JP2002134833A - Temperature independent laser - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In an external resonator type frequency-stabilized laser composed of a Gragg grating in an optical waveguide and a semiconductor LD, not only mode hopping is suppressed, but also the oscillation frequency becomes lower than the ambient temperature. Provide a temperature-independent laser that does not depend on it. SOLUTION: This laser comprises an optical waveguide composed of a core 13 and a clad 14 formed on a substrate 16, a semiconductor LD 11, a Bragg grating 15, and a semiconductor L.
D and a portion where the core portion of the optical waveguide disposed between the grating and the semiconductor LD is replaced with a material 12 having a temperature coefficient of refraction index opposite to that of the semiconductor LD. A bimetal plate 51 made of two kinds of metals is bonded to at least one surface. The bimetal plate acts to narrow the pitch of the grating as the temperature rises, thereby canceling the temperature dependence of the grating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external resonator type frequency-stabilized laser comprising a Gragg grating in an optical waveguide and a semiconductor LD, in which not only mode hopping is suppressed but also the oscillation frequency is reduced. The present invention relates to a temperature-independent laser that does not depend on the ambient temperature.

[0002]

2. Description of the Related Art A frequency-stabilized laser configured to suppress temperature-dependent mode hopping has been proposed. This frequency-stabilized laser has a configuration in which silicone resin is inserted between a Bragg grating in a silica-based waveguide and a semiconductor LD, and can perform single-mode oscillation using the frequency selectivity of the grating. It has characteristics such as low temperature coefficient compared to semiconductor lasers, no mode hopping even if the temperature is changed, and easy control of oscillation frequency. Various applications are expected as light sources (Reference: T. Tanaka, et al., Electron.
Lett., Vol. 35, no. 13, 149, (199
9), and Tanaka et al., Proceedings of the 1999 IEICE General Conference, C-3-7).

[0003] In many cases, photo-induced gratings are used for the Bragg gratings.
Hill, et al. (Reference: JP-A-7-17-1)
No. 40311). In the following description, the Bragg grating and the light-induced grating will be simply referred to as a grating for simplification of names.

FIG. 14 is a schematic view of a frequency-stabilized laser having the above-mentioned structure manufactured by using a conventional technique, which is observed obliquely from above. In the figure, reference numeral 11 denotes a semiconductor LD (laser diode), reference numeral 12 denotes a temperature coefficient adjusting material mounted in a groove provided so as to intersect with the quartz waveguide, and reference numeral 13 denotes a quartz waveguide which transmits light. And a cladding 14 having a low refractive index around the core constituting the quartz waveguide. Reference numeral 15 denotes a grating (black grating) formed at a predetermined position of the quartz waveguide (optical waveguide), and reference numeral 16 denotes a Si substrate (plane substrate) on which these members are mounted. 18 is a semiconductor LD11
This is called the silicon terrace where the quartz glass is removed in order to mount it. The temperature coefficient adjusting material 12 is disposed so as to replace a part of the quartz waveguide between the semiconductor LD 11 and the grating 15 that constitute the resonator.

The oscillation mode of the frequency-stabilized laser constituted by the grating 15 and the semiconductor LD 11 in the quartz-based waveguide will be described below. When an injection current is applied to the semiconductor LD 11 to emit light, only light having a frequency corresponding to the reflection spectrum of the grating 15 is reflected by the grating 15. Therefore, the section from the rear end face of the semiconductor LD 11 to the grating 15 oscillates as a laser cavity.

An output surface of the semiconductor LD is provided with an antireflection film (not shown) for an interface with air so that there is no reflected light returning to the semiconductor LD 11 from portions other than the grating 15 and the rear end face of the semiconductor LD 11. The end face of the quartz waveguide on the semiconductor LD side has a core 1 near the core 13.
3 is inclined with respect to the direction orthogonal to the optical axis (see Reference: JP-A-6-230237).

In general, the reflection frequency band of the grating 15 is about 50 GHz. On the other hand, since the laser cavity length is about 0.5 cm, the frequency interval of the longitudinal mode is about 20 GHz, and about three longitudinal modes can exist. Therefore, the grating 15
Only the one closest to the reflection center frequency is selected and oscillates. This oscillation light is emitted to the outside from the core 13 on the rear end face side of the grating 15.

In addition, the oscillation frequency does not cause mode hopping in response to a temperature change. The reason is as follows. Since the temperature coefficient of the center frequency of the grating 15 and the temperature coefficient of the longitudinal mode have the same value as described below, the interval between the reflection center frequency of the grating 15 and the longitudinal mode frequency does not change. That is, even when a temperature change occurs, the same vertical mode is always selected, and "mode hopping" that changes from one mode to another vertical mode does not occur.

The reason why the temperature coefficient of the reflection center frequency of the grating 15 is equal to the temperature coefficient of the longitudinal mode will be described below. The temperature coefficient of the center frequency of the grating 15 is the temperature coefficient of quartz glass, that is, the temperature coefficient of the resonance frequency of a resonator made of quartz glass. Further, as shown in FIG. 14, the temperature coefficient adjusting material 12 is
And the grating 15, the temperature coefficient of the longitudinal mode is determined by adding the respective optical path lengths to the temperature coefficient of the quartz glass (13, 14), the temperature coefficient of the temperature coefficient adjusting material 12, and the temperature coefficient of the semiconductor LD 11. It is the value of the weighted average multiplied. The temperature coefficient of the semiconductor LD 11 has the same sign as the temperature coefficient of the quartz glass (13, 14), and its size is about 10 times the temperature coefficient of the quartz glass. here,
Temperature coefficient adjusting material 12 having a temperature coefficient opposite to that of semiconductor LD 11
Is used to cancel the temperature coefficient of the semiconductor LD11, and the temperature coefficient of the longitudinal mode of the entire external cavity laser is reduced to the temperature coefficient of the quartz glass (13, 14), that is, the grating 1
5 can be matched with the temperature coefficient of the center frequency.

