JPS60107004A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To obtain an optical demultiplexer which has wide passing wavelength band width by allowing diffracted light from a diffraction grating to travel backward through a corner cube, and making it incident to the diffraction grating again. CONSTITUTION:An incident light beam from an incidence fiber 13 is converted by a distributed index rod lens 14 into parallel luminous flux, which strikes the diffraction grating 16 installed at a specific angle through a glass block 15. The diffracted light within a wavelength range lambda-lambda2 converges on the reflective surface of a corner cube 17-a and then guided as backward traveling divergent light to the diffraction grating 16 again. The parallel luminous flux diffracted again by the diffraction grating 16 passes through the distributed index type rod lens 14 to converge on the end surface of a projection fiber 18-a. Similarly, diffracted light within a wavelength range lambda3-lambda4 is reflected by a corner cube 17-b to converge on a projection fiber 18-b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a demultiplexer for optical fibers, and particularly to an angularly dispersive optical demultiplexer having a wide passing wavelength bandwidth.

[Background of the invention]

An optical demultiplexer separates the wavelength-multiplexed light transmitted through the input fiber into waves of multiple wavelengths and sends each wave to a separate output fiber, and is used for this type of wavelength-multiplexed optical fiber transmission. Conventional interference film type optical demultiplexers and angle dispersion type optical demultiplexers have been developed as demultiplexers. Interference film type optical demultiplexers have the advantage that the center wavelength and bandwidth can be designed arbitrarily, but forming the interference film requires extremely advanced technology and a great deal of work, and the interference film has the same number of demultiplexers. Since it is necessary to combine the two, there is a drawback that manufacturing becomes difficult as the number of demultiplexing waves increases. - Although the blade angle dispersion type optical demultiplexer has the advantage of being capable of multiple demultiplexing with one angle dispersion element, it has the disadvantage that the passing wavelength bandwidth is limited for the following reason. FIG. 1 is an example of a conventional angle dispersive optical demultiplexer.

In FIG. 1, 1 is an input fiber, 2 is a collimating lens, 6 is a diffraction grating, and 4-a and 4-b (hereinafter referred to as 4 including both) are output fibers.

The incident light from the input fiber 1 is converted into a parallel light beam by the collimating lens 2, and enters the diffraction grating B. The diffracted light is converged again by the collimating lens 2 and forms an image on the end face of the output fiber 4. Here, when the end faces of the input fiber 1 and the output fiber 4 are on the same plane, the optical system has a lateral magnification of 1.

At this time, the relative positional relationship between the end face of the output fiber 4 and the image of the input fiber 1 is as shown in FIG. In Figure 2, 5 is the core end face of the input fiber 1, 6 is the clad end face of the input fiber 1, 7 is the core end face of the output fiber 4, including 7-a and 7-b, and 8 is the core end face of the output fiber 4, including 8-a and B-b. 8 is the clad end face of the output fiber 4, and 9, 10, 11, and 12 are the west lengths of λ1, respectively.
, λ2, λ3, and λ4 are images of the core end face 5 of the input fiber 1. In the wavelength band λ1 to λ2, the core end face image of the input fiber 1 is imaged inside the core end face 7-a of the output fiber 4-a, so that a coupling efficiency of 100% is obtained.

That is, λ1 to λ2 become the wavelength band passing to the output fiber 4-a. Similarly, λ6 to λ4 are the wavelength bands passing through the output fiber 4. At this time, each passage is D1
C is the core diameter of the input fiber 1, Do is the core diameter of the output fiber 4, f is the focal length of the collimating lens 2, and /dλ is the angular dispersion of the diffraction grating 6. On the other hand, the passing wavelength center spacing 'ab to the output fibers 4-a and 4-1] is given by the following equation.

Here, Ca'b is the core center spacing of the output fibers 4-a, 4-1]. By the way, the minimum core center spacing is the cladding diameter of the output fiber 4]). is equal to the fractional band Δλ/
λab is expressed by the following formula.

λdl) are both zero. So it's normal. >Di is required. However. Ori. If the image of the input fiber approaches the core end face 7 of the output fiber 4-a, 4-b,
If images are formed across -a and 7-bK, the wavelength range increases, and the degree of separation deteriorates. The following conditions are necessary to obtain a sufficient degree of separation.

