JP6803158B2 - Optical module test method - Google Patents

Description

The present invention relates to a test method for an optical module used in an optical communication system.

In the field of optical communication, an optical module is used in which a received optical signal is separated into light having a plurality of wavelengths and input to a plurality of light receiving units. For example, in the light receiving device described in Patent Document 1 below, the received optical signal is wavelength-separated using a wavelength separation filter, and a plurality of wavelength-separated lights are coupled to the light receiving unit using a lens array. Further, the optical transmission / reception module described in Patent Document 2 below incorporates an integrated optical combiner / demultiplexer to combine and transmit light of a plurality of wavelengths, and demultiplexes the combined light of a plurality of wavelengths. And receive.

JP-A-2010-160218 JP-A-2009-105106

Generally, in the optical modules described in Patent Documents 1 and 2 described above, an operation confirmation test is performed by inputting test light for each of a plurality of wavelengths included in the received optical signal. Therefore, it is necessary to prepare a light source capable of irradiating light having a plurality of wavelengths, which complicates the configuration of the test equipment. In addition, it is necessary to evaluate the characteristics of the light receiving unit corresponding to each input of test light having a plurality of wavelengths, which increases the test process.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a test method for an optical module whose operation can be confirmed with a small number of man-hours without complicating the configuration of test equipment. ..

In order to solve the above problems, the test method of the optical module according to one aspect of the present invention divides the signal light into a plurality of light receiving elements for converting the signal light into an electric signal and the input signal light into signal light having a plurality of wavelength bands. This is a test method for an optical module including a filter element for injecting signal light in a plurality of wavelength bands into each of a plurality of light receiving elements, in which test light in a wavelength band different from the plurality of wavelength bands is incident on the filter element. Each electric signal output from a plurality of light receiving elements is acquired according to the input of the test light, and the conversion characteristic value for each of the plurality of light receiving elements is acquired based on each electric signal.

According to one aspect of the present invention, the operation can be confirmed with a small number of man-hours without complicating the configuration of the test equipment.

It is sectional drawing of the optical receiving module 10 which is the object of the test method which concerns on embodiment of this invention, seen from the side. It is a top view for demonstrating the schematic structure and the function | function of the optical demultiplexer 31 of FIG. It is a schematic block diagram which shows the connection structure of the light receiving element 34 of FIG. 1 and the preamplifier circuit 35. It is a figure which shows the structure of the test system for carrying out the test method of the optical module of this embodiment. It is a flowchart which shows the procedure of the test method of the optical module of this embodiment.

The method for testing an optical module according to one aspect of the present invention includes a plurality of light receiving elements that convert signal light into an electric signal, and signal light having a plurality of wavelength bands by branching the input signal light into signal light having a plurality of wavelength bands. This is a test method for an optical module including a filter element for incidenting on each of a plurality of light receiving elements, in which test light having a wavelength band different from that of the plurality of wavelength bands is incident on the filter element according to the input of the test light. Each electric signal output from a plurality of light receiving elements is acquired, and a conversion characteristic value for each of the plurality of light receiving elements is acquired based on each electric signal.

According to the test method of such an optical module, electric signals from a plurality of light receiving elements are acquired using test light having a wavelength band different from that of the plurality of wavelength components contained in the input signal light, and based on these electric signals. The conversion characteristic values of a plurality of light receiving elements are acquired. This eliminates the need to evaluate the characteristics of each test light in a plurality of wavelength bands, so that it is possible to confirm the operation of a plurality of light receiving elements with a small number of man-hours without complicating the configuration of the test equipment.

In the above-mentioned optical module test method, a filter element that incidents signal light in the wavelength band of 1300 nm on a plurality of light receiving elements may be used, and light in the 1550 nm band may be incident on the filter element as test light. In this case, the test light can be efficiently incident on a plurality of light receiving elements via the filter element. As a result, it is possible to efficiently evaluate the characteristics of the plurality of light receiving elements.

Further, the transimpedance gain may be acquired as the conversion characteristic value. By doing so, it is possible to realize the characteristic evaluation including the plurality of light receiving elements and the circuit unit connected to the subsequent stage thereof at one time.

Further, as the test light, light having a wavelength band having a central wavelength separated from the central wavelengths of a plurality of wavelength bands by 200 nm or more may be incident. In this case, the test light can be more efficiently incident on the plurality of light receiving elements via the filter element.

