JPS623205A - Bidirectional optical repeating system - Google Patents

Abstract

PURPOSE:To transmit light at a low loss and low noise by connecting polarization couplers respectively to both ends of a polarization maintaining optical fiber and coupling the orthogonally polarized waves to the poralization maintaining optical fiber via such polarization couplers. CONSTITUTION:Both ends of the polarization maintaining optical fiber 1 are respectively connected to a port 43 of the polarization maintaining optical fiber type polarization coupler 4 and a port 53 of the polarization maintaining optical fiber type polarization coupler 5. The (y) polarized wave emitted from a semiconductor laser 2 is made incident from the port 41 via a lens 3 on the polarization maintaining optical fiber polarization coupler 4, passes through the port 43, the fiber 1 to arrive at the port 53, is emitted from the port 51 and is made incident on a photodetector 7. The (x) polarized wave emitted from a semiconductor laser 8 is made incident on a photodetector 11 via a lens 9, the port 52 of the coupler 5, a port 53, the fiber 1, the port 43 of the coupler 4, a port 42 and a lens 10. The light is thus bidirectionally transmitted at the low loss and low noise.

Description

[Detailed description of the invention] [Industrial application field]
The present invention relates to a low-loss and low-noise bidirectional optical weaving method.
, ; [Summary], : ;/4 The present invention uses polarized waves orthogonal to each other to transmit bidirectional signals.
2” 6 oka, 43 and 1. U,,, kakaka and yukae 6
．． oh. , 7, P/P°, 'Transmission medium 0 polarization maintaining optical fiber 9 P/0 both ends 9 polarization coupling
; By connecting a combiner and coupling the orthogonal polarized waves to this polarization-maintaining optical fiber, 7. IPA is a small device that performs low-loss, low-noise optical transmission at low cost and without being affected by mechanical vibrations.
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;) Ru.
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[Conventional technology]
”・5; Bidirectional light transmission using a single optical fiber as a transmission medium, □P:゛.

To transmit a signal, the refractive index distribution must be refracted within the cross section.
・2. Forms an index ellipsoid, single mode, single-linear polarization
A polarization-maintaining optical fiber with polarity is used.

FIG. 5 shows a configuration diagram of a conventional bidirectional optical repeating system using such an optical fiber as a transmission medium.

The oscillation light output from the semiconductor laser 2 is incident on one end of the polarization-maintaining optical fiber 1 via the lens 3 , the polarized beam splitting prism 101 , and the lens 102 .

The linearly polarized wave plane of the oscillated light from the semiconductor laser 2 coincides with the long axis of the index ellipsoid of the polarization-maintaining optical fiber 1 . This optical signal is output from the other end of the polarization-maintaining optical fiber 1 and enters the photodetector 7 via the lens 103, the polarized beam splint prism 104, and the lens 6.

Further, the oscillation light output from the semiconductor laser 8 is incident on the other end of the polarization-maintaining optical fiber 1 via the lens 9, the polarization beam splitting prism 104, and the lens 103. The linear polarization plane of the oscillated light from the semiconductor laser 8 coincides with the axle of the index ellipsoid of the polarization-maintaining optical fiber 1 .

This optical signal is output from one end of the polarization-maintaining optical fiber 1, and is sent to a lens 102 and a polarized beam splinting prism 10.
1 and enters the photodetector 11 via the lens 10.

Inside the cast wave holding optical fiber 1, the wave propagates in both directions.
.

The vibration directions of the light beams are orthogonal to each other, and these light beams are separated by polarization beam splinting prisms 101 and 104.

[Problem that the invention seeks to solve]

However, in the conventional bidirectional optical relay system, a polarized beam splitting prism is used to separate the light.
The disadvantage is that the size of the device is large and it is susceptible to mechanical vibration.

Such mechanical vibration causes polarization coupling to occur at the input end of a polarization-maintaining optical fiber, which is a transmission medium. Due to the polarization coupling at the input end, the incident light from the semiconductor laser is reflected, and this reflected light enters the semiconductor laser again. This causes deterioration in the oscillation characteristics of the semiconductor laser and generates noise. Re-incidence of such reflected light can be prevented by using an isolator. However, it has the disadvantage that the equipment is expensive.

The present invention solves the above drawbacks and is compact and mechanical.
The object of the present invention is to provide a bidirectional optical relay system that is not affected by vibrations, and can perform optical transmission at low cost, with low loss, and with (E-noise).

[Means for solving problems]

The bidirectional optical repeater system of the present invention uses a polarization-maintaining optical fiber as a transmission medium that propagates two polarized waves orthogonal to each other, and transmits one of the two polarized waves from one end of the polarization-maintaining optical fiber. the other end of this polarization-maintaining optical fiber receives this one polarization; the other end of this polarization-maintaining optical fiber transmits a polarization orthogonal to the one polarization; In a bidirectional optical repeater system in which the orthogonal polarized waves are received at one end of the polarization-maintaining optical fiber, a polarization coupler is connected to each end of the polarization-maintaining optical fiber, and the polarization is transmitted through the polarization coupler. It is characterized in that the orthogonal polarized waves are coupled to the polarization-maintaining optical fiber.

