JPS6225710A - Optical multiplexer/demultiplexer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical multiplexer/demultiplexer used in optical communications and the like to perform multiplex transmission using light of a plurality of different wavelengths.

Conventional technology Conventionally, diffraction gratings used in optical multiplexers and demultiplexers include those using a flat linear diffraction grating made of a hologram created by interference between plane waves, and those using a mechanical scoring method or concave gratings created optically. Those using a diffraction grating are generally known. Among these, those using planar linear diffraction gratings are
FIG. 1 shows, as an example, multiplexed incident light (wavelengths λ4, λ2, λ5, etc.) entering from the input optical fiber 1, as shown in Japanese Patent Laid-Open No. 54-4147. are collimated into parallel light by the collimation lens 2, and converted into wavelengths λ1 by the diffraction grating 3. λ2. An optical demultiplexer has a structure in which it is diffracted and demultiplexed according to As shown in 17045/1984, multiplexed incident light (wavelength λ,

λ2. λ3. ) enters from the input optical fiber 1 into the first electric flux optical transmitter 6 whose refractive index gradually decreases from the center to the periphery, and travels in a meandering manner. The transmission type diffraction grating 3 transmits the wavelength λ.

λ2. λ3. An optical demultiplexer has a structure in which the optical demultiplexer is diffracted and demultiplexed in accordance with As far as is known, all of them require lens-like lenses such as collimation lenses, focusing lenses, or focusing light transmitters, and their optical systems are I-Pheasant. On the other hand, those using concave diffraction gratings create holograms by mechanical scoring method or by optical method by interference of spherical waves, so collimation lenses and focusing lenses are particularly required. However, since it has a concave shape, it is difficult to manufacture and has the disadvantage of being expensive.

Problems to be Solved by the Invention Conventional optical multiplexers and demultiplexers using planar linear diffraction gratings require lens-like products such as collimation lenses and focusing lenses, resulting in complicated optical systems. Those using η multiple diffraction gratings do not require a focusing lens, etc.
Since the shape is concave, it is difficult to manufacture, both are expensive, and it is difficult to increase the multiplicity in terms of performance.

The present invention takes this point into consideration and provides an optical multiplexer/demultiplexer that uses a planar diffraction grating, does not require lenses, and has a high degree of multiplicity.

Means to Solve the Problems In order to solve the above problems, the present invention uses aspherical waves to correct aberrations, and diffracts a hologram due to the interference between a wavefront consisting of a combination of an aspherical wave and a spherical wave and a spherical wave. By using it as a grating, it is a planar diffraction grating that provides a simple optical multiplexer/demultiplexer that does not require lenses or the like.

action The present invention provides multiplexed wavelengths λ4. λ2. λ,.

. . . enters from one input optical fiber, is diffracted and demultiplexed by the diffraction grating made of the above-described plane hologram, and then exits from a plurality of output optical fibers. Alternatively, multiplexed incident light that enters separately from a plurality of input optical fibers is diffracted and multiplexed by the above-described diffraction grating made of a plane hologram, and is emitted from a single output optical fiber.

Embodiments A method for producing a diffraction grating used in the present invention and an embodiment of an optical demultiplexer using the diffraction grating will be described with reference to FIGS. 3 to 6. FIG. 3 shows a principle diagram for creating a hologram that serves as a diffraction grating for use in an optical multiplexer/demultiplexer. In the present invention, the hologram is created by interference between an aspherical wave and a spherical wave in order to create a hologram that is planar (plane diffraction grating) and has little aberration. The aspherical wave may be a single aspherical wave, but even a combination of an aspherical wave and a spherical wave is essentially an aspherical wave. The aspherical wave transforms the laser beam into an appropriately designed computer hologram (Computer hologram).
ter Generated Hologram,C
GH). Computer-generated holograms can be produced by direct electron beam drawing or by optical methods, which are drawn using a plotter and reduced in size, but for high precision, electron beam drawing is better. To create a hologram, a convergent or diverging aspherical wave made of laser light and a convergent or diverging spherical wave are incident on both sides or one side of a hologram photosensitive material layer, the hologram photosensitive material layer is exposed, and a hologram consisting of interference fringes is created. create. As an example, FIG. 3 shows that if the perpendicular Z-axis is the optical axis of the holographic photosensitive material layer 8, the convergent aspherical wave 9 is incident in the optical axis direction and converged at a point ○ on the optical axis. (OA=Ro), and the divergent spherical wave 10 is made incident from the opposite side of the convergent aspherical wave 9 at an angle of Or to the optical axis in the direction of Rm from the point R (RA==Rr). Thus, the hologram 11 was created.

