Optical module

Abstract

An optical coupler (11), an optical demultiplexer (13), a first light-receiving element (14), a second light-receiving element (15), and a waveguide-type interferometer (16) are formed on a surface of a semiconductor substrate (10) of a wavelength monitor chip (6). The optical coupler (11) inputs rear surface light of a light-emitting element (7) as incident light. The optical demultiplexer (13) branches the incident light into first branched light and second branched light. The first light-receiving element (14) receives the first branched light. The second light-receiving element (15) receives the second branched light via the waveguide-type interferometer (16). A control unit (8) controls a current of the light-emitting element (7) so that a light-receiving current of the first light-receiving element (14) is constant, and controls a temperature of the light-emitting element (7) so that a value obtained by dividing a light-receiving current of the second light-receiving element (15) by the light-receiving current of the first light-receiving element (14) is constant. A surface protective film (20) covers the surface of the semiconductor substrate (10) and prevents the rear surface light from entering the semiconductor substrate (10).

Description

Optical Module

[0001] The present disclosure relates to an optical module incorporating a wavelength monitor chip that monitors backside light of a light-emitting element.

[0002] With the spread of the Internet, optical communication systems are becoming increasingly large-capacity. High-capacity optical communication systems are being introduced, including dense wavelength division multiplexing (DWDM), which densely multiplexes optical signals at predetermined wavelength intervals, and digital coherent systems, which encode multiple pieces of information into a single modulation by encoding information not only in intensity modulation but also in phase. In DWDM systems, wavelengths must be controlled to match predetermined wavelengths with high precision in order to reduce signal filter losses and inter-channel crosstalk. Digital coherent systems also require the wavelengths of transmitted / received optical signals and local light to be matched and interfere with each other, so wavelengths must be controlled to match predetermined wavelengths with high precision.

[0003] On the other hand, light-emitting elements such as laser diodes, which are light sources in optical communication systems, have the characteristic that their wavelengths change depending on factors such as temperature and drive current. Therefore, a wavelength monitor chip monitors the backside light of the light-emitting element and controls the light-emitting element based on the monitoring results. In the wavelength monitor chip, a grating coupler inputs the backside light of the light-emitting element as incident light and couples it to an optical waveguide (see, for example, Patent Document 1).

[0004] Japanese Patent No. 5969811

[0005] However, the coupling efficiency of grating couplers is not high, and most of the incident light does not couple with the waveguide but enters the semiconductor substrate and becomes stray light. The waveguide-type photodetector in the wavelength monitor chip receives not only the light propagating through the waveguide, but also the stray light propagating through the semiconductor substrate. This causes noise in the photodetector's photocurrent, which reduces the control accuracy of the light-emitting element.

[0006] The present disclosure has been made to solve the above-mentioned problems, and its object is to obtain an optical module that can improve the control accuracy of a light-emitting element.

[0007] an optical module according to the present disclosure, comprising: a light-emitting element; a wavelength monitor chip that monitors backside light of the light-emitting element; and a control unit that controls the light-emitting element based on the monitoring results of the wavelength monitor chip; the wavelength monitor chip having a semiconductor substrate; an optical coupler, an optical demultiplexer, first and second light-receiving elements, and a waveguide interferometer formed on a surface of the semiconductor substrate; and a surface protection film that covers the surface of the semiconductor substrate and prevents the backside light from entering the semiconductor substrate; the optical coupler inputs the backside light as incident light; the optical demultiplexer demultiplexes the incident light into first and second branched lights; the first light-receiving element receives the first branched light; and the second light-receiving element receives the second branched light via the waveguide interferometer; and the control unit controls the current of the light-emitting element so that a light-receiving current of the first light-receiving element is constant, and controls the temperature of the light-emitting element so that a value obtained by dividing the light-receiving current of the second light-receiving element by the light-receiving current of the first light-receiving element is constant.

[0008] In the present disclosure, a surface protection film is formed on the surface of the wavelength monitor chip. The surface protection film prevents incident light from reaching the semiconductor substrate, thereby reducing stray light. This improves the control accuracy of the light-emitting element.

