JP2008053966A - Optical transceiver module, optical loop-back module, and method of adjusting wavelength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transceiver module which simply adjusts the light emission wavelength of a laser diode which is provided to a compact optical transceiver module that is to be used for WDM communication, and to provide an optical loop-back module and a method of adjusting the wavelength. <P>SOLUTION: In order to adjust the light emission wavelength of the laser diode 21 for the optical transceiver module 1 for the WDM communication, an optical filter 51 having a band-pass characteristics, corresponding to a wavelength grid for the WDM communication, is provided outside of the optical transceiver module 1, to optically connect the laser diode 21 and a photodiode 31 with each other, via the optical filter 51. Then, while the temperature T<SB>LD</SB>of the laser diode 21 is varied, a light intensity signal S7 is obtained from the photodiode 31; and by obtaining the temperature T<SB>LD</SB>of the laser diode 21 when light intensity indicated by the light intensity signal S7 becomes a maximum, the setting temperature (operating temperature) of the laser diode 21 is decided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transceiver module, an optical loopback module, and a wavelength adjustment method.

  In an optical communication system using a wavelength division multiplexing (WDM) system, a plurality of communication channels communicate with optical signals having different wavelengths on the same optical transmission line. Therefore, it is desirable for the optical transceiver module used for WDM communication that the wavelength of the optical signal does not fluctuate excessively due to secular change or the like. This is because if the wavelength of the optical signal fluctuates excessively, the optical signals of adjacent wavelengths will interfere with each other. For this reason, various methods for maintaining the wavelength of the optical signal at a predetermined value have been devised.

  For example, the wavelength division multiplexing communication apparatus disclosed in Patent Document 1 includes an acousto-optic tunable bandpass filter (AOTF). In this apparatus, the optical signal output from the laser diode is input to the AOTF, and the output signal is observed while sweeping the passband of the AOTF, and the passband of the AOTF when the output signal becomes maximum is specified in advance. The light emission wavelength of the laser diode is controlled so as to be the value set. The laser module disclosed in Patent Document 2 includes an optical filter such as an etalon. In this laser module, the wavelength of the optical signal output from the laser diode is detected using an etalon, and the wavelength of the optical signal is controlled by changing the temperature of the laser diode.

  As a conventional optical loopback connector, there is one disclosed in Patent Document 3, for example.

Japanese Patent Laid-Open No. 8-293853 JP 2001-196690 A JP 2006-039310 A

  In any of the systems described in Patent Documents 1 and 2, optical filters such as AOTF and etalon are arranged in the apparatus. For example, small optical transceiver modules such as SFP (Small Form-Factor Pluggable) Due to restrictions such as size and cost, it may be difficult to incorporate an optical filter. However, if the emission wavelength of the laser diode is not controlled, the emission wavelength may gradually shift due to aging or the like. In such a case, for example, there is a method of adjusting the emission wavelength while observing the spectrum by connecting a measuring instrument such as an optical spectrum analyzer to the transmission side port of the optical transceiver module via an optical connector and an optical fiber. The method requires additional measuring equipment and takes time to adjust.

  The present invention has been made in view of the above problems, and is used with an optical transceiver module that can easily adjust the emission wavelength of a laser diode included in a small optical transceiver module used for WDM communication, and the optical transceiver module. An object of the present invention is to provide an optical loopback module and a wavelength adjustment method.

  In order to solve the above-described problems, an optical transceiver module according to the present invention is an optical transceiver module for wavelength division multiplexing communication that transmits and receives an optical transmission signal and an optical reception signal via an optical transmission medium, and is an electrical transmission module. A laser diode for converting a signal into an optical transmission signal, a thermoelectric conversion element for adjusting the temperature of the laser diode, and a light receiving element for converting an optical reception signal into an electrical reception signal, and further an optical transceiver When the laser diode and the light receiving element are optically coupled via an optical filter provided outside the module and having a band pass characteristic corresponding to the wavelength grid in wavelength division multiplex communication, the light receiving element is changed while changing the temperature of the laser diode. A control circuit that obtains the received signal to provide and determines the temperature of the laser diode when the received signal reaches a maximum. Characterized in that it has a.

  In this optical transceiver module, the control circuit obtains the received signal from the light receiving element while changing the temperature of the laser diode, and obtains the temperature of the laser diode when the received signal becomes maximum. This operation is useful when the optical filter is provided outside the optical transceiver module, and the laser diode and the light receiving element are optically coupled to each other via the optical filter. For example, a command signal is received from the outside of the optical transceiver module. Operates by input.

