Optical Module

Abstract

To provide an optical module capable of highly accurately controlling the wavelength of a laser beam to be controlled.SOLUTION: An optical module according to one aspect of the present invention includes: a semiconductor laser element; a plurality of optical filters having periodic transmission characteristics in terms of the frequency of light, the optical filters respectively transmitting, at transmittances corresponding to the transmission characteristics, a plurality of branched laser beams, which are one portion of laser beams output by the semiconductor laser element; and a plurality of temperature adjusters respectively adjusting the temperatures of the plurality of optical filters to be mutually different temperatures. The transmission characteristics of the plurality of optical filters are adjusted such that the phases are made to differ from each other by adjusting the temperatures of the plurality of optical filters by means of the plurality of temperature adjusters. Wavelength lock control of the semiconductor laser element is performed based on the intensity of a portion of the laser beams, and the intensity of the plurality of branched laser beams transmitted through the respective optical filters after temperature adjustment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical module. [Background technology]

[0002] In the field of wavelength division multiplexing (WDM) communications, in which multiple optical signals with different wavelengths are multiplexed and simultaneously transmitted through a single optical fiber, there has been a demand for multiplexing optical signals at narrower wavelength intervals as the volume of information communication increases. To multiplex optical signals at narrower wavelength intervals, it is necessary to precisely control the wavelength of the laser light output from a semiconductor laser element, which serves as signal light. For this reason, optical modules have been proposed that include an etalon filter that selectively transmits laser light output from a semiconductor laser element (see, for example, Patent Documents 1 and 2).

[0003] The optical module includes a thermoelectric module that adjusts the temperature of a semiconductor laser element by the Peltier effect. A portion of the laser light output from the semiconductor laser element is branched off toward an etalon filter, and the thermoelectric module is operated based on the intensity of the branched light that has passed through the etalon filter, thereby adjusting the temperature of the semiconductor laser element. The etalon filter has periodic transmission characteristics with respect to the frequency of the laser light. Therefore, by adjusting the temperature of the semiconductor laser element so that the intensity of the branched light that has passed through the etalon filter becomes a predetermined value, the wavelength of the laser light output from the semiconductor laser element can be controlled to a predetermined wavelength.

[0004] Furthermore, the transmission characteristics of the etalon filter change depending on the temperature. For this reason, the optical module further includes a thermoelectric element module that adjusts the temperature of the etalon filter by the Peltier effect, in addition to the thermoelectric element module that adjusts the temperature of the semiconductor laser element. The thermoelectric element module adjusts the temperature of the etalon filter to a constant temperature, thereby fixing the transmission characteristics of the etalon filter. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-110190 [Patent Document 2] Japanese Patent Application Publication No. 2019-140306 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to control the wavelength of the laser light output from the semiconductor laser element with high precision, it is preferable to set the wavelength of the laser light to be controlled to a wavelength in a frequency region where the rate of change of the transmittance with respect to the frequency of light in the transmission characteristics of the etalon filter (hereinafter referred to as the transmittance change rate) is large.

[0007] However, in the conventional optical module described above, the etalon filter is adjusted to a constant temperature to fix the transmission characteristics of the etalon filter, so there is a possibility that the wavelength of the laser light to be controlled will be a wavelength in a frequency region where the rate of change in transmittance is small. In this case, it is difficult to control the wavelength of the laser light with high precision.

[0008] Furthermore, since the transmission characteristics of the etalon filter are temperature-dependent as described above, it is possible to adjust the temperature of the etalon filter so that it changes within a predetermined range, thereby changing the phase of the transmission characteristics of the etalon filter in accordance with the wavelength of the laser light to be controlled. However, in this case, the temperature of the etalon filter must be changed significantly (for example, by nearly 30°C). This temperature change in the etalon filter increases the amount of phase change (phase shift) in the transmission characteristics, which may result in a large error in the phase change of the transmission characteristics. Therefore, it is difficult to control the wavelength of the laser light to be controlled with high precision.

[0009] The present invention has been made in view of the above, and has an object to provide an optical module that can control the wavelength of laser light to be controlled with high precision. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, an optical module according to the present invention comprises a semiconductor laser element, a plurality of optical filters having a transmission characteristic that is periodic in terms of optical frequency and that transmit a plurality of branched laser beams that are portions of the laser beam output by the semiconductor laser element, each with a transmittance corresponding to the transmission characteristic, and a plurality of temperature regulators that adjust the temperatures of the plurality of optical filters to temperatures different from each other, wherein the transmission characteristics of the plurality of optical filters are adjusted so that the phases are different from each other by adjusting the temperatures of the plurality of optical filters with the plurality of temperature regulators, and wavelength lock control of the semiconductor laser element is performed based on the intensity of the portion of the laser beam and the intensity of the plurality of branched laser beams that have passed through the plurality of optical filters after temperature adjustment.

[0011] The optical module according to the present invention is characterized in that, in the above invention, the plurality of temperature regulators include a temperature regulator that regulates both the temperature of one of the plurality of optical filters and the temperature of the semiconductor laser element.

[0012] In the optical module according to the present invention, in the above invention, the optical module further comprises a temperature regulator separate from the plurality of temperature regulators, for regulating the temperature of the semiconductor laser element.

[0013] In the optical module according to the present invention, in the above invention, the plurality of temperature adjusters adjust the temperatures of the plurality of optical filters to constant target temperatures that are different from one another.

[0014] In the optical module according to the present invention, in the above invention, the plurality of temperature adjusters adjust the temperatures of the plurality of optical filters to a temperature equal to or higher than the temperature of the semiconductor laser element.

[0015] In the optical module according to the present invention, in the above invention, each of the plurality of optical filters is an etalon filter, a ring resonator filter, or a Mach-Zehnder interference filter.

[0016] In the optical module according to the present invention, in the above invention, each of the plurality of temperature regulators is a thermoelectric cooler.