[0009] 1 is a side view showing an optical module according to a first embodiment. FIG. 2 is a perspective view showing a wavelength monitor chip according to the first embodiment. FIG. 3 is a perspective view showing a state in which the surface protection film is omitted from the wavelength monitor chip of FIG. 2. FIG. 4 is a cross-sectional view taken along I-II in FIG. 2. FIG. 5 is a cross-sectional view taken along III-IV in FIG. 2. FIG. 6 is a diagram showing the relationship between the wavelength of incident light and the photocurrent received by the second photodetector. FIG. 7 is a diagram showing the operation of an optical module according to a comparative example. FIG. 8 is a diagram showing the relationship between the wavelength of incident light and the photocurrent received by the photodetector in the comparative example. FIG. 9 is a perspective view showing a wavelength monitor chip according to a second embodiment. FIG. 10 is a perspective view showing a wavelength monitor chip according to a third embodiment. FIG. 11 is a perspective view showing a wavelength monitor chip according to a fourth embodiment.

[0010] An optical module according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0011] Embodiment 1. Figure 1 is a side view showing an optical module according to embodiment 1. A Peltier element 2, which is a thermoelectric element, is formed on a stem 1. A block 3 is formed on the Peltier element 2. A submount 4, a lens 5, and a wavelength monitor chip 6 are formed on the side of the block 3. A light-emitting element 7, such as a laser diode, is formed on the submount 4. The lens 5 converts the light emitted from the light-emitting element 7 into parallel light. A lens (not shown) formed on the cap focuses the parallel light into an optical fiber. As a result, the light emitted from the light-emitting element 7 is used as a light source for an optical communication system. The wavelength monitor chip 6 monitors the backside light of the light-emitting element 7. A control unit 8 controls the Peltier element 2 and the light-emitting element 7 based on the monitoring results of the wavelength monitor chip 6.

[0012] Fig. 2 is a perspective view showing a wavelength monitor chip according to the first embodiment. Fig. 3 is a perspective view showing the wavelength monitor chip of Fig. 2 with the surface protection film omitted. Fig. 4 is a cross-sectional view taken along line I-II in Fig. 2. Fig. 5 is a cross-sectional view taken along line III-IV in Fig. 2.

[0013] As shown in FIGS. 4 and 5, the semiconductor substrate 10 is formed by depositing a SiO ２ The SOI substrate is formed by stacking a layer 10b and a Si layer 10c in this order. An optical coupler 11, an optical waveguide 12, an optical demultiplexer 13, first and second waveguide-type light-receiving elements 14 and 15, a waveguide-type interferometer 16, and a phase adjuster 17 are formed on the surface of the semiconductor substrate 10 and monolithically integrated.

[0014] The optical coupler 11 is, for example, a grating coupler, and receives backside light from the light-emitting element 7 as incident light and couples it to the optical waveguide 12. The optical demultiplexer 13 is, for example, an MMI (Multimode Interference) coupler, and demultiplexes the incident light into first and second branched lights.

[0015] The first light-receiving element 14 receives the first branched light. The light-receiving current of the first light-receiving element 14 reflects the optical output of the light-emitting element 7. The second light-receiving element 15 receives the second branched light via a waveguide interferometer 16. The light-receiving current of the second light-receiving element 15 reflects the oscillation wavelength of the light-emitting element 7. The waveguide interferometer 16 is a ring resonator having a straight waveguide and a ring waveguide. The phase adjustment unit 17 is, for example, a heater made of a thin-film resistor.

[0016] 4 and 5, the second light receiving element 15 is a photodiode having a p-type Ge layer 15a, an i-type Ge light absorbing layer 15b, and an n-type Ge layer 15c stacked in this order on the semiconductor substrate 10. An electrode 18 is formed on the p-type Ge layer 15a, and an electrode 19 is formed on the n-type Ge layer 15c. The first light receiving element 14 is also a photodiode with a similar configuration.

[0017] The receiving characteristics change when the optical output of the light-emitting element 7 changes. Therefore, the control unit 8 adjusts the current of the light-emitting element 7 so that the light-receiving current of the first light-receiving element 14 of the wavelength monitor chip 6 becomes constant, thereby maintaining the optical output of the light-emitting element 7 constant.