FIG. 4 shows a configuration similar to the hologram creation method shown in FIG. 3, including an input optical fiber 13 and an output optical fiber 14! L, 1
4b, 140. . . . is a diagram showing an example of an optical demultiplexer in which an output optical fiber group 14 and a diffraction grating 12 are arranged. To explain its configuration in comparison with FIG. 3, if the center point of the diffraction grating 12 made up of the hologram 11 is a person, it is at an angle of 0° with respect to the optical axis Z axis, which is equal to the angle of or, and the same distance as Rr. The tip of the input optical fiber 13 is placed at a position Rc, and the tip of the output optical fiber group 14 is placed at a position corresponding to the same distance R1 as Ro on the Z axis.

The multiplexed input optical signal (wavelength; λ1, λ2, λ5, etc.) entering the input optical fiber 13 is diffracted and demultiplexed by the diffraction grating 12, and is outputted according to the wavelength. Optical fibers 141L, 14b, 140. It enters and exits. Figure 6 is a partially enlarged view of Figure 4, where the distance between the output optical fibers is 'i + the diffraction angle of the imaging light during reproduction is θi, and the incident angle of the reproduction light during reproduction is θC1. The imaging distance, that is, the distance between the diffraction grating surface and the tip position of the output optical fiber group is defined as R4.

The configurations shown in FIGS. 4 and 5 are determined by the grating equation shown below.

λC sln θ4=sin Oc + −(sin θ0
-S! n θr ) −・=(1) λO λC; Reproduction wavelength λ0; Recording wavelength θ0; Incident angle of object light during recording 0r; Incident angle of reference light during recording Oc; Incident angle of reproduction light during reproduction 3rd As shown in the figure, when a convergent aspherical wave is incident perpendicularly on the hologram surface, θQ: 180°, so sir+0□20 Also, as shown in Figure 4, if θC2or...
...(2) becomes. According to Figure 5, the distance Re between the optical fibers is 6i
= R1tanOlλC: Ritan sin''''(sinθc(1--
) Jλ0 (3) R1: Imaging distance.

Therefore, as an example, Ro "800 nm.

λO=820 nm, J=36.70111'l
l, Rc = 32.20ffl, and the outer diameter of the optical fiber (corresponding to the distance 64 between the optical fibers when the output optical fibers are lined up next to each other) is 300μ, then θQ: 19.08° (=θr) Become. That is, the reference light or the incident light from the input optical fiber is preferably made incident at an angle of 19.08° with respect to the optical axis.

To create a computer hologram (CGH), the phase function φyo of the hologram is determined. When recording is performed using the electron beam direct writing method, there is a method in which the exposure amount applied to the resist film on the substrate, that is, the electron beam irradiation amount, is changed by computer control according to the phase function φyo, and a method equivalent to interference fringes. There is an optical method of recording and reducing the pattern with a plotter.

The phase function φ of the hologram film is the phase function φ0 of the object light
．． ! : Difference between reference phase functions φr. In other words, φyo=φ. -φ1 River... (4) For aberration correction, when an aspherical wave consisting of phase function φG is added to the object beam, φyo = (φ0+φ.)-φ1 ・・・・・・
(5) becomes. Since the slope and slope are spherical waves, they are expressed by the following equation.

A.

-R0〕 ...Song・(6)-Rr)
・・・・・・(A) θ. =0.0
Substitute r=19.08° and further, R6=36.70
1M, Rr =32.20MM, λ. = 8
o.

Substituting nm becomes a function of X and y.

Aspherical wave φ. is given as a function of X and y by the following equation.

Su0 ten C02y2+C04y4+C06y6+Co8y8 ten C22x272+Cas! '3'') '-・”(
8) In equation (8), due to the symmetry of the wavefront, there are no odd terms in C, and there are only even terms.

In addition, the phase function φ of the reconstructed image light using this hologram film is
, is expressed by the following equation.

λC φ,=φ. +-((φ.+φ.)-φ1)λ0 (9) The coefficient C of the aspherical wave is obtained by finding the direction cosine of φ, and tracing the rays for each wavelength. The radius of gyration of the point image is determined from the dispersion locations of each spot diagram, and an evaluation function (merit function) is determined.

At this time, the nonlinear least squares method (DLSmethod)
By repeating the calculation as many times as necessary using
Determine optimal conditions. As a result of calculation, under one condition of this example, the C value corresponding to the optimal aspherical wavefront is: C2o; 6.7100 c40; 1.4259 C6o; 0.60353 Cso; 0.22731 c02; 1 1.81 3 C,; 0.79928 Co6; 0.27268 c08; 0.80916 C22; 5.9671 C4,; 1.8714. Substituting this C-factor j coefficient into equation (8), further, φ8 is determined from equations (5) to (8).

