the light receiving unit 43 high, the direction of the polarization plane of the light beam LT3 must be considered for each device, and the optical fiber 31 and the diffraction grating element 51 and other members Setting relative placement becomes difficult.

  On the other hand, in the optical device 12 of this embodiment whose examples are shown in Tables 9-1 to 9-7, as described above, there is a difference in diffraction efficiency between p-polarized light and s-polarized light for both the light beams LR1 and LR2. The amount of light received by the light receiving portions 42 and 43 is not so dependent on the direction of the polarization plane of the light beams LR1 and LR2. Therefore, the amount of light received by the light receiving portions 42 and 43 can be kept high without considering the direction of the polarization plane of the light beams LR1 and LR2.

  It is also possible to provide the diffraction grating 52 on a curved surface. In that case, as described in the ninth embodiment, the diffraction grating 52 is projected onto the tangent plane P at an arbitrary position on the diffraction grating 52, the incident angle with respect to the tangential plane P is θ1, and the period on the tangent plane P is As Λ, the conditions of the expressions (K1) to (K5) are satisfied.

  In the setting examples shown in Tables 9-1 to 9-7, Table 11 shows diffraction efficiency when the width of the convex portion of the diffraction grating 52 varies by 0.05 μm. Table 11 lists the diffraction efficiencies of the light beams LT, LR1, and LR2 at the wavelength with the lowest diffraction efficiency among the shortest wavelength, the center wavelength, and the longest wavelength. In addition, a value is a dB conversion value.

[Table 11]
Convex width
Decrease Design value Increase
0.401 μm 0.451 μm 0.501 μm
Light beam LT (1310 nm wavelength band)
Reflectance -1.337 -0.490 -0.095
Reflectance fluctuation amount -0.847 0.395
Light beam LR1 (1490 nm wavelength band)
Diffraction efficiency -1.226-1.136 -2.562
Diffraction efficiency fluctuation amount -0.090 -1.425
Difference in diffraction efficiency between p-polarized light and s-polarized light 1.851 0.149 3.458
P-polarized light and s-polarized light diffraction efficiency difference variation 1.702 3.309
Light flux LR2 (1555 nm wavelength band)
Diffraction efficiency -0.501 -0.552 -1.184
Diffraction efficiency fluctuation amount 0.051 -0.632
Difference in diffraction efficiency between p-polarized light and s-polarized light 0.558 0.113 1.762
p-polarized light and s-polarized light diffraction efficiency difference variation 0.445 1.649

  From Table 11, it can be seen that when the width of the convex portion fluctuates from the design value, a large fluctuation occurs in the difference in diffraction efficiency between the p-polarized light and the s-polarized light of the relatively long wavelength light beams LR1 and LR2. However, as will be described below, it is possible to reduce the variation in the diffraction efficiency difference due to the variation in the width of the convex portion.

<13th Embodiment>
In the optical device 13 of the thirteenth embodiment, the optical device 12 is modified so that the difference in diffraction efficiency between p-polarized light and s-polarized light does not vary greatly even if the width of the convex portion of the diffraction grating 52 varies. It is what I did. In the optical device 13, as in the optical device 11 of the eleventh embodiment, as shown in FIG. 16, the first and second directions perpendicular to the irregularities of the diffraction grating 52 have a period. . The period Λx in the first direction is less than or equal to the period Λy in the second direction, and the former is called a main period and the latter is called a sub period. However, in the optical device 13, the light beams LT, LR1, and LR3 are incident on the diffraction grating 52 from a direction perpendicular to the direction of the sub period. Accordingly, the azimuth angle φ shown in FIG. 17 is 0 °.

  Also in the present embodiment, the diffraction grating 52 satisfies the relationships of the above-described formulas (K1) to (K5). Here, the main period Λx is Λ in the equations (K3) to (K5).

  Tables 12-1 to 12-7 show parameters in the settings corresponding to Tables 9-1 to 9-7. Here, the main period Λx and the subperiod Λy are made equal. The optical paths of the light beams LT, LR1, and LR2 are as shown in FIG.