[Effect]

The bidirectional optical relay system of the present invention uses a polarization-maintaining optical fiber type polarization coupler to couple orthogonal polarized waves to a polarization-maintaining optical fiber that is a transmission medium. Polarization-maintaining optical fiber type polarization couplers have excellent matching with optical fibers, are not affected by mechanical vibration, are compact, and have flexibility in arrangement.
2. .

〔Example〕

FIG. 1 is a block diagram of a bidirectional optical relay system according to an embodiment of the present invention.

Both ends of the polarization-maintaining optical fiber 1 are connected to a boat 43 of a polarization-maintaining optical fiber type polarization coupler 4 and a polarization-maintaining optical fiber type polarization coupler 4, respectively.
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to the boat 53 of the wave-maintaining optical fiber type polarization coupler 5.
.

Connected. The boat 41 of the polarization-maintaining optical fiber type polarization coupler 4 receives the oscillation output from the semiconductor laser 2.
The light enters through the lens 3. Polarization maintaining optical fiber.

The light output from the boat 42 of the eyeglass polarization coupler 4 enters the photodetector 11 via the lens 10.

The boat 51 of the polarization-maintaining optical fiber type polarization coupler 5 includes:
The oscillation light output from the semiconductor laser 8 enters through the lens 9 . The light output from the boat 52 of the polarization-maintaining optical fiber type polarization coupler 5 passes through the lens 6 to the photodetector 7.
incident on .

The polarization-maintaining optical fiber 1 has two main axes that are perpendicular to each other, and the polarization-maintaining optical fiber type polarization coupler 4.5 is connected so that its main axis coincides with the main axis of the polarization-maintaining optical fiber 1. .

In such a configuration, the semiconductor laser 2 outputs an X-polarized wave (the direction of vibration of light is perpendicular to the drawing), and the semiconductor laser 8 outputs an X-polarized wave (the direction of vibration of light is parallel to the drawing).
Assume that it outputs . The X-polarized wave and the X-polarized wave are indicated by rOJ and "1" in the figure, respectively.

The X-polarized wave emitted by the semiconductor laser 2 enters the polarization-maintaining optical fiber type polarization coupler 4 from the port 41 via the lens 3 . Furthermore, this X-polarized wave passes through port 43 and polarization-maintaining optical fiber 1, reaches port 53, and reaches port 53.
1 and enters a photodetector 7 via a lens 6. The X-polarized wave emitted from the semiconductor laser 8 is transmitted through the lens 9, the port 52 of the polarization-maintaining optical fiber type polarization coupler 5, the same port 53, the polarization-maintaining optical fiber 1, and the polarization-maintaining optical fiber type polarization coupler. 4 port 43, also port 42, and enters the photodetector 11 via the lens 10.

Two orthogonal linearly polarized lights propagate bidirectionally within the polarization-maintaining optical fiber 1, and these polarized lights can propagate independently without mode conversion. Therefore, the linear polarization of the polarized light emitted by the semiconductor laser 2 is maintained on the output side of the polarization-maintaining optical fiber, and all the power is transferred to the photodetector 7 by the polarization-maintaining optical fiber type polarization coupler 5. incident. Similarly, the polarized light emitted from the semiconductor laser 8 passes through the polarization-maintaining optical fiber type polarization coupler 4, and all of its power is incident on the photodetector 11.

Figure 2 shows the structure of a polarization-maintaining optical fiber type polarization coupler.
・：Power.

Fig. 3 shows a cross-sectional view.
; The polarization-maintaining optical fiber type polarization coupler 4.5 is
95': PAN is a type of force-added polarization-maintaining optical fiber.
5. It was formed by fusion drawing using D A'□ fiber. P
ANDA fiber is explained in detail in the newsletter of the 5th Optical Fiber Conference held in 1982. Although the polarization-maintaining optical fiber type polarization coupler 4 will be explained here as an example, the structure and operation of the polarization-maintaining optical fiber type polarization coupler 5 are also equivalent.

Light incident from port 41 or port 42 is transmitted to area 4.
4 waveguides 45 and 46, and is emitted from port 43. In addition, the light incident from the port 43 passes through the waveguide 4
5.Separated at 46, port 41 or port 4
It is emitted from 2.

The waveguides 45, 46 are each clad 450, 460
A core 451.461 is provided therein, and a stress applying portion 452.462 for maintaining polarization is further provided. The mode birefringence generated in the waveguide 45.46 by this stress applying portion 452.462 is one order of magnitude smaller than the refractive index difference Δ between the core and the craft, and the coupling of polarized waves between the waveguides 45.46 is substantially has no effect on the

FIG. 4 shows the optical transmission characteristics of the waveguide 45, and (a) shows the transmission power P at two points of the X polarized wave incident from the port 41.
+ (z), and (b) shows the transmission power pg(z) at two points of the X polarized wave incident from the port 42. Here, the x, y, and two directions correspond to the vertical direction, vertical direction, and horizontal direction, respectively, with respect to the paper surface of FIG.

