JP3242332B2 - Optical demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple optical demultiplexer for accurately separating wavelength-multiplexed signal light with high sensitivity in a wavelength division multiplex transmission optical communication system.

[0002]

2. Description of the Related Art For the early 21st century, the realization of a multimedia concept by optical communication is urgently required. In this multimedia concept, it is said that an optical fiber network will be laid not only for business use but also for ordinary households, and it will be possible to obtain information and two-way communication on an individual basis, and enormous demand and employment in both hardware and software Is expected. To realize this concept, large-capacity optical multiplexing transmission technology is indispensable. As this technology, wavelength division multiplexing transmission that multiplexes and transmits multiple signal lights with different wavelength bands and separates and extracts individual signal lights An optical communication system is employed. In this system, particularly, a simple optical demultiplexer for accurately separating individual signal lights having different wavelength bands is required.

FIG. 7 shows an example of a conventional optical demultiplexer generally used. In FIG. 7, the optical demultiplexing device 40 generally includes an irradiation collimator 41, a transmission interference filter (hereinafter, simply referred to as "interference filter") 42, a light receiving collimator 43, and an inclination angle control system 44. The irradiation collimator 41 irradiates the wavelength-multiplexed signal light (hereinafter simply referred to as “multiplexed light”) transmitted from the input optical fiber 45 as a parallel beam bm. Interference filter 4
Reference numeral 2 denotes a transmission interference filter having a dielectric multilayer film. By tilting the interference filter with respect to the multiplex light beam bm, signal light of a specific wavelength band (hereinafter simply referred to as “specific light”) is selected from the multiplex light beam bm at an angle corresponding to each wavelength. The light receiving collimator 43 receives light. The light-receiving collimator 43 receives the selected specific light beam b _1, passes through the output optical fiber 46,
Although not shown, the data is transmitted to, for example, a photoelectric conversion device. In this case, so as to receive the specific light beam b ₁ on the light receiving collimator 43, the inclination angle control system 44 controls the rotation of the angle (inclination angle) with respect to the beam bm interference filter 42. Here, the “tilt angle” refers to an angle at which the interference filter is inclined from a state perpendicular to the multiplex light beam.

FIGS. 8 (a) and 8 (b) show an outline of an optical system of the conventional optical demultiplexer 40. FIG. In this optical system, the opposing irradiation collimator 41 and light receiving collimator 43 form an optical system in which the beam bm travels from the irradiation collimator 41 to the light receiving collimator 43 in a state where no interference filter is inserted (hereinafter, referred to as an “empty state”). The relative alignment is adjusted so that the loss (hereinafter, referred to as “transmission loss”) Δ is minimized. The interference filter 42 is formed by alternately laminating high-refractive-index dielectrics and low-refractive-index dielectrics deposited on a glass substrate 47 so that their thicknesses are about １ ／ wavelength or 波長 wavelength, respectively. It is formed of an interference film 48 of about a layer.

In FIG. 8A, an irradiation collimator 41 is used.
, A multiplexed light beam b containing wavelengths λ ₁ and λ ₂ (λ ₁ > λ ₂ )
m (λ ₁ , λ ₂ ) is the glass substrate 47 of the interference filter 42
Irradiated toward The interference filter 42 rotatable by the tilt angle control system 44 in FIG. 7 changes the tilt angle θ in the range of 0 ° to 90 ° when the state perpendicular to the beam bm is 0 °. be able to. In particular, in the case of the wavelength division multiplexing transmission system, the inclination angle θ is changed within the range of 0 ° to 25 °.

Now, the inclination angle of the interference filter 42 is θ
₁ and the multiple light beam bm from the irradiation collimator 41
, This multiplexed light enters the glass substrate 47,
In interference film 48 portion, as shown in FIG. 8 (a), by the interference action of light, only the beam b ₁ of the specific wavelength corresponding to the inclination angle θ ₁ (λ1) is transmitted through incident on the light receiving collimator 43, it beam b ₂ wavelength (.lambda.2) other than reflects.