[Table 12-1]
Diffraction grating 52
Cross-sectional shape: Rectangle Uneven main period Λx (Λ): 0.645 μm
Uneven sub-period Λy: 0.645 μm
Sub period / main period (Λy / Λx): 1
Uneven height difference h: 0.645 μm
Convex main period direction width Wx: 0.387 μm
Protrusion sub-period direction width Wy: 0.064 μm
Medium refractive index: 1.48
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λx / λS): 0.492
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 0.84 (−0.77 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λx / λM): 0.433
Incident angle θ1: 53 ° Output angle θ2: −49.7 ° p-polarization reflection diffraction efficiency: 0.89 (−0.50 dB)
s-polarized reflection diffraction efficiency: 0.85 (−0.68 dB)
Average reflection diffraction efficiency: 0.87 (−0.59 dB)
p-polarized light, s-polarized light diffraction efficiency difference: 0.18 dB
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λx / λL): 0.415
Incident angle θ1: 53 ° Output angle θ2: −56.2 ° p-polarization reflection diffraction efficiency: 0.87 (−0.62 dB)
s-polarized reflection diffraction efficiency: 0.96 (−0.20 dB)
Average reflection diffraction efficiency: 0.91 (−0.40 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.42 dB

[Table 12-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λx / λ1L): 0.512
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 0.91 (−0.40 dB)
[Table 12-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λx / λ1U): 0.474
Incident angle θ1: 53 ° Output angle θ2: 53 ° Reflectance: 0.76 (−1.19 dB)

[Table 12-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λx / λ2L): 0.436
Incident angle θ1: 53 ° Output angle θ2: −48.8 ° p-polarization reflection diffraction efficiency: 0.86 (−0.63 dB)
s-polarized reflection diffraction efficiency: 0.80 (−0.96 dB)
Average reflection diffraction efficiency: 0.83 (−0.80 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.33 dB
[Table 12-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λx / λ2U): 0.430
Incident angle θ1: 53 ° Output angle θ2: −50.7 ° p-polarization reflection diffraction efficiency: 0.91 (−0.42 dB)
s-polarized reflection diffraction efficiency: 0.90 (−0.47 dB)
Average reflection diffraction efficiency: 0.90 (−0.45 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.05 dB

[Table 12-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λx / λ3L): 0.416
Incident angle θ1: 53 ° Output angle θ2: −55.7 ° p-polarization reflection diffraction efficiency: 0.88 (−0.56 dB)
s-polarized reflection diffraction efficiency: 0.96 (−0.17 dB)
Average reflection diffraction efficiency: 0.92 (−0.36 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.39 dB
[Table 12-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λx / λ3U): 0.413
Incident angle θ1: 53 ° Output angle θ2: −56.8 ° p-polarization reflection diffraction efficiency: 0.85 (−0.68 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.23 dB)
Average reflection diffraction efficiency: 0.90 (−0.45 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.45 dB

  In this setting, the lower limit value and the upper limit value of the formula (K3) are 0.376 and 0.458, respectively, and the lower limit value and the upper limit value of the formula (K4) are 0.458 and 0.751, respectively, Satisfies (K4). Also, the value of 1 / (2 · n1 · sinθ1) is 0.423, which also satisfies the equation (K5).

  In the setting examples shown in Tables 12-1 to 12-7, the diffraction efficiencies when the widths of the convex portions in the main period direction and the sub period direction of the diffraction grating 52 are changed by 0.05 μm are shown in Tables 13-1 and 13-2. Shown in Tables 13-1 and 13-2 list the diffraction efficiencies of the light beams LT, LR1, and LR2 at the wavelength with the lowest diffraction efficiency among the shortest wavelength, the center wavelength, and the longest wavelength. In addition, a value is a dB conversion value.

