JP3200161B2 - Optical oscillation frequency stabilizing method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for stabilizing an optical oscillation frequency of a semiconductor laser in a lightwave communication device.

[0002]

2. Description of the Related Art The optical oscillation frequency of a semiconductor laser largely depends on the ambient temperature and the driving current value. For example, wavelength 1.5μ
For m band DFB semiconductor laser has temperature dependency of 13GH _z / ℃, also with driving current dependency of 500 MHz / mA. FIG. 4 is a diagram showing the temperature dependence of the optical oscillation frequency of a 1.5 μm wavelength DFB semiconductor laser, and FIG. 5 is the diagram showing the drive current dependence of the optical oscillation frequency of a 1.5 μm wavelength DFB semiconductor laser. Therefore, in lightwave (coherent) communication that requires high oscillation frequency stability,
It is necessary to stabilize the temperature of the semiconductor laser by driving the semiconductor laser at a constant current and controlling the temperature near the semiconductor laser. For example, when the temperature control at the 0.01 ° C. stability, stabilization of the oscillation frequency within computationally 130MH _z is expected.

FIG. 6 is a block diagram of a conventional optical oscillation frequency stabilizing device. A conventional optical oscillation frequency stabilizing method and its device will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a semiconductor laser module, and a laser beam generated by the semiconductor laser module 1 is guided to an optical fiber 17 via a first lens 14, a second lens 16 and an optical isolator 15. . The semiconductor laser module 1 has a semiconductor laser 11 and means for stabilizing the temperature of the semiconductor laser 11. The semiconductor laser 11 is driven by a constant current from the current supply circuit 6. The current value of the drive current i is set by the input voltage Ei. On the other hand, the means for stabilizing the temperature of the semiconductor laser 11 includes, for example, a first temperature measuring element 12 composed of a thermistor or the like, an electronic cooling element 13 composed of a Peltier element, and a temperature control circuit 2. . The semiconductor laser 11 and the first temperature measuring element 12 are arranged on the same metal provided on the electronic cooling element 13 at an interval of 2 to 3 mm, and the temperature measured by the first temperature measuring element 12 is almost It can be said that the temperature is around the semiconductor laser 11 . When a positive current flows through the Peltier element of the thermoelectric cooler 13, the temperatures of the semiconductor laser 11 and the first temperature measuring element 12 decrease, and when a negative current flows, the temperatures of the semiconductor laser 11 and the first temperature measuring element 12 increase. I do. The electronic cooling element 13 is connected to a temperature control circuit 2 that enables temperature control with a stability of 0.01 ° C., and the control temperature of the first temperature measuring element 12 is set by an input voltage Et.

The light output from the semiconductor laser 11 has an oscillation frequency ν, and the first lens 14 and the optical isolator 1
5 and the second lens 16, and are condensed and input to the optical fiber 17. That is, the temperature is detected by the first temperature measuring element 12 and the temperature control circuit 2 is operated based on the measured temperature.
Then, a control current for controlling the temperature of the semiconductor laser 11 is formed. By returning this control current to the electronic cooling element 12, the temperature near the semiconductor laser 11 is stabilized, and the oscillation frequency ν of the semiconductor laser 11 is stabilized.

[0006]

However, the apparatus having the above configuration has the following problems.

The first temperature measuring element 12 in the semiconductor laser module 1 does not detect the temperature of the semiconductor laser 11 itself. Therefore, it is impossible to always control the temperature of the semiconductor laser 11 with a stability of 0.01 ° C. In particular, when the environmental temperature at which the semiconductor laser module 1 is placed changes, the temperature of the semiconductor laser chip can be controlled even if the temperature detected by the first temperature measuring element 12 is controlled at a stability of 0.01 ° C. Changes delicately, causing a drift in the light oscillation frequency.

FIG. 7 is a graph showing a change in light oscillation frequency with respect to the ambient temperature of a semiconductor laser module in a temperature control operation state by a temperature control circuit having a stability of 0.01 ° C. In the figure, the optical oscillation frequency of the semiconductor laser of the semiconductor laser module 1 is, for example, 10 to the ambient temperature.
A drift of the optical oscillation frequency of 1.2 GHz occurs in the environmental temperature range of 40 ° C. to 40 ° C.