[0007] Then when changing the inclination angle of the interference filter 42 to theta ₁ is greater than theta _2, in this angle, the beam b ₂ having a wavelength lambda ₂ shorter than the wavelength lambda ₁ of the beam b ₁ is incident on the light receiving collimator 43 Will be. At this time, the beam b ₁
Is reflected by the interference film 48 and does not enter the light receiving collimator 43.

Similarly, when the tilt angle of the interference filter 42 is appropriately changed, a specific light beam having a wavelength depending on the magnitude of the tilt angle θ is received by the light receiving collimator 43, and the signal included in each specific light is tilted. It is individually taken out by the change of the angle θ.

[0009]

In the above-mentioned conventional type of optical demultiplexing device 40, the tilt angle θ of the interference filter 42 is set.
Is increased, the optical transmission loss (hereinafter, referred to as “insertion loss”) δ due to the insertion of the interference filter 42 into the optical system
However, there is a problem that the angle increases depending on the inclination angle θ. Further, it was found that even half width lambda _h a particular light received by the light receiving collimator 43 increases depending on the inclination angle theta. When the insertion loss δ increases, an output fluctuation depending on the wavelength of the specific light is caused, which adversely affects the entire optical communication system of the wavelength division multiplexing transmission system. If the full width at half maximum lambda _h is increased, so leading to poor separation of adjacent other specific light, it increases the possibility of interference, a problem that the multiplicity can not be increased in this order a predetermined wavelength band is generated. The present invention has been made to solve the above problems, therefore its object is small both insertion loss δ and half width lambda _h, yet even the inclination angle of the interference filter 2 theta varies thereof It is an object of the present invention to provide a simple optical demultiplexing device with little fluctuation of the light.

[0010]

An object of the present invention is to provide an optical system comprising: an irradiating section for irradiating multiplexed light as a parallel beam; and a light receiving section for receiving at least a part of the multiplexed light. An optical demultiplexer in which an interference filter capable of changing an inclination angle with respect to is inserted, wherein the light receiving unit is inclined from a reference alignment position where the transmission loss of the beam is minimized in an empty state. In a direction approaching one end of the interference filter, and
Opposite to the direction of refraction when the beam is incident on the substrate
This problem can be solved by providing an optical demultiplexer that is disposed at a position that is translated in the direction by a certain distance.

In the empty state, the distance that the light receiving unit has moved in parallel is 1 unit less than the transmission loss value at the reference alignment position.
It is preferable to set the gain within a range where the gain is reduced in the range of 2 dB to 2 dB. The above parallel movement distance is 10
It is preferable that the thickness be in the range of 0 μm to 250 μm. It is preferable that the irradiating section and the light receiving section each include a collimator connected to an optical fiber.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of the optical demultiplexer of the present invention. In FIG. 1, the optical demultiplexing device 10 is an opposing optical system generally including an irradiation collimator 1 for irradiating multiplexed light as a parallel beam bm and a light receiving collimator 2 for receiving at least a part of the multiplexed light beam bm. An interference filter 3 that can change the tilt angle θ with respect to the beam bm is inserted in the optical path.

The interference filter 3 is rotated in a horizontal plane by a tilt angle control unit 5 installed below a horizontal optical bench 4. The irradiation collimator 1 is connected to an input optical fiber 6 for inputting multiplexed light, and the light receiving collimator 2 is connected to an output optical fiber 7 for outputting specific light.

The light receiving collimator 2 includes an interference filter 3
Direction Y but approaching the reference alignment position L ₀ of the transmission loss of the inserted non state (empty state) in the beam bm is minimized, the one end portion 3e of the inclined interference filter 3
It is disposed at a position L ₁ which is translated by distance d.