[Table 13-1]
Convex width in main period direction
Decrease Design value Increase
0.337 μm 0.387 μm 0.437 μm
Light beam LT (1310 nm wavelength band)
Reflectance-1.608-1.188 -0.589
Reflectance fluctuation amount -0.419 0.599
Light beam LR1 (1490 nm wavelength band)
Diffraction efficiency -0.724 -0.795 -1.071
Diffraction efficiency variation 0.071 -0.276
Difference between p-polarized light and s-polarized light diffraction efficiency 0.678 0.332 1.052
p-polarized light, s-polarized light diffraction efficiency difference variation 0.346 0.720
Light flux LR2 (1555 nm wavelength band)
Diffraction efficiency -0.394 -0.448 -0.663
Diffraction efficiency variation 0.054-0.214
Difference in diffraction efficiency between p-polarized light and s-polarized light 0.458 0.453 0.928
p-polarized light, s-polarized light diffraction efficiency difference fluctuation amount 0.004 0.475

[Table 13-2]
Convex width in sub period direction
Decrease Design value Increase
0.014 μm 0.064 μm 0.114 μm
Light beam LT (1310 nm wavelength band)
Reflectance -1.556-1.188 -0.806
Reflectance fluctuation amount -0.367 0.383
Light beam LR1 (1490 nm wavelength band)
Diffraction efficiency -0.757 -0.795 -0.937
Diffraction efficiency variation 0.038 -0.142
Difference between p-polarized light and s-polarized light diffraction efficiency 0.754 0.332 0.511
P-polarized light and s-polarized light diffraction efficiency difference variation 0.422 0.179
Light flux LR2 (1555 nm wavelength band)
Diffraction efficiency -0.375 -0.448 -0.580
Diffraction efficiency variation 0.073 -0.131
p-polarized light, s-polarized diffraction efficiency difference 0.256 0.453 0.768
p-polarized light, s-polarized light diffraction efficiency difference fluctuation amount -0.198 0.314

  The variation amount of the width of the convex portion of the diffraction grating 52 is the same (± 0.05 μm) in Table 11 and Tables 13-1 and 13-2, but in this embodiment, the light fluxes LR1 and LR2 having relatively long wavelengths are used. It can be seen that an increase in the difference in diffraction efficiency between p-polarized light and s-polarized light is suppressed.

The relationship between the sub period Λy of the diffraction grating 52 and the diffracted light will be described. Assuming that the wavelength of light is λ, the order of diffraction generated by the main period Λx is mx, and the order of diffraction generated by the subperiod Λy is my, the condition for generating the diffracted light of the diffraction order (mx, my) is Is done.
[(n2 / n1) · sinθ1 · cosφ + mx · λ / (n2 / Λx)] ² +
[(n2 / n1) · sinθ1 · cosφ + my · λ / (n2 · Λy)] ² ≦ 1 Equation (M1)

In the optical device 13, it is necessary to cause diffraction of the (−1, 0) order, that is, mx = −1 and my = 0 in the light beams LR <b> 1 and LR <b> 2 to increase the diffraction efficiency. Must be suppressed. Here, diffracted light of the (−1, ± 1) order, that is, mx = −1 and my = ± 1 is most likely to occur except the (−1, 0) order. A condition for preventing (−1, ± 1) -order diffracted light from being generated in the light beams LR1 and LR2 is expressed by the equation (M2).
[sinθ1−λ2L / (n1 · Λx)] ² + [λ2L / (n1 · Λy)] ² > 1 Equation (M2)

When formula (M2) is transformed, formula (M3) is obtained.
Λy ² / λ2L ² <1 / [n1 ² · [1- (sinθ1−λ2L / (n1 · Λx)) ² ]] Equation (M3)

However, if the expression (M4) is satisfied, it is possible to suppress the (−1, ± 1) -order diffracted light generated in the light beams LR1 and LR2.
Λy ² / λ2L ² <1 / [n1 ² · [1- (sinθ1−1.1 · λ2L / (n1 · Λx)) ² ]]
... Formula (M4)

In order to facilitate the creation of the diffraction grating 52, the sub period Λy is preferably set to be equal to or greater than the main period Λx. That is, it is preferable to satisfy the formula (M5).
Λx ² / λ2L ² ≤ Λy ² / λ2L ² Equation (M5)

  Tables 14-1 to 14-7 show various parameters set so as to satisfy the expressions (M4) and (M5) in addition to the expressions (K1) to (K5). The sub period Λy is twice the main period Λx.