The design of a conventional frequency stabilized laser will be described. Temperature coefficient m of longitudinal mode of conventional frequency stabilized laser
Is approximately expressed by the following equation (1). That is, the temperature coefficient m of the longitudinal mode, frequency-stabilized laser structure to be equal to the temperature coefficient m _WG of the silica waveguide is designed.

[0011]

(Equation 1)

[0012] _{However, m LD, m WG, m} m , the temperature coefficient of the resonance frequency in the case where the temperature coefficient of the resonant frequency of the resonator of the semiconductor LD 11, a quartz waveguide portion and the resonator, respectively,
This is the temperature coefficient of the temperature coefficient adjusting material 12. Also, n _{LD ,}
n _{WG and nm} are the effective refractive index of the waveguide layer of the semiconductor LD 11, the effective refractive index of the quartz waveguide between the semiconductor LD 11 and the grating 15, and the refractive index of the temperature coefficient adjusting material 12, respectively. Further, L _{LD ,} L _{m , and} L _WG are respectively the resonator length of the semiconductor _{LD 11 ,} the length in the optical path of the portion where the temperature coefficient adjusting material 12 is mounted, and the distance from the emission end of the semiconductor _{LD 11} to the center of the grating 15. It represents the length of the quartz waveguide portion (excluding the region where the temperature coefficient adjusting material 12 is sealed).

As shown in the above equation (1), the temperature in the vertical mode
The temperature coefficient m is the temperature coefficient m of the quartz waveguide. _WGTo be equal to
Of the part on which the temperature coefficient adjusting material 12 is mounted_WGTones
It has been set.

The specific values of each parameter in the above equation (1) are as follows. Equivalent refractive index of quartz waveguide n = n _WG =
1.45, refractive index n = _nm = of temperature coefficient adjusting material 12
1.39, equivalent refractive index n of waveguide layer of semiconductor LD11
_LD 3.5. The length L _LD of the semiconductor _{LD 11} is 0.60 mm. The length from the emission end face of the semiconductor LD 11 to a position short of the grating 15 is 1.5 mm, and the length of the grating 15 is 3.0 mm. Therefore, the grating 15 is connected from the emission end of the semiconductor LD 11.
The length L _WG of the quartz waveguide portion (excluding the region where the temperature coefficient adjusting material 12 is sealed) up to the center of (3.0-
L _m ) mm.

The value of the temperature coefficient is as follows.
Temperature coefficient m _LD of the waveguide layer of the semiconductor _{LD 11} = −12.9
(GHz / K), temperature coefficient of quartz waveguide m _WG = -1.4
(GHz / K), the temperature coefficient of the temperature coefficient adjusting material 12 m _m
= 54 (GHz / K). As the temperature coefficient adjusting material 12, a silicone resin is used.

The above parameters are substituted into equation (1).
And L_m= 300 μm. In conventional frequency-stabilized lasers, the temperature coefficient
Length L of adjustment material _mIs, as described above, in equation (1)
Designed based on In this connection,
For the detailed calculation, see JP-A-11-97784.
It is described in.

In general, the reflectance of the grating 15 is 40 to 99%, the coupling loss of light between the semiconductor LD 11 and the silica-based waveguide is about 4 dB ± 1.5 dB, and the loss of the temperature coefficient adjusting material 12 is 1 dB. ing.

[0018]

However, in the above-mentioned conventional frequency-stabilized laser, the temperature coefficient of the selected longitudinal mode frequency is equal to the temperature coefficient of the quartz waveguide. Further, since the oscillation frequency is the selected longitudinal mode frequency, the oscillation frequency changes with the temperature coefficient at the temperature coefficient of the quartz waveguide without mode hopping. This temperature coefficient is m _WG = −1.4 (GHz / K).

The use of a frequency-stabilized laser without a temperature controller eliminates the need for a complicated control system for temperature control, and is very attractive for communication systems in terms of cost reduction.

However, when a conventional frequency-stabilized laser is used for communication without using a temperature controller, the oscillation frequency is shifted by about 42 GHz due to a temperature change of 30 ° C. Here, a light source of WDM (wavelength division multiplex) transmission has an oscillation wavelength within ± 20% of a frequency interval and an ITU (International Telecommunication).
It must be controlled by the ions Union (International Telecommunication Union) grid. That is, W at 100 GHz intervals
In the case of DM transmission, the allowable value of the oscillation frequency is ± 20 GHz. Therefore, room temperature of 30 without temperature controller
In an environment where the temperature changes by more than ° C., the conventional frequency stabilized laser as described above cannot be used.

Therefore, there has been a demand for a frequency-stabilized laser that can be used in an environment where the room temperature changes greatly (for example, 30 ° C. or more) without a temperature controller. In other words, a temperature-independent laser whose oscillation frequency does not depend on the environmental temperature as well as mode hopping is desired.

The present invention has been made to solve such a problem, and an object of the present invention is to eliminate the temperature dependence of the reflection center frequency of the grating and the temperature dependence of the longitudinal mode frequency. Accordingly, it is an object of the present invention to provide a temperature-independent laser in which mode hopping is suppressed and the oscillation frequency does not depend on temperature.