2(Do-Do)≧D1-=-(4) ■). -125 μm, DI=50 ttmφ From equation 4, φ I). ≦100 μmφ. In this case, the specific band Δλ/λ
ab=0.4 reaches the maximum. As mentioned above, in the conventional technology, if input and output fibers with the same parameters are used, the bandwidth becomes zero, making it difficult to insert a demultiplexer in the middle of the transmission line, and even if the core diameters of the input and output fibers are changed, the maximum There was a drawback that the band was limited to about 0.4.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and
An object of the present invention is to provide an optical demultiplexer that can obtain a wide passing wavelength bandwidth without being limited by the optical parameters of an input fiber.

[Summary of the invention]

A feature of the present invention is that the diffracted light from the angle dispersion element is made to travel backwards through the corner keave and enters the angle dispersion element again to obtain re-diffracted light. The object of the present invention is to form a configuration in which an incident fiber image is formed on a fiber.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 5 is a perspective view for explaining one embodiment of the present invention, in which 15 is an input fiber, 14 is a distributed index rod lens, 15 is a glass block, 16i11 diffraction grating, 1
7-a and 17-b are: If key f, 18-a and 18-1) are output fibers. This embodiment operates as follows. The incident light beam from the input fiber 16 is converted into a parallel beam by the Rondre/Z of distributed index type 14, and is incident on the diffraction grating 16 set at a predetermined angle by the glass block 15.

After the diffracted light in the wavelength range C to λ2 converges within the reflecting surface of the corner key 17-a, it becomes retrograde divergent light, passes through the distributed index rod lens 14, and is converted into a parallel beam of light, which is then applied to the diffraction grating 16. It is grooved again. The parallel light beam diffracted again by the diffraction grating 16 passes through the distributed index Ronde lens 14 and converges on the end face of the output fiber 18-a. Similarly, the diffracted light in the wavelength range λ3 to λ4 is reflected by the corner cube 17-b and converged on the output fiber 18-1]. This relationship will be explained in detail with reference to FIG. FIG. 4 shows the relative positions of the input/output fiber and the corner keep on the fiber side end face of the distributed index rod lens in FIG. 6. In FIG. 4, 19 is the core end face of the input fiber 16, 20 is the clad end face of the input fiber 13, and 21
-a is the incident side reflection surface of the corner keave 17-a, 22-
23-a and 24-a are regions where the diffracted light with wavelength λ1 is reflected by reflection surfaces 21-a and 22-a, and 25-a and 26-a are the wavelength λ2 This is the region where the diffracted light of is reflected by the reflecting surfaces 21-a and 22-a. Similarly, 21-b and 22-b are the reflection surfaces on the exit side of the corner key 17-b, and 23-b and 24-b are the reflection surfaces 21-b and 22-b of which the diffracted light of wavelength λ6 is reflected. area, 25-b
, 26-11, the diffracted light of wavelength λ4 is reflected by the reflecting surfaces 21-b, 2
This is the area reflected by 2-b. 27-a, 28-
a is the core and clad end face of the output fiber 18-a, and 27-b, 28-1) is the core and clad end face of the output fiber 18-b.

The operation of this embodiment will be described below with reference to FIG. The light beam emitted from the core end face 19 of the input fiber is transmitted through the diffraction grating 1
6 on the incident side reflective surface 21-a of the corner key 17-a in the wavelength range of λ1 to λ2.
The light converges and is reflected near the area from 3-a to 25-a. The wavelength range Δλ3-λ2-λ1 is approximately given by the following equation.

Here, La is the side length of the corner key 17-a, DI is the core diameter of the input fiber 1, f is the focal length of the collimating lens 14, and (d0/dλ) is the angular dispersion of the diffraction grating 160. Strictly speaking, the fact that it is given approximately means that the focal point is given by the bifocal planes 21-a and 22-a of the corner key 17-a.
It is provided on the perpendicular bisector of
-a, 2: The distance at 2-at is short, and furthermore, the angular spread of the diffracted light is a small value determined by the NA (numerical aperture) of the incident core ino; −
This is because the image on a and the image on the focal plane are considered to be approximately equal.