[Table 14-1]
Diffraction grating 52
Cross-sectional shape: rectangle Uneven main period Λx (Λ): 0.649 μm
Uneven sub-period Λy: 1.298 μm
Sub period / main period (Λy / Λx): 2
Uneven height difference h: 0.649 μm
Convex main period direction width Wx: 0.389 μm
Protrusion sub-cycle direction width Wy: 0.130 μm
Medium refractive index: 1.48
Luminous flux LT
Wavelength (λS): 1310nm
Period / wavelength (Λx / λS): 0.495
Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.81 (−0.90 dB)
Luminous flux LR1
Wavelength (λM): 1490 nm
Period / wavelength (Λx / λM): 0.436
Incident angle θ1: 52.5 ° Output angle θ2: −49.3 ° p-polarization reflection diffraction efficiency: 0.88 (−0.55 dB)
s-polarized reflection diffraction efficiency: 0.85 (−0.71 dB)
Average reflection diffraction efficiency: 0.86 (−0.63 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.16 dB
Luminous flux LR2
Wavelength (λL): 1555nm
Period / wavelength (Λx / λL): 0.417
Incident angle θ1: 52.5 ° Output angle θ2: −55.7 ° p-polarization reflection diffraction efficiency: 0.87 (−0.59 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.23 dB)
Average reflection diffraction efficiency: 0.91 (−0.41 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.35 dB

[Table 14-2]
Luminous flux LT
Shortest wavelength (λ1L): 1260nm
Period / wavelength (Λx / λ1L): 0.515
Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectance: 0.88 (−0.57 dB)
[Table 14-3]
Luminous flux LT
Maximum wavelength (λ1U): 1360 nm
Period / wavelength (Λx / λ1U): 0.477
Incident angle θ1: 52.5 ° Output angle θ2: 52.5 ° Reflectivity: 0.76 (–1.21 dB)

[Table 14-4]
Luminous flux LR1
Shortest wavelength (λ2L): 1480 nm
Period / wavelength (Λx / λ2L): 0.438
Incident angle θ1: 52.5 ° Output angle θ2: −48.4 ° p-polarization reflection diffraction efficiency: 0.85 (−0.70 dB)
s-polarized reflection diffraction efficiency: 0.79 (-1.00 dB)
Average reflection diffraction efficiency: 0.82 (−0.85 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.30 dB
[Table 14-5]
Luminous flux LR1
Maximum wavelength (λ2U): 1500nm
Period / wavelength (Λx / λ2U): 0.433
Incident angle θ1: 52.5 ° Output angle θ2: −50.2 ° p-polarized reflection diffraction efficiency: 0.90 (−0.45 dB)
s-polarized reflection diffraction efficiency: 0.89 (−0.50 dB)
Average reflection diffraction efficiency: 0.90 (−0.48 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.05 dB

[Table 14-6]
Luminous flux LR2
Shortest wavelength (λ3L): 1550 nm
Period / wavelength (Λx / λ3L): 0.419
Incident angle θ1: 52.5 ° Output angle θ2: −55.1 ° p-polarized reflection diffraction efficiency: 0.88 (−0.53 dB)
s-polarized reflection diffraction efficiency: 0.95 (−0.21 dB)
Average reflection diffraction efficiency: 0.92 (−0.37 dB)
Difference in diffraction efficiency between p-polarized light and s-polarized light: 0.33 dB
[Table 14-7]
Luminous flux LR2
Longest wavelength (λ3U): 1560 nm
Period / wavelength (Λx / λ3U): 0.416
Incident angle θ1: 52.5 ° Output angle θ2: −56.2 ° p-polarized reflection diffraction efficiency: 0.86 (−0.64 dB)
s-polarized reflection diffraction efficiency: 0.94 (−0.26 dB)
Average reflection diffraction efficiency: 0.90 (−0.45 dB)
p-polarization, s-polarization diffraction efficiency difference: 0.38 dB

In this setting example, the lower limit value and the upper limit value of the formula (K3) are 0.377 and 0.460, respectively, and the lower limit value and the upper limit value of the formula (K4) are 0.460 and 0.754, respectively. In addition, the value of 1 / (2 · n1 · sinθ1) in the formula (K5) is 0.426. The sub period Λy corresponding to the upper limit value of the equation (M3) is 1.338 μm.