[0017] The optical module according to the present invention is characterized in that, in the above invention, the semiconductor laser element is a vernier type wavelength tunable laser element or a DFB integrated type wavelength tunable laser element in which a plurality of distributed feedback laser elements are integrated. [Effects of the Invention]

[0018] According to the present invention, it is possible to control the wavelength of the laser light to be controlled with high precision. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an optical module according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of the transmission characteristics of one etalon filter applied to each of the two etalon filters according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing an example of the transmission characteristics of two etalon filters according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of an optical module according to the second embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing an example of the configuration of an optical module according to a modified example of the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of an optical module according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment. In addition, the same or corresponding components in each drawing are appropriately designated by the same reference numerals. It should be noted that the drawings are schematic, and the thicknesses and thickness ratios of each layer may differ from the actual ones. Furthermore, the drawings may include portions where the dimensional relationships and ratios differ from one another.

[0021] (Embodiment 1) Fig. 1 is a diagram showing an example of the configuration of an optical module according to a first embodiment of the present invention. As shown in Fig. 1, the optical module 1 according to the first embodiment includes a housing 2, temperature regulators 3 and 4, an LD carrier 5, a semiconductor laser element 6, a collimating lens 7, an optical isolator 8, beam splitters 9, 10, and 11, photodiodes 12, 13, and 14, PD carriers 12a, 13a, and 14a, mirrors 15 and 16, etalon filters 17 and 18, thermistors 19 and 20, a condenser lens 21, a ferrule 22, an optical fiber 23, and a controller 50.

[0022] As shown in FIG. 1 , the housing 2 is a box-like structure having a rounded rectangular shape in a plan view, and houses the components of the optical module 1 inside. Specifically, as shown in FIG. 1 , the housing 2 houses temperature regulators 3 and 4, an LD carrier 5, a semiconductor laser element 6, a collimating lens 7, an optical isolator 8, beam splitters 9, 10, and 11, photodiodes 12, 13, and 14, PD carriers 12a, 13a, and 14a, mirrors 15 and 16, etalon filters 17 and 18, and thermistors 19 and 20 inside. Although not shown in FIG. 1 , the housing 2 includes a lid that closes the internal space housing the components. For ease of explanation of the optical module 1, FIG. 1 shows the housing 2 with the lid removed.

[0023] The two temperature regulators 3 and 4 are an example of a plurality of temperature regulators in the present invention that respectively adjust the temperatures of a plurality of optical filters to different temperatures. Each of these two temperature regulators 3 and 4 is, for example, a thermoelectric cooler (TEC), and is composed of a plurality of Peltier elements (not shown) arranged on a substrate having electrodes and wiring, and a base provided on the upper surface (the end surface opposite the substrate) of the plurality of Peltier elements. As shown in FIG. 1, the base is base 3a in one temperature regulator 3, and base 4a in the other temperature regulator 4. Temperature regulator 3 adjusts the temperature of each component on base 3a by the Peltier effect, and temperature regulator 4 adjusts the temperature of each component on base 4a by the Peltier effect.

[0024] For example, the temperature regulator 3 cools the semiconductor laser element 6 and the etalon filter 17 on the base 3a in accordance with the drive current supplied from the controller 50. As a result, the temperature regulator 3 regulates both the temperature of the semiconductor laser element 6 and the temperature of one etalon filter 17 of the two etalon filters 17, 18 in the first embodiment. At this time, the temperature regulator 3 regulates the temperatures of the semiconductor laser element 6 and the etalon filter 17 to be the same temperature.

[0025] Furthermore, the temperature regulator 4 cools the etalon filter 18 on the base 4a in accordance with the drive current supplied from the controller 50. As a result, the temperature regulator 4 regulates the temperature of this etalon filter 18 separately from the etalon filter 17 whose temperature is regulated by the temperature regulator 3. At this time, the temperature regulator 4 regulates the temperature of this etalon filter 18 to a temperature higher than the temperature of the etalon filter 17.

[0026] The bases 3a and 4a of the temperature regulators 3 and 4 are plate-shaped members made of a material with high thermal conductivity, such as aluminum nitride, aluminum oxide, copper tungsten, silicon carbide, silicon, copper, and diamond.

[0027] The LD carrier 5 is a member for mounting components such as a semiconductor laser element 6. For example, as shown in FIG. 1, the semiconductor laser element 6, a collimating lens 7, and a thermistor 19 are mounted on the LD carrier 5. The LD carrier 5 on which the components such as the semiconductor laser element 6 are mounted is provided on the base 3a of the temperature regulator 3 as shown in FIG. 1. That is, the semiconductor laser element 6 is placed on the base 3a of the temperature regulator 3 via the LD carrier 5. From the viewpoint of efficiently adjusting the temperature of the semiconductor laser element 6 by the temperature regulator 3, the LD carrier 5 is preferably made of a material with high thermal conductivity. Examples of materials with high thermal conductivity include the same materials as those used for the bases 3a and 4a of the temperature regulators 3 and 4 described above.

[0028] The semiconductor laser element 6 is a wavelength-tunable laser element that outputs laser light L1 when a drive current is supplied from the controller 50. The wavelength of the laser light L1 is within a wavelength band used for optical communications (e.g., a wavelength band of 1520 nm or more and 1620 nm or less). Examples of such a semiconductor laser element 6 include a vernier-type wavelength-tunable laser element that uses the vernier effect to tune the oscillation wavelength of laser light, or a DFB-integrated wavelength-tunable laser element in which multiple distributed feedback laser elements are integrated. When the semiconductor laser element 6 is a vernier-type wavelength-tunable laser element, the wavelength of the laser light L1 output from the semiconductor laser element 6 is controlled by a drive current supplied from the controller 50 to a microheater provided in an oscillation wavelength selection variable element within the semiconductor laser element 6. The oscillation wavelength selection variable element is, for example, an element having a comb-shaped reflection spectrum, such as a distributed Bragg reflector sampled grating or a ring resonator filter. Furthermore, when the semiconductor laser element 6 is a DFB integrated wavelength tunable laser element, the wavelength of the laser light L1 output by the semiconductor laser element 6 is controlled by the drive current supplied from the controller 50 to the distributed feedback laser element and the temperature of the semiconductor laser element 6 adjusted by the temperature regulator 3.

[0029] 1, the collimating lens 7 is disposed on the LD carrier 5 so as to be located on the front side of the semiconductor laser element 6. The front side of the semiconductor laser element 6 is the side from which the semiconductor laser element 6 outputs the laser light L1. The collimating lens 7 converts the laser light L1 output from the semiconductor laser element 6 into parallel light.