Hereinafter, embodiments of the optical module test method according to one aspect of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.
(Optical module configuration)

First, the configuration of the optical module that is the target of this embodiment will be described.

FIG. 1 is a cross-sectional view of the optical receiving module 10 as viewed from the side. The optical receiving module 10 includes a receptacle portion 11 to which an optical fiber is connected, a package portion 12 in which an optical component such as a light receiving element is housed, and a terminal portion 13 for electrical connection with an external circuit. It is composed. The package portion 12 is formed of a metal material having high thermal conductivity in a rectangular box shape, and is configured by mounting optical components such as a light receiving element, which will be described later, in a sealed state. The terminal portion 13 is formed, for example, by laminating a plurality of ceramic substrates, is provided in a state of being fitted to the end portion of the package housing 20 of the package portion 12, and is provided at the opposite end portion of the package housing 20. Is formed with electrodes for electrical connection with the outside.

The positioning block 40 is fixed inside the package portion 12. An optical demultiplexer (filter element) 31 that branches the input signal light incident on the package portion 12 from the optical fiber via the receptacle portion 11 into a plurality of signal lights having different wavelength bands in the positioning block 40. A reflector 32 formed of a prism or the like that reflects the plurality of branched signal lights (hereinafter referred to as “demultiplexed signal light”) and a plurality of demultiplexed signal lights reflected by the reflector 32 are not shown. A light receiving element 34 such as a photodiode that receives light through the lens is mounted. The number of branches of the signal light by the optical demultiplexer 31 and the number of light receiving elements 34 are not limited to a specific number, but are four in the present embodiment. Further, inside the package portion 12, a preamplifier circuit 35 is housed adjacent to a plurality of light receiving elements 34. The preamplifier circuit 35 is electrically connected to a plurality of light receiving elements 34 and terminal portions 13, converts current signals (electrical signals) output from the respective light receiving elements 34 into voltage signals, and passes through the terminal portions 13. Output to the outside.

FIG. 2 is a plan view for explaining a schematic configuration of the optical demultiplexer 31 and its function. The optical demultiplexer 31 shown in FIG. 2 is a demultiplexing signal light having four wavelength bands with respect to four photodiodes (hereinafter, referred to as “PD”) 34a, 34b, 34c, and 34d, which are light receiving elements 34. Has the function of branching and incident. Specifically, the optical demultiplexer 31 emits a mirror 42 arranged along the incident surface 41 of the input signal light L ₁ and four demultiplexing signal lights L _2a , L _2b , L _2c , and L _2d . It is configured to include four bandpass filters 44a, 44b, 44c, 44d arranged along the surface 43.

Bandpass filter 44a is disposed on the incident light path of the input signal light L _1, the output from the exit surface 43 by transmitting first demultiplexed signal light L _2a in the wavelength band lambda ₁ of the input signal light L ₁ Then, the signal light L _1a of a component other than the _first wavelength band λ ₁ of the input signal light L ₁ is reflected toward the mirror 42 on the incident surface 41. The band pass filter 44b is arranged on the optical path of the signal light L _1a reflected by the mirror 42, and transmits the demultiplexed signal light L _2b of the second wavelength band λ ₂ of the signal light L _1a to the exit surface. 43 is output from, and reflects toward the second wavelength band lambda ₂ other than the component of the signal light L _1b of the signal light L _1a to the mirror 42 on the incident surface 41. The band pass filter 44c is arranged on the optical path of the signal light L _1b reflected by the mirror 42, and transmits the demultiplexed signal light L _2c of the third wavelength band λ ₃ of the signal light L _1b to the exit surface. 43 is output from, is reflected toward the third wavelength band lambda ₃ other components of the signal light L _1c of the signal light L _1b to the mirror 42 on the incident surface 41. The bandpass filter 44d is arranged on the optical path of the signal light L _1c reflected by the mirror 42, and transmits the demultiplexed signal light L _2d of the fourth wavelength band λ ₄ of the signal light L _1c to the exit surface. Output from 43. The demultiplexing signal lights L _2a , L _2b , L _2c , and L _2d transmitted through the bandpass filters 44a, 44b, 44c, and 44d are sent to PD34a, 34b, 34c, and 34d via the reflector 32 and a lens (not shown, respectively). Incident.