  In the setting examples shown in Tables 14-1 to 14-7, the diffraction efficiencies when the widths of the convex portions in the main period direction and the sub period direction of the diffraction grating 52 are changed by 0.05 μm are shown in Tables 15-1 and 15-2. Shown in Tables 15-1 and 15-2 list the diffraction efficiencies of the light beams LT, LR1, and LR2 at the wavelength with the lowest diffraction efficiency among the shortest wavelength, the center wavelength, and the longest wavelength. In addition, a value is a dB conversion value.

[Table 15-1]
Convex width in main period direction
Decrease Design value Increase
0.339 μm 0.389 μm 0.439 μm
Light beam LT (1310 nm wavelength band)
Reflectance -1.685-1.208 -0.597
Reflectance fluctuation amount -0.477 0.611
Light beam LR1 (1490 nm wavelength band)
Diffraction efficiency -0.796 -0.848 -1.125
Diffraction efficiency fluctuation amount 0.052-0.276
Difference in diffraction efficiency between p-polarized light and s-polarized light 0.808 0.300 1.155
p-polarized light, s-polarized diffraction efficiency difference variation amount 0.508 0.855
Light flux LR2 (1555 nm wavelength band)
Diffraction efficiency -0.370 -0.449 -0.649
Diffraction efficiency variation 0.079 -0.200
Difference in diffraction efficiency between p-polarized light and s-polarized light 0.340 0.382 0.898
p-polarized light, s-polarized light diffraction efficiency difference fluctuation amount -0.042 0.515

[Table 15-2]
Convex width in sub period direction
Decrease Design value Increase
0.080 μm 0.130 μm 0.180 μm
Light beam LT (1310 nm wavelength band)
Reflectance -1.388 -1.208 -1.103
Reflectance fluctuation amount -0.180 0.105
Light beam LR1 (1490 nm wavelength band)
Diffraction efficiency -0.803 -0.848 -0.933
Diffraction efficiency variation 0.045 -0.085
Difference in diffraction efficiency between p-polarized light and s-polarized light 0.808 0.300 0.327
p-polarization, s-polarization diffraction efficiency difference variation amount 0.508 0.027
Light flux LR2 (1555 nm wavelength band)
Diffraction efficiency -0.370 -0.449 -0.522
Diffraction efficiency variation 0.079 -0.073
p-polarized light, s-polarized light diffraction efficiency difference 0.340 0.382 0.579
p-polarized light, s-polarized light diffraction efficiency difference fluctuation amount -0.042 0.197

  From comparison between Tables 13-1 and 13-2 and Tables 15-1 and 15-2, by making the sub period Λy larger than the main period Λx, the p-polarized light beams LR1 and LR2 due to fluctuations in the width of the convex portions It can be seen that an increase in the difference in diffraction efficiency of s-deflection can be suppressed better.