The distance d by which the light-receiving collimator 2 is translated is _{1 from} the transmission loss value Δ ₀ at the reference alignment position L ₀ in the empty state (hereinafter referred to as “reference transmission loss”).
It is selected within the distance range where the gain is reduced in the range of dB to 2 dB. The distance d of this parallel movement is 1
It is preferable that the thickness be in the range of 00 μm to 250 μm.

When multiplexed light is input from the input optical fiber 6 to the irradiation collimator 1 of the optical demultiplexer 10 and the tilt angle θ of the interference filter 3 is appropriately changed, the specific light corresponding to each tilt angle θ is obtained. The beam is received by the receiving collimator 2. At this time, the specific light beam received in any wavelength band has a half-value width λ of a conventional optical demultiplexer in which the light receiving collimator is disposed at the reference alignment position L _0.
It was found that _h was small and the loss (insertion loss) δ caused by inserting the interference filter 3 into the optical path was also small. Moreover, even if the tilt angle θ of the interference filter 3 changes, the change is small.

For example, the irradiation collimator 1 has 1560n
m, 1550 nm, 1540 nm, and multiplexed light of 4 lines having center wavelengths of 1525 nm are input, and the inclination angle θ of the interference filter 3 is set to 0 °, 10 °, 15 °, and 20 °.
° and output optical fiber 7 at each angle.
The center wavelength of the signal light output from lambda, the half width of lambda _h,
And the insertion loss δ were measured, the inclination angle θ
, Signal light having center wavelengths at 1560 nm, 1550 nm, 1540 nm, and 1525 nm are taken out in this order. At this time, the half-width λ _h is smaller than that of the conventional optical demultiplexer.
Is 0.63 at 1525 nm as shown in FIG.
from 0.3 nm to 0.39 nm and decreased to about 2/3. Moreover the conventional optical demultiplexing device, whereas varied from 0.63nm depending on the wavelength of the half-width lambda _h is the signal light to 0.33 nm, the variation width of the optical demultiplexing device of the present invention , From 0.39 nm to 0.33 nm,
The amount of variation of FWHM lambda _h which depends on the wavelength is low.

The insertion loss δ is, as shown in FIG.
At 1525 nm, the conventional 5 dB drops to 3 dB, about 3/5. Moreover, in the conventional optical demultiplexer, the insertion loss δ fluctuated from 5 dB to 0.8 dB depending on the wavelength of the signal light, whereas the fluctuation width in the optical demultiplexer of the present invention was 3 dB. It is reduced within the range of 1.5 dB, and the fluctuation amount of the insertion loss δ depending on the wavelength is also reduced.

[0019] By the parallel movement of the arrangement position of the light receiving section 2 from the reference alignment position L ₀ to L _1, the reason that has been separated from the half-width lambda _h of each specific light and the insertion loss δ is improved, this Although the present invention is not limited by the theory, it is considered as follows. As shown in FIG. 2, the interference filter 3 is composed of a multilayer interference film 3b in which a high-refractive-index dielectric and a low-refractive-index dielectric are alternately deposited on a glass substrate 3a. The light passing through the film repeats complicated reflection and transmission in the film. Thereby, the radiation position E of the specific light is such that the beam bm is
a in the direction opposite to the refraction direction when the light is incident on the interference film 3.
Move along the plane b. Therefore, by shifting the light receiving unit 2 from the reference alignment position L ₀ by a distance d corresponding to the moving distance of the radiation position E, the light receiving unit 2 can capture the center wavelength λ of the specific light in the interference film spectrum. As a result, the half width λ _h and the insertion loss δ are improved.

The parallel movement distance d of the light receiving unit 2 is selected within a range where the gain is reduced within a range of 1 dB to 2 dB from a transmission loss value (reference transmission loss) Δ ₀ at the reference alignment position in the empty state. Is preferred. If you choose a distance where the gain drop is less than 1 dB or more than 2 dB,
It was found that the half width λ _h and the insertion loss δ were not sufficiently improved. The parallel movement distance d is preferably selected from a range of 100 μm to 250 μm, depending on the number of stacked interference films 3 b in the actual interference filter 3.