[0023]

In order to achieve the above object, a temperature-independent laser according to the first aspect of the present invention comprises a core formed on a planar substrate and having a high refractive index for transmitting light and a core surrounding the core. An optical waveguide composed of a clad having a low refractive index;
Semiconductor LD mounted on the same substrate as the flat substrate
A Bragg grating formed at a predetermined position of the optical waveguide, and a material having a refractive index temperature coefficient opposite to that of the semiconductor LD by forming the core portion of the optical waveguide disposed between the semiconductor LD and the grating. A frequency stabilized laser having a temperature coefficient adjusting portion replaced with a bimetal plate made of two kinds of metals is adhered to at least one of the lower surface of the planar substrate or the upper surface of the clad. I do.

A temperature-independent laser according to a second aspect of the present invention is the same frequency-stabilized laser as described above, wherein at least the semiconductor LD to the Bragg grating are formed on the lower surface of the planar substrate by using two kinds of metals. Characterized in that a bimetal plate is bonded.

Here, the optical waveguide may be made of quartz glass.

Further, the temperature coefficient adjusting portion may cross the optical waveguide at an angle of about 82 degrees.

Further, the temperature coefficient adjusting portion may be divided into a plurality of portions.

Further, the semiconductor LD may be characterized by having a high temperature characteristic LD.

Also, a plurality of the temperature-independent lasers may be integrated on the same substrate to form a laser array.

The temperature coefficient adjusting portion of each of the temperature-independent lasers constituting the laser array may be continuously connected to each other, and may be continuously connected to a reservoir.

Further, a multi-wavelength laser is formed by integrating an array grating type 1 × N wavelength demultiplexer or a 1 × N coupler connected to the rear end of the grating of each of the temperature-independent lasers. It can be.

(Operation) In the present invention, mode hopping can be suppressed by the above configuration as follows.

First, similarly to the prior art, by mounting a material having a refractive index temperature coefficient opposite to that of the semiconductor LD between the grating and the LD, the optical path of the semiconductor LD due to a temperature change in the laser cavity of the frequency stabilized laser. The change in length and the change in optical path length of the optical waveguide can be canceled. By appropriately designing the size of the region (temperature coefficient adjusting portion) in which the material having the refractive index temperature coefficient opposite to that of the semiconductor LD is mounted, the temperature coefficient of the resonance frequency (longitudinal mode frequency) of the laser cavity is reduced to 0. [GHz / ° C.].

In the present invention, a bimetal plate made of two kinds of metals is bonded to the cladding surface or the substrate surface or both of the PLC type laser having the grating. The bimetal plate bends in a concave or convex shape depending on the temperature, and changes the pitch of the grating carved in the optical waveguide. Since the pitch of the grating has a temperature dependence of expanding as the temperature rises (Reference: Hibino et al., “Temperature-Independent Lightwave Circuit Device”, Japanese Patent Application No. 11-191)
If the bimetal plate is designed to be concavely curved when the temperature rises, the bimetal plate acts to narrow the pitch of the grating as the temperature rises, thereby canceling the temperature dependency of the grating. The temperature coefficient of the reflection center frequency of the grating can be set to 0 [GHz / ° C.].

Therefore, according to the present invention, the temperature coefficient of the longitudinal mode can be made equal to the reflection center frequency of the grating, and both temperature coefficients can be set to 0 [GHz / ° C.]. That is, it is possible to realize a temperature-independent laser in which mode hopping is suppressed in response to a temperature change and the oscillation frequency does not change.

Hereinafter, the temperature coefficient of the refractive index of the semiconductor LD
The material opposite to the above is referred to as a temperature coefficient adjusting material.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

(First Embodiment) As a first embodiment of the present invention, a temperature-independent laser in which an optical waveguide is made of silica glass will be described as an example.

FIGS. 1 and 2 show the configuration of the first embodiment of the present invention. FIG. 1 is a sectional view of the laser, and FIG. 2 is a top view of the laser. Here, 11 is a semiconductor LD that emits laser light, 12 is a temperature coefficient adjusting material mounted in the groove, 13 is a core having a high refractive index of a quartz waveguide through which light propagates, and 14 is a refractive index lower than the core. A quartz waveguide clad around the core, 15 is a grating formed on the quartz waveguide, and 16 is a planar substrate Si on which these are mounted.
The substrate 18 is a silicon terrace from which quartz glass is removed for mounting the semiconductor LD 11, and 5
Reference numeral 1 denotes a bimetal plate which is a characteristic component of the present invention.
The bimetal plate 51 is bonded to the lower surface of the Si substrate 16 in this example.

The wavelength of the semiconductor LD is 1.55 μm.
Therefore, the approximate light frequency of the temperature-independent laser is expressed by the following equation (2).

Ν = 193 (THz) (2) The temperature dependence of the reflection center frequency of the grating 15 of the temperature-independent laser shown in FIG. 1 will be described.

The reflection center frequency f of the grating 15
_BraggIs the reflection center wavelength λ_BraggAnd using the following equation (3)
Is represented. Here, c represents the speed of light, and c = 3.0.
× 10 ⁸(M / s).

[0044]

(Equation 2)

Here, the reflection center wavelength λ _Bragg is defined by the effective refractive index n _WG of the quartz waveguide and the pitch Λ of the grating 15.
Is represented by the following equation (4).

Λ _Bragg = 2n _WG Λ (4) Therefore, the temperature coefficient of the reflection center frequency f _Bragg of the grating 15 of the temperature-independent laser shown in FIG. 1 can be obtained from the above equations (3) and (4). Yes, but Si substrate 1
As shown in FIG. 1, a bimetal plate 51 is adhered to the lower part of 6, thereby eliminating the temperature dependence of the reflection center frequency.