The figure which shows typically the structure of the optical apparatus of 1st Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 1st Embodiment. The figure which shows the relationship between the change of the parameter in the diffraction grating of the optical apparatus of 1st Embodiment, and the change of diffraction efficiency. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 2nd Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 3rd Embodiment. The figure which shows typically the structure of the optical apparatus of 4th Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 4th Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 5th Embodiment. The figure which shows the relationship between the change of the parameter in the diffraction grating of the optical apparatus of 5th Embodiment, and the change of diffraction efficiency. The figure which shows typically the structure of the optical apparatus of 6th Embodiment. The figure which shows typically the principal part of the optical apparatus of 7th Embodiment. The figure which shows typically the principal part of the optical apparatus of 8th Embodiment. The side view (a) and top view (b) which show typically the diffraction grating element of the optical apparatus of 9th Embodiment. The figure which shows typically the structure of the optical apparatus of 10th Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 10th Embodiment. The top view which shows typically the diffraction grating of the optical apparatus of 11th Embodiment. The perspective view which shows typically the relationship between the diffraction grating of the optical apparatus of 11th Embodiment, and the angle of a light beam. The figure which shows typically the optical path in the example of 1 setting of the diffraction grating of the optical apparatus of 11th Embodiment. The figure which shows typically the optical path in the setting example of the diffraction grating of the optical apparatus of 12th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-13 Optical apparatus 21, 23 Light emission part 22, 24 Light emission control part 25 Arc-shaped rail 26 Temperature sensor 27, 28, 29 Light emission part 31 Optical fiber 35 Optical sensor 41, 43 Light reception part 42, 44 Signal detection part 51 Diffraction grating Element 52 Diffraction grating 52a Diffraction grating convex part 52b Diffraction grating concave part 53, 54 Convex part 55, 57 Diffraction grating element 56, 58 Diffraction grating 61 Objective lens

Claims (9)

A diffraction grating that causes a first light flux having a first wavelength and a second light flux having a longer wavelength than the first wavelength to enter from different directions and emits the first light flux in the direction of the incident source of the second light flux. In an optical device having an element,
Of the medium sandwiching the diffraction grating, the refractive index of the first medium located on the incident side of the first light beam and the second medium located on the opposite side are n1 and n2, respectively, and the period of the irregularities of the diffraction grating is Λ, When the wavelengths of the first light beam and the second light beam are represented by λs and λL, respectively, and the incident angle of the first light beam on the diffraction grating is represented by θ,
n2 ≧ n1 ・ sinθ
Λ / λL ≤ 1 / (n1 + n1 · sinθ)
And Λ / λ S> 1 / (n 1 + n 1 · sin θ) −0.04
An optical device characterized by satisfying the relationship: A diffraction grating that causes a first light flux having a first wavelength and a second light flux having a longer wavelength than the first wavelength to enter from different directions and emits the first light flux in the direction of the incident source of the second light flux. In an optical device having an element,
Of the medium sandwiching the diffraction grating, the refractive index of the first medium located on the incident side of the first light flux and the second medium located on the opposite side are n1 and n2, respectively, and the period of the irregularities of the diffraction grating is Λ, When the wavelengths of the first light beam and the second light beam are represented by λs and λL, respectively, and the incident angle of the first light beam on the diffraction grating is represented by θ,
n2 ≧ n1 ・ sinθ
Λ / λL ≤ 1 / (n2 + n1 · sinθ)
and
1 / (n2 + n1 · sinθ) −0.04 <Λ / λS <1 / (n2 + n1 · sinθ) +0.02
An optical device characterized by satisfying the relationship: 3. The optical apparatus according to claim 1, further comprising a surface having a light collecting function in addition to the surface on which the diffraction grating is provided. The optical apparatus according to claim 1, wherein the diffraction grating is provided on a curved surface. When the diffraction grating is projected onto a tangential plane at an arbitrary position on the curved surface where the diffraction grating is provided, the period of the irregularities of the diffraction grating on the plane is Λ, and the incident angle with respect to the plane is θ, the above relationship The optical device according to claim 4, wherein: 3. The optical apparatus according to claim 1, wherein a cross section of each unevenness parallel to the direction of the period of the unevenness of the diffraction grating is substantially rectangular. The optical apparatus according to claim 1, further comprising a mechanism that changes an incident angle of the light beam with respect to the diffraction grating. The optical apparatus according to claim 1, further comprising an optical component that causes the light beam having the second wavelength to enter the diffraction grating and that receives the light beam having the first wavelength emitted from the diffraction grating. The optical apparatus according to claim 1, further comprising an optical component that collects a light beam incident on the diffraction grating or a light beam emitted from the diffraction grating.

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