φ, = 2 yr p (μ; fring 1nd
ex, integer)......(1 (1),
Plotting X and y yields a hologram corresponding to interference fringes. Since the diffraction efficiency of this hologram is low as it is, by changing the exposure conditions and making the groove shape triangular or sawtooth,
Diffraction efficiency can be increased. The hologram thus produced was used as a diffraction grating 12, as shown in FIGS. 4 and 5, with a wavelength of 800 nm and an 820 nu18
When a multiplexed optical signal of 40 nm, 860nl11, 880nu is inputted from the input optical fiber 13, it is diffracted and demultiplexed by the diffraction grating 12, and then sent to the output optical fiber 142L.
soonm, 820 nm to the output optical fiber 14b, 8401 m to the output optical fiber 140, output optical fiber 14
860 nm to d, 880 nm to output optical fiber 1415
The optical signal enters and exits. FIG. 6 shows a point spread distribution obtained by ray tracing at a point 16 within the core of the optical fiber. That is, the optical fiber 1 jLL , 14b has an outer diameter of 300 μ.

14C, 14d, 14el each core diameter 200μ
All output light enters the cores 16a, 16b, 160, 16d, and 1615.

4 and 6 are explained as an optical demultiplexer, but when used as an optical multiplexer, the input optical fiber is 141L.
, 14b, 140, 14d, 146° The output optical fibers are 13, and the input optical fibers each have an 800 nm
, 820nm, 840nm.

When light of 860 nm and 880 nm is incident, it is diffracted and multiplexed by the diffraction grating 12, enters the output optical fiber 13, and is emitted. Therefore, it can be used as an optical demultiplexer or an optical multiplexer.

The present invention creates a pattern corresponding to the interference fringes of an aspherical wave and a plane wave for aberration correction using a computer hologram, generates an aspherical wave by passing the plane wave through this, and converges this wavefront once, then diverges it. , a wavefront is created by combining an aspherical wave and a spherical wave, and a hologram optically created by interference between this wavefront and the spherical wave is used as a diffraction grating. Furthermore, in this example, a reflection type was explained in which an aspherical wave and a spherical wave were made incident from both sides of the holographic photosensitive material layer, but an aspherical wave and a spherical wave were made incident from one side of the holographic photosensitive material layer. Transmission type holograms made using holograms, or holograms in which a reflective film of gold, aluminum, or the like is formed on the hologram surface have exactly the same effect. Furthermore, in this example,
Although a so-called flat diffraction grating having a planar shape has been described, a concave diffraction grating having a concave shape has exactly the same effect. Alternatively, when the present invention is used as a spectrometer, it has exactly the same effect. In this example, a 5-wave optical multiplexer/demultiplexer was explained, but by using an aspherical wave, a 10-wave optical multiplexer/demultiplexer is also possible. can be created.

Effects of the Invention The present invention uses a hologram created by interference between an aspherical wave and a spherical wave, so that it is flat and has a simple optical system.
It is possible to create an optical multiplexer/demultiplexer that is easy to manufacture and has high multiplicity in terms of performance.

[Brief explanation of drawings]

1 and 2 are conceptual diagrams showing an optical demultiplexer using a conventional diffraction grating, FIG. 3 is a principle diagram showing an example of a method for creating a hologram or diffraction grating according to the present invention, and FIG. 4 is a conceptual diagram showing an optical demultiplexer using a conventional diffraction grating. Figure 3 is a conceptual diagram of an optical demultiplexer using a diffraction grating created by the method shown in Figure 6. Figure 6 is a partially enlarged conceptual diagram of Figure 4. FIG. 3 is a diagram showing a point spread distribution within an output optical fiber. 1... Input optical fiber, 2... Collimation lens, 3... Diffraction grating, 4...
...Focusing lens, 5... Output optical fiber group, 6
. . . First focusing light transmission body, 7 . . . Second focusing light transmission body, 8 . . . Hologram photosensitive material layer, 9 . . . Convergent aspherical wave, 10...
-Speech spherical wave, 11...Hologram, 12...
... Diffraction grating, 13 ... Input optical fiber,
14... Output optical fiber group, 14&, 14b,
140, 14d. 140... Each output optical fiber, 16...
...Points of point spread distribution by ray tracing, 16m, 16b
. 16c, 16d, 18e... Cores of output optical fibers, respectively. Name of agent: Patent attorney Toshio Nakao and 1 other person f1
1. Input/JL fiber 4...11 floor lens 5... Output/F light 2 fin ζ stone E Fig. 2 11- O, Ω2゛F person Fig. 5 Fig. 6/61 points. 7k ・Output fiber '0 core

Claims (4)

[Claims] (1) An optical multiplexer/demultiplexer characterized in that a hologram formed by interference between an aspherical wave and a spherical wave is used as a diffraction grating. (2) The optical multiplexer/demultiplexer according to claim (1), wherein the aspherical wave is substantially composed of a combination of an aspherical wave and a spherical wave. (3) The aspherical wave is created by a computer-generated hologram.
Optical multiplexer/demultiplexer described in section 2). (4) The optical multiplexer/demultiplexer according to claim (1), wherein the hologram is created by a computer-generated hologram.