Hereinafter, the principle will be described in detail. The bimetal plate 51 is composed of two types of metal layers having different coefficients of thermal expansion, and the amount of warpage changes depending on the temperature. Therefore, when the temperature rises, the bimetal plate 51 bends, and the bimetal plate 51 is adhered to the substrate 16, so that the substrate 16 can be bent in response to the temperature rise. By bending the substrate 16 as the temperature increases, by changing the pitch Λ of the grating 15, represented by the above formula (4), the reflection center wavelength lambda _Bragg (reflection center frequency f _{Bra gg),} it is possible to control the .

In particular, when the substrate 16 bends in the concave direction shown in FIG. 3 as the temperature rises, the pitch Λ of the grating 15 is narrowed, and the reflection center wavelength λ _Bragg can be shifted to the short wave side.

On the other hand, the grating 1 formed on a normal quartz waveguide without the bimetal plate 51 mounted thereon
In the case of 5, the reflection center wavelength λ _Bragg shifts to the longer wavelength side with a temperature coefficient of 0.11 nm / ° C. Therefore, in the present embodiment, by mounting the bimetal plate 51 on the lower surface side of the substrate 16, the shift amount to the longer wavelength side is compensated, and the reflection center wavelength λ of the grating 15 is
_{The Bragg} temperature coefficient can be set to 0 [nm / ° C]. At this time, the reflection center frequency f of the grating 15
Temperature coefficient of _{br agg} is 0 [GHz / ℃].

Hereinafter, parameters for making the grating 15 temperature independent will be described.

In this example, reference is made to Japanese Patent Application No. 11-191.
No. 373, and Hibino, et al, “Temperature-insens
itive UV-induced Bragg gratings in silica-based pl
anarlightwave circuits on Si ", Electron. Lett.,
vol., 1999, 35, no, 21, pp. 1844-1
845, a bimetal plate 5 having a thickness of 1.5 mm
1 is mounted on the lower surface of the Si substrate 16 so that the temperature coefficient of the center frequency of the grating 15 is 0 [GHz /
° C]. The size of the quartz waveguide chip used at this time is 30 mm in length, 10 mm in width, and 1 mm in thickness, and the bimetal plate 51 is mounted in a 10 mm area covering directly below the grating 15.

Next, the temperature coefficient of the longitudinal mode of the temperature-independent laser shown in FIG. 1 will be described.

The temperature coefficient m of the longitudinal mode is approximately calculated by the following equation (5).
It is represented by

[0054]

(Equation 3)

[0055] _{However, m LD, m WG, m} m , the temperature coefficient of the resonance frequency in the case where the temperature coefficient of the resonant frequency of the resonator of the semiconductor LD 11, a quartz waveguide portion and the resonator, respectively,
This is the temperature coefficient of the temperature coefficient adjusting material 12. n _LD , n _WG ,
_nm is the effective refractive index of the waveguide layer of the semiconductor LD 11, the effective refractive index of the quartz waveguide between the semiconductor LD 11 and the grating 15, and the refractive index of the temperature coefficient adjusting material 12, respectively.

As shown in FIG. 2, L _LD , L _m , and L _WG are the resonator length of the semiconductor _{LD 11} , the length of the portion on which the temperature coefficient adjusting material 12 is mounted, and the emission length of the semiconductor _{LD 11} , respectively. It represents the length of the quartz waveguide portion up to the center of the grating 15 (excluding the region where the temperature coefficient adjusting material 12 is sealed).

When the temperature coefficient m of the longitudinal mode represented by the above equation (5) is m = 0 [GHz / ° C.] (6), the longitudinal mode frequency remains constant even when the temperature changes. Also, the reflection center frequency f of the grating 15
_{Since the Bragg} temperature coefficient is 0 [GHz / ° C.] as described above, the reflection center frequency f
_Bragg also remains constant with changes in temperature. here,
In this frequency stabilized laser, the longitudinal mode having the frequency closest to the reflection center frequency of the grating 15 is selected and oscillates. Since the frequencies of the two do not depend on the temperature, the same longitudinal mode is always selected and oscillates even when the temperature changes. That is, mode hopping depending on temperature is suppressed. Accordingly, it can be seen that a temperature-independent laser that is temperature-independent and that suppresses temperature-dependent mode hopping is realized.

Hereinafter, in the first embodiment of the present invention,
Temperature coefficient of longitudinal mode frequencies 0 Request [GHz / ° C.] to become the total length L _m of the containment zone of the temperature compensation material 12 for.

From the above equations (5) and (6), the condition of the temperature-independent laser is given by the following equation (7).

[0060]

(Equation 4)

Hereinafter, the temperature compensation material 12 satisfying the expression (7)
Determining the total length L _m of the containment zone. Here, a silicone resin was used as the temperature coefficient adjusting material 12. The value of the temperature coefficient _mWG of the quartz waveguide portion excluding the region where the silicone resin 12 is sealed is expressed by the following equation (8).

[0062]

(Equation 5)

[0063] The temperature coefficient m _m of the mounting portion of the silicone resin 12 is expressed by the following equation (9).

[0064] _{m m = 54 (GHz / K} ) (9)

The method of deriving the equations (8) and (9) is described in detail in Japanese Patent Application Laid-Open No. H11-97784.

The length L _LD of the semiconductor _{LD 11} is 0.6.
The equivalent refractive index n _LD of the waveguide layer of the semiconductor _{LD 11} is 0 mm, and the equivalent refractive index n _WG of the quartz waveguide is 1.45. Refractive index n _m of the silicone resin 12 is 1.39. From the output end face of the semiconductor LD 11 to the grating 15
Is 5.0 mm, and the length of the grating 15 is 3.0 mm. Therefore, the semiconductor LD1
The length L _WG of the quartz waveguide portion from the exit end face of the first to the center of the grating 15 (excluding the region where the temperature coefficient adjusting material 12 is sealed) is (6.5-L _m ) mm. Further, the temperature coefficient of the semiconductor _LD 11 is m _LD = −12.9 (G
Hz / K).

