Optical module and method for controlling optical module

Abstract

The optical module includes a semiconductor laser (5) and an optical monitor (6) that receives laser light from the semiconductor laser (5) and outputs a first monitor value and a second monitor value for estimating the intensity and wavelength of the laser light from the semiconductor laser (5). The optical monitor (6) includes a first optical coupler (61a) that receives the laser light from the semiconductor laser (5), a second optical coupler (61b) that receives the laser light from the semiconductor laser (5), a first optical receiver (65a) that outputs the first monitor value, and a second optical receiver (65b) that outputs the second monitor value, and constitutes an optical interferometer in which a first path from the first optical coupler (61a) to the first optical receiver (65a) and a second path from the second optical coupler (61b) to the second optical receiver (65b) are asymmetric.

Description

[Technical field]

[0001] The present disclosure relates to an optical module and a control method for the optical module, and more particularly to an optical module including a single-wavelength semiconductor laser and a control method for the optical module. [Background technology]

[0002] One method for increasing the capacity of optical communication systems is the digital coherent communication method. Digital coherent communication is a method for transmitting multiple channels by carrying signals not only on the intensity of light but also on the phase. Since the phenomenon of optical interference is used to extract the optical phase information, it is necessary to precisely control the wavelengths of both the light source of the transmitter that sends the signal and the local light that becomes the interference light at the receiver that receives the signal.

[0003] A single mode laser is used as the light source for these. Although a single mode laser oscillates at a single wavelength, the oscillation wavelength and optical output intensity change due to manufacturing errors and environmental temperature. Therefore, a wavelength locker for wavelength control and an optical intensity monitor are essential in a light source module for digital coherent communication equipped with a single-mode laser.

[0004] A laser module that locks the wavelength of a laser to a desired range is shown in US Pat. No. 5,399,633. The laser module shown in Patent Document 1 compares the monitor output of a photodetector that monitors light emitted from the rear end face of the laser through a lens and beam splitter with the monitor output of a photodetector that monitors light that has passed through an etalon, and locks the wavelength of the laser within a desired range by controlling the temperatures of the first Peltier element and the second Peltier element. The laser module shown in Patent Document 1 has a laser, a third collecting lens, a first collecting lens, a beam splitter, two light receiving elements, and a thermistor mounted on the mounting surface of the first Peltier element, and an etalon mounted on the mounting surface of the second Peltier element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-69130 A Summary of the Invention [Problem to be solved by the invention]

[0006] The laser module disclosed in Patent Document 1 has a Peltier element for each of the laser and the etalon, and has a large number of parts. In addition, since an etalon is used, a part for collimating the light to be incident on the etalon is necessary, and the etalon itself needs to be of a certain size.

[0007] The present disclosure has been made in consideration of the above-mentioned points, and has an object to provide an optical module that emits a single wavelength, has a small number of parts, and can be miniaturized. [Means for solving the problem]

[0008] The optical module according to the present disclosure includes a semiconductor laser and an optical monitor that receives laser light from the semiconductor laser and outputs a first monitor value and a second monitor value for estimating the intensity and wavelength of the laser light from the semiconductor laser. The optical monitor includes a first optical coupler that receives the laser light from the semiconductor laser, a second optical coupler that receives the laser light from the semiconductor laser, a first optical receiver that outputs the first monitor value, and a second optical receiver that outputs the second monitor value, forming an optical interferometer in which a first path from the first optical coupler to the first optical receiver and a second path from the second optical coupler to the second optical receiver are asymmetric. Effect of the Invention

[0009] According to the present disclosure, precise control can be performed for a single wavelength, and the number of parts can be reduced, allowing for miniaturization. [Brief description of the drawings]

[0010] [Figure 1] 2 is a perspective view showing a state in which a cap is removed in the optical module according to the first embodiment. FIG. [Diagram 2] 1 is a perspective view showing an optical module according to a first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III of FIG. [Figure 4] 1 is a block diagram showing an optical monitor in an optical module according to a first embodiment. [Diagram 5] 2 is a schematic perspective view showing an optical monitor in the optical module according to the first embodiment. FIG. [Figure 6] 1 is a schematic block diagram showing an optical module device according to a first embodiment. [Figure 7] 4 is a diagram showing an output obtained by an optical monitor in the optical module device according to the first embodiment. FIG. [Figure 8] FIG. 11 is a diagram showing an optical power monitor value Ip, which is the sum of a first monitor value and a second monitor value obtained by an optical monitor in an optical module device according to the first embodiment, and a wavelength monitor value Iλ, which is the difference between the first monitor value and the second monitor value. [Figure 9] 5 is a flowchart showing an operation of the optical module according to the first embodiment. [Figure 10] 4 is a diagram illustrating a state in which a backward laser light of a semiconductor laser is misaligned with respect to a first optical coupler and a second optical coupler in the optical module according to the first embodiment. FIG. [Figure 11] 10 is a diagram showing an equiphase surface in a state in which a rear laser light of a semiconductor laser is misaligned with respect to a first optical coupler and a second optical coupler in the optical module according to the first embodiment. FIG. [Figure 12] 11 is a diagram showing the results of trial calculations of mounting misalignment and coupling inclination in the optical module according to the first embodiment. FIG. [Figure 13] FIG. 11 is a schematic perspective view showing an optical monitor in an optical module according to a second embodiment. [Figure 14] 13 is a diagram showing an output obtained by an optical monitor in the optical module according to the second embodiment. FIG. [Figure 15] FIG. 11 is a schematic perspective view showing an optical monitor in an optical module according to a third embodiment. [Figure 16] 13A and 13B are diagrams illustrating waveforms of an I photocurrent, a Q photocurrent, and an I photocurrent, and a relationship between the Q photocurrent and an optical power monitor value Ip and a wavelength monitor value Iλ in an optical module according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Embodiment 1 The optical module according to the first embodiment will be described with reference to FIGS. The optical module according to the first embodiment is suitable for use as a light source module for digital coherent communication. The optical module according to the first embodiment is an example applied to a TO-CAN type optical transmission module for optical communications.

[0012] The optical module according to the first embodiment is an optical module equipped with a single-wavelength semiconductor laser. The optical module according to the first embodiment is an optical module having a function of adjusting the temperature of a semiconductor laser, and a function of monitoring the optical output and oscillation wavelength from the semiconductor laser. Therefore, the following description will be given taking a TO-CAN type optical transmission module for optical communications as an example.

[0013] As shown in Figures 1 to 3, the optical module of embodiment 1 includes a stem 1, a temperature regulator 2, a base 3, a submount for a semiconductor laser (hereinafter abbreviated as submount) 4, a semiconductor laser 5, a planar waveguide type optical monitor (hereinafter abbreviated as optical monitor) 6, a cap 7, a number of lead pins P1 to P6, and a ground lead pin P7. In order to avoid complication, wires for electrically and optically connecting the components 2, 5, and 6 to the lead pins P1 to P6 are omitted in FIGS.

[0014] The stem 1 is made of a metal disk. The shape of the stem 1 is not limited to a disk shape, but may be a cylinder or a square prism, or may be a flat plate having an inner plane 1a and an outer plane 1b parallel to the inner plane 1a. An inner flat surface 1a of the stem 1 is a mounting surface, which serves as an area for mounting components. In this example, the stem 1 is a metal disk having a diameter of 5.6 mm.

[0015] The stem 1 is combined with a cap 7 to form a package 10. The package 10 is a TO-CAN type package. The cap 7 is a windowed cap having a bottom and a side wall, one end of which is open. The cap 7 is a cylindrical lens cap made of metal and has an outer diameter slightly smaller than the diameter of the stem 1 .

[0016] The cap 7 has an opening at the center of its bottom, which is a window 8, in which a flat piece of glass or a lens is mounted. The window 8, which is a flat glass or lens, is attached to an opening formed in the bottom portion by bonding with an adhesive or by melting so that airtightness is maintained inside and outside the cap.

[0017] The end face of the side wall of the cap 7 is in contact with the peripheral end of the inner flat surface 1a of the stem 1 and is joined and fixed by electric welding. The interior enclosed by the stem 1 and the cap 7 is filled with an inert gas or is in a vacuum state, and the semiconductor laser 5 is isolated from the outside air and hermetically sealed. From the window 8, the semiconductor laser 5 emits a forward laser beam Lf.

[0018] The temperature regulator 2 is housed in a package 10 and placed on the stem 1 . The temperature regulator 2 has a flat lower surface 2a and a flat upper surface 2b parallel to the lower surface 2a, and the lower surface 2a is fixed to the inner flat surface 1a of the stem 1 by solder or a conductive adhesive, and the upper surface 2b serves as the mounting surface. Hereinafter, the upper surface 2b will be referred to as the mounting surface. The temperature regulator 2 heats or cools the mounting surface 2b by the flow of a photocurrent.

[0019] The temperature regulator 2 performs control to change the temperatures applied to the semiconductor laser 5 and the optical monitor 6 when the monitor value from the optical monitor 6 deviates from the set monitor value. That is, the temperature regulator 2 regulates the temperature of the semiconductor laser 5 and the temperature of the optical monitor 6 . The temperature regulator 2 is a thermo-electric cooler (TEC) constituted by a Peltier element.

[0020] The base 3 is an L-shaped metal member that is placed on the mounting surface 2b of the temperature controller 2 and has a flat portion 3a whose upper and lower surfaces are flat, and a vertical portion 3b whose vertical surface is flat and formed integrally with the flat portion 3a. The lower surface of the flat portion 3a of the base 3 is fixed to the mounting surface 2b of the temperature regulator 2 by solder or a conductive adhesive.

[0021] A semiconductor laser 5 is mounted and fixed on the vertical surface of the vertical portion 3b of the base 3 via a submount 4 for a semiconductor laser. The semiconductor laser 5 is fixed to the vertical surface of the vertical portion 3b of the base 3 so that the optical axis of the forward laser light Lf and the optical axis of the backward laser light Lb of the semiconductor laser 5 coincide with the central axis of the stem 1. The submount 4 is configured, for example, by a base made of a dielectric material such as aluminum nitride (AlN) on whose surface a metal wiring layer is patterned.

[0022] An optical monitor 6 is placed and fixed on the upper surface of the flat portion 3 a of the base 3 . The optical monitor 6 is fixed to the upper surface of the flat portion 3 a of the base 3 so as to receive the rear laser light Lb from the semiconductor laser 5 . The optical monitor 6 is disposed at an angle where it can receive the rear laser light Lb from the semiconductor laser 5 . That is, the optical monitor 6 and the semiconductor laser 5 are arranged at an angle that provides the maximum coupling efficiency of the first optical coupler 61a and the second optical coupler 61b (see FIGS. 4 and 5) in the optical monitor 6 for the backward laser light Lb from the semiconductor laser 5.

[0023] For example, the semiconductor laser 5 is disposed so that the backward laser light Lb of the semiconductor laser 5 strikes the first optical coupler 61a and the second optical coupler 61b in the optical monitor 6 substantially perpendicularly. In this example, the pedestal 3 is fabricated so that the upper surface of the flat portion 3a and the surface of the vertical portion 3b, i.e., the mounting surface for the submount 4, are inclined. The interior angle between the upper surface of the flat portion 3a and the surface of the vertical portion 3b is inclined at an angle exceeding 90 degrees, and the semiconductor laser 5 and the optical monitor 6 are disposed on the pedestal 3 at an angle.

[0024] In this way, by making the interior angle between the upper surface of the planar portion 3a and the surface of the vertical portion 3b not completely perpendicular but at an angle shifted from 90 degrees, it is possible to prevent the reflected return light of the rear laser light Lb of the semiconductor laser 5 reflected from the first optical coupler 61a and the second optical coupler 61b in the optical monitor 6 from being incident on the semiconductor laser 5. As a result, unstable laser operation in the semiconductor laser 5 can be avoided.

[0025] The base 3 conducts heat from the mounting surface 2 b of the temperature regulator 2 through the submount 4 to regulate the temperature of the semiconductor laser 5 , that is, to heat or cool the semiconductor laser 5 . At the same time, the base 3 conducts heat from the mounting surface 2 b of the temperature regulator 2 to adjust the temperature of the optical monitor 6 , that is, to heat or cool the optical monitor 6 . Since the semiconductor laser 5 and the optical monitor 6, whose temperature is adjusted by the temperature regulator 2, are arranged vertically on the base 3, the area occupied by the semiconductor laser 5 and the optical monitor 6 on the mounting surface 2b of the temperature regulator 2 can be reduced, resulting in a reduction in the size of the temperature regulator 2 and a reduction in the size of the optical module.

[0026] The semiconductor laser 5 is a single-wavelength semiconductor laser, i.e., a single-mode laser that oscillates at a single wavelength. As the single-wavelength semiconductor laser, for example, a distributed feedback (DFB) laser diode element (chip) or a distributed Bragg reflector (DBR) laser diode element (chip) is used. The semiconductor laser 5 emits a forward laser light Lf from the emission surface and emits a backward laser light Lb from the rear surface. The forward laser light Lf is used for optical communication, and the backward laser light Lb is monitored.

[0027] In this type of single-wavelength semiconductor laser, the light intensity varies depending on the driving photocurrent supplied, and also varies depending on the temperature of the semiconductor laser itself. In general, the lower the temperature, the greater the light output. Furthermore, the oscillation wavelength of the laser light from a single-wavelength semiconductor laser varies depending on the temperature of the laser and also on Joule heat due to the driving photocurrent. Therefore, in the first embodiment, the backward laser light Lb from the semiconductor laser 5 is monitored by the optical monitor 6, and the temperature of the semiconductor laser 5 is adjusted by the temperature regulator 2 to maintain the wavelength of the laser light oscillated from the semiconductor laser 5 constant.

[0028] The optical monitor 6 outputs a monitor value for controlling the temperature regulator 2 to change the temperature applied to the semiconductor laser 5 and the optical monitor 6, to a control unit 9 (see FIG. 6) that controls the temperature regulator 2. The control unit 9 controls the temperature regulator 2, the semiconductor laser 5, and the optical monitor 6. The control unit 9 exchanges signals with each of the semiconductor laser 5, the optical monitor 6, and the temperature regulator 2, and controls the optical current and voltage to each of the semiconductor laser 5, the optical monitor 6, and the temperature regulator 2, thereby controlling the optical intensity and wavelength of the laser light from the semiconductor laser 5.

[0029] The optical monitor 6 measures the optical intensity of the backward laser light Lb from the semiconductor laser 5, and outputs a first monitor value and a second monitor value for estimating the intensity and wavelength of the forward laser light Lf from the semiconductor laser 5. The optical monitor 6 has a first optical coupler 61a that receives the backward laser light Lb from the semiconductor laser 5, a second optical coupler 61b that receives the backward laser light Lb from the semiconductor laser 5, a first optical receiver 65a that outputs a first monitor value, and a second optical receiver 65b that outputs a second monitor value, and constitutes an optical interferometer in which a first path from the first optical coupler 61a to the first optical receiver 65a and a second path from the second optical coupler 61b to the second optical receiver 65b are asymmetric. The optical interferometer is, for example, a Mach-Zehnder interferometer.

[0030] The sum of the first monitor value and the second monitor value becomes an optical power monitor value Ip consisting of an optical current value for controlling the value of the drive optical current to the semiconductor laser 5 so that the optical output of the semiconductor laser 5 becomes a target value. The difference between the first monitor value and the second monitor value becomes the wavelength monitor value Iλ, which is a photocurrent value used to control the value of the photocurrent supplied to the temperature regulator 2 so that the wavelength of the laser light from the semiconductor laser 5 becomes the target value. The optical monitor 6 constitutes a part of a wavelength locker for controlling the wavelength of the laser light from the semiconductor laser 5 .

[0031] When the optical power monitor value Ip is larger than the optical current setting value, the temperature regulator 2 heats the mounting surface 2b in accordance with the value of the optical current supplied to increase the temperature applied to the semiconductor laser 5 and the optical monitor 6, and when the optical power monitor value Ip is smaller than the optical current setting value, the temperature regulator 2 cools the mounting surface 2b in accordance with the value of the optical current supplied to decrease the temperature applied to the semiconductor laser 5 and the optical monitor 6. The photocurrent set value is set, for example, to ±10% of the target value Ip_target of the optical power monitor value Ip when the optical output of the semiconductor laser 5, i.e., the optical intensity, becomes the target value and a driving photocurrent is supplied to the semiconductor laser 5.

[0032] When a wavelength monitor value Iλ / Ip, which is the ratio between the optical power monitor value Ip and the wavelength monitor value Iλ, deviates from the wavelength set value, the temperature regulator 2 changes the temperature of the mounting surface 2b in accordance with the value of the supplied photocurrent, thereby changing the temperatures applied to the semiconductor laser 5 and the optical monitor 6. In this example, when the wavelength monitor value Iλ / Ip is larger than the wavelength set value, the temperature regulator 2 heats the mounting surface 2b in accordance with the value of the supplied photocurrent to increase the temperature applied to the semiconductor laser 5 and the optical monitor 6, and when the wavelength monitor value Iλ / Ip is smaller than the wavelength set value, the temperature regulator 2 cools the mounting surface 2b in accordance with the value of the supplied photocurrent to decrease the temperature applied to the semiconductor laser 5 and the optical monitor 6. The wavelength set value is set, for example, to ±10% of a target value Iλ_target of the wavelength monitor value Iλ / Ip when the wavelength λLD of the laser light from the semiconductor laser 5 is set to a target value λ_target.

