JP2000209162A - Light source for optical wavelength multiplex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily construct an optical wavelength multiplex transmission system at a low cost by combining a multi-mode laser diode and a narrow band filter and extracting and transmitting only the light of a prescribed wavelength among the light emission wavelengths of the multi-mode laser diode. SOLUTION: Optical signals outputted from the LD 1a-1n of these respective light sources 6a-6n are transmitted through the respective narrow band filters (B.P.F) 2a-2n, then gathered through an optical coupler to one optical fiber cable 3 and sent to an optical receiver (O/E) 5. For multi-mode light inputted to the respective B.P.F 2a-2n, the light of the wavelength on the outside of a transmission band is suppressed by the B.P.F 2a-2n and only the light of the wavelength (one wavelength) within the transmission band is selected and outputted from the B.P.F 2a-2n. As a result, the optical signals of a single mode are sent from the respective light sources 6a-6n to the O/E 5. Since unrequired light on the outside of the transmission band is suppressed in the B.P.F 2a-2n, the wavelength multiplex transmission is made possible without interference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light source for wavelength division multiplexing.

[0002]

2. Description of the Related Art In a conventional optical wavelength division multiplexing transmission system, a plurality of lights of different wavelengths are multiplexed on one optical fiber cable via an optical coupler or the like and transmitted to an optical receiver.

The light source (laser diode) of this system
Used a single longitudinal mode oscillation distributed feedback laser diode.

FIG. 5 shows an emission spectrum of a laser diode used in a conventional optical wavelength division multiplexing transmission system. In the figure, the horizontal axis indicates the wavelength, and the vertical axis indicates the relative light output.

This emission spectrum is a spectrum in which higher-order modes are suppressed and only the fundamental mode exists. The reason for using a laser diode having such an emission spectrum as a light source is as follows.

In an optical wavelength division multiplexing transmission system, a light receiving element in an optical receiver collectively performs optic-to-electric conversion on multiplexed light.
At this time, if there is light interference on the optical receiver side, the reception sensitivity is reduced. Therefore, it is necessary to use light sources having different wavelengths.

FIG. 2 is a diagram showing an emission spectrum of a multi-mode laser diode. In FIG. 2, the horizontal axis indicates the wavelength, and the vertical axis indicates the relative light output.

[0008] Since a laser diode having such an emission spectrum interferes between higher-order modes, a single-mode laser diode having only a fundamental mode is used.

[0009]

In the above-described conventional system, light from a plurality of light sources is collectively subjected to optical / electrical conversion by a light receiving element via one optical fiber. At this time, it is necessary to use light of different wavelengths for each light source in order to avoid interference. However, as the number of multiplexed wavelengths increases, it becomes difficult to prepare light sources having different wavelengths. Further, in order to avoid interference between higher-order modes, it is necessary to use a distributed feedback laser diode having only a fundamental mode as a light source. Since this distributed feedback laser diode is very expensive, it has been a factor that hinders the cost reduction of the entire system.

It is an object of the present invention to solve the above-mentioned problems and to provide an optical wavelength multiplexing light source capable of easily constructing an optical wavelength multiplexing transmission system at low cost.

[0011]

In order to achieve the above object, a wavelength multiplexing light source according to the present invention is used for an optical wavelength multiplexing transmission system for multiplexing a plurality of optical signals and transmitting the multiplexed optical signals through a single optical fiber. In the light source, a multi-mode laser diode and a narrow-band optical filter are combined, and only light having a predetermined wavelength is extracted from the emission wavelength of the multi-mode laser diode, and transmitted through an optical fiber.

In addition to the above configuration, the wavelength multiplexing light source of the present invention preferably uses a Fabry-Perot laser diode as a multimode laser diode and a waveguide filter as a narrow band optical filter.

According to the present invention, by combining an inexpensive multi-mode laser diode and a narrow-band optical filter that allows only light of a predetermined wavelength to pass, it is not necessary to prepare light sources of different wavelengths, and it is inexpensive and easy. An optical wavelength division multiplexing transmission system can be constructed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an optical wavelength division multiplexing transmission system to which an optical wavelength division multiplexing light source according to the present invention is applied.