[0067] Therefore, in the design of the first embodiment, the above parameters and equation (8) In the above formula (7), based on the equation (9), 0.52 mm and the total length L _m
And designed.

The temperature-independent laser shown in FIGS. 1 and 2 was designed in accordance with the above parameters, and actually manufactured. This manufacturing process is shown in FIG. This manufacturing process includes the following eight steps as shown in FIG. (1) A Si substrate 16 having a step is formed by etching. (2) Flame deposition method using optical fiber fabrication technology and L
A quartz waveguide is formed on a Si substrate 16 by using a photolithography technique used for manufacturing an SI (Large Scale Integrated Circuit). Reference numeral 13 denotes a quartz waveguide core, and 14 denotes a quartz waveguide clad. (3) The quartz layer is partially etched using photolithography and reactive ion etching to form the semiconductor laser mounting portion (Si terrace) 18 and the groove 21. (4) A solder pattern 19 for mounting a semiconductor laser is formed on the Si terrace 18. (5) The grating 15 is formed at the position of the core 13 by irradiating the waveguide with the excimer laser light (or the second harmonic of the argon laser) 31 through the phase mask 30. (6) The semiconductor laser (semiconductor LD) 11 is positioned and fixed on the solder pattern 19 covering the silicon terrace 18. (7) The groove 21 is filled with the silicone resin 12 and heated to cure the silicone resin. (8) The bimetal plate 51 is bonded directly below the grating 15 on the lower surface of the Si substrate 16.

FIG. 5 is a characteristic diagram showing a measurement result of the temperature dependence of the oscillation frequency of the temperature-independent laser according to the first embodiment of the present invention. As a result of the measurement, it was confirmed that the oscillation frequency was constant in a range from -15 ° C. to 65 ° C. and that mode hopping was suppressed. The threshold current for oscillation at 25 ° C. was 200 mA.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 6 shows a cross-sectional configuration of a temperature-independent laser according to the second embodiment of the present invention. The difference from the first embodiment is that the bimetal plate 51 is attached to the entire back surface of the Si substrate 16 in the second embodiment. The bimetal plate 51 is connected to the Si substrate 16
The optical path length of the quartz waveguide portion from the grating 15 to the semiconductor LD 11 can be made temperature-independent by attaching to the entire back surface (lower surface). Therefore,
In the present embodiment, the part to be compensated by the temperature coefficient adjusting material 12 is only the semiconductor LD 11.

Hereinafter, specific numerical examples will be shown. The thickness of the bimetal plate 51 to be affixed is 1. as in the first embodiment.
5 mm, and the size of the quartz waveguide chip used was 30 mm in length, 10 mm in width, and 1 mm in thickness, as in the first embodiment, and the bimetal plate 51 was bonded to the entire 30 mm length portion. It is installed by. Thus, as in the first embodiment, the center frequency of the grating 15 can be made temperature-independent, and the grating 1
The optical path length of the quartz waveguide portion from 5 to the semiconductor LD 11 is also made temperature-independent.

Hereinafter, when the longitudinal mode frequency m is 0 [GHz /
The ℃], and therefore, to calculate the groove width L _m of inserting the temperature coefficient adjusting material 12. As described above, grating 15
Since the optical path length of the quartz waveguide portion from to the semiconductor LD 11 is made temperature-independent, the second term of the numerator of the above equation (7) is 0 [GHz · mm / ° C.]. Therefore, from the equation (7), the condition of the temperature-independent laser is given by the following equation (10).
Given by

M _LD n _LD L _LD + m _{nm nm} L _m = 0 (10)

[0074] When calculated in the same way as the first embodiment described above, the overall length L _m becomes 0.36 [mm].

[0075] The length of the groove width L _m is L _m in a nearly half the length of (the first embodiment of the first embodiment 0.52
mm). Since the length of the groove is reduced to almost half, the energy of light transmitted through the groove is increased to almost twice.

Hereinafter, the transmission loss due to the groove will be described.

A groove 21 in the waveguide (see (3) in FIG. 4)
And a material 12 different from the waveguide constituting material is formed in the groove 21.
, The waveguide mode of light transmitted through the waveguide changes, and transmission loss occurs as compared with the case where the groove 21 is not provided.

The transmittance η when light having a mode diameter ω and a wavelength λ passes through a groove having a groove width d is represented by the following equation (11).

[0079]

(Equation 6)

Here, λ is a wavelength and λ = 1.55 μm, n is a refractive index of the silicone resin 12, and n = n
_m = 1.39, ω is the mode field diameter (radius) in the waveguide, and ω = 4 to 4.5 μm.

From the above equation (11), it can be seen that the transmittance η sharply decreases as the groove width d increases.

By substituting the above values into the equation (11), the second embodiment in which the groove width d is reduced has twice the transmittance by the groove as compared with the first embodiment. It can be seen that it can be done to the extent. As a result, the loss in the laser cavity is reduced and the threshold current of the temperature independent laser is reduced.

FIG. 7 shows a measurement result of the temperature dependence of the oscillation frequency of the temperature-independent laser according to the second embodiment. As in the case of the first embodiment, it was confirmed that the oscillation frequency was constant in the range of −15 ° C. to 65 ° C. and mode hopping was suppressed. The threshold current at 25 ° C. is 100
mA.

(Third Embodiment) As a third embodiment of the present invention, a sectional structure similar to that of the second embodiment will be described.
FIG. 8 shows an example of a temperature-independent laser in which the angle formed by the quartz waveguide is 82 degrees. FIG. 8 shows a top view of a temperature-independent laser.

