Rare earth containing P2O5-WO3-Na2O glass for laser applications

Abstract

A rare earth containing glass nominally based on the ternary P2O5 —WO3—Na2O—Ln2O3 compositional space, with WO3>30-65 mole %, Na2O 15-35 mole %, P2O5 5-65 mole %, Ln2O3 (Ln=one or more cations selected from lanthanum or any of the rare earth oxides) up to the limit of solubility; with optional additives, MoO3 being a preferred additive, that can be employed alone or in combination at levels up to 15 mole %.

Description

[0001] The glasses of the present invention are useful as active materials for generation and/or amplification of optical laser radiation. They are advantageously employed as sources or amplifying medium of light when doped with suitable active rare earth cations. They are particularly advantageously employed as sources or amplifying medium in telecommunications applications where they are doped with lanthamide cations, preferably with erbium cations, alone or in combination with ytterbium cations. When employed in this manner, the glasses of the present invention offer a lasing range that is broader, and more flat (uniform) in its gain, than the conventional erbium doped phosphate gain material commonly employed today. The glasses of this invention can be prepared in bulk or fiber form, and are structurable by conventional techniques such as ion exchange, allowing the preparation of planar and fiber waveguide structures that can be employed as these gain media.

[0002] The use of the glasses according to the invention enables small, compact amplifiers to be constructed from either fibers or planar waveguides that offer flat (uniform) amplification over an increased wavelength range compared to the currently existing EDFA for application to the C-band telecommunications wavelength region (from 1530 to 1562 nm) as well as for the L-band region (1570 to 1610 nm) that is expected to be employed in the future as there continues to be increased requirements for increased bandwidth.

[0003] In addition, glasses with broad emission are known to offer the potential to construct laser systems that operate with extremely short pulse lengths, less than 1 nsec or even shorter, e.g., at less than 1 psec or less than 500 fsec.

[0004] In one aspect, the invention relates to rare earth, Ln, doped glasses prepared within the ternary P2O5—WO3—Na2O compositional space, with WO3>30-65 mole %, preferably 50-60 mole %, more preferably about 55 mole %; Na2O 5-35 mole %, preferably 15-25 mole %; P2O5 5-65 mole %, preferably >15-65 mole %, e.g., 16-, 17-, 18-, 19-65 mole %, more preferably 20-30 mole %, that are also doped with Ln2O3 (where Ln refers to one or more cations selected from lanthanum or any of the rare earth oxides) at a content level up to the limit of solubility in the glass, preferably in the range of 0.01 to 2.0 mole %, more preferably 0.1-1.5 mole %, and even more preferably in the range of 0.2-0.4 mole %; with other optional additives such as MoO3, Nb2O5, TiO2, B2O3, Ga2O3, Sb2O3, BaO, Bi2O3, SnO2, Y2O3, ZrO2, TaO5, In2O3, MO, and/or R2O, wherein R is Li or K with or without the presence of another alkali, or is at least two elements selected from the group consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn; preferably MoO3, that can be employed alone or in combination with other additives at levels preferably up to 15 mole %, preferably at levels below 10 mole %, e.g., for example for TeO2, more preferably up to about 5 mole %, that may enhance the gain characteristics for particular applications, improve meltability and/or resultant optical quality of produced glass, and increase solubility for rare earth ions. MoO3 can be advantageously included at levels of about 10 mole %. TeO2 affects the bandwidth of glasses. The glasses of the present invention offer increased cross section for stimulated emission and broader emission bandwidth compared to state of the art phosphate glass.

[0005] It is within the scope of the invention to batch the glasses with fluoride, carbonate, nitrate, and/or chloride compounds instead of, or in combination with, the oxide compounds. In each case when other than oxides are used to batch the glasses, enough material is input to be equivalent to the needed oxide amount.