Therefore, in the case of a lightwave communication device using the semiconductor laser module 1 having such a configuration as a light source,
For example, in the short period of about one hour, the stability of the light oscillation frequency of about 130 MHz can be obtained, but in the long term, the drift of the light oscillation frequency described above occurs because the environmental temperature where the device is actually placed changes. There is a problem that occurs.

The present invention solves the problems of the conventional optical oscillation frequency stabilization method, and provides an optical oscillation frequency stabilization method and apparatus for reducing the drift of the optical oscillation frequency due to a change in environmental temperature. It is an object of the present invention to obtain a highly reliable lightwave communication device.

[0011]

In order to achieve the above object, a method for stabilizing an optical oscillation frequency of a semiconductor laser includes measuring an ambient temperature of a semiconductor laser module,
The drive dynamic current demanded of the semiconductor laser corresponding to the drift amount of the light oscillation frequency due to the change of the environmental temperature, the driving current component
The drive current of the semiconductor laser is changed based on
And controls the oscillation frequency of the semiconductor laser .
In the optical oscillation frequency stabilizing device for a semiconductor laser,
A first temperature measuring means for measuring the temperature in the vicinity of the semiconductor laser, and a temperature control means for controlling the temperature in the vicinity of the semiconductor laser based on the signal of the first temperature measuring unit, the environmental temperature of the semiconductor laser module a second temperature measuring means for measuring, consists of a temperature compensating means for forming a temperature compensation signal based on the signal of the second temperature measuring means, a current supply circuit for supplying a driving current to the semiconductor laser, the The optical oscillation frequency of the semiconductor laser is stabilized by changing the supply current of the current supply circuit by the temperature compensation signal.

[0012]

To achieve this, in the optical oscillation frequency stabilizing method of the present invention, the temperature compensation based on the ambient temperature of the semiconductor laser module is performed through the semiconductor laser temperature control means or the current supply circuit of the driving current, thereby reducing the temperature. The influence of the oscillation frequency of the semiconductor laser due to the change can be reduced. Thereby, a light source with a small temperature drift can be provided, and a highly reliable lightwave communication device can be obtained.

[0013]

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

FIG. 1 is a block diagram of an optical oscillation frequency stabilizing device according to a first embodiment of the present invention.

In FIG. 1, an optical oscillation frequency stabilizing device is a semiconductor laser module 1 and the semiconductor laser module 1.
And a means for stabilizing the temperature of the semiconductor laser 11, and the laser light generated by the semiconductor laser module 1 is transmitted through a first lens 14, a second lens 16, and an optical isolator 15. The point of leading out to the fiber 17 is the same as that of the conventional optical oscillation frequency stabilizing device.

The optical oscillation frequency stabilizing device of the present invention is different from the conventional optical oscillation frequency stabilizing device in the means for stabilizing the temperature of the semiconductor laser 11 of the semiconductor laser module 1. The means for stabilizing the temperature of the semiconductor laser 11 according to the present invention includes, in addition to the first temperature measuring element 12 for measuring the temperature of the conventional semiconductor laser 11, a second means for measuring the environmental temperature of the semiconductor laser module 1. , And a temperature compensation signal of the environmental temperature compensation circuit 3 is fed back to the temperature control circuit of the semiconductor laser 11.

In FIG. 1, the temperature measured by the second temperature measuring element 4 is input to an environmental temperature compensation circuit 3 to form a temperature compensation signal for compensating the temperature of the semiconductor laser 11. The temperature compensation signal is
It is added to the temperature control circuit 2 by the adder 5.

Next, the semiconductor laser 11 having the above configuration
The stabilization of the oscillating frequency will be described.

The first temperature measuring element 12 of the semiconductor laser 11 detects the temperature t near the semiconductor laser 1 and inputs the measured temperature to the temperature control circuit 2. The temperature control circuit 2 controls the amount and direction of the current supplied to the electronic cooling element 13 such as a Peltier element so that the temperature t of the temperature measuring element 12 is kept constant at a stability of 0.01 ° C. The temperature t can be set by the input voltage E of the temperature control circuit, and has, for example, the following relationship: t = A · E (1) Here, A is a constant.

If the light oscillation frequency of the semiconductor laser 11 is ν, the relationship between the light oscillation frequency ν and the temperature t is expressed as follows: ν = a ₁ t + b ₁ (2) Assuming that the initial temperature set value is t ₀ , the initial light oscillation frequency ν ₀ is as follows: ν ₀ = a ₁ t ₀ + b ₁ (3)

On the other hand, considering the drift due to the environmental temperature T where the semiconductor laser module 1 is placed, the light oscillation frequency changes as follows: ν ′ = a ₁ t ₀ + b ₁ + a ₂ (T−t ₀ ) (4) I do.

