JP2626586B2 - Laser light output device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light output device, for example, a laser light output device used in an optical communication system.

[0002]

2. Description of the Related Art In recent years, devices using a semiconductor laser as a laser light source have been used in various fields. However, the wavelength of the laser beam output from the semiconductor laser varies with changes in ambient temperature and aging. Conventionally, in fields where wavelength stability is required, such as optical communication, the output light wavelength is stabilized by various methods.

In order to stabilize the wavelength of the output light of a semiconductor laser, generally, a part of the output light of the semiconductor laser is passed through a filter having a predetermined wavelength characteristic, and the amount of change in the light intensity after passing is monitored. This is performed by controlling the drive current or temperature of the semiconductor laser according to the monitored value. However, since there is no filter having steep wavelength characteristics and high stability with time, the output light wavelength of the semiconductor laser is reduced by such a method.
It has not been possible to stabilize with high accuracy over a long period of time.

As a technique for solving such a problem, Japanese Patent Application Laid-Open No. 61-102081 discloses a technique for monitoring the output light wavelength of a semiconductor laser using an optical fiber amplifier.

[0005] Referring to FIG.
An outline of the technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. H10-206 will be described. In this technique, in order to monitor the output light wavelength of the semiconductor laser 31, a part of the output light of the semiconductor laser 31 is supplied to an optical fiber 34 as an optical amplification medium via an optical coupler 32. The output light wavelength of the semiconductor laser 31 is a wavelength that can be used as excitation light for the optical fiber 34, and the reference light from the reference light source 35 is amplified according to the excitation light. The amplified reference light is input to the photodiode 36 via the optical coupler 33, and the level of the photodiode 36 is detected.

The detection output of the photodiode 36 is input to a control circuit 37. The control circuit 37 drives the semiconductor laser 31 so that the detection output from the photodiode 36 is at a predetermined level. Drive current). In this technique, the temperature of the semiconductor laser 31 is kept constant by the temperature control circuit 30, and the output light of the semiconductor laser 31 stabilized by the feedback loop is output to the outside by the optical coupler 32. I have.

[0007]

As described above,
In the technique disclosed in Japanese Patent Application Laid-Open No. 61-102081, the fluctuation of the output light wavelength of a semiconductor laser is detected by utilizing the fact that the gain of an optical fiber amplifier changes depending on the level and wavelength of pump light. Has been stabilized. The gain of an optical fiber amplifier strongly depends on the wavelength of the pump light, and its characteristics are stable over time.Therefore, in this technique, the output light wavelength of the semiconductor laser is reduced as compared with the case where a filter is used. It is possible to stabilize with high accuracy over a long period of time.

However, Japanese Patent Application Laid-Open No. Sho 61-102081
In the technology described in Japanese Patent Application Laid-Open Publication No. H11-260, wavelength control is performed using only the gain of an optical fiber amplifier, and the wavelength control accuracy is the highest obtained when an optical fiber amplifier is used. Not.

It is an object of the present invention to provide a laser light output device using an optical fiber amplifier, which can stabilize the output light wavelength with higher accuracy.

[0010]

According to the first aspect of the present invention,
(A) a laser light source, (b) an optical fiber amplifier for amplifying the laser light output from the laser light source, and (c) first detection means for detecting a level of the laser light amplified by the optical fiber amplifier. (D) second detection means for detecting the level of spontaneous emission light of the optical fiber amplifier; and (e) a laser light source such that the ratio of the levels detected by the first detection means and the second detection means becomes a predetermined value. Temperature control means for controlling the temperature.

That is, in the laser light output device according to the first aspect of the present invention, the laser light output from the laser light source is amplified by the optical fiber amplifier, and as a result, the spontaneous emission light output from the optical fiber amplifier is amplified. The temperature of the laser light source is controlled so that the ratio between the level and the level of the amplified laser light becomes a predetermined value.

Since the dependency of the gain of the optical fiber amplifier on the input light wavelength and the dependency of the spontaneous emission light level on the input light wavelength have completely opposite dependencies, the level of the amplified laser light and the spontaneous emission The ratio of the light levels will show greater input light wavelength dependence. Therefore, in the laser light output device according to the first aspect of the present invention, in which the control is performed based on information indicating a large input light wavelength dependency, the output light wavelength of the laser light source is stabilized with high accuracy. The wavelength-stabilized laser light may be extracted from the output side of the optical fiber amplifier or between the laser light source and the optical fiber amplifier.

