JPH07109927B2 - Semiconductor laser module and operating method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module light source used for analog optical transmission using an optical fiber which requires low noise and low distortion transmission characteristics, and an operating method thereof. It is a thing.

2. Description of the Related Art It is known that a distributed feedback semiconductor laser stably oscillates in a single longitudinal mode even with changes in current and temperature, and can stably obtain low noise characteristics. Therefore, compared to the Fabry-Perot type semiconductor laser, high-quality analog optical transmission with lower noise is possible.

However, the second-order distortion characteristic due to the non-linearity of the semiconductor laser itself is not a sufficiently small value, and is not suitable for analog optical transmission applications in which analog signals are multiplexed and transmitted. However, there is a problem that crosstalk occurs between multiplexed signals, and as a result, restrictions such as limiting the number of multiplexed signals are given.

The present invention, in order to solve the above problems, in a semiconductor laser module using a single longitudinal mode semiconductor laser such as a distributed feedback semiconductor laser as a light source, without distorting the low noise characteristics of the semiconductor laser itself, distortion A semiconductor laser module having improved characteristics and an operating method thereof are provided.

Means for Solving the Problems The present invention is a so-called semiconductor laser module including a single longitudinal mode semiconductor laser, at least an optical lens, an optical isolator, and an optical fiber, in which the semiconductor laser is modulated with an analog optical transmission signal. In the optical path until the laser light emitted from the semiconductor laser is coupled into the optical fiber, at least two reflection points for the laser light are formed to form an optical resonator (etalon). The semiconductor laser module is formed so that the temperature of the semiconductor laser module can be controlled so that the second-order distortion component with respect to the modulation signal of the output light of the semiconductor laser module is minimized.

One of at least two reflection points is a semiconductor laser module which is the laser light emitting end face of the semiconductor laser.

In this semiconductor laser module, an FSR (Free Spectral Range) formed by the distance L between at least two reflection points is smaller than the oscillation wavelength (frequency) variable Δλo of the semiconductor laser controlled by temperature and injection current.

A semiconductor laser module in which a single longitudinal mode semiconductor laser is a distributed feedback semiconductor laser.

The semiconductor laser module according to claim 1, further comprising a light receiving element inside which detects a part of the semiconductor laser light after passing through the optical resonator.

In a so-called semiconductor laser module composed of a single longitudinal mode semiconductor laser, at least an optical lens, an optical isolator, and an optical fiber, the semiconductor laser is modulated for analog optical transmission, and the laser emitted from the semiconductor laser. At least two reflection points for the laser light are formed in the optical path until the light is coupled into the optical fiber to form an optical resonator (etalon). It is a method of operating a semiconductor laser module, which is used by controlling the temperature of the semiconductor laser module so that the second-order distortion component of the modulated signal of the output light is minimized.

It is a method of operating a semiconductor laser module that operates with a circuit configuration that controls the temperature of the semiconductor laser module so that the second-order distortion component of the semiconductor laser is minimized from the output of the light receiving element.

Action The action of the present invention will be described below.

Distortions are generated by various nonlinearities, but since basically they have polarities depending on the direction of nonlinearity, distortions of different polarities can be compensated for each other.

In the analog optical transmission system as described above, factors causing distortion include an optical fiber transmission line, a light receiving element, an electric signal amplifier, etc. in addition to the semiconductor laser module light source. It is a combination of distortion characteristics. The distortion generated by the semiconductor laser module light source is "A", the distortion generated by other sources is "B",
If the polarity of the distortion is represented by "+" and "-" for each,
When the combination of "A +" and "B +" or "A-" and "B-" is added, the amount of distortion increases by adding "A +".
And "B +" or "A-" and "B-" are combined, the distortion amount is compensated for and becomes very small.

The differential coefficient of the transmittance characteristic of the optical resonator formed inside the semiconductor laser module is proportional to the amount of secondary distortion, and the sign thereof is the polarity of distortion. By scanning, an operating point in which the amount of distortion is compensated and becomes extremely small can be obtained. As a result, a value smaller than the distortion characteristic of the semiconductor laser itself can be obtained.

Embodiments Two embodiments of the present invention are shown in FIG. 1, FIG. 2 and FIG.
This will be described with reference to FIGS.

FIG. 1 is a configuration diagram of a semiconductor laser module according to a first embodiment of the present invention. In Fig. 1, 1 is the oscillation wavelength of 1.3.
μm distributed feedback semiconductor laser, 2 optical lens, 3 optical isolator, 4 single mode optical fiber, 5 laser light emitted from the semiconductor laser 1 and incident on the optical fiber 4, 6 laser having a reflectance of 2% The side reflection surfaces 1 and 7 are reflection surfaces 2 and 8 which are vertical surfaces of the optical lens 2 and are semiconductor laser modules.