Here, considering a new set temperature t _{1 at} which the light oscillation frequency becomes the same as the initial light oscillation frequency, the condition that ν ′ always becomes ν ₀ is obtained from the equations (3) and (4). And a ₁ t ₀ + b ₁ = a ₁ t ₁ + b ₁ + a ₂ (T−t ₁ ) (5), and the above equation (5) is further transformed to t ₁ −t ₀ = −a ₂ / ( a ₁ −a ₂ ) · (T−t ₀ ) (6) Here, since a ₁ has a value that is 100 times or more larger than a ₂ , Expression (6) approximates t ₁ −t ₀ = −a ₂ / a ₁ (T−t ₀ ) (7) can do.

[0023] That is, by constantly controlling the power sale by satisfying the equation (7) to control the temperature t ₁ near the semiconductor laser 11 is also the environmental temperature T is changed, the light oscillation frequency of the semiconductor laser 11 is always [nu ₀ Thus, the frequency can be stabilized.

To convert the control temperature t ₀ to t ₁ , the environmental temperature T is measured by the second temperature measuring element 4 and the measured environmental temperature is converted by the environmental temperature compensating circuit 6 to the temperature compensation signal voltage ΔE (Δ
E = (t ₁ −t ₀ ) / A), and adding a new temperature control voltage E (E = t ₁ / A) obtained by adding the temperature compensation signal voltage ΔE to the temperature control voltage E _0. This is made possible by inputting to the control circuit 5.

An embodiment of a circuit for obtaining the temperature control voltage E will be described below. FIG. 2 shows an embodiment of a circuit for obtaining the temperature control voltage E.

[0026] In view, a temperature control voltage the supply voltage provided to the second temperature sensing element 4 and E ₁ and E _0. R ₄ is FIG.
Temperature measurement body 4. R ₄ is, for example, 100Ω by platinum
Resistance. The temperature characteristic of the temperature measuring element 4 can be expressed as follows: R ₄ = R ₀ (1 + αT) (8) Here, for example, R ₀ is 100Ω,
α is a temperature coefficient of 0.004 (° C. ⁻¹ ), and T is a temperature (° C.).

In the circuit shown, R ₁ = R ₂ , R ₃ = R
_If it is set to ₀ , E = E ₁ · αT / (R ₂ + R ₀ ) · R ₆ / R ₅ -E ₀ (R ₈ / R ₇ · R ₆ / R ₅ -1) (9)

In the equation (9), E ₁ · αT / (R ₂ + R
₀ ) · R ₆ / R ₅ −E ₀ (R ₈ / R ₇ · R ₆ / R ₅ The term corresponds to the temperature compensation signal voltage obtained from the second temperature measuring element 4 at the environmental temperature T. .

From the equation (1), the left side of the equation (7) is expressed as t ₁ −t ₀ = A (E−E ₀ ) (10), and the equation (9) is substituted into the equation (10). t ₁ −t ₀ = AE ₁ α / (R ₂ + R ₀ ) · R ₆ / R ₅ · T−R ₈ / R ₇ · R ₆ / R ₅ · t ₀ (11) For expression (11) satisfies the right side of the equation (7) _{is, -a 2 / a 1 = AE} 1 α / (R 2 + R 0) · R 6 / R 5 = R 8 / R 7 · R 6 / R ₅ (12) may be satisfied.

Usually, a ₂ is about 100 times larger than a ₁ , and −a ₂ / a ₁ is, for example, 3 × 10 ⁻³ .

A = 100 (° C./v), E ₁ = 10 v, R
Assuming that ₂ = 2.4 kΩ, from equation (12), for example, R ₅
= 16 kΩ, R ₆ = 30 kΩ, R ₇ = 1 kΩ, R ₈ =
By setting 1.6 kΩ, −a ₂ / a ₁ becomes 3 ×
10 ⁻³ .

FIG. 3 is a graph showing the temperature characteristics of the oscillation frequency of the semiconductor laser. The method for stabilizing the optical oscillation frequency according to the present invention will be described with reference to FIG.