[0006] The glasses of the present invention can be doped with rare earth oxides, including, but not limited to La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Pm, Lu, Tm, Er and/or Yb, preferably with Nd, Pr, Dy, Tm, Er, and/or, Yb, more preferably with Er, Yb, and/or Nd. Preferred ranges for Er are 0.01 to 0.40 mole %, more preferably 0.15-0.35 mole %, and even more preferably about 0.28-0.32 mole %. Preferred ranges for Yb are 0.1-1.4 mole %, more preferably about 0.3-1.2 mole %. Preferred ranges for Nd are 0.01-1.4, more preferably 0.3 to 1.2 mole %. These rare earth oxides can be employed alone or in combination of one or more in order to take advantage of other available lasing wavelengths and sensitization or up conversion schemes for generating or amplifying light at various wavelengths. Examples include Nd at nominally 0.9 μM, 1.0 μm, and 1.3 μM, Yb at nominally 1.0 μm, Tm at 1.4 and 2.0 μg, Dy at 1.3 μg, and Er at wavelengths other than 1.54 μm, for example Er at 2.9 μm.

[0007] In another aspect, the invention relates to the glass family based on P2O5—WO3—MO3—Na2O as a rare earth containing, structurable, laser glass to offer broad emission bandwidth for 1.54 μM radiation when doped with Ln ions, for example, erbium cations.

[0008] The glasses according to the invention offer a) a broader emission bandwidth compared to the state of the art erbium doped phosphate glass, b) a flatter gain curve compared to the state of the art erbium doped phosphate material, and c) structurability by ion exchange in a molten salt bath.

[0009] The glasses of the present invention are also useful as upconversion materials such as disclosed in JPH3-295828, and as a nonlinear optical medium for applications such as optical switches as disclosed in J. Am. Ceram. Soc. 85[5] 1083-1088 (2002). The low melting temperatures and high thermal expansion values of the glasses of this invention may make them attractive for non-optical applications such as soldering (joining) and sealing with high expansion glasses, metals and alloys, and encapsulation of electronic components without thermal damage.

[0010] In another aspect, the invention relates to a hybrid structure of one or more materials in which one or more of the materials is/are a glass of the present invention. For example, hybrid structures can be created by bonding the glasses of this invention to other materials, including but not limited to variants of the glasses of this invention containing no active ions. Further examples include bonding of the glasses of this invention to each other (for example a glass containing erbium and/or ytterbium to a glass containing another rare earth cation such as thulium, dysprosium or neodymium), or to other optical materials such as glasses and/or crystals, for example, lithium niobate, lithium tantalate, or other crystals, or even to other materials or components such as semiconductor materials and actual semiconductor laser diodes. In this way, multiple optical functionalites can be combined into a single structure, increasing integration of multiple optical functions into a small package. For example, it becomes possible in a single package to combine: multiple laser sources or amplifiers each operating at a different power level or wavelength, the excitation or pump laser with the amplifiers or source lasers, and/or the source lasers or amplifiers with frequency conversion or frequency and amplitude modulation elements.

[0011] Upon further study of the specification and appended claims, further objects and advantages of this invention will become-apparent to those skilled in the art.

[0012] The maximum rare earth content (Ln) of these glasses, due to solubility issues, appears to be about 2×1020 Ln/cm3, however, higher concentrations, if successfully incorporated into the glasses, are within the scope of the invention. The Ln/cm3 value is a calculated value based on the mole % Ln in the glass composition. First, the weight % composition of Ln is calculated from the mole % composition, followed by calculating the number of ions/cm3 based on an assumed density of the glass. It is to be noted that the mole % of compounds in the glass compositions need not add up to a total of 100 mole % each time, as can be seen in some of the examples later in this application. In this art, deviations from compositions having 100 mole % material are common and well understood by those of ordinary skill.

[0013] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

[0014] In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by mol, unless otherwise indicated.

EXAMPLES

[0015] The examples were all prepared from the general heavy metal oxide system based on P2O5—WO3—MoO3—Na2O with a number of additional additives, including Ln2O3. Initial melts, summarized in Table 1, were selected to offer acceptable glass forming stability with a maximum (WO3+MoO3)/P2O5 ratio in combination with a Na2O level that would be more than sufficient for ion exchange process ability (i.e. nominally 10 to 25 mole %), while batching WO3 into the glass composition.

TABLE 1
Initial P2O5—WO3—MoO3—Na2O
Glass Melting without Ln2O3
	Oxide	PWD-78	PWD-85
	Na2O	25	25
	WO3	55	40
	MoO3		20
	P2O5	20	15
	PWD-78 and PWD-85 represent undoped base glasses used during the identification of this invention.