The invention according to claim 2 provides (a) a laser light source, (b) an optical fiber amplifier for amplifying the incident laser light, and (c) a laser light output from the laser light source to the optical fiber amplifier. And an optical coupler for branching the return light from the optical fiber amplifier, and (d) a first for detecting the level of the laser light amplified by the optical fiber amplifier.
Detecting means; (e) second detecting means for detecting the level of the return light split by the optical coupler; and (f) a ratio of the level detected by the first detecting means to the level detected by the second detecting means is predetermined. Temperature control means for controlling the temperature of the laser light source to obtain a value.

That is, in the laser light output device according to the second aspect of the present invention, the level of the spontaneous emission light from the optical fiber amplifier is detected by branching the light from the optical fiber amplifier between the optical fiber amplifier and the laser light source. This is performed by providing an optical coupler that performs the above operation.

When the laser light output device according to the first or second aspect of the present invention is used as a transmission source for optical communication, a laser light having a wavelength with a small attenuation in an optical fiber as a transmission line is stable. It is desirable to use an optical fiber amplifier using an erbium-doped optical fiber so that the output can be obtained at a high speed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

FIG. 1 shows a schematic configuration of a laser light output device according to one embodiment of the present invention. Hereinafter, the configuration and operation of the laser light output device according to the embodiment will be described with reference to FIG.

The semiconductor laser module 11 includes a semiconductor laser (LD) 21, a photodiode (PD) 22 for detecting an output level of the LD 21, an LD 21 and a PD 22.
The LD 21 is an APC (Automatic Power Controller) to which a detection signal of the PD 22 is input.
er) 12 controls the level of the output laser light (hereinafter, referred to as signal light) to be a predetermined level. A control signal from a temperature control circuit 18 to be described later is input to the electronic cooler 23, and the control temperature of the electronic cooler 23 is changed according to the control signal.

The signal light from the semiconductor laser module 11 is input to the optical fiber amplifier 14 via the optical coupler 13. The optical fiber amplifier 14 is an optical direct amplifier using an erbium-doped fiber (EDF) 25, and a signal light input to the optical fiber amplifier 14 is an excitation light source input via a wavelength division multiplexing coupler 26 in the EDF 25. The signal is amplified according to the level of the pumping light from 27 and output from the optical fiber amplifier 14. During this amplification, EDF
The spontaneous emission light is generated in the optical coupler 14, and the spontaneous emission light propagating to the optical coupler 13 is introduced into the PD 15 by the optical coupler 13.

The output of the optical fiber amplifier 14 is input to an optical coupler 16, and a part of the output is branched by the optical coupler 16 and introduced to a PD 17. The output of the PD 17 and the output of the PD 15 are both input to the temperature control circuit 20, and the temperature control circuit 20 sets a ratio between the input signal from the PD 17 and the input signal from the PD 15 in advance. Create a control signal according to the deviation from the set value,
The control signal is sent to the electronic cooler 2 in the LD module 11.
Supply to 3

The wavelength of the signal light output from the LD module 11 (the optical coupler 16
The reason why the wavelength of the signal light output via the) is controlled to a constant wavelength will be described. 2 and 3 respectively show
FIG. 4 is a diagram illustrating spectra of light input to the PDs 17 and 15, and FIG. 4 is a diagram illustrating a dependency of an optical spectrum output from the optical fiber amplifier 14 on an input light wavelength.

As shown in FIG. 2, the PD 17 has an ED
The signal light component and the spontaneous emission light component from the LD module 11 that have been amplified by the F25 are incident. The intensity of the spontaneous emission light component is significantly smaller than the intensity of the signal light component. The detection output corresponds to the signal light component level.

Also, as shown in FIG. 3, only the spontaneous emission light component is incident on the PD 15, so that
The detection output of the PD 15 corresponds to the spontaneous emission light level.