As shown in FIG. 4, the transmission power within the waveguide 45 is
P+(z) and Pg(z) reach their maximum intensity at different intervals. That is, the X polarized wave and the X polarized wave □ are the waveguides 45
．． It propagates while moving between 46. Tradition
゛Interval at which the intensity of the sending power P, (z), Pz(z) is maximum;.

are different, so the mth maximum of the transmission power P+(z)
The position of □“□ coincides with the position 1 of the first maximum of the transmission power Pz(z).Here, m and n are natural numbers that satisfy m≧n. Therefore, the length l of the region 44 is
When the length is set such that the maximum positions of the transmission powers P+(z) and P2(2) match, the y1゜ polarization incident from port 41 and the X polarization incident from port 42 both with
It is coupled to the large door wave path 45 and can output two polarized waves from the port 43 with a maximum power of 1.5.

5; For example,
Clad 450.460, Core 451.461
.

and the stress applying parts 452 and 462 are made of silica □
1 (SiO□), germanium dioxide (GeO□)-added silica 1□ power, diboron trioxide (Bzoi)-added silica,
1, U7 F450.460 Core 451
．． 46□. Relative refraction ′ (′ index difference Δ is 3%
When the core diameter 2a is 0.8- and the core spacing d is 8-, two polarized waves can be emitted with maximum power with a coupling length l of 20 mm for light with a wavelength of 1.3-.

By selecting the parameters of the waveguides 45 and 46, the values of m and n, and the coupling length l, an optimal design can be made for other wavelengths as well.

Although the case where the light enters from the boat 41 and the boat 42 has been described here, the polarization-maintaining optical fiber type polarization coupler 4 is capable of bidirectional operation. Therefore, the X-polarized wave incident from the boat 41 is transferred to the polarization-maintaining optical fiber l with maximum power.
The X-polarized wave incident on the boat 43 is transmitted to the boat 4
1 can be transmitted to boat 42 without transmitting to boat 1 .

The coupling length l of the polarization-maintaining optical fiber type polarization coupler 4.5 is:
As long as the above-mentioned conditions are satisfied, the present invention can be implemented with different values.

Further, in the above embodiments, the case where the same wavelength is used in both directions has been described, but the present invention can be implemented in the same way even when different wavelengths are used depending on the direction. That is, for each wavelength, the coupling length 2 is set so that all the X-polarized waves incident from the boat 41 are transmitted to the polarization-maintaining optical fiber 1, and all the X-polarized waves incident from the boat 43 are transmitted to the boat 42. can be set.
'Furthermore, in the above embodiment,
The X polarized wave enters from the boat 41 and propagates to the boat 51,
Although an example has been described in which the X-polarized wave is incident from the boat 52 and propagated to the boat 42, the present invention can be implemented in the same manner even if the combination is changed by setting the respective coupling lengths l.

〔Effect of the invention〕

As explained above, in the bidirectional optical relay system of the present invention, two orthogonal linearly polarized lights are separated at both ends of a polarization-maintaining optical fiber without suffering any loss. Therefore, there is an effect that bidirectional optical transmission can be realized with low loss and low noise.

Furthermore, in conventional systems using prisms for polarized beam splinters, the incident beam on the transmission medium fluctuates due to mechanical vibrations, and reflections inevitably occur, making the oscillation of the semiconductor laser unstable. Since the present invention does not use bulk type elements, it is not subject to mechanical vibration, and therefore has the advantage of being able to perform low-noise optical bidirectional relay. Furthermore, there is an effect that bidirectional optical relay can be performed using the same wavelength.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a bidirectional optical relay system according to an embodiment of the present invention. FIG. 2 is a diagram showing the structure of a polarization-maintaining optical fiber type polarization coupler. Figure 3 is a sectional view. FIG. 4 is a diagram showing the optical transmission characteristics of one waveguide. FIG. 5 is a block diagram of a conventional bidirectional optical relay system. 1... Polarization maintaining optical fiber, 2.8... Semiconductor laser, 3.6.9.10... Lens, 4.5... Polarization maintaining optical fiber type polarization coupler, 7. 11... Photodetector, 41.42.43.51.52.53... Boat,
45.46... Waveguide, 101.104... Prism for polarized beam splint, 102.103... Lens, 450.460... Clad, 451.461...
...Core, 452.462...Stress applying part. Pl(z)

Claims (1)

[Claims] (1) A polarization-maintaining optical fiber that propagates two mutually orthogonal polarized waves is used as a transmission medium, and one of the two polarized waves is transmitted from one end of this polarization-maintaining optical fiber, and this polarization is The other end of the polarization-maintaining optical fiber receives this one polarization, and the other end of the polarization-maintaining optical fiber transmits a polarization orthogonal to the one polarization. In a bidirectional optical repeater system that receives the orthogonal polarized waves at one end, polarization couplers are connected to both ends of the polarization-maintaining optical fiber, and the orthogonal polarized waves are transmitted through the polarization couplers. A bidirectional optical repeater system characterized by coupling to polarization-maintaining optical fiber.