[0030] 1, the optical isolator 8 is disposed on the base 4a of the temperature regulator 4 so as to be located between the beam splitter 9 on the upstream side (the semiconductor laser element 6 side) and the beam splitter 10 on the downstream side (the optical fiber 23 side). The optical isolator 8 transmits the laser light L1 traveling in the forward direction from the upstream side to the downstream side (i.e., the beam splitter 10 side), and prevents the light from returning from the beam splitter 10 side to the semiconductor laser element 6.

[0031] 1, the beam splitter 9 is disposed on the base 3a of the temperature regulator 3 so as to be located between the collimator lens 7 and the optical isolator 8. The beam splitter 9 branches a part of the laser beam L1, which has been collimated by the collimator lens 7, as a branched laser beam L2, and reflects this branched laser beam L2 toward the mirror 15, while transmitting the remaining laser beam L1 toward the optical isolator 8.

[0032] 1, the beam splitter 10 is disposed on the base 4a of the temperature regulator 4 so as to be located between the optical isolator 8 and the beam splitter 11. The beam splitter 10 branches a part of the laser light L1 that has passed through the optical isolator 8 as a branched laser light L3, reflects this branched laser light L3 toward the mirror 16, and transmits the remaining laser light L1 toward the beam splitter 11.

[0033] 1, the beam splitter 11 is disposed on the base 4a of the temperature regulator 4 so as to be located downstream of the beam splitter 10. The beam splitter 11 branches a portion of the laser light L1 that has passed through the beam splitter 10 as a branched laser light L4, reflects the branched laser light L4 toward the photodiode 12, and transmits the remaining laser light L1 toward the condenser lens 21.

[0034] The photodiode 12 is a photodiode for power monitoring, and as shown in Fig. 1, is mounted on a PD carrier 12a and placed on a base 4a of the temperature regulator 4. The photodiode 12 receives the branched laser light L4 reflected from the beam splitter 11 and detects the intensity of the received branched laser light L4. The photodiode 12 outputs a current signal corresponding to the detected intensity of the branched laser light L4 to the controller 50.

[0035] 1, the condenser lens 21 is disposed in a holder provided on the side wall on the light output side of the housing 2. A ferrule 22, through which one end of an optical fiber 23 is inserted and fixed, is attached to this holder. The condenser lens 21 condenses the laser light L1 that has passed through the beam splitter 11 and couples it into the optical fiber 23. The optical fiber 23 transmits the laser light L1 coupled by the condenser lens 21 to a predetermined device or the like (not shown).

[0036] 1, the mirror 15 is disposed on the base 3a of the temperature regulator 3 so as to be located on the upstream side of the etalon filter 17. The mirror 15 reflects the branched laser light L2 reflected from the beam splitter 9 toward the etalon filter 17.

[0037] 1, the mirror 16 is disposed on the base 4a of the temperature regulator 4 so as to be located on the upstream side of the etalon filter 18. The mirror 16 reflects the branched laser light L3 reflected from the beam splitter 10 toward the etalon filter 18.

[0038] The two etalon filters 17 and 18 are examples of the plurality of optical filters of the present invention. Each of the two etalon filters 17 and 18 has a transmission characteristic that is periodic in terms of optical frequency, and transmits a plurality of branched laser beams, which are part of the laser beam L1 output from the semiconductor laser element 6, at a transmittance corresponding to the transmission characteristic.

[0039] Specifically, as shown in FIG. 1 , one etalon filter 17 is disposed on the base 3 a of the temperature regulator 3 so as to be located, for example, between the photodiode 13 and the mirror 15, in the optical path of the branched laser beam L2 branched from the laser beam L1 by the beam splitter 9. The etalon filter 17 is temperature-adjusted by the temperature regulator 3, and selectively transmits the branched laser beam L2 reflected from the mirror 15 toward the photodiode 13 at a transmittance corresponding to its transmission characteristics after the temperature adjustment. Also, as shown in FIG. 1 , the other etalon filter 18 is disposed on the base 4 a of the temperature regulator 4 so as to be located, for example, between the photodiode 14 and the mirror 16 in the optical path of the branched laser beam L3 branched from the laser beam L1 by the beam splitter 10. The etalon filter 18 is adjusted to a temperature different from that of the etalon filter 17 by the temperature regulator 4, and selectively transmits the branched laser beam L3 reflected from the mirror 16 toward the photodiode 14 at a transmittance corresponding to its transmission characteristics after the temperature adjustment.

[0040] In the first embodiment, the transmission characteristics of these two etalon filters 17 and 18 are adjusted to have different phases from each other by adjusting the temperatures of the etalon filters 17 and 18 using the temperature regulators 3 and 4. Details of the transmission characteristics of the etalon filters 17 and 18 having different phases from each other will be described later.

[0041] The photodiodes 13 and 14 are photodiodes for wavelength monitoring. Specifically, as shown in FIG. 1 , the photodiode 13 is mounted on a PD carrier 13a and placed on a base 3a of the temperature regulator 3, and receives the branched laser light L2 that has passed through the etalon filter 17. The photodiode 13 detects the intensity of the received branched laser light L2 and outputs a current signal corresponding to the detected intensity of the branched laser light L2 to the controller 50. The photodiode 14 is mounted on a PD carrier 14a and placed on a base 4a of the temperature regulator 4, and receives the branched laser light L3 that has passed through the etalon filter 18. The photodiode 14 detects the intensity of the received branched laser light L3 and outputs a current signal corresponding to the detected intensity of the branched laser light L3 to the controller 50.

[0042] 1, the thermistor 19 is disposed near the semiconductor laser element 6, for example, on the LD carrier 5, and detects the temperature of the semiconductor laser element 6 adjusted by the temperature adjuster 3. The thermistor 19 outputs a detection signal indicating the detected temperature of the semiconductor laser element 6 to the controller 50. In the first embodiment, the temperature detected by the thermistor 19 is the same as the temperature of the etalon filter 17, the temperature of which is adjusted together with the semiconductor laser element 6 by the temperature adjuster 3.