(Test Example 1) In order to more clearly show the effects of the present invention, a description will be given below of a test example in which an embodiment is compared with a conventional example. FIG. 3 shows the configuration of the optical demultiplexer used in this test example. The optical demultiplexer 20 includes an irradiation collimator 21, a light receiving collimator 22, and an interference filter 23. The irradiation collimator 21 is connected to an LED light emitter 25 via an input optical fiber 24. The light receiving collimator 22 is connected to an optical spectrum analyzer 27 by an output optical fiber 26. The LED light emitter 25 has a built-in edge emission type LED, and can emit light in a wavelength range of about 1560 nm to about 1520 nm. Optical spectrum analyzer 27
Is an interference type with an accuracy of 0.1 nm. In addition, the LED light emitter 25 and the optical spectrum analyzer 27
Separately, a 1.5 μm LD and an optical power meter were prepared for alignment adjustment.

The irradiation collimator 21 and the light receiving collimator 22 are opposed to each other, and are fixed to XYZ three-axis fine movement tables 28 and 29 which can independently adjust the horizontal and vertical positions. The facing distance between the irradiation collimator 21 and the light receiving collimator 22 is 10 mm. The interference filter 23 is freely detachably supported by a holder 31. The holder 31 is capable of adjusting its inclination angle θ by driving a pulse motor.
It is fixed to the θ4 axis fine movement table 30.

The used interference filter 23 has a diameter of 30 m.
m, silicon oxide and tantalum oxide were alternately deposited on a glass substrate having a thickness of 0.3 to 1 mm by using an ion-assisted evaporation method so that the number of layers was 39 to 43, and 4 mm ×
It is cut into 5 mm chips. The center wavelength of the interference filter 23 was around 1560 nm, and the half width was about 0.3 nm.

As the input / output optical fibers 24 and 26, 1.3 μm single mode optical fibers were used, and the end faces thereof were polished at an angle of 5 ° or more and subjected to an anti-reflection coating to minimize the influence of return light. . Both the irradiation collimator 21 and the light receiving collimator 22 were manufactured using an aspheric lens.

First, in the empty state, the irradiation collimator 2
The relative reference alignment position between the light-receiving collimator 22 and the light-receiving collimator 22 was adjusted. For the input / output optical fibers 24 and 26,
1.5 μmLD and an optical power meter are connected instead of the LED light emitter 25 and the optical spectrum analyzer 27, and the interference filter 23 is not mounted on the holder 31 (empty state), and the 1.5 μmLD light from the irradiation collimator 21 is received by the collimator 21. irradiated toward 22, the reference transmission loss delta ₀ of opposing optical system was less than 0.5dB is finely adjusted independently of XYZ3 axis fine movement stage 28, 29. Measured value of the reference transmission loss delta ₀ was 0.3 dB.

Next, the light receiving collimator 22 is left empty.
The XYZ3 axis fine movement stage 29 side, and moves in the Y-axis direction from the reference alignment position (the direction perpendicular to the beam axis), the transmission loss delta ₁ in the light receiving collimator 22 is 1.5
It was adjusted to be dB. The translation distance d at this time
Was 200 μm. Thus, the optical demultiplexer according to the embodiment of the present invention was configured.

The interference filter 23 was mounted on the holder 31, the 1.5 μm LD and the optical power meter were removed from each collimator, and the LED emitter 25 and the optical spectrum analyzer 27 were connected instead.

The interference filter 23 is set to be perpendicular to the parallel beam of LED light (tilt angle θ = 0 °),
The XYZθ four-axis fine moving table 30 is moved in the Y-axis direction to remove the interference filter 23 from the beam optical path, while the optical spectrum analyzer 27 sets the measurement center wavelength to 1560n.
m, and the measurement wavelength width was set to 10 nm. In this state, the reference level was adjusted, and the reference was measured.