Here, if a flat reflecting mirror with the same side length L2 is provided at the same location instead of the corner cube 17-a, the wavelength range λ1~
It is obvious that the diffracted light of λ2 travels backward, is diffracted again by the diffraction grating 16, and is imaged on the input fiber core end face 19. By the way, in this embodiment using the corner cube 17-a, the luminous flux incident on the incident side reflective surface 21-a is 2-a~
It is reflected at the area 25-a and guided to the output-side reflecting surface 22-a, and then reflected at the areas 24-a to 26-a above this and guided to the diffraction grating.

That is, while the diffracted light travels backward via the corner keeper, the image position moves by a distance T within a plane including the input and output fibers and the corner keeper. The amount of movement T is the corner key 17
It is determined by the position of the diffracted light incident on -a. Output side reflective surface 2
The light flux that has gone backwards from 2-a is diffracted again by the diffraction grating 16, and the light beam is re-diffracted by the diffraction grating 16, and the light beam is reflected from the input fiber 18-a to the core end face 27- of the output fiber 18-a, which is provided at a predetermined position moved by a distance T from the core end face.
The image is formed on a.

Similarly, the diffracted light in the wavelength range λ6 to λ4 is corner kept at 17.
-11, is refracted 1] degree by the diffraction grating 16, and is imaged on the core end face 27-13 of the output fiber 18-1). Wavelength range Δλb - λ4 - λ3 Ni1, Jj in the following formula
available.

Here, is the side length of the corner key 17-b.

On the other hand, the passing wavelength center spacing Δ'ab of the output fibers 18-a, 13-1) is given by the following equation.

Here, G is the distance between the corner keeves 17-a and 17-1). Since the relationship G≧D is required to obtain a sufficient degree of separation, the fractional bands Δλ3, Δλ1 . )/Δλ31° is given by the following formula.

Δλab(T-30Lb)/2+D1 In equations (5) 2 to (8), La and Lb are quantities independent of the input and output fibers, so even if the same input and output fibers are used, any passband can be obtained. Widths Δλ3, Δλb and large comparison ranges Δλa/Δλab, Δλb/Δλab can be obtained, L, , = 500 μm, Lb = 500 μm
m, D1 = 5011 m, Δλa/Δλab=Δλb/Δλab=0.8...
...(9), which is twice the specific bandwidth of the conventional technology.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a wide passband and a large fractional band without depending on the optical parameters of input and output fibers, and it is extremely effective in configuring a demultiplexer for wavelength division multiplexing optical communication. It is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional example, and FIG. 2 is a diagram of the relative positional relationship between the output fiber end face and the input fiber image in FIG.
FIG. 3 is a perspective view of one embodiment of the present invention, and FIG. 4 is a diagram showing the relative positional relationship between the input/output fiber and the corner keave in FIG. 6. Explanation of symbols 1.13...Input fiber 2...Collimating lens 6.16...Diffraction grating 4
-a, 4-b, IL-a, '18-b... Output 7 fiber 14... Gradient index type Rondo lens 15... Glass block 17-a, 17-b... Corner key 19 ...Core end face 20 of input fiber 16...Input fiber 13
clad end faces 21-a, 22-a...corner keys
Incident side of corner key 17-a, exit side reflective surfaces 21-b, 22-b...Incidence side, exit side reflective surfaces 26-a, 24-a of corner key 17-b...Diffracted light of wavelength λ1 is 21-a
, 22-a, 25+-a, 26-8...The diffracted light of wavelength λ2 is reflected by 21-
Areas reflected by a, 22-a 27-a, 28-a...Core and clad end surfaces of output fiber 18-a 27-b, 28-b...Core and clad end surfaces of output fiber 18-b Patent Applicant Nippon Telegraph and Telephone Public Corporation Patent Attorney Junnosuke Nakamura

Claims (1)

[Claims] In an optical splitter that separates wavelength-multiplexed light transmitted through an input fiber into waves of multiple wavelengths and distributes them to separate output fibers, the incident light from the input fiber is guided to an angular dispersion element and converted into diffracted light. , near the image formation position of this diffracted light, a plurality of corner keaves each having a reflecting surface larger than the real image of the incident fiber covering each passing wavelength band and returning the incident diffracted light antiparallel are spaced apart by a certain distance. and guide the diffracted light to the angle dispersion element again,
An optical demultiplexer characterized in that the obtained re-diffracted light is focused on each of a plurality of output fiber end faces installed near the end face of an input fiber.