[0018] The light propagating through the ring waveguide of the waveguide interferometer 16 and the light propagating through the straight waveguide interfere constructively or destructively. The transmittance of the waveguide interferometer 16 is determined by the phase relationship (relative phase) between the interfering lights, resulting in a characteristic in which peaks and valleys are repeated with respect to wavelength. The oscillation wavelength is monitored using this wavelength dependency of transmittance. Wavelength change can be detected most efficiently when the slope of the transmittance of the waveguide interferometer 16 with respect to wavelength becomes large. Therefore, the phase adjustment unit 17 heats a portion of the ring waveguide to change the length and refractive index of the waveguide and thereby change the phase of the light propagating through the ring waveguide. This changes the transmittance with respect to wavelength, allowing adjustment to increase the slope of the transmittance for the desired wavelength. Note that although the heater adjusts the temperature of a portion of the waveguide of the waveguide interferometer 16, the temperature of the entire waveguide of the waveguide interferometer 16 may also be adjusted. Furthermore, the phase adjusting unit 17 is not limited to a heater, but may be a means for changing the refractive index of the waveguide material by applying an electric field.

[0019] 6 is a diagram showing the relationship between the wavelength of incident light and the photocurrent of the second photodetector. The transmittance of the waveguide interferometer 16, located upstream of the second photodetector 15, exhibits a characteristic in which peaks and valleys repeat periodically with respect to the wavelength of the incident light. Therefore, the photocurrent of the second photodetector 15 changes depending on the wavelength of the incident light. The phase adjustment unit 17 adjusts the refractive index of the waveguide material so that the set value of the photocurrent falls within the range where this change is greatest.

[0020] The optical output of the light-emitting element 7 may change over time. Therefore, even if the temperature of the light-emitting element 7 is adjusted so that the light-receiving current of the second light-receiving element 15 is constant, the wavelength may not necessarily be constant, and wavelength deviation may occur. Therefore, the control unit 8 calculates the transmittance by dividing the light-receiving current of the second light-receiving element 15 by the light-receiving current of the first light-receiving element 14, which corresponds to the optical output of the light-emitting element 7, and adjusts the temperature of the light-emitting element 7 by the Peltier element 2 so that this value becomes constant. This makes it possible to maintain the oscillation wavelength of the light emitted from the light-emitting element 7 at a predetermined wavelength. For example, the wavelength of the light emitted from the light-emitting element 7 may be set to λ ０ When the transmittance of the waveguide interferometer 16 is set to T ０ The wavelength is adjusted to λ by adjusting the temperature of the light emitting element 7 so that ０ can be maintained.

[0021] A metal film 20 covers the surface of the semiconductor substrate 10 as a surface protection film. The metal film 20 prevents backside light from the light-emitting element 7 from entering the semiconductor substrate 10. Openings are formed in the metal film 20, and the light-receiving portion of the optical coupler 11, which is the optical input portion of the wavelength monitor chip 6, and the output electrodes of the light-receiving signals of the first and second light-receiving elements 14 and 15, which are the electrical signal output portions of the wavelength monitor chip 6, are exposed from the metal film 20. The optical demultiplexer 13, the optical waveguide 12, the waveguide interferometer 16, and the like are covered with the metal film 20.

[0022] Next, the effects of this embodiment will be explained in comparison with a comparative example. Figure 7 is a diagram showing the operation of an optical module according to the comparative example. In this example, metal film 20 is not formed on the surface of wavelength monitor chip 6. The coupling efficiency of optical coupler 11 is not high, and most of the incident light enters semiconductor substrate 10 without being coupled to optical waveguide 12, becoming stray light. First and second light-receiving elements 14 and 15 of wavelength monitor chip 6 receive not only light propagating through optical waveguide 12, but also stray light propagating through semiconductor substrate 10.

[0023] 8 is a diagram showing the relationship between the wavelength of incident light and the photocurrent of the photodetector in a comparative example. Fig. 8 corresponds to the area surrounded by the dashed line in Fig. 6. When the first and second photodetectors 14 and 15 receive stray light, noise is introduced into the photocurrent. If the light-emitting element 7 is controlled based on this photocurrent, the control accuracy will be reduced.

[0024] In contrast to this, in this embodiment, metal film 20 is formed on the surface of wavelength monitor chip 6. Metal film 20 prevents light from entering semiconductor substrate 10, thereby reducing stray light. This improves the control accuracy of light-emitting element 7.

[0025] Furthermore, it is preferable that the material and thickness of the metal film 20 are the same as those of the electrodes 18, 19 of the first and second light-receiving elements 14, 15. In this case, the metal film 20 and the electrodes 18, 19 of the first and second light-receiving elements 14, 15 can be formed simultaneously, and therefore the metal film 20 can be formed without increasing the number of manufacturing steps.

[0026] Second Embodiment. Figure 9 is a perspective view showing a wavelength monitor chip according to a second embodiment. Instead of a metal film 20, a light absorbing layer 21 is formed on the surface of the semiconductor substrate 10 of the wavelength monitor chip 6 as a surface protection film. The light absorbing layer 21 absorbs backside light from the light emitting element 7, thereby preventing light from entering the semiconductor substrate 10 and reducing stray light. This improves the control accuracy of the light emitting element 7. The light absorbing layer 21 may be formed of the same material as the light absorbing layers of the first and second light receiving elements 14 and 15. The other configurations and effects are the same as those of the first embodiment.

[0027] Third Embodiment Fig. 10 is a perspective view showing a wavelength monitor chip according to a third embodiment. Unlike the first and second embodiments, no surface protection film is formed, and a phase modulation unit 22 utilizing the Pockels effect or the like is formed in a part of the ring waveguide of the waveguide interferometer 16. Note that the phase adjustment unit 17 may also be used as the phase modulation unit 22. The rest of the configuration of the wavelength monitor chip and optical module is the same as that of the first embodiment.

[0028] The phase modulation unit 22 applies (dithers) a pilot signal, which is a modulated wave such as a sine wave, to the light propagating through the ring waveguide of the waveguide interferometer 16. This allows phase modulation to be applied only to the light that has passed through the ring waveguide of the waveguide interferometer 16, and does not apply phase modulation to stray light that does not pass through the ring waveguide. Note that a heater can be used as the phase modulation unit 22 if the pilot signal is 1 kHz or less. A phase modulation unit 22 that uses an electric field can widen the frequency range of the pilot signal.

[0029] The second light-receiving element 15 receives the second branched light via the waveguide interferometer 16. The oscillation wavelength of the light-emitting element 7 can be monitored by detecting only the light-receiving current modulated according to the pilot signal. The control unit 8 controls the temperature of the light-emitting element 7 so that the value obtained by dividing the modulated signal component of the light-receiving current of the second light-receiving element 15 modulated according to the pilot signal by the light-receiving current of the first light-receiving element 14 (i.e., the transmittance of the waveguide interferometer 16 is constant) remains constant. This allows the oscillation wavelength of the light-emitting element 7 to be kept constant.

[0030] Next, the effects of this embodiment will be explained in comparison with a comparative example. In the comparative example, a pilot signal is not applied. In this case, the transmittance of the ring resonator of waveguide interferometer 16 is calculated as follows. The temperature of light-emitting element 7 is controlled so that this transmittance is constant.

[0031] Here, I ０ is the DC component of the light-receiving current of the first light-receiving element 14. ０ is the stray light component of the light-receiving current of the first light-receiving element 14. １ is the DC component of the light-receiving current of the second light-receiving element 15.１ is the stray light component of the light-receiving current of the second light-receiving element 15. Although the stray light is large, the size of the light-receiving element is small, so the received stray light is smaller than the light propagating through the waveguide. Therefore, the above approximate calculation is possible.

[0032] The noise component due to stray light in the comparative example is expressed as follows:

[0033] where σ ０ Is I ０ is the standard deviation of the variation of σ １ Is I １ σ is the standard deviation of the variation of the stray light component i of the received light current. However, assuming that the stray light component received by all light receiving elements is the same, σ ０ ≒σ １ Since the incident light is split into two halves by the optical splitter 13, it is assumed that the transmittance of the ring resonator is set to 50%, and I ０ ≒2I １ Finally, the variations were combined by taking the square root of the sum of the squares of the standard deviations of each variation.

[0034] In contrast to this, in this embodiment, only the photocurrent modulated in accordance with the pilot signal is detected to monitor the oscillation wavelength of the light-emitting element 7. In this case, the transmittance of the ring resonator of the waveguide interferometer 16 is calculated as follows:

[0035] Here, S １ is the modulated signal component of the light-receiving current of the second light-receiving element 15. As a result, the noise component due to stray light in this embodiment is σ / I ０ The noise component in the comparative example is √5σ / I ０ Therefore, it can be seen that in this embodiment, the influence of noise due to stray light is smaller than in the comparative example, and the wavelength control precision is improved.

[0036] As described above, in this embodiment, the temperature of the light-emitting element 7 is controlled so that the value obtained by dividing the modulated signal component of the light-receiving current of the second light-receiving element 15 modulated in accordance with the pilot signal by the light-receiving current of the first light-receiving element 14 becomes constant. This makes it possible to eliminate the influence of stray light, thereby improving the control accuracy of the oscillation wavelength of the light-emitting element 7.

[0037] 11 is a perspective view showing a wavelength monitor chip according to embodiment 4. Unlike embodiment 3, the optical demultiplexer 13 is not used, and instead, the optical coupler 11, optical waveguide 12, first and second waveguide-type light-receiving elements 23 and 24, and waveguide-type interferometer 16 are formed on the surface of semiconductor substrate 10 and monolithically integrated.

[0038] The optical coupler 11 receives the rear surface light of the light-emitting element 7 as incident light and couples it to the optical waveguide 12. The first light-receiving element 23 is formed at an output port (through port) on the input side of the waveguide interferometer 16. The second light-receiving element 24 is formed at an output port (cross port) on the output side of the waveguide interferometer 16.

[0039] The phase modulation unit 22 applies (dithers) a pilot signal, which is a modulated wave such as a sine wave, to the light propagating through the ring waveguide of the waveguide interferometer 16. This makes it possible to apply phase modulation only to the light that has passed through the ring waveguide of the waveguide interferometer 16, and not to stray light that does not pass through the ring waveguide. The first light-receiving element 23 and the second light-receiving element 24 receive the incident light via the waveguide interferometer 16.

[0040] The wavelength dependence of the transmittance observed by the first light-receiving element 23 and the second light-receiving element 24 are opposite characteristics. Furthermore, the loss in the waveguide of the waveguide interferometer 16 is small and can be ignored. Therefore, the sum of the light-receiving current of the first light-receiving element 23 and the light-receiving current of the second light-receiving element 24 does not depend on the wavelength, but reflects the optical output of the light-emitting element 7. The control unit 8 controls the current of the light-emitting element 7 so that this sum remains constant. This makes it possible to maintain the optical output of the light-emitting element 7 constant.

[0041] Furthermore, the modulation signal components of the light-receiving currents of the first light-receiving element 23 and the second light-receiving element 24 also have inverse characteristics, and their magnitudes reflect the slope of the transmittance. Therefore, the control unit 8 adjusts the temperature of the light-emitting element 7 so that the value obtained by dividing the sum of the modulation signal components of the light-receiving currents of the first light-receiving element 23 and the second light-receiving element 24, which are added in opposite phases, by the sum of the light-receiving currents of the first light-receiving element 23 and the second light-receiving element 24, becomes constant. This makes it possible to maintain a constant oscillation wavelength of the light-emitting element 7.

[0042] In this embodiment, the oscillation wavelength of the light-emitting element 7 is monitored by detecting the modulated signal components of the light-receiving currents of the first and second light-receiving elements 23 and 24 modulated in accordance with the pilot signal, so the transmittance of the ring resonator of the waveguide interferometer 16 is calculated as follows:

[0043] Here, I １ is the DC component of the light-receiving current of the first light-receiving element 23. １ is the stray light component of the light-receiving current of the first light-receiving element 23. １ is the modulated signal component of the light-receiving current of the first light-receiving element 23. ２ is the DC component of the light-receiving current of the second light-receiving element 24. ２ is the stray light component of the light-receiving current of the second light-receiving element 24. ２ is the modulated signal component of the photocurrent of the second photodetector 24.

[0044] The noise component due to stray light in this embodiment is expressed as follows:

[0045] The noise component due to stray light in this embodiment is σ / √2I ０ is the noise component √5σ / I of the comparative example ０ Therefore, it can be seen that the present embodiment is less susceptible to noise due to stray light than the comparative example, and the wavelength control precision is improved.

[0046] As described above, in this embodiment, the current of the light-emitting element 7 is controlled so that the sum of the light-receiving currents of the first light-receiving element 23 on the through port side and the second light-receiving element 24 on the cross port side is constant. This makes it possible to maintain the optical output of the light-emitting element 7 constant. Furthermore, the temperature of the light-emitting element 7 is controlled so that the value obtained by adding, in opposite phase, the modulated signal components of the light-receiving currents of the first and second light-receiving elements 23, 24 modulated according to the pilot signal, and dividing this sum by the sum of the light-receiving currents of the first and second light-receiving elements 23, 24 remains constant. This makes it possible to maintain the oscillation wavelength of the light-emitting element 7 constant.

[0047] Furthermore, since the optical demultiplexer 13 is not formed, the wavelength monitor chip 6 can be made smaller. And, by detecting only the photocurrent modulated in response to the pilot signal and monitoring the oscillation wavelength of the light-emitting element 7, the influence of stray light can be eliminated. Furthermore, by monitoring the sum of the modulated signal components of the photocurrents of the first and second light-receiving elements 23 and 24, which are added in opposite phases, the modulated signal component is doubled, thereby improving wavelength control accuracy.

[0048] 7 Light-emitting element, 6 Wavelength monitor chip, 8 Control unit, 10 Semiconductor substrate, 11 Optical coupler, 13 Optical demultiplexer, 14 First light-receiving element, 15 Second light-receiving element, 16 Waveguide interferometer, 18, 19 Electrode, 20 Metal film (surface protection film), 21 Light absorption layer (surface protection film), 22 Phase modulation unit, 23 First light-receiving element, 24 Second light-receiving element

Claims

1. A light-emitting element, a wavelength monitor chip that monitors backside light of the light-emitting element, and a control unit that controls the light-emitting element based on the monitoring results of the wavelength monitor chip, wherein the wavelength monitor chip has: a semiconductor substrate; an optical coupler, an optical splitter, first and second light-receiving elements, and a waveguide-type interferometer formed on a surface of the semiconductor substrate; and a surface protection film that covers the surface of the semiconductor substrate and prevents the backside light from being incident on the semiconductor substrate, wherein the optical coupler inputs the backside light as incident light, the optical splitter splits the incident light into first branched light and second branched light, the first light-receiving element receives the first branched light, and the second light-receiving element receives the second branched light via the waveguide-type interferometer, The control unit controls the current of the light-emitting element so that the light-receiving current of the first light-receiving element is constant, and controls the temperature of the light-emitting element so that the value obtained by dividing the light-receiving current of the second light-receiving element by the light-receiving current of the first light-receiving element is constant.

2. The optical module according to claim 1, wherein the surface protection film is a metal film.

3. The optical module according to claim 2, wherein the material and thickness of said metal film are the same as those of the electrodes of said first and second light receiving elements.

4. The optical module according to claim 1, wherein the surface protection film is a light absorbing layer that absorbs the backside light.

5. A light-emitting element, a wavelength monitor chip that monitors backside light of the light-emitting element, and a control unit that controls the light-emitting element based on the monitoring results of the wavelength monitor chip, wherein the wavelength monitor chip has a semiconductor substrate, and an optical coupler, an optical splitter, first and second light receiving elements, a waveguide interferometer, and a phase modulation unit that are formed on a surface of the semiconductor substrate, wherein the optical coupler inputs the backside light as incident light, the optical splitter splits the incident light into first branched light and second branched light, the first light receiving element receives the first branched light, the phase modulation unit applies a pilot signal to light propagating through a ring waveguide of the waveguide interferometer, and the second light receiving element receives the second branched light via the waveguide interferometer, The control unit controls the current of the light-emitting element so that the light-receiving current of the first light-receiving element is constant, and controls the temperature of the light-emitting element so that the value obtained by dividing the modulated signal component of the light-receiving current of the second light-receiving element modulated according to the pilot signal by the light-receiving current of the first light-receiving element is constant.

6. A light-emitting element, a wavelength monitor chip that monitors backside light of the light-emitting element, and a control unit that controls the light-emitting element based on the monitoring results of the wavelength monitor chip, wherein the wavelength monitor chip has a semiconductor substrate, an optical coupler formed on a front surface of the semiconductor substrate, first and second light-receiving elements, a waveguide interferometer, and a phase modulation unit, wherein the optical coupler inputs the backside light as incident light, the first light-receiving element is formed at a through port of the waveguide interferometer, and the second light-receiving element is formed at a cross port of the waveguide interferometer, the first and second light-receiving elements receive the incident light via the waveguide interferometer, and the phase modulation unit applies a pilot signal to light propagating through a ring waveguide of the waveguide interferometer, an optical module characterized in that the control unit controls the current of the light-emitting element so that the sum of the light-receiving currents of the first and second light-receiving elements is constant, and controls the temperature of the light-emitting element so that the sum of the modulated signal components of the light-receiving currents of the first and second light-receiving elements modulated according to the pilot signal, added in opposite phases, divided by the sum of the light-receiving currents of the first and second light-receiving elements, becomes constant.

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