The XYZθ four-axis fine movement table 30 is driven to put the interference filter 23 into the beam optical path, and the reference is normalized while measuring with the optical spectrum analyzer 27, so that the light receiving center wavelength λ at θ = 0 °, the half width λ _h , And the insertion loss δ due to the insertion of the interference filter 23 was measured.

Next, the θ-axis system of the XYZ θ 4-axis fine moving table 30 was driven to rotate the one end of the interference filter 23 by 5 ° in a direction approaching the light receiving collimator 22 (θ = 5 °). In this state, the XYZθ 4-axis fine moving table 30 is moved in the Y-axis direction to remove the interference filter 23 from the beam optical path, while the optical spectrum analyzer 27 sets the measurement center wavelength to 1555n.
m, and the measurement wavelength width was set to 10 nm. The reference level was adjusted and the reference was measured.

The drives XYZθ4 axis fine movement stage 30 put an interference filter 23 to the beam path, normalize a reference while measuring the optical spectrum analyzer 27, receiving the central wavelength in the θ = 5 ° λ, the half-width lambda _h and inserted The loss δ was measured.

The same operation is repeated, except that the inclination angles θ are set to 10 °, 15 °, and 20 °, respectively, and the measurement center wavelengths in each case are 1550 nm, 1540 nm, 1
At 525 nm, the light receiving center wavelength λ, half width λ _h and insertion loss δ were measured.

FIGS. 4 and 5 show the characteristics of the optical demultiplexer of the embodiment measured by the above operation. FIG. 4 shows the half width λ _h with respect to the light receiving center wavelength λ, and FIG. 5 shows the insertion loss δ with respect to the light receiving center wavelength λ.

[0034] (Comparative Example 1) empty, the reference transmission loss delta ₀ sets the relative position of the light receiving collimator and the irradiation collimator reference alignment position as a 0.3 dB, similar to the conventional optical demultiplexing device configuration And Using the configuration of Comparative Example 1, the interference filter 23 was set at 0 °, 5 °
, 10 °, 15 °, and 20 °, and set the measurement center wavelength of each optical spectrum analyzer 27 to 15 °.
60nm, 1555nm, 1550nm, 1540n
m and 1525 nm, the respective light-receiving center wavelength λ, half-width λ _h and insertion loss δ were measured. The characteristics of the optical demultiplexer of Comparative Example 1 are shown in FIGS.

From the results shown in FIG. 4, the half-value width λ _h of the embodiment is obtained in each of the separated wavelength bands (reception center wavelength λ).
Is 2/3 or less as compared with the comparative example 1 of the conventional configuration, and it can be seen that the variation due to the wavelength is extremely small. This indicates that the optical demultiplexer of the present invention can greatly increase the multiplexing degree of the signal light in the selected wavelength band as compared with the conventional one.

Further, from the results of FIG. 5, the insertion loss δ of the embodiment is about ３ in the separated wavelength band (the center wavelength λ of light reception) as compared with the comparative example 1 of the conventional configuration. It can be seen that the fluctuation has also been reduced. This indicates that the optical demultiplexer of the present invention can separate specific light with high sensitivity over a wide wavelength band.

Test Example 2 In the optical demultiplexer of the present invention, the position L ₁ of the light receiving collimator 22 was changed to
560 nm, 1550 nm, 1540 nm, and 15
The insertion loss δ at 25 nm was measured by an optical spectrum analyzer in the same manner as in Test Example 1. Fig. 6 shows the results.
Shown in 6, the vertical axis represents the insertion loss δ, and the horizontal axis represents the light receiving collimator 22 from the reference alignment positions L ₀ to L _1.
To indicate the transmission loss delta ₁ in arrangement position L ₁ when translated.