In the figure, the vertical axis represents the oscillation frequency ν of the semiconductor laser and the temperature control voltage E, and the horizontal axis represents the temperature t. The temperature characteristic of the oscillation frequency of the semiconductor laser when the environmental temperature is not considered is represented by ν = a ₁ t + b ₁ in equation (3).
On the other hand, the temperature characteristic of the oscillation frequency of the semiconductor laser in consideration of the environmental temperature is given by ν ′ = a ₁ t + b ₁ + a in equation (4).
₂ (Tt). The relationship between the temperature t and the temperature control voltage E is represented by t = A · E in the equation (1).

Here, the case where the temperature in the initial state is t ₀₁ will be described. When the temperature is t ₀₁ , the oscillation frequency of the semiconductor laser is ν ₁ = a ₁ t ₀₁ + b _{1 according} to the equation (3). At this time, when the environmental temperature becomes T, the oscillation frequency of the semiconductor laser 11 becomes ν ′ = a ₁ t + b ₁ + a expressed by the equation (4) from the characteristic line of ν = a ₁ t + b ₁ expressed by the equation (3).
_{2 The} line shifts to the characteristic line of (T−t), and the oscillation frequency increases. In the figure, moves from point P ₁ to the point Q _1. Due to this movement, the oscillation frequency of the semiconductor laser 11 becomes ν ₁ = a ₁
From t ₀₁ + b ₁ ν ₁ ′ = a ₁ t ₀₁ + b ₁ + a ₂ (T−t
₀₁ ). At this time, in order to set the temperature of the semiconductor laser 11 to t ₀₁ , the temperature control circuit is supplied with a temperature control voltage of E ₀₁ = t ₀₁ / A. In order to return the oscillation frequency of the semiconductor laser 11 changed to ν ₁ ′ to the oscillation frequency ν ₁ before the change, the temperature control voltage supplied from the temperature control circuit 2 is set to E ₁ = t ₁ / A, and The oscillation frequency is changed along the characteristic line of ν ′ = a ₁ t + b ₁ + a ₂ (T−t).

The supply of the temperature control voltage from the temperature control circuit 2 causes the semiconductor laser 11 to move from the point Q ₁ to S ₁ on ν ′ = a ₁ t + b ₁ + a ₂ (Tt).
Has an oscillation frequency of ν ₁ .

Next, a case where the temperature in the initial state is t ₀₂ will be described.

When the temperature is t ₀₂ , the oscillation frequency of the semiconductor laser is ν ₂ = a ₁ t ₀₁ + b _{1 according} to equation (3). At this time, when the environmental temperature becomes T, the oscillation frequency of the semiconductor laser 11 becomes ν ′ = a ₁ t + b ₁ + a expressed by the equation (4) from the characteristic line of ν = a ₁ t + b ₁ expressed by the equation (3). ₂ (T
The operation shifts to the characteristic straight line of -t), and the oscillation frequency decreases. In the figure, moves from point P ₂ to the point Q _2. Due to this movement, the oscillation frequency of the semiconductor laser 11 becomes ν ₂ = a ₁ t ₀₂ + b
_{From 1} changes to ν ₁ ′ = a ₁ t ₂ + b ₁ + a ₂ (T−t ₂ ). At this time, in order to set the temperature of the semiconductor laser 11 to t ₀₂ , the temperature control circuit supplies a temperature control voltage of E ₀₂ = t ₀₂ / A. Semiconductor laser 11 changed to ν ₂ ′
In order to return the oscillation frequency to the oscillation frequency ν ₂ before the change, the temperature control voltage supplied from the temperature control circuit 2 is changed to E ₂
= T ₂ / A and the oscillation frequency of the semiconductor laser 11 is ν ′
= A ₁ t + b ₁ + a ₂ (T−t).

The supply of the temperature control voltage from the temperature control circuit 2 causes the semiconductor laser 11 to move from the point Q ₂ to S ₂ on ν ′ = a ₁ t + b ₁ + a ₂ (Tt).
Has an oscillation frequency of ν ₂ .

FIG. 8 is a block diagram showing a second embodiment of the optical oscillation frequency stabilizing device according to the present invention.

In the figure, an optical oscillation frequency stabilizing device is a semiconductor laser module 1 and the semiconductor laser module 1.
And a means for stabilizing the temperature of the semiconductor laser 11, and the laser light generated by the semiconductor laser module 1 is transmitted through a first lens 14, a second lens 16, and an optical isolator 15. The point of leading out to the fiber 17 is the same as that of the conventional optical oscillation frequency stabilizing device.