The reason why the angle formed between the groove for accommodating the silicone resin 12 and the quartz waveguide 13 composed of the core 13 and the clad 14 is 82 degrees will be described below. When a temperature coefficient adjusting material having a refractive index difference between the quartz waveguide and the silicone resin 12 is larger than that of the silicone resin 12, a large refractive index difference causes light reflection at the interface between the quartz waveguide and the temperature coefficient adjusting material. growing. When a large amount of reflected light returns to the semiconductor LD 11, the oscillation of the temperature-independent laser becomes unstable. Therefore, depending on the type of the temperature coefficient adjusting material, it may be difficult to suppress the mode hopping with respect to the temperature change.

However, the angle between the groove and the quartz waveguide is set to 8
If it is twice, the reflected light does not return to the semiconductor LD 11 by passing from the core 13 to the cladding 14 of the waveguide, and the oscillation of the temperature-independent laser becomes stable. That is, a temperature coefficient adjusting material having a large refractive index difference from the quartz waveguide can be used for suppressing mode hopping of the temperature-independent laser.

Also in the case of the third embodiment, as in the first embodiment, it was confirmed that the oscillation frequency was constant and the mode hopping was suppressed in the range of −15 ° C. to 65 ° C. 25
The threshold current at 100 ° C. was 100 mA.

(Fourth Embodiment) As a fourth embodiment of the present invention, an example of a temperature-independent laser having a plurality of the grooves in the third embodiment is shown in FIGS. FIG. 9 is a sectional view of the temperature-independent laser, and FIG. 10 is a top view of the temperature-independent laser. 9 and 1
0 is characterized in that a 0.36 mm groove is divided into a plurality of narrow grooves. Specifically, width 15
24 μm grooves are produced. Each of the 24 grooves is filled with the silicone resin 12. As a result of the measurement, suppression of mode hopping was confirmed from −15 ° C. to 65 ° C., and the threshold current at 25 ° C.
10 mA was obtained, which is an order of magnitude lower than that of.

The reason why a low threshold current was obtained by forming a plurality of narrow grooves will be described below.

The dependence of the transmission loss on the groove width is expressed by the above equation (11). From equation (11), it can be seen that the longer the total length of the groove in the waveguide direction, the more the transmission loss increases. Therefore, compared to the case where the temperature coefficient adjusting material is mounted collectively in one thick groove, the loss of transmitted light is better when the temperature coefficient adjusting material is mounted in a plurality of narrow grooves. Less. Therefore, compared to the former case using a single groove as shown in FIGS. 7 and 8, the latter using a plurality of grooves as shown in FIGS. 9 and 10 reduces the loss in the laser cavity. In addition, the threshold current of the temperature-independent laser can be reduced.

(Fifth Embodiment) As a fifth embodiment of the present invention, an example of a temperature-independent laser having a configuration of the above-described fourth embodiment and mounting a semiconductor LD having excellent high-temperature characteristics is provided. Is shown in FIG. FIG. 11 shows a cross-sectional view of this temperature-independent laser. Here, 52 is a semiconductor LD having excellent high-temperature characteristics. The present embodiment is characterized in that a temperature-independent laser is mounted with a semiconductor LD 52 having excellent high-temperature characteristics. That is, the semiconductor LD 52 has a threshold current of 15 mA and an output (at an injection current of 60 mA) even in a high-temperature region of about 85 ° C. in a state where the front end face has a high reflection coating of about 95% of the rear end face without coating. Is a semiconductor LD having about 出力 of the output at 25 ° C.

In the case of the fifth embodiment, the temperature ranges from −15 ° C. to 6 ° C.
The oscillation wavelength was temperature-independent in the temperature range of 5 ° C., and the threshold current was 10 mA at 25 ° C. The threshold current was 15 mA even at 65 ° C. The output fluctuation was about 3 dB in a temperature range from -15 ° C to 65 ° C. As described above, by using a semiconductor LD having excellent high-temperature characteristics, not only does the oscillation frequency not depend on temperature, but also
A temperature-independent laser with low temperature dependence of threshold current and optical output was realized.

The results show that, in the state of high reflection coating in which the front end face has no coating and the rear end face is about 95% with respect to the temperature, the temperature independent laser is used by using the semiconductor LD 52 with small fluctuation of the threshold current and the output. This indicates that the fluctuation of the threshold current and the fluctuation of the output of the present temperature-independent laser are also suppressed.

(Other Embodiments) The first to the fourth embodiments of the present invention described above.
In the fifth embodiment, a silicone resin is used as the temperature coefficient adjusting material 12, but the present invention is not limited to this.

Further, in the first embodiment of the present invention,
One groove having a length of 520 μm was prepared, and in the second to fifth embodiments, a groove having a total length of 360 μm was prepared and a groove having a length of 3 μm was formed.
One groove of 60 μm or 24 grooves of 15 μm width was produced. However, the design of the interval and the number of grooves is not limited to this. A plurality of grooves having a width of 5 to 50 μm are formed, and if the total length is the form of the first embodiment, 500 μm
± 80 μm, if the total length is 360 ± 50 μm in the case of the second to fifth embodiments, the first embodiment and the second to fifth embodiments of the present invention will be described. Similarly to the result, the oscillation frequency is independent of the temperature, and the mode hopping depending on the temperature is suppressed.

In the first to fifth embodiments of the present invention, a single temperature-independent laser has been described. However, the effects of the present invention are not limited to a single temperature-independent laser. . The effect of the present invention is also effective for a laser having a configuration in which a plurality of temperature-independent lasers are integrated on the same substrate. Hereinafter, specific examples will be described in detail in (# 1) to (# 6).