From the results shown in FIG.
Distribution and installation position L _1, if to no 1dB than the reference transmission loss delta ₀ at the reference alignment position L ₀ is a gain in the range of 2dB selected within the distance range to be lowered, the maximum value of the insertion loss δ is 3.3dB below And the insertion loss δ when the arrangement position of the light receiving collimator 22 is L ₀ (maximum value 5d
It can be seen that it is significantly reduced from B).

The variation of the insertion loss δ at 1560 nm and 1525 nm is 1.8 dB or less.
Compared to the amount of variation of the insertion loss δ when the arrangement position of the light receiving collimator 22 and the L ₀ (about 4dB), is suppressed to the amount of variation of about 1/2 or less. Here, the parallel movement distance d when lowering the 1 dB gain from the transmission loss value at the reference alignment position L ₀ corresponds to 100 μm, and similarly, 2 d
The parallel movement distance d for lowering the B gain is 250 μm
Is equivalent to Thereby, the effect of moving the light receiving collimator 22 in parallel has become clear.

[0040]

According to the optical demultiplexing device of the present invention, the light receiving section is arranged such that the light receiving section has a predetermined distance from the reference alignment position where the reference transmission loss in the empty state is minimized in a direction approaching one end of the inclined interference filter. In this case, both the insertion loss and the half-value width are small, and even if the tilt angle of the interference filter fluctuates, these fluctuations are small. Therefore, in the wavelength division multiplexing transmission type optical communication system, even if the center wavelength of each signal light is made closer to increase the degree of multiplexing, a specific signal light can be accurately separated. Further, this optical demultiplexer has an advantage that it can be easily manufactured because it can be obtained only by changing the alignment of the conventional optical demultiplexer.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of the present invention.

FIG. 2 is a plan view showing the operation of the optical demultiplexer of the present invention.

FIG. 3 is a plan view showing a configuration of an optical demultiplexer used in a test example.

FIG. 4 is a graph showing a relationship between a center wavelength and a half width.

FIG. 5 is a graph showing a relationship between a center wavelength and an insertion loss.

FIG. 6 is a graph showing a relationship between transmission loss and insertion loss due to parallel movement of a light receiving unit.

FIG. 7 is a longitudinal sectional view showing an example of a conventional optical demultiplexer.

FIGS. 8A and 8B are plan views showing a general operation of the optical demultiplexer.

[Explanation of symbols]

1 ... radiation collimator 2 ... light receiving collimator 3 ... transmissive interference filter 3e ... transmissive interference filter end 10 ... optical demultiplexing device L ₀ ... standard alignment position L ₁ ... moving alignment position d ... translation distance theta ... transmission interference Filter tilt angle bm: Multiple light beam

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 26/00-26/08

Claims (4)

(57) [Claims] 1. An optical path of a facing optical system comprising an irradiating unit for irradiating a wavelength multiplexed signal light as a parallel beam and a light receiving unit for receiving at least a part of the wavelength multiplexed signal light, an inclination angle with respect to the beam. An optical demultiplexer having a variable transmission interference filter inserted therein, wherein the light receiving unit is inclined from a reference alignment position where the transmission loss of the beam is minimized in a state where the transmission interference filter is not inserted. In the direction approaching one end of the transmission-type interference filter and the substrate of the transmission-type interference filter.
The optical demultiplexer is disposed at a position parallel-moved by a predetermined distance in a direction opposite to the refraction direction at the time of incidence of the beam . 2. The method according to claim 1, wherein a distance of the light receiving unit translated by 1 dB from a transmission loss value at the reference alignment position.
2. The optical demultiplexer according to claim 1, wherein the optical demultiplexer is selected from a range where a gain is reduced within a range of 2 dB to 2 dB. 3. The method according to claim 1, wherein the distance that the light receiving section is translated is 10
The optical demultiplexer according to claim 1, wherein the optical demultiplexer is selected from a range of 0 µm to 250 µm. 4. The optical demultiplexer according to claim 1, wherein the irradiating section and the light receiving section each include a collimator connected to an optical fiber.