[0043] 1, the thermistor 20 is disposed on the base 4a of the temperature regulator 4, and detects the temperature of the etalon filter 18 adjusted by the temperature regulator 4. The thermistor 20 outputs a detection signal indicating the detected temperature of the etalon filter 18 to the controller 50. From the viewpoint of detecting the temperature of the etalon filter 18, the thermistor 20 is preferably disposed near the etalon filter 18.

[0044] The controller 50 controls the temperature adjustment of the semiconductor laser element 6 and the etalon filters 17 and 18 by the two temperature adjusters 3 and 4. In detail, the controller 50 supplies drive currents to the two temperature adjusters 3 and 4, respectively, thereby controlling the temperature adjusters 3 and 4 so that the temperatures of the etalon filters 17 and 18 are different from each other.

[0045] Here, the two temperature regulators 3, 4 controlled by the controller 50 include a temperature regulator 3 that regulates both the temperature of one etalon filter 17 of the two etalon filters 17, 18 and the temperature of the semiconductor laser element 6. The controller 50 supplies a drive current to the temperature regulator 3, thereby controlling the temperature regulator 3 so that the temperature of the semiconductor laser element 6 is adjusted to a target temperature suitable for outputting the laser light L1 and the temperature of the etalon filter 17 is adjusted to the same target temperature as the semiconductor laser element 6. At this time, the controller 50 receives a detection signal from the thermistor 19 and, based on this detection signal, acquires the temperatures of the semiconductor laser element 6 and the etalon filter 17 after adjustment by the temperature regulator 3. The controller 50 determines the value of the drive current so that the acquired temperatures become the target temperatures, and supplies this drive current to the temperature regulator 3. As a result, the controller 50 performs feedback control of the temperature regulator 3 so that the temperatures of the semiconductor laser element 6 and the etalon filter 17 are adjusted to the target temperatures.

[0046] Furthermore, the controller 50 supplies a drive current to another temperature adjuster 4, thereby controlling the temperature adjuster 4 so that the temperature of the etalon filter 18 is adjusted to a higher target temperature different from that of the etalon filter 17. At this time, the controller 50 receives a detection signal from the thermistor 20 and, based on this detection signal, acquires the temperature of the etalon filter 18 after adjustment by the temperature adjuster 4. The controller 50 determines the value of the drive current so that the acquired temperature becomes the target temperature of the etalon filter 18, and supplies this drive current to the temperature adjuster 4. In this way, the controller 50 feedback-controls the temperature adjuster 4 so that the temperature of the etalon filter 18 is adjusted to the target temperature.

[0047] The controller 50 also performs wavelength locking control, which is a control for adjusting the laser beam L1 output from the semiconductor laser element 6 to a laser beam with a desired wavelength and intensity. The wavelength locking control of the semiconductor laser element 6 is performed based on the intensity of the branched laser beam L4, which is a part of the laser beam L1, and the intensities of the two branched laser beams L2 and L3 that have passed through the temperature-adjusted etalon filters 17 and 18, respectively.

[0048] Specifically, the controller 50 acquires the intensity of the branched laser light L4 detected by the photodiode 12 based on the current signal input from the photodiode 12. The controller 50 also acquires the intensities of the branched laser light L2 and L3 detected by the photodiodes 13 and 14 based on the current signals input from the photodiodes 13 and 14, respectively. The intensity of the branched laser light L2 detected by the photodiode 13 is the intensity of the branched laser light L2 after passing through the etalon filter 17, and the intensity of the branched laser light L3 detected by the photodiode 14 is the intensity of the branched laser light L3 after passing through the etalon filter 18. The controller 50 performs wavelength locking control of the semiconductor laser element 6 so that the ratio between the intensity of the detected branched laser light L4 and the intensity of the detected branched laser light L2 or branched laser light L3 (hereinafter referred to as the detected intensity ratio of the branched laser light L2, L3, and L4) becomes the ratio when the wavelength and intensity of the laser light L1 become the desired wavelength and intensity (hereinafter referred to as the target ratio of the laser light L1).

[0049] For example, if the semiconductor laser element 6 is a vernier-type wavelength-tunable laser element, the controller 50 controls the temperature regulator 3 by supplying a drive current to the temperature regulator 3 so that the temperature of the semiconductor laser element 6 becomes a constant target temperature suitable for temperature control of the microheater during wavelength lock control of the semiconductor laser element 6. As a result, the temperature regulator 3 adjusts the temperature of the semiconductor laser element 6 to the constant target temperature by cooling or the like, and also adjusts the temperature of the etalon filter 17 to the same constant target temperature as the semiconductor laser element 6 by cooling or the like. In addition, the controller 50 determines a drive current so that the detected intensity ratio of the branched laser beams L2, L3, and L4 becomes the target ratio of the laser beam L1, and supplies this drive current to the semiconductor laser element 6, thereby controlling the wavelength and intensity of the laser beam L1 to the desired wavelength and intensity.

[0050] Furthermore, when the semiconductor laser element 6 is a DFB-integrated wavelength-tunable laser element, the controller 50 determines each drive current for drive control and temperature adjustment of the semiconductor laser element 6 so that the detected intensity ratio of the branched laser beams L2, L3, and L4 becomes the target ratio of the laser beam L1. The controller 50 supplies the determined drive current for temperature adjustment to the temperature adjuster 3 to control the temperature adjuster 3 so that the temperature of the semiconductor laser element 6 becomes the variable target temperature within a predetermined range. As a result, the temperature adjuster 3 adjusts the temperature of the semiconductor laser element 6 to the variable target temperature by cooling or the like, and also adjusts the temperature of the etalon filter 17 to the same variable target temperature as the semiconductor laser element 6 by cooling or the like. In addition, the controller 50 controls the semiconductor laser element 6 by supplying the determined drive current for drive control to the semiconductor laser element 6. By controlling the semiconductor laser element 6 and the temperature adjuster 3 as described above, the controller 50 controls the wavelength and intensity of the laser beam L1 to the desired wavelength and intensity.

[0051] (Transmission characteristics of optical filters) Next, as an example of the transmission characteristics of the plurality of optical filters in the first embodiment of the present invention, the transmission characteristics of the two etalon filters 17 and 18 will be described in detail. The two etalon filters 17 and 18 have transmission characteristics with approximately the same period, and as described above, are adjusted to different temperatures by the two temperature regulators 3 and 4. As a result, the transmission characteristics of the two etalon filters 17 and 18 are adjusted to have different phases from each other.