[0016] Rare earth incorporation was completed in the melts presented in Table 2. All Rare earth containing glasses exhibited decreasing optical quality with increasing rare earth input. Analysis of several castings indicated that the crystals within each casting were enriched in Yb, Er, and P, as well as depleted in W, compared to the surrounding base glass. SEM and XRD analysis of crystals in many of these melts determined the composition to be a rare earth orthophosphate. These orthophosphates are of interest in identifying glass ceramic materials of high transparency containing a Ln(PO4) crystal phase.

TABLE 2
Rare Earth Doping of P2O5—WO3—Na2O
Oxide	PWD-83	PWD-83/2	PWD-108	PWD-109	PWD-110	PWD-111	PWD-112	PWD-113
Na2O	23.79	23.48	10	10	10	25	25	15
Er2O3	0.24	0.3	0.32	0.31		0.29	0.3	0.31
Yb2O3	0.97	1.21	1.26		1.25		—
Nd2O3	—	—	—	—	—	—	—	—
WO3	55	55	55	55	55	40	55	45
MoO3			10	10	10	20	—	20
P2O5	20	20	25	25	25	15	20	20
Oxide	PWD-114	PWD-115	PWD-116	PWD-121	PWD-122	PWD-123	PWD-142
Na2O	15	25	25	15	25	25	20
Er2O3	0.32	0.3	0.3	0.31		0.3	—
Yb2O3	—	1.21	0.6	—	0.29	0.3	—
Nd2O3	—	—	—	—	—	—	0.27
WO3	60	55	55	55	55	55	55
P2O5	25	20	20	30	20	20	25

[0017] The glasses of this invention can be ion exchanged using conventional thermal salt bath techniques well known in the industry, see for example “Glass waveguides by ion exchange: a review” Optical Engineering, Vol. 24, Number 2, pg 244-250 (1985). Glass PWD-85 was successfully ion exchanged by employing such standard molten salt bath procedures. Typical processing conditions were 30 minutes at a temperature of 180° C. with the glass placed in a salt bath prepared from 25 mole % NH4NO3 and 75 mole % AgNO3. Resultant analysis indicated the presence of Ag2O to depths of 10 to 14 μm and concentrations exceeding 25 mass % at the glass surface. FIG. 1 shows a typical Ag2O profile. The rate of ion exchange found is actually higher than required. Exchange times of several hours would still be acceptable to the industry.

[0018] One way to increase the ion exchange time is to reduce the Na2O content in the glass. Reduction of Na2O content in P2O5—WO3—Na2O compositions results in a blue coloration of produced glass at regions where laser light generation or amplification is generally desired, see FIG. 2. This blue coloration is due to a valence change of W6+ to W5+ (to even W3+, see for example, C. R. Bamford, Colour Generation and Control in Glass, Elsevier, pg 118 (1977)). At the same time, once the probable mechanism was understood to be reduction of W, efforts to solve the blue color problem included melts prepared where different batching patterns to adjust the melt redox condition to a more oxidizing condition. Alternatively, a lower Na2O content glass can be prepared by substituting some of the Na2O by one or more other alkali that do not exchange as well for Ag2O.

[0019] An alternative path to lower diffusion coefficient for Na in P2O5—WO3—Na2O glasses is to introduce glass modifiers that act as ion exchange barriers. Possible modifier additions include alkaline earths, B2O3, Sb2O3 and Ga2O3. Glasses prepared along these lines of reasoning are detailed in Table 3.

TABLE 3
Additional P2O5—WO3—Na2O Glass Melting
	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-	PWD-
Oxide	124	125	127	128	129	130	131	132	133	134	135	136	20326
Bi2O3									4
B2O3		5			5		5	5		5
Na2O	23	25	25	23	25	25	20	20	21	25	25	25	25
Er2O3	0.3	0.28	0.29	0.29	0.28	0.29	0.3	0.15	0.32	0.15	0.15	0.6	0.6
Yb2O3				0.29	0.28	0.29		0.15		0.15	0.15
Ga2O3			5			5	5	5			5
Sb2O3													5
BaO	2			2
WO3	55	50	50	55	50	50	55	55	55	50	50	55	55
P2O5	20	20	20	20	20	20	15	15	20	20	20	20	20