The signal light level and spontaneous emission light level output from the optical fiber amplifier are in accordance with the input signal light wavelength in the principle of operation of the optical fiber amplifier. In the optical fiber amplifier using the EDF, the wavelength of the input signal light is approximately 1
If it is 554 nm or less, as shown in FIG.
As the input light wavelength becomes longer, the signal light level increases, and conversely, the spontaneous emission light level decreases.

Therefore, the ratio between the signal light level and the spontaneous emission light level for which the deviation from the set value is calculated in the temperature control circuit 18 is higher than the individual light levels. Information. Therefore, for example, if the ratio between the signal light level and the spontaneous emission light level when the input signal light wavelength is 1551 nm is set as the set value, the deviation between the ratio between the signal light level and the spontaneous emission light level and the set value becomes Since different signs are taken at the wavelength of 1551 nm, the laser light output device of the embodiment in which the electronic cooler is controlled in accordance with the deviation, makes the output light wavelength of the semiconductor laser constant with high accuracy. Will be kept.

Since the laser light output device of the embodiment is configured as a device for an optical communication system, the laser light whose wavelength is stabilized is extracted from the output side of the optical fiber amplifier. If is not necessary, the laser light may be extracted at a stage before being input to the optical fiber amplifier. Further, the optical fiber used as the optical amplifying medium may be other than EDF, but when used in an optical communication system, it is desirable to use EDF whose output wavelength is around 1550 nm.

[0027]

As described in detail above, according to the present invention, the output light wavelength is stabilized based on information having a high wavelength dependency, and therefore, compared with the conventional apparatus. hand,
The laser light whose wavelength is stabilized can be obtained with high accuracy.

If the spontaneous emission light is detected between the optical fiber amplifier and the laser light source as in the second aspect of the present invention, it is not necessary to extract only the spontaneous emission light. The configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a laser light output device according to an embodiment of the present invention.

FIG. 2 is a spectrum diagram of light incident on a photodiode provided after an optical fiber amplifier among two photodiodes used for wavelength control by the laser light output device of the embodiment.

FIG. 3 is a spectrum diagram of light incident on a photodiode provided after an optical fiber amplifier among two photodiodes used for wavelength control by the laser light output device of the embodiment.

FIG. 4 is a diagram showing the input light wavelength dependence of the output spectrum of the optical fiber amplifier used in the laser light output device of the embodiment.

FIG. 5 is a block diagram showing an outline of a conventional technique for performing wavelength control using an optical fiber amplifier.

[Explanation of symbols]

 Reference Signs List 11 semiconductor laser module 12 APC 13, 16, 17, 32, 33 optical coupler 14 optical fiber amplifier 15, 22 photodiode (LD) 18 temperature control circuit 21, 31 semiconductor laser (LD) 23 electronic cooler 25 erbium-doped fiber ( EDF) 26 Wavelength division multiplex coupler 27 Excitation light source 30 Temperature controller 34 Optical fiber (optical amplification medium) 35 Reference light source 37 Control circuit 38 Drive circuit

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H04B 10/04 H04B 9/00 S 10/06 10/14

Claims (4)

(57) [Claims] A laser light source; an optical fiber amplifier for amplifying a laser beam output from the laser light source; a first detector for detecting a level of the laser beam amplified by the optical fiber amplifier; Second detecting means for detecting the level of the spontaneous emission of light, and temperature controlling means for controlling the temperature of the laser light source such that a ratio between the levels detected by the first detecting means and the second detecting means becomes a predetermined value. And a laser beam output device. 2. A laser light source; an optical fiber amplifier for amplifying incident laser light; and a laser light output from the laser light source is supplied to the optical fiber amplifier, and a return light from the optical fiber amplifier is branched. An optical coupler; first detection means for detecting the level of the laser light amplified by the optical fiber amplifier; second detection means for detecting the level of return light split by the optical coupler; and the first detection means And a temperature control unit for controlling the temperature of the laser light source so that a ratio of the level detected by the second detection unit to the level detected by the second detection unit becomes a predetermined value. 3. The laser light output device according to claim 1, wherein the optical fiber amplifier uses an erbium-doped fiber. 4. The laser light output device according to claim 1, wherein said optical fiber amplifier supplies pump light from behind to a fiber where light is amplified.