  In this optical transceiver module, the light output from the laser diode enters the optical filter. And only the component contained in the pass band of an optical filter among the wavelength components contained in this light passes an optical filter, and injects into a light receiving element. At this time, the amount of passing light increases as the emission wavelength of the laser diode is closer to the center wavelength of the optical filter. Further, the emission wavelength of the laser diode can be changed by changing the temperature of the laser diode. Therefore, by obtaining a signal from the light receiving element while changing the temperature of the laser diode, obtaining the temperature of the laser diode when the light intensity becomes maximum, and driving the laser diode with this temperature as a set temperature The emission wavelength of the laser diode can be brought close to the pass band of the optical filter, that is, the wavelength grid in wavelength division multiplexing communication.

  As described above, by including the control circuit, it is possible to suitably adjust (calibrate) the emission wavelength of the laser diode as described above even in a small optical transceiver module in which it is difficult to incorporate an optical filter. Moreover, it is only necessary to arrange an optical filter outside the optical transceiver module, and no measuring instrument such as an optical spectrum analyzer is required, so that the emission wavelength can be easily adjusted.

  An optical loopback module according to the present invention is an optical loopback module used together with the optical transceiver module, and includes an optical filter having a band pass characteristic corresponding to a wavelength grid in wavelength division multiplexing communication, and an optical filter. And an optical coupling means for optically coupling the transmitting laser diode and the receiving light receiving element of the optical transceiver module to each other. By using this optical loopback module, the emission wavelength of the laser diode in the optical transceiver module described above can be adjusted more easily.

  Further, the wavelength adjustment method according to the present invention includes a laser diode that converts an electrical transmission signal into an optical transmission signal, a thermoelectric conversion element for adjusting the temperature of the laser diode, and an optical reception signal as an electrical reception signal. A method of adjusting a light emission wavelength of a laser diode in an optical transceiver module for wavelength division multiplex communication including a light receiving element that converts the optical filter to an optical transceiver having a band pass characteristic corresponding to a wavelength grid in wavelength division multiplex communication Provided outside the module, the laser diode and the light receiving element are optically coupled to each other via the optical filter, and the signal provided by the light receiving element is acquired while changing the temperature of the laser diode, and the intensity of the signal is maximized. The set temperature is determined by determining the temperature of the laser diode at that time.

  According to this wavelength adjusting method, similarly to the optical transceiver module described above, the light emitting wavelength of the laser diode can be adjusted (calibrated) suitably even in a small optical transceiver module in which it is difficult to incorporate an optical filter. . Moreover, it is only necessary to arrange an optical filter outside the optical transceiver module, and no measuring instrument such as an optical spectrum analyzer is required, so that the emission wavelength can be easily adjusted.

  According to the optical transceiver module, the optical loopback module, and the wavelength adjusting method according to the present invention, the emission wavelength of the laser diode provided in the small optical transceiver module used for WDM communication can be easily adjusted.

  Hereinafter, embodiments of an optical transceiver module, an optical loopback module, and a wavelength adjusting method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a block diagram showing a configuration of an optical transceiver module 1 according to the present invention and a configuration of an optical loopback module 50 used together with the optical transceiver module 1.

  The optical transceiver module 1 is an optical transceiver module for WDM communication (particularly DWDM: Dense WDM) that transmits and receives an optical transmission signal including an RF signal and an optical reception signal via an optical transmission medium such as an optical fiber. When the optical transceiver module 1 performs a normal communication operation, the optical loopback module 50 is not used, and the transmission optical connector 11 and the reception optical connector 12 of the optical transceiver module 1 are respectively used for transmission and reception. Optical fiber is connected.

  The optical transceiver module 1 includes an optical transmission module 2 that generates an optical transmission signal, an optical reception module 3 that receives an optical reception signal, a control circuit 4, a bias current circuit 5, a modulation current circuit 6, an optical intensity detection circuit 7, and a limit amplifier 8. And a housing 10 for housing these components. The optical transmission module 2 includes a laser diode 21, a monitoring photodiode 22, a TEC (ThermoElectric Controller) 23, and a thermistor 24. The optical receiving module 3 includes a photodiode (light receiving element) 31 and a preamplifier 32. The control circuit 4 includes an APC (Automatic Power Control) circuit 41, an ATC (Auto Temperature Controller) circuit 42, a D / A (Digital / Analog) conversion circuit 43, an A / D (Analog / Digital) conversion circuit 44, and a central operation. A processing circuit (CPU) 45 is included.

