JPS6095508A - Diffraction grating type optical multiplexer - Google Patents

Abstract

PURPOSE:To obtain a small-sized, high density multiplexer which has low loss, a wide band, and low noise by constituting the multiplexer integrally with a laser. CONSTITUTION:A laser array 11 is incorporated directly instead of an array of optical fibers for incidence and only one optical fiber 12 for projection is therefore used. This laser array 11 has four mutually-sectioned light emission parts 11-1a, 11-1b, 11-1c, and 11-1d, which are controlled precisely to four mutually different wavelengths by distributed feedback type Bragg reflectors (DFB) 11-2a, 11-2b, 11-2c, and 11-2d which are formed closely to the respective light emission parts and differ in grating interval slightly from one another. Individual lasers are driven independently by respective electrodes 11-3a, 11-3b, 11-3c, 11-3d, and 11-4. Projection light from the laser array 11 is invariably linear polarized light and an S wave to all diffraction gratings, realizing high-efficiency, wide-band, and stable diffraction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diffraction grating type optical multiplexer applied to an optical wavelength division multiplexing transmission system for optical communications.

Generally, in optical wavelength division multiplexing transmission systems, optical signals of multiple different wavelengths are generated on the transmitting side.

These optical signals are multiplexed onto one optical fiber by a multiplexer and transmitted. There are two types of multiplexers used for this, an interference film type and a diffraction grating type, but the latter is more suitable for high-density wavelength multiplexing.

A conventionally used diffraction grating multiplexer has one output fiber 1-0 connected to a transmission line and a plurality of output fibers connected to each light source, as shown in the configuration in Figure 1. Input fiber 1-1. ..., 1-N are arranged closely to form a fiber array. The light beams respectively emitted from the input fibers are turned into parallel beams by the lens 2 and reach the nine diffraction gratings 6.

The diffraction grating 3 diffracts the light beam according to the wavelength of the light that has arrived, and as a result, each of the input fibers 1-1 to
All the light beams with wavelengths λ1 to λN emitted from the fiber 1-N are combined into the output fiber 1-0. In addition, in FIG. 1, if the arrow indicating the direction of light is reversed, it can be used as a demultiplexer.

This type of diffraction grating type is not limited to one multiplexer.

Even in a duplexer, the smaller the core diameter of the input fiber is compared to the output fiber core diameter, the lower the loss and the flatter the passband of the loss spectrum. In addition, the rise characteristic to the cutoff region becomes steeper, which is a desirable characteristic for a five-wave multiplexer or a demultiplexer.

Preliminary lecture for the 1981 IEICE General Conference, S4-
11. In the study by Mr. Watanabe, Mr. Nosu, and Mr. Fujii, "Study of long wavelength band multiplexing and demultiplexing filters", the loss spectrum was improved by using a core diameter of 40 μm for the input fiber, while the core diameter of the output fiber was 60 μm. There is a description that it is measured.

As a semiconductor laser suitable for high-density wavelength multiplexed transmission,
DFB lasers, DBR lasers, and the like have been developed which have characteristics such that one emission wavelength can be easily and precisely controlled during manufacture, two emission spectrum widths are narrow during operation, and the center wavelength is stable.

A graph and a diffraction diagram are shown for general explanation of the ratio of output energy to input energy to a diffraction grating, that is, diffraction efficiency. Figure 2 (
In the graph a), it can be seen that the 2nd diffraction efficiency spectrum differs depending on the polarization direction. Referring to Figure (b), the polarized light whose electric field component is perpendicular to the groove direction of the two-diffraction grating 3 is represented by S, and the polarized light which is parallel to it is represented by P.

Generally, S-polarized light has high efficiency and a wide band, whereas P-polarized light has low efficiency and a narrow band. In the conventional configuration, the light beam emitted from the input fiber includes both S and P lights, so the single diffraction efficiency is approximately the average value of P and S (curve N).

The drawback is that sufficient characteristics cannot be obtained in terms of both efficiency and bandwidth. Also, due to variations in the polarization direction of the light beam propagating within the input fiber.

Diffraction efficiency fluctuates, resulting in generation of unwanted noise, especially in analog transmission systems.

On the other hand, in the conventional multiplexer/demultiplexer as shown in Figure 1.

Since a fiber array has a large number of fibers arranged close to each other, there is a limit to the miniaturization of the dual multiplexer/demultiplexer itself.
During implementation, fibers must be routed to connect the light source and receiver for each channel, which has the disadvantage of requiring a large space. Furthermore, it is possible to flatten the passband characteristics of the loss spectrum by reducing the core diameter of the input fiber, but in the 9-wave multiplexer,
This is because the smaller diameter of the core makes it difficult to combine it with a semiconductor laser or manufacture a connector.

This has the disadvantage that it is difficult to flatten the characteristics.

An object of the present invention is to provide a diffraction grating type optical multiplexer that has low loss and flat passband loss characteristics, is small, and can be mounted at high density.