[0052] FIG. 2 is a diagram showing an example of the transmission characteristics of one etalon filter applied to each of the two etalon filters in the first embodiment of the present invention. In FIG. 2, the horizontal axis represents the frequency of light, and the vertical axis represents the transmittance of light passing through one etalon filter. As exemplified by the curves in FIG. 2, one etalon filter has transmission characteristics that are periodic in terms of the frequency of light. The rate of change in transmittance in the transmission characteristics of this etalon filter is smaller in the frequency region around the valley of the curve and in the frequency region around the peak of the curve than in other frequency regions. For example, when the frequency of light to be controlled is fa (the valley of the curve) or fb (the peak of the curve), the rate of change in transmittance is small, making it difficult to control the wavelength of the light.

[0053] In contrast, the two etalon filters 17 and 18 in the first embodiment of the present invention are adjusted to different temperatures by the two temperature adjusters 3 and 4. As a result, the transmission characteristics of the two etalon filters 17 and 18 are adjusted so that the frequency region with a small transmittance change rate complements the frequency region with a large transmittance change rate. FIG. 3 is a diagram showing an example of the transmission characteristics of the two etalon filters in the first embodiment of the present invention. In FIG. 3, curve C1 is a frequency discrimination curve showing the transmission characteristics of the etalon filter 17, and curve C2 is a frequency discrimination curve showing the transmission characteristics of the etalon filter 18. The temperatures of these two etalon filters 17 and 18 are adjusted by the two temperature adjusters 3 and 4 to different temperatures that are equal to or higher than the temperature of the semiconductor laser element 6.

[0054] For example, if the semiconductor laser element 6 is a vernier-type wavelength-tunable laser element, the two temperature adjusters 3 and 4 adjust the temperatures of the two etalon filters 17 and 18 to different constant target temperatures. As a result, the temperature of the etalon filter 17 is adjusted to the same constant target temperature (e.g., 50°C) as the semiconductor laser element 6. The temperature of the etalon filter 18 is adjusted to a constant target temperature (e.g., 70°C) that is higher than the etalon filter 17. If the semiconductor laser element 6 is a DFB-integrated wavelength-tunable laser element, the temperature adjuster 3 adjusts the temperature of the etalon filter 17 to the same variable target temperature as the semiconductor laser element 6. As a result, the temperature of the etalon filter 17 is adjusted to change within a predetermined range (e.g., 35°C to 65°C) like the semiconductor laser element 6. On the other hand, the temperature adjuster 4 adjusts the temperature of the etalon filter 18 to a constant target temperature that is higher than the temperature of the semiconductor laser element 6, regardless of the temperature change of the etalon filter 17. As a result, the temperature of the etalon filter 18 is adjusted to a constant target temperature (for example, 70° C.) that is higher than the temperature of the etalon filter 17.

[0055] Here, the two etalon filters 17 and 18 each have a property in which the phase of their transmission characteristics changes in response to temperature changes (temperature dependence of transmission characteristics). Therefore, by adjusting the two etalon filters 17 and 18 to different temperatures as described above, a phase difference ΔP occurs between the transmission characteristics of the low-temperature etalon filter 17 and the high-temperature etalon filter 18 depending on the temperature difference between the two etalon filters 17 and 18, as shown in FIG. 3 . As a result, the frequency region where the transmittance change rate is small in the transmission characteristics of the etalon filter 17 (thin line portion of curve C1) overlaps with the frequency region where the transmittance change rate is large in the transmission characteristics of the etalon filter 18 (bold line portion of curve C2). The frequency region where the transmittance change rate is large in the transmission characteristics of the etalon filter 17 (bold line portion of curve C1) overlaps with the frequency region where the transmittance change rate is small in the transmission characteristics of the etalon filter 18 (thin line portion of curve C2). As a result, the two etalon filters 17 and 18 have transmission characteristics in which the frequency range in which the transmittance change rate is small is complemented by the frequency range in which the transmittance change rate is large, and the frequency range in which the transmittance change rate is large and light wavelength control can be performed with high precision is wider than in the case of the transmission characteristics of a single etalon filter as shown in FIG. 2.

[0056] The temperature difference between the etalon filters 17 and 18 at which the phase difference ΔP in the transmission characteristics is obtained varies depending on the type of the etalon filters 17 and 18, but from the viewpoint of ensuring that the frequency range in which the rate of change in transmittance is large exists over a wide range, it is preferable to adjust the phase difference ΔP in the transmission characteristics to an ideal phase difference. An example of the ideal phase difference is a phase difference that falls within a range of ⅕ to ⅓ of one period of the transmission characteristics of the etalon filter.

[0057] Although it is preferable that the periods of the transmission characteristics of the two etalon filters 17 and 18 are approximately equal to each other, it is also preferable that the difference be within one-third of one period, since this allows the frequency region with a large rate of change in transmittance to be distributed over a wide wavelength range even if they are different from each other. It is even more preferable that the periods of the transmission characteristics of the two etalon filters 17 and 18 are identical to each other.

[0058] In wavelength locking control of the semiconductor laser element 6, the controller 50 uses either the intensity of the branched laser light L2 detected by the photodiode 13 or the intensity of the branched laser light L3 detected by the photodiode 14 as the detection result of the intensity of the laser light after passing through the etalon filters. In this case, it is preferable that the controller 50 uses the intensity of the branched laser light that has passed through one of the two etalon filters 17, 18, which has a larger rate of change in transmittance at the wavelength of the laser light L1 to be controlled.

[0059] For example, as shown in FIG. 3, when the wavelength of the laser light L1 to be controlled is in the frequency range of not less than f1 but less than f2, the controller 50 uses the intensity (detected intensity by the photodiode 13) of the branched laser light L2 that has passed through the etalon filter 17, which has a transmittance change rate greater than that of the etalon filter 18, for wavelength locking control. When the wavelength of the laser light L1 to be controlled is in the frequency range of not less than f2 but less than f3, the controller 50 uses the intensity (detected intensity by the photodiode 14) of the branched laser light L3 that has passed through the etalon filter 18, which has a transmittance change rate greater than that of the etalon filter 17, for wavelength locking control. By selectively using the detected intensities by the photodiodes 13 and 14 in this manner, the controller 50 can control the wavelength of the laser light L1 with high precision. Regarding which transmittance change rate is greater at the wavelength to be controlled, a table showing the correspondence between the control wavelength and the transmittance change rate may be stored in a memory unit (not shown) of the controller 50, and the controller 50 may appropriately select the transmittance change rate according to the control wavelength based on the table.