  The laser diode 21 is a light emitting element for converting a drive current that is an electrical transmission signal into an optical transmission signal. The laser diode 21 receives a drive current including the bias current Ib and the modulation current Im, and emits laser light having an intensity corresponding to the drive current. This laser light is provided to the outside of the optical transceiver module 1 as an optical transmission signal. The bias current circuit 5 generates a steady bias current Ib and supplies the bias current Ib to the laser diode 21. The modulation current circuit 6 generates a modulation current Im based on a transmission signal Tx that is a high-frequency signal provided from the outside of the optical transceiver module 1, and supplies the modulation current Im to the laser diode 21.

  The monitoring photodiode 22 receives the laser beam generated in the laser diode 21 and converts it into an electric signal S1 such as a photocurrent, and provides the electric signal S1 to the APC circuit 41 of the control circuit 4. Based on the signal S1, the APC circuit 41 instructs the magnitude of the bias current Ib so that the emission intensity of the laser diode 21 (specifically, the signal S1 output from the monitoring photodiode 22) is constant. The signal S2 to be generated is generated. The APC circuit 41 sends this signal S2 to the bias current circuit 5. The bias current circuit 5 generates a bias current Ib having a magnitude corresponding to the signal S2. In addition, the APC circuit 41 modulates the modulation current Im so that the extinction ratio of the optical transmission signal output from the laser diode 21 (ratio between the light intensity at the H level and the light intensity at the L level) becomes a predetermined value. A signal S3 is generated that indicates the magnitude of the. The APC circuit 41 sends this signal S3 to the modulation current circuit 6. The modulation current circuit 6 generates a modulation current Im having a magnitude corresponding to the signal S3. Further, the APC circuit 41 has an operation mode for suppressing the magnitude of the modulation current Im so that the magnitude of the modulation current Im is reduced according to a signal S4 provided from the arithmetic unit 45 described later. A signal S3 is generated.

  The TEC 23 is a thermoelectric conversion element for adjusting the temperature of the laser diode 21. The TEC 23 is configured by, for example, a Peltier element or the like, and is disposed in the vicinity of the laser diode 21 (a position where the thermal resistance with the laser diode 21 is small). As a preferred form, the laser diode 21 is mounted on the TEC 23. The TEC 23 absorbs heat and generates heat according to the TEC drive current Itec supplied from the ATC circuit 42. The laser diode 21 is heated and lowered by the heat absorption and heat generation by the TEC 23. The thermistor 24 is a temperature sensing element for detecting the temperature of the laser diode 21 and is disposed in the vicinity of the laser diode 21 (or in the vicinity of the TEC 23). The thermistor 24 detects the temperature of the laser diode 21 (or the temperature of the TEC 23), and provides a signal S5 representing the detection result to the ATC circuit 42. Further, the D / A conversion circuit 43 converts the digital signal D6 output from the arithmetic unit 45 into an analog signal S6 to set the temperature of the laser diode 21, and provides the signal S6 to the ATC circuit 42. Based on the signals S5 and S6, the ATC circuit 42 generates a TEC drive current Itec so that the temperature of the laser diode 21 approaches the temperature indicated by the signal S6. The ATC circuit 42 supplies this TEC drive current Itec to the TEC 23.

  The photodiode 31 is an element for converting an optical reception signal that is a high-frequency optical signal received from the outside of the optical transceiver module 1 into an electrical reception signal such as a photocurrent Irx. The photocurrent Irx output from the photodiode 31 is converted into a voltage signal by the preamplifier 32, amplified by the limit amplifier 8, and then output to the outside of the optical transceiver module 1 as differential signals RX + and RX−. A light intensity detection circuit 7 is connected to the photodiode 31. The light intensity detection circuit 7 generates a light intensity signal S7 indicating the intensity of light incident on the photodiode 31 based on the signal (photocurrent Irx) provided from the photodiode 31. Such a light intensity detection circuit 7 is constituted by a filter circuit including, for example, a resistance element provided in series with the photodiode 31 and a capacitance element connected between one end of the resistance element and a ground potential line. The That is, the average magnitude of the photocurrent Irx can be detected by measuring the voltage drop in the resistance element. The light intensity detection circuit 7 generates a light intensity signal S7 indicating the average magnitude of the photocurrent Irx, and provides the light intensity signal S7 to the arithmetic unit 45 via the A / D conversion circuit 44.