According to the present invention, one laser array is formed by arranging a plurality of semiconductor lasers each emitting at different wavelengths on the same substrate, and at least one lens that converts an emitted beam from the laser array into a parallel beam; Diffract the parallel beam.

A diffraction grating type optical multiplexer is obtained which includes at least one diffraction grating for returning to the lens and at least one optical fiber for combining the parallel beams of different wavelengths.

Next, two embodiments of the diffraction grating type optical multiplexer according to the present invention will be described with reference to nine drawings.

FIG. 3 shows the configuration of an embodiment according to the present invention in a side view. In this figure, the lens 2 and the diffraction grating 3 are the same as in the conventional example, but a laser array 11 is directly incorporated in place of the input fiber array.
therefore.

Only one optical fiber 12 for output is used. FIGS. 4(a) and 4(b) show the specific configuration of the laser array 11 in FIG. 6 using a side sectional view and a front sectional view, respectively. This laser array 11 has four light emitting sections 1l-1a, 1l-1b, 1l-
1c, 1l-1d.

Distributed feedback Bragg reflector (DFB) with slightly different lattice spacing formed close to each light emitting part 11
-2a, 11-2b, 11-2c, 11-2d
The light is precisely controlled to four different wavelengths on the door. The individual lasers can be driven independently by electrodes 1l-d 3a, 11-3b, 11-3c, 11-3dl and 11-4, respectively. The light emitted from the laser array 11 is always linearly polarized light, and its direction is shown by the arrow in FIG. Therefore, the emitted light becomes the S wave in the second factor for all the diffraction gratings, and a highly efficient and broadband diffraction efficiency can be stably obtained.

As a result, noise caused by fluctuations in polarization direction in conventional multiplexers is not generated. Furthermore, the emission diameter of the semiconductor laser is very small (about 5×0.5 μm).

This has the same effect as reducing the core diameter of the input fiber in the conventional configuration. therefore.

Even with fluctuations in the laser emission wavelength, stable coupling efficiency to the output fiber t can be obtained. Regarding laser arrays such as 1 or more, there are a few but basic experimental results such as "K, A1K1., M.

NaKamura,and,J,Umeda,”
Frequency multiplexing lig
ht 5source with mo-nolith
ically integrated distri
but-ted-feedbaCh diode core a,
5ers”, Applj, edphysi, cs L
etters, Vol. 29. No, 8. pp-506
-507, Ocl: 1976J.

This is a device that can be fully realized industrially as manufacturing technology advances in the future.

FIGS. 5(a) and 5(b) show the structure of another embodiment according to the present invention in a top view and a side view, respectively. In the figure, an output optical fiber 22. lens 2
6 and a diffraction grating 24 are responsible for the multiplexing function, and the laser array 21 is fixed on a heat sink 25. A plurality of lasers emitted at different wavelengths in the laser array 21 are respectively driven from a plurality of terminals 28 via bonding wires 29. All the above elements are fixed to a base 26 and protected by a cover 27. The mounting method uses the same package format as conventional ICs, so it can be mounted directly on the printed board.
It can be mounted together with S-engineering, etc., and the device can also be made smaller.

As is clear from the following explanation, according to the present invention,
Since it is integrated with a laser, it has lower loss, wider bandwidth, and lower noise than conventional multiplexers.

A compact and high-density multiplexer is obtained. In particular, D.B.
When combined with a laser array of R or DFB structure, the high stability of nine emission wavelengths and single-axis mode oscillation make it possible to achieve high-density wavelength multiplexing transmission with a narrow wavelength interval, which was previously impossible. In addition, such a multiplexer can be applied not only to short-distance transmission using multimode fibers, but also to long-distance high-capacity transmission using single-mode fibers, where it is essential to suppress material dispersion, making it economically viable. The benefits of improvement are significant.

[Brief explanation of the drawing]

Fig. 1 shows an example of the structure of a conventional diffraction grating multiplexer) and a diffraction diagram, Fig. 6 is a side view showing the structure of an embodiment according to the present invention, and Figs. 6 is a side sectional view and a front sectional view showing the specific structure of the laser array, respectively, and FIGS. 5(a) and (1)) are a top view and a side view, respectively, showing the structure of another embodiment according to the present invention. It is a diagram. In the figure, 2.23 is a lens, 3.24 is a diffraction grating,
11.21 is a laser array, 12.22 is an optical noiba,
25 is the heat sink, 26 is the base. 27 is a cover, 28 is a terminal, 1l-1a, 1l-1
b. 1l-1c, 1l-1d are light emitting parts, 1l-2a is a black reflector, 11-3a, 11-3b, 11-3c,
11-3d. 11-4 is an electrode. Sa (Go to 1. Jyu circular wave +!r-E

Claims (1)

[Claims] 1. A laser array formed by arranging a plurality of semiconductor lasers each emitting at different wavelengths on the same substrate, at least one lens that converts the emitted beam from the laser array into a parallel beam, and the parallel beam. A diffraction grating type optical multiplexer comprising at least one diffraction grating for diffracting and returning to the lens, and at least one optical fiber for combining the parallel beams of different wavelengths.