In this system, a Fabry-Perot type laser diode 1a and a waveguide-type band-pass filter (BP.1) serving as a narrow-band optical filter connected to the laser diode (LD) 1a via an optical fiber 3a. F) 2
a, and a Fabry-Perot LD
1b and a waveguide type B.1 connected to an LD 1b via an optical fiber 3a. P. F2b and a light source 6b,
A Fabry-Perot LD1n and a waveguide B.I. connected to the LD1n via an optical fiber 3n. P. F2n and B.F2n; P. F2a and B.I. P. F2
b., an optical coupler 4a for connecting B.b. P. F2a and B.I.
P. It comprises an optical coupler 4n connecting the F2n and an optical receiver (O / E) 5 connected to the optical fiber cable 3. Each B. P. The transmission wavelengths of F2a, 2b, and 2n are all different. Although the number of the light sources 6a to 6n is three in the drawing, the number is not limited.

Next, the operation of the present system will be described.

FIG. 3 is a graph showing the transmission characteristics of the bandpass filter used in the system shown in FIG. 1. The horizontal axis shows the wavelength and the vertical axis shows the relative transmission. FIG. 4 is a diagram showing an emission spectrum of the multi-mode laser diode after passing through the band-pass filter shown in FIG.

The optical signals output from the LDs 1a to 1n of the light sources 6a to 6n are P. After passing through F2a to F2n, they are collected in one optical fiber cable 3 via an optical coupler and sent to O / E5.

As shown in FIG. P. F2a-2n
The multi-mode light input to B.B. P. F2a to F2n suppress light having a wavelength outside the transmission band, and select only light having a wavelength (one wavelength) within the transmission band. P. F2a ~
2n. As a result, each light source 6 is supplied to the O / E 5.
Single mode optical signals are transmitted from a to 6n. B. P. Since unnecessary waves outside the transmission band are suppressed by F2a to 2n, wavelength multiplex transmission becomes possible without interference. Note that a plurality of light sources can be easily obtained by changing the transmission wavelength of the optical filter.

Here, in this embodiment, a waveguide filter is used as the narrow-band optical filter, but a fiber grating filter, an interference film filter, or a Fabry-Perot resonator filter may be used.

As described above, according to the present invention, (1) it is easy to prepare light sources having different wavelengths by combining a pass band of an optical filter and a multimode laser diode.

(2) An inexpensive multi-mode laser diode can be used.

[0024]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to provide an optical wavelength multiplexing light source that can easily and inexpensively construct an optical wavelength multiplexing transmission system.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical wavelength division multiplexing transmission system to which an optical wavelength division multiplexing light source of the present invention is applied.

FIG. 2 is a diagram showing an emission spectrum of a multimode laser diode.

FIG. 3 is a diagram showing transmission characteristics of a band-pass filter used in the system shown in FIG. 1;

FIG. 4 is a diagram showing an emission spectrum of the multi-mode laser diode after passing through the band-pass filter shown in FIG.

FIG. 5 is a diagram showing an emission spectrum of a laser diode used in a conventional optical wavelength division multiplexing transmission system.

[Explanation of symbols]

 1a-1n Multi-mode laser diode (LD) 2a-2n Narrow band optical filter (BPF) 3a-3n Optical fiber 3 Optical fiber cable 5 Optical receiver (O / E)

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Claims (2)

[Claims] 1. A light source for an optical wavelength division multiplexing transmission system for multiplexing a plurality of optical signals and transmitting the signals through one optical fiber, wherein the multimode laser diode and a narrow band optical filter are combined. A wavelength multiplexing light source, wherein only light having a predetermined wavelength is extracted from the light emission wavelength of a diode and transmitted through the optical fiber. 2. The method according to claim 1, wherein a Fabry-Perot laser diode is used as the multi-mode laser diode, and a waveguide filter is used as the narrow-band optical filter.
The light source for wavelength division multiplexing according to 1.