[0060] As described above, the optical module according to the first embodiment of the present invention comprises a semiconductor laser element, a plurality of optical filters having transmission characteristics that are periodic in terms of optical frequency and that transmit a plurality of branched laser beams, which are portions of the laser beam output by the semiconductor laser element, at a transmittance corresponding to the transmission characteristics, and a plurality of temperature regulators that adjust the temperatures of the plurality of optical filters to temperatures different from one another, wherein the transmission characteristics of the plurality of optical filters are adjusted by the plurality of temperature regulators to have different phases from one another, and wavelength lock control of the semiconductor laser element is performed based on the intensity of a portion of the laser beam (i.e., the branched laser beam that has not passed through any of the plurality of optical filters) and the intensity of the plurality of branched laser beams that have passed through the plurality of optical filters after temperature adjustment.

[0061] Therefore, in the transmission characteristics of the plurality of optical filters having different phases from one another, a frequency region with a large rate of change in transmittance that can be used for highly accurate wavelength control of the laser beam can be distributed over a wide wavelength range of the wavelength to be controlled of the laser beam, and the amount of change in temperature of each of the plurality of optical filters due to temperature adjustment at this time can be reduced. As a result, while ensuring a suitable phase difference between the transmission characteristics of the plurality of optical filters, the amount of phase shift of each of the transmission characteristics due to temperature adjustment of the plurality of optical filters can be reduced. As a result, the phase error due to the phase shift of each of the transmission characteristics can be reduced, and the wavelength of the laser beam to be controlled can be controlled with high accuracy.

[0062] Furthermore, in the optical module according to the first embodiment of the present invention, the plurality of temperature regulators include a first temperature regulator that regulates both the temperature of one optical filter (first optical filter) among the plurality of optical filters and the temperature of the semiconductor laser element. Therefore, the first temperature regulator regulates the temperature of the first optical filter to the same temperature as the temperature of the semiconductor laser element, and at least one second temperature regulator other than the first temperature regulator regulates the temperature of at least one second optical filter other than the first optical filter to a constant temperature higher than the first optical filter. This reduces the power consumption required to regulate the temperatures of the plurality of optical filters. In particular, when the semiconductor laser element is a vernier-type tunable laser element, the temperature of the first optical filter can be adjusted to the same constant temperature as the temperature of the semiconductor laser element. As a result, the temperatures of all of the plurality of optical filters can be adjusted to a constant temperature equal to or higher than the temperature of the semiconductor laser element. This reduces the power consumption required to regulate the temperature of the semiconductor laser element and further reduces the power consumption required to regulate the temperatures of the plurality of optical filters. Furthermore, even if the semiconductor laser element is a DFB integrated wavelength tunable laser element, the temperature of at least the second optical filter can be adjusted to a constant temperature higher than that of the first optical filter, and therefore the power consumption required to adjust the temperature of each of the plurality of optical filters can be kept lower than that of conventional optical modules.

[0063] Furthermore, since the temperature of each of the optical filters is adjusted by the temperature regulators to a constant temperature equal to or higher than the temperature of the semiconductor laser element, warping of the base of each of the temperature regulators can be minimized. As a result, deviation in the optical coupling of the laser light (including the branched laser light) traveling through the optical module can be prevented, which contributes to high precision wavelength locking control of the semiconductor laser element.

[0064] (Embodiment 2) Fig. 4 is a diagram showing an example of the configuration of an optical module according to embodiment 2 of the present invention. As shown in Fig. 4, an optical module 1A according to embodiment 2 includes temperature regulators 30 and 31 instead of the temperature regulator 3 of the optical module 1 according to embodiment 1 described above, a controller 50A instead of the controller 50, and a thermistor 25. The other configurations are the same as those of embodiment 1, and the same components are designated by the same reference numerals.

[0065] The three temperature regulators 4, 30, and 31 are an example of a plurality of temperature regulators in the present invention that respectively regulate the temperatures of a plurality of optical filters to different temperatures. Each of the temperature regulators 30 and 31 is, for example, a TEC, and is configured in the same manner as the temperature regulator 4 described above. That is, as shown in FIG. 4, the temperature regulator 30 includes a base 30a and regulates the temperature of each component on the base 30a by the Peltier effect. The temperature regulator 31 includes a base 31a and regulates the temperature of each component on the base 31a by the Peltier effect. The temperature regulator 4 is the same as that in the first embodiment described above, and therefore a description thereof will be omitted.

[0066] For example, the temperature adjuster 30 is separate from the multiple (two in the second embodiment) temperature adjusters 4 and 31 for adjusting the temperatures of the multiple optical filters, respectively, and cools the semiconductor laser element 6 on the base 30a in accordance with the drive current supplied from the controller 50A. In this way, the temperature adjuster 30 adjusts the temperature of the semiconductor laser element 6. Furthermore, the temperature adjuster 31 cools the etalon filter 17 on the base 31a in accordance with the drive current supplied from the controller 50A. In this way, the temperature adjuster 31 adjusts the temperature of the etalon filter 17 separately from the semiconductor laser element 6 whose temperature is adjusted by the temperature adjuster 30 and the etalon filter 18 whose temperature is adjusted by the temperature adjuster 4. In this case, the temperature adjuster 31 adjusts the temperature of the etalon filter 17 to a temperature higher than the temperature of the semiconductor laser element 6 and different from the temperature of the etalon filter 18. The material forming the bases 30a and 31a of the temperature regulators 30 and 31 is a material with high thermal conductivity, similar to the base 4a of the temperature regulator 4 described above.