The demultiplexing signal lights L _2a , L _2b , L _2c , and L _2d branched from the input signal light L ₁ by the optical demultiplexer 31 having the above configuration are received by PD34a, 34b, 34c, and 34d, respectively, and are current signals. Converted to (electric signal). Here, the characteristic values relating to the branchable wavelength bands λ ₁ , λ ₂ , λ ₃ , and λ ₄ in the optical demultiplexer 31, and the light-receiving wavelength bands λ ₁ , λ ₂ , and λ in the PD 34a, 34b, 34c, and 34d. _{3. The} characteristic values related to λ ₄ can be set to various values depending on the wavelength band used for optical communication. For example, it is set to a wavelength band of 1550 nm for a backbone optical communication network connecting cities, and is set to a wavelength band of 1300 nm for a branch line optical communication network branched from this backbone system. There are two standards for branch line optical communication networks, LAN-WDM (Wavelength Division Multiplexing) and CWDM (Coarse Wavelength Division Multiplexing), and the wavelength bands λ ₁ , λ ₂ , λ according to these standards. _The characteristic values related to ₃ and λ ₄ are set. For example, in accordance with the LAN-WDM standard, the wavelength band λ ₁ is set to include the range of 1294.53 nm to 1296.59 nm, and the wavelength band λ ₂ is set to include the range of 1290.02 nm to 1301.09 nm. The wavelength band λ ₃ is set to include the range of 1303.54 nm to 1305.63 nm, and the wavelength band λ ₄ is set to include the range of 1308.09 nm to 1310.19 nm. In the case of a configuration corresponding to the CWDM standard, the wavelength band λ ₁ is set to include the range of 1264.5 nm to 1277.5 nm, and the wavelength band λ ₂ is set to include the range of 1284.5 nm to 1297.5 nm. Band λ ₃ is set to include the range 1304.5 nm to 1317.5 nm, and wavelength band λ ₄ is set to include the range 1324.5 nm to 1337.5 nm.

FIG. 3 is a schematic configuration diagram showing a connection configuration between PD34a, 34b, 34c, 34d and the preamplifier circuit 35. The preamplifier circuit 35 contains four trans-impedance amplifier (TIA) circuits 45a, 45b, 45c, 45d corresponding to PD34a, 34b, 34c, 34d. In the TIA circuits 45a, 45b, 45c, 45d, the respective input terminals are electrically connected to the anodes of the PD34a, 34b, 34c, 34d, and the respective output terminals are connected to the terminal portion 13, and the external output terminals 46a, 46b. , 46c, 46d are electrically connected. Further, the cathodes of the PDs 34a, 34b, 34c, and 34d are electrically connected to the power supply terminals 47a, 47b, 47c, and 47d connected to the terminal portion 13 via the preamplifier circuit 35.

With such a configuration, in each of the PD34a, 34b, 34c, and 34d, the power supply voltage is supplied from the outside to the power supply terminals 47a, 47b, 47c, and 47d via the terminal portion 13, so that the power supply voltage is supplied between the anode and the cathode. A reverse bias is applied to. Further, in each of the TIA circuits 45a, 45b, 45c and 45d, the current signals generated in response to the light reception of the demultiplexing signal lights L _2a , L _2b , L _2c and L _{2d in} the PD 34a, 34b, 34c and 34d are input. By doing so, the current signal is converted into a voltage signal and output to the outside via the external output terminals 46a, 46b, 46c, 46d and the terminal portion 13.
(Test method for optical module)

Next, the details of the test method of the optical module according to the present embodiment will be described. FIG. 4 shows the configuration of a test system for carrying out the test method for the optical module of the present embodiment. The test system 60 includes a light source device 61, a voltage measuring device 62, and a power supply device 63. The light source device 61 is a device that injects test light into the light receiving module 10 via an optical fiber (not shown). The wavelength band of the test light generated by the light source device 61 is a wavelength band different from the wavelength bands λ ₁ , λ ₂ , λ ₃ , and λ ₄ included in the input signal light used in the light receiving module 10, for example. , Wavelength band It is preferable to set the wavelength band of the central wavelength 200 nm or more away from the central wavelengths of λ ₁ , λ ₂ , λ ₃ , and λ ₄ . More specifically, when the wavelength bands λ ₁ , λ ₂ , λ ₃ , and λ ₄ are the 1300 nm band corresponding to the LAN-WDM and CWDM standards, the wavelength band of the test light is the 1550 nm band. For example, a wavelength band of 1530 to 1570 nm is used. The voltage measuring device 62 is connected to the TIA circuits 45a, 45b, 45c, 45d of the preamplifier circuit 35 via the terminal portion 13 (FIG. 1) of the optical receiving module 10, and the test light is transmitted from the TIA circuits 45a, 45b, 45c, 45d. It is a device for measuring the voltage signal output according to the incident of. The power supply device 63 is a device for supplying a reverse bias voltage to PD34a, 34b, 34c, 34d in the optical receiving module 10 via the terminal portion 13, and is a cathode-anode of each of PD34a, 34b, 34c, 34d. The current flowing between them is also measurable.

Hereinafter, the test method of the optical receiving module 10 using the above test system 60 will be described in detail. FIG. 5 is a flowchart showing the procedure of the test method of the optical receiving module 10.

First, the optical receiving module used as the test reference was incorporated into the test system 60, and the test light was incident and output from the TIA circuits 45a, 45b, 45c, 45d under the same conditions as when the optical receiving module 10 to be tested was tested. The voltage signal is measured and the output currents of PD34a, 34b, 34c, and 34d are measured. As a result, in a computer such as a computer device, the data of the following reference values for each of PD34a, 34b, 34c, and 34d is acquired and stored (step S01).
RL: Load resistance [Ω] for each TIA circuit 45a, 45b, 45c, 45d,
Vref: Gain of output voltage for each TIA circuit 45a, 45b, 45c, 45d [dBm],
Iref: Input current [mA] for each TIA circuit 45a, 45b, 45c, 45d
The input current Iref can be measured as the output current of PD34a, 34b, 34c, 34d, and the load resistance RL can be determined from the output voltage of the TIA circuit and the input current Iref. For example, the output voltage Vref when the input current Iref is 100 μA can be measured, and the load resistance RL can be calculated.

Next, the optical receiving module 10 to be tested is incorporated into the test system 60 (step S02). Further, the test light is started to be incident on the optical duplexer 31 in the optical receiving module 10 from the test system 60. Then, the values of the voltage signals output from each of the TIA 45a, 45b, 45c, and 45d of the optical receiving module 10 and the values of the output currents of the PD 34a, 34b, 34c, and 34d are acquired according to the incident of the test light. (Step S03).

Then, using a computer, the conversion characteristic value Zt for each PD34a, 34b, 34c, 34d is acquired by the following formula based on the measured voltage signal, output current, and stored reference value (step S04). ..
Zt = RL x 10 ^{(Vout-Vref) / 20} x Iref / IR
Here, IR is an input current [mA] for each TIA circuit 45a, 45b, 45c, 45d determined by the output current of PD34a, 34b, 34c, 34d, and Vout is every TIA circuit 45a, 45b, 45c, 45d. Is the gain [dBm] of the output voltage of. According to this equation, the transimpedance gain, which is the conversion gain from the input current to the output voltage in the TIA circuit, is acquired as the conversion characteristic value Zt. Finally, the acquired data of the conversion characteristic value Zt for each of PD34a, 34b, 34c, 34d is stored in the computer (step S05).

According to the test method of the optical module described above, the _four PD34a, 34b, using the test light having a wavelength band different from the four wavelength bands λ ₁ , λ ₂ , λ ₃ , and λ ₄ included in the input signal light, The voltage signals converted from the output currents of 34c and 34d are acquired, and the conversion characteristic values for each of the four PD34a, 34b, 34c and 34d are acquired based on those voltage signals. This eliminates the need to evaluate the characteristics of each test light in a plurality of wavelength bands, so that the operation of a plurality of light receiving elements can be confirmed with a small number of man-hours without complicating the configuration of the test equipment.

The light-receiving element built into the conventional optical module is composed only of PD, but in recent years, due to demands for higher functionality, miniaturization, and integration, IC parts in the latter stage of PD and optical parts in the front stage of PD have been changed. Integrated optical modules are the mainstream. Therefore, the evaluation of the characteristics of the optical module and the inspection after assembly are complicated, and the restrictions are increasing. For example, a device that receives input signal light in which four wavelength signals are multiplexed, such as the light receiving module 10 of the present embodiment, has a built-in optical demultiplexer, and only light in a specific wavelength band is separated. It is configured to be waved and incident on the PD. It may be difficult to evaluate the characteristics of an optical receiver module having such a configuration using existing test equipment. Specifically, when measuring the gain of the TIA circuit in the subsequent stage of PD, it is necessary to match the emission wavelength of the light source included in the test equipment with a plurality of wavelength bands included in the input signal light for each test. .. Therefore, it is necessary to add a tunable light source or the like to the test equipment, and it is necessary to modify the test equipment so that a modulated signal can be generated based on the light from the tunable light source. As a result, higher functionality of test equipment is required. Furthermore, in order to evaluate the characteristics of each of a plurality of PDs, it is necessary to evaluate the characteristics a plurality of times using test lights in a plurality of wavelength bands, and the test man-hours tend to increase.

On the other hand, in the test method of the present embodiment, the characteristics are evaluated by injecting the test light in the wavelength band of the wavelength band included in the input signal light into the optical demultiplexer 31 in the optical receiving module 10. ing. By injecting such test light, the bandpass filters 44a, 44b, 44c, 44d in the optical demultiplexer 31 simultaneously receive the test light incident or reflected from the incident surface 41 side, respectively PD34a, 34b. , 34c, 34d are supposed to be transmitted. This is because the bandpass filters 44a, 44b, 44c, 44d have a characteristic of transmitting the wavelength band of the test light. Specifically, if the optical input power is set to 0 dBm or more, the attenuation of the optical demultiplexer is, for example, about 30 dB, so that a PD output current of several tens of mA can be obtained, and characteristic evaluation at a small input power is possible. To. As a result, in the present embodiment, a tunable light source is not required, and the test can be performed with a configuration corresponding to the conventional test equipment. Further, it is not necessary to evaluate the characteristics a plurality of times using the test lights of a plurality of wavelength bands, and it is possible to evaluate the characteristics corresponding to a plurality of PDs 34a, 34b, 34c, 34d at a time.

Further, in the test method of the present embodiment, an optical demultiplexer 31 that causes signal light in the wavelength band of 1300 nm to be incident on four PD34a, 34b, 34c, 34d is used, and light in the 1550 nm band is used as test light. It is incident on the wave device 31. In this case, the test light can be efficiently incident on the four PDs 34a, 34b, 34c, 34d via the optical demultiplexer 31. As a result, the characteristic evaluation of a plurality of PDs can be efficiently executed. Further, since the transimpedance gain is acquired as the conversion characteristic value, the characteristic evaluation including the plurality of PDs and the TIA circuit connected to the subsequent stages thereof can be realized at one time.

Although the principles of the invention have been illustrated and described above in preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. Therefore, we claim all amendments and changes that come from the claims and their spiritual scope.

10 ... Optical receiving module, 31 ... Optical demultiplexer (filter element), 34, 34a to 34d ... Photodiode (light receiving element), 35 ... Preamplifier circuit, 44a, 44b, 44c, 44d ... Bandpass filter, 45a, 45b , 45c, 45d ... Transimpedance amplifier circuit.

Claims (3)

A plurality of light receiving elements that convert signal light into an electric signal, and a plurality of light receiving elements that branch the input signal light into signal lights of a plurality of wavelength bands and incident the signal light of the plurality of wavelength bands into each of the plurality of light receiving elements . In the test method of an optical module including a filter element,
Test light in a wavelength band separated from the signal light in the plurality of wavelength bands is incident on the plurality of filter elements.
The test light is input to each of the plurality of light receiving elements corresponding to each of the plurality of filter elements, and each electric signal output from the plurality of light receiving elements is acquired.
Based on each of the electric signals, the conversion characteristic value for each of the plurality of light receiving elements is acquired.
Optical module test method. The signal light of the plurality of wavelength bands is a plurality of wavelength bands of the 1300 nm band, and the test light is the 1550 nm band.
The method for testing an optical module according to claim 1. As the test light, light in a wavelength band having a central wavelength separated from the center wavelengths of the plurality of wavelength bands by 200 nm or more is incident.
The method for testing an optical module according to claim 1 or 2.

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