[0020] Tables 2 and 3 demonstrate a continual trend of rare earth content solubility limit, independent of the identity of the employed rare earth, to about ≦2×1020 Ln/cm3. The Er and Er codoped with Yb glasses offer improved Er spectroscopic properties over state-of-the-art phosphate glasses such as IOG-1 (IOG-1 is the example glass in U.S. Pat. No. 5,334,559). The Yb and Nd doped glasses offer lasing action, for example, PWD-122 and PWD-142 at roughly 1.02 um and 1.05 um, respectively. In addition, the broad width of emission in the glasses lends itself to the development of laser systems with short pulse lengths in the range of less than 1 nsec.

[0021] Many of the example glasses discussed here have been characterized for other properties as disclosed in Table 5.

TABLE 5
Glass Properties
Tungsten-Alkali-Phosphate
Property	PWD-78	PWD-85	PWD-109	PWD-112	PWD-114	Units
Density	4.85	4.57	4.767	4.863	4.867	g/cc
CTE	155.8			157.8		10−7/° C.
Tg	465.2	397				° C. (DTA)
Tg	459.4			463		° C. (Dilatometer)
T soft	525.9	450.3		526.4		° C.
Young's Modulus	52.82	48.05				Gpa
2900 nm	0.93			1.1	1.62	cm−1
3000 nm	1.34			1.58	2.31	cm−1
3333 nm	1.88			2.18	3.07	cm−1
Property	PWD-124	PWD-125	PWD-127	PWD-133	PWD-134	PWD-135	Units
Density	4.925	4.66	4.77	5.197	4.663	4.765	g/cc
CTE		158.3	160.5	147.9	161.6	156.3	10−7/° C.
Tg		452	439	451	457	443	° C. (Dilatometer)
T soft	530.6						° C.
2900 nm	0.95	0.96	0.84	1.13	0.97	0.63	cm−1
3000 nm	1.35	1.09	0.97	1.52	1.05	0.74	cm−1
3333 nm	1.87	1.39	1.07	1.95	1.36	0.85	cm−1

[0022] FIG. 3 shows the improvement in gain possible with Example PWD-112 of the present invention in comparison to the prior art phosphate glass exemplified by glass IOG-1 when employed for C-band use.

[0023] FIG. 4 shows the improvement in gain possible with Example PWD-112 of the present invention in comparison to the prior art phosphate glass exemplified by glass IOG-1 when employed in both the C-band and L-band wavelength regions.

[0024] The entire disclosures of all applications, patents and publications, cited herein are incorporated by reference herein.

[0025] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0026] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to, adapt it to various usages and conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1—Ag2O Profile in Ion Exchanged PWD Glass.

[0028] FIG. 2—Transmission Curve and Photo of 2 mm Thick Sample of Melt.

[0029] FIG. 3—Normalized C-band gain improvement compared to state-of-the-art phosphate glass.

[0030] FIG. 4—Normalized C-band and L-band gain improvement compared to state-of-the-art phosphate glass.

Claims

1. A glass comprising >30-65 mole % WO3, 5-35 mole % Na2O, and 5-65 mole % P2O5, and doped with Ln2O3 up to the limit of solubility of Ln2O3 in the glass.

2. A glass according to claim 1, comprising 50-60 mole % WO3.

3. A glass according to claim 1, comprising about 55 mole % WO3.

4. A glass according to claim 1, comprising 15-25 mole % Na2O.

5. A glass according to claim 1, comprising 16-65 mole % P2O5.

6. A glass according to claim L, comprising 20-30 mole % P2O5.

7. A glass according to claim 1, comprising 0.01-2.0 mole % Ln2O3.

8. A glass according to claim 1, wherein Ln2O3 is Er2O3 or Yb2O3 or a mixture thereof.

9. A glass according to claim L, comprising 0.15-0.35 mole % Er2O3.

10. A glass according to claim 1, comprising 0.28-0.32 mole % Er2O3.

11. A glass according to claim L, comprising 0.1-1.4 mole % Yb2O3.

12. A glass according to claim 1, comprising 0.3-1.2 mole % Yb2O3.

13. A glass according to claim 1, further comprising MoO3, Nb2O5, TiO2, B2O3, Ga2O3, Sb2O3, BaO, Bi2O3, SnO2, Y2O3, ZrO2, TaO5, In2O3, MO, or R2O, wherein R is a mixture of a) Li or K and b) another alkali metal, or R is a mixture of at least two elements selected from the group consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a total amount of up to 15 mole %.

14. A glass according to claim 1, further comprising MoO3, Nb2O5, TiO2, B2O3, Ga2O3, Sb2O3, BaO, Bi2O3, SnO2, Y2O3, ZrO2, TaO5, In2O3, Mo, or R20, wherein R is Li or K without the presence of another alkali metal, or is a mixture of at least two elements selected from the group consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a total amount of up to 15 mole %.

15. A glass according to claim 1, further comprising MoO3, Nb2O5, TiO2, B2O3, Ga2O3, Sb2O3, BaO, Bi2O3, SnO2, Y2O3, ZrO2, TaO5, In2O3, Mo, or R20, wherein R is a mixture of a) Li or K and b) another alkali metal, or R is a mixture of at least two elements selected from the group consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a total amount of up to 15 mole %.

16. A glass according to claim 1, further comprising MoO3, Nb2O5, TiO2, B2O3, Ga2O3, Sb2O3, BaO, Bi2O3, SnO2, Y2O3, ZrO2, TaO5, In2O3, Mo, or R2O, wherein R is Li or K without the presence of another alkali metal, or is a mixture of at least two elements selected from the group consisting of Li, Na, K, Rb, Cs, Ag, and Tl, and M is Mg, Ca, Sr or Zn, or a mixture thereof, in a total amount of less than 10 mole %.

17. A glass according to claim 1, further comprising MoO3.

18. A glass according to claim 1, further comprising MoO3 in an amount of about 10 mole %.

19. A method for preparing a glass according to claim 1, comprising bringing into a composition >30-65 mole % WO3, 5-35 mole % Na2O, 5-65 mole % P2O5, and Ln2O3 up to the limit of solubility of Ln2O3 in the glass.

20. A glass according to claim 1, which is in a bulk or fiber form.

21. A laser generator or amplifier containing a glass according to claim 1.

22. A method of generating and/or amplifying optical laser radiation comprising using a glass according to claim 1 as an amplifying medium.

23. A planar or fiber waveguide structure comprising a glass according to claim 1.

24. An upconversion material, a nonlinear optical medium, an optical switch, a soldering or sealing material, or an encapsulating material over an electronic component, comprising a glass according to claim 1.

25. A glass comprising >30-65 mole % WO3, 5-35 mole % Na2O, and 17-65 mole % P2O5, and doped with Ln2O3 up to the limit of solubility of Ln2O3 in the glass.

26. A glass comprising >30-65 mole % WO3, 5-35 mole % Na2O, and 5-65 mole % P2O5, and doped with Ln2O3 up to the limit of solubility of Ln2O3 in the glass, and wherein the glass contains an amount of tip to 15 mole % of only one of Li2O or K2O without the presence of another alkali metal.

27. A glass comprising >30-65 mole % WO3, 5-35 mole % Na2O, and 5-65 mole % P2O5, and doped with Ln2O3 up to the limit of solubility of Ln2O3 in the glass, and wherein the glass contains less than 10 mol % TeO2.

28. A glass according to claim 25 that contains less than 10 mol % TeO2.

29. A glass according to claim 26 that contains less than 10 mol % TeO2.

30. A laser glass comprising a glass lasing medium and an exit surface for laser radiation, wherein said glass lasing medium comprises >30-65 mole % WO3, 5-35 mole % Na2O, and 5-65 mole % P2O5, and doped with Ln2O3 up to the limit of solubility of Ln2O3 in the glass.

31. A laser glass according to claim 30, comprising 16-65 mole % P2O5.

32. A laser glass according to claim 30, comprising 20-25 mole % Na2O.

33. A laser glass according to claim 30 that contains less than 10 mol % TeO2.

34. A hybrid structure of one or more materials comprising one or more materials in which one or more of the materials is/are a glass according to claim 1.

35. A hybrid structure according to claim 34, which comprises a glass according to claim 1 bonded to another glass according to claim 1.