[0067] 4, in the second embodiment, the LD carrier 5 on which the semiconductor laser element 6, the collimator lens 7, and the thermistor 19 are mounted, and the beam splitter 9 are arranged on the base 30a of the temperature regulator 30, similarly to the first embodiment. The photodiode 13 mounted on the PD carrier 13a, the mirror 15, and the etalon filter 17 are arranged on the base 31a of the temperature regulator 31, similarly to the first embodiment. A thermistor 25 is also provided on the base 31a of the temperature regulator 31.

[0068] 4, the thermistor 25 is disposed on a base 31a of the temperature regulator 31, and detects the temperature of the etalon filter 17 adjusted by the temperature regulator 31. The thermistor 25 outputs a detection signal indicating the detected temperature of the etalon filter 17 to the controller 50A. From the viewpoint of detecting the temperature of the etalon filter 17, the thermistor 25 is preferably disposed near the etalon filter 17.

[0069] The controller 50A controls the temperature adjustment of the semiconductor laser element 6 and the etalon filters 17 and 18 by the three temperature adjusters 30, 31, and 4. In detail, the controller 50A supplies a drive current to the temperature adjuster 30, thereby controlling the temperature adjuster 30 to adjust the temperature of the semiconductor laser element 6. At this time, the controller 50A feedback-controls the temperature adjuster 30 based on a detection signal from the thermistor 19, similar to the temperature adjuster 3 in the first embodiment described above.

[0070] Here, of the three temperature regulators 30, 31, and 4 controlled by the controller 50A, the two temperature regulators 31 and 4 regulate the temperatures of the two etalon filters 17 and 18 to constant target temperatures that are different from each other. The controller 50A supplies a drive current to the temperature regulator 31, thereby controlling the temperature regulator 31 so that the temperature of the etalon filter 17 is a constant target temperature that is different from the temperature of the etalon filter 18. The target temperature of the etalon filter 17 may be, for example, a constant temperature that is higher than that of the semiconductor laser element 6 and lower than that of the etalon filter 18. The controller 50A receives a detection signal from the thermistor 25 and, based on this detection signal, acquires the temperature of the etalon filter 17 after adjustment by the temperature regulator 31. The controller 50A determines the value of the drive current so that the acquired temperature becomes the target temperature of the etalon filter 17, and supplies this drive current to the temperature regulator 31. As a result, the controller 50A performs feedback control of the temperature regulator 31 so that the temperature of the etalon filter 17 is adjusted to a constant target temperature. Note that the control of the temperature regulator 4 by the controller 50A is similar to that of the controller 50 in the first embodiment described above.

[0071] Furthermore, the controller 50A performs wavelength locking control of the semiconductor laser element 6, similar to the controller 50 of the first embodiment described above. At this time, the controller 50A controls the temperature regulator 30 for temperature regulation of the semiconductor laser element 6, similar to the temperature regulator 3 of the first embodiment.

[0072] As described above, the optical module according to the second embodiment of the present invention is similar to that of the first embodiment except that it further includes a temperature regulator that adjusts the temperature of the semiconductor laser element, separate from the plurality of temperature regulators that adjust the temperatures of the plurality of optical filters to different temperatures. Therefore, the same effects as those of the first embodiment can be obtained, and the temperatures of the plurality of optical filters can be adjusted independently of the temperature adjustment of the semiconductor laser element, regardless of the type of semiconductor laser element. This allows the temperatures of the plurality of optical filters to be adjusted to, for example, constant temperatures that are different from each other and higher than the temperature of the semiconductor laser element, making it possible to more easily keep the power consumption required for adjusting the temperature of each of the plurality of optical filters low.

[0073] (Modification of the second embodiment) Fig. 5 is a diagram showing an example of the configuration of an optical module according to a modification of the second embodiment of the present invention. As shown in Fig. 5, the optical module 1B according to this modification includes a temperature regulator 40 instead of the temperature regulator 30 of the optical module 1A according to the second embodiment, a temperature regulator 41 instead of the temperature regulator 4, and a controller 50B instead of the controller 50A. The other configurations are the same as those of the second embodiment, and the same components are designated by the same reference numerals.

[0074] Of the three temperature regulators 31, 40, and 41 in this modification, the two temperature regulators 31 and 41 are an example of a plurality of temperature regulators in the present invention that respectively regulate the temperatures of a plurality of optical filters to different temperatures. The temperature regulator 41 is, for example, a TEC, and is configured in the same manner as the temperature regulator 31 described above. That is, as shown in FIG. 5, the temperature regulator 41 includes a base 41a, and regulates the temperature of each component on this base 41a by the Peltier effect. The temperature regulator 31 is the same as that in the second embodiment described above, and therefore a description thereof will be omitted.

[0075] For example, the temperature adjuster 41 cools the etalon filter 18 on the base 41a in accordance with the drive current supplied from the controller 50B. As a result, the temperature adjuster 41 adjusts the temperature of this etalon filter 18 separately from the semiconductor laser element 6 whose temperature is adjusted by the temperature adjuster 40 and the etalon filter 17 whose temperature is adjusted by the temperature adjuster 31. In this case, the temperature adjuster 41 adjusts the temperature of this etalon filter 18 to a temperature higher than the temperature of the semiconductor laser element 6 and different from the temperature of the etalon filter 17.

[0076] Furthermore, of the three temperature regulators 31, 40, and 41 in this modification, the temperature regulator 40 is an example of a temperature regulator that regulates the temperature of the semiconductor laser element 6, and is configured separately from the multiple (two in this modification) temperature regulators 31 and 41 that regulate the temperatures of the multiple optical filters. As shown in FIG. 5, the temperature regulator 40 includes a base 41a and regulates the temperature of each component on the base 41a by the Peltier effect. For example, the temperature regulator 40 cools the semiconductor laser element 6 on the base 40a in accordance with the drive current supplied from the controller 50B. In this way, the temperature regulator 40 regulates the temperature of the semiconductor laser element 6.

[0077] 5, in this modification, the LD carrier 5 on which the semiconductor laser element 6, collimator lens 7, and thermistor 19 are mounted, the beam splitters 9, 10, and 11, the optical isolator 8, and the photodiode 12 mounted on the PD carrier 12a are arranged on the base 40a of the temperature regulator 40, similarly to the above-described embodiment 2. The photodiode 14 mounted on the PD carrier 14a, the mirror 16, the etalon filter 18, and the thermistor 20 are arranged on the base 41a of the temperature regulator 41, similarly to the above-described embodiment 2. The material constituting the bases 40a and 41a of the temperature regulators 40 and 41 is a material with high thermal conductivity, similar to the base 31a of the temperature regulator 31.