[0033] As shown in Figures 4 and 5, the optical monitor 6 includes a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, a second optical receiver 65b, and a phase adjuster 66. The output side optical multiplexer / demultiplexer 64, the first photoreceiver 65a, and the second photoreceiver 65b function as an interference measurement system for observing the wavelength dependency. The output side optical multiplexer / demultiplexer 64 is an optical circuit that configures an interference measurement system together with a first photoreceiver 65a and a second photoreceiver 65b.

[0034] The optical monitor 6 is, for example, a planar waveguide type optical monitor using a silicon photonics chip formed by integrating a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, and a second optical receiver 65b on the flat surface of a silicon (Si) substrate 6A. Phase adjuster 66 is located on a portion of second asymmetric arm 63b, and is formed on an insulating film (not shown) formed on the surface of the silicon photonics chip.

[0035] The first optical coupler 61 a receives the backward laser light Lb from the semiconductor laser 5 , and couples the backward laser light Lb, which is incident perpendicularly to the flat surface 6 a of the optical monitor 6 , to a first optical waveguide 62 a that constitutes the input-side optical multiplexer / demultiplexer 62 . The second optical coupler 61b receives the backward laser light Lb from the semiconductor laser 5 and couples the backward laser light Lb, which is incident perpendicularly to the flat surface 6a of the optical monitor 6, to a second optical waveguide 62b that constitutes the input-side optical multiplexer / demultiplexer 62.

[0036] The first optical coupler 61a and the second optical coupler 61b are, for example, grating couplers. The grating coupler has a function of coupling the backward laser light Lb from the semiconductor laser 5 coming from above the flat surface 6a of the optical monitor 6 to the first optical waveguide 62a and the second optical waveguide 62b constituting the input side optical multiplexer / demultiplexer 62, respectively, so that the flat surface 6a of the optical monitor 6 and the semiconductor laser 5 are arranged by the pedestal 3 at an angle at which the maximum coupling efficiency of the grating coupler is obtained.

[0037] The optical coupler 61 may be an elephant coupler. A grating coupler can increase the optical mode and has the characteristic of being less position dependent than end face coupling of a waveguide, so that a grating coupler is preferable for the first optical coupler 61a and the second optical coupler 61b in this example.

[0038] The input-side optical multiplexer / demultiplexer 62 is a 2x2 optical multiplexer / demultiplexer having a first port to a fourth port, a first optical waveguide 62a connecting the first port and the second port, and a second optical waveguide 62b connecting the third port and the fourth port. In the input-side optical multiplexer / demultiplexer 62, the first port is coupled to the first optical coupler 61a, and the third port is coupled to the second optical coupler 61b.

[0039] The input-side optical multiplexer / demultiplexer 62 is an asymmetric optical multiplexer / demultiplexer, and in this example, the power branching ratio is set to, for example, 0.8. In other words, the power branching ratio for the first optical waveguide 62a and the second optical waveguide 62b is set to 2:8. An asymmetric optical multiplexer / demultiplexer is an optical multiplexer / demultiplexer having a power branching ratio that is changed from 0.5. One feature of the optical module according to the first embodiment is that an asymmetric optical multiplexer / demultiplexer is used as the input-side optical multiplexer / demultiplexer 62.

[0040] When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the first optical waveguide 62a and the second optical waveguide 62b constituting the input side optical multiplexer / demultiplexer 62 are silicon waveguides made of silicon. The first optical waveguide 62a and the second optical waveguide 62b have the same length.

[0041] The input-side optical multiplexer / demultiplexer 62 may be, for example, a directional coupler or a multi-mode interference waveguide (MMI: Multi-Mode Interferometer) having a first port to a fourth port and an optical propagation path from the first port to the second port and an optical propagation path from the third port to the fourth port. In this example, the optical propagation path from the first port to the second port is referred to as the first optical waveguide 62a, and the optical propagation path from the third port to the fourth port is referred to as the second optical waveguide 62b.

[0042] The input node of the first asymmetric arm 63 a is optically connected to the second port of the input-side optical multiplexer / demultiplexer 62 . When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the first asymmetric arm 63a is a silicon waveguide made of silicon. In addition, the second port of the input-side optical multiplexer / demultiplexer 62 and the input node of the first asymmetric arm 63a are not physically separate structures, but are the connection point of the first optical waveguide 62a constituting the input-side optical multiplexer / demultiplexer 62 and the silicon waveguide that continuously forms the first asymmetric arm 63a.

[0043] The input node of the second asymmetric arm 63 b is optically connected to the fourth port of the input-side optical multiplexer / demultiplexer 62 . When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the second asymmetric arm 63b is a silicon waveguide made of silicon. It should be noted that the fourth port of the input-side optical multiplexer / demultiplexer 62 and the input node of the second asymmetric arm 63b are not physically separate structures, but are the connection points of silicon waveguides that continuously form the first optical waveguide 62a and the second asymmetric arm 63b that constitute the input-side optical multiplexer / demultiplexer 62.

[0044] The length of the optical waveguide in the first asymmetric arm 63a is longer than the length of the optical waveguide in the second asymmetric arm 63b by a length ΔL. Since the length of the optical waveguide in the first asymmetric arm 63a is different from the length of the optical waveguide in the second asymmetric arm 63b, the light propagating through the first asymmetric arm 63a and the light propagating through the second asymmetric arm 63b are obtained with a phase shift due to an anti-phase relationship.

[0045] The output-side optical multiplexer / demultiplexer 64 is a 2x2 optical multiplexer / demultiplexer having a first port to a fourth port, a third optical waveguide 64a connecting the first port and the second port, and a fourth optical waveguide 64b connecting the third port and the fourth port. In the output-side optical multiplexer / demultiplexer 64, the first port is a first input node of an optical circuit for constituting an interference measurement system, the second port is a first output node of an optical circuit for constituting an interference measurement system, the third port is a second input node of an optical circuit for constituting an interference measurement system, and the fourth port is a second output node of an optical circuit for constituting an interference measurement system. In the output-side optical multiplexer / demultiplexer 64, the first port is optically connected to the output node of the first asymmetric arm 63a, and the third port is optically connected to the output node of the second asymmetric arm 63b.

[0046] The output-side optical multiplexer / demultiplexer 64 is an asymmetric optical multiplexer / demultiplexer, and in this example, the power branching ratio is set to, for example, 0.8. In other words, the power branching ratio for the third optical waveguide 64a and the fourth optical waveguide 64b is set to 2:8. An asymmetric optical multiplexer / demultiplexer is an optical multiplexer / demultiplexer having a power branching ratio that is changed from 0.5. One feature of the optical module according to the first embodiment is that an asymmetric optical multiplexer / demultiplexer is used as the output-side optical multiplexer / demultiplexer 64 .

[0047] When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the third optical waveguide 64a and the fourth optical waveguide 64b constituting the output side optical multiplexer / demultiplexer 64 are silicon waveguides made of silicon. The third optical waveguide 64a and the fourth optical waveguide 64b have the same length.

[0048] In addition, the first port of the output-side optical multiplexer / demultiplexer 64 and the output node of the first asymmetric arm 63a are not physically separate structures, but are the connection point of the third optical waveguide 64a constituting the output-side optical multiplexer / demultiplexer 64 and the silicon waveguide that continuously forms the first asymmetric arm 63a.

[0049] Furthermore, the third port of the output-side optical multiplexer / demultiplexer 64 and the output node of the second asymmetric arm 63b are not physically separate structures, but are the connection point of the fourth optical waveguide 64b constituting the output-side optical multiplexer / demultiplexer 64 and the silicon waveguide that continuously forms the second asymmetric arm 63b. The output-side optical multiplexer / demultiplexer 64 can be, for example, a directional coupler or an MMI waveguide having a first port to a fourth port, an optical propagation path from the first port to the second port, and an optical propagation path from the third port to the fourth port.

[0050] In this example, the optical propagation path from the first port to the second port is referred to as the third optical waveguide 64a, and the optical propagation path from the third port to the fourth port is referred to as the fourth optical waveguide 64b. The input-side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a, the second asymmetric arm 63b, and the output-side optical multiplexer / demultiplexer 64 constitute a so-called optical interferometer.

[0051] The first photoreceiver 65a receives the light from the second port of the output-side optical multiplexer / demultiplexer 64, performs photoelectric conversion, and outputs a first monitor value consisting of a photocurrent. The first photoreceiver 65a is a waveguide type photoreceiver or a surface incidence type photoreceiver, and in this example, a photodiode that is a SiGe (silicon germanium) photoreceiver is used. The second photoreceiver 65b receives the light from the fourth port of the output-side optical multiplexer / demultiplexer 64, performs photoelectric conversion, and outputs a second monitor value consisting of a photocurrent. The second photoreceiver 65b is a waveguide type photoreceiver or a surface incident type photoreceiver, and in this example, a photodiode, which is a SiGe photoreceiver, is used.

[0052] When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the first path is an optical propagation path along a silicon waveguide that runs from a first port of the input side optical multiplexer / demultiplexer 62, via the input side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a, and the output side optical multiplexer / demultiplexer 64, to a second port of the output side optical multiplexer / demultiplexer 64. The second path is an optical propagation path through a silicon waveguide that runs from the third port of the input-side optical multiplexer / demultiplexer 62, via the input-side optical multiplexer / demultiplexer 62, the second asymmetric arm 63b, and the output-side optical multiplexer / demultiplexer 64, to the fourth port of the output-side optical multiplexer / demultiplexer 64.

[0053] The backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b are each split and interfered with by the input-side optical multiplexer / demultiplexer 62, and propagated from the second port of the input-side optical multiplexer / demultiplexer 62 to the first asymmetric arm 63a, and from the fourth port of the input-side optical multiplexer / demultiplexer 62 to the second asymmetric arm 63b.

[0054] The laser light propagated through the first asymmetric arm 63a and the laser light propagated through the second asymmetric arm 63b are each split and interfered with by the output side optical multiplexer / demultiplexer 64, and propagated from the second port of the output side optical multiplexer / demultiplexer 64 to the first optical receiver 65a and from the fourth port of the output side optical multiplexer / demultiplexer 64 to the second optical receiver 65b.

[0055] The backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a is incident on both the first optical receiver 65a and the second optical receiver 65b, although the proportion varies depending on the wavelength due to the power branching ratios of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64. Similarly, the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b is incident on both the first optical receiver 65a and the second optical receiver 65b, although the proportion varies depending on the wavelength due to the power branching ratios of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64.

[0056] In short, the backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b are split and interfered with by the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64, respectively, and are propagated to the first optical receiver 65a and the second optical receiver 65b in a ratio determined by the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 depending on the wavelength.

[0057] The backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b respectively enter the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 without being reflected, so the total output of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 can be regarded as the combined power of the backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b.

[0058] The first photoreceiver 65a receives the laser light from the second port of the output-side optical multiplexer / demultiplexer 64, and outputs a photoelectrically converted photocurrent as a first monitor value. The second photoreceiver 65b receives the laser light Lb from the second port of the output-side optical multiplexer / demultiplexer 64, and outputs a photoelectrically converted photocurrent as a second monitor value. The photocurrent obtained from the first photodetector 65a has wavelength dependency because the backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light from the semiconductor laser 5 received by the second optical coupler 61b are interfered with by the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 that constitute an interferometer. Therefore, the first monitor value and the second monitor value also have wavelength dependency.

[0059] If the length (physical length) of the light propagation path in the first asymmetric arm 63a is L1 and the length (physical length) of the light propagation path in the second asymmetric arm 63b is L2, the relationship between L1 and L2 is expressed by the following equation (1). L1 = L2 + ΔL (1) ΔL is the difference between the length of the optical waveguide in the first asymmetric arm 63a and the length of the optical waveguide in the second asymmetric arm 63b.

[0060] Moreover, the phase θ after interference in the optical monitor 6, that is, the phase difference θ between the first and second monitor values ​​in the optical monitor 6, can be expressed by the following equation (2). n0·L1-n0·L2=n0ΔL=m·λ=(λ / 2π)·θ (2) n0 is the group refractive index of each of the first asymmetric arm 63a and the second asymmetric arm 63b, λ is the wavelength of the backward laser light Lb, and m is a coefficient connecting the wavelength λ and the optical path length nL, and is a variable that is proportional to the phase θ.

[0061] The phase difference θ changes with temperature, and by determining the group refractive index n0, the length L1 of the optical propagation path in the first asymmetric arm 63a, and the length L2 of the optical propagation path in the second asymmetric arm 63b so that the temperature derivative of the above equation (2) is always 0, an optical monitor 6 is obtained in which the first monitor value and the second monitor value have no temperature dependency.

[0062] An example of a waveform obtained from the first monitor value from the first optical receiver 65a is shown in FIG. 7 as waveform A, and an example of a waveform obtained from the second monitor value from the second optical receiver 65b is shown in FIG. 7 as waveform B. The waveform shown in Fig. 7 has a ΔL of 2,000 μm, an electric field transmission coefficient t of 0.9, and a T si =T LD 13 shows an example of the photocurrent values ​​obtained by the first photoreceiver 65a and the second photoreceiver 65b, respectively.

[0063] In FIG. 7, the horizontal axis indicates the wavelength of the backward laser light Lb, and the vertical axis indicates the intensity of the monitored value. As can be seen from FIG. 7, the waveform A obtained from the first monitored value and the waveform B obtained from the second monitored value are in an anti-phase relationship, that is, the waveforms are inverted and are out of phase with each other by 180 degrees. Therefore, in the control unit 9, by simply taking the sum of the first monitor value due to the photocurrent from the first photoreceiver 65a and the second monitor value due to the photocurrent from the second photoreceiver 65b, the optical power monitor value Ip, which is the sum of the first monitor value and the second monitor value, can be calculated.

[0064] In other words, the sum of the photocurrent from the first photoreceiver 65a, which is the first monitor value from the first photoreceiver 65a, and the photocurrent from the second photoreceiver 65b, which is the second monitor value from the second photoreceiver 65b, is proportional to the total power of the backward laser light Lb from the semiconductor laser 5 received by the first optical coupler 61a and the backward laser light Lb from the semiconductor laser 5 received by the second optical coupler 61b, so the sum of the first monitor value and the second monitor value can be used as the optical power monitor value Ip. The obtained optical power monitor value Ip is twice the optical power value compared to the case where one optical coupler and one optical receiver are used.

[0065] An example of a waveform obtained by adding up the first monitor value and the second monitor value is shown as waveform C in FIG. Waveform C shown in Fig. 8 has a ΔL of 2,000 μm, an electric field transmission coefficient t of 0.9, and a T si =T LD This is an example when the photocurrent value obtained by the first photoreceiver 65a and the photocurrent value obtained by the second photoreceiver 65b are simply added together. In FIG. 8, the horizontal axis indicates the wavelength of the backward laser light Lb, and the vertical axis indicates the intensity.

[0066] Furthermore, since the photocurrent from the first photoreceiver 65a and the photocurrent from the second photoreceiver 65b have wavelength dependency, the difference between the first monitor value and the second monitor value can be used as the wavelength monitor value Iλ. An example of a waveform obtained from the difference between the first monitor value and the second monitor value is shown as waveform D in FIG. Waveform D shown in Fig. 8 has a ΔL of 2,000 μm, an electric field transmission coefficient t of 0.9, and a T si =T LD This is an example when the photocurrent value obtained by the second photoreceiver 65b is simply subtracted from the photocurrent value obtained by the first photoreceiver 65a.

[0067] By taking the difference between the first and second monitor values, a slope of the intensity of the photocurrent flowing through the photoreceiver that is twice as large as that of the photocurrent flowing through the photoreceiver when one optical coupler and one photoreceiver are used is obtained. The wavelength monitor value Iλ changes not only with the wavelength of the backward laser light Lb of the semiconductor laser 5 but also with the light intensity of the backward laser light Lb.

[0068] Therefore, by dividing the wavelength monitor value Iλ by the optical power monitor value Ip, the wavelength monitor value Iλ / Ip based only on the wavelength of the backward laser light Lb can be obtained. The first photoreceiver 65a and the second photoreceiver 65b experience sensitivity changes due to temperature changes, but by dividing the wavelength monitor value Iλ by the optical power monitor value Ip and normalizing the wavelength monitor value with the optical power monitor value Ip, it is possible to obtain a wavelength monitor value with high accuracy.

[0069] In the optical module of the first embodiment, the optical monitor 6 has a first optical coupler 61a and a second optical coupler 61b, and constitutes an optical interferometer in which a first path from the first optical coupler 61a to the first optical receiver 65a and a second path from the second optical coupler 61b to the second optical receiver 65b are asymmetric, and a first monitor value is obtained from the first optical receiver 65a, a second monitor value is obtained from the second optical receiver 65b, and an optical power monitor value Ip and a wavelength monitor value Iλ / Ip are obtained.

[0070] Therefore, compared to the case where the backward laser light Lb from the semiconductor laser 5 is received by one optical coupler and the backward laser light Lb received by the optical coupler is split into two halves to obtain the optical power monitor value Ip and the wavelength monitor value Iλ / Ip from each halve, in the optical module of embodiment 1, the first optical coupler 61a and the second optical coupler 61b double the receiving area of ​​the backward laser light Lb per optical coupler.

[0071] Furthermore, since the wavelength monitor value Iλ is obtained from the difference between the first and second monitor values, the wavelength monitor value Iλ can be obtained from a slope of the intensity of the photocurrent that is twice as large as the slope of the intensity of the photocurrent that flows through the photoreceiver when one optical coupler and one photoreceiver are used. Therefore, for the assumed use of one optical coupler, four times the backward laser light Lb from the semiconductor laser 5 can be used to obtain the optical power monitor value Ip and the wavelength monitor value Iλ / Ip. As a result, an optical monitor 6 having four times the sensitivity to the backward laser light Lb from the semiconductor laser 5 can be obtained, and a highly accurate optical power monitor value Ip and wavelength monitor value Iλ / Ip can be obtained.

[0072] By adjusting the temperature in the semiconductor laser 5, the wavelength of the forward laser light Lf of the semiconductor laser 5 can be adjusted. Since the temperatures of the semiconductor laser 5 and the optical monitor 6 are adjusted by the heat from the mounting surface 2b of the temperature regulator 2 via the base 3, the temperature rise in the semiconductor laser 5 and the temperature rise in the optical monitor 6 are the same. As the temperature in the optical monitor 6 increases, the wavelength monitor value Iλ / Ip exhibits a downward slope. By knowing the wavelength monitor value Iλ / Ip, the wavelength shift in the laser light from the semiconductor laser 5 can be known.

[0073] When the forward laser light Lf from the semiconductor laser 5 deviates from a target wavelength (hereinafter referred to as a target value λ_target) of the forward laser light Lf from the semiconductor laser 5, the wavelength monitor value Iλ / Ip also deviates. Therefore, the value of the photocurrent supplied to the temperature regulator 2 is controlled to adjust the temperature in the semiconductor laser 5 and the temperature in the optical monitor 6 so that the wavelength monitor value Iλ / Ip does not deviate from the wavelength setting value (±10% of the target value Iλ_target). As a result, precise control can be performed on the single wavelength of the laser light from the semiconductor laser 5.

[0074] In this example, the optical monitor 6 further includes a phase adjuster 66 disposed on the second asymmetric arm 63b. The phase adjuster 66 sets the phase state of the photocurrent output from the optical monitor 6 to a position where the wavelength dependency of the photocurrent output from the optical monitor 6 is greatest at the target wavelength (hereinafter referred to as the target value λ_target) of the forward laser light Lf from the semiconductor laser 5. The phase adjuster 66 is, for example, a heater.

[0075] By passing a photocurrent through a heater which serves as a phase adjuster 66, the second path of the optical monitor 6, in this example the second asymmetric arm 63b, is heated so that the target value Iλ_target becomes the wavelength monitor value Iλ / Ip suitable for control, thereby adjusting the temperature in the second asymmetric arm 63b. The target value Iλ_target is determined by adjusting the temperature in the second path of the optical monitor 6 using the phase adjuster 66 so that the wavelength monitor value Iλ / Ip becomes near the median value in the region where the slope of the wavelength dependency with respect to the change in temperature of the optical monitor 6 is large.

[0076] The phase adjuster 66 may adjust the temperature in the first path of the optical monitor 6, for example, in the first asymmetric arm 63a. The phase adjuster 66 is not limited to a heater as long as it can change the phase state of the photocurrent output from the optical monitor 6. It may be a pin-type photocurrent injection type refractive index adjuster or a photocurrent extraction type refractive index adjuster, or a phase changer that injects or extracts photocurrent using a pn junction, or that exerts the quantum confined Stark effect or Pockels effect using voltage application.

[0077] The optical monitor 6 may be a planar waveguide type optical monitor in which a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, and a second optical receiver 65b are integrated on the plane of an indium phosphide (InP) substrate 6A, which is a compound semiconductor. The optical monitor 6 may be a planar waveguide type optical monitor in which a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, and a second optical receiver 65b are integrated on the plane of a glass substrate 6A.

[0078] Furthermore, the first optical coupler 61a, the second optical coupler 61b, the input side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a, the second asymmetric arm 63b, the output side optical multiplexer / demultiplexer 64, the first optical receiver 65a, and the second optical receiver 65b do not necessarily have to be integrated, and individual components may be modularized. The first photoreceiver 65a and the second photoreceiver 65b may each be an InP-based photoreceiver or a GaAs-based photoreceiver.

[0079] The temperature regulator 2, the semiconductor laser 5 and the optical monitor 6 are controlled by a control unit 9, as shown in FIG. The control unit 9 exchanges signals with each of the semiconductor laser 5, the optical monitor 6, and the temperature regulator 2, and controls the photocurrent and voltage to each of the semiconductor laser 5, the optical monitor 6, and the temperature regulator 2, thereby controlling the light intensity and wavelength of the laser light from the semiconductor laser 5.

[0080] The control unit 9 receives as input a first monitor value which is the photocurrent from the first photoreceiver 65a and a second monitor value which is the photocurrent from the second photoreceiver 65b, and calculates an optical power monitor value Ip which is the sum of the first monitor value and the second monitor value, a wavelength monitor value Iλ which is the difference between the first monitor value and the second monitor value, and a wavelength monitor value Iλ / Ip which is the ratio of the optical power monitor value Ip to the wavelength monitor value Iλ.

[0081] In this example, the optical power monitor value Ip is the sum of the first monitor value obtained from the first optical receiver 65a and the second monitor value obtained from the second optical receiver 65b (see line C in FIG. 4). In this example, the wavelength monitor value Iλ is obtained by subtracting the first monitor value obtained from the first optical receiver 65a from the second monitor value obtained from the second optical receiver 65b (see waveform curve D in FIG. 4).

[0082] The control unit 9 controls the driving optical current supplied to the semiconductor laser 5 so that the calculated optical power monitor value Ip falls within a range of ±10% of the target value Ip_target of the optical power monitor value, which is the optical current setting value. The control unit 9 controls the optical current supplied to the temperature regulator 2 so that the calculated optical power monitor value Ip falls within the optical current setting value range of ±10% of the target value Ip_target of the optical power monitor value.

[0083] When the optical power monitor value Ip is larger than the optical current setting value, the control unit 9 supplies an optical current to the temperature regulator 2 for heating the mounting surface 2b of the temperature regulator 2, and when the optical power monitor value Ip is smaller than the optical current setting value, the control unit 9 supplies an optical current to the temperature regulator 2 for cooling the mounting surface 2b of the temperature regulator 2. As a result, the temperature regulator 2 controls so as to increase the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the optical power monitor value Ip is larger than the optical current set value, and to decrease the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the optical power monitor value Ip is smaller than the optical current set value.

[0084] In addition, the control unit 9 controls the photocurrent supplied to the temperature regulator 2 so that the calculated wavelength monitor value Iλ / Ip falls within a wavelength setting value range of ±10% of the target value Iλ_target of the wavelength monitor value Iλ / Ip when the wavelength λLD of the laser light from the semiconductor laser 5 is set to the target value λ_target. When the wavelength monitor value Iλ / Ip deviates from the wavelength setting value, the control unit 9 supplies a photocurrent to the temperature regulator 2 for changing the temperature of the mounting surface 2b.

[0085] In this example, when the wavelength monitor value Iλ / Ip is larger than the wavelength set value, the control unit 9 supplies to the temperature regulator 2 a photocurrent for heating the mounting surface 2b of the temperature regulator 2, and when the wavelength monitor value Iλ / Ip is smaller than the wavelength set value, the control unit 9 supplies to the temperature regulator 2 a photocurrent for cooling the mounting surface 2b of the temperature regulator 2. As a result, the temperature regulator 2 controls so as to increase the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the wavelength monitor value Iλ / Ip is larger than the wavelength set value, and to decrease the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the wavelength monitor value Iλ / Ip is smaller than the wavelength set value.

[0086] In addition, the temperature regulator 2 increases the driving photocurrent supplied to the semiconductor laser 5 when the wavelength monitor value Iλ / Ip is greater than the wavelength setting value and the optical power monitor value Ip is smaller than the optical current setting value by raising the temperature applied to the semiconductor laser 5 and the optical monitor 6, and controls to reduce the driving photocurrent supplied to the semiconductor laser 5 when the wavelength monitor value Iλ / Ip is smaller than the wavelength setting value and the optical power monitor value Ip is greater than the optical current setting value by lowering the temperature applied to the semiconductor laser 5 and the optical monitor 6.

[0087] The control unit 9 supplies to the phase adjuster 66 a photocurrent of the target value Ih_target when the optical intensity of the laser light of the semiconductor laser 5 reaches the target value and the optical output of the laser light with the wavelength λLD of the laser light of the semiconductor laser 5 reaches the target value λ_target is obtained. As a result, the heater which is the phase adjuster 66 heats the optical monitor 6 under the control of the controller 9, specifically, adjusts the temperature in the second path of the optical monitor 6, in this example, the second asymmetric arm 63b. The control unit 9 and the optical monitor 6 constitute a wavelength locker for controlling the wavelength of the laser light from the semiconductor laser 5 . The optical module and the control unit 9 constitute an optical module device.

[0088] The semiconductor laser 5, the optical monitor 6, and the temperature regulator 2 are electrically connected to the lead pins P1 to P6 by wires (not shown) such as gold wires by wire bonding in order to exchange signals with the control unit 9. The lead pins P1 to P6 each pass through a through hole in the stem 1, and are fixed to the stem 1 by sealing glass that is filled and solidified between the lead pins P1 to P6 and the through holes. The sealing glass electrically insulates the lead pins P1 to P6 from the stem 1, and maintains airtightness.

[0089] The connection of the inner lead portions of the lead pins P1 to P6 exposed from the inner flat surface of the stem 1 is, for example, as follows: However, the relationship between the lead pins P1 to P6 and each component is shown as an example, and is not limited to this. The lead pin P1 is connected to one electrode of the semiconductor laser 5 and transmits a driving photocurrent from the control unit 9 to the semiconductor laser 5. The lead pin P1 is a lead pin for the semiconductor laser 5 for transmitting a main signal.

[0090] The lead pin P2 is connected to the first photoreceiver 65a of the optical monitor 6, and transmits a photocurrent indicating a first monitor value from the first photoreceiver 65a to the control unit 9. The lead pin P2 is a first monitor lead pin for the optical monitor 6. The lead pin P3 is connected to the second photoreceiver 65b of the optical monitor 6, and transmits a photocurrent indicating a second monitor value from the second photoreceiver 65b to the control unit 9. The lead pin P3 is a second monitor lead pin for the optical monitor 6.

[0091] The lead pins P4 and P5 are connected to a pair of electrodes in the temperature regulator 2, and transmit a photocurrent supplied from the control unit 9 to the temperature regulator 2. The lead pins P4 and P5 are a pair of lead pins for temperature control for the temperature regulator 2. The lead pin P6 is connected to the phase adjuster 66 and transmits a photocurrent supplied from the control unit 9 to the phase adjuster 66. The lead pin P6 is a lead pin for phase adjustment for the phase adjuster 66.

[0092] One end face of the ground lead pin P7 is in contact with the outer flat surface 1b of the stem 1 and joined thereto by electric welding or brazing, so that the ground lead pin P7 is fixed to the stem 1. The ground lead pin P7 is electrically grounded, and the stem 1 is set to the ground potential by the ground lead pin P7, that is, the stem 1 also serves as a ground node.

[0093] The optical module according to the first embodiment requires a total of seven lead pins, six signal lead pins P1 to P6 and one ground lead pin P7 for each component, and the optical module can be configured with a small number of lead pins. As a result, it is possible to use a standard CAN package with a diameter of 5.6 mm, which has a maximum number of lead pins of seven, thereby enabling miniaturization.

[0094] Next, the operation of the optical module according to the first embodiment will be described. The optical module is intended to be one that incorporates a semiconductor laser 5, which is a laser chip that has been confirmed to produce a target or higher optical output within the operating temperature range and to produce the target oscillation wavelength within a controllable temperature range.

[0095] First, the following steps are carried out as preparations for operating the optical module. When an optical output is obtained from the semiconductor laser 5 such that the wavelength λLD is the target value λ_target and the optical intensity is the target value Ip_target of the optical power monitor value Ip, a target value ILD_target of the driving optical current to be supplied to the semiconductor laser 5, a target value ITEC_target of the optical current to be supplied to the temperature regulator 2, and a target value Ih_target of the optical current to be supplied to the phase regulator 66 are obtained. These target values ​​are obtained using a commonly known optical intensity measuring device and optical wavelength measuring device.

[0096] Also, at the same timing, when an optical output is obtained from the semiconductor laser 5, the target value Ip_target of the optical power monitor value Ip, where the optical intensity is the target value, and the wavelength λLD is the target value λ_target, is obtained, and the wavelength dependence of the wavelength monitor value Iλ / Ip near the target value Iλ_target and the target value Iλ_target of the wavelength monitor value Iλ / Ip when the target value Ip_target of the optical power monitor value Ip and the wavelength λLD are the target value λ_target are obtained.

[0097] In the semiconductor laser 5, the photocurrent value ILD of the drive photocurrent and the optical power monitor value Ip are proportional to each other, and the lower the temperature in the semiconductor laser 5, the greater the optical output, that is, the greater the optical power monitor value Ip. In this example, a driving photocurrent of the target value ILD_target is supplied to the semiconductor laser 5, and the temperature of the semiconductor laser 5 at which an optical output is obtained in which the optical power monitor value Ip has the target value Ip_target and the wavelength λLD has the target value λ_target is 55° C.

[0098] In addition, the target value Iλ_target of the wavelength monitor value Iλ / Ip is set near the median of the wavelength monitor value Iλ / Ip when the temperature at the semiconductor laser 5 and the temperature at the optical monitor 6 are changed, in a region where the slope of the wavelength dependency is large.

[0099] Next, the operation of the optical module will be described mainly with reference to FIG. When the optical module is started up, the control unit 9 supplies a photocurrent of the target value Ih_target to the phase adjuster 66 (step ST1). Next, the control unit 9 supplies a driving photocurrent of the target value ILD_target to the semiconductor laser 5 (step ST2).

[0100] When a driving photocurrent of the target value ILD_target is supplied to the semiconductor laser 5, the semiconductor laser 5 emits a forward laser light Lf to the outside of the cap 7 through the window 8, and emits a backward laser light Lb to the first optical coupler 61a and the second optical coupler 61b in the optical monitor 6. The optical monitor 6, to which the backward laser light Lb is incident, monitors the optical intensities of the laser lights from the semiconductor laser 5, which are out of phase with each other and inverted with each other. That is, the optical monitor 6 obtains a first monitor value and a second monitor value, which are asymmetric with each other.

[0101] That is, the laser light from the first optical coupler 61a which receives the backward laser light Lb of the semiconductor laser 5 is incident on the first optical waveguide 62a constituting the input side optical multiplexer / demultiplexer 62 from the first port of the input side optical multiplexer / demultiplexer 62. On the other hand, the laser light from the second optical coupler 61b that receives the backward laser light Lb from the semiconductor laser 5 is input to the second optical waveguide 62b that constitutes the input side optical multiplexer / demultiplexer 62 from the third port of the input side optical multiplexer / demultiplexer 62.

[0102] The laser light from the first optical coupler 61a and the laser light from the second optical coupler 61b input to the input-side optical multiplexer / demultiplexer 62 are each split and interfered with by the input-side optical multiplexer / demultiplexer 62, and propagated from the second port of the input-side optical multiplexer / demultiplexer 62 to the first asymmetric arm 63a and from the fourth port of the input-side optical multiplexer / demultiplexer 62 to the second asymmetric arm 63b.

[0103] The laser light propagated through the first asymmetric arm 63 a is propagated from the first port of the output-side optical multiplexer / demultiplexer 64 to the third optical waveguide 64 a constituting the output-side optical multiplexer / demultiplexer 64 . The laser light propagated through the second asymmetric arm 63 b is propagated from the third port of the output-side optical multiplexer / demultiplexer 64 to the fourth optical waveguide 64 b constituting the output-side optical multiplexer / demultiplexer 64 .

[0104] The laser light that has propagated through the first asymmetric arm 63a and the second asymmetric arm 63b is propagated to the output side optical multiplexer / demultiplexer 64, and is separated and interfered with by the output side optical multiplexer / demultiplexer 64, and is incident on the first optical receiver 65a from the second port of the output side optical multiplexer / demultiplexer 64, and is incident on the second optical receiver 65b from the fourth port of the output side optical multiplexer / demultiplexer 64.

[0105] The laser light incident on the first photoreceiver 65a is photoelectrically converted by the first photoreceiver 65a, and a photocurrent indicating a first monitor value is output to the control unit 9. The laser light incident on the second photoreceiver 65b is photoelectrically converted by the second photoreceiver 65b, and a photocurrent indicating a second monitor value is output to the control unit 9. The relationship between the first monitor value and the second monitor value corresponds to the relationship between waveform curve A and waveform curve B shown in FIG.

[0106] The control unit 9 converts the first monitor value based on the photocurrent into a voltage, and further converts the voltage from analog to digital to obtain the first monitor value based on digital information. The control unit 9 converts the second monitor value based on the photocurrent into a voltage, and further converts the voltage from analog to digital to obtain the second monitor value based on digital information. Conversion from the photocurrent to a voltage in the control section 9 may be performed by the optical monitor 6. In short, the control unit 9 needs only to obtain a first monitor value in the form of digital information from the output from the first photoreceiver 65a, and a second monitor value in the form of digital information from the output from the second photoreceiver 65b.

[0107] The control unit 9, having obtained the first monitor value and the second monitor value, calculates an optical power monitor value Ip, which is the sum of the first monitor value and the second monitor value, a wavelength monitor value Iλ, which is the difference between the first monitor value and the second monitor value, and a wavelength monitor value Iλ / Ip, which is the ratio between the optical power monitor value Ip and the wavelength monitor value Iλ (step ST3).

[0108] The control unit 9 judges whether or not the optical power monitor value Ip is within the range of the optical current setting value (step ST4). If the optical power monitor value Ip is outside the range of the optical current set value, the control unit 9 proceeds to step ST5, and if the optical power monitor value Ip is within the range of the optical current set value, the control unit 9 proceeds to step ST6. The photocurrent set value is set, for example, to ±10% of the target value Ip_target of the optical power monitor value Ip.

[0109] Step ST5 is a temperature adjustment step prior to controlling the photocurrent supplied to the temperature regulator 2. Step ST5 includes a preliminary temperature increasing step in which the temperature regulator 2 increases the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the optical power monitor value Ip calculated by the control unit 9 in step ST3 is larger than the optical current set value, and a preliminary temperature decreasing step in which the temperature regulator 2 decreases the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the optical power monitor value Ip is smaller than the optical current set value.

[0110] When a driving photocurrent of the target value ILD_target is supplied to the semiconductor laser 5, for example, if the optical power monitor value Ip calculated by the control unit 9 is greater than the photocurrent setting value, it can be said that the temperature of the semiconductor laser is lower than 55°C. Therefore, the control unit 9 controls the photocurrent supplied to the temperature regulator 2 so as to heat the mounting surface 2b of the temperature regulator 2, and the process returns to step ST3. As a result, the semiconductor laser 5 and the optical monitor 6 are heated via the base 3, and the temperatures of the semiconductor laser 5 and the optical monitor 6 rise towards 55°C.

[0111] On the other hand, when a driving photocurrent of the target value ILD_target is supplied to the semiconductor laser 5, if the optical power monitor value Ip calculated by the control unit 9 in step ST3 is smaller than the photocurrent setting value, for example, it can be said that the temperature of the semiconductor laser is higher than 55°C. Therefore, the control unit 9 controls the photocurrent supplied to the temperature regulator 2 so as to cool the mounting surface 2b of the temperature regulator 2, and the process returns to step ST3. As a result, the semiconductor laser 5 and the optical monitor 6 are cooled via the base 3, and the temperatures of the semiconductor laser 5 and the optical monitor 6 decrease toward 55°C.

[0112] By repeating step ST5, the temperature of the semiconductor laser 5 and the temperature of the optical monitor 6 are adjusted by the temperature regulator 2, and when the optical power monitor value Ip calculated by the control unit 9 falls within the range of the optical current set value, the control unit 9 ends the previous temperature adjustment step and proceeds to step ST6. Proceed to the wavelength locker step after step ST6.

[0113] Step ST6 is a step of calculating the optical power monitor value Ip, the wavelength monitor value Iλ, and the wavelength monitor value Iλ / Ip, similar to step ST3. Step ST7 is a step in which the control unit 9 judges whether or not the optical power monitor value Ip is within the range of the optical current setting value. If the optical power monitor value Ip is outside the range of the optical current set value, the control unit 9 proceeds to step ST8, and if the optical power monitor value Ip is within the range of the optical current set value, the control unit 9 proceeds to step ST9. Immediately after proceeding from step ST5 to step ST7, the optical power monitor value Ip is within the range of the optical current setting value, so the process proceeds to step ST9.

[0114] Step ST9 is a step in which the control unit 9 judges whether or not the wavelength monitor value Iλ / Ip is within the range of the wavelength setting value. If the wavelength monitor value Iλ / Ip is outside the range of the wavelength set value, the control unit 9 proceeds to step ST10, and if the wavelength monitor value Iλ / Ip is within the range of the wavelength set value, the control unit 9 proceeds to step ST11. The wavelength set value is set, for example, to ±10% of the target value Iλ_target of the wavelength monitor value Iλ / Ip.

[0115] Step ST10 is a temperature adjustment step for controlling the photocurrent supplied to the temperature adjuster 2. The temperature adjustment step is a step in which the temperature adjuster 2 adjusts the temperature applied to the semiconductor laser 5 and the optical monitor 6 when the wavelength monitor value Iλ / Ip deviates from the wavelength set value, and in this example, includes the following temperature increase step and temperature decrease step. That is, step ST10 includes a temperature increase step in which the control unit 9 increases the temperature applied to the semiconductor laser 5 and the optical monitor 6 by the temperature regulator 2 when the wavelength monitor value Iλ / Ip calculated by the control unit 9 in step ST6 is larger than the wavelength set value, and a temperature decrease step in which the control unit 9 decreases the temperature applied to the semiconductor laser 5 and the optical monitor 6 by the temperature regulator 2 when the wavelength monitor value Iλ / Ip is smaller than the wavelength set value.

[0116] In the temperature increase step, the control unit 9 controls the photocurrent supplied to the temperature regulator 2 so as to heat the mounting surface 2b of the temperature regulator 2, thereby increasing the temperature of the semiconductor laser 5 and the temperature of the optical monitor 6, thereby increasing the wavelength λLD of the laser light from the semiconductor laser 5, and decreasing the wavelength monitor value Iλ / Ip, and the process returns to step ST7 via step ST6. On the other hand, in the temperature decreasing step, the control unit 9 controls the photocurrent supplied to the temperature regulator 2 so as to cool the mounting surface 2b of the temperature regulator 2, thereby decreasing the temperature of the semiconductor laser 5 and the temperature of the optical monitor 6, thereby decreasing the wavelength λLD of the laser light from the semiconductor laser 5, and increasing the wavelength monitor value Iλ / Ip, and the process returns to step ST7 via step ST6.

[0117] In the temperature increasing step of step ST10, the temperature of the semiconductor laser 5 is also increased, and as a result, the optical intensity of the laser light from the semiconductor laser 5 decreases, and the optical power monitor value Ip decreases. On the other hand, in the temperature decreasing step in step ST10, the temperature of the semiconductor laser 5 is also decreased, and as a result, the optical intensity of the laser light from the semiconductor laser 5 increases, and the optical power monitor value Ip increases. Therefore, in step ST10, when the temperature is adjusted by the temperature regulator 2 to adjust the wavelength λLD of the laser light from the semiconductor laser 5, the optical power monitor value Ip also changes, so in step ST7, the control unit 9 determines whether or not the optical power monitor value Ip is within the range of the optical current set value.

[0118] In step ST7, if the optical power monitor value Ip calculated by the control unit 9 in step ST6 is within the range of the optical current setting value, the process proceeds to step ST9, and steps ST10 to ST7 are repeated. On the other hand, if it is determined in step ST7 that the optical power monitor value Ip calculated by the control unit 9 in step ST6 is outside the range of the optical current setting value, the process proceeds to step ST8. Step ST8 is a drive photocurrent control step for controlling the drive photocurrent supplied to the semiconductor laser 5.

[0119] Step ST8 includes a drive photocurrent increasing step in which the temperature applied to the semiconductor laser 5 and the optical monitor 6 by the temperature regulator 2 is increased by a temperature increasing step in step ST10, and when the optical power monitor value Ip calculated by the control unit 9 in step ST6 becomes smaller than the optical current setting value, the drive photocurrent increasing step in which the temperature applied to the semiconductor laser 5 and the optical monitor 6 by the temperature regulator 2 is decreased by a temperature decreasing step in step ST10, and when the optical power monitor value Ip calculated by the control unit 9 becomes larger than the optical current setting value, the drive photocurrent decreasing step in which the drive photocurrent supplied to the semiconductor laser 5 is decreased.

[0120] Therefore, the control unit 9 repeats step ST8 until the optical power monitor value Ip falls within the range of the optical current set value, and when the optical power monitor value Ip falls within the range of the optical current set value, the control unit 9 proceeds to step ST9, and the temperature adjustment step of controlling the optical current supplied to the temperature regulator 2 in step ST10 is repeated. That is, the repeated loop of the temperature adjustment steps of step ST7-step ST9-step ST10-step ST6-step ST7-step ST9 and the repeated loop of the drive photocurrent control steps of step ST7-step ST8-step ST6-step ST7 are wavelength locker steps.

[0121] This wavelength locker step brings the optical power monitor value Ip into the range of the optical current set value, and brings the wavelength monitor value Iλ / Ip into the range of the wavelength set value. As a result, the semiconductor laser 5 enters a stable operation state in which both conditions are satisfied: the condition where the light intensity of the laser light from the semiconductor laser 5 is based on the target value Ip_target, and the condition where the wavelength of the laser light from the semiconductor laser 5 is based on the target value Iλ_target of the wavelength monitor value Iλ / Ip, in other words, the target value λ_target.

[0122] When the semiconductor laser 5 enters a stable operation, the process proceeds to step ST11. In step ST11, the control unit 9 continues to monitor the first monitor value by the first photoreceiver 65a and the second monitor value by the second photoreceiver 65b, thereby continuing to monitor the optical power monitor value Ip and the wavelength monitor value Iλ / Ip, and continues the wavelength locker step until the optical module is powered off, and terminates the wavelength locker step when the power is turned off.

[0123] After the semiconductor laser 5 enters stable operation, the semiconductor laser 5 operates with the drive photocurrent set by the wavelength locker step, the temperature regulator 2 operates with the supply photocurrent set by the wavelength locker step, and the semiconductor laser 5 continues stable operation until the optical power monitor value Ip falls outside the range of the photocurrent setting value or the wavelength monitor value Iλ / Ip falls outside the range of the wavelength setting value.

[0124] When the optical power monitor value Ip falls outside the range of the optical current setting value or the wavelength monitor value Iλ / Ip falls outside the range of the wavelength setting value, the wavelength locking function is activated by the wavelength locker step, and the control unit 9 repeats a loop of the temperature adjustment steps of step ST7-step ST9-step ST10-step ST6-step ST7-step ST9 and a loop of the drive optical current control steps of step ST7-step ST8-step ST6-step ST7.

[0125] As a result, the semiconductor laser 5 again enters stable operation satisfying both the condition that the light intensity of the laser light from the semiconductor laser 5 is based on the target value Ip_target, and the condition that the wavelength of the laser light from the semiconductor laser 5 is based on the target value Iλ_target of the wavelength monitor value Iλ / Ip.

[0126] Next, the results of verifying the relationship between the backward laser light Lb of the semiconductor laser 5 and the first and second optical couplers 61a and 61b when a mounting misalignment occurs between the semiconductor laser 5 and the optical monitor 6 will be described. When a deviation occurs in the relationship between the backward laser light Lb of the semiconductor laser 5 and the first and second optical couplers 61a and 61b, a phase difference and an optical power difference occur in the coupled light between the backward laser light Lb of the semiconductor laser 5 and the first and second optical couplers 61a and 61b.

[0127] That is, as shown in FIG. 10, when the central axis of the backward laser light Lb of the semiconductor laser 5 shifts toward the first optical coupler 61a, the equiphase front of the backward laser light Lb of the semiconductor laser 5 relative to the first optical coupler 61a and the second optical coupler 61b becomes as shown in FIG. 11. As a result, a phase difference and an optical power difference due to mounting misalignment occur between the coupled light between the backward laser light Lb of the semiconductor laser 5 and the first optical coupler 61a and the coupled light between the backward laser light Lb of the semiconductor laser 5 and the second optical coupler 61b. In FIG. 10, IS indicates a schematic light distribution of the backward laser light Lb of the semiconductor laser 5 with respect to the first optical coupler 61a and the second optical coupler 61b.

[0128] The experiment was carried out with the wavelength of the laser light from the semiconductor laser 5 set to 1.55 μm, the first optical coupler 61a and the second optical coupler 61b set to grating couplers, and the distance between the emission surface of the laser light from the semiconductor laser and the grating coupler set to 0.3 mm. It was confirmed that within the range of expected mounting misalignment, the power branching ratio of the laser light from the semiconductor laser and the coupled light between the first optical coupler 61a and the second optical coupler 61b changes from 1:1 to 2:1, and the phase difference of the coupled light between the two changes from 0 degrees to 150 degrees.

[0129] Within this assumed range of mounting deviation, the slope of the photocurrent due to the first optical receiver 65a and the second optical receiver 65b versus the power branching ratio in the coupled light of the first optical coupler 61a and the second optical coupler 61b, that is, the slope of the output of the optical monitor, was estimated when the electric field transmission coefficient t of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 were 0.3, 0.5, 0.7, and 0.9, respectively.

[0130] The calculation results are shown in Figure 12. In FIG. 12, the upper horizontal axis indicates the power branching ratio in the coupled light of the first optical coupler 61a and the second optical coupler 61b, the lower horizontal axis indicates the phase difference, and the vertical axis indicates the gradient of the output of the optical monitor. Lines t1 to t4 indicate the electric field transmission coefficients t set for the input-side optical multiplexer / demultiplexer 62 and the output-side optical multiplexer / demultiplexer 64, respectively. Line t1 indicates an electric field transmission coefficient t of 0.3, line t2 indicates an electric field transmission coefficient t of 0.5, line t3 indicates an electric field transmission coefficient t of 0.7, and line t4 indicates an electric field transmission coefficient t of 0.9.

[0131] The calculations were performed for a total of 16 points, where the electric field transmission coefficients t of the input-side optical multiplexer / demultiplexer 62 and the output-side optical multiplexer / demultiplexer 64 were 0.3 (t1), 0.5 (t2), 0.7 (t3), and 0.9 (t4), respectively, and for four points in the coupled light of the first optical coupler 61a and the second optical coupler 61b: power branching ratio (0.8:0.8)·phase difference of 0 degrees, power branching ratio (0.9:0.7)·phase difference of 45 degrees, power branching ratio (0.95:0.6)·phase difference of 90 degrees, and power branching ratio (1:0.5)·phase difference of 150 degrees.

[0132] As can be seen from FIG. 12, when the electric field transmission coefficient t of each of the input-side optical multiplexer / demultiplexer 62 and the output-side optical multiplexer / demultiplexer 64 is 0.7 (t3), the power branching ratio is (0.8:0.8) and the phase difference is 0 degrees, that is, when the power branching ratio is 0.5 and the coupled light of the first optical coupler 61a and the second optical coupler 61b are in phase, the output slope is 0.036 GHz. -1 The maximum slope of On the other hand, when the electric field transmission coefficient t is 0.7 (t3), the power branching ratio is (0.95:0.6) and the phase difference is 90 degrees, that is, when the power branching ratio is 0.6 and the coupled light of the first optical coupler 61a and the second optical coupler 61b has a phase difference of 90 degrees, the output slope is 0.01 GHz. -1 The following is shown.

[0133] That is, when the electric field transmission coefficient t of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 is 0.7 (t3), that is, when the power branching ratio of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 is 0.5, if there is a phase difference of 90 degrees compared to when the coupled light of the first optical coupler 61a and the second optical coupler 61b are in phase, the slope of the photocurrent due to the first optical receiver 65a and the second optical receiver 65b will be significantly reduced.

[0134] On the other hand, when the electric field transmission coefficient t of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 is 0.9 (t4), within the range of expected mounting misalignment in the coupled light between the first optical coupler 61a and the second optical coupler 61b and the input side optical multiplexer / demultiplexer, the slope of the photocurrent by the first optical receiver 65a and the second optical receiver 65b becomes approximately 0.025 GHz. -1 It is found to be stable at . That is, within the range of expected mounting misalignment in the coupled light between the first optical coupler 61a and the second optical coupler 61b and the input-side optical multiplexer / demultiplexer, the maximum amount of slope variation indicating the tolerance for wavelength dependency in the photocurrent due to the first optical receiver 65a and the second optical receiver 65b is kept within 30%.

[0135] Considering the control unit 9 located downstream of the optical monitor 6, the control unit 9 processes the photocurrent from the first photodetector 65a and the photocurrent from the second photodetector 65b. Therefore, from a design perspective, it is undesirable for the slope of the photocurrent due to the first photodetector 65a and the second photodetector 65b to change significantly. It is therefore preferable that the maximum slope variation amount, which indicates the tolerance for wavelength dependency in the photocurrent due to the first photodetector 65a and the second photodetector 65b, be within 30% within the range of expected mounting deviation in the coupled light between the first optical coupler 61a and the second optical coupler 61b and the input side optical multiplexer / demultiplexer.

[0136] Therefore, it is preferable to design an optical monitor in which the electric field transmission coefficient t of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 is 0.9, in other words, the power branching ratio of each of the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 is 0.8 (power branching ratio 2:8). In short, within the range of expected mounting deviation in the coupled light between the first optical coupler 61a and the second optical coupler 61b and the input-side optical multiplexer / demultiplexer, that is, within the range of expected power branching ratio in the coupled light of the first optical coupler 61a and the second optical coupler 61b, it is preferable that the maximum slope fluctuation amount, which indicates the tolerance for wavelength dependency in the photocurrent from the first optical receiver 65a and the photocurrent from the second optical receiver 65b, be within 30% even if the coupling efficiency and coupling phase of the rear laser light Lb of the semiconductor laser 5 to the first optical coupler 61a and the second optical coupler 61b change.

[0137] As described above, the optical module according to the first embodiment includes an optical monitor 6 that includes a first optical coupler 61a that receives laser light from the semiconductor laser 5, a second optical coupler 61b that receives laser light from the semiconductor laser 5, a first optical receiver 65a that outputs a first monitor value, and a second optical receiver 65b that outputs a second monitor value, and constitutes an optical interferometer in which the first path from the first optical coupler 61a to the first optical receiver and the second path from the second optical coupler to the second optical receiver are asymmetric. Therefore, the optical power monitor value Ip and the wavelength monitor value Iλ / Ip can be obtained from the first monitor value and the second monitor value, and the laser light from the semiconductor laser 5 can be precisely controlled to a single wavelength.

[0138] The optical module of the first embodiment uses first optical coupler 61a and second optical coupler 61b, which provides twice the effect compared to the case where a single optical coupler is used, and the wavelength monitor value Iλ is obtained from the difference between the first monitor value and the second monitor value, which provides twice the effect. As a result, an optical monitor 6 with four times the sensitivity is obtained.

[0139] The optical module according to the first embodiment includes an optical monitor 6 that includes an input-side optical multiplexer / demultiplexer 62 having a first optical waveguide 62a and a second optical waveguide 62b, a first asymmetric arm 63a formed by an optical waveguide, a second asymmetric arm 63b formed by an optical waveguide and having a length of the optical waveguide different from that of the optical waveguide forming the first asymmetric arm 63a, and an output-side optical multiplexer / demultiplexer 64 having a third optical waveguide 64a and a fourth optical waveguide 64b. Therefore, the optical monitor 6 can be formed by a planar waveguide type optical monitor, which requires fewer parts and can be made smaller.

[0140] In the optical module of embodiment 1, the input side optical multiplexer / demultiplexer 62 and the output side optical multiplexer / demultiplexer 64 are each configured as optical multiplexers / demultiplexers with a power branching ratio of 0.8. Therefore, within the range of expected mounting misalignment in the coupled light with the input side optical multiplexer / demultiplexer of the first optical coupler 61a and the second optical coupler 61b, the slope of the photocurrent due to the first optical receiver 65a and the slope of the photocurrent due to the second optical receiver 65b are stable, making it easy to process the photocurrent in the control unit 9 located downstream of the optical monitor 6. In particular, if the maximum value of the slope fluctuation amount indicating the tolerance for wavelength dependency in the photocurrent indicating the first monitor value output from the first photoreceiver 65a and the photocurrent indicating the second monitor value output from the second photoreceiver 65b is within 30%, processing of the photocurrent in the control unit 9 is easy.

[0141] In the optical module of embodiment 1, the semiconductor laser 5, the optical monitor 6, the temperature regulator 2, and the base 3 are arranged within the space formed by the stem 1 and the cap 7, so that the number of lead pins for the semiconductor laser 5, the optical monitor 6, and the temperature regulator 2 can be reduced.

[0142] Embodiment 2 The optical module according to the second embodiment will be described with reference to FIGS. The optical module according to the second embodiment is different from the optical module according to the first embodiment in the configuration of the optical monitor 6, but is otherwise the same or similar to the optical module according to the first embodiment. That is, in the optical module according to the first embodiment, when the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the first asymmetric arm 63a and the second asymmetric arm 63b are configured with waveguides having the same group refractive index, specifically, silicon waveguides.

[0143] In contrast, when the optical module according to the second embodiment is configured using a planar waveguide type optical monitor made of a silicon photonics chip as the optical monitor 6, the optical module differs from the optical module according to the first embodiment in that the first asymmetric arm 63a and the second asymmetric arm 63b are configured with optical waveguides having a common portion and a non-common portion, the non-common portion of the first asymmetric arm 63a is configured with an optical waveguide having a first group refractive index, and the non-common portion of the second asymmetric arm 63b is configured with an optical waveguide having a second group refractive index different from the first group refractive index. Otherwise, the optical module according to the second embodiment is the same as the optical module according to the first embodiment. In FIG. 13, the same reference numerals as those in FIG. 5 denote the same or corresponding parts. Moreover, the overall configuration of the optical module is the same as that of the first embodiment shown in FIGS. 1 to 3, and therefore will not be described.

[0144] The following describes the optical monitor 6 when it is configured as a planar waveguide type optical monitor using a silicon photonics chip, focusing in particular on the first asymmetric arm 63a and the second asymmetric arm 63b.

[0145] The optical monitor 6 includes a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, a second optical receiver 65b, and a phase adjuster 66. The output side optical multiplexer / demultiplexer 64, the first optical receiver 65a, and the second optical receiver 65b function as an interference measurement system for observing wavelength dependence, similar to the output side optical multiplexer / demultiplexer 64, the first optical receiver 65a, and the second optical receiver 65b in embodiment 1. The output side optical multiplexer / demultiplexer 64 is an optical circuit that configures an interference measurement system together with a first photoreceiver 65a and a second photoreceiver 65b.

[0146] The optical monitor 6 is, for example, a planar waveguide type optical monitor using a silicon photonics chip formed by integrating a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, and a second optical receiver 65b on the flat surface of a silicon (Si) substrate 6A.

[0147] The first optical coupler 61a, the second optical coupler 61b, the input side optical multiplexer / demultiplexer 62, the output side optical multiplexer / demultiplexer 64, the first optical receiver 65a, the second optical receiver 65b, and the phase adjuster 66 are respectively the same as the first optical coupler 61a, the second optical coupler 61b, the input side optical multiplexer / demultiplexer 62, the output side optical multiplexer / demultiplexer 64, the first optical receiver 65a, the second optical receiver 65b, and the phase adjuster 66 that constitute the optical monitor 6 in the optical module of embodiment 1.

[0148] An input node of the first asymmetric arm 63a is optically connected to a second port of the input-side optical multiplexer / demultiplexer 62, and an output node of the first asymmetric arm 63a is optically connected to a first port of the output-side optical multiplexer / demultiplexer. The input node of the second asymmetric arm 63b is optically connected to the fourth port of the input-side optical multiplexer / demultiplexer 62, and the output node of the second asymmetric arm 63b is optically connected to the third port of the output-side optical multiplexer / demultiplexer.

[0149] Each of the first asymmetric arm 63a and the second asymmetric arm 63b is formed of an optical waveguide having a common portion A and a non-common portion B as shown in FIG. The first asymmetric arm 63a is composed of silicon nitride waveguides 63a1 and 63a2 and a silicon waveguide 63a3. The temperature dependence of the group refractive index n2 in the silicon nitride waveguide differs from the temperature dependence of the group refractive index n1 (described as n0 in the first embodiment) in the silicon waveguide. The first asymmetric arm 63a has a U-shape, although it is not limited to the U-shape.

[0150] The silicon nitride waveguide 63a1 and the silicon nitride waveguide 63a2 are located on the legs of the U-shape and are disposed opposite each other. The length (physical length) of the silicon nitride waveguide 63a1 and the length (physical length) of the silicon nitride waveguide 63a2 are the same length (physical length). One end of the silicon nitride waveguide 63a1 is optically connected to the second port of the input-side optical multiplexer / demultiplexer 62 via a silicon waveguide.

[0151] The other end of the silicon nitride waveguide 63a2 is optically connected to a first port of the output-side optical multiplexer / demultiplexer 64 via a silicon waveguide. The silicon waveguide 63a3 is optically connected between the other end of the silicon nitride waveguide 63a1 and one end of the silicon nitride waveguide 63a2, and is located at the turn-back portion of the first asymmetric arm 63a.

[0152] The first asymmetric arm 63a is an optical propagation path that extends from an input node to an output node through an optically connected silicon nitride waveguide 63a1, silicon waveguide 63a3, and silicon nitride waveguide 63a2 in this order. The first asymmetric arm 63a is bilaterally symmetric.

[0153] The silicon nitride waveguide 63a1 and the silicon nitride waveguide 63a2 have a common portion A and a non-common portion B. In the silicon nitride waveguide 63a1, as shown in FIG. 13, the common portion A is a portion of the side that is optically connected to the silicon waveguide 63a3 and a portion of the side that is optically connected to the second port of the input-side optical multiplexer / demultiplexer 62, and the non-common portion B is the remaining portion of the silicon nitride waveguide 63a1, i.e., the central portion. Similar to the common portion A and non-common portion B in the silicon nitride waveguide 63a1, the common portion A is at both ends and the non-common portion B is at the center.

[0154] The length (physical length) of the non-common portion B in the silicon nitride waveguide 63a1 and the length (physical length) of the non-common portion B in the silicon nitride waveguide 63a2 are each set to (L+ΔL) / 2. Therefore, the non-common portion B in the first asymmetric arm 63a is made of a silicon nitride waveguide and has a length (physical length) of (L+ΔL). The silicon waveguide 63a3 is the common portion A.

[0155] The second asymmetric arm 63b is composed of silicon waveguides 63b1 to 63b3 and silicon nitride waveguides 63b4 and 63b5. The second asymmetric arm 63b has a U-shape, although it is not limited to the U-shape. The silicon waveguide 63b1 and the silicon waveguide 63b2 are located on the legs of the U-shape and are disposed opposite to each other. The length (physical length) of the silicon waveguide 63b1 and the length (physical length) of the silicon waveguide 63b2 are the same length (physical length).

[0156] One end of the silicon waveguide 63b1 is optically connected via a silicon waveguide to the fourth port of the input-side optical multiplexer / demultiplexer 62. Note that the silicon waveguide 63b1 and the silicon waveguide that is the second optical waveguide 62b of the input-side optical multiplexer / demultiplexer 62 are formed continuously, so that one end of the silicon waveguide 63b1 and the fourth port of the input-side optical multiplexer / demultiplexer 62 do not physically exist. The other end of the silicon waveguide 63b2 is optically connected via a silicon waveguide to the third port of the output-side optical multiplexer / demultiplexer 64. Note that the silicon waveguide 63b2 and the silicon waveguide that is the fourth optical waveguide 64b of the output-side optical multiplexer / demultiplexer 64 are formed continuously, so the other end of the silicon waveguide 63b2 and the third port of the output-side optical multiplexer / demultiplexer 64 do not physically exist.

[0157] The silicon nitride waveguide 63b4 and the silicon nitride waveguide 63b5 are located on the legs of the U-shape and are disposed opposite to each other. The length (physical length) of the silicon nitride waveguide 63b4 and the length (physical length) of the silicon nitride waveguide 63b5 are the same length (physical length). One end of the silicon nitride waveguide 63b4 is optically connected to the other end of the silicon waveguide 63b1. The other end of the silicon nitride waveguide 63b5 is optically connected to one end of the silicon waveguide 63b2.

[0158] The silicon waveguide 63b3 is optically connected between the other end of the silicon nitride waveguide 63b4 and one end of the silicon nitride waveguide 63b5, and is located at the turn-back portion of the second asymmetric arm 63b. The second asymmetric arm 63b is an optical propagation path that extends from the input node to the output node through optically connecting the silicon waveguide 63b1, the silicon nitride waveguide 63b4, the silicon waveguide 63b3, the silicon nitride waveguide 63b5, and the silicon waveguide 63b3 in this order. The second asymmetric arm 63b is bilaterally symmetric.

[0159] As shown in FIG. 13, the silicon nitride waveguide 63b4, the silicon nitride waveguide 63b5 and the silicon waveguide 63b3 form a common portion A for the first asymmetric arm 63a. That is, the length of the silicon nitride waveguide 63b4 in the second asymmetric arm 63b is the same as the length of a portion of the silicon nitride waveguide 63a1 in the first asymmetric arm 63a, the length of the silicon nitride waveguide 63b5 in the second asymmetric arm 63b is the same as the length of a portion of the silicon nitride waveguide 63a2 in the first asymmetric arm 63a, and the length of the silicon waveguide 63b3 in the second asymmetric arm 63b is the same as the length of the silicon waveguide 63a3 in the first asymmetric arm 63a.

[0160] The length (physical length) of L / 2 in each of the silicon waveguides 63b1 and 63b2 is defined as a non-common portion B with respect to the first asymmetric arm 63a. That is, in the second asymmetric arm 63b, a portion of the silicon waveguide 63b1 and a portion of the silicon waveguide 63b2 excluding a common portion A located at the folded back portion of the U-shape are the non-common portion B. The length (physical length) of the non-common portion B in the silicon waveguide 63b1 and the length (physical length) of the non-common portion B in the silicon waveguide 63b2 are each L / 2. Therefore, the non-common portion B in the second asymmetric arm 63b is made of a silicon waveguide and has a length (physical length) of L. The length (physical length) of the non-common portion B in the first asymmetric arm 63a is longer than the length (physical length) of the non-common portion B in the second asymmetric arm 63b by a length ΔL.

[0161] When the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the first path is an optical propagation path from a first port of the input side optical multiplexer / demultiplexer 62, via the input side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a composed of silicon nitride waveguides 63a1, 63a2 and silicon waveguide 63a3, and the output side optical multiplexer / demultiplexer 64, to a second port of the output side optical multiplexer / demultiplexer 64.

[0162] The second path is an optical propagation path from the third port of the input-side optical multiplexer / demultiplexer 62 through the second asymmetric arm 63b composed of the input-side optical multiplexer / demultiplexer 62, silicon waveguides 63b1-63b3 and silicon nitride waveguides 63b4, 63b5, and the output-side optical multiplexer / demultiplexer 64 to the fourth port of the output-side optical multiplexer / demultiplexer 64.

[0163] Next, a method for determining the length (physical length) of the non-common portion B of the first asymmetric arm 63a and the length (physical length) of the non-common portion B of the second asymmetric arm 63b will be described. Since the common portion A of the first asymmetric arm 63a and the common portion A of the second asymmetric arm 63b have the same length and shape, the phase difference between the common portion A of the first asymmetric arm 63a and the common portion A of the second asymmetric arm 63b does not change even if the temperature changes. The non-common portion B of the first asymmetric arm 63a and the non-common portion B of the second asymmetric arm 63b are made of different materials, a silicon nitride waveguide and a silicon waveguide, and have lengths different from each other, that is, (L+ΔL). Therefore, it is only necessary to consider the phase change due to temperature for the non-common portion B of the first asymmetric arm 63a and the non-common portion B of the second asymmetric arm 63b.

[0164] The linear expansion coefficient of the substrate in the planar waveguide optical monitor is denoted by α. Since the physical length L and the physical length ΔL must be positive values, the following formula (3) is satisfied. dn1 / dT+n1α>dn2 / dT+n2α (3) The phase difference θ between the first monitor value (photocurrent from the first photoreceiver 65a) and the second monitor value (photocurrent from the second photoreceiver 65b) in the optical monitor 6 can be expressed by the following equation (4). n2(L+ΔL)-n1·L=m·λ=(λ / 2π)·θ(4)

[0165] In the above equations (3) and (4), n2 is the group refractive index of the silicon nitride waveguide, n1 is the group refractive index of the silicon waveguide, (L+ΔL) is the length (physical length) of the non-common part B of the first asymmetric arm 63a, L is the length (physical length) of the non-common part B of the second asymmetric arm 63b, λ is the wavelength of the backward laser light Lb, and m is a coefficient connecting the wavelength λ and the optical path length nL.

[0166] In the above formula (4), by determining n1, n2, L, and ΔL so that the temperature derivative of the above formula (4) is always 0, the formula becomes independent of temperature. That is, in the above equation (4), by differentiating the left side with respect to temperature and setting the right side to 0, the following equation (5) is obtained by solving the above equation (4). The following equation (5) is obtained by making the temperature derivative of the above equation (4) always 0, and is a relational equation that is independent of the environmental temperature and the operating temperature.

[0167] TIFF0007642180000001.tif25166(5)

[0168] By making the relationship between L and ΔL satisfy the above formula (5), provided that the backward laser light Lb from the semiconductor laser 5 does not change, the wavelength monitor value Iλ / Ip obtained from the first monitor value obtained from the first photodetector 65a and the second monitor value obtained from the second photodetector 65b will not have temperature dependency, and it will be possible to obtain a highly accurate wavelength monitor value Iλ / Ip that is not dependent on the environmental temperature and the operating temperature.

[0169] Here, the group refractive index n2 can be determined by the group refractive index of the silicon nitride waveguide, and the group refractive index n1 can be determined by the group refractive index of the silicon waveguide. In other words, the value in the parentheses in the above formula (5) can be determined. Moreover, the physical length ΔL can be determined by the FSR design of the Mach-Zehnder interferometer output. Therefore, the physical length L can be calculated by the above formula (5).

[0170] When it is desired to increase the slope of the photocurrent from the first photoreceiver 65a and the slope of the photocurrent from the second photoreceiver 65b, ΔL is increased to decrease the FSR determined by the FSR design, and when it is desired to decrease the slope, ΔL is decreased to increase the FSR.

[0171] FIG. 14 shows the results of calculations of the temperature characteristics of the optical monitor 6 when the temperatures in the optical monitor 6 are 20 degrees, 30 degrees, 40 degrees, and 50 degrees. In FIG. 14, the horizontal axis indicates the wavelength of the backward laser light Lb, and the vertical axis indicates the output from the light receiver. Waveform T1 shows the temperature characteristics at 20 degrees, waveform T2 shows the temperature characteristics at 30 degrees, waveform T3 shows the temperature characteristics at 40 degrees, and waveform T4 shows the temperature characteristics at 50 degrees. As is clear from FIG. 14, the waveforms T1 to T4 overlap, and it can be seen that an optical monitor 6 can be realized that can obtain first and second monitor values ​​that are not temperature dependent.

[0172] In the optical monitor 6 described above, the first asymmetric arm 63a is configured with the silicon nitride waveguides 63a1, 63a2 and the silicon waveguide 63a3, and the second asymmetric arm 63b is configured with the silicon waveguides 63b1-63b3 and the silicon nitride waveguides 63b4, 63b5. Therefore, the first asymmetric arm 63a and the second asymmetric arm 63b have the same number of connection points between waveguides having different characteristics. In other words, in the first asymmetric arm 63a, the silicon nitride waveguides 63a1, 63a2 have a total of four connection points with the silicon waveguides, and in the second asymmetric arm 63b, the silicon nitride waveguides 63b4, 63b5 have a total of four connection points with the silicon waveguides, which is the same number. This makes it possible to minimize the difference in propagation loss in the first asymmetric arm 63a and the second asymmetric arm 63b.

[0173] The second asymmetric arm 63b may be constructed from a single silicon waveguide from the input node to the output node. In this case, the common portion A of the first asymmetric arm 63a and the common portion A of the second asymmetric arm 63b are both made of a silicon waveguide, the non-common portion B of the first asymmetric arm 63a is made of a silicon nitride waveguide, and the non-common portion B of the second asymmetric arm 63b is made of a silicon waveguide.

[0174] Even in this case, since the relationship between L and ΔL satisfies the above formula (5), as long as the backward laser light Lb from the semiconductor laser 5 does not change, an optical monitor 6 can be realized in which the wavelength monitor value Iλ / Ip obtained from the first monitor value obtained from the first optical receiver 65a and the second monitor value obtained from the second optical receiver 65b does not have temperature dependency.

[0175] Furthermore, the relationship between the first asymmetric arm 63a and the second asymmetric arm 63b only needs to be such that the lengths of the optical waveguides are different and the group refractive indices are different in the non-common portion B, and the planar waveguide-type optical monitor is not limited to a silicon photonics chip, but may be a planar waveguide-type optical monitor using an indium phosphide substrate, which is a compound semiconductor, or a glass substrate.

[0176] The operation of the optical module according to the second embodiment is substantially the same as that of the optical module according to the first embodiment. The only differences are as follows, and explanations of other points will be omitted. That is, the laser light from the first optical coupler 61a which receives the backward laser light Lb of the semiconductor laser 5 is incident on the first optical waveguide 62a constituting the input side optical multiplexer / demultiplexer 62 from the first port of the input side optical multiplexer / demultiplexer 62. On the other hand, the laser light from the second optical coupler 61b that receives the backward laser light Lb from the semiconductor laser 5 is input to the second optical waveguide 62b that constitutes the input side optical multiplexer / demultiplexer 62 from the third port of the input side optical multiplexer / demultiplexer 62.

[0177] The laser light from the first optical coupler 61a and the laser light from the second optical coupler 61b input to the input-side optical multiplexer / demultiplexer 62 are each split and interfered with by the input-side optical multiplexer / demultiplexer 62, and propagated from the second port of the input-side optical multiplexer / demultiplexer 62 to the first asymmetric arm 63a and from the fourth port of the input-side optical multiplexer / demultiplexer 62 to the second asymmetric arm 63b.

[0178] The laser light propagated through the first asymmetric arm 63 a is propagated from the first port of the output-side optical multiplexer / demultiplexer 64 to the third optical waveguide 64 a constituting the output-side optical multiplexer / demultiplexer 64 . The laser light propagated through the second asymmetric arm 63 b is propagated from the third port of the output-side optical multiplexer / demultiplexer 64 to the fourth optical waveguide 64 b constituting the output-side optical multiplexer / demultiplexer 64 .

[0179] The laser light that has propagated through the first asymmetric arm 63a and the second asymmetric arm 63b is propagated to the output side optical multiplexer / demultiplexer 64, and is separated and interfered with by the output side optical multiplexer / demultiplexer 64, and is incident on the first optical receiver 65a from the second port of the output side optical multiplexer / demultiplexer 64, and is incident on the second optical receiver 65b from the fourth port of the output side optical multiplexer / demultiplexer 64.

[0180] The laser light incident on the first photoreceiver 65a is photoelectrically converted by the first photoreceiver 65a, and a photocurrent indicating a first monitor value is output to the control unit 9. The laser light incident on the second photoreceiver 65b is photoelectrically converted by the second photoreceiver 65b, and a photocurrent indicating a second monitor value is output to the control unit 9. The wavelength monitor value Iλ / Ip calculated by the control unit 9 does not depend on the environmental temperature and the operating temperature due to the action of the first asymmetric arm 63a and the second asymmetric arm 63b.

[0181] In the optical module according to the second embodiment, a trial calculation showed that, by performing the wavelength locker step, the amount of shift in the wavelength direction of the wavelength-dependent wavelength monitor value, which is the ratio between the optical power monitor value calculated from the photocurrent obtained from the first photodetector 65a and the photocurrent obtained from the second photodetector 65b and the wavelength monitor value, varied by 0.05 nm or less within a temperature change range of 100 degrees in the oscillation wavelength from the semiconductor laser 5. That is, within a temperature change range of 100 degrees, the oscillation wavelength from the semiconductor laser 5 varies by 0.05 nm or less, and the optical module according to the second embodiment has very little temperature dependency.

[0182] In the optical module of embodiment 2, an oscillation wavelength from the semiconductor laser 5 can be obtained that is 0.1 nm or less within a temperature change range of 100 degrees in the wavelength direction of the wavelength monitor value Iλ / Ip, which is the ratio between the optical power monitor value Ip and the wavelength monitor value Iλ, and is calculated from the photocurrent indicating the first monitor value output from the first photodetector 65a and the photocurrent indicating the second monitor value output from the second photodetector 65b, and precise control can be performed on the laser light from the semiconductor laser 5.

[0183] As described above, the optical module according to the second embodiment, like the optical module according to the first embodiment, can precisely control the laser light from the semiconductor laser 5 to a single wavelength, has a reduced number of parts, and can be made compact.

[0184] Furthermore, in the optical module of embodiment 2, the optical monitor 6 is configured such that the lengths of the optical waveguides in the non-common portion B in the first asymmetric arm 63a and the non-common portion B in the second asymmetric arm 63b are different and also have different group refractive indices. Therefore, by appropriately selecting the length and group refractive index of the non-common portion B, the wavelength monitor value Iλ / Ip obtained from the first monitor value obtained from the first optical receiver 65a and the second monitor value obtained from the second optical receiver 65b can be a wavelength monitor value that has no temperature dependency.

[0185] Embodiment 3 The optical module according to the third embodiment will be described with reference to FIGS. The optical module according to the third embodiment is different from the optical module according to the second embodiment in the configuration of the optical monitor 6, but is otherwise the same or similar to the optical module according to the second embodiment. That is, in the optical module according to the second embodiment, when the optical monitor 6 is configured as a planar waveguide type optical monitor using a silicon photonics chip, the optical circuit after the first asymmetric arm 63a and the second asymmetric arm 63b is configured to include an output side optical multiplexer / demultiplexer 64, a first optical receiver 65a, and a second optical receiver 65b, and further includes a phase adjuster 66.

[0186] In contrast, the optical module according to the third embodiment, when configured with a planar waveguide type optical monitor using a silicon photonics chip as the optical monitor 6, differs from the optical module according to the second embodiment in that the optical circuits after the first asymmetric arm 63a and the second asymmetric arm 63b are configured to include a 90 degree hybrid configuration optical circuit OC, a first photoreceiving unit 65a, and a second photoreceiving unit 65b, and in that the optical circuit does not include a phase adjuster 66. In other respects, the optical module according to the second embodiment is the same as the optical module according to the second embodiment.

[0187] That is, in the second embodiment, the output side optical multiplexer / demultiplexer 64, the first photodetector 65a, and the second photodetector 65b function as an interference measurement system for observing wavelength dependence, whereas in the third embodiment, the 90 degree hybrid configuration optical circuit OC, the first photodetector 65a, and the second photodetector 65b function as an interference measurement system for observing wavelength dependence; otherwise, the third embodiment is similar to the second embodiment. The 90-degree hybrid optical circuit OC is an optical circuit that constitutes an interference measurement system by the first optical receiver 65a and the second optical receiver 65b.

[0188] In FIG. 15, the same reference numerals as those in FIG. 13 indicate the same or corresponding parts. Further, the overall configuration of the optical module is the same as that of the first embodiment shown in FIGS. 1 to 3, as in the second embodiment, and therefore will not be described. Hereinafter, we will explain the optical monitor 6 when it is configured as a planar waveguide type optical monitor using a silicon photonics chip, and in particular, the optical circuit after the first asymmetric arm 63a and the second asymmetric arm 63b, that is, the optical circuit that functions as an interference measurement system for observing wavelength dependence.

[0189] The optical monitor 6 includes a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, a 90 degree hybrid structure optical circuit OC, a first photoreceiver 65a, and a second photoreceiver 65b. The optical monitor 6 is, for example, a planar waveguide type optical monitor using a silicon photonics chip formed by integrating a first optical coupler 61a, a second optical coupler 61b, an input side optical multiplexer / demultiplexer 62, a first asymmetric arm 63a, a second asymmetric arm 63b, a 90 degree hybrid configuration optical circuit OC, a first photoreceiving unit 65a, and a second photoreceiving unit 65b on the flat surface of a silicon substrate 6A.

[0190] The first optical coupler 61a, the second optical coupler 61b, the input side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a, and the second asymmetric arm 63b are respectively the same as the first optical coupler 61a, the second optical coupler 61b, the input side optical multiplexer / demultiplexer 62, the first asymmetric arm 63a, and the second asymmetric arm 63b that constitute the optical monitor 6 in the optical module of embodiment 2.

[0191] The 90-degree hybrid configuration optical circuit OC has a first input node, a second input node, a first output node, and a second output node, the first input node is optically connected to an output node of a first asymmetric arm 63a, the second input node is optically connected to an output node of a second asymmetric arm 63b, and outputs an optical output for I to the first output node and outputs an optical output for Q to the second output node. In this example, the I optical output is made up of a first I output light and a second I output light. In this example, the Q optical output is made up of a first Q output light and a second Q output light.

[0192] The first light receiving section 65a receives the I optical output from the first output node of the 90-degree hybrid configuration optical circuit OP, and outputs a first monitor value which is the I signal shown in FIG. In the I signal shown in FIG. 16, the horizontal axis indicates the wavelength of the backward laser light Lb, and the vertical axis indicates the output from the first light receiving part 65a. The first light receiving unit 65a has a first light receiving device 65a1 for I and a second light receiving device 65a2 for I connected in series between a light receiving unit power supply potential node and a ground node. In this case, the first light receiving unit 65a having the first light receiving device 65a1 for I and the second light receiving device 65a2 for I is also included as the first light receiving device.

[0193] The first I-use optical receiver 65a1 receives the first I-use output light from the 90-degree hybrid configuration optical circuit OC. The second I-use optical receiver 65a2 receives the second I-use output light from the 90-degree hybrid configuration optical circuit OC. A first monitor value, which is an I signal, is output to a connection point between the first I photoreceiver 65a1 and the second I photoreceiver 65a2.

[0194] The second light receiving section 65b receives the Q optical output from the second output node of the 90-degree hybrid configuration optical circuit OP, and outputs a second monitor value which is the Q signal shown in FIG. In the Q signal shown in FIG. 16, the horizontal axis indicates the wavelength of the backward laser light Lb, and the vertical axis indicates the output from the second light receiving part 65b. There is a 90 degree phase difference between the Q and I signals. The second light receiving unit 65b has a first light receiving device for Q 65b1 and a second light receiving device for Q 65b2 connected in series between a power supply potential node for the light receiving unit and a ground node. In this case, the second light receiving unit 65b having the first light receiving device for Q 65b1 and the second light receiving device for Q 65b2 is also included as the second light receiving device.

[0195] The first Q optical receiver 65b1 receives the first Q output light from the 90-degree hybrid optical circuit OC. The second Q optical receiver 65b2 receives the second Q output light from the 90-degree hybrid optical circuit OC. A second monitor value, which is a Q signal, is output to the connection point between the first Q photoreceiver 65b1 and the second Q photoreceiver 65b2.

[0196] The 90-degree hybrid configuration optical circuit OC includes a first 1×2 optical multiplexer / demultiplexer 67 a , a second 1×2 optical multiplexer / demultiplexer 67 b , a first 2×2 optical multiplexer / demultiplexer 68 a , a second 2×2 optical multiplexer / demultiplexer 68 b , and a 90-degree delay device 69 . The first 1×2 optical multiplexer / demultiplexer 67a has a first port to a third port. A first port of the first 1×2 optical multiplexer / demultiplexer 67a is optically connected to an output node of the first asymmetric arm 63a. The first 1×2 optical multiplexer / demultiplexer 67a demultiplexes the optical output from the first asymmetric arm 63a into two optical outputs.

[0197] The first 1×2 optical multiplexer / demultiplexer 67a is, for example, any one of a directional coupler, an MMI waveguide, or a Y-branch waveguide. In this example, an MMI waveguide is used as the first 1×2 optical multiplexer / demultiplexer 67a. It should be noted that the first port of the first 1×2 optical multiplexer / demultiplexer 67a and the output node of the first asymmetric arm 63a are not physically separate structures, but are a connection point of a silicon waveguide that continuously forms the first port of the first 1×2 optical multiplexer / demultiplexer 67a and the first asymmetric arm 63a.

[0198] The second 1×2 optical multiplexer / demultiplexer 67b has a first port to a third port. A first port of the second 1×2 optical multiplexer / demultiplexer 67b is optically connected to an output node of the second asymmetric arm 63b. The second 1×2 optical multiplexer / demultiplexer 67b demultiplexes the optical output from the second asymmetric arm 63b into two optical outputs.

[0199] The second 1×2 optical multiplexer / demultiplexer 67b is, for example, a directional coupler, an MMI waveguide, or a Y-branch waveguide. In this example, an MMI waveguide is used as the second 1×2 optical multiplexer / demultiplexer 67b. In addition, the first port of the second 1×2 optical multiplexer / demultiplexer 67b and the output node of the second asymmetric arm 63b are not physically separate structures, but are a connection point of a silicon waveguide that continuously forms the first port of the second 1×2 optical multiplexer / demultiplexer 67b and the second asymmetric arm 63b.

[0200] The 90-degree delay device 69 delays the input optical output by 90 degrees, that is, shifts the phase by 90 degrees, and outputs the delayed optical output. The input node of the 90 degree delay device 69 is optically connected to the third port of the second 1×2 optical multiplexer / demultiplexer 67 b. The 90-degree delay device 69 is composed of an optical waveguide. It should be noted that the input node of the 90-degree delay device 69 and the third port of the second 1×2 optical multiplexer / demultiplexer 73 b are not physically separate components, but are the connection points of silicon waveguides that continuously form the optical waveguides that constitute the 90-degree delay device 69 and the other output side of the second 1×2 optical multiplexer / demultiplexer 67 b.

[0201] The first 2×2 optical multiplexer / demultiplexer 68a has a first port to a fourth port, a fifth optical waveguide connecting the first port and the second port, and a sixth optical waveguide connecting the third port and the fourth port. In the first 2×2 optical multiplexer / demultiplexer 68a, the first port is optically connected to the second port of the first 1×2 optical multiplexer / demultiplexer 67a, and the third port is optically connected to the second port of the second 1×2 optical multiplexer / demultiplexer 67b.

[0202] The fifth optical waveguide and the sixth optical waveguide in the first 2×2 optical multiplexer / demultiplexer 68a are silicon waveguides. The fifth optical waveguide and the sixth optical waveguide have the same length. The first 2×2 optical multiplexer / demultiplexer 68a is an asymmetric optical multiplexer / demultiplexer, and in this example, the power branching ratio is set to, for example, 0.8. In other words, the power branching ratio for the fifth optical waveguide and the sixth optical waveguide is set to 2:8.

[0203] Note that the first port of the first 2×2 optical multiplexer / demultiplexer 68a and the second port of the first 1×2 optical multiplexer / demultiplexer 67a are not physically separate configurations, but are the connection points of silicon waveguides that continuously form the fifth optical waveguide constituting the first 2×2 optical multiplexer / demultiplexer 68a and the optical waveguide constituting one output side of the first 1×2 optical multiplexer / demultiplexer 67a. Furthermore, the third port of the first 2×2 optical multiplexer / demultiplexer 68a and the second port of the second 2×2 optical multiplexer / demultiplexer 67b are not physically separate structures, but are the connection points of silicon waveguides that continuously form the sixth optical waveguide constituting the second 2×2 optical multiplexer / demultiplexer 67b and the optical waveguide constituting one output side of the second 1×2 optical multiplexer / demultiplexer 67a. The first 2×2 optical multiplexer / demultiplexer 68a is, for example, any one of a directional coupler, an MMI waveguide, or a Y-branch waveguide. In this example, an MMI waveguide is used as the first 2×2 optical multiplexer / demultiplexer 68a.

[0204] The second 2×2 optical multiplexer / demultiplexer 68b has a first port to a fourth port, a seventh optical waveguide connecting the first port and the second port, and an eighth optical waveguide connecting the third port and the fourth port. In the second 2×2 optical multiplexer / demultiplexer 68 b , the first port is optically connected to the third port of the first 1×2 optical multiplexer / demultiplexer 67 a , and the third port is optically connected to the output node of the 90 degree delay device 69 .

[0205] The seventh and eighth optical waveguides in the second 2×2 optical multiplexer / demultiplexer 68b are silicon waveguides. The seventh optical waveguide and the eighth optical waveguide have the same length. The second 2×2 optical multiplexer / demultiplexer 68b is an asymmetric optical multiplexer / demultiplexer, and in this example, the power branching ratio is set to, for example, 0.8, in other words, the power branching ratio for the seventh optical waveguide and the eighth optical waveguide is set to 2:8.

[0206] It should be noted that the first port of the second 2×2 optical multiplexer / demultiplexer 68b and the third port of the first 1×2 optical multiplexer / demultiplexer 67a are not physically separate components, but are the connection points of silicon waveguides that continuously form the seventh optical waveguide constituting the second 2×2 optical multiplexer / demultiplexer 68b and the optical waveguide constituting the other output side of the first 1×2 optical multiplexer / demultiplexer 67a. Furthermore, the third port of the second 2×2 optical multiplexer / demultiplexer 68b and the output node of the 90-degree delay device 69 are not physically separate structures, but are the connection point of a silicon waveguide that continuously forms the eighth optical waveguide that constitutes the second 2×2 optical multiplexer / demultiplexer 68b and the optical waveguide that constitutes the 90-degree delay device 69. The second 2×2 optical multiplexer / demultiplexer 68b is, for example, any one of a directional coupler, an MMI waveguide, or a Y-branch waveguide. In this example, an MMI waveguide is used as the second 2×2 optical multiplexer / demultiplexer 68b.

[0207] In the first I photoreceiver 65a1 constituting the first photoreceiver 65a, the anode electrode is connected to the power supply potential node for the photoreceiver, and the cathode electrode is connected to the first output terminal of the optical monitor 6 that outputs a first monitor value. In the second I-photoreceiver 65a2 constituting the first light receiving section 65a, the anode electrode is connected to the first output terminal, and the cathode electrode is connected to the ground node.

[0208] In the first Q photoreceiver 65b1 constituting the second photoreceiver 65b, the anode electrode is connected to the photoreceiver power supply potential node, and the cathode electrode is connected to the second output terminal of the optical monitor 6 that outputs a second monitor value. In the second Q light receiver 65b2 constituting the second light receiving section 65b, the anode electrode is connected to the second output terminal, and the cathode electrode is connected to the ground node. The first I-photoreceiver 65a1 and the second I-photoreceiver 65a2, and the first Q-photoreceiver 65b1 and the second Q-photoreceiver 65b2 are each a waveguide-type photoreceiver or a surface-incident type photoreceiver, and in this example use a photodiode that is a SiGe photoreceiver.

[0209] The relationship between the semiconductor laser 5, the optical monitor 6, the temperature regulator 2, and the lead pins P1 to P6 will be described. The lead pin P 1 is a lead pin for a main signal to the semiconductor laser 5 . The lead pin P2 is a first monitor lead pin for the optical monitor 6, which is connected to a first output terminal of the optical monitor 6. The lead pin P3 is a second monitor lead pin for the optical monitor 6, which is connected to a second output terminal of the optical monitor 6. The lead pins P4 and P5 are a pair of lead pins for controlling temperature for the temperature regulator 2.

[0210] The lead pin P6 is a power supply pin for supplying power to the first light receiving unit 65a and the second light receiving unit 65b, and is connected to the anode electrode of the first I light receiving unit 65a1 and the anode electrode of the first Q light receiving unit 65b1. The lead pin P6 is a power supply lead pin for the light receiving units, and also serves as a power supply potential node for the light receiving units. The lead pin P7 is a ground lead pin.

[0211] The optical module according to the third embodiment also requires a total of seven lead pins, six signal lead pins P1 to P6 and one ground lead pin P7 for each component, making it possible to configure the optical module with a small number of lead pins. As a result, it is possible to use a standard CAN package with a diameter of 5.6 mm, which has a maximum number of lead pins of seven, thereby enabling miniaturization.

[0212] Next, the operation of the optical module according to the third embodiment will be described. The preparations for operating the optical module are similar to those for the optical modules of the first and second embodiments, and involve obtaining a target value ILD_target of the driving photocurrent supplied to the semiconductor laser 5, a target value ITEC_target of the photocurrent supplied to the temperature regulator 2, a target value Ip_target of the optical power monitor value Ip, and a target value Iλ_target of the wavelength monitor value Iλ / Ip when the wavelength λLD is set to the target value λ_target.

[0213] When the optical module is started up, a driving photocurrent having a target value ILD_target is supplied to the semiconductor laser 5 in the same manner as in the operations of the optical modules according to the first and second embodiments (step ST2). When a driving photocurrent of the target value ILD_target is supplied to the semiconductor laser 5, the semiconductor laser 5 emits a forward laser light Lf to the outside of the cap 7 through the window 8, and emits a backward laser light Lb to the first optical coupler 61a and the second optical coupler 61b in the optical monitor 6.

[0214] The laser light from the first optical coupler 61a that receives the backward laser light Lb of the semiconductor laser 5 is incident on the first optical waveguide 62a made of a silicon waveguide that constitutes the input side optical multiplexer / demultiplexer 62 from the first port of the input side optical multiplexer / demultiplexer 62. On the other hand, the laser light from the second optical coupler 61b that receives the backward laser light Lb from the semiconductor laser 5 is input to the second optical waveguide 62b that constitutes the input side optical multiplexer / demultiplexer 62 from the third port of the input side optical multiplexer / demultiplexer 62.

[0215] The laser light from the first optical coupler 61a and the laser light from the second optical coupler 61b input to the input-side optical multiplexer / demultiplexer 62 are each split and interfered with by the input-side optical multiplexer / demultiplexer 62, and propagated from the second port of the input-side optical multiplexer / demultiplexer 62 to the first asymmetric arm 63a and from the fourth port of the input-side optical multiplexer / demultiplexer 62 to the second asymmetric arm 63b.

[0216] The laser light propagated through the first asymmetric arm 63a is input as a first input light to the first input node of the 90-degree hybrid configuration optical circuit OC. The laser light propagated through the second asymmetric arm 63b is input as the second incident light to the second input node of the 90-degree hybrid configuration optical circuit OC.

[0217] In the 90-degree hybrid configuration optical circuit OC, a first incident light input to a first input node is split into a first branched light and a second branched light by a first 1×2 optical multiplexer / demultiplexer 67a, and a second incident light input to a second input node is split into a third branched light and a fourth branched light by a second 1×2 optical multiplexer / demultiplexer 67b.

[0218] The first branched light is input from the first port of the first 2×2 optical multiplexer / demultiplexer 68a to the fifth optical waveguide that constitutes the first 2×2 optical multiplexer / demultiplexer 68a. On the other hand, the third branched light is input from the third port of the first 2×2 optical multiplexer / demultiplexer 68a to the sixth optical waveguide that constitutes the first 2×2 optical multiplexer / demultiplexer 68a.

[0219] The first branched light and the third branched light incident on the first 2×2 optical multiplexer / demultiplexer 68a are each split and interfered with by the first 2×2 optical multiplexer / demultiplexer 68a, and are emitted from the second port of the first 2×2 optical multiplexer / demultiplexer 68a to the first I-use photodetector 65a1 constituting the first photodetector 65a as the first I-use output light, and are emitted from the fourth port of the first 2×2 optical multiplexer / demultiplexer 68a to the second I-use photodetector 65a2 constituting the first photodetector 65a as the second I-use output light.

[0220] The first I output light is photoelectrically converted by the first I photoreceiver 65a1, and the second I output light is photoelectrically converted by the second I photoreceiver 65a2, a photocurrent flows through the first I photoreceiver 65a1 and the second I photoreceiver 65a2, and an I signal shown in FIG. 16 appears at the first output terminal which is the connection point between the first I photoreceiver 65a1 and the second I photoreceiver 65a2. The I signal is a first monitor value indicating an analog photocurrent, and is input to the control unit 9 .

[0221] The second branched light is input from the first port of the second 2×2 optical multiplexer / demultiplexer 68b to the seventh optical waveguide that constitutes the second 2×2 optical multiplexer / demultiplexer 68b. On the other hand, the fourth branched light is delayed by 90 degrees by the 90-degree delay device 69 and is input from the third port of the second 2×2 optical multiplexer / demultiplexer 68b to the eighth optical waveguide that constitutes the second 2×2 optical multiplexer / demultiplexer 68b.

[0222] The second branched light and the fourth branched light delayed by 90 degrees incident on the second 2×2 optical multiplexer / demultiplexer 68b are each branched and interfered with by the second 2×2 optical multiplexer / demultiplexer 68b, and are emitted from the second port of the second 2×2 optical multiplexer / demultiplexer 68b to the first Q photodetector 65b1 constituting the second photodetector 65b as first Q output light, and are emitted from the fourth port of the second 2×2 optical multiplexer / demultiplexer 68b to the second Q photodetector 65b2 constituting the second photodetector 65b as second Q output light. The first to third branched lights are not phase-shifted, and the fourth branched light is delayed by 90 degrees by the 90-degree delay device 69, that is, its phase is shifted by 90 degrees.

[0223] The first output light for Q is photoelectrically converted by the first photodetector for Q 65b1, and the second output light for Q is photoelectrically converted by the second photodetector for Q 65b2, a photocurrent flows through the first photodetector for Q 65b1 and the second photodetector for Q 65b2, and a Q signal as shown in FIG. 16 appears at the first output terminal which is the connection point between the first photodetector for Q 65b1 and the second photodetector for Q 65b2. The Q signal has a phase shift of 90 degrees relative to the I signal. The Q signal has a phase shift of 90 degrees with respect to the I signal, is a second monitor value indicating an analog photocurrent, and is input to the control unit 9.

[0224] As shown in FIG. 16, a constellation can be mapped onto an IQ plane using an I signal that is an analog photocurrent indicating the first monitor value and a Q signal that is an analog photocurrent indicating the second monitor value. In the constellation map shown in Figure 16, the I axis represents the magnitude of the I signal, i.e., the value of the analog photocurrent indicating the first monitor value, and the Q axis represents the magnitude of the Q signal, i.e., the value of the analog photocurrent indicating the second monitor value.

[0225] If the optical power of the backward laser light Lb of the semiconductor laser 5 is constant, then the constellation moves on a circumference having a constant radius corresponding to the optical power in response to changes in the wavelength of the backward laser light Lb. If the optical power is large, the radius of the circle is large, and if the optical power is small, the radius of the circle is small. Therefore, by knowing the position of the constellation based on the first and second monitor values ​​from the center on the constellation map, the optical power monitor value Ip can be obtained.

[0226] On the other hand, when the wavelength of the backward laser light Lb of the semiconductor laser 5 changes, the angle of the radius vector formed by the constellation changes. Therefore, by knowing the angle, relative to the I axis, of the line segment connecting the center on the constellation map and the position of the constellation based on the first and second monitor values, the wavelength monitor value Iλ can be obtained. By obtaining the optical power monitor value Ip and the wavelength monitor value Iλ, the wavelength monitor value Iλ / Ip can be obtained (step ST3a).

[0227] That is, since the change in wavelength of the backward laser light Lb is proportional to the rotation of the constellation, the change in wavelength of the backward laser light Lb can be observed seamlessly, and there is no need to perform a separate phase adjustment for the optical monitor 6.

[0228] The control unit 9 converts the first monitor value based on the photocurrent into a voltage, and further converts the analog to digital form to obtain a first monitor value based on digital information, converts the second monitor value based on the photocurrent into a voltage, and further converts the analog to digital form to obtain a second monitor value based on digital information, and compares these with a constellation map obtained in advance and stored in the memory unit to obtain the optical power monitor value Ip, the wavelength monitor value Iλ, and the wavelength monitor value Iλ / Ip.

[0229] After obtaining the optical power monitor value Ip, the wavelength monitor value Iλ, and the wavelength monitor value Iλ / Ip, the control unit 9 performs operations from step ST4 onwards in the same manner as the optical modules according to the first and second embodiments, and adjusts the temperature of the semiconductor laser and adjusts the optical output and oscillation wavelength from the semiconductor laser.

[0230] As described above, the optical module according to the third embodiment, like the optical modules according to the first and second embodiments, can precisely control the laser light from the semiconductor laser 5 to a single wavelength, has a reduced number of components, and can be made compact. Furthermore, in the optical module according to the third embodiment, like the optical module according to the second embodiment, in the optical monitor 6, the wavelength monitor value Iλ / Ip obtained from the first monitor value obtained from the first light receiving unit 65a and the second monitor value obtained from the second light receiving unit 65b can be a wavelength monitor value that does not have temperature dependency. Furthermore, the optical module according to the third embodiment can obtain a highly accurate optical power monitor value Ip, wavelength monitor value Iλ, and wavelength monitor value Iλ / Ip without performing a separate phase adjustment for the optical monitor 6.

[0231] In the optical module of the third embodiment, the first asymmetric arm 63a is composed of silicon nitride waveguides 63a1, 63a2 and a silicon waveguide 63a3, as in the optical module of the second embodiment, and the second asymmetric arm 63b is composed of silicon waveguides 63b1-63b3 and silicon nitride waveguides 63b4, 63b5. However, as in the optical module of the first embodiment, each of the first asymmetric arm 63a and the second asymmetric arm 63b may be composed of a single silicon waveguide.

[0232] The optical module according to the third embodiment is not limited to a planar waveguide type optical monitor using a silicon photonics chip, but may be a planar waveguide type optical monitor using an indium phosphide substrate, which is a compound semiconductor, or a glass substrate.

[0233] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted. [Industrial Applicability]

[0234] The optical module according to the present disclosure is suitable for use in a large-capacity optical communication system, and in particular, for use in a digital coherent communication system. [Explanation of symbols]

[0235] REFERENCE SIGNS LIST 1 stem, 2 temperature regulator, 3 base, 4 semiconductor laser submount, 5 semiconductor laser, 6 optical monitor (planar waveguide type optical monitor), 61a first optical coupler, 61b second optical coupler, 62 input side optical multiplexer / demultiplexer, 63a first asymmetric arm, 63b second asymmetric arm, 64 output side optical multiplexer / demultiplexer, 65a first optical receiver, 65b second optical receiver, 66 phase adjuster, 7 cap, 8 window, 9 control unit, 10 package, P1 to P7 lead pins.

Claims

1. a semiconductor laser; and an optical monitor that receives laser light from the semiconductor laser and outputs a first monitor value and a second monitor value for estimating an intensity and a wavelength of the laser light from the semiconductor laser, The optical monitor has a first optical coupler that receives laser light from the semiconductor laser, a second optical coupler that receives laser light from the semiconductor laser, a first optical receiver that outputs the first monitor value, and a second optical receiver that outputs the second monitor value, and is an optical module that constitutes an optical interferometer in which a first path from the first optical coupler to the first optical receiver and a second path from the second optical coupler to the second optical receiver are asymmetric.

2. The optical interferometer in the optical monitor includes: an input-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being coupled to the first optical coupler, and the third port being coupled to the second optical coupler; a first asymmetric arm including an optical waveguide, an input node being optically connected to a second port of the input-side optical multiplexer / demultiplexer; a second asymmetric arm including an optical waveguide having an input node optically connected to a fourth port of the input-side optical multiplexer / demultiplexer, the second asymmetric arm having a physical length different from a physical length of the optical waveguide constituting the first asymmetric arm; an output-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being optically connected to an output node of the first asymmetric arm, the third port being optically connected to an output node of the second asymmetric arm, the second port being coupled to the first optical receiver, and the fourth port being coupled to the second optical receiver; the first path is an optical propagation path from a first port of the input-side optical multiplexer / demultiplexer to a second port of the output-side optical multiplexer / demultiplexer via the input-side optical multiplexer / demultiplexer, the first asymmetric arm, and the output-side optical multiplexer / demultiplexer; the second path is an optical propagation path from a second port of the input-side optical multiplexer / demultiplexer to a fourth port of the output-side optical multiplexer / demultiplexer via the input-side optical multiplexer / demultiplexer, the second asymmetric arm, and the output-side optical multiplexer / demultiplexer; 2. The optical module according to claim 1.

3. a semiconductor laser; and an optical monitor that receives laser light from the semiconductor laser and outputs a first monitor value and a second monitor value for estimating an intensity and a wavelength of the laser light from the semiconductor laser, The optical monitor includes: a first optical coupler that receives a laser beam from the semiconductor laser, a second optical coupler that receives a laser beam from the semiconductor laser, a first optical receiver that outputs the first monitor value, a second optical receiver that outputs the second monitor value, and an optical interferometer; The optical interferometer comprises: an input-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being coupled to the first optical coupler, and the third port being coupled to the second optical coupler; a first asymmetric arm including an optical waveguide, an input node being optically connected to a second port of the input-side optical multiplexer / demultiplexer; a second asymmetric arm including an optical waveguide having an input node optically connected to a fourth port of the input-side optical multiplexer / demultiplexer, the second asymmetric arm having a physical length different from a physical length of the optical waveguide constituting the first asymmetric arm; the optical circuit includes a first input node, a second input node, a first output node, and a second output node, the first input node being optically connected to an output node of the first asymmetric arm, the second input node being optically connected to an output node of the second asymmetric arm, the first output node being optically coupled to the first optical receiver, and the second output node being optically coupled to the second optical receiver, and is used to configure an interference measurement system for observing wavelength dependency by the first optical receiver and the second optical receiver; Optical module.

4. the optical waveguide in the first asymmetric arm has a common portion and a non-common portion, the optical waveguide in the non-common portion having a first group refractive index; the optical waveguide in the second asymmetric arm has a common portion and a non-common portion, and the optical waveguide in the non-common portion is an optical waveguide having a second group refractive index having a temperature dependence of the group refractive index different from the first group refractive index; 4. The optical module according to claim 3.

5. a semiconductor laser; and an optical monitor that receives laser light from the semiconductor laser and outputs a first monitor value and a second monitor value for estimating an intensity and a wavelength of the laser light from the semiconductor laser, The optical monitor includes: a first optical coupler that receives a laser beam from the semiconductor laser, a second optical coupler that receives a laser beam from the semiconductor laser, a first optical receiver that outputs the first monitor value, a second optical receiver that outputs the second monitor value, and an optical interferometer; The optical interferometer comprises: an input-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being coupled to the first optical coupler, and the third port being coupled to the second optical coupler; a first asymmetric arm, an input node being optically connected to a second port of the input-side optical multiplexer / demultiplexer, the first asymmetric arm having a common portion optical waveguide and a non-common portion optical waveguide, the non-common portion optical waveguide being an optical waveguide having a first group refractive index; a second asymmetric arm, an input node being optically connected to a fourth port of the input-side optical multiplexer / demultiplexer, the second asymmetric arm having a common portion optical waveguide and a non-common portion optical waveguide, the non-common portion optical waveguide having a second group refractive index having a temperature dependency of the group refractive index different from the first group refractive index, and the physical length of the non-common portion being different from the physical length of the non-common portion optical waveguide in the first asymmetric arm; the optical circuit includes a first input node, a second input node, a first output node, and a second output node, the first input node being optically connected to an output node of the first asymmetric arm, the second input node being optically connected to an output node of the second asymmetric arm, the first output node being optically coupled to the first optical receiver, and the second output node being optically coupled to the second optical receiver, and is used to configure an interference measurement system for observing wavelength dependency by the first optical receiver and the second optical receiver; Optical module.

6. 6. The optical module according to claim 3, wherein the optical circuit for constituting the interference measurement system is an output-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being a first input node of the optical circuit, the second port being a first output node of the optical circuit, the third port being a second input node of the optical circuit, and the fourth port being a second output node of the optical circuit.

7. the input-side optical multiplexer / demultiplexer has a power split ratio of 2:8; the output-side optical multiplexer / demultiplexer has a power branching ratio of 2:8; 7. The optical module according to claim 6.

8. a maximum value of a slope fluctuation amount indicating a tolerance for wavelength dependency in a photocurrent indicating a first monitor value output from the first optical receiver and a photocurrent indicating a second monitor value output from the second optical receiver is within 30% within an expected range of mounting deviation in coupled light between the first optical coupler and the second optical coupler and the input-side optical multiplexer / demultiplexer; 7. The optical module according to claim 6.

9. a wavelength monitor value, which is a ratio between an optical power monitor value and a wavelength monitor value calculated from a photocurrent indicating a first monitor value output from the first photodetector and a photocurrent indicating a second monitor value output from the second photodetector, has a wavelength-dependent shift amount in a wavelength direction of 0.1 nm or less within a temperature change range of 100 degrees, and the oscillation wavelength from the semiconductor laser is 0.1 nm or less; 7. The optical module according to claim 6.

10. the optical monitor is a planar waveguide type optical monitor using a silicon photonics chip formed by integrating the first optical coupler, the second optical coupler, the input side optical multiplexer / demultiplexer, the first asymmetric arm, the second asymmetric arm, the output side optical multiplexer / demultiplexer, the first optical receiver, and the second optical receiver on a plane of a silicon substrate, the first optical coupler and the second optical coupler are each a grating coupler; 7. The optical module according to claim 6.

11. an optical circuit for constituting the interference measurement system is an output-side optical multiplexer / demultiplexer having a first port to a fourth port, the first port being a first input node of the optical circuit, the second port being a first output node of the optical circuit, the third port being a second input node of the optical circuit, and the fourth port being a second output node of the optical circuit; the optical monitor is a planar waveguide type optical monitor in which the first optical coupler, the second optical coupler, the input side optical multiplexer / demultiplexer, the first asymmetric arm, the second asymmetric arm, the output side optical multiplexer / demultiplexer, the first optical receiver, and the second optical receiver are integrated, The physical length of the optical waveguide of the non-common portion in the first asymmetric arm is (L+ΔL), and the group refractive index is n ２ The physical length of the optical waveguide of the second asymmetric arm is L, and the group refractive index is n １ , the linear expansion coefficient of the substrate in the planar waveguide type optical monitor is α, and dn 1 / dT+n 1 α>dn 2 / dT+n 2 α, and the phase difference θ between the photocurrent from the first photodetector and the photocurrent from the second photodetector is n 2 (L + ΔL) −n 1 The physical length L can be expressed as L = (λ / 2π) θ, and the temperature differential of the above formula is always 0, and the physical length L is calculated using the following formula:

6. The optical module according to claim 5.

12. 6. The optical module according to claim 3, further comprising a temperature regulator that adjusts the temperature in the semiconductor laser and the temperature in the optical monitor, and that performs control to change the temperatures applied to the semiconductor laser and the optical monitor when a wavelength monitor value Iλ / Ip, which is the ratio between an optical power monitor value Ip, which is the sum of the first monitor value and the second monitor value, and a wavelength monitor value Iλ, which is the difference between the first monitor value and the second monitor value, deviates from a wavelength setting value.

13. A stem on which the temperature regulator is mounted; a base that is mounted and fixed on a mounting surface of the temperature regulator, the base having a vertical surface portion on which the semiconductor laser is mounted and fixed, and a flat surface portion that is formed integrally with the vertical surface portion and on which the optical monitor is mounted and fixed at a position where the optical monitor receives a rear laser beam from the semiconductor laser; a cylindrical cap having a bottom and a side wall, the bottom having a window through which a forward laser beam of the semiconductor laser is emitted, covering the inner flat surface side of the stem, and fixed with an open end surface of the side wall in contact with a peripheral end of the inner flat surface of the stem; The optical module according to claim 12 .

14. a main signal lead pin which penetrates the stem and has an inner lead portion exposed from an inner flat surface of the stem to which an electrode of the semiconductor laser is connected; a first monitor lead pin that penetrates the stem and has an inner lead portion exposed from an inner flat surface of the stem, the first light receiver of the optical monitor being connected to the inner lead portion; a second monitor lead pin that penetrates the stem and has an inner lead portion exposed from an inner flat surface of the stem, the second light receiver of the optical monitor being connected to the inner lead portion; a pair of temperature control lead pins which penetrate the stem and have inner lead portions exposed from an inner flat surface of the stem, and a pair of electrodes of the temperature regulator are connected to the inner lead portions; The optical module according to claim 13 .

15. an optical circuit for constituting the interference measurement system is a 90-degree hybrid configuration optical circuit that receives an optical output from the first asymmetric arm at the first input node, receives an optical output from the second asymmetric arm at the second input node, outputs an optical output for I to the first output node, and outputs an optical output for Q to the second output node; the first optical receiver receives an I optical output from the 90-degree hybrid configuration optical circuit and outputs the first monitor value which is an I signal; the second optical receiver receives the Q optical output from the 90-degree hybrid configuration optical circuit and outputs the second monitor value which is a Q signal; The optical module according to any one of claims 3 to 5.

16. the first optical receiver has a first optical receiver for I and a second optical receiver for I connected in series, and outputs the first monitor value to a connection point between the first optical receiver for I and the second optical receiver for I; the second optical receiver has a first optical receiver for Q and a second optical receiver for Q connected in series, and outputs the second monitor value to a connection point between the first optical receiver for Q and the second optical receiver for Q; The 90-degree hybrid optical circuit is a first 1×2 optical multiplexer / demultiplexer having a first port to a third port, the first port being optically connected to an output node of the first asymmetric arm; a second 1×2 optical multiplexer / demultiplexer having a first port to a third port, the first port being optically connected to an output node of the second asymmetric arm; a 90-degree delay device having an input node optically connected to a third port of the second 1×2 optical multiplexer / demultiplexer; a first 2×2 optical multiplexer / demultiplexer having a first port to a fourth port, the first port being optically connected to a second port of the first 1×2 optical multiplexer / demultiplexer, the third port being optically connected to a second port of the second 1×2 optical multiplexer / demultiplexer, and outputting a first output light for I from the third port to the first optical receiver for I and outputting a second output light for I from the fourth port to the second optical receiver for I; a second 2×2 optical multiplexer / demultiplexer having a first port to a fourth port, the first port being optically connected to a third port of the second 1×2 optical multiplexer / demultiplexer, the third port being optically connected to an output node of the 90-degree delay device, and outputting a first output light for Q from the third port to the first optical receiver for Q and outputting a second output light for Q from the fourth port to the second optical receiver for Q; the I optical output is composed of the first I output light and the second I output light, and the Q optical output is composed of the first Q output light and the second Q output light; 16. The optical module according to claim 15.

17. an optical circuit for constituting the interference measurement system is a 90-degree hybrid configuration optical circuit that receives an optical output from the first asymmetric arm at the first input node, receives an optical output from the second asymmetric arm at the second input node, outputs an optical output for I to the first output node, and outputs an optical output for Q to the second output node; the first optical receiver receives an I optical output from the 90-degree hybrid configuration optical circuit and outputs the first monitor value which is an I signal; the second optical receiver receives the Q optical output from the 90-degree hybrid configuration optical circuit and outputs the second monitor value which is a Q signal; the optical monitor is a planar waveguide type optical monitor in which the first optical coupler, the second optical coupler, the input side optical multiplexer / demultiplexer, the first asymmetric arm, the second asymmetric arm, the 90 degree hybrid configuration optical circuit, the first optical receiver, and the second optical receiver are integrated, The physical length of the optical waveguide of the non-common portion in the first asymmetric arm is (L+ΔL), and the group refractive index is n ２ The physical length of the optical waveguide of the second asymmetric arm is L, and the group refractive index is n １ , the linear expansion coefficient of the substrate in the planar waveguide type optical monitor is α, and dn 1 / dT+n 1 α>dn 2 / dT+n 2 α, and the phase difference θ between the photocurrent from the first photodetector and the photocurrent from the second photodetector is n 2 (L + ΔL) −n 1 The physical length L can be expressed as L = (λ / 2π) θ, and the temperature differential of the above formula is always 0, and the physical length L is calculated using the following formula:

6. The optical module according to claim 5.

18. 16. The optical module according to claim 15, further comprising a temperature regulator that adjusts the temperature in the semiconductor laser and the temperature in the optical monitor, and that performs control to change the temperatures applied to the semiconductor laser and the optical monitor when a wavelength monitor value Iλ / Ip, which is a ratio of an optical power monitor value Ip obtained by a constellation mapped on an IQ plane by the I signal indicated by the first monitor value and the Q signal indicated by the second monitor value, deviates from a wavelength setting value.

19. The first photoreceiver has a first photoreceiver for I and a second photoreceiver for I connected in series between a power supply potential node for a photoreceiver and a ground node, the second photodetector has a first photodetector for Q and a second photodetector for Q connected in series between a power supply potential node for a photodetector and a ground node; a temperature regulator that regulates the temperature in the semiconductor laser and the temperature in the optical monitor, the temperature regulator controlling the temperature applied to the semiconductor laser and the optical monitor being changed when a wavelength monitor value Iλ / Ip, which is a ratio between an optical power monitor value Ip and a wavelength monitor value Iλ obtained by a constellation mapped on an IQ plane by an I signal indicated by the first monitor value and a Q signal indicated by the second monitor value, deviates from a wavelength setting value; A stem on which the temperature regulator is mounted; a base that is mounted and fixed on a mounting surface of the temperature regulator, the base having a vertical surface portion on which the semiconductor laser is mounted and fixed, and a flat surface portion that is formed integrally with the vertical surface portion and on which the optical monitor is mounted and fixed at a position where the optical monitor receives a rear laser beam from the semiconductor laser; a cylindrical cap having a bottom and a side wall, the bottom having a window through which a forward laser beam of the semiconductor laser is emitted, covering the inner flat surface side of the stem, and fixed with an open end surface of the side wall in contact with a peripheral end of the inner flat surface of the stem; a main signal lead pin which penetrates the stem and has an inner lead portion exposed from an inner flat surface of the stem to which an electrode of the semiconductor laser is connected; a first monitor lead pin which penetrates the stem and has an inner lead portion exposed from an inner plane of the stem, and a connection point between the first I-use light receiver and the second I-use light receiver is connected to the inner lead portion; a second monitor lead pin which penetrates the stem and has an inner lead portion exposed from an inner flat surface of the stem, and a connection point between the first Q-use optical receiver and the second Q-use optical receiver is connected to the inner lead portion; a pair of temperature control lead pins which penetrate the stem and have inner lead portions exposed from an inner flat surface of the stem, and a pair of electrodes of the temperature regulator are connected to the inner lead portions; a light receiving unit power supply lead pin to which a power supply side electrode of a first I light receiving unit located on the power supply side of the first light receiving unit and a power supply side electrode of a first Q light receiving unit located on the power supply side of the second light receiving unit are connected; The optical module according to claim 15 .

20. A method for controlling an optical module comprising: a semiconductor laser; an optical monitor that receives laser light from the semiconductor laser and outputs a first monitor value and a second monitor value for estimating an intensity and a wavelength of the laser light from the semiconductor laser; and a temperature regulator that regulates a temperature in the semiconductor laser and a temperature in the optical monitor, wherein the optical monitor comprises a first optical coupler that receives the laser light from the semiconductor laser, a second optical coupler that receives the laser light from the semiconductor laser, a first optical receiver that outputs the first monitor value, and a second optical receiver that outputs the second monitor value, and a first path from the first optical coupler to the first optical receiver and a second path from the second optical coupler to the second optical receiver are asymmetric, a temperature adjusting step of adjusting a temperature applied to the semiconductor laser and the optical monitor by the temperature adjuster when a wavelength monitor value Iλ / Ip, which is a ratio between an optical power monitor value Ip, which is a sum of the first monitor value and the second monitor value, and a wavelength monitor value Iλ, which is a difference between the first monitor value and the second monitor value, deviates from a wavelength set value; A method for controlling an optical module comprising:

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