(# 1) The effect of the present invention is also effective in a laser array manufactured by integrating a plurality of temperature-independent lasers. FIG. 12 is a schematic top view of a laser array in which a temperature-independent laser of the present invention is integrated. Here, the number of outputs of the laser array is not limited to eight, but may be any number as long as it is plural. In the same figure, the groove (position 12) is connected, and is connected to the reservoir (position 42). Since the injected silicon resin 12 is a liquid, the appropriate amount of the silicon resin 12 can be efficiently and collectively injected into each groove by injecting the liquid into the reservoir. 41 is a temperature coefficient adjusting material in the connecting groove,
Reference numeral 42 denotes a temperature coefficient adjusting material in the reservoir. This reservoir can be applied to all temperature coefficient adjusting materials as long as the material to be injected at the time of injection into the groove is a liquid.

(# 2) In the configuration of the above (# 1), the reflection center frequency (wavelength) of each of the gratings 15 is controlled, and an array grating type 1 × N wavelength multiplexer / demultiplexer or 1
The effect of the present invention is effective even in a multi-wavelength laser in which a × N coupler is integrated. FIG. 13 is a schematic top view of a multi-wavelength laser in which the temperature-independent laser of the present invention is integrated in this case. In the figure, reference numeral 20 denotes an array grating type 1 × N wavelength multiplexer / demultiplexer or a 1 × N coupler connected to each output side of the grating 15. Here, the number of wavelength multiplexes of the multi-wavelength laser is not limited to eight, but may be any number as long as it is plural. In this configuration, since the wavelength is determined simultaneously with the determination of the frequency, the stabilization or control of the frequency and the wavelength can be used in the same meaning. In short, a temperature-independent laser and a wavelength-stabilized laser can be used interchangeably.

(# 3) In the configuration of the above (# 2), in order to collectively manufacture the gratings 15 having different reflection center wavelengths, the core width of the waveguide in the portion where these gratings 15 are formed is provided. Or a multi-wavelength laser formed such that the angle formed by the grating vector and the optical axis of the waveguide in the portion where the grating 15 is formed is different for each of the waveguides. The effect of the present invention is also effective in Japanese Unexamined Patent Publication No. 10-242591).

(# 4) Further, in the configuration of (# 2) or (# 3), a semiconductor optical amplifier (amplifier) is integrated to amplify the combined output light. The effect of the present invention is also effective in a multi-wavelength laser.

(# 5) In the configuration of (# 2), (# 3) or (# 4), each semiconductor LD 11 is provided with an EA (electroabsorption type) in order to modulate each wavelength output at high speed. The effect of the present invention is also effective in a multi-wavelength laser characterized by integrating an electro-absorption modulator.

(# 6) In the configuration of (# 2), (# 3) or (# 4), in order to modulate each wavelength output at high speed, a LiNbO ₃ modulator or E
The effects of the present invention are also effective in a multi-wavelength laser characterized by integrating an A modulator.

Further, in the first embodiment of the present invention, the bimetal plate 516 is bonded to the back surface of the flat substrate 16,
Even if the surface to which the bimetal plate 51 is bonded is the upper surface of the clad 14, or both the substrate back surface and the clad upper surface,
It goes without saying that a similar effect can be obtained if the substrate 16 is adhered so as to deflect the substrate 16 in an appropriate direction with respect to a temperature change.

Further, in the first to fifth embodiments of the present invention, the semiconductor LD mounted on the substrate has an oscillation wavelength of 1.5.
Although a semiconductor LD of 5 μm was used, in general, even if a semiconductor LD of another oscillation wavelength is used, the shape of the bimetal plate and the region to which the bimetal plate is bonded are appropriately designed to adjust the size of the optical waveguide and the temperature coefficient. Needless to say, by appropriately designing the entire length of the material mounting region, the oscillation frequency can be made temperature-independent and mode hopping can be suppressed.

In putting a semiconductor LD mounted device to practical use, long-term reliability should be ensured by sealing the semiconductor LD with a resin, that is, by not exposing the semiconductor LD to moisture. Is commonly done. Therefore, when the temperature coefficient adjusting material 12 described in the first to fifth embodiments of the present invention is a material also serving as a resin sealing material, the semiconductor LD is removed from the groove for mounting the temperature coefficient adjusting material. Needless to say, by mounting the temperature coefficient adjusting material all over the entire area covered by the above, it is possible to suppress mode hopping and to ensure the reliability of the semiconductor LD at the same time. However, in this case, since this temperature coefficient adjusting material is also mounted in a slight gap between the semiconductor LD and the quartz waveguide, the antireflection film on the front end face of the semiconductor LD has a refractive index that is lower than the refractive index of the temperature coefficient adjusting material. It must be designed for

For example, in the above configuration, when the refractive index of the temperature coefficient adjusting material is equal to the refractive index n = 1.45 of the quartz waveguide, the distance between the end face of the quartz waveguide on the semiconductor LD side and the temperature coefficient adjusting material is changed. Does not cause light reflection. Therefore, in this case, the quartz waveguide end face on the semiconductor LD side may have a portion near the core orthogonal to the optical axis of the core.

[0107]

As described above, according to the present invention,
Attach a bimetal plate made of two metals to at least one of the lower surface of the substrate and the upper surface of the clad, and adjust the temperature coefficient to the groove where the upper clad and core are removed or the groove where the upper clad, core and lower clad are removed By using a simple method of enclosing the material, the temperature coefficient of the longitudinal mode and the temperature coefficient of the reflection center wavelength of the grating are both made equal to 0 [GHz / ° C.], and the oscillation frequency, which has been a problem to be solved conventionally, is The temperature dependence of
At the same time, there is an effect that mode hopping can be easily suppressed.