FIG. 2 shows the temperature characteristic of the secondary distortion during the operation of the constant output laser. Now, when the reflecting surface 6 and the reflecting surface 7 form an optical resonator (etalon) and the distance between them is set to 1 mm,
The FSR (Free Spectral Range) of the etalon is 150 GHz, which is 8.3 A (angstrom) when converted to the wavelength. As explained in the action, the distortion characteristic can be defined by the differential coefficient of the transmittance characteristic of the etalon, so the transmittance characteristic depends on the polarity. It can be uniquely set to the minimum value near the top of either the peak or the valley at 75 GHz intervals. Since the wavelength temperature change of the distributed feedback semiconductor laser is about 0.8 A / ° C, the best strain characteristic can be selected by changing the temperature by about 10 ° C.

FIG. 3 is a configuration diagram of a semiconductor laser module according to the second embodiment of the present invention. In FIG. 3, 9 is a half mirror, 10 is a laser beam divided by the half mirror 9,
A light receiving element 11 detects the laser beam 10. In the following text, the same parts as those described above are designated by the same reference numerals and the description thereof will be omitted.

With this configuration, it is possible to easily detect the operating point where the distortion is minimum. At this time, the light receiving element 11 needs to respond up to the frequency band in which the secondary distortion of the system used is generated.

FIG. 4 is a block diagram of the operating method of the second embodiment of the present invention. In FIG. 4, 12 is a strain detector, 13 is a minimum value judgment circuit, 14 is a control signal generator, and 15 is a temperature control device.

The distortion amount of the laser light 10 received by the light receiving element 11 is detected by the distortion amount detector 12, and then the minimum value judgment circuit 13 judges that there is a deviation from the minimum value and sends a signal to the temperature control device. The temperature of the semiconductor laser is controlled so that the strain amount is always the minimum.

With this configuration, it is possible to stably obtain a low distortion characteristic for a long time.

EFFECTS OF THE INVENTION The effects of the present invention are to stably supply a semiconductor laser module having low noise and low distortion characteristics, which greatly contributes to the construction of an analog optical transmission system using an optical fiber, and has great industrial significance. Is to have.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a semiconductor laser module according to a first embodiment of the present invention, FIG. 2 is a temperature characteristic diagram of secondary distortion during operation of a constant output laser, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a block diagram of the semiconductor laser module of FIG. 4, and FIG. 4 is a block diagram of the operating method of the third embodiment of the present invention. 1 ... Distributed feedback semiconductor laser, 2 ... Optical lens, 3
...... Optical isolator, 4 ...... Optical fiber, 5 ...... Laser light, 6,7 ...... Reflecting surface, 8 ...... Semiconductor laser module, 1
1 ... Light receiving element, 12 ... Strain amount detector, 13 ... Minimum value judgment circuit, 14 ... Control signal generator, 15 ... Temperature control device.

Claims (7)

[Claims] 1. A so-called semiconductor laser module comprising a single longitudinal mode semiconductor laser, at least an optical lens, an optical isolator, and an optical fiber, wherein the semiconductor laser is modulated by a signal for analog optical transmission, An optical resonator (etalon) is formed by forming at least two reflection points for the laser light in the optical path until the laser light emitted from the laser light is coupled into the optical fiber. A semiconductor laser module, wherein the temperature of the semiconductor laser module can be controlled so that the second-order distortion component with respect to the modulation signal of the output light of the semiconductor laser module is minimized. 2. One of at least two reflection points,
The semiconductor laser module according to claim 1, wherein the semiconductor laser module is a laser light emitting end face of the semiconductor laser. 3. An FSR (Free Spectral Range) formed by a distance L between at least two reflection points is smaller than an oscillation wavelength (frequency) variable Δλo of a semiconductor laser controlled by temperature and injection current. The semiconductor laser module according to claim 1, which is characterized in that. 4. The semiconductor laser module according to claim 1, wherein the single longitudinal mode semiconductor laser is a distributed feedback semiconductor laser. 5. The semiconductor laser module according to claim 1, further comprising a light receiving element inside which detects a part of the semiconductor laser light after passing through the optical resonator. 6. A so-called semiconductor laser module comprising a single longitudinal mode semiconductor laser, at least an optical lens, an optical isolator, and an optical fiber, wherein the semiconductor laser is modulated for analog optical transmission. At least two reflection points for the laser light are formed in the optical path until the emitted laser light is coupled into the optical fiber to form an optical resonator (etalon). A method for operating a semiconductor laser module, wherein the temperature of the semiconductor laser module is controlled and used so that the second-order distortion component with respect to the modulation signal of the output light of the laser module is minimized. 7. The semiconductor device according to claim 5, wherein the semiconductor laser module is operated by a circuit configuration that controls the temperature of the semiconductor laser module from the output of the light receiving element so that the second-order distortion component of the semiconductor laser is minimized. How to operate the laser module.