  The arithmetic device 45 is a digital processor having a CPU, a ROM, a RAM, and the like, and controls various operations of the optical transceiver module 1 by executing various programs stored in the ROM.

  The computing device 45 of this embodiment controls the operation of the optical transceiver module 1 according to the following two operation modes. The first operation mode is a mode in which the temperature of the laser diode 21 is maintained at a set temperature (operation temperature), and is set when the optical transceiver module 1 performs a normal communication operation. In this operation mode, the arithmetic unit 45 outputs a signal D6 corresponding to the set temperature. Thereby, the ATC circuit 42 generates the TEC drive current Itec so that the temperature of the laser diode 21 approaches the temperature indicated by the signal S6.

  The second operation mode is an operation mode for adjusting (calibrating) the emission wavelength of the laser diode 21 and determines a set temperature at which the emission wavelength becomes a predetermined wavelength. In this operation mode, as shown in FIG. 1, an optical loopback module 50 including an optical filter 51 is provided in advance outside the optical transceiver module 1 and is connected between the transmission optical connector 11 and the reception optical connector 12. Is done. The optical filter 51 has a band pass characteristic with the highest transmittance in the wavelength grid of the WDM communication (for example, the wavelength grid in the DWDM communication is set at an interval of 0.8 nm). For example, the multilayer filter It is suitably realized by a spectroscope such as.

  The optical loopback module 50 further includes optical fibers 52 and 53 as optical coupling means for optically coupling the laser diode 21 and the photodiode 31 to each other via the optical filter 51. One end of the optical fiber 52 is detachably connected to the transmission optical connector 11, and the other end is optically coupled to the light incident surface of the optical filter 51. One end of the optical fiber 53 is detachably connected to the receiving optical connector 12, and the other end is optically coupled to the light emitting surface of the optical filter 51. The optical coupling means for optically coupling the laser diode 21 and the photodiode 31 to each other includes, for example, an optical input terminal corresponding to the transmission optical connector 11 and an optical output terminal corresponding to the reception optical connector 12 (these terminals). Is optically coupled through the optical filter 51).

  In this second operation mode, the arithmetic unit 45 gradually changes the signal D6 to change the temperature of the laser diode 21 and changes the light intensity signal S7 from the light intensity detection circuit 7 to the A / D conversion circuit 44. To get through. Then, the arithmetic unit 45 stores the temperature of the laser diode 21 when the light intensity signal S7 becomes maximum (that is, when the intensity of light incident on the photodiode 31 becomes maximum) as the set temperature described above.

Here, the reason why the emission wavelength of the laser diode 21 is adjusted (calibrated) by determining the set temperature as described above will be described. FIG. 2A is a graph (G1) schematically showing a light emission wavelength-light intensity characteristic of a laser diode. As shown in FIG. 2A, the emission intensity of the laser diode has a finite width distribution having a peak at the emission wavelength λ _LD . Since the emission wavelength λ _LD of the laser diode 21 depends on the temperature of the laser diode 21, when the temperature of the laser diode 21 is continuously changed, the emission wavelength λ _LD also changes continuously. In the optical transceiver module of the present embodiment, the APC circuit 41 controls the light emission intensity to be constant even when the temperature of the laser diode 21 changes.

FIG. 2B is a graph (G2) schematically showing the wavelength transmission characteristics of a band pass filter used as the optical filter 51. FIG. As shown in FIG. 2 (b), the transmittance of the band-pass filter is also a distribution of finite width having a peak at the center wavelength lambda _FT. Therefore, the intensity of the light that has passed through the optical filter 51 is equivalent to the area of the overlapping portion (region A in the drawing) of the graph G1 and the graph G2, as shown in FIG. When the emission wavelength λ _LD of the laser diode 21 changes and the emission wavelength λ _LD and the center wavelength λ _FT of the optical filter 51 approach each other, the area of the region A increases as shown in FIG. That is, the intensity of light passing through the optical filter 51 is increased.

Therefore, the intensity of the light that has passed through the optical filter 51 is maximized at the grid wavelength (= center wavelength λ _FT ) of the WDM communication system. That is, as shown in FIG. 4, when the temperature of the laser diode 21 reaches a temperature T _LD corresponding to the wavelength λ _FT , the intensity of light incident on the photodiode 31 is maximized. Therefore, in the second operation mode, the temperature of the laser diode 21 when the temperature of the light incident on the photodiode 31 (that is, the light intensity signal S7) is maximized while continuously changing the temperature of the laser diode 21 is increased. By setting the temperature to the set temperature, the emission wavelength of the laser diode 21 can be calibrated.

  Note that the temperature characteristic of the optical filter 51 is negligibly small compared to the temperature characteristic of the laser diode 21. Moreover, since the optical filter 51 is installed outside the optical transceiver module 1, the ambient temperature of the optical filter 51 is a so-called room temperature, and the temperature change itself is small. Therefore, in the wavelength adjustment by the above method, the fluctuation of the band pass characteristic of the optical filter 51 may be ignored.

  Next, a specific operation of the optical transceiver module 1 in the second operation mode will be described with reference to FIG. 5 together with the wavelength adjustment method according to the present embodiment. FIG. 5 is a flowchart showing the wavelength adjustment method according to this embodiment including the operation of the optical transceiver module 1.

  First, the optical filter 51 is provided outside the optical transceiver module 1, and the laser diode 21 and the photodiode 31 are optically coupled to each other via the optical filter 51 (step Sa). In the case of the form shown in FIG. 1, one end of the optical fiber 52 of the optical loopback module 50 is connected to the transmission optical connector 11, and one end of the optical fiber 53 is connected to the reception optical connector 12.

Next, an instruction signal S8 (see FIG. 1) indicating the start of wavelength calibration is input from the outside of the optical transceiver module 1 to the arithmetic unit 45. At this time, the instruction signal S8 may be input to the arithmetic unit 45 through a communication line in accordance with a protocol such as I2C. In the case of an optical transceiver module such as SFF, SFP, or XFP, communication with an external device is possible according to the I2C protocol, and other types of optical transceiver modules also comply with proprietary standards and other general standards. Therefore, the external device can access an arithmetic device (controller, memory, etc.) inside the optical transceiver module. Upon receiving this instruction signal S8, the arithmetic unit 45 sets the temperature T _LD of the laser diode 21 as the sweep start temperature Tmin. That is, the arithmetic unit 45 generates a signal D6 corresponding to the sweep start temperature Tmin, and sends this signal D6 to the ATC circuit 42 via the D / A conversion circuit 43. Thereby, the temperature T _LD of the laser diode 21 is controlled to the sweep start temperature Tmin by the ATC circuit 42 and the TEC 23. In addition, the arithmetic unit 45 initializes variables T _λ and P _λ used for the subsequent arithmetic operations (step Sb).

  Note that, in the memory in the control circuit 4 (in this embodiment, the memory included in the arithmetic unit 45; a memory associated with the controller, a memory built in the CPU, or the like), the sweep start temperature Tmin and the sweep end temperature Tmax are previously stored. The sweep width ΔT is stored. The stored value may be the temperature value itself, the resistance value of the thermistor 24 at that temperature, or a value obtained by standardizing this resistance value.

  Further, the light emission intensity of the laser diode 21 is stabilized by the APC circuit 41. At this time, the signal S4 is provided from the arithmetic unit 45 to the APC circuit 41, and the APC circuit 41 suppresses the magnitude of the modulation current Im from that during the normal communication operation. Further, a calibration transmission signal Tx is input from the outside of the optical transceiver module 1, and the APC circuit 41 generates a modulation current Im in accordance with the transmission signal Tx. Note that a pulse signal having a duty ratio of 50% may be used as the calibration transmission signal Tx. The APC circuit 41 stabilizes the magnitude of the bias current Ib in the vicinity of the threshold current value of the laser diode 21 even when the temperature of the laser diode 21 changes.

  The reason for suppressing the magnitude of the modulation current Im from the normal communication operation is as follows. In the normal communication operation, the signal light attenuated during propagation through the optical fiber is input to the optical receiving module 3, whereas the laser diode 21 and the photodiode 31 are optically coupled to each other via the optical filter 51. Then, the light included in the pass band of the optical filter 51 reaches the light receiving module 3 with almost no attenuation. Accordingly, by reducing the magnitude of the modulation current Im as compared with the normal communication operation as in the present method, it is possible to prevent the light receiving module 3 from entering light having an excessive intensity. As another method for suppressing the intensity of incident light to the optical receiving module 3, for example, there is a method of adjusting the light transmittance in the pass band of the optical filter 51.

Subsequently, the arithmetic unit 45 repeats the following steps Sc to Sf until the temperature T _LD of the laser diode 21 exceeds the sweep end temperature Tmax. First, the intensity P of light incident on the photodiode 31 is detected. That is, the arithmetic unit 45 acquires the light intensity signal S7 corresponding to the light intensity P via the A / D conversion circuit 44 (step Sc). Then, the detected light intensity P is compared with the variable P _λ (step Sd). When the light intensity P is larger than the variable P _λ , the light intensity P is stored in the variable P _λ and The laser diode temperature T _{LD at} that time is stored in the variable T _λ (step Se). Note that when the light intensity P is less than the variable P _lambda proceeds to the next step Sf without this step Se. Then, the arithmetic unit 45 changes the signal D6 so that the temperature T _LD of the laser diode 21 is increased by the sweep width ΔT regardless of the magnitude of the light intensity P and the variable P _λ, and this signal D6 is changed to the ATC circuit. Send to 42. The temperature T _LD is increased by ΔT by the ATC circuit 42 and the TEC 23 (step Sf).

When the temperature T _LD of the laser diode 21 reaches the sweep end temperature Tmax, the arithmetic unit 45 determines the value stored as the variable T _{λ at} this time as the set temperature of the laser diode 21 and stores the memory in the control circuit 4. (Step Sg). During normal communication operation, the laser diode temperature T _LD is controlled to the set temperature determined in this way. Thereby, the emission wavelength λ _LD of the laser diode 21 can be brought close to the pass band of the optical filter 51, that is, the wavelength grid in WDM communication. The bias current Ib and the modulation current Im are controlled by the APC circuit 41 so that the light emission intensity of the laser diode 21 approaches a predetermined value after the laser diode temperature T _LD is stabilized at the set temperature.

  The effects obtained by the optical transceiver module 1 and the wavelength adjustment method of the present embodiment described above will be described. It is difficult in terms of size and cost to mount a wavelength stabilization function as described in Patent Documents 1 and 2 on a small-sized and low-cost optical transceiver module such as SFP. However, if the emission wavelength of the laser diode is not adjusted, the emission wavelength will fluctuate due to aging of the laser diode and thermistor (the actual temperature of the laser diode deviates from the set temperature due to fluctuations in thermistor characteristics). This is not preferable. In addition, as a wavelength adjustment method at the time of manufacturing an optical transceiver module, an adjustment method using a wavelength meter is generally used. However, measuring equipment capable of measuring wavelengths in picometer units is expensive, so that the cost of capital investment or manufacturing capability is considered. It can be a bottleneck during mass production. Therefore, the present inventor has devised a configuration that can automatically calibrate the emission wavelength by using the optical filter 51 having band pass characteristics corresponding to the wavelength grid of WDM communication.

That is, according to the optical transceiver module 1 and wavelength adjustment method of this embodiment, the optical coupling together the laser diode 21 and the photodiode 31 via the optical filter 51, the light intensity signal S7 while changing the laser diode temperature T _LD And obtaining the laser diode temperature T _LD when the light intensity P to the photodiode 31 becomes maximum, the light emission of the laser diode 21 even in a small optical transceiver module in which it is difficult to incorporate an optical filter. Wavelength adjustment (calibration) can be suitably performed. Moreover, it is only necessary to arrange the optical filter 51 outside the optical transceiver module 1, and no measuring device such as an optical spectrum analyzer is required, so that the emission wavelength of the laser diode 21 can be easily adjusted. And long-term stability of the light emission wavelength can be ensured by periodically calibrating the light emission wavelength in the second operation mode.

In the optical transceiver module 1 and the wavelength adjustment method of the present embodiment, the wavelength (center wavelength λ _FT ) at which the transmittance of the optical filter 51 is maximized accurately matches the wavelength grid of the WDM communication. This is preferable, but can be realized with much higher accuracy than the wavelength control of the laser diode 21. That is, it is easy to accurately form the thickness of each layer in the multilayer filter used as the optical filter 51 to obtain an extremely narrow bandpass filter.

  The optical transceiver module, the optical loopback module, and the wavelength adjusting method according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment, the optical loopback module 50 coupled to the optical transceiver module 1 by the optical fibers 52 and 53 is used. However, the optical loopback module may have a form of an optical loopback connector. In other words, the optical loopback module includes a pair of optical connectors that incorporate an optical filter and fits with each of the transmission optical connector 11 and the reception optical connector 12 of the optical transceiver module 1, and between the pair of optical connectors. You may provide the structure provided with the optical filter. In the present invention, wavelength calibration, which has been conventionally performed using a measuring instrument such as an optical spectrum analyzer, is diverted to the optical reception function of the optical transceiver module itself, and a laser diode as in the method described in Patent Document 1 is used. Rather than scanning the emission wavelength and observing the maximum intensity wavelength every time the temperature is changed, the overlapping part of the bandpass characteristic of the optical filter and the emission wavelength (region A in FIGS. 3A and 3B) Focusing on the area (integrated value), the characteristic is that the temperature at which the maximum value is obtained is set as the set temperature of the laser diode. The wavelength adjusting method according to the present invention is not limited to when the optical transceiver module is used, but can also be used at the time of shipment.

FIG. 1 is a block diagram showing a configuration of an optical transceiver module according to the present invention and a configuration of an optical loopback module used together with the optical transceiver module. FIG. 2A is a graph showing the emission wavelength-light intensity characteristics of a laser diode. FIG. 2B is a graph showing the wavelength transmission characteristics of a band-pass filter used as an optical filter. FIGS. 3A and 3B are diagrams showing the emission wavelength-light intensity characteristic of the laser diode and the wavelength transmission characteristic of the band-pass filter in an overlapping manner. FIG. 4 is a graph showing the correlation between the temperature of the laser diode and the intensity of light incident on the photodiode. FIG. 5 is a flowchart showing a wavelength adjustment method including the operation of the optical transceiver module.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical transceiver module, 2 ... Optical transmission module, 3 ... Optical reception module, 4 ... Control circuit, 5 ... Bias current circuit, 6 ... Modulation current circuit, 7 ... Light intensity detection circuit, 8 ... Limit amplifier, 10 ... Housing 11, optical connector for transmission, 12, optical connector for reception, 21, laser diode, 22, photodiode for monitoring, 23 TEC, 24, thermistor, 31, photodiode, 32, preamplifier, 41, APC circuit, 42 ... ATC circuit, 43 ... D / A conversion circuit, 44 ... A / D conversion circuit, 45 ... arithmetic unit, 50 ... optical loopback module, 51 ... optical filter, 52, 53 ... optical fiber, Ib ... bias current, Im: Modulation current, Irx: Photocurrent.

Claims (3)

An optical transceiver module for wavelength division multiplexing communication that transmits and receives an optical transmission signal and an optical reception signal via an optical transmission medium,
A laser diode for converting an electrical transmission signal into the optical transmission signal;
A thermoelectric conversion element for adjusting the temperature of the laser diode;
A light receiving element that converts the optical reception signal into an electrical reception signal, and
Further, when the laser diode and the light receiving element are optically coupled via an optical filter provided outside the optical transceiver module and having a band pass characteristic corresponding to a wavelength grid in the wavelength division multiplex communication, the laser diode An optical transceiver module, comprising: a control circuit that obtains a reception signal provided by the light receiving element while changing a temperature of the laser diode and obtains a temperature of the laser diode when the reception signal reaches a maximum. An optical loopback module for use with the optical transceiver module of claim 1, comprising:
An optical filter having bandpass characteristics according to a wavelength grid in wavelength division multiplex communication;
An optical loopback module comprising: an optical coupling means for optically coupling the transmitting laser diode and the receiving light receiving element of the optical transceiver module to each other through the optical filter. Wavelength division multiplexing including a laser diode that converts an electrical transmission signal into an optical transmission signal, a thermoelectric conversion element for adjusting the temperature of the laser diode, and a light receiving element that converts an optical reception signal into an electrical reception signal A method for adjusting an emission wavelength of the laser diode in an optical transceiver module for communication,
An optical filter having a band pass characteristic corresponding to a wavelength grid in the wavelength division multiplex communication is provided outside the optical transceiver module, and the laser diode and the light receiving element are optically coupled to each other through the optical filter, and the laser diode Obtaining the signal provided by the light receiving element while changing the temperature of the laser, and determining the set temperature by determining the temperature of the laser diode when the intensity of the signal is maximized. Adjustment method.

Images