The means for stabilizing the temperature of the semiconductor laser 11 in the optical oscillation frequency stabilizing device of the present invention is not limited to the first temperature measuring element 12 for measuring the temperature of the conventional semiconductor laser 11 but also to the semiconductor laser. The semiconductor laser 11 comprises a second temperature measuring element 4 for measuring the environmental temperature of the module 1 and an environmental temperature compensating circuit 3.
To the current supply circuit 6 of FIG.

In the figure, the measured temperature of the second temperature measuring element 4 is input to the environmental temperature compensating circuit 3 to form a temperature compensating signal ΔE for compensating the temperature of the semiconductor laser 11. The temperature compensation signal ΔE is added to the drive voltage Ei and supplied to the current supply circuit 6 to drive the semiconductor laser 11.

Next, the semiconductor laser 11 having the above configuration
The stabilization of the oscillating frequency will be described.

The first temperature measuring element 12 of the semiconductor laser 11 detects the temperature t near the semiconductor laser 1 and inputs the measured temperature to the temperature control circuit 2. Temperature control circuit 2 controls the amount and direction of the current temperature t of the first temperature sensing element 12 has on the electronic cooling element 13, such as a Peltier element to be kept constant at stability of 0.01 ° C. . The temperature t can be set by the input voltage Et of the temperature control circuit. For example, there is a relationship of t = A · Et (13). Here, A is a constant.

The current supply circuit 6 supplies the current i ₀ to cause the semiconductor laser 11 to emit light. The supply current i ₀ is set by the input voltage Ei of the current supply circuit 6. Further, assuming that the optical oscillation frequency of the semiconductor laser 11 operating at the current i ₀ is ν, the relationship between the optical oscillation frequency ν and the temperature t is represented by ν = a ₁ t + b ₁ (14). Assuming that the initial temperature set value is t ₀ , the initial light oscillation frequency ν ₀ is ν ₀ = a ₁ t ₀ + b ₁ (15).

On the other hand, considering the drift due to the environmental temperature T in which the semiconductor laser module 1 is placed, the light oscillation frequency changes to ν ′ = a ₁ t ₀ + b ₁ + a ₂ (T−t ₀ ) (16) I do.

Here, assuming that the current i ₀ of the current supply circuit 6 is the second current i ₁ , the light oscillation frequency is as follows: ν ′ = a ₁ t ₀ + b ₁ + a ₂ (T−t ₀ ) + a ₃ (i ₁ −i ₀ ) (17)

Assuming that a ₂ (T−t ₀ ) = − a ₃ (i ₁ −i ₀ ) (18) holds in the above equation (17), the above equation (17) gives: ν ′ = a ₁ t ₀ + b ₁ = ν ₀ (19) The optical oscillation frequency can be stabilized irrespective of the environmental temperature T without depending on the environmental temperature T.

From the equation (18), the current i ₀ is represented by i ₀ −i ₁ = a ₂ (Tt ₀ ) / a ₃ (20).

The conversion of the current i ₀ from the current i ₀ into the current i ₁ in the current supply circuit 6 is carried out by measuring the environmental temperature T by the second temperature measuring element 4 and corresponding to the environmental temperature T by the environmental temperature compensating circuit 3. The voltage ΔE is converted, and the voltage ΔE is converted to a voltage E
This is performed by adding to i and inputting it to the current supply circuit 6.

Hereinafter, a circuit according to a second embodiment of the present invention will be described. FIG. 9 is a circuit diagram of a second embodiment of the present invention.

In the figure, R ₄ is the second temperature measuring element 4 in FIG.
It is. R ₄ can be made to have a resistance of 100Ω by, for example, platinum. The temperature characteristic of the second temperature measuring element 4 can be expressed as R ₄ = R ₀ (1 + αT) (21). Here, for example, R ₀ is 100Ω,
α is a temperature coefficient of 0.004 (° C. ⁻¹ ), and T is a temperature (° C.).

The driving current i ₁ of the semiconductor laser is as follows: i ₁ = (ΔE + Ei−E2) / R ₉ (22)

In the circuit shown, R ₁ = R ₂ , R ₃ = R
Assuming ₀ , ΔE = [E ₁ · αT / (R ₂ + R ₀ ) −Et · R ₈ / R ₇ ] · R ₆ / R ₅ (23)

By substituting equation (14) into equation (23), ΔE = [E ₁ · αT / (R ₂ + R ₀ ) −t · R ₈ / A · R ₇ ] · R ₆ / R ₅ (24) ).

Here, if E ₁ · α / (R ₂ + R ₀ ) = R ₈ / A · R ₇ (25), when T = t, the above equation (25) becomes ΔE = 0 and the current value i ₀ is expressed as i ₀ = Ei−E2 (26).

From the above equations (22), (24) and (25), the following equation is obtained.

I ₀ −i ₁ = − [E ₁ · αT / (R ₂ + R ₀ ) -t · R ₈ / A · R ₇ ] · R ₆ / R ₅ · R ₉ (27) In order to satisfy the condition (20), it is necessary to satisfy E ₁ · α · R ₆ / (R ₂ + R ₀ ) · R ₅ · R ₉ = −R ₆ · R ₈ / R ₅ · R ₉ · A · R ₇ = a ₂ / A ₃ (28) may be satisfied.

A = 100 (° C./v), E ₁ = 10 v, R
Assuming that ₂ = 2.4 kΩ and R ₉ = 10Ω, from equation (28), for example, R ₅ = 800, R ₆ = 30 kΩ, and R ₇ = 1M
By setting Ω, R ₈ = 1.6 kΩ, -a ₂ /
a ₁ can be set to −6 × 10 ⁻⁵ (A / ° C.).

[0060] Figure 10 and 11 is a temperature characteristic diagram of the oscillation frequency of the semiconductor laser, the optical oscillation frequency stabilizing method of the second embodiment of the present invention will be described by the figures.

In the figure, the vertical axis represents the oscillation frequency ν of the semiconductor laser, and the horizontal axis represents the temperature t. The temperature characteristic of the oscillation frequency of the semiconductor laser when the environmental temperature is not taken into consideration is represented by ν = a ₁ t + b ₁ in equation (14). On the other hand, the temperature characteristic of the oscillation frequency of the semiconductor laser in consideration of the ambient temperature is given by ν ′ = a ₁ t + b ₁ + a ₂ (T−
t).

Here, the case where the temperature in the initial state is t ₀₁ will be described with reference to FIG. When the temperature is t ₀₁ , the oscillation frequency of the semiconductor laser is given by ν ₁ = a ₁ t ₀₁ from equation (14).
A + b _1. At this time, when the environmental temperature becomes T, the oscillation frequency of the semiconductor laser 11 becomes ν = a expressed by the equation (14).
_From the characteristic line of ₁ t + b ₁ , ν ′ =
The operation shifts to the characteristic straight line of a ₁ t + b ₁ + a ₂ (T−t), and the oscillation frequency increases. In the figure, moves from point P ₃ to the point Q _3. By this movement, the oscillation frequency of the semiconductor laser 11 changes from ν ₃ = a ₁ t ₀₁ + b ₁ to ν ₃ ′ = a ₁ t ₀₁ + b ₁
+ A ₂ (T−t ₀₁ ). At this time, in order to set the temperature of the semiconductor laser 11 to t ₀₁ , the temperature control circuit sets E ₀₁
= T ₀₁ / A. To return the oscillation frequency of the semiconductor laser 11 changed to ν ₃ ′ to the oscillation frequency ν ₃ before the change, the current value supplied to the current supply circuit 6 is set to i _{1 and} the oscillation frequency of the semiconductor laser 11 is set to ν ′ = a ₁ t + b ₁ + a ₂ (T−t) + a ₃ (i ₁ −i
₀ ) Change along the characteristic line.

The current value supplied to the current supply circuit 6 is i
By the supply of _1, moves from point Q ₃ on the S _3, the oscillation frequency of the semiconductor laser 11 becomes [nu _3.

Next, the case where the temperature in the initial state is t ₀₂ will be described with reference to FIG. When the temperature is t ₀₂ , the oscillation frequency of the semiconductor laser is given by ν ₃ = a ₁ t ₀₁ +
a b _1. At this time, when the environmental temperature becomes T, the oscillation frequency of the semiconductor laser 11 becomes ν = a ₁ represented by the equation (14).
From the characteristic line of t + b ₁ , ν ′ = a represented by equation (16)
It shifts to the characteristic line of ₁ t + b ₁ + a ₂ (T−t), and the oscillation frequency decreases. In the figure, moves from point P ₃ to the point Q _3. By this movement, the oscillation frequency of the semiconductor laser 11 changes from ν ₃ = a ₁ t ₀₂ + b ₁ to ν ₃ ′ = a ₁ t ₂ + b ₁ +
a ₂ (T−t ₂ ). At this time, in order to set the temperature of the semiconductor laser 11 to t ₀₂ , the temperature control circuit sets E ₀₂ =
A temperature control voltage of t ₀₂ / A is supplied. [nu ₃ 'to return the oscillation frequency of the semiconductor laser 11 changes the oscillation frequency [nu ₃ before the change, the oscillation frequency of the semiconductor laser 11 a current value the current supply circuit 6 supplied as i ₁ ν' =
It is varied along the characteristic line of a ₁ t + b ₁ + a ₂ (T−t) + a ₃ (i ₁ −i ₀ ).

[0065] the supply of a current value supplied to the current supply circuit 6 i _1, moves from point Q ₃ on the S _3, the oscillation frequency of the semiconductor laser 11 becomes [nu _3.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0067]

As described above in detail, according to the present invention, since the environmental temperature compensation circuit is added in addition to the conventional temperature control circuit, the drift of the light oscillation frequency due to the environmental temperature can be reduced. Can be expected.

[0068] For example, the drift amount of the light oscillation frequency due to the environmental temperature of 40 ° C. from 10 ° C. was 1.2GH _z is can be reduced to about 1/10 by the practice of the present invention. Therefore, it is possible to provide a highly reliable light source unit of the optical communication device.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical oscillation frequency stabilizing device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram for obtaining a temperature control voltage E according to the present invention.

FIG. 3 is a temperature characteristic diagram of an oscillation frequency of a semiconductor laser.

FIG. 4 is a diagram showing the temperature dependence of the optical oscillation frequency of a 1.5 μm wavelength DFB semiconductor laser.

FIG. 5 is a diagram showing a drive current dependency of an optical oscillation frequency of a 1.5 μm wavelength DFB semiconductor laser.

FIG. 6 is a configuration diagram of a conventional optical oscillation frequency stabilizing device.

FIG. 7 is a diagram showing a change in light oscillation frequency with respect to an ambient temperature of a semiconductor laser module in a temperature control operation state by a temperature control circuit having a stability of 0.01 ° C.

FIG. 8 is a block diagram showing a second embodiment of the optical oscillation frequency stabilizer according to the present invention.

FIG. 9 is a circuit diagram of a second embodiment of the present invention.

FIG. 10 is a temperature characteristic diagram of an oscillation frequency of a semiconductor laser.

FIG. 11 is a temperature characteristic diagram of an oscillation frequency of a semiconductor laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser module 2 temperature measurement control circuit 3 environmental temperature compensation circuit 4 second temperature measurement element 5 adder 6 current supply circuit 11 semiconductor laser 12 first temperature measurement element 13 electronic cooling device 14 first lens 15 optical isolator 16 Second lens 17 Optical fiber

Claims (3)

(57) [Claims] 1. A method for stabilizing an optical oscillation frequency of a semiconductor laser, comprising: (a) measuring an ambient temperature of a semiconductor laser module; and (b) a semiconductor corresponding to a drift of the optical oscillation frequency due to a change in the environmental temperature. (C) controlling the oscillation frequency of the semiconductor laser by changing the drive current of the semiconductor laser based on the drive current. 2. An optical oscillation frequency stabilizing device for a semiconductor laser, comprising: (a) first temperature measuring means for measuring a temperature in the vicinity of the semiconductor laser; and (b) based on a signal from the first temperature measuring means. Temperature control means for controlling the temperature in the vicinity of the semiconductor laser, (c) second temperature measurement means for measuring the environmental temperature of the semiconductor laser module, and (d) based on a signal from the second temperature measurement means. (E) a current supply circuit for supplying a drive current to the semiconductor laser, and (f) changing a supply current of the current supply circuit by the temperature compensation signal. An optical oscillation frequency stabilizing device for stabilizing an optical oscillation frequency of a semiconductor laser. 3. The optical oscillation frequency stabilizing device according to claim 2 , wherein the supply current is changed by a drive current of the semiconductor laser corresponding to a drift of the optical oscillation frequency due to a change in environmental temperature.