Therefore, according to the present invention, at low cost,
A stable single mode laser without temperature dependency can be realized, and a great effect is expected in a field using a laser such as optical communication.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a structure of a temperature-independent laser according to a first embodiment of the present invention.

FIG. 2 is a schematic top view showing the structure of the temperature-independent laser according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a state in which the substrate is warped as the temperature rises in the first embodiment of the present invention.

FIG. 4 is a schematic view showing a manufacturing process of the temperature-independent laser according to the first embodiment of the present invention.

FIG. 5 is a characteristic diagram showing a measurement result of the temperature dependence of the oscillation frequency of the temperature-independent laser according to the first embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view illustrating a structure of a temperature-independent laser according to a second embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a measurement result of a temperature dependence of an oscillation frequency of a temperature-independent laser according to a second embodiment of the present invention.

FIG. 8 is a schematic top view showing the structure of a temperature-independent laser in which the angle between a groove and a waveguide is 82 degrees in a third embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing a structure of a temperature-independent laser in which a groove is divided into fine grooves in a fourth embodiment of the present invention.

FIG. 10 is a schematic top view showing a structure of a temperature-independent laser in which a groove is divided into fine grooves in a fourth embodiment of the present invention.

FIG. 11 is a schematic cross-sectional view illustrating a structure of a temperature-independent laser mounted with a semiconductor LD having excellent high-temperature characteristics in a fifth embodiment of the present invention.

FIG. 12 is a schematic top view showing the structure of a laser array manufactured by integrating the temperature-independent lasers according to the embodiment of the present invention as another embodiment of the present invention.

FIG. 13 is a schematic top view showing a structure of a multi-wavelength laser manufactured by integrating the temperature-independent laser according to the embodiment of the present invention as still another embodiment of the present invention.

FIG. 14 is a schematic perspective view of a frequency-stabilized laser using a conventional grating, which is observed from above the lick.

[Explanation of symbols]

Reference Signs List 11 semiconductor LD 12 temperature coefficient adjusting material (silicone resin) 13 core layer of quartz waveguide 14 cladding layer of quartz waveguide 15 grating 16 Si substrate 18 silicon terrace 19 solder pattern for mounting semiconductor laser 20 array lattice type 1 × N Wavelength multiplexer / demultiplexer or 1 × N
Coupler 21 Groove 30 Face mask 31 Second excimer laser beam or argon laser
High frequency 41 Material for adjusting temperature coefficient in connection groove 42 Material for adjusting temperature coefficient in liquid reservoir 51 Bimetal plate 52 Semiconductor LD with excellent high temperature characteristics

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/026 G02B 6/12 A H (72) Inventor Naoki Ohba 2-3 Otemachi 2-chome, Chiyoda-ku, Tokyo No. 1 Within Nippon Telegraph and Telephone Corporation (72) Atsushi Abe Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 2H037 BA02 CA00 CA02 CA33 CA37 DA37 2H041 AA21 AB10 AB38 AC01 AZ01 AZ05 2H047 LA03 LA19 MA07 NA10 TA00 5F073 AA65 AA67 AB02 AB25 BA02 EA03 FA06 FA13

Claims (9)

[Claims] An optical waveguide formed on a planar substrate and having a high refractive index core for transmitting light and a low refractive index clad around the core; and an optical waveguide mounted on the same substrate as the planar substrate. Semiconductor LD
A Bragg grating formed at a predetermined position of the optical waveguide; and a material having a temperature coefficient of a refractive index opposite to that of the semiconductor LD by changing the core portion of the optical waveguide disposed between the semiconductor LD and the grating. A frequency stabilized laser having a temperature coefficient adjusting portion replaced by: a bimetal plate made of two kinds of metals bonded to at least one of the lower surface of the planar substrate or the upper surface of the clad. Temperature independent laser. 2. An optical waveguide comprising a core formed on a planar substrate and having a high refractive index for transmitting light, and a clad having a low refractive index around the core, and mounted on the same substrate as the planar substrate. Semiconductor LD
A Bragg grating formed at a predetermined position of the optical waveguide; and a part of the core of the optical waveguide disposed between the semiconductor LD and the grating has a refractive index temperature coefficient opposite to that of the semiconductor LD. A frequency-stabilized laser having a temperature coefficient adjusting portion replaced with a material, wherein a bimetal plate made of two kinds of metals from at least the semiconductor LD to the Bragg grating is bonded to a lower surface of the planar substrate. Temperature independent laser. 3. The temperature-independent laser according to claim 1, wherein said optical waveguide is made of silica-based glass. 4. The temperature-independent laser according to claim 1, wherein said temperature coefficient adjusting portion crosses said optical waveguide at an angle of approximately 82 degrees. 5. The temperature-independent laser according to claim 1, wherein the temperature coefficient adjusting portion is divided into a plurality of portions. 6. The temperature-independent laser according to claim 1, wherein said semiconductor LD has a high-temperature characteristic LD. 7. The temperature-independent laser according to claim 1, wherein a plurality of said temperature-independent lasers are integrated on the same substrate to form a laser array. 8. The temperatureless laser according to claim 7, wherein the temperature coefficient adjusting portions of the respective temperature-independent lasers constituting the laser array are continuously connected to each other and are connected to a reservoir. Dependent laser. 9. A multi-wavelength laser is constructed by integrating an array grating type 1 × N wavelength demultiplexer or a 1 × N coupler connected to the rear end of the grating of each of the temperature-independent lasers. 9. The temperature-independent laser according to claim 7, wherein: