JP2000049419A - Laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser device with excellent variable characteristics of a pulse cycle/oscillation wavelength. SOLUTION: A laser rosonator 100 is provided with mutually aligned distribution Bragg reflection(DBR) laser element 150 and grating fiber 160. The DBR laser element 150 is provided with an optical waveguide 110 extending to a second end face and formed of a DBR area 110a where a uniform grating 132 is formed, a saturable absorption area 110b and an active area 110c. Also, at the granting fiber 160, a chirp grating for changing a grating cycle not shown in the Figure is formed. As a result, in the laser resonator 100 between a reflection position in the DBR area 110a and the reflection position in the grating fiber 160, plural resonator length are realized, a circulating optical route to which the saturable adsorption area 110b and the active area 110c are interposed is formed and an oscillation operation with the excellent variable characteristics of the pulse cycle/oscillation wavelength is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a laser device.

[0002]

2. Description of the Related Art In a mode-locked laser device, the frequency interference between modes is made uniform and the mutual phase between the modes is kept constant, so that the regular interference of a number of longitudinal modes existing in a laser resonator is achieved. Is realized. A mode-locked laser device can generate a high-speed repetitive optical pulse (optical pulse train) with a narrow time interval, and is useful as a light source for optical communication in recent years, in which the speed and capacity have been remarkably increased.

Conventionally, as a mode-locked laser device, for example, S.K. Arahira et. al. , "T
transform limited optical
short pulse generation at
high repetition rate ove
r 40GHz from a monolithic
passive mode locked DBR 1
aser diode ", IEEE Photon. T
chnol. Lett. vol. 5, pp1362-1
365 (1993) has disclosed a passive mode-locked laser device.

Here, the laser device described in the above document will be briefly described with reference to FIG. FIG. 7 shows an LD (La), which is one laser device according to the above document.
1 schematically shows the configuration of a laser diode (ser diode) 300. As shown in FIG.
Is a passive mode-locked D-type laser that generates laser light in the optical waveguide 310 extending between the first end face 300a and the second end face 300b.
It is a BR laser.

In the LD 300, the optical waveguide 310 is
It is divided into four regions where current injection can be performed independently. In order from the first end face 300a side, DBR
(Distributed Bragg Reflect
region; distributed Bragg reflection) region 310a, phase adjustment region 310b, active region 310c, and saturable absorption region 31
0d. In the LD 300 having such a configuration, light emission in the active region 310c, wavelength-selective reflection of light in the DBR region 310a, and adjustment of the phase relationship between each mode in the saturable absorption region 310d cause short pulse pulses. Oscillation of laser light is realized.

In such laser oscillation, the phase adjustment of light for resonance operation is realized by adjusting the current injected into the phase adjustment region 310b. Also, DB
By adjusting the current injected into the R region 310a, the grating period of the uniform Bragg diffraction grating 320a formed in the DBR region 310a is extended uniformly, and the oscillation wavelength is adjusted. Further, by controlling the bias current injected into the active region 310c and the bias current injected into the saturable absorption region 310d, a mode-locked operation is realized, and the pulse period of the oscillation laser pulse train is adjusted.

[0007]

However, in the above-mentioned conventional laser device, particularly when an optical device such as the LD 300 is used, the frequency adjustment of the mode-locking operation depending on the cavity length cannot be performed with high accuracy. It has been difficult to obtain a laser pulse train having a desired period. One reason for this is that the cavity length of a laser element is usually determined by cleavage, but it is difficult to adjust with a precision of several tens μm or less in this cleavage process. Another factor is that the refractive index of the optical waveguide of the laser element, which determines the effective resonator length, is easily changed by an oscillation threshold or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the conventional laser device, and has as its object to provide a new and improved laser device capable of adjusting the period of a laser pulse train with high accuracy. And Still another object of the present invention is to provide a new and improved laser device capable of changing the wavelength of an emitted laser beam in a wide range.

[0009]

In order to solve the above-mentioned problems, the present invention is directed to a reflection region in which a first Bragg diffraction grating having a substantially uniform effective grating period is formed. A waveguide end face through which light enters and exits, and an optical waveguide formed with at least a relay region having an active region and interconnecting the reflection region and the waveguide end face; An optical fiber on which the second Bragg grating is formed and which enters and exits the light from the end face of the waveguide.

According to the first aspect of the present invention having such a configuration, since the effective grating period of the second Bragg diffraction grating is non-uniform, the light reflection position in the reflection region has a wavelength dependence. Show. Accordingly, the length of the orbital path of light formed between the reflection position in the reflection region and the reflection position in the optical fiber and functioning as a laser resonator changes depending on the wavelength of the resonating light. As a result, according to the second aspect of the invention, the functions of a plurality of laser resonators having different resonator lengths are realized on one optical path. by this,
First, the degree of freedom of laser light oscillation conditions is improved, and excellent wavelength tunable characteristics of the laser device are realized.

[0011] The first aspect of the present invention is the second aspect of the present invention.
By adopting a configuration in which the relay region also has a saturable absorption region as in the invention described in (1), the present invention can be applied to a passive mode-locked laser device. According to the second aspect of the present invention having such a configuration, a self-pulsation (self pulse) is provided by providing a saturable absorption region in which the light absorption decreases as the light intensity increases.
ation) phenomenon occurs, and passive mode-locked laser short pulse oscillation becomes possible.

In mode-locked laser oscillation, the frequency of mode-locking operation is determined by the length of the resonator in the laser device. Therefore, according to the second aspect of the present invention, since a plurality of laser resonator lengths are substantially realized on one optical path, excellent tunability of the oscillation wavelength is achieved. , A very large frequency change of the mode locking operation is realized. As a result, it is possible to provide a laser device capable of generating a laser light pulse train having a desired period.

Further, in the second aspect of the present invention, a part of the orbiting optical path is formed in the optical fiber. In general, an optical fiber has a higher light confinement effect and a smaller propagation loss than an optical waveguide formed on a substrate, so that the invention according to claim 2 realizes an effective self-pulsation together with a reduction in the optical loss. .

[0014] In the first or second aspect of the present invention, the optical waveguide is provided as in the third aspect of the present invention.
It is possible to adopt a configuration formed in a semiconductor optical device. Such a configuration employed in the third aspect of the present invention can be formed without making significant changes to a conventional laser device. For example, when a conventionally proposed DBR laser device is surface-mounted, the D
It can be formed by forming a Bragg diffraction grating having an uneven grating period at an end portion of an optical fiber connected to the BR laser element.

According to another aspect of the present invention, there is provided a first reflection waveguide on which a first Bragg diffraction grating having a substantially uniform effective grating period is formed. A second reflection waveguide on which a second Bragg diffraction grating having an effective non-uniform grating period is formed, and a first reflection waveguide having an active region and a saturable absorption region, and a second reflection waveguide. And a relay waveguide that interconnects the waveguides.

According to a fourth aspect of the present invention having such a configuration, for example, when the first and second reflection waveguides and the relay waveguide are formed on the same substrate, a pulse train having a desired pulse interval is formed. A laser device in which generation and excellent tunability of the oscillation wavelength are realized can be made into an optical element. Therefore, integration with other optical elements on the same substrate becomes possible, and a high degree of freedom is provided between the function of changing the oscillation wavelength and the function of changing the pulse train period without causing, for example, an increase in cost or an increase in the scale of the device. The application of the laser device to optical communication equipment is facilitated.

Here, it is preferable that the second Bragg diffraction grating has a structure in which the effective grating period sequentially changes with a constant change amount, as in the invention described in claim 5. . In the invention according to claim 5 having such a configuration, mode jump is prevented by appropriately changing the constant change amount, and continuous wavelength tuning of the oscillation wavelength becomes possible.

Incidentally, the adjustment of the effective grating period of the second Bragg diffraction grating employs a structure further provided with a heat generating means as in the invention according to claim 6 or the structure according to claim 7. This can be realized by adopting a configuration further including a current injection unit as in the invention. In addition, the adjustment of the effective grating period of the first Bragg diffraction grating is also achieved as in the invention according to claim 8, further including a configuration including a heat generating means, or as in the invention according to claim 9. This can be realized by adopting a configuration including current injection means.

Here, when the heating means is provided, a TO effect (Thermo-optic effect) is used, and when the current injection means is provided, an EO effect (Electro-optic effect) is used. The effective grating period can be adjusted by changing the refractive index of the core in the waveguide structure.

[0020]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description will be omitted.

(First Embodiment) First, a first embodiment will be described with reference to FIGS. Here, FIG. 1 is a cross-sectional view showing a schematic configuration of a laser resonator 100 which is an example of the laser device according to the present embodiment. FIG. 2 is a cross-sectional view of a DBR laser element 150 applied to the laser resonator 100. It is a top view which shows a schematic structure. Also,
FIG. 3 is an explanatory diagram of the oscillation operation of the laser resonator 100.

As shown in FIG. 1, a laser resonator 100 according to the present embodiment includes, as main components, a DBR laser device 150 corresponding to a semiconductor optical device and a grating fiber 160 corresponding to an optical fiber. ing. The DBR laser device 150 will be described.
In the R laser element 150, an optical waveguide 110 as a laminated waveguide is formed over a second end face 150b coated with an anti-reflection film and a first end face 150a opposite to the second end face 150b. In such an optical waveguide 110,
Lower cladding layer 120d, which is a layer on the element rear surface 150d side
By adopting a configuration in which the core layer 130 and the upper clad layer 120c are sequentially laminated on the surface, light confinement in the core layer 130 is realized.

In the DBR laser device 150, three regions are formed in the optical waveguide 110. Of the three regions, the one formed closest to the first end face 150a is the DBR region 110a corresponding to the reflection region. The DBR region 110a is a passive waveguide region to which the optical waveguide layer 130a is applied as the core layer 130. DBR
In the region 110a, a uniform grating 132 corresponding to the first Bragg diffraction grating is formed at the boundary between the optical waveguide layer 130a and the lower cladding layer 120d. Selective light reflection is achieved. When no current is flowing through the resistance film 180a described later, the DB
The Bragg wavelength λ of the R region 110a is λ1.

The saturable absorption region 110c corresponding to the saturable absorption region of the relay region is formed closest to the second end face 150b among the three regions. In the saturable absorption region 110c, the saturable absorption layer 1
30c is applied, and a saturable absorption characteristic in which light absorption decreases as light intensity increases is realized. In the laser resonator 100, a self-pulsation phenomenon occurs due to the saturable absorption characteristic of the saturable absorption region 110c,
Pulse oscillation of laser light is realized.

Further, an active region 110b corresponding to the active region of the relay region is formed between the DBR region 110a and the saturable absorption region 110c. In the active region 110b, the active layer 130 is used as the core layer 130.
b is applied, and a light emitting function and a gain function are realized.

In the present embodiment, for example,
The lower cladding layer 120d can be formed from p-InP and the upper cladding layer 120c can be formed from n-InP. Further, the optical waveguide layer 130a can be formed of, for example, an inactive material having a composition having a band gap wavelength of about 1.2 μm. Further, the active layer 13
0b is, for example, a band gap wavelength of about 1.55 μm.
Can be formed from InGaAsP having the following composition. Furthermore, similarly to the active layer 130b, the saturable absorption layer 130c has, for example, a bandgap wavelength of about 1.
It can be formed from InGaAsP having a composition of 55 μm.

DB having optical waveguide 110 described above
A common electrode 140 is provided on the R laser element 150 so as to cover the entire back surface 150d of the element. As shown in FIG. 2, the DBR laser element 150 has an element surface 1
A first electrode 140b is provided so as to cover a portion of the active region 110c corresponding to the active region 110b.
The second electrode 140c is provided so as to cover a portion corresponding to the saturable absorption region 110c. In the DBR laser device 150, the active layer 130
Independent current injection into each of b and the saturable absorption layer 130c becomes possible, and passive mode-locked laser light pulse oscillation becomes possible.

Further, in the DBR laser device 150, a resistance film 180a corresponding to a heating means is provided on a portion of the device surface 150c corresponding to the DBR region 110a via an insulating film 170a. As shown in FIG. 1, the resistance film 180a generates heat when a current flows, heats the optical waveguide layer 130a via the insulating film 170a and the upper cladding layer 120c, and uses the TO effect to form the optical waveguide layer 130a.
The refractive index of a is changed. As a result of such a refractive index change, D
The Bragg wavelength λ of the BR region 110a changes from λ1 to λ2. Here, the insulating film 170a is a resistive film 180.
This is for electrically isolating a from the element surface 150c.

In the present embodiment, the common electrode 1
The first electrode 140b, the first electrode 140b, and the second electrode 140c can be formed of, for example, Au. The resistance film 18
0a can be formed, for example, from Pt. Further, the insulating film 170a can be formed from, for example, SiO ₂ .

The grating fiber 160, which is another main component of the laser resonator 100, will be described. The grating fiber 160 has a chirped grating (not shown) corresponding to a second Bragg diffraction grating. I have. Such a chirped grating has a grating spacing of the grating fiber 160.
Is formed so as to change continuously along the traveling direction of the light. With this configuration, the grating fiber 1
In 60, a characteristic is realized in which the Bragg wavelength changes continuously from λ1 to λ2 (λ1 <λ2) along the traveling direction.

Laser resonator 100 according to the present embodiment
Is formed by aligning the above-described DBR laser element 150 and grating fiber 160 with each other via an optical lens 190. In such an alignment, the second end face 150b of the DBR laser element 150
And the Bragg wavelength of the grating fiber 160 is λ1
Are optically connected to each other.

In this embodiment, instead of the optical lens 190, another optical coupling device such as a spherical fiber can be used. The end surface of the grating fiber 160 at the position where the Bragg wavelength is λ2 can be connected to another optical element such as a laser light pulse receiving device or a transmitting device.

The laser resonator 1 having the configuration described above
The operation of 00 will be described with reference to FIG. As shown in FIG. 3, both the DBR region 110a and the grating fiber 160 have a function of reflecting light by backward coupling by Bragg reflection. Therefore, in the laser resonator 100, a circulating light path in which the saturable absorption region 110c and the active region 110b are interposed between the light reflection position in the DBR region 110a and the light reflection position in the grating fiber 160. Is formed. As a result, the accumulation of the light wave power by the reciprocating propagation of the orbiting optical path and the mode locking by the saturable absorption operation in the saturable absorption region 110c cause the laser generated from the component generated in the active region 110b to satisfy the predetermined resonance condition. An optical pulse is formed.

Here, first, assuming that no current flows through the resistive film 180a, the Bragg wavelength λ of the DBR region 110a is λ1 as described above. Therefore,
The orbiting optical path is formed between the light reflection position in the DBR region 110a and the position where the Bragg wavelength of the grating fiber 160 is λ1 (point P in FIG. 3). As a result, the cavity length formed in the laser cavity 100 is La
+ Lb + L1, and the mode locking frequency f of the laser resonator 100 is f1 = c / 2 (naLa + nbLb + n
1L1).

Note that La indicates the actual distance between the light reflection position in the DBR region 110a of the DBR laser device 150 and the second end face 150b, and na indicates the average refractive index of the same distance region. Lb is the laser cavity 1
00 second end surface 150 of DBR laser element 150
b indicates the actual distance between the end surface 160a of the grating fiber 160, and nb indicates the average refractive index in the same distance region. L1 is the grating fiber 1
At 60, the actual distance between the end grating fiber 160b and the position (point P) where the Bragg wavelength is λ1 is shown, and n1 is the average refractive index of the core of the grating fiber 160. Furthermore, c indicates the speed of light.

Next, assuming that a current flows through the resistive film 180a, the Bragg wavelength λ of the DBR region 110a changes from λ1 to λ2. Therefore, the orbiting optical path is located at a position where the Bragg wavelength of the grating fiber 160 is λ2 (see FIG. 3).
And the middle point Q). As a result, the cavity length formed in the laser cavity 100 is La + Lb + L2
And the mode locking frequency f of the laser resonator 100
Is represented by f2 = c / 2 (naLa + nbLb + n1L2). L2 is the grating fiber 16
0 indicates the actual distance between the end surface 160a and the position (point Q) where the Bragg wavelength is λ2.

In the laser resonator 100, the end face 160
A large value can be obtained for L1 and L2, which are the distances between a and the reflection position of light on the grating fiber 160, by increasing the modulation amount of the grating period of the chirped grating formed on the grating fiber 160. . Therefore, in the laser resonator 100, by injecting a current from the outside into the resistive film 180a, the mode locking frequency is largely changed, and a laser light pulse train having a desired pulse frequency can be obtained.

In the laser resonator 100, when a current is passed through the resistive film 180a in order to modulate the pulse period, the wavelength of the laser beam forming the pulse train can be adjusted at the same time. That is, the laser resonator 100
Can tune the oscillation wavelength.

As described above, according to the present embodiment, it is possible to generate a laser light pulse having a desired pulse frequency by changing the mode locking frequency by adjusting the current flowing through the resistive film. it can. In addition, by using a low-loss optical fiber for a part of the laser resonator, the mode-locking frequency can be greatly changed. In the present embodiment, an electrode is applied instead of the resistive film corresponding to the heating means, and the DBR is utilized by utilizing the EO effect by carrier injection, electric field application, and the like.
It is also possible to achieve a change in the refractive index of the area.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. FIG. 4 is a cross-sectional view showing a schematic configuration of a laser device 200 as an example of the laser device according to the present embodiment. FIG. 5 is a plan view showing a schematic configuration of the laser element 200, and FIG. 6 is an explanatory diagram of an oscillation operation of the laser element 200.

As shown in FIG. 4, the laser device 200 according to the present embodiment is a one-chip type laser device, and the functions and functions of the laser resonator 100 according to the first embodiment shown in FIG. Substantially equivalent functions are realized. More specifically, the laser device 200 according to the present embodiment has a first end face 200a and a second end face 200a facing each other.
The optical waveguide 210 is formed over the end face 200b. The optical waveguide 210 has a lower cladding layer 220d.
, A core layer 230 and an upper cladding layer 220c are sequentially laminated, and the first DBR region 21
0a, the active region 210b, the saturable absorption region 210c, and the second DBR region 210d.

In the optical waveguide 210, the first end face 2
The first DBR region 210a located on the 00a side is a passive waveguide to which the optical waveguide layer 230a is applied as the core layer 230, and corresponds to a first reflection waveguide. Such first DBR
In the region 210a, a uniform grating 232a corresponding to the first Bragg diffraction grating is formed at a uniform grating period at a boundary between the optical waveguide layer 230a and the lower cladding layer 220d. Since the uniform grating 232a is formed in the first DBR region 210a, light of a predetermined wavelength satisfying the Bragg reflection condition is selectively reflected at a predetermined position.

The second DBR region 210d closest to the second end face 200b is a passive waveguide to which the optical waveguide layer 230d is applied as the core layer 230, and corresponds to a second reflection waveguide. In the second DBR region 210d, a non-uniform lattice 232d is formed at the boundary between the optical waveguide layer 230d and the lower cladding layer 220d, the lattice period being shortened as approaching the second end face 200b. In the second DBR region 210d, since the non-uniform grating 232d corresponding to the second Bragg diffraction grating is formed, light is Bragg-reflected at different positions for each wavelength.

Further, in the optical waveguide 210, the first D
A region corresponding to a relay waveguide is formed between the active region 210b and the saturable absorption region 210c between the BR region 210a and the second DBR region 210d. 1st DB
The active region 210b located on the R region 210a side has the active layer 230b applied as the core layer 230, and corresponds to the active region. In the active region 210b, a light emitting function and a gain function in the active layer 230b are realized by current injection. On the other hand, the saturable absorption region 210c located on the second DBR region 210d side has the saturable absorption layer 230c applied as the core layer 230, and corresponds to the saturable absorption region. The saturable absorption region 210c exhibits saturable absorption characteristics. Therefore, in the optical waveguide 210, a self-pulsation phenomenon occurs, and a passive mode-locking operation is realized.

In this embodiment, for example, the lower cladding layer 220d can be formed from p-InP and the upper cladding layer 220c can be formed from n-InP. Further, the optical waveguide layers 230a and 230d can be formed of, for example, an inactive material having a composition having a band gap wavelength of about 1.2 μm. Further, the active layer 230b and the saturable absorption layer 230c can be formed of, for example, InGaAsP having a composition having a band gap wavelength of about 1.55 μm.

In order to perform the laser light pulse oscillation operation, the oscillation wavelength modulation operation, and the oscillation pulse pulse modulation operation in the optical waveguide 210 described above,
Electrodes and a heating film are provided on the element front surface 200c and the element back surface 200d. More specifically, in the laser device 200, a common electrode 240 is provided on the entire back surface 200d of the device. A first electrode 240b is provided on the device surface 200c so as to cover a portion of the device surface 200c which is on the active region 210b, and a second electrode 240b is provided so as to cover a portion of the device surface 200c which is on the saturable absorption region 210c. An electrode 240c is provided.

Further, as shown in FIG.
A first heating film 280a corresponding to a heating unit is provided on a portion corresponding to the first DBR region 210a of Oc via a first insulating film 270a. Such a first heating film 28
0a is given by giving a potential difference between the electrode pad 282a and the electrode pad 284a formed at both ends thereof.
An electric current flows through the heat generating portion to generate Joule heat. Similarly, a second heating film 280d corresponding to a heating unit is provided on a portion corresponding to the second DBR region 210d of the element surface 200c via a second insulating film 270d. Like the first heating film 280a, the second heating film 280d also has the electrode pads 2 formed on both ends thereof.
By applying a potential difference between the electrode pad 82d and the electrode pad 284d, an electric current flows through the heat generating portion to generate Joule heat. Here, the first insulating film 270a and the second insulating film 270d are for electrically insulating the first heating film 280a and the second heating film 280d from the element surface 200c.

In the present embodiment, the common electrode 2
40, the first electrode 240b, and the second electrode 240c can be formed of, for example, Au. Further, the first heating film 280a and the second heating film 280d can be formed of, for example, Pt. Furthermore, the insulating film first insulating film 27
Oa can be formed, for example, from SiO ₂ .

As shown in FIG. 4, the laser device 200 having the configuration described above can perform the same operation in principle as the laser resonator 100 according to the first embodiment shown in FIG. . That is, in the laser element 200, the position of light reflection at the first DBR region 210a and the second D
The active region 2 is located between the light reflection position in the BR region 210d and the light reflection position.
A circulating optical path in which the saturable absorption region 210c and the saturable absorption region 210c are interposed is formed, and laser light pulse oscillation is performed by passive mode locking operation. Further, by changing the Bragg wavelength λ of the first DBR region 210a due to the heat generated by the first heating film 280a, the length of the resonator defined in the circulating optical path is adjusted, and the oscillation pulse is periodically modulated.

In such an operation, the laser device 200 according to the present embodiment is different from the laser device 100 shown in FIG.
It has features different from those described above. That is, the wavelength tuning of the oscillation pulse train and the modulation of the pulse period can be controlled. Hereinafter, the laser device 20 according to the present embodiment will be described.
The feature of such an operation of zero will be described with reference to both FIG. 4 and FIG.

In FIG. 6, the vertical axis indicates the wavelength of light, and the horizontal axis indicates the position in the optical waveguide 210. In FIG. 6, the solid line of the second DBR region 210d indicates the non-uniform lattice 2
The change in the grating period of 32d is not directly shown, but the wavelength dependence of the penetration length of light into the second DBR region 210d determined by the results of light loss and diffraction efficiency.

(1) As a first case, the first heating film 28
It is assumed that no current is flowing to either the first heating film 0a or the second heating film 280d. In such a case, the first DBR region 21
The Bragg wavelength of 0a is constant at λc regardless of the position, and the oscillation wavelength is λc. On the other hand, the second DBR region 21
The Bragg wavelength of 0d has a characteristic that it becomes longer as approaching the second end face 200b. FIG. 5 shows an example of the Bragg wavelength characteristic of the second DBR region 210d that can be expressed as a linear function of the position. In this case, assuming that the resonator length is Lc, the mode locking frequency f is f = c / 2nLc.

(2) Next, as a second case, consider a case in which no current flows through the second heating film 280d but a current flows through the first heating film 280a. In such a case, the Bragg wavelength of the first DBR region 210a is constant at λd longer than λc in the first case, and the oscillation wavelength is λd longer than in the first case. On the other hand, the second DBR region 21
The Bragg wavelength of 0d remains the same as in the first case. As a result, the resonator length becomes Ld longer than Lc in the first case, and the mode locking frequency f becomes f =
c / 2 nLd.

(3) Further, as a third case, consider a case in which a current is supplied not only to the first heating film 280a but also to the second heating film 280d. In such a case, the first DBR region 210
Since the Bragg wavelength of a is constant at λd as in the second case, the oscillation wavelength is λd as in the second case. However, the Bragg wavelength of the second DBR region 210d shifts to a longer wavelength side than the characteristics in the first and second cases. As a result, the resonator length is longer than Lc in the first case but shorter than Ld in the second case, and the mode locking frequency f is f = c / 2nLc ′.

From the above consideration of the first to third cases, in the laser device 200 according to this embodiment,
It can be seen that the mode locking frequency f is adjusted by the relationship between the current flowing through the first heating film 280a and the current flowing through the second heating film 280d. On the other hand, the oscillation wavelength is the first
It can be adjusted only by the current flowing through the heating film 280a.

Accordingly, in the laser element 200, even when the oscillation wavelength is fixed, that is, even when the current flowing through the first heating film 280a is kept constant, the current flowing through the second heating film 280d is adjusted to achieve mode synchronization. Frequency f
Can be modulated. Further, even when the mode locking frequency is fixed, the current flowing through the first heating film 280a and the second
If a predetermined relationship with the current flowing through the heating film 280d is maintained, the oscillation wavelength can be changed.

As described above, according to the present embodiment, a laser light pulse having a desired pulse frequency can be generated as in the first embodiment. Further, according to the present embodiment, it is possible to control the wavelength of the oscillation laser light pulse and the pulse period substantially independently. In the present embodiment, it is also possible to apply an electrode in place of the resistive film corresponding to the heat generating means and realize a change in the refractive index of the DBR region by utilizing the EO effect due to carrier injection or electric field application. It is possible.

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to such a configuration. Within the scope of the technical idea described in the appended claims, those skilled in the art will be able to conceive various changes and modifications, and those changes and modifications are also within the technical scope of the present invention. It is understood that it belongs to.

For example, in the above embodiment, Au
Although a laser device using an electrode made of Pt, a heating film made of Pt, and an insulating film made of SiO ₂ has been described as an example, the present invention is not limited to such a configuration. The present invention can also be applied to a laser device to which electrodes, heating films, and insulating films made of other various materials are applied.

In the above embodiment, the GaAs
Although a laser device using an s-based or InP-based semiconductor material has been described as an example, the present invention is not limited to such a configuration. The present invention relates to various other materials such as LiNbO3
The present invention can also be applied to a laser device using a silicon or Si type.

Further, in the above embodiment, the laser device using the resistance film as the heating means has been described as an example, but the present invention is not limited to such a configuration. The present invention can also be applied to a semiconductor device to which various other heating means are applied.

[0062]

According to the present invention, in a laser device usable as an optical pulse generator, a DBR having a uniform periodic Bragg diffraction grating functioning as a facet mirror is provided.
The configuration in which the reflecting mirror and the DBR reflecting mirror having the periodic modulation Bragg diffraction grating are formed on both sides of the active region realizes a high oscillation wavelength variable ability and a high pulse cycle variable ability. Therefore, by using the laser device to which the present invention is applied, a laser light pulse train having a desired frequency and a desired pulse period can be obtained. That is, according to the present invention, it is possible to provide a transmission source such as a carrier wave suitable for an optical communication system with remarkably high speed and large capacity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a laser resonator to which the present invention can be applied.

FIG. 2 is a plan view showing a schematic configuration of a DBR laser device applied to the laser resonator shown in FIG.

FIG. 3 is an explanatory diagram illustrating an oscillation operation of the laser resonator illustrated in FIG. 1;

FIG. 4 is a sectional view showing a schematic configuration of a laser device to which the present invention can be applied.

FIG. 5 is a plan view showing a schematic configuration of the laser device shown in FIG.

6 is an explanatory diagram of an oscillation operation of the laser device shown in FIG.

FIG. 7 is a cross-sectional view illustrating a schematic configuration of a conventional laser device.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 Laser resonator 110, 210 Optical waveguide 110a, 210a, 210d DBR region 110b, 210b Active region 110c, 210c Saturable absorption region 132, 232a, 232d Bragg diffraction grating 150 DBR laser device 150b Second end face 160 Grating fiber 180a, 280d Resistive film 200 Laser element

Claims (9)

[Claims] 1. A method according to claim 1, wherein the effective grating period is substantially uniform.
A reflection region on which a Bragg diffraction grating is formed, a waveguide end surface through which light enters and exits, and a relay region having at least an active region and interconnecting the reflection region and the waveguide end surface. A laser device comprising: an optical waveguide; and an optical fiber formed with a second Bragg grating having a non-uniform effective grating period and configured to input and output light to and from the waveguide end face. 2. The laser device according to claim 1, wherein said relay region also has a saturable absorption region. 3. The laser device according to claim 1, wherein the optical waveguide is formed in a semiconductor optical device. 4. A method according to claim 1, wherein said first grating has a substantially uniform effective grating period.
A first reflective waveguide on which a Bragg diffraction grating of
A second reflection waveguide on which a second Bragg diffraction grating having an effective non-uniform grating period is formed; an active region and a saturable absorption region; the first reflection waveguide and the second reflection waveguide; And a relay waveguide for interconnecting the reflection waveguide and the reflection waveguide. 5. The second Bragg diffraction grating according to claim 1, wherein the effective grating period changes sequentially with a constant change amount. 3. The laser device according to claim 1. 6. The apparatus according to claim 1, further comprising a heating means for adjusting an effective grating period of said second Bragg diffraction grating. A laser device according to claim 1. 7. The apparatus according to claim 1, further comprising current injection means for adjusting an effective grating period of said second Bragg diffraction grating. 3. The laser device according to claim 1. 8. The apparatus according to claim 1, further comprising heating means for adjusting an effective grating period of said first Bragg diffraction grating.
The laser device according to any one of the above. 9. The apparatus according to claim 1, further comprising a current injection means for adjusting an effective grating period of said first Bragg diffraction grating. 8. The laser device according to any one of 7.