[0078] The controller 50B controls the temperature adjustment of the semiconductor laser element 6 and the etalon filters 17 and 18 by the three temperature adjusters 40, 31, and 41. The controller 50B controls the temperature adjuster 40 that adjusts the temperature of the semiconductor laser element 6 in the same manner as the temperature adjuster 30 in the second embodiment described above. The controller 50B also controls the temperature adjuster 41 that adjusts the temperature of the etalon filter 18 in the same manner as the temperature adjuster 4 in the second embodiment described above. The control of the temperature adjuster 31 by the controller 50B is the same as in the second embodiment described above.

[0079] Furthermore, the controller 50B performs wavelength lock control of the semiconductor laser device 6, similar to the controller 50A of the above-described embodiment 2. At this time, the controller 50B controls the temperature regulator 40 for temperature regulation of the semiconductor laser device 6, similar to the temperature regulator 30 of embodiment 2.

[0080] As explained above, in the optical module according to the modification of the second embodiment of the present invention, although the aspect of the temperature regulator differs from that of the second embodiment, it is substantially the same as the second embodiment, for example, it has a temperature regulator that regulates the temperature of the semiconductor element and a plurality of temperature regulators that regulate the temperatures of the plurality of optical filters to different temperatures separately provided. Therefore, this modification also enjoys the same effects as the second embodiment.

[0081] In the above-described first and second embodiments and modifications, the temperatures of the etalon filters 17 and 18 are adjusted to mutually different constant temperatures, but the present invention is not limited to this. In the present invention, the temperatures of the plurality of optical filters exemplified by the etalon filters 17 and 18 may be finely adjusted as long as the error in the phase shift due to temperature changes in the transmission characteristics of the optical filters is within a predetermined tolerance. For example, the temperatures of the plurality of optical filters may be finely adjusted within a range having a certain temperature width (e.g., 5°C) centered on a target temperature.

[0082] In addition, in the above-described first and second embodiments and the modified examples, etalon filters have been exemplified as an example of optical filters having frequency-periodic transmission characteristics of light, but the present invention is not limited to this. In the present invention, the optical filters having the above transmission characteristics may be, for example, etalon filters, ring resonator filters, or Mach-Zehnder interference filters.

[0083] Furthermore, in the above-described first and second embodiments and the modified example, an optical module including two etalon filters having frequency-periodic transmission characteristics of light has been exemplified, but the present invention is not limited to this. In the present invention, the number of optical filters having the above transmission characteristics may be two, or three or more. Furthermore, the number of temperature regulators that adjust the temperatures of the optical filters may be two or three as described above, or four or more, as long as the temperatures of the plurality of optical filters can be adjusted to different temperatures.

[0084] Furthermore, the present invention is not limited to the above-described first and second embodiments and modifications. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, other embodiments, examples, operational techniques, etc., made by those skilled in the art based on the above-described first and second embodiments and modifications are all included in the scope of the present invention. [Explanation of symbols]

[0085] 1, 1A, 1B Optical Module 2. Case 3, 4, 30, 31, 40, 41 Temperature regulator 3a, 4a, 30a, 31a, 40a, 41a base 5 LD Carrier 6. Semiconductor laser element 7 Collimating Lens 8 Optical isolator 9, 10, 11 Beam splitter 12, 13, 14 Photodiodes 12a, 13a, 14a PD carrier 15, 16 Mirror 17, 18 Etalon filters 19, 20, 25 Thermistor 21 Condenser lens 22 Ferrule 23 Optical Fiber 50, 50A, 50B controller C1, C2 curve L1 laser light L2, L3, L4 branched laser light

Claims

1. A semiconductor laser element that is a wavelength tunable laser element; a plurality of optical filters each having a transmission characteristic that is periodic in terms of optical frequency and transmitting a plurality of branched laser beams that are parts of the laser beam output from the semiconductor laser element at a transmittance corresponding to the transmission characteristic; a plurality of temperature adjusters that adjust the temperatures of the plurality of optical filters to different temperatures; a controller that performs wavelength lock control to set the variable wavelength of the laser light output from the semiconductor laser element to a desired wavelength; Equipped with the transmission characteristics of the plurality of optical filters are adjusted by adjusting the temperatures of the plurality of optical filters using the plurality of temperature regulators so that the phases are different from each other; the wavelength locking control is performed based on the intensity of a portion of the laser light output from the semiconductor laser element and the intensities of the plurality of branched laser lights that have passed through the plurality of optical filters after temperature adjustment; each time the controller performs the wavelength locking control, the plurality of temperature adjusters change the temperature of at least one optical filter among the plurality of optical filters so that the temperatures of the plurality of optical filters are different from each other; An optical module characterized by:

2. the plurality of temperature regulators include a temperature regulator that regulates both the temperature of one of the plurality of optical filters and the temperature of the semiconductor laser element; 2. The optical module according to claim 1.

3. 2. The optical module according to claim 1, further comprising a temperature regulator separate from the plurality of temperature regulators, for regulating the temperature of the semiconductor laser element.

4. the plurality of temperature regulators respectively adjust the temperatures of the plurality of optical filters to constant target temperatures different from one another; 4. The optical module according to claim 1, wherein the optical module is a semiconductor device.

5. the plurality of temperature adjusters adjust the temperatures of the plurality of optical filters to temperatures equal to or higher than the temperature of the semiconductor laser element, respectively; 5. The optical module according to claim 1, wherein the optical module is a semiconductor device.

6. Each of the plurality of optical filters is an etalon filter, a ring resonator filter, or a Mach-Zehnder interference filter.

6. The optical module according to claim 1, wherein the optical module is a semiconductor device.

7. Each of the plurality of temperature regulators is a thermoelectric cooler.

7. The optical module according to claim 1, wherein the optical module is a semiconductor device.

8. the semiconductor laser element is a vernier type wavelength tunable laser element or a DFB integrated type wavelength tunable laser element in which a plurality of distributed feedback laser elements are integrated; 8. The optical module according to claim 1, wherein the optical module is a semiconductor device.

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