JP2010212472A - Wavelength variable light source and adjusting method of oscillation wavelength thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength variable light source largely enlarging a wavelength variable range even though the light source is constituted relatively easily using a flat light circuit without a movable part. <P>SOLUTION: In the wavelength variable light source, a waveguide oscillator 105 includes: closed loop-type optical circuits M1, M2, M3 with a directional coupler 106 having an optionally determined power branching ratio of 2×2 input and output and a loop-shaped light guide 107 connecting two output terminals of the directional coupler 106; and light guides (light guide etalon) 108, 109 in which a light guide 108 connects one input terminal of the optical circuit M1 with one input terminal of the optical circuit M2 and a light guide 109 connects one input terminal of the optical circuit M3 with the other input terminal of the optical circuit M2, so that the light guides 108, 109 connect the optical loop-type circuits M1, M2, M3 in series. In the light guide etalons 108, 109, as an execution refractive index varying means for varying the execution refractive index of the light guide of the light guide etalons 108, 109, for example, heaters 110, 111 are provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light source used for optical communication, optical information processing, optical interconnection, and the like, and more particularly to a wavelength tunable light source having a wavelength tunable function and a method for adjusting an oscillation wavelength thereof.

  In recent years, Internet traffic has increased rapidly, and technology for expanding communication capacity has also been developed in response to this. Wavelength division multiplex communication (WDM) increases capacity by increasing the number of wavelengths, but is more flexible in combination with the progress of ROADM (reconfigurable optical add / drop multiplexer), optical cross-connect by wavelength routing, etc. Expansion of communication capacity with excellent performance is being actively studied.

  In this method, wavelength resources are not only used for capacity expansion, but are also actively used for improving network functions. The expansion of communication capacity and the enhancement of communication system functionality are related to each other, and it is possible to provide a low-cost and highly secure communication service, and the wavelength tunable light source constructs such a communication system. It is one of the key devices above.

  In general, a wavelength division multiplexing system supports a plurality of fixed wavelength light sources having a fixed wavelength interval, and the cost of a maintenance management backup light source (for the number of wavelengths) is particularly large, which hinders cost reduction of the system. It was a factor. On the other hand, by applying a wavelength tunable light source, the types of light sources can be integrated into one, so that the system cost can be greatly reduced. In addition, a wavelength tunable light source having a high switching speed is an indispensable element for realizing a new network function even in wavelength routing.

  Various types of wavelength tunable light sources have been proposed. For example, as a wavelength variable light source capable of covering the C band or the L band, a wavelength variable light source using a movable MEMS (Micro Electro Mechanical Systems) mirror has been published as Non-Patent Document 1 by Jill D. Berger et al. Although the wavelength tunable light source disclosed in Non-Patent Document 1 shows relatively good light output characteristics, there is a concern about its practicality in terms of manufacturing cost and impact resistance. Further, a wavelength tunable light source that improves the mode stability of a DBR (Distributed Bragg Reflector) laser and is further integrated with a modulator has been reported as Non-Patent Document 2 by B.Mason et al. The wavelength tunable light source disclosed in Non-Patent Document 2 has problems in terms of cost reduction and reliability.

  A wavelength tunable light source using a planar optical circuit (PLC) as an external resonator is relatively easy to manufacture and has no moving parts like MEMS, so that it has a high manufacturing yield and reliability (especially vibration resistance). It is considered to be excellent and suitable for mass production, and several configurations have been proposed at present. For example, a configuration using a ring-type external resonator and a semiconductor amplifier has been reported by H. Yamazaki et al. As Non-Patent Document 3, and as a wavelength tunable light source having no movable part, a wavelength tunable range, an optical output In terms of the above, good characteristics are obtained.

Optical Communication, 2001.ECOC '01 .27th European Conference on Volume 2,30 198 pages. IEEE Photonics Letters Volume 11 Number 11,1999 p. 638. 30th European Conference on Optical Communication 2004, th4.2.3.

  In a high-density wavelength division multiplexing (DWDM) system for optical communication, a communication wavelength band is divided into a C band and an L band, and a large number of wavelength signal lights are introduced in a wavelength range of about 40 nm. At present, many wavelength variable light sources are being developed based on a wavelength range of 40 nm, and there are few wavelength variable light sources with a wavelength variable range of 80 nm or more that can cover both C and L bands with one light source. Further, in the CWDM (Coarse WDM) system in which the signal light wavelength is set at intervals of about 20 nm, a wider range of wavelength variation is required.

  However, in the variable wavelength light source having the configuration shown in Non-Patent Document 3, the variable wavelength range is limited by the FSR (Free Spectrum Range) of the ring type external resonator, that is, the wavelength period. In order to expand the wavelength tunable range, it is necessary to reduce the bend radius of the waveguide to reduce the size of the ring resonator. However, the reduction of the bend radius of the waveguide is limited from the viewpoint of optical loss, There is a problem that the wavelength tunable range is limited, and the wavelength tunable range cannot be greatly expanded.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide a relatively simple configuration using a planar optical circuit having no moving parts, while increasing the wavelength variable range. An object of the present invention is to provide a variable wavelength light source that can be expanded and a method for adjusting the oscillation wavelength.

  In order to achieve such an object, the present invention provides a 2 × 2 input / output 3 dB directional coupler, an optical amplifier connected to at least one of the input ends of the 3 dB directional coupler, and a 3 dB directional coupler. A first output optical waveguide connected to one of the output ends of the first output optical waveguide, a second output optical waveguide connected to the other of the output ends of the 3 dB directional coupler, a first output optical waveguide, and a second output. A waveguide resonator connected between the waveguide and the waveguide resonator, the directional coupler having an arbitrarily determined power branching ratio of 2 × 2 input / output, and the directional coupler A plurality of closed-loop optical circuits composed of a loop-shaped optical waveguide connecting the two output ends of the two, and these closed-loop optical circuits are connected in series by connecting one side of the two input ends of the directional coupler. Optical waveguide that connects between closed-loop optical circuits At least one of them is provided with effective refractive index changing means for changing the effective refractive index of the optical waveguide.

  In the present invention, at least one of the optical waveguides connecting the closed loop optical circuits is provided with effective refractive index changing means for changing the effective refractive index of the optical waveguide. By changing the effective refractive index of the optical waveguide by the effective refractive index changing means, the light wave transmittance peak when the light wave emitted from one end of the optical amplifier returns to the optical amplifier again along the wavelength axis. The oscillation wavelength can be adjusted over a wide range, and the wavelength tunable range can be greatly expanded while having a relatively simple configuration using a planar optical circuit having no movable part.

It is a schematic diagram which shows the outline of a structure of one Example (Example 1) of the wavelength variable light source which concerns on this invention. It is the figure which showed typically the transmission wavelength spectrum and gain wavelength spectrum of an optical amplifier in case the light wave emitted from the end of the optical amplifier in the wavelength variable light source of Example 1 returns to an optical amplifier again. It is a schematic diagram which shows the outline of a structure of the other Example (Example 2) of the wavelength variable light source which concerns on this invention. It is a figure which shows the wavelength spectrum of the reflected light intensity calculated on the predetermined conditions in the wavelength variable light source of this Example 2. FIG. It is a schematic diagram which shows the outline of a structure of the other Example (Example 3) of the wavelength variable light source which concerns on this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[Example 1]
FIG. 1 is a schematic diagram showing an outline of the configuration of an embodiment (embodiment 1) of a wavelength variable light source according to the present invention. In the figure, 1 is a 2 × 2 input / output 3 dB directional coupler, 2 is an optical amplifier connected to one of the input ends of the 3 dB directional coupler 1, and 3 is an output end of the 3 dB directional coupler 1. The first output optical waveguide connected to one side, 4 is the second output optical waveguide connected to the other output end of the 3 dB directional coupler 1, and 5 is the first output optical waveguide 3 and the second output. It is a waveguide resonator connected between the optical waveguide 4.

  The waveguide resonator 5 includes a directional coupler 6 (6-1, 6-2) having an arbitrarily determined power branching ratio of 2 × 2 inputs and outputs, and two output terminals of the directional coupler 6. Two closed-loop optical circuits (loop mirror optical circuits) M (M1, M2) composed of a loop-shaped optical waveguide 7 (7-1, 7-2) connecting the two, and loop mirror optical circuits M1 and M2 The optical waveguide 8 is formed by connecting one side of two input ends of the directional couplers 6-1 and 6-2 and connecting them in series. The optical waveguide 8 is provided with a heater 9 as means for changing the effective refractive index of the optical waveguide 8.

  Note that the loop mirror optical circuits M1 and M2 are provided in the first closed-loop optical circuit when a loop-like circuit connecting the two output ends of the 3 dB directional coupler 1 is a first closed-loop optical circuit. It can also be called the second and third closed-loop optical circuits arranged in the above. Further, since the loop mirror optical circuits M1 and M2 are connected by the linear optical waveguide 8, the both ends of the optical waveguide 8 are waveguide resonances to which mirrors having appropriate reflectivity are added. It will fulfill the function of the vessel.

  In this wavelength tunable light source, one end of the optical amplifier 2 is optically connected to one of the input ends of the 3 dB directional coupler 1, and the other end of the optical amplifier 2 has a reflectance of about 10%. A dielectric film 10 is added. Further, a non-reflection mechanism 11 is added to the other input end of the 3 dB directional coupler 1. In this example, an antireflective coating is applied.

  In this wavelength tunable light source, the dielectric emission light generated from the optical amplifier 2 is branched into two by the 3 dB directional coupler 1 and then passes through the waveguide resonator 5 including the two loop mirror optical circuits M1 and M2. It again reaches the 3 dB directional coupler 1 and is multiplexed and returns to the optical amplifier 2. The light wave that does not pass through the waveguide resonator 5 returns to the 3 dB directional coupler 1 as reflected light, is combined, and is emitted from the other non-reflective mechanism 11 at the input end of the 3 dB directional coupler 1. That is, only the wavelength light that can pass through the waveguide resonator 5 is amplified by reciprocating feedback to the optical amplifier 2 and oscillates as laser light.

  FIG. 2 schematically shows a transmission wavelength spectrum and a gain wavelength spectrum of the optical amplifier 2 when a light wave emitted from one end of the optical amplifier 2 returns to the optical amplifier 2 again. Laser oscillation occurs at a wavelength that maximizes the sum of transmittance and gain. In this case, the light wave emitted from one end of the optical amplifier 2 returns to the optical amplifier 2 again by changing the effective refractive index of the optical waveguide 8 connecting the loop mirror optical circuits M1 and M2 in the waveguide resonator 5. The transmittance peak of the light wave when coming can be moved along the wavelength axis. As a result, the oscillation wavelength can be adjusted (tuned) over a wide range.

  In this embodiment, the effective refractive index of the optical waveguide 8 is changed using the thermo-optic effect obtained by driving the heater 9, but a voltage is applied to the core layer and the cladding layer of the optical waveguide 8. The effective refractive index of the optical waveguide 8 may be changed using an electro-optic effect obtained by applying a voltage to the electrode structure.

[Example 2]
FIG. 3 is a schematic diagram showing an outline of the configuration of another embodiment (embodiment 2) of the variable wavelength light source according to the present invention. In the figure, 101 is a 2 × 2 input / output 3 dB directional coupler, 102 is an optical amplifier (semiconductor optical amplifier) connected to one input end of the 3 dB directional coupler 101, and 103 is a 3 dB directional coupler. 101 is a first output optical waveguide connected to one of the output ends, 104 is a second output optical waveguide connected to the other output end of the 3 dB directional coupler 101, and 105 is a first output optical waveguide 103. And a second output optical waveguide 104.

  The waveguide resonator 5 includes a directional coupler 106 (106-1, 106-2, 106-3) having an arbitrarily determined power branching ratio of 2 × 2 inputs and outputs, and the directional coupler 106. Three closed-loop optical circuits (loop mirror optical circuits) M (M1, M2, M3) composed of a loop-shaped optical waveguide 107 (107-1, 107-2, 107-3) connecting two output ends An optical waveguide 108 connecting the two input ends of the directional couplers 106-1 and 106-2 to each other in series, and the loop mirror optical circuits M2 and M3. The directional couplers 106-2 and 106-3 are composed of an optical waveguide 109 that connects one side of two input ends and connects them in series. Hereinafter, the optical waveguides 108 and 109 are referred to as waveguide etalon. The waveguide etalons 108 and 109 are provided with heaters 110 and 111 as means for changing the effective refractive index of the waveguide etalons 108 and 109.

In addition, in this wavelength tunable light source, a planar optical circuit configured as a 3 dB directional coupler 101, a waveguide resonator 105, a first output optical waveguide 103, and a second output optical waveguide 104 functions as a wavelength tunable resonator. It is formed on an SOI (Silicon on insulator) substrate 112. The core layer of the optical waveguide constituting this planar optical circuit is Si (silicon), and the cladding layer is SiO ₂ (quartz).

In the loop mirror optical circuits M1, M2, and M3, the loop-shaped optical waveguides 107-1, 107-2, and 107-3 are set to appropriate lengths L ₁ , L ₂ , and L ₃ , and the directional coupler 106 is used. -1, 106-2, 106-3 have appropriate power branching ratios K1 ² , K2 ² , K3 ² . Further, the length of the waveguide etalon 108 formed with the loop mirror optical circuits M1 and M2 as both ends and the length of the waveguide etalon 109 formed with the loop mirror optical circuits M2 and M3 as both ends are set to the target wavelength variable range. Are set to appropriate values L ₄ and L ₅ , respectively.

  One end of the semiconductor optical amplifier 102 is optically connected to one input end of the 3 dB directional coupler 101 via the input / output optical waveguide 113. The reflected light spectrum R for the light wave emitted from one end of the semiconductor optical amplifier 102 is expressed by the following equation (1).

In FIG. 4, K1 ² = K3 ² = 0.8, K2 ² = 0.4, L ₁ = L ₂ = L ₃ = 100 um, L ₄ = 20 um, L ₅ = 23 um, N _eff = 3.3. The wavelength spectrum of the reflected light intensity at the time is calculated using the above equation (1). N _eff is the effective refractive index of the waveguide etalons 108 and 109.

As can be seen from FIG. 4, the wavelength spectrum of the reflected light intensity in this case has a shape in which the long-period spectrum is superimposed on the envelope pattern in the short-period spectrum. The long-period wavelength interval of the reflectance peak indicates the upper limit of the wavelength variable range, and this range Δλ is the ratio of the lengths of the two waveguide etalons 108 and 109 (L ₄ / L ₅ ) to the waveguide etalon 108, 109 FSR (λFSR = λ ² / 2L ₄ · N _eff ) can be calculated using the following equation (2).

This equation (2) shows that the tuning range can be expanded by the ratio of the lengths of the two waveguide etalons 108 and 109, and M is a parameter representing the extent of the expansion. In this embodiment, M = 7.7 is set. In this embodiment, the peak wavelength (oscillation wavelength) of the reflectance can be tuned by changing the effective refractive index N _eff of the waveguide etalons 108 and 109. For this purpose, heaters 110 and 111 for changing the effective refractive index N _eff of the waveguide etalons 108 and 109 are provided above the waveguide etalons 108 and 109 by the thermo-optic effect.

  In this tunable light source, the semiconductor optical amplifier 102 is mounted on the SOI substrate 112 in a state of being optically coupled with an end face of the input / output optical waveguide 113 (one of the input ends of the 3 dB directional coupler 101) with low loss. A dielectric film 114 is added to the other end surface of the semiconductor optical amplifier 102 so as to have a reflectivity of about 10%. A non-reflective mechanism 116 is added to the end face of the input / output optical waveguide 115 (the other input end of the 3 dB directional coupler 101). In this example, an antireflective coating is applied.

  The operation mechanism of this embodiment will be described in detail below. When current is injected into the semiconductor optical amplifier 102, a part of the excitation light is bifurcated by the 3 dB directional coupler 101 via the input / output optical waveguide 113 and propagates through both the output optical waveguides 103 and 104 to be a waveguide etalon. 108 and 109 propagate with transmittances corresponding to the wavelength components, respectively, and after being guided through the waveguide etalons 108 and 109, they are multiplexed again by the 3dB directional coupler 101, and the semiconductor is transmitted through the input / output optical waveguide 113. The light enters the optical amplifier 102 again.

  The light wave spectrum re-input to the semiconductor optical amplifier 102 via the input / output optical waveguide 113 has the distribution shape shown in FIG. 4, and light having the largest wavelength component in this distribution is selectively used as laser oscillation light. The light is emitted from the end face of the semiconductor optical amplifier 102 (end face to which the dielectric film 114 is added).

  On the other hand, the wavelength components reflected without passing through the waveguide etalons 108 and 109 run backward in the output optical waveguides 103 and 104, and are combined by the 3 dB directional coupler 101 and guided to the input / output optical waveguide 115. Accordingly, the light is emitted from the end face of the input / output optical waveguide 115 (the end face to which the antireflection mechanism 116 is added).

The reason why the reflected light at the ends of the waveguide etalons 108 and 109 propagates in the direction of the input / output optical waveguide 115 after passing through the 3 dB directional coupler 101 is that the waveguide etalons 108 and 109 are transmitted from the 3 dB directional coupler 101. This is because the lengths of the output optical waveguides 103 and 104 to the end of are set equal. The oscillation wavelength can be tuned by driving at least one of the heaters 110 and 111 disposed above the waveguide etalons 108 and 109 and changing the effective refractive index N _eff thereof.

Example 3
As a third embodiment of a wavelength tunable light source according to the present invention, an embodiment of a wavelength tunable light source that enables expansion of a tuning range and an increase in optical output by mounting two semiconductor optical amplifiers having different gain bands is shown in FIG. Shown in

In FIG. 5, a planar optical circuit functioning as a wavelength tunable resonator is formed on an SOI substrate 112 by an optical waveguide having Si (silicon) as a core layer and SiO ₂ (quartz) as a cladding layer. As in the second embodiment, the planar optical circuit includes a 3 dB directional coupler 101, a first output optical waveguide 103, a second output optical waveguide 104, and a waveguide resonator 105. The waveguide resonator 105 includes loop mirror optical circuits M1, M2, and M3 and waveguide etalons 108 and 109. Heaters 110 and 111 for changing the effective refractive index N _eff of the waveguide etalons 108 and 109 by the thermo-optic effect are provided above the waveguide etalons 108 and 109.

  The input / output optical waveguides 113 and 115 are optically coupled to one ends of semiconductor optical amplifiers 117 and 118 having gain bands on the short wave side and the long wave side, respectively, and the other ends of the semiconductor optical amplifiers 117 and 118 are connected to each other. High reflection films 119 and 120 are added. Further, an optical waveguide 121 for extracting laser light is disposed so as to be close to a part of the output optical waveguide 104, and an antireflection film 122 is added to the output end of the optical waveguide 121.

  The operation mechanism of this embodiment will be described in detail below. Laser oscillation in the short wavelength band can be realized by injecting current into the semiconductor optical amplifier 117 having a short wave gain band. The pumping light generated by the semiconductor optical amplifier 117 is branched into two output optical waveguides 103 and 104 by a 3 dB directional coupler 101 and input to a waveguide resonator 105 including three loop mirror optical circuits M1, M2, and M3. Since only the wavelength component that passes through the two waveguide etalons 108 and 109 is fed back to the semiconductor optical amplifier 117 and amplified again, it oscillates as laser light.

  The wavelength light reflected without passing through the two waveguide etalons 108 and 109 returns to the 3 dB directional coupler 101 and is multiplexed again, and is guided to the input / output optical waveguide 115 side to be a semiconductor on the long wave side. Although input to the optical amplifier 118, the semiconductor optical amplifier 118 is in an electrically OFF state, and the input light is absorbed.

  The light wave laser-oscillated by the semiconductor optical amplifier 117 is coupled and guided to the optical waveguide 121 disposed in the vicinity of the output optical waveguide 104, and is emitted from the output end of the optical waveguide 121 (end surface provided with the antireflection film 122). Be done

  On the other hand, laser oscillation in the long wavelength band can be realized by injecting current into the semiconductor optical amplifier 118 having a long wave gain band. In this case, the roles of the semiconductor optical amplifiers 118 and 1117 are reversed, but the oscillation mechanism is equivalent to the oscillation mechanism in the short wavelength band described above.

In Examples 2 and 3, the core layer of the optical waveguide constituting the planar optical circuit on the SOI substrate 112 is Si and the clad layer is SiO _2. However, the core layer is SiON (silicon oxynitride film). And the cladding layer may be made of SiO ₂ .
Alternatively, a compound semiconductor substrate may be used as the substrate 112, and the core layer of the optical waveguide constituting the planar optical circuit may be configured with a compound semiconductor composition having a refractive index larger than that of the surrounding cladding layer.

  In the second and third embodiments described above, the effective refractive index of the waveguide etalons 108 and 109 is changed using the thermo-optic effect obtained by driving the heaters 110 and 111. An electrode structure for applying a voltage to the core layer and the clad layer of the etalons 108 and 109 is provided, and the electro-optical effect obtained by applying a voltage to the electrode structure is used to make the waveguide etalons 108 and 109. The effective refractive index may be changed. For example, the clad of the optical waveguide may be a dielectric film having an electro-optic effect, and may have a structure having an electrode structure for applying a voltage to the dielectric film.

  In the second and third embodiments described above, the directional coupler 6 constituting the loop mirror optical circuit M in the 3 dB directional coupler 101 and the waveguide resonator 105 has a 2 × 2 input / output MMI (Multimode interference). ) Couplers (multi-mode interference couplers) may be used.

  As described above, the wavelength tunable light source according to the present invention changes the oscillation wavelength by electrical control from the outside, and is characterized by a particularly wide wavelength tunable range.

  The first effect of the wavelength tunable light source according to the present invention is that it is easier to expand the FSR (Free Spectrum Range) of the external resonator constituting the wavelength tunable resonator as compared to other resonators. Therefore, the wavelength variable range of the laser oscillation light can be expanded. For example, in a ring resonator, the FSR is limited by the bend radius of the ring, but in the present invention, as a resonator included in a wavelength tunable resonator, a striped waveguide resonator that can be expanded by simply shortening its length. Is adopted.

  A second effect of the wavelength tunable light source according to the present invention is that a planar optical circuit can be applied to a portion constituting the wavelength tunable resonator, and the configuration is also in the middle of the 3 dB directional coupler and the closed loop waveguide. The loop mirror for forming the waveguide resonator is the main element, and since there are few components and a simple circuit configuration, the manufacturing cost can be reduced.

  The third effect of the wavelength tunable light source according to the present invention is that, in the configuration of the waveguide resonator, a loop mirror is employed instead of an end face mirror, so that a discontinuous portion does not occur in the external resonator optical circuit. . Accordingly, since the diffraction scattering loss of the light wave can be reduced, it is possible to reduce the loss of the external resonator, and it is possible to realize a low threshold of laser oscillation and a high output of oscillation light.

  The fourth effect of the wavelength tunable light source according to the present invention is that the size of the resonator constituting the wavelength tunable resonator can be reduced (the length of the striped resonator is shortened), so that the entire wavelength tunable resonator can be reduced. Therefore, it is possible to realize a small wavelength tunable light source.

  The fifth effect of the wavelength tunable laser according to the present invention is that the wavelength tunable resonator and the semiconductor optical amplifier can be hybrid-integrated or monolithically integrated on the same semiconductor substrate. Since the number of points can be reduced, the cost can be reduced.

  The wavelength variable light source of the present invention can be used as a wavelength variable light source having a wavelength variable function in various fields such as optical communication, optical information processing, and optical interconnection.

  DESCRIPTION OF SYMBOLS 1 ... 3dB directional coupler, 2 ... Optical amplifier, 3 ... 1st output optical waveguide, 4 ... 2nd output optical waveguide, 5 ... Waveguide resonator, 6 (6-1, 6-2) ... direction Sexual coupler, 7 (7-1, 7-2) ... Loop optical waveguide, M (M1, M2) ... Closed loop optical circuit (loop mirror optical circuit), 8 ... Optical waveguide, 9 ... Heater, 10 ... Dielectric film, 11 ... Non-reflection mechanism, 101 ... 3 dB directional coupler, 102 ... Optical amplifier (semiconductor optical amplifier), 103 ... First output optical waveguide, 104 ... Second output optical waveguide, 105 ... Waveguide Resonator, 106 (106-1, 106-2, 106-3) ... Directional coupler, 107 (107-1, 107-2, 107-3) ... Loop optical waveguide, M (M1, M2, M3) ... closed loop type optical circuit (loop mirror optical circuit), 108, 109 ... optical waveguide (waveguide error) Ron), 110, 111 ... heater, 112 ... SOI substrate, 113, 115 ... input / output optical waveguide, 114 ... dielectric film, 116 ... non-reflection mechanism, 117 ... semiconductor optical amplifier (short wave side), 118 ... semiconductor optical amplifier (Long wave side), 119, 120 ... high reflection film, 121 ... optical waveguide, 122 ... antireflection film.

Claims (15)

A 2 × 2 input / output 3 dB directional coupler;
An optical amplifier connected to at least one of the input ends of the 3 dB directional coupler;
A first output optical waveguide connected to one of the output ends of the 3 dB directional coupler;
A second output optical waveguide connected to the other output end of the 3 dB directional coupler;
A waveguide resonator connected between the first output optical waveguide and the second output optical waveguide;
The waveguide resonator is composed of a directional coupler having an arbitrarily determined power branching ratio of 2 × 2 input / output and a loop-shaped optical waveguide connecting two output ends of the directional coupler. A plurality of closed-loop optical circuits, and an optical waveguide connecting the closed-loop optical circuits in series by connecting one side of two input ends of the directional coupler,
An effective refractive index changing means for changing the effective refractive index of the optical waveguide is provided in at least one of the optical waveguides connecting the closed-loop optical circuits. In the wavelength tunable light source according to claim 1,
An optical amplifier is optically connected to one of the input ends of the 3 dB directional coupler;
A reflection mechanism having a predetermined reflectance is added to the other end of the optical amplifier,
A wavelength tunable light source, wherein a non-reflection mechanism is added to the other input end of the 3 dB directional coupler. In the wavelength tunable light source according to claim 1,
A first optical amplifier is optically connected to one of the input ends of the 3 dB directional coupler;
A second optical amplifier is optically connected to the other input end of the 3 dB directional coupler;
A wavelength tunable light source, wherein a high reflection mechanism having a high reflectance is added to the other ends of the first optical amplifier and the second amplifier. In the wavelength tunable light source according to claim 1,
A planar optical circuit composed of the 3 dB directional coupler, the waveguide resonator, the first output optical waveguide, and the second output optical waveguide is formed on the same substrate, and the light is formed on the substrate. A variable wavelength light source characterized in that a semiconductor amplifier is hybrid-integrated as an amplifier. In the wavelength tunable light source according to claim 4,
The wavelength tunable light source, wherein the core layer of the optical waveguide constituting the planar optical circuit is SiON and the cladding layer is SiO ₂ . In the wavelength tunable light source according to claim 4,
A tunable light source, wherein an SOI substrate in which Si is formed on an insulating substrate is used as the substrate, the core layer of the optical waveguide constituting the planar optical circuit is Si, and the cladding layer is SiO ₂ . In the wavelength tunable light source according to claim 4,
A compound semiconductor substrate is used as the substrate, and the core layer of the optical waveguide constituting the planar optical circuit is configured with a compound semiconductor composition having a refractive index larger than that of the surrounding cladding layer. A tunable light source. In the wavelength tunable light source described in claim 7,
The wavelength tunable light source, wherein the planar optical circuit and the optical amplifier are monolithically integrated on the substrate. In the wavelength tunable light source described in any one of Claims 1-8,
The effective refractive index changing means changes the effective refractive index of the optical waveguide using a thermo-optic effect. The wavelength tunable light source according to claim 9,
The variable wavelength light source, wherein the effective refractive index changing means is a heater provided in the vicinity of the optical waveguide. In the wavelength tunable light source described in any one of Claims 1-8,
The effective refractive index changing means changes the effective refractive index of the optical waveguide using an electro-optic effect. The tunable light source according to claim 11,
The variable wavelength light source, wherein the effective refractive index changing means has an electrode structure for applying a voltage to the core layer of the optical waveguide. The tunable light source according to claim 11,
The variable wavelength light source, wherein the effective refractive index changing means has an electrode structure for applying a voltage to the cladding layer of the optical waveguide. In the wavelength tunable light source described in any one of Claims 1-13,
The tunable coupler constituting the closed-loop optical circuit in the 3 dB directional coupler and the waveguide resonator is a multi-mode interference type coupler with 2 × 2 inputs and outputs. . An optical amplifier is connected to at least one of the input ends of the 2 × 2 input / output 3 dB directional coupler;
A first output optical waveguide is connected to one of the output ends of the 3 dB directional coupler;
A second output optical waveguide is connected to the other output end of the 3 dB directional coupler;
A directional coupler having an arbitrarily determined power branching ratio of 2 × 2 input / output between the first output optical waveguide and the second output optical waveguide, and two of the directional couplers A plurality of closed-loop optical circuits composed of a loop-shaped optical waveguide connecting the output ends, and an optical waveguide connecting these closed-loop optical circuits in series by connecting one side of two input ends of the directional coupler A waveguide resonator having
An oscillation wavelength adjustment method for a wavelength tunable light source, characterized in that an oscillation wavelength is adjusted by changing at least one effective refractive index of an optical waveguide connecting between the closed loop optical circuits.

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