JP2005085815A - Wavelength stabilizing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a wavelength stabilizing unit for performing the wavelength control of a laser beam stably at high speed. <P>SOLUTION: A wavelength stabilizing unit is equipped with an LD 101 which is capable of changing a laser beam in wavelength with a temperature change; a Peltier element 102 and a Peltier drive circuit 110 which control the temperature of the LD 101; a thermistor 109 which detects the temperature of the LD 101; a PD1 (104) which detects the volume of light emitted from the LD 101 as a first PD current; a PD2 (105) which detects light penetrating through an etalon filter 103 as a second PD current so as to detect a wavelength; and a memory in which a table is previously stored wherein the temperature of the LD 101, the wavelength of a laser beam emitted from the LD 101, the first PD current, and the second PD current are measured while the LD 101 is changed in temperature, and are tabled with the measurement data as a target value. A CPU 107 computes a present wavelength from outputs of the PD2 and the PD1, and the present wavelength is compared with the data stored in the memory to detect a present position for control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wavelength stabilization device, and more particularly to a wavelength stabilization device for stabilizing the wavelength of an optical communication laser diode (hereinafter referred to as LD).

  The wavelength of light can be confirmed by passing through an etalon filter whose light transmission characteristics change as the wavelength changes, and detecting it with a photodetector (hereinafter referred to as PD) made of a photodiode. However, the frequency characteristic of the passing attenuation is not simple and shows periodicity. Naturally, the PD current for light detection also shows the same characteristics. The interval of one cycle is called FSR (free spectral region).

  Since the wavelength of laser light changes with age and temperature change of the etalon filter, a wavelength control system has been proposed to stabilize and lock the absolute wavelength of the laser light by compensating for it. (In particular, see Patent Document 1).

  Further, as a wavelength control circuit, a wavelength control circuit that uses an optical bandpass filter as a wavelength discriminating element and performs wavelength control within a fine adjustment range in which the wavelength of the laser signal can be discriminated by the optical bandpass filter has been proposed ( In particular, see Patent Document 2.)

As a method for controlling the wavelength according to the characteristics of the etalon filter, for example, there are the following methods.
1) Wavelength control first controls the LD temperature and moves the LD temperature to the FSR having the target wavelength.
2) Change the LD temperature minutely, check the PD current change (ΔPD current / ΔLD temperature), and check the position in the FSR.
3) From the position in the FSR, check the relationship between temperature change and wavelength change.
4) While controlling the LD temperature, the PD current value is detected and locked to the target wavelength.

Japanese Patent Laid-Open No. 2001-44558 Japanese Patent Laid-Open No. 11-251673

Conventionally, wavelength control is performed by the method as described above, and there are the following problems.
1) The control procedure is complicated and the control time until the wavelength is locked is long.
2) In the vicinity of the capability limit point of a temperature control device such as a Peltier element, it takes time to cool and raise the temperature, making it difficult to confirm the position in the FSR and the control becomes unstable.

  The present invention has been made to solve such a problem, and an object thereof is to obtain a wavelength stabilizing device for performing stable wavelength control at high speed.

  The present invention relates to a semiconductor laser diode capable of changing the wavelength of laser light emitted according to temperature, LD temperature adjusting means for controlling the temperature of the semiconductor laser diode, driving means for driving and controlling the LD temperature adjusting means, LD temperature detection means for detecting the temperature of the semiconductor laser diode, a first photodiode for detecting the light emission amount of the laser light of the semiconductor laser diode as a first PD current, and the wavelength of the laser light of the semiconductor laser diode While changing the wavelength of the laser beam by changing the temperature of the semiconductor laser diode by changing the temperature of the second photodiode that detects the laser beam that has passed through the etalon filter for detection as a second PD current, Measure the temperature and wavelength of the semiconductor laser diode and the first and second PD currents. The measured data is tabulated as a target value and stored in advance, and the wavelength of the laser beam is calculated by dividing the second PD current after converting the second PD current into a voltage using the first PD current. Wavelength calculating means and control means for outputting a control signal to the driving means so that the temperature obtained by the LD temperature detecting means and the wavelength obtained by the wavelength calculating means approach the target wavelength and the target temperature in the memory, respectively. The control means is a wavelength stabilization device that performs temperature control more gently as the rate of change of the wavelength obtained by the wavelength calculation means with respect to temperature change increases.

  According to the present invention, the temperature, the wavelength of the laser light, and the PD current measured by the first and second photodiodes are changed to the target value while changing the wavelength by changing the temperature of the semiconductor laser diode in the adjustment stage. As a table and stored in the memory, at the time of actual control, the temperature and PD current are measured and compared with the table data, so that the current position of the wavelength is detected and controlled. Since the control procedure can be simplified and the control time until the wavelength is locked can be shortened, wavelength control can be performed stably at high speed.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a wavelength division multiplexing optical communication module (hereinafter referred to as an optical module 100) and a microcomputer unit connected thereto in the wavelength stabilization apparatus according to the embodiment of the present invention. As shown in FIG. 1, an LD (semiconductor laser diode) 101 capable of changing the wavelength depending on the temperature is provided in the optical module 100. The LD 101 is a Peltier element that controls the LD temperature in order to control the wavelength. 102 (LD temperature adjusting means) is attached. The Peltier element 102 is driven by a Peltier drive circuit 110 (drive means). The LD light emitted from the LD 101 enters the optical fiber 114 in the adjustment stage, and enters the optical splitter 115 in the actual control. The optical splitter 115 has one output connected to the etalon filter 103 and the other output connected to a photodiode element 1 (hereinafter referred to as PD1) (reference numeral 104). The PD1 (reference numeral 104) is connected to a PD1 current-voltage conversion circuit 111 that converts the current detected by the PD1 (reference numeral 104) into a voltage (Vdp1). A photodiode element 2 (hereinafter referred to as PD2) (reference numeral 105) is connected to the etalon filter 103, and the current detected by PD2 (reference numeral 105) is converted into a voltage (Vdp2) in PD2 (reference numeral 105). A PD2 current-voltage conversion circuit 112 is connected. A thermistor 109 (LD temperature detecting means) for detecting the temperature is attached in the vicinity of the LD 101. The thermistor 109 is provided with a temperature-voltage conversion circuit 113 for converting the LD temperature into a voltage (Tld).

  An AD converter 106 is provided in the microcomputer unit 120. The AD converter receives an output Vdp2 from the PD2 current-voltage conversion circuit 112, an output Vdp1 from the PD1 current-voltage conversion circuit 111, and an output Tld from the temperature-voltage conversion circuit 113. The AD converter 106 converts them into digital values. Vpd1, Vpd2, and Tld converted into digital values are taken into the CPU 107. A DA converter 108 is connected to the CPU 107, whereby the digital output from the CPU 107 is converted into an analog value, and the Peltier drive circuit 110 in the optical module 100 is controlled to control the Peltier element 102 based on the analog value. Is input.

  Next, the operation will be described. At the time of control, the LD light emitted from the LD 101 is detected as a current by the PD2 (reference numeral 105) through the etalon filter 103 for wavelength detection, and the detected current value is converted into a voltage ( Vpd2). In addition, in order to detect the amount of light emitted from the LD 101, it is detected as a current by the PD1 (reference numeral 104) that directly detects the LD light, and the PD1 current-voltage conversion circuit 111 converts the detected current value into a voltage (Vpd1). A thermistor 109 that detects the LD temperature is attached in the vicinity of the LD 101, and the detected LD temperature is converted into a voltage (Tld) by the temperature-voltage conversion circuit 113. Vpd1, Vpd2, and Tld are converted into digital values by the AD converter 106 and taken into the CPU 107. The CPU 107 obtains the value of Vdp2 / Vpd1 (wavelength calculation means) and controls the Vdp2 / Vpd1 and Tld so as to approach a target value stored in advance in a memory described later (control means).

  In the memory of the CPU 107, the etalon characteristics shown in FIG. 3 are converted into digital data and stored as table data. Data on the target point of the wavelength to be locked is also stored in the memory. Those memory data are created in the adjustment stage.

  FIG. 2 is a configuration diagram at the adjustment stage. The correspondence relationship between FIG. 2 and FIG. 1 will be described. The optical module 100 in FIG. 2 is an optical module 100 composed of components 101 to 105 and 109 to 115 surrounded by broken lines in FIG. Further, the microcomputer unit 120 in FIG. 2 is the microcomputer unit 120 including constituent elements 106 to 108 surrounded by a solid line in FIG. An optical wavelength measuring device 201 is connected to the optical module 100 via the optical fiber 114 shown in FIG. This optical wavelength measuring device 201 is for measuring the wavelength in the adjustment stage, and is not used during actual control. A personal computer 202 is connected to the optical wavelength measuring instrument 201 and the microcomputer unit 120.

  In the configuration of FIG. 2, the LD temperature is changed by controlling the Peltier element 102 from a low temperature to a high temperature. At that time, the wavelength measured by the optical wavelength measuring instrument 201, the LD temperature measured by the thermistor 109, Vpd1 and Vpd2 measured using PD1 (reference numeral 104) and PD2 (reference numeral 105), and Vpd2 / Vpd1, respectively. Is processed as digital data by the personal computer 202 and stored as table data in the memory of the CPU 107 in the microcomputer unit 120 (the etalon filter characteristics shown in FIG. 3 are tabulated). At that time, the target value data to be locked is also created and stored.

  Further, if necessary, Δ wavelength detection PD current / ΔLD temperature is also calculated and tabulated. The Δ wavelength detection PD current and the ΔLD temperature are both the difference obtained by subtracting the data measured this time from the previously measured data (this will be described later). The value of Δwavelength detection PD current / ΔLD temperature may be calculated from the table data at the time of control without being tabulated.

  In addition, the temperature, LD temperature, Vpd1 and Vpd2 measured using PD1 (reference numeral 104) and PD2 (reference numeral 105), and Vpd2 / Vpd1 are measured in the thermostatic chamber. Then, the amount of change in the etalon characteristic due to temperature change is measured, and the characteristic correction data for the etalon characteristic due to temperature is stored in the memory of the CPU 107 as digital data.

  Next, the wavelength control operation will be described in detail. The wavelength control is performed according to the procedure shown in FIGS. 4 and 5 (Flowcharts 1 and 2). Flowchart 1 is a procedure for roughly controlling the LD temperature so as to approach the target temperature Tldp by a factor of only the temperature. When the predetermined condition (condition of Step S4) is satisfied in Flowchart 1, the process proceeds to Flowchart 2. Then, the LD temperature is controlled so as to approach the target value. That is, a control voltage is output from the DA converter 108, converted into a current by the Peltier drive circuit 110, and based on this, the Peltier element 102 is controlled to control the LD 101 in the vicinity of a desired temperature.

First, the procedure of the flowchart 1 will be described.
First, in step S1, the LD temperature detected by the thermistor 109 as described above is converted into a voltage (Tld), and then converted into a digital value by the AD converter 106.

  Next, in step S2, the LD light detected as a current by PD2 (reference numeral 105) and PD1 (reference numeral 104) as described above is converted into a voltage (Vpd2, Vpd1) and then converted to a digital value by the AD converter 106. Convert. Next, the CPU 107 calculates and calculates Vpd2 / Vpd1. This is because the signal relating to the wavelength is Vpd2, but the data is proportional not only to the wavelength but also to the light emission amount of the LD, so that the factor of the light emission amount of the LD is divided by Vpd1.

  Next, in step 3, the temperature target value Tldp and the target value Vpdp of (Vpd2 / Vpd1) are read from the table in the memory of the CPU 107.

  Next, in step S4, it is determined whether or not the absolute value of the difference between Tld obtained in step S1 and the target temperature value Tldp is smaller than a predetermined reference value 1. If it is larger than the predetermined reference value, the process proceeds to step S5. On the other hand, if it is smaller than the predetermined reference value 1, it is determined that the rough control based only on the temperature in step S1 has been completed, and the flow proceeds to the flowchart 2 to shift to detailed control. The flowchart 2 will be described later.

  Next, in step S5, it is determined whether or not a value obtained by subtracting the temperature target value Tldp from Tld obtained in step S1 is smaller than zero. If the value is smaller than 0, the temperature is lower than the target value Tldp. Therefore, the process proceeds to step S7, and the CPU 107 raises the temperature of the Peltier element 102 to the Peltier drive circuit 110 via the DA converter 108. Such a control signal is output, and the process proceeds to step S8. On the other hand, when the temperature is 0 or more, the temperature is higher than the target value Tldp. Therefore, the process proceeds to step S6, and the CPU 107 causes the temperature of the Peltier element 102 to the Peltier drive circuit 110 via the DA converter 108. A control signal for lowering is output, and the process proceeds to step S8.

Next, in step S8, the values of Tld and Vpd2 / Vpd1 are confirmed again by the same method as in steps S1 and S2, and an error from the previously confirmed data is obtained by the following equation.
ΔTld = Tld (1) −Tld (2)
Δ (Vpd2 / Vpd1) = (Vpd2 / Vpd1) (1) − (Vpd2 / Vpd1) (2)
(1): Data confirmed last time (however, the first time is the data of steps S1 and S2, the second time is the previous data of step S8)
(2): Data confirmed this time in step S8

  Next, in step S9, it is determined whether or not the absolute value of ΔTld obtained in step S8 is greater than a predetermined reference value.

  If the temperature is smaller than the reference value, that is, if the temperature change per unit time (Tld / t) is equal to or less than the reference value, it is determined that the temperature is near the Peltier temperature control limit point. After sending out as an alarm (message screen display and / or alarm sound generation), the process proceeds to step S11. On the other hand, if larger than the reference value, the process proceeds to step S11 as it is.

  Next, in step S11, Vpd2 / Vpd and Tld are compared with the data in the memory of the CPU 107, and the position in the traced data is confirmed for the current wavelength and etalon characteristics.

  Next, in step S12, “Δ (Vpd2 / Vpd1) / ΔTld” (the slope of the etalon characteristic) is calculated, and the positive / negative (increase / decrease) of the slope of the change in wavelength with respect to the change in temperature is obtained. Compared with the slope obtained from the table data, the accuracy of position recognition is improved (as shown in FIG. 3, near the peak of the etalon characteristic, the temperature between the points a and b is close and the Vpd2 / Vpd1 data is The position may be misidentified due to equality).

  Next, the process returns to step S4. Since the process of step S4 is as described above, here, a case where it is smaller than the predetermined reference value 1 will be described. In this case, it is determined that the rough control in step S1 has been completed, and the process proceeds to the flowchart 2 and proceeds to detailed control. Next, the flowchart 2 will be described with reference to FIG.

  When controlling the temperature in detail, as can be seen from FIG. 3, since the slope of the change of Vpd2 / Vpd1 differs with respect to the temperature, if it changes suddenly, change the temperature more slowly than the normal control speed. Stabilize control. As the gradient with respect to temperature, Δ (Vpd2 / Vpd1) / ΔTld obtained in step S12 or step S22 is used.

In the flowchart 2, first, in step S20, Tld and Vpd2 / Vpd1 are measured again by the same method as in steps S1 and S2 described above, and an error from the previously confirmed data is obtained by the following equation.
ΔTld = Tld (1) −Tld (2)
Δ (Vpd2 / Vpd1) = (Vpd2 / Vpd1) (1) − (Vpd2 / Vpd1) (2)
(1): Data confirmed last time (however, the first time is the data of step S8, and the second and subsequent times are the previous data of step S20.)
(2): Data confirmed this time in step S20

  Next, in step S21, Vpd2 / Vpd1 and Tld are compared with the data in the memory, and the position in the data traced for the current wavelength and etalon characteristics is confirmed.

  Next, in step S22, “Δ (Vpd2 / Vpd1) / ΔTld” (the slope of the etalon characteristic) is calculated, and the positive / negative (increase / decrease) of the slope of the change in wavelength with respect to the temperature change is obtained. Compared with the inclination obtained from the table data, the accuracy of position recognition is improved (as shown in FIG. 3, near the peak of the etalon characteristic, the temperature is close between points a and b, and Vpd2 Since the data of / Vpd1 are equal, the position may be misidentified).

  Next, in step S23, the current position is compared with the target position, and the CPU 107 sends a control signal to the Peltier element drive circuit 110 to control the Peltier element 102 so that Vpd2 / Vpd1 approaches the target position (Vpdp). Send. At that time, the Peltier element is controlled so that the temperature can be controlled more gradually as Δ (Vpd2 / Vpd1) / ΔTld increases.

  Next, in step S24, it is checked whether the absolute value of the error between Tld and Tldp and the error between Vpd2 / Vpd1 and Vpdp (at least one of them) is smaller than the reference value. S20 to step S23 are repeated. On the other hand, if it is smaller than the reference value, the wavelength control is completed.

  As described above, according to the present embodiment, the wavelength measured by the standard measurement system in the memory of the CPU 107, the wavelength detection PD current passed through the etalon filter, and the LD temperature are tabulated as digital data, and the actual data During wavelength control, the LD temperature and wavelength detection PD current value are detected, and the two data and the table data are collated, so that the current LD emission wavelength can be specified, and the error from the target wavelength is clear. Can be detected. After detection, control is performed with a Peltier device toward the LD temperature at the target wavelength. At that time, as the rate of change of the wavelength with respect to the temperature change increases, the temperature is controlled more gently, and the control is stabilized, so that stable wavelength control can be performed smoothly and at high speed up to the target value. It becomes. In addition, stable control is possible even in the vicinity of the capability limit point of a temperature control device such as a Peltier element because the current wavelength and the position on the etalon characteristic are clear.

  In addition, when obtaining the current wavelength from the table created with the characteristics of the etalon, not only the LD temperature and wavelength detection PD current but also (Δ wavelength detection PD current / ΔLD temperature) was obtained from the table data. Alternatively, since the control accuracy of the wavelength is increased by collating it with the table data (Δ wavelength detection PD current / ΔLD temperature), the temperature (wavelength) can be seen from points a and b in FIG. When the change is small and Vpd2 / Vpd1 is equal, even if it is difficult to confirm the wavelength, the accuracy of wavelength confirmation can be increased by determining the slope (Δ wavelength detection PD electric energy value / ΔLD temperature).

  Also, ΔLD temperature / Δtime is measured with respect to the amount of current flowing to the Peltier element, and if the time change in temperature falls below the reference value, it is determined that it is close to the limit point of temperature control. Since it is determined that it takes a long time to stabilize, the information is sent to the outside as an alarm. By notifying the outside that it takes more time than usual to stabilize the wavelength, it is not possible to control the wavelength in the past due to overtime. It is possible to control what has been determined to be, and the usable wavelength region can be increased.

It is the block diagram which showed the structure of the optical module and microcomputer part of the wavelength stabilization apparatus at the time of the wavelength control which concerns on Embodiment 1 of this invention. It is the block diagram which showed the whole structure of the adjustment stage in the wavelength stabilization apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which showed the etalon characteristic of the wavelength stabilizer which concerns on Embodiment 1 of this invention. It is the flowchart which showed the flow of the process of wavelength control of the wavelength stabilizer which concerns on Embodiment 1 of this invention. It is the flowchart which showed the flow of the process of wavelength control of the wavelength stabilizer which concerns on Embodiment 1 of this invention.

Explanation of symbols

  100 optical module, 101 LD, 102 Peltier element, 103 etalon filter, 104 PD1, 105 PD2, 106 AD converter, 107 CPU, 108 DA converter, 109 thermistor, 110 Peltier drive circuit, 111 PD1 current voltage conversion circuit, 112 PD2 current Voltage conversion circuit, 113 Temperature voltage conversion circuit, 114 Optical fiber, 115 Optical splitter, 120 Microcomputer part, 201 Optical wavelength measuring device, 202 Personal computer.

Claims (3)

A semiconductor laser diode capable of changing the wavelength of the laser beam emitted by the temperature;
LD temperature adjusting means for controlling the temperature of the semiconductor laser diode;
Driving means for driving and controlling the LD temperature adjusting means;
LD temperature detection means for detecting the temperature of the semiconductor laser diode;
A first photodiode for detecting the amount of laser light emitted from the semiconductor laser diode as a first PD current;
A second photodiode for detecting, as a second PD current, the laser light that has passed through an etalon filter to detect the wavelength of the laser light of the semiconductor laser diode;
The measurement data obtained by measuring the temperature and wavelength of the semiconductor laser diode and the first and second PD currents while changing the wavelength of the laser beam by changing the temperature of the semiconductor laser diode is tabulated as a target value. Memory to store in advance,
Wavelength calculating means for calculating the wavelength of the laser beam by dividing the second PD current into a voltage with the first PD current and then dividing the voltage;
Control means for outputting a control signal to the driving means so that the temperature obtained by the LD temperature detecting means and the wavelength obtained by the wavelength calculating means approach the target wavelength and the target temperature in the memory, respectively.
The wavelength stabilizing device, wherein the control means gradually controls the temperature as the change rate of the wavelength obtained by the wavelength calculating means with respect to a temperature change increases. A wavelength change amount calculating means for obtaining a wavelength change amount obtained by subtracting the wavelength obtained by the wavelength calculating means this time from the wavelength obtained by the wavelength calculating means during the previous control;
A temperature change amount calculating means for obtaining a temperature conversion amount obtained by subtracting the temperature obtained by the current LD temperature detecting means from the temperature obtained by the LD temperature detecting means during the previous control;
A value obtained by dividing the wavelength change amount by the temperature change amount is obtained, and the positive / negative (increase / decrease) of the slope of the change in the wavelength change amount with respect to the temperature change amount is obtained based on the measurement data stored in the memory. The wavelength stabilization apparatus according to claim 1, further comprising: an inclination confirmation unit that outputs to the control unit.   The apparatus further comprises warning output means for outputting a warning notifying that the wavelength control time is longer than normal when the temperature change amount obtained by the temperature change amount calculation means is not more than a predetermined reference value. The wavelength stabilization device according to claim 2.

Images